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Editor Work2020 Vol. 28, No. 6
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2020, 28(6): 1147-1159.
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To appropriately evaluate the mechanical behavior of herb roots, we select five types of indigenous herbs in Henan county of Qinghai province as the tested objectives. They are Oxytropis ochrocephala, Poa annua, Stipapurpure, Carex moorcroftii, and Kobresia humilis. Tensile tests are conducted to the roots of these selected species to obtain their tensile resistance and tensile strength. Based on these results, statistical models are adapted to qualitatively analyze the distribution patterns of the obtained values. The models include Weibull model, Gamma model, Poisson model, Rayleigh model, and Normal model. Then Kolmogorov-skmirov tests are used to quantitatively investigate the optimal distribution functions. The results show that for the five types of statistical models, Poisson model is poor for describing the distribution pattern of these values, while Weibull and Gamma distributions are excellent at describing the distribution patterns. Moreover, the optimal distribution model for root diameter is Gamma function. The optimal distribution model for tensile resistance and tensile strength of E.nutans and C.moorcroftii is Weibull model. The optimal distribution models for K.humilis tensile resistance and tensile strength for K.humilis Weibull and Gamma distributions, respectively. The optimal distribution models for tensile resistance and tensile strength of O.ochrocephala and P.annua is Gamma and Weibull distributions respectively. The results of this study play an important role in accurately estimating the mechanical behavior of herb roots.
To appropriately evaluate the mechanical behavior of herb roots, we select five types of indigenous herbs in Henan county of Qinghai province as the tested objectives. They are Oxytropis ochrocephala, Poa annua, Stipapurpure, Carex moorcroftii, and Kobresia humilis. Tensile tests are conducted to the roots of these selected species to obtain their tensile resistance and tensile strength. Based on these results, statistical models are adapted to qualitatively analyze the distribution patterns of the obtained values. The models include Weibull model, Gamma model, Poisson model, Rayleigh model, and Normal model. Then Kolmogorov-skmirov tests are used to quantitatively investigate the optimal distribution functions. The results show that for the five types of statistical models, Poisson model is poor for describing the distribution pattern of these values, while Weibull and Gamma distributions are excellent at describing the distribution patterns. Moreover, the optimal distribution model for root diameter is Gamma function. The optimal distribution model for tensile resistance and tensile strength of E.nutans and C.moorcroftii is Weibull model. The optimal distribution models for K.humilis tensile resistance and tensile strength for K.humilis Weibull and Gamma distributions, respectively. The optimal distribution models for tensile resistance and tensile strength of O.ochrocephala and P.annua is Gamma and Weibull distributions respectively. The results of this study play an important role in accurately estimating the mechanical behavior of herb roots.
2020, 28(6): 1160-1171.
There are many unstable anti-dip slopes in the Gongjiafang-Dulong section of the Three Gorges Reservoir area. These slopes are generally over 500 m high, and usually possess thin-thick interbedded and soft-hard interbedded structures. Field investigation show that D7 slope has obvious S-shaped flexible deformation. In order to further explore the mechanism of S-type toppling, this paper adopts the methods combining investigation, statistics, GPS monitoring and DEM simulation. Through field investigation and UAV tilt photography, a three-dimensional model of Dulong slope is established. And then through extracting the aerial data, the statistical laws of broken length and layer thickness are obtained. Based on the statistical laws, the S-type toppling mechanism of D7 slope under the action of reservoir water softening is simulated by the discrete element software of UDEC. The results show that:(1)Dulong slope has a steep anti-dipped layered structure, and three sets of structural planes cut the rock mass into blocks. (2)According to the proportion of soft rock, the Dulong slope can be divided into two types. The soft layer number of A-type slope account for about 20%, larger than that of B-type slopes with a proportion of 10%. The ratio of broken thickness and layer thickness(S/T) of A-type slopes is situated between 0.7 and 2.8 and concentrates on 1.2~1.8. The ratio of B-type slopes situates between 0.5 and 3.3 and concentrates on 0.6~1.5. (3)Long-term monitoring shows that the slope moving is larger when the reservoir water level dropping, and the continuously increasing displacement of the D7 slope makes it possible to lose integral stability. (4)The DEM simulation shows that the fracture surface extends from the slope toe, and the hard rock layers in the middle slope restrain the deformation of the upper part. The differential deformation between hard and soft rock layers and the inertia difference in different parts of deformable body are the main causes of S-type toppling. Two shear belts form across the two inversion points of S-shaped layers respectively, and the slope finally form flexible bending-slip failure. (5)The ratio of S/T can affect the slope failure mode. The larger the ratio is, the smaller the reverse deformation area and the toe collapse area are. When the S/T≥2, the slope failure mode turns to flexural toppling without S-shaped deformation.
There are many unstable anti-dip slopes in the Gongjiafang-Dulong section of the Three Gorges Reservoir area. These slopes are generally over 500 m high, and usually possess thin-thick interbedded and soft-hard interbedded structures. Field investigation show that D7 slope has obvious S-shaped flexible deformation. In order to further explore the mechanism of S-type toppling, this paper adopts the methods combining investigation, statistics, GPS monitoring and DEM simulation. Through field investigation and UAV tilt photography, a three-dimensional model of Dulong slope is established. And then through extracting the aerial data, the statistical laws of broken length and layer thickness are obtained. Based on the statistical laws, the S-type toppling mechanism of D7 slope under the action of reservoir water softening is simulated by the discrete element software of UDEC. The results show that:(1)Dulong slope has a steep anti-dipped layered structure, and three sets of structural planes cut the rock mass into blocks. (2)According to the proportion of soft rock, the Dulong slope can be divided into two types. The soft layer number of A-type slope account for about 20%, larger than that of B-type slopes with a proportion of 10%. The ratio of broken thickness and layer thickness(S/T) of A-type slopes is situated between 0.7 and 2.8 and concentrates on 1.2~1.8. The ratio of B-type slopes situates between 0.5 and 3.3 and concentrates on 0.6~1.5. (3)Long-term monitoring shows that the slope moving is larger when the reservoir water level dropping, and the continuously increasing displacement of the D7 slope makes it possible to lose integral stability. (4)The DEM simulation shows that the fracture surface extends from the slope toe, and the hard rock layers in the middle slope restrain the deformation of the upper part. The differential deformation between hard and soft rock layers and the inertia difference in different parts of deformable body are the main causes of S-type toppling. Two shear belts form across the two inversion points of S-shaped layers respectively, and the slope finally form flexible bending-slip failure. (5)The ratio of S/T can affect the slope failure mode. The larger the ratio is, the smaller the reverse deformation area and the toe collapse area are. When the S/T≥2, the slope failure mode turns to flexural toppling without S-shaped deformation.
2020, 28(6): 1172-1177.
Travertine is a kind of macroporous secondary calcium carbonate, formed by Karst water. Travertine can create beautiful natural landscapes such as the Huanglong scenic spot in China, the Pamukkale in Turkey, and the Yellowstone Park Mammoth Hot Springs in the United States. While travertine is mainly distributed in the carbonate areas with frequent water flow, it is rarely used as foundation of buildings and its engineering characteristics are less studied. The project location is in Bolivia, South America, where a steel plant is to be built upon a Travertine land. The travertine in this area is formed by the lacustrine facies, grayish-white, visible honeycomb-like or spongy voids, with some of the voids filled with clay. The SPT N value of the travertine is 39 to 77, which has good mechanical properties in the natural state. But when the travertine is submerged in water, it collapses quickly. Rain in Bolivia lasts for four months annually, it is worried that rain can damage the travertine foundation. A study is thus conducted to test the properties of travertine in the construction site. It is found that the permeability of travertine is 1.7×10-3cm·s-1. The load test is divided into two groups, P1 and P2. The P1 test point is used to test the bearing capacity and collapsibility under the condition of immersion. P1 is soaked in water before the test, and the water head height was 30 cm for 5 days. The P2 test site is used to test the elastic modulus of the natural state and evaluate the collapsibility. In both tests, the first load is kept to 200 kPa and then the test pit is injected water evenly, with a constant head height of 30 cm. The results show that the deformation modulus of the travertine can reach 45.39 MPa in natural state and 36.85 MPa in immersion state; that the foundation bearing capacity is more than 280 kPa in immersion state; and that the depth of infiltration is 0.65 m after 3 hours of immersion. It is concluded that the stability of the travertine in water is poor and the construction in the dry season is recommended. The bearing capacity of travertine is sufficiently high in natural condition but reduced somewhat in case of immersion so that the base should be kept dry as far as possible. The permeability of travertine is small. If the foundation is waterproof in rainy seasons, it keeps a sufficient bearing capacity.
Travertine is a kind of macroporous secondary calcium carbonate, formed by Karst water. Travertine can create beautiful natural landscapes such as the Huanglong scenic spot in China, the Pamukkale in Turkey, and the Yellowstone Park Mammoth Hot Springs in the United States. While travertine is mainly distributed in the carbonate areas with frequent water flow, it is rarely used as foundation of buildings and its engineering characteristics are less studied. The project location is in Bolivia, South America, where a steel plant is to be built upon a Travertine land. The travertine in this area is formed by the lacustrine facies, grayish-white, visible honeycomb-like or spongy voids, with some of the voids filled with clay. The SPT N value of the travertine is 39 to 77, which has good mechanical properties in the natural state. But when the travertine is submerged in water, it collapses quickly. Rain in Bolivia lasts for four months annually, it is worried that rain can damage the travertine foundation. A study is thus conducted to test the properties of travertine in the construction site. It is found that the permeability of travertine is 1.7×10-3cm·s-1. The load test is divided into two groups, P1 and P2. The P1 test point is used to test the bearing capacity and collapsibility under the condition of immersion. P1 is soaked in water before the test, and the water head height was 30 cm for 5 days. The P2 test site is used to test the elastic modulus of the natural state and evaluate the collapsibility. In both tests, the first load is kept to 200 kPa and then the test pit is injected water evenly, with a constant head height of 30 cm. The results show that the deformation modulus of the travertine can reach 45.39 MPa in natural state and 36.85 MPa in immersion state; that the foundation bearing capacity is more than 280 kPa in immersion state; and that the depth of infiltration is 0.65 m after 3 hours of immersion. It is concluded that the stability of the travertine in water is poor and the construction in the dry season is recommended. The bearing capacity of travertine is sufficiently high in natural condition but reduced somewhat in case of immersion so that the base should be kept dry as far as possible. The permeability of travertine is small. If the foundation is waterproof in rainy seasons, it keeps a sufficient bearing capacity.
2020, 28(6): 1178-1185.
