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Editor Work2019 Vol. 27, No. 1
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2019, 27(1): 1-13.
Abstract
2563KB
Natural locked segments dominate the stability of locked-segment-type slopes and the evolutionary process of tectonic earthquakes. They fail in order of bearing capacity from low to high. Therefore, it is very important to study the mechanical response mechanism of the next locked segment while the current locked segment is broken, and predict the fracture behavior of the latter. We found that a high-energy-level characteristic cracking event (characteristic event) at the volume-expansion point of locked segment can be viewed as both the indicator of the point and the precursor to the rupture of locked segment. We established a mechanical model consisting of two locked segments that are subjected to shear loading, discussed the mechanical behavior resulted from different combinations of locked segments' bearing capacity based on the theoretical analysis and numerical simulations, and stated that the mechanical action between natural locked segments follows a strong action mode. In other words, when the current locked segment is loaded to reach its peak-stress point, the load applied to it will be transferred to the next locked segment; the load transfer with a negligible increase in shear displacement or strain can make the latter evolve to its volume-expansion point. The mode can well explain many kinds of seismic observation phenomena and experimental results.
Natural locked segments dominate the stability of locked-segment-type slopes and the evolutionary process of tectonic earthquakes. They fail in order of bearing capacity from low to high. Therefore, it is very important to study the mechanical response mechanism of the next locked segment while the current locked segment is broken, and predict the fracture behavior of the latter. We found that a high-energy-level characteristic cracking event (characteristic event) at the volume-expansion point of locked segment can be viewed as both the indicator of the point and the precursor to the rupture of locked segment. We established a mechanical model consisting of two locked segments that are subjected to shear loading, discussed the mechanical behavior resulted from different combinations of locked segments' bearing capacity based on the theoretical analysis and numerical simulations, and stated that the mechanical action between natural locked segments follows a strong action mode. In other words, when the current locked segment is loaded to reach its peak-stress point, the load applied to it will be transferred to the next locked segment; the load transfer with a negligible increase in shear displacement or strain can make the latter evolve to its volume-expansion point. The mode can well explain many kinds of seismic observation phenomena and experimental results.
2019, 27(1): 14-20.
The key point of mining safety is backfill stability in the mine which used in the filling method. And the backfill also could control the ground pressure and constrain the surrounding rock mass deformation. The filling mining method is widely used in metal mining engineering and the backfill is the substitution of ore body. There are some stages of backfill after injected into the worked out section, as phase change-consolidation-load bearing-support counter force-make the interaction with surrounding rock mass. The backfill, overlying rock mass, unexcavated ore body and surrounding rock mass form an interacted system of mining operation to resist the external load. The system deformation and stability is the key issues. The large backfill is formed in No.2 zone of Jinchuan Mine by mining in decades. The mining operation has carried out in the deep, so the stability of large backfill is effect on the work safety. This article, based on the actual mining condition of No.2 zone of Jinchuan Mine in China, described the elaborated boundary shape and simulated the backfill mechanical behaviour. The backfill have occurred overall deformation because of compression. The shear stress is the major factor of backfill and surrounding rock local failure. Finally, the hazardous area is curtained by yield function and shear stress distribution.
The key point of mining safety is backfill stability in the mine which used in the filling method. And the backfill also could control the ground pressure and constrain the surrounding rock mass deformation. The filling mining method is widely used in metal mining engineering and the backfill is the substitution of ore body. There are some stages of backfill after injected into the worked out section, as phase change-consolidation-load bearing-support counter force-make the interaction with surrounding rock mass. The backfill, overlying rock mass, unexcavated ore body and surrounding rock mass form an interacted system of mining operation to resist the external load. The system deformation and stability is the key issues. The large backfill is formed in No.2 zone of Jinchuan Mine by mining in decades. The mining operation has carried out in the deep, so the stability of large backfill is effect on the work safety. This article, based on the actual mining condition of No.2 zone of Jinchuan Mine in China, described the elaborated boundary shape and simulated the backfill mechanical behaviour. The backfill have occurred overall deformation because of compression. The shear stress is the major factor of backfill and surrounding rock local failure. Finally, the hazardous area is curtained by yield function and shear stress distribution.
