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Editor Work2016 Vol. 24, No. 4
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2016, 24(4): 485-491.
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The mechanism of irrigation-induced loess landslide is one of the top topics of loess geo-hazard researches. Furthermore, the key areas are the hydraulic and mechanical property changes of loess after drying and watering alternation medium under irrigation condition, as well as the slope stability changes due to groundwater flow field response. This paper discusses the developing mechanism of irrigation-induced loess landslide in Heifangtai, which is on the basis of the hydraulic and mechanical property tests of unsaturated loess in Heifangtai, the unsaturated seepage evolving process and developing trend of the slope area due to irrigation. The results demonstrate the following. With the lasting of irrigation, long-term positive water equilibrium field can trigger the rising of the groundwater table. Moistening of the unsaturated zone leads the matric suction to decline and the strength to reduce drastically. Meanwhile, the thickness of the saturated zone increases. This causes build-up of porewater pressure as well as augmentation of the hydraulic gradient in the slope. The seepage velocity fastens. Hence the seepage force on the slope escalates too. Then the slope stability drops. The factor of slope stability declines linearly with the rising of groundwater table. The slope reaches limit equilibrium state when the groundwater table is close to 55m, under which condition it may slide under certain negative triggering factors. The groundwater table change, however, has limited impact on the critical sliding surface.
The mechanism of irrigation-induced loess landslide is one of the top topics of loess geo-hazard researches. Furthermore, the key areas are the hydraulic and mechanical property changes of loess after drying and watering alternation medium under irrigation condition, as well as the slope stability changes due to groundwater flow field response. This paper discusses the developing mechanism of irrigation-induced loess landslide in Heifangtai, which is on the basis of the hydraulic and mechanical property tests of unsaturated loess in Heifangtai, the unsaturated seepage evolving process and developing trend of the slope area due to irrigation. The results demonstrate the following. With the lasting of irrigation, long-term positive water equilibrium field can trigger the rising of the groundwater table. Moistening of the unsaturated zone leads the matric suction to decline and the strength to reduce drastically. Meanwhile, the thickness of the saturated zone increases. This causes build-up of porewater pressure as well as augmentation of the hydraulic gradient in the slope. The seepage velocity fastens. Hence the seepage force on the slope escalates too. Then the slope stability drops. The factor of slope stability declines linearly with the rising of groundwater table. The slope reaches limit equilibrium state when the groundwater table is close to 55m, under which condition it may slide under certain negative triggering factors. The groundwater table change, however, has limited impact on the critical sliding surface.
2016, 24(4): 492-500.
This paper aims to research risk classification for high cut slope during design stage, arrange project investment reasonably and control risk in slope engineering. The classification is based on analysis principles of slope engineering geology and correlative experience summary or feedback analysis, through the analysis of terrain conditions, geological conditions, meteorology and hydrology, and other factors. As a result, the evaluation index system of risk factors for the cut slope is built. It then clears the significance of each evaluation index and determines its risk rating criteria. The system is applied to the risk evaluation of the 71 high slopes along Shuangyong Expressway in Yongding Country. A risk classification method of high cutting slopes during design stage is established. Firstly, an assessment value of each factor is determined according to the survey and design results. Secondly, using analytical hierarchy process, the weights of factors are calculated. Thirdly, 4 different risk classes are divided and the relative countermeasures are proposed to prevent and control risk. Furthermore, the system is applied to evaluation of the K227 landslide and other two low failed slopes. The result shows that this risk classification method is reasonable and feasible, and has evident advantage of avoiding omissions for selecting dangerous slopes. The findings demonstrate this highway is the best section of risk control in construction process and operation period although it has the most complex slopes along the whole highway.
This paper aims to research risk classification for high cut slope during design stage, arrange project investment reasonably and control risk in slope engineering. The classification is based on analysis principles of slope engineering geology and correlative experience summary or feedback analysis, through the analysis of terrain conditions, geological conditions, meteorology and hydrology, and other factors. As a result, the evaluation index system of risk factors for the cut slope is built. It then clears the significance of each evaluation index and determines its risk rating criteria. The system is applied to the risk evaluation of the 71 high slopes along Shuangyong Expressway in Yongding Country. A risk classification method of high cutting slopes during design stage is established. Firstly, an assessment value of each factor is determined according to the survey and design results. Secondly, using analytical hierarchy process, the weights of factors are calculated. Thirdly, 4 different risk classes are divided and the relative countermeasures are proposed to prevent and control risk. Furthermore, the system is applied to evaluation of the K227 landslide and other two low failed slopes. The result shows that this risk classification method is reasonable and feasible, and has evident advantage of avoiding omissions for selecting dangerous slopes. The findings demonstrate this highway is the best section of risk control in construction process and operation period although it has the most complex slopes along the whole highway.
2016, 24(4): 501-509.
In order to explore the influence of landslide stability by the change of reservoir water level, a reservoir bank landslide in Southwest China is researched. According to the engineering geological conditions and genetic mechanism of landslide, the effect of variation of water level impacting on the landslide stability and sliding mode based on fluid-solid coupling is analyzed through a three-dimensional numerical model. The plastic zone distribution and X-displacements under nature state, initial impoundment, water level rise and water level fall are obtained through numerical calculation. The stability of reservoir bank landslide under different water levels is analyzed comprehensively. The results of numerical calculation and actual deformation features are also taken into account in the analysis. The results show the follows. The landslide deformation due to the first water storage of reservoir can cause the slope into unstable state. The water level rise has little influences on the landslide stability. The landslide stability is reduced sharply and the slope is likely to occur instability damage when the water level falls. The failure mode of landslide would be diverted from push mode to drag mode after the water storage of reservoir.
In order to explore the influence of landslide stability by the change of reservoir water level, a reservoir bank landslide in Southwest China is researched. According to the engineering geological conditions and genetic mechanism of landslide, the effect of variation of water level impacting on the landslide stability and sliding mode based on fluid-solid coupling is analyzed through a three-dimensional numerical model. The plastic zone distribution and X-displacements under nature state, initial impoundment, water level rise and water level fall are obtained through numerical calculation. The stability of reservoir bank landslide under different water levels is analyzed comprehensively. The results of numerical calculation and actual deformation features are also taken into account in the analysis. The results show the follows. The landslide deformation due to the first water storage of reservoir can cause the slope into unstable state. The water level rise has little influences on the landslide stability. The landslide stability is reduced sharply and the slope is likely to occur instability damage when the water level falls. The failure mode of landslide would be diverted from push mode to drag mode after the water storage of reservoir.
2016, 24(4): 510-518.
On January 11, 2013,a super catastrophic landslide took place in Zhaojiagou village of Zhenxiong County, Yunnan Province, and made 46 people died and serious economic losses. Based on multiple in-situ investigations and geologic survey, the landslide features and its failure mechanism are studied in the paper. The landslide took place in a natural accumulation slope mainly composed of colluviums and diluvium, and the slope structure has the characteristics of increasing in clay content and denseness but decreasing in porosity and permeability from slope crown to its foot. The main scarp developed along the steep interface of the accumulations and the strongly weathered sandstone bedrock, while the sliding belt developed along the soft layer of diluvium. Before the landslide there already existed a remarkable tension crack in current main scarp and a compression failure in the slope front, which typically is the failure mechanism of Creep-Crack. The main landslide body moved first and the 3 small landslides followed in its left and right flanks as well as the back slopes, and the landslide debris moved in belts. The natural water content of the sliding belt is very close to its liquid limit, and its plastic index is more than 10,which means that the soil is in the liquefied-plastic state and with low shear strength. The high speed at the moment of departure is the result of the long-term accumulation of strain energy but instantly releasing, the high speed during movement is related with the liquefaction of the landslide debris and the bed soil, and there exists proofs of debris flying. It is suggested to strengthen the deformation monitoring of adjacent slopes and the geohazard forecasting of similar accumulation slopes in Wumengshan region.