Brittleness has an important influence on rock failure mechanism and acoustic emission characteristics. Uniaxial compression and acoustic emission tests were carried out using two different lithological rocks of granite and marble. The strength and deformation characteristics of the two rocks were obtained, and the brittleness was quantitatively evaluated. The evolution characteristics of acoustic emission(AE)energy of two rocks during uniaxial compression were analyzed. Combined with the calculation results of AE b value and their physical meanings, the differences of two rock failure mechanisms were compared. The results are summarized as follows. (1)The ratio of σcd/σp of the granite used in the experiment is between 0.676~0.745, with an average of 0.706, while that of the marble is in the range of 0.439 to 0.615, with an average value of 0.52. (2)Based on the brittleness evaluation index, combined with the macroscopic failure phenomenon and morphology of the sample, the granite used in this test is more brittle than the marble. (3)In the case of the same axial compression deformation generated during the crack unstable propagation stage, the greater the brittleness of the rock, the larger the amount of circumferential deformation. (4)The high-brittle granite exhibits sustained high-level acoustic emission signals during the crack unstable propagation stage, whereas the weak brittle marble shows a continuously decreasing trend. After the peak strength, the AE signal with high-value energy is more active for the weak brittle marble. (5)The ratio of macro-crack to micro-crack is larger for granite than that of marble during the destruction process under uniaxial compression.
Brittleness has an important influence on rock failure mechanism and acoustic emission characteristics. Uniaxial compression and acoustic emission tests were carried out using two different lithological rocks of granite and marble. The strength and deformation characteristics of the two rocks were obtained, and the brittleness was quantitatively evaluated. The evolution characteristics of acoustic emission(AE)energy of two rocks during uniaxial compression were analyzed. Combined with the calculation results of AE b value and their physical meanings, the differences of two rock failure mechanisms were compared. The results are summarized as follows. (1)The ratio of σcd/σp of the granite used in the experiment is between 0.676~0.745, with an average of 0.706, while that of the marble is in the range of 0.439 to 0.615, with an average value of 0.52. (2)Based on the brittleness evaluation index, combined with the macroscopic failure phenomenon and morphology of the sample, the granite used in this test is more brittle than the marble. (3)In the case of the same axial compression deformation generated during the crack unstable propagation stage, the greater the brittleness of the rock, the larger the amount of circumferential deformation. (4)The high-brittle granite exhibits sustained high-level acoustic emission signals during the crack unstable propagation stage, whereas the weak brittle marble shows a continuously decreasing trend. After the peak strength, the AE signal with high-value energy is more active for the weak brittle marble. (5)The ratio of macro-crack to micro-crack is larger for granite than that of marble during the destruction process under uniaxial compression.
2020, 28(6): 1186-1192.
Humidification-dehumidification cycle is one of the main causes of engineering diseases in the loess area. It is of great theoretical and engineering significance to explore the mechanism of the humidification-dehumidification cycle to damage the loess structure. In this paper, the loess in Yan'an area is taken as the research object. The undisturbed loess humidification-dehumidification cycle tests with different water contents and different times are carried out to analyze the change rules of porosity, shear strength and parameters of loess induced by dry and wet cycles. NMR technology is used to obtain the damage evolution of crack development in loess. The results show that with the increase of the times of dry-wet cycling, the soil exhibits a gradual increase in porosity, a decrease in the liquid limit and plasticity index, and a basically constant plastic limit. The reason is the dynamic changes in the internal particles loess damage. The increase of dry-wet cycling times and water content weakens the cementation of the soil particles, which reduces the shear strength, cohesion, and internal friction angle. When the water content of the sample exceeds the plastic limit, the decline becomes more obvious. The NMR of the loess shows that with the increase of the times of dry-wet cycling, micropores smaller than 0.025 μm inside the sample gradually transits to small pore groups of 0.025~0.63 μm and new pores begin to occur.
Humidification-dehumidification cycle is one of the main causes of engineering diseases in the loess area. It is of great theoretical and engineering significance to explore the mechanism of the humidification-dehumidification cycle to damage the loess structure. In this paper, the loess in Yan'an area is taken as the research object. The undisturbed loess humidification-dehumidification cycle tests with different water contents and different times are carried out to analyze the change rules of porosity, shear strength and parameters of loess induced by dry and wet cycles. NMR technology is used to obtain the damage evolution of crack development in loess. The results show that with the increase of the times of dry-wet cycling, the soil exhibits a gradual increase in porosity, a decrease in the liquid limit and plasticity index, and a basically constant plastic limit. The reason is the dynamic changes in the internal particles loess damage. The increase of dry-wet cycling times and water content weakens the cementation of the soil particles, which reduces the shear strength, cohesion, and internal friction angle. When the water content of the sample exceeds the plastic limit, the decline becomes more obvious. The NMR of the loess shows that with the increase of the times of dry-wet cycling, micropores smaller than 0.025 μm inside the sample gradually transits to small pore groups of 0.025~0.63 μm and new pores begin to occur.
2020, 28(6): 1193-1204.
As a basic attribute of Soil-Rock Mixtures(S-RMs), particle breakage has complex formation mechanism and many influencing factors. To systematically explore the influencing factors and basic laws of the breakage characteristics of S-RMs, we construct a PFC2D particle discrete element numerical model by the thought of Monte Carlo. The model can truly reflect the breakage process of the rock block. Based on the indoor direct shear test and screening test, we carry out a series of numerical shear tests. The results show that: the sample appears obvious breakage phenomenon after shearing to disperse stress. The diameter of rock block has a significant effect on the breakage degree of rock block. The larger the diameter of rock block is, the greater the breakage potential is, and the easier it is to be broken. When the edges and corners of rock block are obvious, the stress concentration degree is stronger, and the breakage rate is larger. When the grain group is continuous and good, the particles contact more and completely, so the interface is larger and the breakage is less likely to occur. The initial porosity of the sample has little effect on the breakage rate. Under the same normal stress, with the increase of porosity, the breakage degree of the rock block shows a slight increasing trend.
As a basic attribute of Soil-Rock Mixtures(S-RMs), particle breakage has complex formation mechanism and many influencing factors. To systematically explore the influencing factors and basic laws of the breakage characteristics of S-RMs, we construct a PFC2D particle discrete element numerical model by the thought of Monte Carlo. The model can truly reflect the breakage process of the rock block. Based on the indoor direct shear test and screening test, we carry out a series of numerical shear tests. The results show that: the sample appears obvious breakage phenomenon after shearing to disperse stress. The diameter of rock block has a significant effect on the breakage degree of rock block. The larger the diameter of rock block is, the greater the breakage potential is, and the easier it is to be broken. When the edges and corners of rock block are obvious, the stress concentration degree is stronger, and the breakage rate is larger. When the grain group is continuous and good, the particles contact more and completely, so the interface is larger and the breakage is less likely to occur. The initial porosity of the sample has little effect on the breakage rate. Under the same normal stress, with the increase of porosity, the breakage degree of the rock block shows a slight increasing trend.
2020, 28(6): 1205-1212.
As the most active component of particles, clay minerals play an important role in the physical and mechanical properties of soil, such as liquid plasticity, strength and expansibility. One of the core problems of soil solidification is the use of suitable curing agents to solidify the clay minerals. This paper carries out scanning electron microscopy(SEM), Fourier infrared spectroscopy(FTIR), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS), studies the microstructure, material composition and physicochemical reaction process of clay minerals solidified by alkali-activated geopolymers with different alkali dosages, and discussed the interaction mechanism of alkali-activated geopolymers and clay minerals. The results show that Alkali activated geopolymers can solidify clay minerals well. The clay minerals are transformed from loose particles to bulky dense structure after solidified by alkali-activated geopolymers. With the alkali dosage of geopolymers increases, the electronic binding energy of Si, Al, and Ca elements decreases. The diffraction peak of montmorillonite shifts to the right(001) at a diffraction angle of about 5°, and the interlayer distance is decreased. The absorbed water content and hydrophilic capacity of montmorillonite are decreased, and the mineral activity is limited.
As the most active component of particles, clay minerals play an important role in the physical and mechanical properties of soil, such as liquid plasticity, strength and expansibility. One of the core problems of soil solidification is the use of suitable curing agents to solidify the clay minerals. This paper carries out scanning electron microscopy(SEM), Fourier infrared spectroscopy(FTIR), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS), studies the microstructure, material composition and physicochemical reaction process of clay minerals solidified by alkali-activated geopolymers with different alkali dosages, and discussed the interaction mechanism of alkali-activated geopolymers and clay minerals. The results show that Alkali activated geopolymers can solidify clay minerals well. The clay minerals are transformed from loose particles to bulky dense structure after solidified by alkali-activated geopolymers. With the alkali dosage of geopolymers increases, the electronic binding energy of Si, Al, and Ca elements decreases. The diffraction peak of montmorillonite shifts to the right(001) at a diffraction angle of about 5°, and the interlayer distance is decreased. The absorbed water content and hydrophilic capacity of montmorillonite are decreased, and the mineral activity is limited.
2020, 28(6): 1213-1220.
Longyao ground fissure is one of the large and hyperactive ground fissures in North China plain. The activity of the fissure has caused damages such as slip dislocation,vertical subsidence and horizontal tension to buildings and highways over the fissure. In order to provide essential data for disaster prevention and mitigation of engineering buildings along the fissure,we carried out field geological survey and OSL dating experiment to ascertain the accurate activity value of Longyao ground fissure. We summarized the horizontal distribution and sectional structure characteristics of Longyao ground fissure at the beginning. Then we determined the strike-slip displacement,vertical dislocation and horizontal tensile width of the ground fissure based on the exploratory trench profile. Finally,we estimated the slip rates of Longyao ground fissure during different periods. Our study results show that the vertical differential settlement rate is the largest on both sides of the fissure,the horizontal strike-slip dislocation rate is the second,and the horizontal tension rate is the smallest. According to the OSL experiment,from 8 ka B.P. to present,the displacement rate of Longyao ground fissure has been increasing. Since the Holocene,the ground fissures have been continuously active and the intensity has been raised constantly. We also found that there were three periods of rapid rise in activity rate.
Longyao ground fissure is one of the large and hyperactive ground fissures in North China plain. The activity of the fissure has caused damages such as slip dislocation,vertical subsidence and horizontal tension to buildings and highways over the fissure. In order to provide essential data for disaster prevention and mitigation of engineering buildings along the fissure,we carried out field geological survey and OSL dating experiment to ascertain the accurate activity value of Longyao ground fissure. We summarized the horizontal distribution and sectional structure characteristics of Longyao ground fissure at the beginning. Then we determined the strike-slip displacement,vertical dislocation and horizontal tensile width of the ground fissure based on the exploratory trench profile. Finally,we estimated the slip rates of Longyao ground fissure during different periods. Our study results show that the vertical differential settlement rate is the largest on both sides of the fissure,the horizontal strike-slip dislocation rate is the second,and the horizontal tension rate is the smallest. According to the OSL experiment,from 8 ka B.P. to present,the displacement rate of Longyao ground fissure has been increasing. Since the Holocene,the ground fissures have been continuously active and the intensity has been raised constantly. We also found that there were three periods of rapid rise in activity rate.