2019, 27(1): 21-28.
Based on the theory of engineering geomechanics of rock mass founded by Professor Gu Dezhen, a concept of mine hydrogeological structure was proposed based on the idea of hydrogeological structure. The types of mine water hazards was reclassified based on the concept of mine hydrogeological structure, combined with the macroscopic geological background of mines in China and foundations of mine water disaster research and controlling. The analysis of the responses of mine hydrogeological structure on mining activity provides a new idea to mine water hazard prevention and safe mining from the points of groundwater sources, pathways and mining influence, combining with the study of case histories, such as water and sand inrush, groundwater inrush from seam floor. This study shows that engineering geomechanics of rock mass plays an important role and has a strong guiding role in research of hydrogeological and engineering geological issues for coal mines.
Based on the theory of engineering geomechanics of rock mass founded by Professor Gu Dezhen, a concept of mine hydrogeological structure was proposed based on the idea of hydrogeological structure. The types of mine water hazards was reclassified based on the concept of mine hydrogeological structure, combined with the macroscopic geological background of mines in China and foundations of mine water disaster research and controlling. The analysis of the responses of mine hydrogeological structure on mining activity provides a new idea to mine water hazard prevention and safe mining from the points of groundwater sources, pathways and mining influence, combining with the study of case histories, such as water and sand inrush, groundwater inrush from seam floor. This study shows that engineering geomechanics of rock mass plays an important role and has a strong guiding role in research of hydrogeological and engineering geological issues for coal mines.
2019, 27(1): 29-37.
A simple and practical tunnel large deformation risk assessment method is of great value for disaster prevention and engineering applications. We applied the index scoring method to establish a dynamic risk assessment method for large deformation of high ground stress tunnels during construction. Then we established a risk assessment index system of large deformation, which includes three primary indicators consisted of geological factors, design factors and construction factors, and 18 secondary indicators such as rock strength and surrounding rock integrity. Statistical analysis was used to determine the weight of each index. Through the on-site scoring of each indicator, the risk probability level was determined according to the large deformation risk probability level standard. Then we used expert surveys to estimate direct economic losses, delays in construction, and determine severity level. Considering the possibility of risk occurrence and the severity of the loss, we used the risk matrix method to obtain the risk comprehensive level. Furthermore, we applied the established risk assessment method to the Miyaluo Tunnel No. 3 in the Wenma Expressway under construction. The evaluation results were consistent with the actual excavation results, which verified the effectiveness and practicability of the method. This risk assessment method provides a scientific basis for the prevention and control of large deformation during tunnel construction.
A simple and practical tunnel large deformation risk assessment method is of great value for disaster prevention and engineering applications. We applied the index scoring method to establish a dynamic risk assessment method for large deformation of high ground stress tunnels during construction. Then we established a risk assessment index system of large deformation, which includes three primary indicators consisted of geological factors, design factors and construction factors, and 18 secondary indicators such as rock strength and surrounding rock integrity. Statistical analysis was used to determine the weight of each index. Through the on-site scoring of each indicator, the risk probability level was determined according to the large deformation risk probability level standard. Then we used expert surveys to estimate direct economic losses, delays in construction, and determine severity level. Considering the possibility of risk occurrence and the severity of the loss, we used the risk matrix method to obtain the risk comprehensive level. Furthermore, we applied the established risk assessment method to the Miyaluo Tunnel No. 3 in the Wenma Expressway under construction. The evaluation results were consistent with the actual excavation results, which verified the effectiveness and practicability of the method. This risk assessment method provides a scientific basis for the prevention and control of large deformation during tunnel construction.
2019, 27(1): 38-47.