On January 11, 2013,a super catastrophic landslide took place in Zhaojiagou village of Zhenxiong County, Yunnan Province, and made 46 people died and serious economic losses. Based on multiple in-situ investigations and geologic survey, the landslide features and its failure mechanism are studied in the paper. The landslide took place in a natural accumulation slope mainly composed of colluviums and diluvium, and the slope structure has the characteristics of increasing in clay content and denseness but decreasing in porosity and permeability from slope crown to its foot. The main scarp developed along the steep interface of the accumulations and the strongly weathered sandstone bedrock, while the sliding belt developed along the soft layer of diluvium. Before the landslide there already existed a remarkable tension crack in current main scarp and a compression failure in the slope front, which typically is the failure mechanism of Creep-Crack. The main landslide body moved first and the 3 small landslides followed in its left and right flanks as well as the back slopes, and the landslide debris moved in belts. The natural water content of the sliding belt is very close to its liquid limit, and its plastic index is more than 10,which means that the soil is in the liquefied-plastic state and with low shear strength. The high speed at the moment of departure is the result of the long-term accumulation of strain energy but instantly releasing, the high speed during movement is related with the liquefaction of the landslide debris and the bed soil, and there exists proofs of debris flying. It is suggested to strengthen the deformation monitoring of adjacent slopes and the geohazard forecasting of similar accumulation slopes in Wumengshan region.
2016, 24(4): 519-526.
Mega-earthquakes often occurred in loess hilly region of China. Earthquake-triggered landslides and other geological hazards can be the main reason for a large number of casualties and property losses. The 1718 great Tongwei earthquake in northwest China caused more than 300 large-scaled landslides near the epicenter. The effects led to the movement of the northern mountains located in the meizoseismal area of Pan'an Town(the old Yongning Town),to the south, resulting in the total burial of Yongning town, with a historical record of over 30,000 deaths. Previous studies agree that the earthquake-induced landslides in the area are loess landslides, which slid along ancient terrain surfaces. Through detailed field investigations, the distribution features, the types of disasters and failure mode are studied. Taking the largest landslide-Weijiawan landslide as a case study and with the help of engineering geological drillings on the sliding mass, deep structure characteristics of the landslide are analyzed and the mechanics mechanism are discussed. The results indicate that the failure surface of the huge earthquake-induced landslide is located in the deep mudstone layer, which reveals that these landslides are loess-mudstone composite landslides. These new findings can help to further unravel the failure mechanisms of these earthquake-induced landslides that are recorded in several literatures. Meanwhile, the present results and conclusions can provide insights and knowledge on early recognition of earthquake-triggered landslides in northwest China towns, especially in the surrounding valley which shares similar geological conditions to the landslides studied in this paper.
Mega-earthquakes often occurred in loess hilly region of China. Earthquake-triggered landslides and other geological hazards can be the main reason for a large number of casualties and property losses. The 1718 great Tongwei earthquake in northwest China caused more than 300 large-scaled landslides near the epicenter. The effects led to the movement of the northern mountains located in the meizoseismal area of Pan'an Town(the old Yongning Town),to the south, resulting in the total burial of Yongning town, with a historical record of over 30,000 deaths. Previous studies agree that the earthquake-induced landslides in the area are loess landslides, which slid along ancient terrain surfaces. Through detailed field investigations, the distribution features, the types of disasters and failure mode are studied. Taking the largest landslide-Weijiawan landslide as a case study and with the help of engineering geological drillings on the sliding mass, deep structure characteristics of the landslide are analyzed and the mechanics mechanism are discussed. The results indicate that the failure surface of the huge earthquake-induced landslide is located in the deep mudstone layer, which reveals that these landslides are loess-mudstone composite landslides. These new findings can help to further unravel the failure mechanisms of these earthquake-induced landslides that are recorded in several literatures. Meanwhile, the present results and conclusions can provide insights and knowledge on early recognition of earthquake-triggered landslides in northwest China towns, especially in the surrounding valley which shares similar geological conditions to the landslides studied in this paper.
2016, 24(4): 527-534.
On April 11, 2015, affected by the continuous rainfall, a large-scale counter-dipping rock landslide occurred at Shazhenxi village of Zigui County. The landslide of about 25×104m3 in volume and about 2.5×104m2 in area damaged the town road and a large number of facilities seriously. It is named as Yangjia Well Landslide. On the basis of the first-hand field investigation, the special geological features and rock mass structure characteristic of the landslide are studied in detail. The origin of the landslide is analyzed from two aspects including geologic origin and the environment origin. The formation mechanism and evolution process of the landslide is proposed tentatively by utilizing the theories of geomorphy and engineering geology mechanics. It is also predicted the deformation trend of the landslide. Conclusions as follows:(1) This landslide is continuous rainfall-induced counter-dipping rock landslide, and has traction sliding deformation mode. (2) The particular geological structure is the long-term breeding inner condition of landslide formation; the continuous rainfall is the main and direct triggering factors of landslide formation. (3) With valley incised, high stress released and the unloading and rebound of slope, layered rock mass bent and toppled to outside of the slope, producing fissures parallel to slope surface; with the development of consequent tension joints gradually, the undersurface of bending belt formed a weak structure plane which plays an important role in landslide deformation. (4) During the flood season, local deformation may happen in a certain time, but barrier lake and debris flow is almost impossible; it is advised that the corresponding engineering management should be carried out after the flood season.
On April 11, 2015, affected by the continuous rainfall, a large-scale counter-dipping rock landslide occurred at Shazhenxi village of Zigui County. The landslide of about 25×104m3 in volume and about 2.5×104m2 in area damaged the town road and a large number of facilities seriously. It is named as Yangjia Well Landslide. On the basis of the first-hand field investigation, the special geological features and rock mass structure characteristic of the landslide are studied in detail. The origin of the landslide is analyzed from two aspects including geologic origin and the environment origin. The formation mechanism and evolution process of the landslide is proposed tentatively by utilizing the theories of geomorphy and engineering geology mechanics. It is also predicted the deformation trend of the landslide. Conclusions as follows:(1) This landslide is continuous rainfall-induced counter-dipping rock landslide, and has traction sliding deformation mode. (2) The particular geological structure is the long-term breeding inner condition of landslide formation; the continuous rainfall is the main and direct triggering factors of landslide formation. (3) With valley incised, high stress released and the unloading and rebound of slope, layered rock mass bent and toppled to outside of the slope, producing fissures parallel to slope surface; with the development of consequent tension joints gradually, the undersurface of bending belt formed a weak structure plane which plays an important role in landslide deformation. (4) During the flood season, local deformation may happen in a certain time, but barrier lake and debris flow is almost impossible; it is advised that the corresponding engineering management should be carried out after the flood season.
2016, 24(4): 535-541.
The finite element strength reduction method and limit equilibrium method are used respectively for the slope stabilities of six typical profiles in the submarine canyon area where the submarine pipeline of Liwan3-1gasfield is laid along its seabed. The soil strength characteristic of increase in depth is considered in the slope stabilities models. The comparison result shows that finite element strength reduction method and limit equilibrium method present consistent results. The stability factors obtained by the finite element strength reduction method are most closed to those of the Spencer method, with a relative error of less than 3.5%.All the slopes are basically stable, although some local areas in the middle and lower parts of the canyon with low soil strength and high slope are close to the critical state. The slopes in the upper canyon area have relatively higher stability factors than those in the other areas. The horizontal seismic acceleration can reduce the slope stability factor greatly, and the sliding depth usually increases with the acceleration. When the horizontal acceleration is 0.2g, most slopes in the middle and lower parts of the canyon would fail. The submarine slope angle and the soil strength are the mainly factors which control the slope stability in the canyon area. The stability factor and sliding depth are sensitive to the local slope angle and the strength distribution of the soil. A reasonable slope stability assessment result is dependent on the accuracy of terrain data and soil mechanics parameters.
The finite element strength reduction method and limit equilibrium method are used respectively for the slope stabilities of six typical profiles in the submarine canyon area where the submarine pipeline of Liwan3-1gasfield is laid along its seabed. The soil strength characteristic of increase in depth is considered in the slope stabilities models. The comparison result shows that finite element strength reduction method and limit equilibrium method present consistent results. The stability factors obtained by the finite element strength reduction method are most closed to those of the Spencer method, with a relative error of less than 3.5%.All the slopes are basically stable, although some local areas in the middle and lower parts of the canyon with low soil strength and high slope are close to the critical state. The slopes in the upper canyon area have relatively higher stability factors than those in the other areas. The horizontal seismic acceleration can reduce the slope stability factor greatly, and the sliding depth usually increases with the acceleration. When the horizontal acceleration is 0.2g, most slopes in the middle and lower parts of the canyon would fail. The submarine slope angle and the soil strength are the mainly factors which control the slope stability in the canyon area. The stability factor and sliding depth are sensitive to the local slope angle and the strength distribution of the soil. A reasonable slope stability assessment result is dependent on the accuracy of terrain data and soil mechanics parameters.