2020, 28(6): 1221-1232.
Daguangbao landslide is the largest landslide triggered by Wenchuan earthquake. How did it reach high speed and long-runout?This question attracted wide attentions of scholars at home and abroad. This paper aims the explanation for the mechanism of high-speed and long-runout and adopts the velocity-depending frictional weakening of sliding bed due to thermal decomposition and dynamic crystallization. This paper modifies the input manner of the strength parameter in the Discontinuous deformation analysis(DDA)method. The constant strength parameter in original DDA is replaced by the velocity-depending strength parameter. The paper realizes the dynamic adjustment of the friction coefficient with the change of relative velocity between two blocks on a contact. The modified DDA is used to simulate the mobility of Daguangbao landslide. The results show that the mechanism of frictional weakening can be an important reason for the characteristic of high-speed and long-runout of Daguangbao landslide. Comparing to the original DDA,the mobility characteristics of high-speed and long-runout landslides can be simulated more reasonably by the modified DDA,where the frictional weakening of the sliding bed can be implemented. Daguangbao landslide was instable during the earthquake. Due to the frictional weakening of sliding bed,more energy was converted into kinetic energy. After the high-speed sliding mass crossing the Huangdongzi valley,the sliding mass was blocked by the opposite Pingliangzi slope,and then the sliding mass stopped. Comparing with the original DDA results,the modified DDA′s simulation is in good agreement with the result from post-earthquake field investigation. It also indirectly proves that the friction coefficient of Daguangbao landslide may be reduced due to the thermal decomposition and powder lubrication caused by friction flash heating between dolomites,which may be an important reason for the high-speed characteristics of Daguangbao landslide.
Daguangbao landslide is the largest landslide triggered by Wenchuan earthquake. How did it reach high speed and long-runout?This question attracted wide attentions of scholars at home and abroad. This paper aims the explanation for the mechanism of high-speed and long-runout and adopts the velocity-depending frictional weakening of sliding bed due to thermal decomposition and dynamic crystallization. This paper modifies the input manner of the strength parameter in the Discontinuous deformation analysis(DDA)method. The constant strength parameter in original DDA is replaced by the velocity-depending strength parameter. The paper realizes the dynamic adjustment of the friction coefficient with the change of relative velocity between two blocks on a contact. The modified DDA is used to simulate the mobility of Daguangbao landslide. The results show that the mechanism of frictional weakening can be an important reason for the characteristic of high-speed and long-runout of Daguangbao landslide. Comparing to the original DDA,the mobility characteristics of high-speed and long-runout landslides can be simulated more reasonably by the modified DDA,where the frictional weakening of the sliding bed can be implemented. Daguangbao landslide was instable during the earthquake. Due to the frictional weakening of sliding bed,more energy was converted into kinetic energy. After the high-speed sliding mass crossing the Huangdongzi valley,the sliding mass was blocked by the opposite Pingliangzi slope,and then the sliding mass stopped. Comparing with the original DDA results,the modified DDA′s simulation is in good agreement with the result from post-earthquake field investigation. It also indirectly proves that the friction coefficient of Daguangbao landslide may be reduced due to the thermal decomposition and powder lubrication caused by friction flash heating between dolomites,which may be an important reason for the high-speed characteristics of Daguangbao landslide.
2020, 28(6): 1233-1245.
The 2008 "5.12" Wenchuan earthquake greatly changed the characteristics of debris flows in the earthquake zone. The earthquake not only enhanced the activity of debris flows,but also made the earthquake area under the threat of debris flows for a long time. During the past 10 years after the earthquake,debris flows occurred frequently. It is of great significance to study the characteristics and development trend of debris flows in Wenchuan County. We analyze the longitudinal gradient,gully density and slope gradient in Wenchuan County by means of remote sensing interpretation and field investigation. We further analyze the rainfall spatial and temporal trends and critical rainfall characteristics of debris flows in Wenchuan County by collecting rainfall data and previous research. According to the study,the average annual rainfall in Wenchuan County increased by 5.17% after the earthquake. The rainfall was mainly in July and September,the amount of rainfall decreased gradually from north to south. The gully density of debris flow gully is between 0.2 and 4,which belongs to the soil erosion area of the micro-degree. The longitudinal gradient of debris flow is large,which is conducive to the occurrence of debris flow. The slope gradient of debris flows is 30°~40°,which is conducive to the occurrence of disasters. The rainfall threshold of the post-earthquake debris flow shows a slow increased in 2008-2013, but declined in 2019. It is expected that it can take a long time to return to the pre-earthquake levels. The provenance of debris flows in Wenchuan County is abundant,and the amount of provenance in the earthquake is decreased in a fluctuating tendency.
The 2008 "5.12" Wenchuan earthquake greatly changed the characteristics of debris flows in the earthquake zone. The earthquake not only enhanced the activity of debris flows,but also made the earthquake area under the threat of debris flows for a long time. During the past 10 years after the earthquake,debris flows occurred frequently. It is of great significance to study the characteristics and development trend of debris flows in Wenchuan County. We analyze the longitudinal gradient,gully density and slope gradient in Wenchuan County by means of remote sensing interpretation and field investigation. We further analyze the rainfall spatial and temporal trends and critical rainfall characteristics of debris flows in Wenchuan County by collecting rainfall data and previous research. According to the study,the average annual rainfall in Wenchuan County increased by 5.17% after the earthquake. The rainfall was mainly in July and September,the amount of rainfall decreased gradually from north to south. The gully density of debris flow gully is between 0.2 and 4,which belongs to the soil erosion area of the micro-degree. The longitudinal gradient of debris flow is large,which is conducive to the occurrence of debris flow. The slope gradient of debris flows is 30°~40°,which is conducive to the occurrence of disasters. The rainfall threshold of the post-earthquake debris flow shows a slow increased in 2008-2013, but declined in 2019. It is expected that it can take a long time to return to the pre-earthquake levels. The provenance of debris flows in Wenchuan County is abundant,and the amount of provenance in the earthquake is decreased in a fluctuating tendency.
2020, 28(6): 1259-1271.
Earthquake-induced landslides are serious secondary geological hazards,and they are also an important force to change the topography of the earth surface. Research on the scale,number,and type of earthquake-induced landslides is an important method for seismic risk assessment and the main method for understanding seismic geological disasters and approaches. The scale,quantity and the type of earthquake-induced landslide is an important way to evaluate the seismic risk,and also the main approach to understand the seismic hazard. There is a prehistoric landslide group of about 50 km long in the middle part of the northern foothills of the Qinling Mountains. It is distributed in parallel with the Qingling Piedmont fault. The recent research generally believes that the prehistoric landslide group was probably induced by the significance earthquake of the Qingling Piedmont fault activity. But there is no detailed study on the magnitude and influence range of this earthquake. In this paper,we use the high-resolution digital elevation model(DEM)that is produced from the ZY-3 satellite stereo image,and multispectral remote sensing image to mapping the landslide area in detail. Combined with the some field investigation,we finally obtain a detailed map of the prehistoric landslide distribution in the Qinling Piedmont area. In the end,totaling 43 prehistoric landslides are interpreted and concentrated in a area of 70×10 km2. Based on the relationship between the moment magnitude and the frequency-area distribution(FAD) of inventories of triggered landslides,we analyze the earthquake scale of the prehistoric landslide group in Qinling Piedmont area. The magnitude of the earthquake that triggered the prehistoric landslide group in the north Qinling Piedmont should be between 7.6 and 8.1. By combining the regional seismic tectonic environment and the comparison with modern earthquake-induced landslide events,we conclude that the Qinling Piedmont fault has the potential to produce earthquakes of more than 7.5 magnitude. This research provides quantitative data support for understanding the causes of the prehistoric landslide group in the Qingling Piedmont area,and also has practical significance for understanding the seismic risk of the Qinling Piedmont fault.
Earthquake-induced landslides are serious secondary geological hazards,and they are also an important force to change the topography of the earth surface. Research on the scale,number,and type of earthquake-induced landslides is an important method for seismic risk assessment and the main method for understanding seismic geological disasters and approaches. The scale,quantity and the type of earthquake-induced landslide is an important way to evaluate the seismic risk,and also the main approach to understand the seismic hazard. There is a prehistoric landslide group of about 50 km long in the middle part of the northern foothills of the Qinling Mountains. It is distributed in parallel with the Qingling Piedmont fault. The recent research generally believes that the prehistoric landslide group was probably induced by the significance earthquake of the Qingling Piedmont fault activity. But there is no detailed study on the magnitude and influence range of this earthquake. In this paper,we use the high-resolution digital elevation model(DEM)that is produced from the ZY-3 satellite stereo image,and multispectral remote sensing image to mapping the landslide area in detail. Combined with the some field investigation,we finally obtain a detailed map of the prehistoric landslide distribution in the Qinling Piedmont area. In the end,totaling 43 prehistoric landslides are interpreted and concentrated in a area of 70×10 km2. Based on the relationship between the moment magnitude and the frequency-area distribution(FAD) of inventories of triggered landslides,we analyze the earthquake scale of the prehistoric landslide group in Qinling Piedmont area. The magnitude of the earthquake that triggered the prehistoric landslide group in the north Qinling Piedmont should be between 7.6 and 8.1. By combining the regional seismic tectonic environment and the comparison with modern earthquake-induced landslide events,we conclude that the Qinling Piedmont fault has the potential to produce earthquakes of more than 7.5 magnitude. This research provides quantitative data support for understanding the causes of the prehistoric landslide group in the Qingling Piedmont area,and also has practical significance for understanding the seismic risk of the Qinling Piedmont fault.
2020, 28(6): 1279-1291.