Different from the commonly occurred deformation of reservoir bank, reservoir plate deformation together with valley deformation are new issues in engineering geology and directly threaten the safety of reservoir dams. Monitoring data shows that settlement or lift deformation has occurred during impoundment at multiple reservoirs that have been built. We take Xiluodu, Tongjiezi, Jiangya, Jinping and Xiaowan hydroelectric power stations as typical examples to investigate the geological causes of reservoir plate deformation from the perspective of regional hydrogeological condition variations. The findings reveal that topography, formation lithology, geologic structure and hydrogeological conditions are internal factors of reservoir plate and valley deformation. Besides, the reservoir level and impoundment processes are external factors triggering such deformation. External factors always act upon the internal ones. The reserch achievements will provide guidance for building physical models for under-construction and to-be-built hydroelectric projects and for accurately calculating, analyzing and predicting potential reservoir plate and valley deformation.
Different from the commonly occurred deformation of reservoir bank, reservoir plate deformation together with valley deformation are new issues in engineering geology and directly threaten the safety of reservoir dams. Monitoring data shows that settlement or lift deformation has occurred during impoundment at multiple reservoirs that have been built. We take Xiluodu, Tongjiezi, Jiangya, Jinping and Xiaowan hydroelectric power stations as typical examples to investigate the geological causes of reservoir plate deformation from the perspective of regional hydrogeological condition variations. The findings reveal that topography, formation lithology, geologic structure and hydrogeological conditions are internal factors of reservoir plate and valley deformation. Besides, the reservoir level and impoundment processes are external factors triggering such deformation. External factors always act upon the internal ones. The reserch achievements will provide guidance for building physical models for under-construction and to-be-built hydroelectric projects and for accurately calculating, analyzing and predicting potential reservoir plate and valley deformation.
2019, 27(1): 48-54.
In recent years, due to the influence of extreme heavy rainfall weather, many medium-sized and large-scale landslides had occurred on the gentle slopes of Ningzhen area. These landslides were mainly manifesting intermittent creep, large scale, and small slip distance, generally less than 30 m, which seriously threatens the safety of lives and property of residents, and causes huge economic losses and serious adverse social effects. In the paper, based on this new type of landslide geological hazard, the stratum structure and sliding mechanism of the landslide had been researched by using the cybernetics of rock mass structure and preferred plane theory. The results show that the landslide mainly occurred in the Piedmont gentle slope area, and there are special stratum structure and hydrogeological characteristics of the landslide body. The confined water would be easily produced in the slope body with heavy rainfall. Under the action of buoyancy of confined water, the burst and shear failure would produce mainly in the gentle slope, and the intermittent creep of the landslide grow with rainfall.
In recent years, due to the influence of extreme heavy rainfall weather, many medium-sized and large-scale landslides had occurred on the gentle slopes of Ningzhen area. These landslides were mainly manifesting intermittent creep, large scale, and small slip distance, generally less than 30 m, which seriously threatens the safety of lives and property of residents, and causes huge economic losses and serious adverse social effects. In the paper, based on this new type of landslide geological hazard, the stratum structure and sliding mechanism of the landslide had been researched by using the cybernetics of rock mass structure and preferred plane theory. The results show that the landslide mainly occurred in the Piedmont gentle slope area, and there are special stratum structure and hydrogeological characteristics of the landslide body. The confined water would be easily produced in the slope body with heavy rainfall. Under the action of buoyancy of confined water, the burst and shear failure would produce mainly in the gentle slope, and the intermittent creep of the landslide grow with rainfall.
2019, 27(1): 55-68.