2016, 24(4): 542-549.
Rainfall-induced landslides are clustery, recorded by Chinese historic documents. Study of early-warning is a significant way to prevent and reduce damages. Conventional forecasting model is based on statistics of landslides, which is short of inducement mechanism and mechanical mechanism, with limited dependability and precision of forecasting. The typical landslide in weathered granitic crust area is studied in this paper. Based on simplified geological model and saturated-unsaturated seepage theory, the process of rainfall infiltration and instability mechanism is studied, then the warning criterion of typical slope is established. (1) Typical dual-structure slopes in weathered granite crust area are soil-like slopes and covering soil is thick. They are divided into two parts on profile. The upper part is collusive clay with loose soil and high permeability, while the lower part is residual clay with compactness soil and lower permeability. (2) Rainfall infiltration under several conditions are simulated. Taking rainfall intensity of 50mm·d-1 for example, within 30 hours, most rain is in upper collusive clay, causing front edge of slope saturated and sliding zone hydropsy. From 40 to 50 hours, infiltration along with tension cracks around rear edge of slope is faster, and water in cracks may generate hydrostatic increasing weight of soil and sliding power. Meanwhile toe of slope saturates and breaks firstly. Then landslide occurs. (3) Porewater pressure increases continually from monitoring in three parts of slope(front, central and rear of slope). Namely slope soil transforms unsaturated to saturated. The toe of slope gets saturated first, central part under continual infiltration, and upper part saturation cause sliding zone deformation and sliding through hydrostatic pressure. (4) Durations needed when landslides occur under different rainfall conditions are:13 days with moderate rain(10mm·d-1), 5 days with heavy rain(25mm·d-1), 2.2 days with rainstorm(50mm·d-1), and 1.1 days with extraordinary rainstorm(100mm·d-1). Duration of hysteresis is about 5 hours when rainstorm. Finally, critical rainfall criterion(I-D curve) of this kind of slopes is established.
Rainfall-induced landslides are clustery, recorded by Chinese historic documents. Study of early-warning is a significant way to prevent and reduce damages. Conventional forecasting model is based on statistics of landslides, which is short of inducement mechanism and mechanical mechanism, with limited dependability and precision of forecasting. The typical landslide in weathered granitic crust area is studied in this paper. Based on simplified geological model and saturated-unsaturated seepage theory, the process of rainfall infiltration and instability mechanism is studied, then the warning criterion of typical slope is established. (1) Typical dual-structure slopes in weathered granite crust area are soil-like slopes and covering soil is thick. They are divided into two parts on profile. The upper part is collusive clay with loose soil and high permeability, while the lower part is residual clay with compactness soil and lower permeability. (2) Rainfall infiltration under several conditions are simulated. Taking rainfall intensity of 50mm·d-1 for example, within 30 hours, most rain is in upper collusive clay, causing front edge of slope saturated and sliding zone hydropsy. From 40 to 50 hours, infiltration along with tension cracks around rear edge of slope is faster, and water in cracks may generate hydrostatic increasing weight of soil and sliding power. Meanwhile toe of slope saturates and breaks firstly. Then landslide occurs. (3) Porewater pressure increases continually from monitoring in three parts of slope(front, central and rear of slope). Namely slope soil transforms unsaturated to saturated. The toe of slope gets saturated first, central part under continual infiltration, and upper part saturation cause sliding zone deformation and sliding through hydrostatic pressure. (4) Durations needed when landslides occur under different rainfall conditions are:13 days with moderate rain(10mm·d-1), 5 days with heavy rain(25mm·d-1), 2.2 days with rainstorm(50mm·d-1), and 1.1 days with extraordinary rainstorm(100mm·d-1). Duration of hysteresis is about 5 hours when rainstorm. Finally, critical rainfall criterion(I-D curve) of this kind of slopes is established.
2016, 24(4): 550-558.
At 16:30 on August 3, 2014, an MS 6.5 earthquake happened in Longtoushan Town, Ludian County, Zhaotong, in Yunnan Province, and caused 617 deaths and triggered a large number of geohazards. The Hongshiyan landslide and Ganjiazhai landslide are notable for their largest scales in mass and many casualties. According to field survey and remote sensing image interpretation of Ganjiazhai landslide by authors, the developing characteristics and evolution periods of landslides mass are analyzed, and the key triggering factors of this landslides are studied from the perspective of active fault rupture. The Ganjiazhai landslides can be divided into two occurred times. The latest landslide mass is of 700m and 250m in length and width, and 690, 000m2 and about 8.7million m3 of landslides mass area and volume, respectively. It is triggered by the Ludian earthquake from the ancient landslide or avalanche that occurred about 20kaBP, and these two occurred times were all controlled by Xiashuigou Holocene faul that extended by NW direction. At last, this article suggests preventing the risks of landslide in further in Ludian earthquake area, and should strengthen to study the recurrence period of Zhaotong-Ludian active faults in the region, in order to provide the basis for geological environmental safety in the geohazards reconstruction after the earthquake.
At 16:30 on August 3, 2014, an MS 6.5 earthquake happened in Longtoushan Town, Ludian County, Zhaotong, in Yunnan Province, and caused 617 deaths and triggered a large number of geohazards. The Hongshiyan landslide and Ganjiazhai landslide are notable for their largest scales in mass and many casualties. According to field survey and remote sensing image interpretation of Ganjiazhai landslide by authors, the developing characteristics and evolution periods of landslides mass are analyzed, and the key triggering factors of this landslides are studied from the perspective of active fault rupture. The Ganjiazhai landslides can be divided into two occurred times. The latest landslide mass is of 700m and 250m in length and width, and 690, 000m2 and about 8.7million m3 of landslides mass area and volume, respectively. It is triggered by the Ludian earthquake from the ancient landslide or avalanche that occurred about 20kaBP, and these two occurred times were all controlled by Xiashuigou Holocene faul that extended by NW direction. At last, this article suggests preventing the risks of landslide in further in Ludian earthquake area, and should strengthen to study the recurrence period of Zhaotong-Ludian active faults in the region, in order to provide the basis for geological environmental safety in the geohazards reconstruction after the earthquake.
2016, 24(4): 559-568.
The debris flow with narrow-steep channels is very common in gully debris flow in Wenchuan earthquake region. High longitudinal slope and narrow average width of the gully and little drainage basin area are observed in this kind of debris flows. Thus, the debris flows with large scale is easily happened due to the quickly converge of the rainfall in earthquake area. In particular, extra-large group debris flows occurred on July 10, 2013 along Duwen freeway in Sichuan province. This paper concentrates on the phenomenon of the impaction, burying, blockage of Duwen freeway and Minjiang River caused by the debris flow. Through the field investigation of the debris flows, the formation conditions and development characteristics are identified. Using of CFX hydrodynamic calculation software, a simulation of the dynamical process of narrow-steep channels featured debris flow during 50-year storm conditions is set up. The paper makes a prediction of the hazardous region, evaluates the destructive effects on the Duwen freeway, Minjiang River and residents of settlements, which can provide the evidence of the prevention measures design of the debris flow.
The debris flow with narrow-steep channels is very common in gully debris flow in Wenchuan earthquake region. High longitudinal slope and narrow average width of the gully and little drainage basin area are observed in this kind of debris flows. Thus, the debris flows with large scale is easily happened due to the quickly converge of the rainfall in earthquake area. In particular, extra-large group debris flows occurred on July 10, 2013 along Duwen freeway in Sichuan province. This paper concentrates on the phenomenon of the impaction, burying, blockage of Duwen freeway and Minjiang River caused by the debris flow. Through the field investigation of the debris flows, the formation conditions and development characteristics are identified. Using of CFX hydrodynamic calculation software, a simulation of the dynamical process of narrow-steep channels featured debris flow during 50-year storm conditions is set up. The paper makes a prediction of the hazardous region, evaluates the destructive effects on the Duwen freeway, Minjiang River and residents of settlements, which can provide the evidence of the prevention measures design of the debris flow.
2016, 24(4): 569-577.