Due to the complex structure of rock and soil mass and various failure mechanisms,landslide early warning has always been a global problem of very challenging. At 5:53 a.m. on 17 February 2019 in Longjing Village,Maling Town,Xingyi City,Guizhou Province,a landslide geological disaster occurred. About 960,000 cubic meters of mountain had a bedding sliding,which posed a serious threat to the road and residential area located at the foot of the front slope. In this paper,we discuss the characteristics and successful early warning process of this Xingyi landslide in Guizhou Province,and analyze the key factors of successful early warning. On the basis of geological investigations on the landslide site,this paper comprehensively use satellite remote sensing,UAV aerial photography,lidar,surface displacement monitoring and other technical means to reveal the historical deformation and pre-sliding deformation characteristics of the landslide. Finally,we analyze the mechanism of the landslide. After preliminary analysis,we conclude that Xingyi landslide belongs to a typical bedding rock landslide with weak intercalation. The slope in the source area of the landslide was an unstable slope formed after the first sliding in 2014. It had a combination of unfavorable slope structure and weak intercalation. Under the action of long-term gravity and groundwater,it eventually evolved into a landslide geological disaster. In the process of landslide evolution,the strength of the weak intercalation decreased after the interaction with groundwater,and its physical and mechanical properties also became poor,which was easy to produce extrusion deformation and led to compression and shear deformation of the sliding body towards the free direction,resulting in cracking of the rear edge and side boundary slope. Such cracks formed the main control structural plane. Before the landslide,the researchers installed two kinds of displacement monitoring sensors,the global navigation satellite system(GNSS) and the adaptive crack meter,to continuously monitor the deformation of the landslide. The on-site monitoring data is transmitted to the"geological disaster monitoring and early warning system" in real time,which was independently developed by researchers. The system automatically calculates the monitoring data and issues the early warning results through a variety of threshold comprehensive early warning models. According to the analysis of monitoring data,the landslide experienced the initial acceleration deformation stage,the intermediate acceleration deformation stage,the temporary sliding stage,and finally the disaster occurred. At each stage,the system released the early warning information in time according to the four-level early warning mechanism. Especially after the landslide entered the critical slide stage,the system sent out the red early warning 53 minutes in advance,which created the time condition for disaster emergency disposal and completely avoided the loss of personnel and economy. The successful early warning of the landslide reflected the applicability of the self-developed geological disaster monitoring and early warning system,early warning model and monitoring instrument,which can provide reference for research and application of similar landslide monitoring and early warning in the future.
Due to the complex structure of rock and soil mass and various failure mechanisms,landslide early warning has always been a global problem of very challenging. At 5:53 a.m. on 17 February 2019 in Longjing Village,Maling Town,Xingyi City,Guizhou Province,a landslide geological disaster occurred. About 960,000 cubic meters of mountain had a bedding sliding,which posed a serious threat to the road and residential area located at the foot of the front slope. In this paper,we discuss the characteristics and successful early warning process of this Xingyi landslide in Guizhou Province,and analyze the key factors of successful early warning. On the basis of geological investigations on the landslide site,this paper comprehensively use satellite remote sensing,UAV aerial photography,lidar,surface displacement monitoring and other technical means to reveal the historical deformation and pre-sliding deformation characteristics of the landslide. Finally,we analyze the mechanism of the landslide. After preliminary analysis,we conclude that Xingyi landslide belongs to a typical bedding rock landslide with weak intercalation. The slope in the source area of the landslide was an unstable slope formed after the first sliding in 2014. It had a combination of unfavorable slope structure and weak intercalation. Under the action of long-term gravity and groundwater,it eventually evolved into a landslide geological disaster. In the process of landslide evolution,the strength of the weak intercalation decreased after the interaction with groundwater,and its physical and mechanical properties also became poor,which was easy to produce extrusion deformation and led to compression and shear deformation of the sliding body towards the free direction,resulting in cracking of the rear edge and side boundary slope. Such cracks formed the main control structural plane. Before the landslide,the researchers installed two kinds of displacement monitoring sensors,the global navigation satellite system(GNSS) and the adaptive crack meter,to continuously monitor the deformation of the landslide. The on-site monitoring data is transmitted to the"geological disaster monitoring and early warning system" in real time,which was independently developed by researchers. The system automatically calculates the monitoring data and issues the early warning results through a variety of threshold comprehensive early warning models. According to the analysis of monitoring data,the landslide experienced the initial acceleration deformation stage,the intermediate acceleration deformation stage,the temporary sliding stage,and finally the disaster occurred. At each stage,the system released the early warning information in time according to the four-level early warning mechanism. Especially after the landslide entered the critical slide stage,the system sent out the red early warning 53 minutes in advance,which created the time condition for disaster emergency disposal and completely avoided the loss of personnel and economy. The successful early warning of the landslide reflected the applicability of the self-developed geological disaster monitoring and early warning system,early warning model and monitoring instrument,which can provide reference for research and application of similar landslide monitoring and early warning in the future.
2020, 28(6): 1281-1289.
The China-Kyrgyzstan-Uzbekistan railway is an international gateway from northwest China to Central Asia and Southern Europe. The forecast of geological disasters along the railway can provide some suggestions for its route selection. The Mamdani fuzzy inference system(Mamdani FIS)model is applied on the prediction of landslide susceptibility of the study area on AK53-AK130 of the north and AK60-AK131 of the south along the railway project line. Based on the nine kinds of landslide influencing factors,768 rules of inference are established. These factors include geological environment background,topographic factors and ecological environment and are collected by remote sensing and regional geological background data. The aim of the study is to apply the Mamdani FIS model for the China-Kyrgyzstan-Uzbekistan railway landslide prediction,and then divides the research area into extremely high prone zones,high prone zones,moderate prone zones,low prone zones,and extremely low prone zones. The result shows that the extremely high prone area and high prone area of landslide are distributed near the Fergana Mountains in the north and the Arthur River Basin in the south. Based on the results,the area under the curve(AUC)obtained from the Receiver Operating Characteristic Curve(ROC curve) is 0.859,which indicates that the prediction results are successful.
The China-Kyrgyzstan-Uzbekistan railway is an international gateway from northwest China to Central Asia and Southern Europe. The forecast of geological disasters along the railway can provide some suggestions for its route selection. The Mamdani fuzzy inference system(Mamdani FIS)model is applied on the prediction of landslide susceptibility of the study area on AK53-AK130 of the north and AK60-AK131 of the south along the railway project line. Based on the nine kinds of landslide influencing factors,768 rules of inference are established. These factors include geological environment background,topographic factors and ecological environment and are collected by remote sensing and regional geological background data. The aim of the study is to apply the Mamdani FIS model for the China-Kyrgyzstan-Uzbekistan railway landslide prediction,and then divides the research area into extremely high prone zones,high prone zones,moderate prone zones,low prone zones,and extremely low prone zones. The result shows that the extremely high prone area and high prone area of landslide are distributed near the Fergana Mountains in the north and the Arthur River Basin in the south. Based on the results,the area under the curve(AUC)obtained from the Receiver Operating Characteristic Curve(ROC curve) is 0.859,which indicates that the prediction results are successful.
2020, 28(6): 1300-1310.
Mountain torrents and debris flows carrying with driftwood are common in nowadays. The damage caused by driftwood has increased in recent years. However, there are few researches about the effect of driftwood in present prevention works for debris flow. Therefore, it is necessary to study the mitigation effect of debris flow check dams with driftwood. Taking the slit dam as an example, we carried out a series of physical model tests. The results show that the driftwood always moves on the surface of the fluid and arrives at the dam before sediment. Whether driftwood accumulates at the openings of the slit dam, it has a significant influence on the sediment deposition in front of the dam, the sediment outflow rates, and the retention rates of driftwood. Without driftwood accumulation, obvious erosion takes place on the sediment deposition before the dam by subsequent flow. Sediment outflow rates are slightly lower than that without driftwood. Once a driftwood accumulation is formed, the sediment deposition in front of the dam has no obvious erosion. The sediment outflow rates obviously decrease, while the total retention rates of driftwood increase remarkably. The retention rates of different driftwood components are various with the difference of driftwood length. The larger the length-width ratio L/b(L:the driftwood length, b: the opening width of slit dam) is, the easier the retention of driftwood is. The total retention rates of driftwood increase along with the increase of the amount of the driftwood with L/b>1. In addition, the existence of the driftwood with L/b>1 is a key condition for the formation of driftwood accumulation.
Mountain torrents and debris flows carrying with driftwood are common in nowadays. The damage caused by driftwood has increased in recent years. However, there are few researches about the effect of driftwood in present prevention works for debris flow. Therefore, it is necessary to study the mitigation effect of debris flow check dams with driftwood. Taking the slit dam as an example, we carried out a series of physical model tests. The results show that the driftwood always moves on the surface of the fluid and arrives at the dam before sediment. Whether driftwood accumulates at the openings of the slit dam, it has a significant influence on the sediment deposition in front of the dam, the sediment outflow rates, and the retention rates of driftwood. Without driftwood accumulation, obvious erosion takes place on the sediment deposition before the dam by subsequent flow. Sediment outflow rates are slightly lower than that without driftwood. Once a driftwood accumulation is formed, the sediment deposition in front of the dam has no obvious erosion. The sediment outflow rates obviously decrease, while the total retention rates of driftwood increase remarkably. The retention rates of different driftwood components are various with the difference of driftwood length. The larger the length-width ratio L/b(L:the driftwood length, b: the opening width of slit dam) is, the easier the retention of driftwood is. The total retention rates of driftwood increase along with the increase of the amount of the driftwood with L/b>1. In addition, the existence of the driftwood with L/b>1 is a key condition for the formation of driftwood accumulation.
2020, 28(6): 1305-1313.
In order to understand the widening process of dam breach in different slope sections of trench bed,seven sets of flume tests were carried out with the gradient of 7°~13°and the interval of 1°. Seven groups of experimental data were compared and analyzed to evaluate the influence of different ditch bed slopes on the process of dam breach widening. The following results and conclusions are obtained. (1)The process of breach widening of dam with overtopping failure is very similar at different slope sections. According to the characteristics of breach,the widening process can be divided into three stages: break through,mutation and formation of stable slope. (2)In the sudden change stage,the slope can lose stability many times along the x-axis direction. The top of the breach is in the shape of "S" on the downstream slope,in the shape of "U" on the dam crest and in the shape of "arc" on the upstream slope. (3)Different slope conditions can affect the outburst characteristics in the abrupt stage. With the increase of the slope of the gully bed,the scale of the single slope instability increases first and then decreases,and the number of the slope instability decreases first and then increases. (4)The stability of the breach slope mainly depends on the width of the side erosion and depth of the vertical erosion of the breach,which has a negative correlation with the difference between the width of the top and bottom side erosion of the breach,and a positive correlation with the depth of the vertical erosion of the breach. (5)The discharge of dam with different slopes has the same change trend with the extension of failure time. However,the peak discharge and the arrival time of the peak discharge are different at different slopes of the channel bed. With the increase of the slope of the channel bed,the peak discharge gradually decreases,and the arrival time of the peak discharge is first advanced and then postponed.