Natural gas hydrate, a pollution-free clean energy, is buried in sediments of the shallow geosphere and widely distributed, therefore considered as the most likely potential substitute resource in the oil and gas sector. Field scale exploitation of gas hydrate have been tried of 5 countries including China, especially the successful offshore production tests in Shenhu area, South China Sea, making a record of gas producing time and cumulative production. Nevertheless, there is no mature solution to realize economical and large-scale exploitation because of the special physical properties and occurrence environment of gas hydrate. In this paper, the offshore production tests carried out by China and Japan are introduced and analyzed according to fundamental understanding of gas hydrate. Our results indicated that:(1)the current production methods could be summarized into two types:in situ decomposition and stratum excavation methods. (2)The exploitation data suggested the temperature and pressure are the main constrain conditions for gas production and they works differently in different stages of production. (3)The first exploitation data of Japan showed that there's fine relevance between production rate and pressure/temperature driving force. The decomposition model based on coupled driving force were proposed using a comprehensive parameter named "distance to phase equilibrium curve". (4)According to the judgments of drastic-rapid and phased-slow depressurization methods, we presented that efficient heat injection are possibly one necessary condition for long-term exploitation of gas hydrate. Furthermore, convection heat supply and depressurization method were proposed according to the integration of hydraulic fracturing horizontal well technology in shale exploitation and the heat convection exchange cycle in hot dry rock exploitation.
Natural gas hydrate, a pollution-free clean energy, is buried in sediments of the shallow geosphere and widely distributed, therefore considered as the most likely potential substitute resource in the oil and gas sector. Field scale exploitation of gas hydrate have been tried of 5 countries including China, especially the successful offshore production tests in Shenhu area, South China Sea, making a record of gas producing time and cumulative production. Nevertheless, there is no mature solution to realize economical and large-scale exploitation because of the special physical properties and occurrence environment of gas hydrate. In this paper, the offshore production tests carried out by China and Japan are introduced and analyzed according to fundamental understanding of gas hydrate. Our results indicated that:(1)the current production methods could be summarized into two types:in situ decomposition and stratum excavation methods. (2)The exploitation data suggested the temperature and pressure are the main constrain conditions for gas production and they works differently in different stages of production. (3)The first exploitation data of Japan showed that there's fine relevance between production rate and pressure/temperature driving force. The decomposition model based on coupled driving force were proposed using a comprehensive parameter named "distance to phase equilibrium curve". (4)According to the judgments of drastic-rapid and phased-slow depressurization methods, we presented that efficient heat injection are possibly one necessary condition for long-term exploitation of gas hydrate. Furthermore, convection heat supply and depressurization method were proposed according to the integration of hydraulic fracturing horizontal well technology in shale exploitation and the heat convection exchange cycle in hot dry rock exploitation.
2019, 27(1): 69-79.
Outcrops and core observations show that sandy and tuff aceous laminas and natural fractures are well developed in the continental shale gas reservoir. This study reports the distribution of laminas and natural fracture networks at different scales and established the 3-D geological structure models, with data obtained from outcrops, wells and cores of Yanchang shale from southern Ordos Basin. Firstly, based on two-dimensional fracture field investigations, a 3-D joint network model of the study area was built using the Monte Carlo simulation method. Then the laminations were identified from macroscopic scales to microscopic scales with multiple probe techniques. Statistical analysis of multi-scale layer thickness suggested that the average thickness of layers at multiple scales showed a fractal feature, with average layer thickness of 2.26 m, 2.09 dm, 1.70 cm, 1.48 mm and 11.7 μm, corresponding to meter scale, decimeter scale, centimeter scale, millimeter scale and 10-micro meter scale respectively, and that the layer thickness at studied scales all followed with an exponential probability distribution. The fitting curves indicated that most of laminas at each scale were relatively thin. In other words, the thicker the layer, the less the number of layers contained in shale. Finally, the lamination models were constructed and superposed over the joint network model to generate 3-D geological structure models at various scales. The models were validated by reproducing fracture and lamina parameters, which were fairly close to those measurements of realistic geological bodies in the study area. The findings of this work could shed light on the characterization and modeling of geological structure for the numerical simulation and physical model test of hydraulic fracturing in shale gas reservoir.