This paper is based on the analysis of landslide and a large number of predecessor research results. It summarizes the works of conventional numerical simulation in the analysis of stability, landslide mechanism analysis and reproducing sliding process. It presents the basic conditions of numerical simulation applicable to geo-hazard emergent rescuing. At the same time, it puts forward the state differences between conventional and emergency numerical analyses. It clearly figures out the characteristics of emergency numerical simulation, and the key problems about the application of numerical simulation to geo-hazard emergent rescuing. It gives an application example of the Wangshan-Zhuakousi landslide on the Mount Emei, Sichuan province. It uses the numerical method of discontinuous deformation analysis(DDA) that has outstanding advantages in the analysis of large deformation in real time. The numerical simulation in the process and reason of the landslide have been taken into a further study. The results show, the sliding process is successfully reproduced and the maximum horizontal displacement of the sliding body reached by DDA mode is 87meters. The peak speed is 7m·s-1. The results show that sliding distance is about 38meters and the leading edge thickness is 53meters. The whole duration of the landslide obtained by DDA method is about 70 seconds. The numerical results are consistent with the results of emergent investigation. It's concluded that numerical simulation in geo-hazard emergency is good for the comprehension of the process of landslide, finding the key point and auxiliary emergency decision.
This paper is based on the analysis of landslide and a large number of predecessor research results. It summarizes the works of conventional numerical simulation in the analysis of stability, landslide mechanism analysis and reproducing sliding process. It presents the basic conditions of numerical simulation applicable to geo-hazard emergent rescuing. At the same time, it puts forward the state differences between conventional and emergency numerical analyses. It clearly figures out the characteristics of emergency numerical simulation, and the key problems about the application of numerical simulation to geo-hazard emergent rescuing. It gives an application example of the Wangshan-Zhuakousi landslide on the Mount Emei, Sichuan province. It uses the numerical method of discontinuous deformation analysis(DDA) that has outstanding advantages in the analysis of large deformation in real time. The numerical simulation in the process and reason of the landslide have been taken into a further study. The results show, the sliding process is successfully reproduced and the maximum horizontal displacement of the sliding body reached by DDA mode is 87meters. The peak speed is 7m·s-1. The results show that sliding distance is about 38meters and the leading edge thickness is 53meters. The whole duration of the landslide obtained by DDA method is about 70 seconds. The numerical results are consistent with the results of emergent investigation. It's concluded that numerical simulation in geo-hazard emergency is good for the comprehension of the process of landslide, finding the key point and auxiliary emergency decision.
2016, 24(4): 578-583.
A large scale of landslide disaster occurred on June 3, 1980 at Yanchihe in Yichang city of Hubei province. Its volume is 130×104m3. The landslide killed 284 people. Based on the site investigation and analysis, underground mining is an important reason of Yanchihe landslide. Considering the limitations of previous research, and the paper uses the stochastic medium theory that has been used widely in ground surface movement and deformation in diggings. The slope movement and deformation principle resulted from underground mining are illuminated with the stochastic medium theory. Combined with slope stability analysis and numerical simulation, deformation of slope movement induced by underground mining is analysed and verified. The conclusions are as follow:The underground mining caused differential settlements. The underground mining deformation exacerbated the formation of crack inside the slope, providing a channel for rainfall infiltration. Rainfall infiltration in crack caused the slip zone softening, causing the landslide.
A large scale of landslide disaster occurred on June 3, 1980 at Yanchihe in Yichang city of Hubei province. Its volume is 130×104m3. The landslide killed 284 people. Based on the site investigation and analysis, underground mining is an important reason of Yanchihe landslide. Considering the limitations of previous research, and the paper uses the stochastic medium theory that has been used widely in ground surface movement and deformation in diggings. The slope movement and deformation principle resulted from underground mining are illuminated with the stochastic medium theory. Combined with slope stability analysis and numerical simulation, deformation of slope movement induced by underground mining is analysed and verified. The conclusions are as follow:The underground mining caused differential settlements. The underground mining deformation exacerbated the formation of crack inside the slope, providing a channel for rainfall infiltration. Rainfall infiltration in crack caused the slip zone softening, causing the landslide.
2016, 24(4): 584-596.
The experiment explores the impact of alkali stress on the growth and single root mechanical effects of herbs.Elymus nutans Griseb and Elymus sibiricus Linn are suitable to survive in cold and semi-arid environment in the Yellow River source region. They are selected as testing species. Through indoor cultivation, the two species are treated with different NaHCO3 concentrations of 25mmol·L-1, 50mmol·L-1, 75mmol·L-1 or 100mmol·L-1.Meanwhile, NaHCO3 concentration at 0mmol·L-1 is taken as the control group. The plant height and relative survival rate of the two herbs are recorded. After being given alkali treatment, on the 15th and 30th day, their single root mechanical effect indexes and physiological indexes are determined respectively. Single root mechanical effect indexes include single root tensile resistance and single root tensile strength. The physiological indexes include proline content, malondialdehyde content, chlorophyll content, and relative conductivity. The test results are as follows:The impact of alkali stress on the single root mechanical effects of the herbs increases as concentration or growth time increases. When the concentration of alkali stress is 25mmol·L-1,the single root tensile resistances of two herbs are greater than that of the herbs in the control group. When concentration of alkali stress is bigger than 25mmol·L-1,the single root tensile resistances of two herbs are smaller than that in the control group. After being given alkali treatment, the single root tensile strength of the two herbs is greater than that in control group, with the amplification of 3%~16%.And with the same concentration, the single root tensile strength decreases 1%~18%with increase in growth time. In the case of the same growth time and concentration, the single root tensile resistance of Elymus sibiricus Linn is 0.13 N~0.53 N greater than that of Elymus nutans Griseb, and the single root tensile strength of Elymus sibiricus Linn is 20~65MPa greater than that of Elymus nutans Griseb. Based on gray correlation analysis, under the condition of alkali stress, among the determined four physiological indexes, chlorophyll content has the greatest correlation with the single root tensile resistance or the single root tensile strength of the two herbs. The correlation analysis 0.888~0.996 reflects that the single root tensile resistance and single root tensile strength of the two herbs are influenced obviously by relative conductivity. The study has theoretical value in further exploring the changing features and mechanism of root mechanical properties of herbs under the condition of alkali stress and in effectively preventing water and soil loss, shallow landslide and desertification which happen in salinized soil areas of the Yellow River source region.
The experiment explores the impact of alkali stress on the growth and single root mechanical effects of herbs.Elymus nutans Griseb and Elymus sibiricus Linn are suitable to survive in cold and semi-arid environment in the Yellow River source region. They are selected as testing species. Through indoor cultivation, the two species are treated with different NaHCO3 concentrations of 25mmol·L-1, 50mmol·L-1, 75mmol·L-1 or 100mmol·L-1.Meanwhile, NaHCO3 concentration at 0mmol·L-1 is taken as the control group. The plant height and relative survival rate of the two herbs are recorded. After being given alkali treatment, on the 15th and 30th day, their single root mechanical effect indexes and physiological indexes are determined respectively. Single root mechanical effect indexes include single root tensile resistance and single root tensile strength. The physiological indexes include proline content, malondialdehyde content, chlorophyll content, and relative conductivity. The test results are as follows:The impact of alkali stress on the single root mechanical effects of the herbs increases as concentration or growth time increases. When the concentration of alkali stress is 25mmol·L-1,the single root tensile resistances of two herbs are greater than that of the herbs in the control group. When concentration of alkali stress is bigger than 25mmol·L-1,the single root tensile resistances of two herbs are smaller than that in the control group. After being given alkali treatment, the single root tensile strength of the two herbs is greater than that in control group, with the amplification of 3%~16%.And with the same concentration, the single root tensile strength decreases 1%~18%with increase in growth time. In the case of the same growth time and concentration, the single root tensile resistance of Elymus sibiricus Linn is 0.13 N~0.53 N greater than that of Elymus nutans Griseb, and the single root tensile strength of Elymus sibiricus Linn is 20~65MPa greater than that of Elymus nutans Griseb. Based on gray correlation analysis, under the condition of alkali stress, among the determined four physiological indexes, chlorophyll content has the greatest correlation with the single root tensile resistance or the single root tensile strength of the two herbs. The correlation analysis 0.888~0.996 reflects that the single root tensile resistance and single root tensile strength of the two herbs are influenced obviously by relative conductivity. The study has theoretical value in further exploring the changing features and mechanism of root mechanical properties of herbs under the condition of alkali stress and in effectively preventing water and soil loss, shallow landslide and desertification which happen in salinized soil areas of the Yellow River source region.