In order to understand the widening process of dam breach in different slope sections of trench bed,seven sets of flume tests were carried out with the gradient of 7°~13°and the interval of 1°. Seven groups of experimental data were compared and analyzed to evaluate the influence of different ditch bed slopes on the process of dam breach widening. The following results and conclusions are obtained. (1)The process of breach widening of dam with overtopping failure is very similar at different slope sections. According to the characteristics of breach,the widening process can be divided into three stages: break through,mutation and formation of stable slope. (2)In the sudden change stage,the slope can lose stability many times along the x-axis direction. The top of the breach is in the shape of "S" on the downstream slope,in the shape of "U" on the dam crest and in the shape of "arc" on the upstream slope. (3)Different slope conditions can affect the outburst characteristics in the abrupt stage. With the increase of the slope of the gully bed,the scale of the single slope instability increases first and then decreases,and the number of the slope instability decreases first and then increases. (4)The stability of the breach slope mainly depends on the width of the side erosion and depth of the vertical erosion of the breach,which has a negative correlation with the difference between the width of the top and bottom side erosion of the breach,and a positive correlation with the depth of the vertical erosion of the breach. (5)The discharge of dam with different slopes has the same change trend with the extension of failure time. However,the peak discharge and the arrival time of the peak discharge are different at different slopes of the channel bed. With the increase of the slope of the channel bed,the peak discharge gradually decreases,and the arrival time of the peak discharge is first advanced and then postponed.
2020, 28(6): 1319-1328.
Tianshan Mountains are a typical periglacial area with high altitude, latitude and temperature difference in China. On the basis of the air temperature data collected from meteorological stations and onsite monitoring, we establish the freeze-thaw(FT)erosion assessment model and discuss the spatial-temporal differentiation characteristics of FT erosion and its effect on erosion rate of rock mass based on field investigation by 3D laser scanning. The results show that the factors of air temperature, rock mass structure, precipitation, slope gradient, earthquake intensity and slope have a decreasing contribution value to the FT erosion in order. The lower elevation of periglacial area is about 2600 m to 2900 m above sea level in Tianshan mountainous area and the FT erosion intensity increases with the increase of altitude and latitude. The seasonal variation and the temperatures fluctuate at the 0 ℃when the freeze and thaw alternating period, thus the FT erosion is the strongest. Geomorphological evolution process can be divided into FT erosion of rock mass, rock fragment slip-slide and deposition. The FT erosion rate of granite(hard rock), sandstone(medium hard rock) and phyllite(soft rock) slope increases with the increase of FT erosion assessment index, and decreases with the increase of rock FT coefficient. The empirical relationship between FT erosion rate and FT erosion assessment index and FT coefficient is established. The results are useful to the understanding of the mechanism and process of FT erosion, for engineering construction and geohazard reduction in periglacial areas.
Tianshan Mountains are a typical periglacial area with high altitude, latitude and temperature difference in China. On the basis of the air temperature data collected from meteorological stations and onsite monitoring, we establish the freeze-thaw(FT)erosion assessment model and discuss the spatial-temporal differentiation characteristics of FT erosion and its effect on erosion rate of rock mass based on field investigation by 3D laser scanning. The results show that the factors of air temperature, rock mass structure, precipitation, slope gradient, earthquake intensity and slope have a decreasing contribution value to the FT erosion in order. The lower elevation of periglacial area is about 2600 m to 2900 m above sea level in Tianshan mountainous area and the FT erosion intensity increases with the increase of altitude and latitude. The seasonal variation and the temperatures fluctuate at the 0 ℃when the freeze and thaw alternating period, thus the FT erosion is the strongest. Geomorphological evolution process can be divided into FT erosion of rock mass, rock fragment slip-slide and deposition. The FT erosion rate of granite(hard rock), sandstone(medium hard rock) and phyllite(soft rock) slope increases with the increase of FT erosion assessment index, and decreases with the increase of rock FT coefficient. The empirical relationship between FT erosion rate and FT erosion assessment index and FT coefficient is established. The results are useful to the understanding of the mechanism and process of FT erosion, for engineering construction and geohazard reduction in periglacial areas.
2020, 28(6): 1323-1332.
Typhoon storm-induced landslides are very common in the hilly and mountainous areas of southeast China. Understanding the evolution law of this kind of landslide failures is great helpful for the monitoring and early warning of rainfall storm landslides in this area. This study takes the Dehua Shishan landslide in Quanzhou,Fujian Province as a research object and combine the on-site geological survey data to establish a landslide physical and numerical model and to simulate the landslide deformation evolution process. After exploring the laws of seepage and landslide displacement in slope instability,results indicate the follows. (1)In the early period,the rainfall vertically infiltrates slope body with a high infiltration rate. The later infiltration rate decreases as the saturation of slope increases. The early rainfall can make the soil layer at the foot of the slope more prone to the saturation. (2)Rainfall infiltration is the main factor of slope instability. During heavy rainfall condition E3(The rainfall intensity is 100 mm·d-1),the factor of safety decreases from 1.197 to 1.125. In the double peak heavy rain condition E4(The early rainfall intensity is 30 mm·d-1,and the later rainfall intensity is 100 mm·d-1),the factor of safety remains basically unchanged during the early rainfall from 1.197 to 1.188. When the rainstorm starts,the factor of safety drops to 1.060. (4)When early rainfall occurs firstly(rainfall intensity ≤30 mm·d-1) and sudden heavy rainstorm occurs in the later period(rainfall intensity ≥100 mm·d-1)in the experiment,the displacement suddenly increases by 20 mm,and then quickly develops to about 90 mm.
Typhoon storm-induced landslides are very common in the hilly and mountainous areas of southeast China. Understanding the evolution law of this kind of landslide failures is great helpful for the monitoring and early warning of rainfall storm landslides in this area. This study takes the Dehua Shishan landslide in Quanzhou,Fujian Province as a research object and combine the on-site geological survey data to establish a landslide physical and numerical model and to simulate the landslide deformation evolution process. After exploring the laws of seepage and landslide displacement in slope instability,results indicate the follows. (1)In the early period,the rainfall vertically infiltrates slope body with a high infiltration rate. The later infiltration rate decreases as the saturation of slope increases. The early rainfall can make the soil layer at the foot of the slope more prone to the saturation. (2)Rainfall infiltration is the main factor of slope instability. During heavy rainfall condition E3(The rainfall intensity is 100 mm·d-1),the factor of safety decreases from 1.197 to 1.125. In the double peak heavy rain condition E4(The early rainfall intensity is 30 mm·d-1,and the later rainfall intensity is 100 mm·d-1),the factor of safety remains basically unchanged during the early rainfall from 1.197 to 1.188. When the rainstorm starts,the factor of safety drops to 1.060. (4)When early rainfall occurs firstly(rainfall intensity ≤30 mm·d-1) and sudden heavy rainstorm occurs in the later period(rainfall intensity ≥100 mm·d-1)in the experiment,the displacement suddenly increases by 20 mm,and then quickly develops to about 90 mm.
2020, 28(6): 1329-1338.
Recently, some scholars have noticed the liquefaction phenomenon of unsaturated sandy silt caused by the impact in the study of loess landslide in south Jingyang platform. This kind of liquefaction phenomenon is special because it is induced by a single impact load rather than a continuous cyclic load. The impact load has the characteristics of high strength, short time, and strong stress wave propagation effect. In order to study the mechanism of this impact liquefaction phenomenon, the paper built a landslide geological generalized model based on the geological background of loess landslide in south Jingyang platform and analyzed the variation of pore water pressure and total stress of sandy silt with different saturations in the same impact condition. The water content and shear strength of sandy silt after impact were also measured. The result shows that:(1)During impact load, the total stress and the pore water pressure in sandy silty are suddenly increased, and several pressure peaks occur because of the transfer of stress waves. While the wave disappears, the excess pore water pressure turns into the residual pore water pressure which remains stable for a period of time; (2)Under the impact of 80% and 90% saturation, sandy silty soil has different degrees of liquefaction at different layers, while sandy silty soil under the same condition of 70% saturation is not liquefied after impact; (3)The water in the lower part migrates to the upper part during and after the impact process. As a result, the water content of the surface soil increased, and the shear strength decreased; (4)The impact liquefaction mechanism of sandy silty is a rapidly destroying and recombining behavior of the original skeleton structure in an undrained condition, which causes the rapid accumulation of pore water pressure.
Recently, some scholars have noticed the liquefaction phenomenon of unsaturated sandy silt caused by the impact in the study of loess landslide in south Jingyang platform. This kind of liquefaction phenomenon is special because it is induced by a single impact load rather than a continuous cyclic load. The impact load has the characteristics of high strength, short time, and strong stress wave propagation effect. In order to study the mechanism of this impact liquefaction phenomenon, the paper built a landslide geological generalized model based on the geological background of loess landslide in south Jingyang platform and analyzed the variation of pore water pressure and total stress of sandy silt with different saturations in the same impact condition. The water content and shear strength of sandy silt after impact were also measured. The result shows that:(1)During impact load, the total stress and the pore water pressure in sandy silty are suddenly increased, and several pressure peaks occur because of the transfer of stress waves. While the wave disappears, the excess pore water pressure turns into the residual pore water pressure which remains stable for a period of time; (2)Under the impact of 80% and 90% saturation, sandy silty soil has different degrees of liquefaction at different layers, while sandy silty soil under the same condition of 70% saturation is not liquefied after impact; (3)The water in the lower part migrates to the upper part during and after the impact process. As a result, the water content of the surface soil increased, and the shear strength decreased; (4)The impact liquefaction mechanism of sandy silty is a rapidly destroying and recombining behavior of the original skeleton structure in an undrained condition, which causes the rapid accumulation of pore water pressure.
2020, 28(6): 1339-1349.
The Haibalo Gully located in the Hengduan Mountain region in northwest Yunnan, where a debris flow broke out at 2:40 am on July 28, 2019. In order to scientifically and accurately carry out debris flow monitoring, early warning and comprehensive prevention work in this area and guarantee the construction and operation safety of Xiangli(Shangri-La to Lijiang) highway in the middle and lower reaches of Haibalo Valley, this paper studied the characteristics and genesis of this debris flow according to the field survey, UAV aerial photography and remote sensing, combined with indoor experimental analysis and calculation. For this debris, the maximum bulk density was 16.77 kN·m-3, so it belonged to low-viscosity debris flow, with flood-peak discharge about 528.16 m3·s-1. Under the influence of geological and climatic conditions, there are 3 types of source in Haibalo Gully, landslide mass on side bank of gully in valley area, moraine and frozen weathered debris in the high position. The debris flow occurred at the tail of the main rainfall process from the evening of the 27th to the early morning of the 28th. According to the monitoring of 9 rainfall processes in Haibalo Gully Basin from August to October in 2019, we found that the main process of rainfall in this area is 6 hours, and the precipitation increases significantly with the elevation. The heavy rainfall that triggered the debris flow concentrated in the peak ridge area of 4200~4800 m in the west of Haba snow mountain, and the average rainfall was 60.43 mm in the main rainfall process of 6 h. In addition to the rainfall, the excitation factors also contain glacier melt water in the peak ridge area. According to calculation, the average melting water equivalent of the glacier is 17.29 mm during the 6 h rainfall. The achievements of this study can provide a reliable scientific basis for the monitoring, early warning and prevention of the rainfall glacier-malt-water mixed type debris flow in the Hengduan Mountain region of northwest Yunnan.