Outcrops and core observations show that sandy and tuff aceous laminas and natural fractures are well developed in the continental shale gas reservoir. This study reports the distribution of laminas and natural fracture networks at different scales and established the 3-D geological structure models, with data obtained from outcrops, wells and cores of Yanchang shale from southern Ordos Basin. Firstly, based on two-dimensional fracture field investigations, a 3-D joint network model of the study area was built using the Monte Carlo simulation method. Then the laminations were identified from macroscopic scales to microscopic scales with multiple probe techniques. Statistical analysis of multi-scale layer thickness suggested that the average thickness of layers at multiple scales showed a fractal feature, with average layer thickness of 2.26 m, 2.09 dm, 1.70 cm, 1.48 mm and 11.7 μm, corresponding to meter scale, decimeter scale, centimeter scale, millimeter scale and 10-micro meter scale respectively, and that the layer thickness at studied scales all followed with an exponential probability distribution. The fitting curves indicated that most of laminas at each scale were relatively thin. In other words, the thicker the layer, the less the number of layers contained in shale. Finally, the lamination models were constructed and superposed over the joint network model to generate 3-D geological structure models at various scales. The models were validated by reproducing fracture and lamina parameters, which were fairly close to those measurements of realistic geological bodies in the study area. The findings of this work could shed light on the characterization and modeling of geological structure for the numerical simulation and physical model test of hydraulic fracturing in shale gas reservoir.
2019, 27(1): 80-87.
Phosphogypsum is a solid waste material. The storage of phosphogypsum wastes a lot of land resources and seriously pollutes the soil and water environment. And it may cause landslides. Therefore, it is extremely urgent to utilize phosphogypsum resources. In this paper we researched the cement-based stabilized phosphogypsum modified by sodium silicate to use in pavement base. Through unconfined compressive strength test, water stability test, dry shrinkage test and scanning electron microscope test, we obtained the physical and mechanical properties of cement-based stabilized phosphogypsum modified by sodium silicate using different dosage, incorporation mode and curing age. Sodium silicate promotes the hydration of cement and produces calcium silicate hydrate. It reveals the improvement mechanism of the strength of the mixture. The experimental results show that the compressive strength, water stability, water loss rate and dry shrinkage strain of cement-based stabilized phosphogypsum mixture can be effectively improved when the content of sodium silicate dissolved in water is 2%~4%. It is suggested that within 4-5 days after the construction of thepavement base, it is the best time to effectively control the water loss and dry shrinkage of the pavement base, so as to avoid the occurrence of cracks caused by rapid water loss.
Phosphogypsum is a solid waste material. The storage of phosphogypsum wastes a lot of land resources and seriously pollutes the soil and water environment. And it may cause landslides. Therefore, it is extremely urgent to utilize phosphogypsum resources. In this paper we researched the cement-based stabilized phosphogypsum modified by sodium silicate to use in pavement base. Through unconfined compressive strength test, water stability test, dry shrinkage test and scanning electron microscope test, we obtained the physical and mechanical properties of cement-based stabilized phosphogypsum modified by sodium silicate using different dosage, incorporation mode and curing age. Sodium silicate promotes the hydration of cement and produces calcium silicate hydrate. It reveals the improvement mechanism of the strength of the mixture. The experimental results show that the compressive strength, water stability, water loss rate and dry shrinkage strain of cement-based stabilized phosphogypsum mixture can be effectively improved when the content of sodium silicate dissolved in water is 2%~4%. It is suggested that within 4-5 days after the construction of thepavement base, it is the best time to effectively control the water loss and dry shrinkage of the pavement base, so as to avoid the occurrence of cracks caused by rapid water loss.
2019, 27(1): 88-97.
Some basic concepts or terminology, such as hazard, disaster vulnerability, risk identification, causes induced, deformation or failure mechanism and disaster modes, et al. are explained in this paper. For to serve effectively in disaster reduction, author puts up methods on the risk identification of landslide disasters which consists historic contrast, direct survey, indirect inversion, remote sensing and telemetering, dynamic monitoring and integrated analysis methods. The model Rt=[(f(a)+f(b)+f(c))d(t)+f(e)]f(v) is set up for integrated analysis of landslide disaster risk based on boundary forms(a), compositions and structures(b), initial states(c), induced factors(d), environmental effects(e) around slopes and disaster vulnerability(f) to objects bearing hazard and its changes to follow with time. Integrated risk analysis of two example, landslide-debris flow disaster happened in Jun. 24, 2017 at Xinmo village, Maoxian county, Sichuan province and rockfall-debris flow disaster happened in Aug. 28, 2017 at Pusa community, Nayong county, Guizhou province in China, have been done which includes its initial, induced and critical states by through suggested parameters based on author's personal experience. The results are coincidence comparatively with realistic situation.