2016, 24(4): 597-603.
Water has a great influence on the physical and mechanical properties of the rock. It is very important to investigate the fractal law of rock crushed under impact load at different moisture contents. Using the Split Hopkinson Pressure Bar(SHPB),the impact tests of argillaceous siltstone with different water contents are carried out. The fragmentation distribution of the broken rock is thoroughly presented. According to the method of Size-Frequency, the fractal law of particle size distribution is analyzed. It shows that, the higher the impact velocity, the larger the volume of the singe fragments, the more the amount of the fragments of argillaceous siltstone, the smaller the fractal dimension. The greater the moisture content, the greater the proportion of small particles, the higher the degree of crushing. The fractal dimension of water-saturated rock is bigger than the samples in other two states. The fractal dimensions both in the natural moisture state and natural water absorbing state are almost the same. When the impact velocity is higher, it can become the main factor that affects the fractal dimension, and the influence of the moisture content is smaller.
Water has a great influence on the physical and mechanical properties of the rock. It is very important to investigate the fractal law of rock crushed under impact load at different moisture contents. Using the Split Hopkinson Pressure Bar(SHPB),the impact tests of argillaceous siltstone with different water contents are carried out. The fragmentation distribution of the broken rock is thoroughly presented. According to the method of Size-Frequency, the fractal law of particle size distribution is analyzed. It shows that, the higher the impact velocity, the larger the volume of the singe fragments, the more the amount of the fragments of argillaceous siltstone, the smaller the fractal dimension. The greater the moisture content, the greater the proportion of small particles, the higher the degree of crushing. The fractal dimension of water-saturated rock is bigger than the samples in other two states. The fractal dimensions both in the natural moisture state and natural water absorbing state are almost the same. When the impact velocity is higher, it can become the main factor that affects the fractal dimension, and the influence of the moisture content is smaller.
2016, 24(4): 610-615.
This paper tries to understand the effect of temperature on hydraulic parameters of loess. It conducts a combined study of the measurement device for determining hydraulic parameters of saturated-unsaturated soils under variable temperature and theoretical analysis. It examines the variation of the permeability coefficient parameters, the water capacity and the diffusion rate due to temperature changes. The results show that the temperature has a significant effect on the saturate permeability coefficient parameters and that the freeze-thaw cycle times are the important factors influencing the saturated permeability coefficient. The unsaturated permeability coefficient and diffusion rate of loess are the function of temperature and moisture content, while the water capacity is a function of moisture content. Hydrodynamic viscous coefficient decreases with the increase of temperature which is a key factor on the increase of the above parameters.
This paper tries to understand the effect of temperature on hydraulic parameters of loess. It conducts a combined study of the measurement device for determining hydraulic parameters of saturated-unsaturated soils under variable temperature and theoretical analysis. It examines the variation of the permeability coefficient parameters, the water capacity and the diffusion rate due to temperature changes. The results show that the temperature has a significant effect on the saturate permeability coefficient parameters and that the freeze-thaw cycle times are the important factors influencing the saturated permeability coefficient. The unsaturated permeability coefficient and diffusion rate of loess are the function of temperature and moisture content, while the water capacity is a function of moisture content. Hydrodynamic viscous coefficient decreases with the increase of temperature which is a key factor on the increase of the above parameters.
2016, 24(4): 616-621.
Environmental temperature affects oil viscosity and then changes the mechanical properties of petroleum contaminated soil. Unconfined compressive strength test is carried out to study the effect of temperature on strength and deformation of saline soils in inshore contaminated by petroleum. Results indicate that:(1) Temperature has significant effects on mechanical properties of oil contaminated saline soil. Compressive strength of petroleum contaminated soil decreases with the increasing of temperature, and reduces nearly 70% at 20℃ and oil content of 15%comparing with that of un-contaminated soils. (2) Unconfined compressive strength increases first and then decreases with the increase of petroleum content. There is an opposite correlation between environmental temperature and petroleum content at maximum strength. The maximum strength with oil content of 15%, 10%, and 5%shows at 10℃, 20℃ and 30℃,respectively. (3) Damage of petroleum contaminated saline soils presents strain softening type with failure plane of 45°±φ/2, and it is intensified with the increasing of petroleum content and temperature. Environmental temperature has obvious effect on the deformation of oil contaminated saline soil.
Environmental temperature affects oil viscosity and then changes the mechanical properties of petroleum contaminated soil. Unconfined compressive strength test is carried out to study the effect of temperature on strength and deformation of saline soils in inshore contaminated by petroleum. Results indicate that:(1) Temperature has significant effects on mechanical properties of oil contaminated saline soil. Compressive strength of petroleum contaminated soil decreases with the increasing of temperature, and reduces nearly 70% at 20℃ and oil content of 15%comparing with that of un-contaminated soils. (2) Unconfined compressive strength increases first and then decreases with the increase of petroleum content. There is an opposite correlation between environmental temperature and petroleum content at maximum strength. The maximum strength with oil content of 15%, 10%, and 5%shows at 10℃, 20℃ and 30℃,respectively. (3) Damage of petroleum contaminated saline soils presents strain softening type with failure plane of 45°±φ/2, and it is intensified with the increasing of petroleum content and temperature. Environmental temperature has obvious effect on the deformation of oil contaminated saline soil.
2016, 24(4): 622-628.
The creep tests of dry and saturated silty mudstone are conducted using rock rheology testing equipment under triaxial compression. Based on the test results, the effects of water on the creep strain, the long-term strength are investigated. Burgers model is selected to describe the creep properties of dry and saturated silty mudstone. Then using the Levenberg-Marquardt algorithm, the Burgers creep model parameters of dry and saturated silty mudstone are obtained. According to the identification results, the effects of water on Burgers creep model parameters are studied. The results show that:(1) Water has little effect on the instantaneous strains of silty mudstone and a great effect on the creep strains of the rock under the same stress level. (2) The long-term strength of saturated silty mudstone is only 39.3 percent of that of the dry rock, so the long-term strength of the rock decrease remarkably owing to the influence of water. (3) The effect of water on the η1 of the Burgers creep model is the highest, followed by the G1, and that on the G2 and η2 is the lowest, which shows water has a greater effect on the series elements than on the parallel elements of Burgers model. (4) The time that the rock needs to reach the steady creep stages significantly increases, and the steady-state creep rate of the rock also increases remarkably owing to the influence of water. (5) Water has very significant effect on the creep properties of silty mudstone, and water greatly enhances the time characteristics of silty mudstone, which change the creep properties of silty mudstone. Therefore, the effect of water on the creep properties of silty mudstone can not be ignored in the engineering design and construction of major project.
The creep tests of dry and saturated silty mudstone are conducted using rock rheology testing equipment under triaxial compression. Based on the test results, the effects of water on the creep strain, the long-term strength are investigated. Burgers model is selected to describe the creep properties of dry and saturated silty mudstone. Then using the Levenberg-Marquardt algorithm, the Burgers creep model parameters of dry and saturated silty mudstone are obtained. According to the identification results, the effects of water on Burgers creep model parameters are studied. The results show that:(1) Water has little effect on the instantaneous strains of silty mudstone and a great effect on the creep strains of the rock under the same stress level. (2) The long-term strength of saturated silty mudstone is only 39.3 percent of that of the dry rock, so the long-term strength of the rock decrease remarkably owing to the influence of water. (3) The effect of water on the η1 of the Burgers creep model is the highest, followed by the G1, and that on the G2 and η2 is the lowest, which shows water has a greater effect on the series elements than on the parallel elements of Burgers model. (4) The time that the rock needs to reach the steady creep stages significantly increases, and the steady-state creep rate of the rock also increases remarkably owing to the influence of water. (5) Water has very significant effect on the creep properties of silty mudstone, and water greatly enhances the time characteristics of silty mudstone, which change the creep properties of silty mudstone. Therefore, the effect of water on the creep properties of silty mudstone can not be ignored in the engineering design and construction of major project.
2016, 24(4): 629-634.