The Haibalo Gully located in the Hengduan Mountain region in northwest Yunnan, where a debris flow broke out at 2:40 am on July 28, 2019. In order to scientifically and accurately carry out debris flow monitoring, early warning and comprehensive prevention work in this area and guarantee the construction and operation safety of Xiangli(Shangri-La to Lijiang) highway in the middle and lower reaches of Haibalo Valley, this paper studied the characteristics and genesis of this debris flow according to the field survey, UAV aerial photography and remote sensing, combined with indoor experimental analysis and calculation. For this debris, the maximum bulk density was 16.77 kN·m-3, so it belonged to low-viscosity debris flow, with flood-peak discharge about 528.16 m3·s-1. Under the influence of geological and climatic conditions, there are 3 types of source in Haibalo Gully, landslide mass on side bank of gully in valley area, moraine and frozen weathered debris in the high position. The debris flow occurred at the tail of the main rainfall process from the evening of the 27th to the early morning of the 28th. According to the monitoring of 9 rainfall processes in Haibalo Gully Basin from August to October in 2019, we found that the main process of rainfall in this area is 6 hours, and the precipitation increases significantly with the elevation. The heavy rainfall that triggered the debris flow concentrated in the peak ridge area of 4200~4800 m in the west of Haba snow mountain, and the average rainfall was 60.43 mm in the main rainfall process of 6 h. In addition to the rainfall, the excitation factors also contain glacier melt water in the peak ridge area. According to calculation, the average melting water equivalent of the glacier is 17.29 mm during the 6 h rainfall. The achievements of this study can provide a reliable scientific basis for the monitoring, early warning and prevention of the rainfall glacier-malt-water mixed type debris flow in the Hengduan Mountain region of northwest Yunnan.
2020, 28(6): 1344-1351.
This paper takes the slope of Yaoshan Village in Anxi County as an example. Through visiting surveys, engineering surveys and professional monitoring, it identifies the study area topography and lithology, the characteristics of the groundwater pipe network seepage system, the deformation and failure modes of the slope. It uses FEFLOW software to construct groundwater seepage model in the study area, explores the variation law of groundwater seepage field with different rain intensity, and utilizes FLAC strength reduction method to calculate the sliding surface depth of slope and its safety factor. The results show the follows. The slope not only exhibits the characteristics of tensile cracking deformation and failure, but also features such as ground subsidence and ground collapse. Under the rain conditions of 165.5 mm·m-1 and 317.7 mm·m-1, the groundwater level increases by 0.5~1.5 m and 0.5~2.5 m respectively, compared with the natural conditions. The depth of the sliding surface is 9~12 m, and the safety factor is 1.04 and 0.97. It is consistent with the site investigation and monitoring results. Based on this, it is recommended to adopt "blind drainage ditch blind pipe+intercepting drainage ditch" as the main engineering treatment measure.
This paper takes the slope of Yaoshan Village in Anxi County as an example. Through visiting surveys, engineering surveys and professional monitoring, it identifies the study area topography and lithology, the characteristics of the groundwater pipe network seepage system, the deformation and failure modes of the slope. It uses FEFLOW software to construct groundwater seepage model in the study area, explores the variation law of groundwater seepage field with different rain intensity, and utilizes FLAC strength reduction method to calculate the sliding surface depth of slope and its safety factor. The results show the follows. The slope not only exhibits the characteristics of tensile cracking deformation and failure, but also features such as ground subsidence and ground collapse. Under the rain conditions of 165.5 mm·m-1 and 317.7 mm·m-1, the groundwater level increases by 0.5~1.5 m and 0.5~2.5 m respectively, compared with the natural conditions. The depth of the sliding surface is 9~12 m, and the safety factor is 1.04 and 0.97. It is consistent with the site investigation and monitoring results. Based on this, it is recommended to adopt "blind drainage ditch blind pipe+intercepting drainage ditch" as the main engineering treatment measure.
2020, 28(6): 1378-1385.
The dynamic response characteristics and long-term cumulative deformation development law of silty sand stratum under the metro train load are important engineering topics. In order to study them, the following works are carried out. At first, we analyze the long-term settlement monitoring data of Nanjing Metro Line 2 in typical silty sand stratum. Then, based on two- and -a-half-dimensional(2.5D)numerical method, we analyze the vibration characteristics of silty sand stratum under the train vibration load. Finally, we sum up the cumulative deformation formula of silty sand under vibration load, and use the stratified summation method to study the long-term cumulative deformation development law of silty sand. We have the following results. (1)With the increase of the depth, the dynamic deviator stress of the silty sand layer under the tunnel increases at first and then decreases. Its maximum value usually appears at 1 m below the bottom of the tunnel and is about 3.5 kPa. (2)The long-term deformation of the silty sand stratum induced by the train vibration load develops rapidly at the initial stage of the metro operation. However, it can reach a stable stage in about one year, then the deformation increases slowly. The total deformation value after stabilization is about 15.1 mm. (3)After 7 years of metro operation, the settlement value of the tunnel silty sand foundation induced by the long-term metro vibration loads takes up about 26% of its total settlement value.
The dynamic response characteristics and long-term cumulative deformation development law of silty sand stratum under the metro train load are important engineering topics. In order to study them, the following works are carried out. At first, we analyze the long-term settlement monitoring data of Nanjing Metro Line 2 in typical silty sand stratum. Then, based on two- and -a-half-dimensional(2.5D)numerical method, we analyze the vibration characteristics of silty sand stratum under the train vibration load. Finally, we sum up the cumulative deformation formula of silty sand under vibration load, and use the stratified summation method to study the long-term cumulative deformation development law of silty sand. We have the following results. (1)With the increase of the depth, the dynamic deviator stress of the silty sand layer under the tunnel increases at first and then decreases. Its maximum value usually appears at 1 m below the bottom of the tunnel and is about 3.5 kPa. (2)The long-term deformation of the silty sand stratum induced by the train vibration load develops rapidly at the initial stage of the metro operation. However, it can reach a stable stage in about one year, then the deformation increases slowly. The total deformation value after stabilization is about 15.1 mm. (3)After 7 years of metro operation, the settlement value of the tunnel silty sand foundation induced by the long-term metro vibration loads takes up about 26% of its total settlement value.
2020, 28(6): 1383-1391.
This paper aims to find out the interaction mechanism between the expansive component and the aggregate in the coarse-grained filler of the high-speed railway subgrade. We select some sections of the ballastless track of the Westem China Passenger Dedicated Line. These sections are deformed by arches. In some of the work sites, the packing of the bed part is collected for sampling analysis, and the expansion test with the porosity-montmorillonite content as a variable is carried out. The variation law of filler expansion rate under the combined action of montmorillonite content and filler porosity is analyzed for the expansion mechanism of this micro-expansion filler. The test results show that the filler expansion rate is positively correlated with the content of expansive minerals(montmorillonite) and negatively correlated with porosity. After further analysis of these data, the parameter β is proposed and defined as the ratio of montmorillonite content to filler porosity for the index of ductility expansion of the roadbed filler. When the bed group A of the structure β=0.365, the expansion property of the group A filler reaches the critical index of the high-speed railway. Conversion of parameter β to expansion rate and numerical simulation proves the incompatibility of the current regulations with the design calculation of the high-speed railway.
This paper aims to find out the interaction mechanism between the expansive component and the aggregate in the coarse-grained filler of the high-speed railway subgrade. We select some sections of the ballastless track of the Westem China Passenger Dedicated Line. These sections are deformed by arches. In some of the work sites, the packing of the bed part is collected for sampling analysis, and the expansion test with the porosity-montmorillonite content as a variable is carried out. The variation law of filler expansion rate under the combined action of montmorillonite content and filler porosity is analyzed for the expansion mechanism of this micro-expansion filler. The test results show that the filler expansion rate is positively correlated with the content of expansive minerals(montmorillonite) and negatively correlated with porosity. After further analysis of these data, the parameter β is proposed and defined as the ratio of montmorillonite content to filler porosity for the index of ductility expansion of the roadbed filler. When the bed group A of the structure β=0.365, the expansion property of the group A filler reaches the critical index of the high-speed railway. Conversion of parameter β to expansion rate and numerical simulation proves the incompatibility of the current regulations with the design calculation of the high-speed railway.
2020, 28(6): 1386-1396.
Rockburst is one of the main geological disasters during construction in deep and long tunnel. The whole process of 'gestation-occurrence-evolution' is extremely complicated. The prediction of rockburst has become a worldwide difficult problem in underground engineering. It is of great significance to accurately reflect the change law of high ground stress and the influence of geological structure in engineering region, and based on the measured data to predict rockburst classification to ensure the preliminary geological survey and safe construction of tunnels. According to the regional geological data of tunnel, we use the COMSOL Multiphysics and Rhino establish a three-dimensional numerical calculation model. By using the boundary load adjustment method, we inverse the whole area of in-situ stress field. Considering the key factors of rockburst comprehensively, four factors are selected as evaluation indexes. They are the ratio of the uniaxial compressive strength(UCS) of rock to maximum principal stress of the cavern (σc/σmax), the ratio of the maximum tangential stress of the cavern to the UCS of rock (σθ/σc), the ratio of UCS to tensile strength of rock(σc/σt), and the elastic strain energy index (Wet). We further use the entropy weight and efficacy coefficient method to determine the weight of indexes and the total efficacy coefficient separately. We construct a rockburst prediction model of deep and long tunnel using the efficiency coefficient method and the ground stress field inversion. The evaluation model is applied to Sangzhuling tunnel and compared with the actual situation to verify the result. The result shows that this method has high accuracy and reliability for rockburst prediction of deep and long tunnel. It provides a new basis for the prediction of rockburst in similar underground engineering.