Some basic concepts or terminology, such as hazard, disaster vulnerability, risk identification, causes induced, deformation or failure mechanism and disaster modes, et al. are explained in this paper. For to serve effectively in disaster reduction, author puts up methods on the risk identification of landslide disasters which consists historic contrast, direct survey, indirect inversion, remote sensing and telemetering, dynamic monitoring and integrated analysis methods. The model Rt=[(f(a)+f(b)+f(c))d(t)+f(e)]f(v) is set up for integrated analysis of landslide disaster risk based on boundary forms(a), compositions and structures(b), initial states(c), induced factors(d), environmental effects(e) around slopes and disaster vulnerability(f) to objects bearing hazard and its changes to follow with time. Integrated risk analysis of two example, landslide-debris flow disaster happened in Jun. 24, 2017 at Xinmo village, Maoxian county, Sichuan province and rockfall-debris flow disaster happened in Aug. 28, 2017 at Pusa community, Nayong county, Guizhou province in China, have been done which includes its initial, induced and critical states by through suggested parameters based on author's personal experience. The results are coincidence comparatively with realistic situation.
2019, 27(1): 98-107.
The liquefaction mechanism to cause rapid and long runout landslides is discussed in this paper. Through ring shear tests under the drained condition and undrained conditions, combined with field investigation on different types of rapid and long runout landslides, it is concluded that spontaneous liquefaction can be triggered due to collapse of loose structure in sandy soil, while grain crushing liquefaction can be caused during the sliding process when the saturated soil in sliding zone is crushable. Based on the results, a model describing sliding zone extension to the sliding mass is proposed, and the difference in the sliding mass deposit caused by the two different liquefaction mechanisms is analyzed. The importance of grain crushing is emphasized in this paper. For landslide disaster prevention, it is important to investigate the susceptibility of grain crushing, as well as the soil structure.
The liquefaction mechanism to cause rapid and long runout landslides is discussed in this paper. Through ring shear tests under the drained condition and undrained conditions, combined with field investigation on different types of rapid and long runout landslides, it is concluded that spontaneous liquefaction can be triggered due to collapse of loose structure in sandy soil, while grain crushing liquefaction can be caused during the sliding process when the saturated soil in sliding zone is crushable. Based on the results, a model describing sliding zone extension to the sliding mass is proposed, and the difference in the sliding mass deposit caused by the two different liquefaction mechanisms is analyzed. The importance of grain crushing is emphasized in this paper. For landslide disaster prevention, it is important to investigate the susceptibility of grain crushing, as well as the soil structure.
2019, 27(1): 108-122.
Rockmass structure is an inherent property of rock mass. The structural plane and rock block are the constituent elements of the rockmass structure which play an important role in the deformation of rockmass(Gu, 1979). The distinct effect of rock mass structure exists during the entire process of the long-runout rock landslide. It controls the deformation, failure mechanism and kinematics modes of the rock mass during the landsliding process. Although there are many theories, hypotheses and associated dynamics models for the long-runout landslide research, most of these models ignore the essential issue of the effect of rock mass structure. This paper systematically summarizes the features of different existing theories and dynamics models of long-runout landslide. It then focuses on the important issues of effect of rockmass structure on the key dynamics parameters, dynamics mechanism and dynamic process modeling of long-runout landslide, and puts forward potential research topics considering the effect of rock mass structure on dynamics of long-run out landslide.