The tensile strength is not independent of fragment size, but decreases with increasing size known as "size effect". Recent developments in fractal theory suggest that fractal model may provide a more realistic representation of solid particle crushing. A fractal model for crushing of rock particle is constructed using the Sammis model. The relationship between crushing strength and diameter and the relationship between crushing power and diameter of rock particle are simulated respectively. The porosity equals to 0.12 and 0.3 of rock particles, which are simulated using the bonded particle model(BPM) in particle flow code(PFC2D). The relationship between crushing strength and diameter of particle is verified and can be expressed by σf∝dD-3. A relationship between crushing power and diameter of rock particle is expressed by Ef∝dD-1. The good application of fractal theory in the analysis of particle size effect in fractured rock is verified and the results provide a reference for determination of crushing strength.
The tensile strength is not independent of fragment size, but decreases with increasing size known as "size effect". Recent developments in fractal theory suggest that fractal model may provide a more realistic representation of solid particle crushing. A fractal model for crushing of rock particle is constructed using the Sammis model. The relationship between crushing strength and diameter and the relationship between crushing power and diameter of rock particle are simulated respectively. The porosity equals to 0.12 and 0.3 of rock particles, which are simulated using the bonded particle model(BPM) in particle flow code(PFC2D). The relationship between crushing strength and diameter of particle is verified and can be expressed by σf∝dD-3. A relationship between crushing power and diameter of rock particle is expressed by Ef∝dD-1. The good application of fractal theory in the analysis of particle size effect in fractured rock is verified and the results provide a reference for determination of crushing strength.
2016, 24(4): 635-641.
This article is based on the project of Guan-Hui inter-city rail transit. It uses field experiment, laboratory model experiments and numerical simulation method and develops a pre-reinforced technology for shallow excavation tunnel crossing sand ground. In analysis of the deformation of surrounding rock and supporting system suitable pre-reinforced method, scope and parameters can be obtained. The conclusions are as follows:Curtain grouting in tunnel and surface grouting are difficult to form waterproof curtain. When crossing sand strata, horizontal jet grouting and tunnel face grouting are the best pre-reinforcement scheme. Increasing grouting range is disadvantageous to control vault subsidence and horizontal convergence in sand strata, but can strengthen the integrity of the surrounding rock in unsand strata. Meanwhile, it is favourable to control the subsidence of ground. Changing the reinforced area parameter is highly advantageous to control the settlement of tunnel vault in sand strata. The better grouting quality accomplished, the greater the self-supporting capability of surrounding rock improved, while the horizontal displacement is nearly unchanged.
This article is based on the project of Guan-Hui inter-city rail transit. It uses field experiment, laboratory model experiments and numerical simulation method and develops a pre-reinforced technology for shallow excavation tunnel crossing sand ground. In analysis of the deformation of surrounding rock and supporting system suitable pre-reinforced method, scope and parameters can be obtained. The conclusions are as follows:Curtain grouting in tunnel and surface grouting are difficult to form waterproof curtain. When crossing sand strata, horizontal jet grouting and tunnel face grouting are the best pre-reinforcement scheme. Increasing grouting range is disadvantageous to control vault subsidence and horizontal convergence in sand strata, but can strengthen the integrity of the surrounding rock in unsand strata. Meanwhile, it is favourable to control the subsidence of ground. Changing the reinforced area parameter is highly advantageous to control the settlement of tunnel vault in sand strata. The better grouting quality accomplished, the greater the self-supporting capability of surrounding rock improved, while the horizontal displacement is nearly unchanged.
2016, 24(4): 642-648.
Drilling and sampling is an important step for the investigation and assessment of contaminated sites. This paper is based on the practical experience of site investigation in European and American Countries and the relevant technical literatures. It states that the quality of drilling and sampling,i.e., keeping physical and chemical intactness of samples, depends on the soil testing items required and the type of contaminants enclosed. Then it summarizes the advantages and disadvantages of the drilling methods being suitable for contaminated sites and their applicable soil types. The characteristics of the sampling methods being suitable for contaminated sites and the applicable samplers are also presented. Thereafter, a table is proposed for the selection of appropriate drilling and sampling methods for different types of contaminated sites. The table provides a guide for the site investigation of contaminated lands by chemistry and mining industry.
Drilling and sampling is an important step for the investigation and assessment of contaminated sites. This paper is based on the practical experience of site investigation in European and American Countries and the relevant technical literatures. It states that the quality of drilling and sampling,i.e., keeping physical and chemical intactness of samples, depends on the soil testing items required and the type of contaminants enclosed. Then it summarizes the advantages and disadvantages of the drilling methods being suitable for contaminated sites and their applicable soil types. The characteristics of the sampling methods being suitable for contaminated sites and the applicable samplers are also presented. Thereafter, a table is proposed for the selection of appropriate drilling and sampling methods for different types of contaminated sites. The table provides a guide for the site investigation of contaminated lands by chemistry and mining industry.
2016, 24(4): 649-660.
Solidification/stabilization(S/S) is an effective technique to disposal sewage sludge. It adds solidifying materials to the sludge. The solidifying materials and sludge occurs a series of physical and chemical reactions. It improves the mechanical strength and stabilizes the heavy metal pollutants in the sludge and can achieve the purpose of the safe disposal of sludge and resource utilization. It is therefore of significance to develop new technology for the treatment and disposal of sludge. This paper is based on the achievements at home and abroad for the recent years in this field and summarizes the advances of several important aspects on this topic. They include the types of sludge, species of solidifying agent, main measures of solidified sludge effect, factors that affects the solidified effect and solidifying/stabilizing mechanisms. The following important knowledge can be drawn:Sludge can be classified into river/lake sludge, municipal sludge and industrial sludge by the source. Due to the big differences of the sludge composition, the corresponding disposal methods are also different. For the widely used S/S technique, the most commonly used solidification agent can be divided into two categories:inorganic and organic agents. The dominant inorganic solidifying agent includes cement, lime, and uses some industrial slag, clay as auxiliary material.the two important indexes are the unconfined compressive strength and leaching toxicity in terms of main measure indexes. The initial moisture content, curing time, and the species of solidifying agent and ratio and the pH and Eh values are the main types of factors which affects the solidifying/stabilizing effect. Solidifying agent and its products form the skeleton in the sludge. The sludge particle is cemented and its pore is filled by the physical and chemical reactions, to achieve treatment effect. Harmful substances will be enclosed in the curing body by physical package, precipitation and absorption between solidifying agent and its products, to achieve the purpose of harmless and stabilization. Finally, based on the above understanding and current research shortages in this topic, some important research topics that should be well investigated in future are proposed. They include increasing the permeability coefficient of sludge, understanding the deformation properties of the cured body, development of new technology for multiple heavy metal ions stabilization, models for simulating and predicting the dissolution and migration of heavy metal ions and development of new solidifying agent.
Solidification/stabilization(S/S) is an effective technique to disposal sewage sludge. It adds solidifying materials to the sludge. The solidifying materials and sludge occurs a series of physical and chemical reactions. It improves the mechanical strength and stabilizes the heavy metal pollutants in the sludge and can achieve the purpose of the safe disposal of sludge and resource utilization. It is therefore of significance to develop new technology for the treatment and disposal of sludge. This paper is based on the achievements at home and abroad for the recent years in this field and summarizes the advances of several important aspects on this topic. They include the types of sludge, species of solidifying agent, main measures of solidified sludge effect, factors that affects the solidified effect and solidifying/stabilizing mechanisms. The following important knowledge can be drawn:Sludge can be classified into river/lake sludge, municipal sludge and industrial sludge by the source. Due to the big differences of the sludge composition, the corresponding disposal methods are also different. For the widely used S/S technique, the most commonly used solidification agent can be divided into two categories:inorganic and organic agents. The dominant inorganic solidifying agent includes cement, lime, and uses some industrial slag, clay as auxiliary material.the two important indexes are the unconfined compressive strength and leaching toxicity in terms of main measure indexes. The initial moisture content, curing time, and the species of solidifying agent and ratio and the pH and Eh values are the main types of factors which affects the solidifying/stabilizing effect. Solidifying agent and its products form the skeleton in the sludge. The sludge particle is cemented and its pore is filled by the physical and chemical reactions, to achieve treatment effect. Harmful substances will be enclosed in the curing body by physical package, precipitation and absorption between solidifying agent and its products, to achieve the purpose of harmless and stabilization. Finally, based on the above understanding and current research shortages in this topic, some important research topics that should be well investigated in future are proposed. They include increasing the permeability coefficient of sludge, understanding the deformation properties of the cured body, development of new technology for multiple heavy metal ions stabilization, models for simulating and predicting the dissolution and migration of heavy metal ions and development of new solidifying agent.