Rockburst is one of the main geological disasters during construction in deep and long tunnel. The whole process of 'gestation-occurrence-evolution' is extremely complicated. The prediction of rockburst has become a worldwide difficult problem in underground engineering. It is of great significance to accurately reflect the change law of high ground stress and the influence of geological structure in engineering region, and based on the measured data to predict rockburst classification to ensure the preliminary geological survey and safe construction of tunnels. According to the regional geological data of tunnel, we use the COMSOL Multiphysics and Rhino establish a three-dimensional numerical calculation model. By using the boundary load adjustment method, we inverse the whole area of in-situ stress field. Considering the key factors of rockburst comprehensively, four factors are selected as evaluation indexes. They are the ratio of the uniaxial compressive strength(UCS) of rock to maximum principal stress of the cavern (σc/σmax), the ratio of the maximum tangential stress of the cavern to the UCS of rock (σθ/σc), the ratio of UCS to tensile strength of rock(σc/σt), and the elastic strain energy index (Wet). We further use the entropy weight and efficacy coefficient method to determine the weight of indexes and the total efficacy coefficient separately. We construct a rockburst prediction model of deep and long tunnel using the efficiency coefficient method and the ground stress field inversion. The evaluation model is applied to Sangzhuling tunnel and compared with the actual situation to verify the result. The result shows that this method has high accuracy and reliability for rockburst prediction of deep and long tunnel. It provides a new basis for the prediction of rockburst in similar underground engineering.
2020, 28(6): 1392-1400.
The characteristics of deformation and mechanical performance of multi-tiered geogrid reinforced soil retaining wall(MGRSRW)need to be further analyzed in detail. In this paper, the model tests are carried out to comprehensively investigate the effect of offset distance, reinforcement length of upper wall and reinforcement spacing on the performance of MGRSRW. The experiments results show that reducing the width of offset distance from 1.3H1 to 0.4H1, decreasing the reinforcement spacing or increasing reinforcement length of upper wall, can cause to reduce settlement or settlement ratio on the top of MGRSRW obviously. At the same time, the ultimate bearing capacity of the retaining wall is enhanced significantly. The horizontal deformation of MGRSRW is closely related with offset distance and reinforcement length of upper wall. The distribution of upper wall is tended to be with "drum belly" in the middle of upper wall, and the deformation of lower wall along the wall gradually increases. With the increase of offset distance and decrease of spacing, the vertical earth pressure at the bottom of upper wall increases and the vertical earth pressure near the facing panels of lower wall decreases obviously. Increasing the length of the upper wall reinforcement and reducing the reinforcement spacing can cause to the vertical earth pressure developing away from the wall side. The slip surface of MGRSRW starts at back edge of the loading plate and passes through the bearing pad of toe of upper wall, and then penetrates the soil at the top of the lower wall. The failure mode is dominant in deep sliding failure of the upper wall.
The characteristics of deformation and mechanical performance of multi-tiered geogrid reinforced soil retaining wall(MGRSRW)need to be further analyzed in detail. In this paper, the model tests are carried out to comprehensively investigate the effect of offset distance, reinforcement length of upper wall and reinforcement spacing on the performance of MGRSRW. The experiments results show that reducing the width of offset distance from 1.3H1 to 0.4H1, decreasing the reinforcement spacing or increasing reinforcement length of upper wall, can cause to reduce settlement or settlement ratio on the top of MGRSRW obviously. At the same time, the ultimate bearing capacity of the retaining wall is enhanced significantly. The horizontal deformation of MGRSRW is closely related with offset distance and reinforcement length of upper wall. The distribution of upper wall is tended to be with "drum belly" in the middle of upper wall, and the deformation of lower wall along the wall gradually increases. With the increase of offset distance and decrease of spacing, the vertical earth pressure at the bottom of upper wall increases and the vertical earth pressure near the facing panels of lower wall decreases obviously. Increasing the length of the upper wall reinforcement and reducing the reinforcement spacing can cause to the vertical earth pressure developing away from the wall side. The slip surface of MGRSRW starts at back edge of the loading plate and passes through the bearing pad of toe of upper wall, and then penetrates the soil at the top of the lower wall. The failure mode is dominant in deep sliding failure of the upper wall.
2020, 28(6): 1397-1405.
Using the discrete element software called PFC2D, we simulate the earth pressure variation of arched cut-and-cover tunnel with different height-span ratios(0.4 to 0.9)under the EPS load reduction measures. Moreover, we also analyze the vertical earth pressure and vertical displacement on top of the cut-and-cover tunnel, horizontal earth pressure on sides of the cut-and-cover tunnel and soil particle contact at the micro level. We understand the change of earth pressure in the inner soil. Meanwhile, we analyze the effects of different groove width ratios and slope angles on earth pressure at the optimal height-span ratio. The result shows that the top of arched cut-and-cover tunnel appears soil arch effect when there is EPS load reduction. The vertical earth pressure on top of the cut-and-cover tunnel changes from the center of the model to the sides with a U-shaped distribution. The vertical displacement on top of the cut-and-cover tunnel decreases from the center of the model to the sides with a V-shaped distribution. The horizontal earth pressure on sides of the cut-and-cover tunnel changes with an inclined S-shaped distribution along the vertical direction. At the optimal height-span ratio of 0.8, the soil particle contact shows a good level, where the contact force and coordination number are the smallest, and the porosity is the largest. In addition, with the increase of the groove width ratio, the average vertical earth pressure gradually increases, the vertical displacement difference and the average horizontal earth pressure gradually decrease, and the soil particle contact level becomes worse. With the increase of the slope angle, the average vertical earth pressure gradually decreases, the vertical displacement difference and the average horizontal earth pressure gradually increase, and the soil particle contact level becomes better. The results can provide reference for the selection and construction of high-filled loess cut-and-covert tunnel in the valley area.
Using the discrete element software called PFC2D, we simulate the earth pressure variation of arched cut-and-cover tunnel with different height-span ratios(0.4 to 0.9)under the EPS load reduction measures. Moreover, we also analyze the vertical earth pressure and vertical displacement on top of the cut-and-cover tunnel, horizontal earth pressure on sides of the cut-and-cover tunnel and soil particle contact at the micro level. We understand the change of earth pressure in the inner soil. Meanwhile, we analyze the effects of different groove width ratios and slope angles on earth pressure at the optimal height-span ratio. The result shows that the top of arched cut-and-cover tunnel appears soil arch effect when there is EPS load reduction. The vertical earth pressure on top of the cut-and-cover tunnel changes from the center of the model to the sides with a U-shaped distribution. The vertical displacement on top of the cut-and-cover tunnel decreases from the center of the model to the sides with a V-shaped distribution. The horizontal earth pressure on sides of the cut-and-cover tunnel changes with an inclined S-shaped distribution along the vertical direction. At the optimal height-span ratio of 0.8, the soil particle contact shows a good level, where the contact force and coordination number are the smallest, and the porosity is the largest. In addition, with the increase of the groove width ratio, the average vertical earth pressure gradually increases, the vertical displacement difference and the average horizontal earth pressure gradually decrease, and the soil particle contact level becomes worse. With the increase of the slope angle, the average vertical earth pressure gradually decreases, the vertical displacement difference and the average horizontal earth pressure gradually increase, and the soil particle contact level becomes better. The results can provide reference for the selection and construction of high-filled loess cut-and-covert tunnel in the valley area.
2020, 28(6): 1401-1410.
This paper takes the combined soil and rock foundation pit with the adjacent buildings in coastal area as example, uses the structure style of micro steel pile-anchor-soil nail, and studies the deformation of the supporting structure induced by excavation under different constitutive models based on PLAXIS software. It chooses the most appropriate constitutive models to study the deformation law of supporting structure under two key factors, i.e., the prestress coefficient of anchor and the flexural rigidity of micro steel pile. The results indicate that the vertical displacements of ground induced by excavation are similar between HS and HSS models, which are converged with the field measured values. The difference of the horizontal displacements of pile between the theoretical values calculated with MC and MCC constitutive models and the field measured values increases gradually with the development of excavation. The HSS model can describe the deformation law of supporting structure induced by overloading of adjacent buildings and excavation unloading accurately. The maximum value of horizontal displacement of pile appears on the ground surface with different prestress coefficient and flexural rigidity of micro steel pile respectively. The prestress coefficient has a significant effect on the control of horizontal displacement at the ground surface and the anchor. It's reasonable to determine the range of the prestress coefficient when the horizontal displacement at the place of the first anchor is zero. Then, the objective value can be chosen in the range of prestress coefficient according the deformation requirements of surrounding environment. Finally, the flexural rigidity of micro steel pile can be determined according to the objective value of prestress coefficient, which leads to the anchor and micro steel pile being made up of supporting system of deformation coordination.
This paper takes the combined soil and rock foundation pit with the adjacent buildings in coastal area as example, uses the structure style of micro steel pile-anchor-soil nail, and studies the deformation of the supporting structure induced by excavation under different constitutive models based on PLAXIS software. It chooses the most appropriate constitutive models to study the deformation law of supporting structure under two key factors, i.e., the prestress coefficient of anchor and the flexural rigidity of micro steel pile. The results indicate that the vertical displacements of ground induced by excavation are similar between HS and HSS models, which are converged with the field measured values. The difference of the horizontal displacements of pile between the theoretical values calculated with MC and MCC constitutive models and the field measured values increases gradually with the development of excavation. The HSS model can describe the deformation law of supporting structure induced by overloading of adjacent buildings and excavation unloading accurately. The maximum value of horizontal displacement of pile appears on the ground surface with different prestress coefficient and flexural rigidity of micro steel pile respectively. The prestress coefficient has a significant effect on the control of horizontal displacement at the ground surface and the anchor. It's reasonable to determine the range of the prestress coefficient when the horizontal displacement at the place of the first anchor is zero. Then, the objective value can be chosen in the range of prestress coefficient according the deformation requirements of surrounding environment. Finally, the flexural rigidity of micro steel pile can be determined according to the objective value of prestress coefficient, which leads to the anchor and micro steel pile being made up of supporting system of deformation coordination.
2020, 28(6): 1425-1432.
Sand can be severely liquefied under the action of earthquakes. The instability of foundation caused by sand liquefaction can cause serious damage to various facilities such as roads, buildings and dams. Therefore, the prediction of sand liquefaction under earthquake action has always been a hot topic in the field of geological disasters. This paper uses 166 sets of identification data of earthquake induced sand liquefaction cases that occurred in the world in the past few decades. Through numerous data training and parameter analysis, we establish the sand liquefaction assessment model based on machine learning. The results show that the network structure is optimized when the network structure is 6(input layer)-15(hidden layer)-1(output layer) and the training function is Levenberg-Marquardt. The best prediction accuracy of test data can reach 96%. The results of parameter analysis show that different parameters have different effects on the accuracy of network prediction. Cone end resistance, the surface normalized peak horizontal acceleration has a relatively large impact. Earthquake magnitude, total vertical stress, effective vertical stress have moderate influence; penetration depth has less effect. Therefore, the input parameters can be simplified appropriately under the conditions of different network prediction accuracy requirements.