2016, 24(4): 661-667.
With the increase of tailings dam height, the groundwater seepage field will change. When the actual hydraulic gradient at the tailings dam is greater than the critical hydraulic gradient, the tailings dam will produce seepage deformation or instability damage. In order to predict the seepage stability of a phosphogypsum tailings dam, the seepage coefficient was determined by using the groundwater level gauge to resume testing, and the hydraulic gradient were calculated. At the same time, the SEEP/W module of Geo-studio was used to analyze the seepage stability of the phosphorus gypsum accumulation dam under different conditions. According calculation and analysis results, it was found that when the accumulation dam was in 945m altitude, in the absence of beach and 100m dry beach, the actual hydraulic gradient were 0.784 and 0.583. When the accumulation dam was in 960m altitude and in the absence of beach, the actual hydraulic gradient were 0.692. In the above two cases, the altitude of the seepage point of the accumulation dam was higher than the initial dam, the accumulation dam would appear the deformation of the flow soil, the dam was unstable state. When the accumulation dam was in 960m altitude and 100m dry beach, there was no seepage point on the accumulation dam, and the accumulation dam was in the stable state. The results of the research will provide the technical basis for the safe operation and maintenance management of the tailings dam, and will provide reference for the seepage stability of the same tailings dam.
With the increase of tailings dam height, the groundwater seepage field will change. When the actual hydraulic gradient at the tailings dam is greater than the critical hydraulic gradient, the tailings dam will produce seepage deformation or instability damage. In order to predict the seepage stability of a phosphogypsum tailings dam, the seepage coefficient was determined by using the groundwater level gauge to resume testing, and the hydraulic gradient were calculated. At the same time, the SEEP/W module of Geo-studio was used to analyze the seepage stability of the phosphorus gypsum accumulation dam under different conditions. According calculation and analysis results, it was found that when the accumulation dam was in 945m altitude, in the absence of beach and 100m dry beach, the actual hydraulic gradient were 0.784 and 0.583. When the accumulation dam was in 960m altitude and in the absence of beach, the actual hydraulic gradient were 0.692. In the above two cases, the altitude of the seepage point of the accumulation dam was higher than the initial dam, the accumulation dam would appear the deformation of the flow soil, the dam was unstable state. When the accumulation dam was in 960m altitude and 100m dry beach, there was no seepage point on the accumulation dam, and the accumulation dam was in the stable state. The results of the research will provide the technical basis for the safe operation and maintenance management of the tailings dam, and will provide reference for the seepage stability of the same tailings dam.
2016, 24(4): 668-673.
During tunneling construction in subways, the settlement in arch crown and ground will greatly impact on the construction safety, engineering function and normal operation of urban roads. The soil around the reserved shaft in Beiwan region of No.1 section, No.7 Subway of Beijing is backfilled and complex. In order to ensure the safety of tunneling construction and structures, it's necessary to do schematic studies on the removal and excavation of horsehead in backfill soils. Based on the data of surface survey drilling and prediction detection of the strata and the engineering design data, the software FLAC3D is used to study the two reinforcement schematics when the horsehead of the reserved shaft is exploded, also, the arch crown and ground settlements resulted from the construction of six pilot tunnels in the rectangular transient cross-section are simulated and compared with the monitoring results of pilot tunnels' excavation. The research showed that when the horsehead is removed, the settlement using non-shrinkage grouting of deep hole method was one third to a half of that using advanced small pipe support method.
During tunneling construction in subways, the settlement in arch crown and ground will greatly impact on the construction safety, engineering function and normal operation of urban roads. The soil around the reserved shaft in Beiwan region of No.1 section, No.7 Subway of Beijing is backfilled and complex. In order to ensure the safety of tunneling construction and structures, it's necessary to do schematic studies on the removal and excavation of horsehead in backfill soils. Based on the data of surface survey drilling and prediction detection of the strata and the engineering design data, the software FLAC3D is used to study the two reinforcement schematics when the horsehead of the reserved shaft is exploded, also, the arch crown and ground settlements resulted from the construction of six pilot tunnels in the rectangular transient cross-section are simulated and compared with the monitoring results of pilot tunnels' excavation. The research showed that when the horsehead is removed, the settlement using non-shrinkage grouting of deep hole method was one third to a half of that using advanced small pipe support method.
2016, 24(4): 674-681.
Sanshandao gold mine is located in coastal zone of Lai-Zhou Bay of Shandong Province. It is one of the main mines of Shandong(Laizhou) Gold Group Co.,Ltd. Owing to its special geographical location and complex hydrogeological conditions, large-scale mining engineering is confronted with water-bursting hidden danger. Based on this background, hydrogeological characteristics of the gold mine is regionally divided and evaluated through consideration of fault influence. Joint fracture survey work for 3 levels, where located in deep position of mine area, is implemented. In addition, joints distribution laws of hanging wall, orebody and footwall are studied. Permeability coefficient of deep rock is calculated and reasonably modified on basis of geometry parameters measurement and Monte-Carlo method. With the help of FLAC3D numerical calculation means, evolution characteristics and influence scope of seepage field during future deep mining process are forecasted. Achieved results can provide certain guiding significance to safety ensuring projects of deep exploitation mine under complex hydrogeological conditions.
Sanshandao gold mine is located in coastal zone of Lai-Zhou Bay of Shandong Province. It is one of the main mines of Shandong(Laizhou) Gold Group Co.,Ltd. Owing to its special geographical location and complex hydrogeological conditions, large-scale mining engineering is confronted with water-bursting hidden danger. Based on this background, hydrogeological characteristics of the gold mine is regionally divided and evaluated through consideration of fault influence. Joint fracture survey work for 3 levels, where located in deep position of mine area, is implemented. In addition, joints distribution laws of hanging wall, orebody and footwall are studied. Permeability coefficient of deep rock is calculated and reasonably modified on basis of geometry parameters measurement and Monte-Carlo method. With the help of FLAC3D numerical calculation means, evolution characteristics and influence scope of seepage field during future deep mining process are forecasted. Achieved results can provide certain guiding significance to safety ensuring projects of deep exploitation mine under complex hydrogeological conditions.
2016, 24(4): 682-692.
This paper examines a planned hydropower station that is one of the important energy projects in overseas invested by China. It has a reservoir with high dam. Its water retaining structure is a roller-compacted concrete gravity dam of 200m high. The dam is located at a regional deep fault(F4). Activities of fault and feasibility of damming technology, as an important technical issue, is key to the establishment of hydropower station. Thus, a lot of work, including regional seismic geological investigation, geophysical prospecting, drilling, exploratory adit, fault age, field and indoor tests for rock and soil physical and mechanical properties, has been conducted. Results show that:(1) Seismic activities in this fault are weak and the latest one is from 0.142 million to 0.798million years ago. The fault is inactive since late Pleistocene. (2) Cataclastic rock belt and the faults F4-1 and F4-2 have the most influence on the dam. The fresh cataclastic rock mainly is the Ⅲ1B class rock. The Ⅳ1B class rock only exists in F4 footwall. Faults F4-1 and F4-2,which is composed of the Ⅴ class rock, have bad engineering properties, and are the most weak part of dam foundation; (3) The possibility of building the dam at fault F4 to induce stereotype reservoir earthquake is less. The main engineering geological problem is deformation and seepage in dam foundation. Seepage stability can be dealt with through appropriate engineering measures such as deep digging and combining with backfilling concrete plug, consolidation grouting, deepening encryption and increasing the curtain row number. With results mentioned above all, an conclusion can be made that conducting hydropower projects on the fault F4 zone is viable in technical way. The results can only provide technical basis for hydropower station design and construction, but also technical reference for similar projects.
This paper examines a planned hydropower station that is one of the important energy projects in overseas invested by China. It has a reservoir with high dam. Its water retaining structure is a roller-compacted concrete gravity dam of 200m high. The dam is located at a regional deep fault(F4). Activities of fault and feasibility of damming technology, as an important technical issue, is key to the establishment of hydropower station. Thus, a lot of work, including regional seismic geological investigation, geophysical prospecting, drilling, exploratory adit, fault age, field and indoor tests for rock and soil physical and mechanical properties, has been conducted. Results show that:(1) Seismic activities in this fault are weak and the latest one is from 0.142 million to 0.798million years ago. The fault is inactive since late Pleistocene. (2) Cataclastic rock belt and the faults F4-1 and F4-2 have the most influence on the dam. The fresh cataclastic rock mainly is the Ⅲ1B class rock. The Ⅳ1B class rock only exists in F4 footwall. Faults F4-1 and F4-2,which is composed of the Ⅴ class rock, have bad engineering properties, and are the most weak part of dam foundation; (3) The possibility of building the dam at fault F4 to induce stereotype reservoir earthquake is less. The main engineering geological problem is deformation and seepage in dam foundation. Seepage stability can be dealt with through appropriate engineering measures such as deep digging and combining with backfilling concrete plug, consolidation grouting, deepening encryption and increasing the curtain row number. With results mentioned above all, an conclusion can be made that conducting hydropower projects on the fault F4 zone is viable in technical way. The results can only provide technical basis for hydropower station design and construction, but also technical reference for similar projects.
2016, 24(4): 693-703.
Landslides are frequent in granite area of Guangxi Province, where rock structure is loose, weathered clinosol and residual soils are thick and distributed widely, and rainfall is abundant. Based on statistics, the indexes of landslide susceptibility evaluation are selected, including slope, elevation, geological structure, vegetation, rainfall and human engineering activities. The landslide susceptibility in the granite area is divided into districts, based on ArcGIS software and information model. The landslide susceptibility evaluation results are compared with the existing landslides and hidden troubles in the granite area. The comparison result shows that the susceptibility assessment is correct and can be used for the forecasting of landslide and early warning in the granite area.
Landslides are frequent in granite area of Guangxi Province, where rock structure is loose, weathered clinosol and residual soils are thick and distributed widely, and rainfall is abundant. Based on statistics, the indexes of landslide susceptibility evaluation are selected, including slope, elevation, geological structure, vegetation, rainfall and human engineering activities. The landslide susceptibility in the granite area is divided into districts, based on ArcGIS software and information model. The landslide susceptibility evaluation results are compared with the existing landslides and hidden troubles in the granite area. The comparison result shows that the susceptibility assessment is correct and can be used for the forecasting of landslide and early warning in the granite area.
2016, 24(4): 704-712.
The rapid development of ground subsidence in the southern Tangshan area is serious and has threated its world-class chemical industry base. Therefore, this paper examines the distribution and evolution of ground subsidence in the coastal area of the Southern Tangshan area, as well as the dominant factors of different subsidence regions. Based on the medium and high resolution radar data, the ground subsidence result in the coastal area of the southern Tangshan is obtained using PSInSAR technique. The results show that the ground subsidence funnel has a well correspondence with the groundwater funnel area. The ground subsidence is distributed along one side of a basement fault. The ground subsidence distribution of the Caofeidian Industrial Area is spotty or patchy, and its area range is small but the settlement gradient very large, which is extremely different from the ground subsidence caused by excessive exploitation groundwater. According to this survey, the geological characteristics are the basic condition of ground subsidence development, while over-exploitation groundwater and large-scale engineering disturbance are external power in Southern Tangshan area.
The rapid development of ground subsidence in the southern Tangshan area is serious and has threated its world-class chemical industry base. Therefore, this paper examines the distribution and evolution of ground subsidence in the coastal area of the Southern Tangshan area, as well as the dominant factors of different subsidence regions. Based on the medium and high resolution radar data, the ground subsidence result in the coastal area of the southern Tangshan is obtained using PSInSAR technique. The results show that the ground subsidence funnel has a well correspondence with the groundwater funnel area. The ground subsidence is distributed along one side of a basement fault. The ground subsidence distribution of the Caofeidian Industrial Area is spotty or patchy, and its area range is small but the settlement gradient very large, which is extremely different from the ground subsidence caused by excessive exploitation groundwater. According to this survey, the geological characteristics are the basic condition of ground subsidence development, while over-exploitation groundwater and large-scale engineering disturbance are external power in Southern Tangshan area.
USE OF UNMANNED AERIAL VEHICLE FOR PRECISE INVESTIGATION OF GEOLOGICAL HAZARD IN STRONG SEISMIC ZONE
2016, 24(4): 713-719.
This paper aims to investigate geological hazard precisely in strong seismic zone. It uses unmanned aerial vehicle based low-altitude photographic system. The system can obtain high-precision, high-resolution and high-altitude remote sensing image, and has the advantage of flexibility and freedom from complex topography. This paper applies the system to the precise investigation of geological hazard, the precise investigation procedure of geological hazard in strong seismic zone. The application of results are discussed. The paper takes the application in the Laohuzui landslide zone as an example. It describes the remote sensing image extraction and the method of DEM,DOM and three-dimensional real space scene. It focuses on introducing the qualitative and quantitative analysis of the geological hazard and the precise description. The practice results show that:(1) compared with the conventional remote sensing investigation method, this method not only obtains higher-resolution and higher-precision basic data for the precise investigation of the geological hazard, but also improves its efficacy and reliability; (2) three-dimensional real space scene of the geological hazard breaks through the traditional two-dimensional interpretation method, improves the precision and accuracy of the geological hazard. The system can be applied to the precise investigation of geological hazard in strong seismic zone.
This paper aims to investigate geological hazard precisely in strong seismic zone. It uses unmanned aerial vehicle based low-altitude photographic system. The system can obtain high-precision, high-resolution and high-altitude remote sensing image, and has the advantage of flexibility and freedom from complex topography. This paper applies the system to the precise investigation of geological hazard, the precise investigation procedure of geological hazard in strong seismic zone. The application of results are discussed. The paper takes the application in the Laohuzui landslide zone as an example. It describes the remote sensing image extraction and the method of DEM,DOM and three-dimensional real space scene. It focuses on introducing the qualitative and quantitative analysis of the geological hazard and the precise description. The practice results show that:(1) compared with the conventional remote sensing investigation method, this method not only obtains higher-resolution and higher-precision basic data for the precise investigation of the geological hazard, but also improves its efficacy and reliability; (2) three-dimensional real space scene of the geological hazard breaks through the traditional two-dimensional interpretation method, improves the precision and accuracy of the geological hazard. The system can be applied to the precise investigation of geological hazard in strong seismic zone.
2016, 24(4): 604-609.
Swelling soil is a special soil often encountered in geotechnical engineering. It is of classic drying shrinkage and water swelling characteristics due to the moisture change in soil. How to quantify the shrinkage deformation and its relationship with desiccation crack is important issue in assessment of the stability and security of earth structures. The analysis based on distribution of water content is proved to be equivalent of that base on matric suction by Bishop's effective stress and generalized Hooke's Law. The shrinkage coefficient measured by shrinkage test of undisturbed soil sample can be associated with shrinkage strain. The total horizontal stress and its relationship with the distribution of water content is obtained with or without consideration of boundary displacement constrains. The results show that the non-uniform of shrinkage deformation and stress level is small and little desiccation cracks will be produced when there are no boundary constrains in soil. But if the displacement constrains are imposed at the ends of soil body, shrinkage deformation can be restrained and desiccation cracks can be produced. The depth of desiccation crack is strongly influenced by Young's modulus and shrinkage coefficient of soil.
Swelling soil is a special soil often encountered in geotechnical engineering. It is of classic drying shrinkage and water swelling characteristics due to the moisture change in soil. How to quantify the shrinkage deformation and its relationship with desiccation crack is important issue in assessment of the stability and security of earth structures. The analysis based on distribution of water content is proved to be equivalent of that base on matric suction by Bishop's effective stress and generalized Hooke's Law. The shrinkage coefficient measured by shrinkage test of undisturbed soil sample can be associated with shrinkage strain. The total horizontal stress and its relationship with the distribution of water content is obtained with or without consideration of boundary displacement constrains. The results show that the non-uniform of shrinkage deformation and stress level is small and little desiccation cracks will be produced when there are no boundary constrains in soil. But if the displacement constrains are imposed at the ends of soil body, shrinkage deformation can be restrained and desiccation cracks can be produced. The depth of desiccation crack is strongly influenced by Young's modulus and shrinkage coefficient of soil.
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