Sand can be severely liquefied under the action of earthquakes. The instability of foundation caused by sand liquefaction can cause serious damage to various facilities such as roads, buildings and dams. Therefore, the prediction of sand liquefaction under earthquake action has always been a hot topic in the field of geological disasters. This paper uses 166 sets of identification data of earthquake induced sand liquefaction cases that occurred in the world in the past few decades. Through numerous data training and parameter analysis, we establish the sand liquefaction assessment model based on machine learning. The results show that the network structure is optimized when the network structure is 6(input layer)-15(hidden layer)-1(output layer) and the training function is Levenberg-Marquardt. The best prediction accuracy of test data can reach 96%. The results of parameter analysis show that different parameters have different effects on the accuracy of network prediction. Cone end resistance, the surface normalized peak horizontal acceleration has a relatively large impact. Earthquake magnitude, total vertical stress, effective vertical stress have moderate influence; penetration depth has less effect. Therefore, the input parameters can be simplified appropriately under the conditions of different network prediction accuracy requirements.
2020, 28(6): 1439-1447.
The large ancient underground rock caverns in Longyou is an important component of grotto cultural. It has important scientific and engineering value. In order to prove the scientific of No.23-1 inclined rock pillar, A series of studies were carried out. The topography, landform, stratum, structure and earthquake were investigated and analyzed. The cavern was scanned by using Leica C10. The microscopic rock properties was analyzed by using electron microscope scanning tests and X ray diffraction tests. The physical and mechanical properties of rock mass were analyzed through the mechanical tests and the back analysis of numerical simulation. On this basis, the comparative analysis was carried out by using FLAC3D between No.23-1 inclined rock pillars and the hypothetical vertical rock column with the same volume and average section. The research results confirmed the scientificity of No.23-1 inclined rock pillars. It has important reference value for modern mining engineering, development and utilization of underground space, design and construction of geotechnical engineering.
The large ancient underground rock caverns in Longyou is an important component of grotto cultural. It has important scientific and engineering value. In order to prove the scientific of No.23-1 inclined rock pillar, A series of studies were carried out. The topography, landform, stratum, structure and earthquake were investigated and analyzed. The cavern was scanned by using Leica C10. The microscopic rock properties was analyzed by using electron microscope scanning tests and X ray diffraction tests. The physical and mechanical properties of rock mass were analyzed through the mechanical tests and the back analysis of numerical simulation. On this basis, the comparative analysis was carried out by using FLAC3D between No.23-1 inclined rock pillars and the hypothetical vertical rock column with the same volume and average section. The research results confirmed the scientificity of No.23-1 inclined rock pillars. It has important reference value for modern mining engineering, development and utilization of underground space, design and construction of geotechnical engineering.
2020, 28(6): 1441-1449.
The interaction of river and groundwater is critical for understanding recharge and water quality for porous aquifer in the mountain front area, Huairou, Beijing. In this area groundwater level was greatly dropped due to heavy abstraction before the year of 2013, and alleviated from 2015 by the arrival and input of Yangtze River water under the south to north water division project. Transported river water could increasingly play roles for recharge into aquifers and help to restore groundwater storage. River and groundwater samples were taken from Huairou area and measured major ions and δD-δ18O to investigate the distribution of river infiltrated into shallow porous aquifers for understanding of effects on groundwater quality. The results demonstrate that:(1)δD-δ18O data indicate along river banks groundwater is a mixture with river water where the infiltrated river water has the signal of enriched oxygen-18. Consequently, a binary mixed model was established according to the balance of δ18O between two mixing components and used to estimate the fraction of infiltrated river water. Based on the spatial variation in δ18O values of groundwater near banks of rivers and estimated fraction of river water in the river and groundwater mixture, the area of river water infiltration was delineated; (2)Cl- was taken as conservative tracer to reveal groundwater quality influenced by the river water infiltration. Groundwater Cl- is closely related to Cl- in river waters and unsaturated zone soils and can be used to assess the variation of quality in groundwater with the infiltration of river water. This work will benefit for evaluating river and groundwater interaction and water resources management.
The interaction of river and groundwater is critical for understanding recharge and water quality for porous aquifer in the mountain front area, Huairou, Beijing. In this area groundwater level was greatly dropped due to heavy abstraction before the year of 2013, and alleviated from 2015 by the arrival and input of Yangtze River water under the south to north water division project. Transported river water could increasingly play roles for recharge into aquifers and help to restore groundwater storage. River and groundwater samples were taken from Huairou area and measured major ions and δD-δ18O to investigate the distribution of river infiltrated into shallow porous aquifers for understanding of effects on groundwater quality. The results demonstrate that:(1)δD-δ18O data indicate along river banks groundwater is a mixture with river water where the infiltrated river water has the signal of enriched oxygen-18. Consequently, a binary mixed model was established according to the balance of δ18O between two mixing components and used to estimate the fraction of infiltrated river water. Based on the spatial variation in δ18O values of groundwater near banks of rivers and estimated fraction of river water in the river and groundwater mixture, the area of river water infiltration was delineated; (2)Cl- was taken as conservative tracer to reveal groundwater quality influenced by the river water infiltration. Groundwater Cl- is closely related to Cl- in river waters and unsaturated zone soils and can be used to assess the variation of quality in groundwater with the infiltration of river water. This work will benefit for evaluating river and groundwater interaction and water resources management.
2020, 28(6): 1448-1457.
During the construction of tunnel, the observational classification of rock mass quality is the most direct method to evaluate the quality of the tunnel face surrounding rock. It is also an important basis for preventing geological disasters in tunnel construction, deciding construction excavation method and supporting measures. The traditional Q method and BQ method of national standard rock mass quality grading evaluation method require on-site and indoor laboratory tests and analysis, which results in the lag time of rock mass quality evaluation, often reduces the construction efficiency, or misses the window time to prevent sudden construction geological disasters. Rapidly and accurately to rock mass quality classification of tunnel face is the primary problem to be solved in observational rock mass classification of highway tunnel during construction period. The artificial intelligence algorithm provides a method to solve the real-time and accurate evaluation of the rock mass of the tunnel. Taking Yanqing-Chongli highway for Beijing Winter Olympic Games as an example, we adopt a method of using photogrammetry and artificial intelligence rock structure parameter to identify working face. In this method, seven index parameters system are established. We use the KNN intelligent algorithm to evaluate the quality of the tunnel rock and select 150 samples from 40 working faces in 8 tunnels for the training and learning. Another 50 samples are selected for rock mass quality evaluation and verification. Compared with the rock mass quality evaluation results of BQ, the accuracy reachs 90%. Conclusions are as follows. (1)KNN method for observational classification of rock mass quality of highway tunnel is a fast and efficient method for observational classification of rock mass quality by using artificial intelligence technology, which can obtain real-time rock mass evaluation results on site. (2)KNN classification method selects seven discriminant indicators, considering the occurrence of rock environment, geological structure, rock structure and other characteristics, and reflecting the operability and applicability of these indicators in the actual engineering. (3)KNN classification method misjudgment rate is very low. It has strong discriminant ability when marking discriminant classification by excluding the influence of artificial factors. This method provides a new way to solve the rock mass grade determination and classification.
During the construction of tunnel, the observational classification of rock mass quality is the most direct method to evaluate the quality of the tunnel face surrounding rock. It is also an important basis for preventing geological disasters in tunnel construction, deciding construction excavation method and supporting measures. The traditional Q method and BQ method of national standard rock mass quality grading evaluation method require on-site and indoor laboratory tests and analysis, which results in the lag time of rock mass quality evaluation, often reduces the construction efficiency, or misses the window time to prevent sudden construction geological disasters. Rapidly and accurately to rock mass quality classification of tunnel face is the primary problem to be solved in observational rock mass classification of highway tunnel during construction period. The artificial intelligence algorithm provides a method to solve the real-time and accurate evaluation of the rock mass of the tunnel. Taking Yanqing-Chongli highway for Beijing Winter Olympic Games as an example, we adopt a method of using photogrammetry and artificial intelligence rock structure parameter to identify working face. In this method, seven index parameters system are established. We use the KNN intelligent algorithm to evaluate the quality of the tunnel rock and select 150 samples from 40 working faces in 8 tunnels for the training and learning. Another 50 samples are selected for rock mass quality evaluation and verification. Compared with the rock mass quality evaluation results of BQ, the accuracy reachs 90%. Conclusions are as follows. (1)KNN method for observational classification of rock mass quality of highway tunnel is a fast and efficient method for observational classification of rock mass quality by using artificial intelligence technology, which can obtain real-time rock mass evaluation results on site. (2)KNN classification method selects seven discriminant indicators, considering the occurrence of rock environment, geological structure, rock structure and other characteristics, and reflecting the operability and applicability of these indicators in the actual engineering. (3)KNN classification method misjudgment rate is very low. It has strong discriminant ability when marking discriminant classification by excluding the influence of artificial factors. This method provides a new way to solve the rock mass grade determination and classification.
2020, 28(6): 1466-1473.
In recent years, with the rapid development of big data, deep learning and other technologies, the development and utilization of big data have brought significant economic and social benefits to various industries. It is of great theoretical and social significances to carry out researches on data mining and application of geological texts, images and sequence data by means of big data technologies. This paper focuses on the geological image data processing, development of network models using the deep learning theory and lithology recognition through performing network-based data acquisition, data preprocessing, network construction, network training and result/evaluations. Results show that the recognition accuracy of lithology images is about 90%. Limited image data employed can be one of the reasons for deviations of recognitions. Positive correlation scores given by machine for some similar characteristics of the rock images, e.g., macroscopic shape and color, etc., also can lead to misjudgments in recognition. Theoretically, adoption of networks like BCNN(Bilinear Convolutional Neural Network) for capturing finer details and solving the problem of fine-grained recognition in computer vision and fundamentally improving the efficiency of image recognition, should be considered in future works.
In recent years, with the rapid development of big data, deep learning and other technologies, the development and utilization of big data have brought significant economic and social benefits to various industries. It is of great theoretical and social significances to carry out researches on data mining and application of geological texts, images and sequence data by means of big data technologies. This paper focuses on the geological image data processing, development of network models using the deep learning theory and lithology recognition through performing network-based data acquisition, data preprocessing, network construction, network training and result/evaluations. Results show that the recognition accuracy of lithology images is about 90%. Limited image data employed can be one of the reasons for deviations of recognitions. Positive correlation scores given by machine for some similar characteristics of the rock images, e.g., macroscopic shape and color, etc., also can lead to misjudgments in recognition. Theoretically, adoption of networks like BCNN(Bilinear Convolutional Neural Network) for capturing finer details and solving the problem of fine-grained recognition in computer vision and fundamentally improving the efficiency of image recognition, should be considered in future works.
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