Rockmass structure is an inherent property of rock mass. The structural plane and rock block are the constituent elements of the rockmass structure which play an important role in the deformation of rockmass(Gu, 1979). The distinct effect of rock mass structure exists during the entire process of the long-runout rock landslide. It controls the deformation, failure mechanism and kinematics modes of the rock mass during the landsliding process. Although there are many theories, hypotheses and associated dynamics models for the long-runout landslide research, most of these models ignore the essential issue of the effect of rock mass structure. This paper systematically summarizes the features of different existing theories and dynamics models of long-runout landslide. It then focuses on the important issues of effect of rockmass structure on the key dynamics parameters, dynamics mechanism and dynamic process modeling of long-runout landslide, and puts forward potential research topics considering the effect of rock mass structure on dynamics of long-run out landslide.
2019, 27(1): 123-133.
In view of the difficulty in implementing active reinforcement for the high-level rockfall disaster occurred in the high-steep slope zone of the "5·12" Wenchuan earthquake area in 2008, the pile-plate retaining wall is a passive protection measure used in the proposed interception site, and its applicable terrain slope is 25°~35°. In order to study the dynamic response of such a pile-plate structure under rockfall impact load, numerical simulation is carried out by coupling finite element and infinite element. Combined with the classical elastoplastic theory, the characteristic parameters such as impact force, penetration depth and structural energy dissipation effect of the pile-plate retaining wall during loading and unloading rebound process under different impact conditions are systematically analyzed, and the impact resistance of the structure is clarified. The results show that the "infinite element" boundary can effectively reduce the error caused by the reflection of the stress wave at the artificial truncation boundary. In the case of impact speeds of 10 m·s-1, 15 m·s-1 and 20 m·s-1, 25 m·s-1, the calculated impact forces are 1.9MN, 2.5MN, 3.1MN, 3.7MN, respectively. The results are consistent with the Kawahara model, but larger than the Labiouse model and the Hertz elastic solution. According to the concrete damage theory, the classification of damage level is proposed and the degree of structural damage is effectively quantified. When the impact speed is greater than 20 m·s-1, the pile and plate concrete tensile damage is seriously damaged, and the structure has the risk of completely losing the bearing capacity. The calculation methods and results in this paper can provide practical guidance for the related structural design.
In view of the difficulty in implementing active reinforcement for the high-level rockfall disaster occurred in the high-steep slope zone of the "5·12" Wenchuan earthquake area in 2008, the pile-plate retaining wall is a passive protection measure used in the proposed interception site, and its applicable terrain slope is 25°~35°. In order to study the dynamic response of such a pile-plate structure under rockfall impact load, numerical simulation is carried out by coupling finite element and infinite element. Combined with the classical elastoplastic theory, the characteristic parameters such as impact force, penetration depth and structural energy dissipation effect of the pile-plate retaining wall during loading and unloading rebound process under different impact conditions are systematically analyzed, and the impact resistance of the structure is clarified. The results show that the "infinite element" boundary can effectively reduce the error caused by the reflection of the stress wave at the artificial truncation boundary. In the case of impact speeds of 10 m·s-1, 15 m·s-1 and 20 m·s-1, 25 m·s-1, the calculated impact forces are 1.9MN, 2.5MN, 3.1MN, 3.7MN, respectively. The results are consistent with the Kawahara model, but larger than the Labiouse model and the Hertz elastic solution. According to the concrete damage theory, the classification of damage level is proposed and the degree of structural damage is effectively quantified. When the impact speed is greater than 20 m·s-1, the pile and plate concrete tensile damage is seriously damaged, and the structure has the risk of completely losing the bearing capacity. The calculation methods and results in this paper can provide practical guidance for the related structural design.
2019, 27(1): 134-143.
Rainfall is one of the important factors that induce geo-hazards. The early warning of regional geo-hazards based on the meteorological factor started in 2003, had achieved good results. The current early warning of regional geo-hazards are step by step from the "danger warning" to "risk warning". Early-warning model study of regional geo-hazards risk based on the meteorological factor is of great significance. This paper put forward the general model of early warning for regional geo-hazards risk based on the meteorological factor, and took a case study of Qingchuan County, Sichuan Province. Finally, the effect of the early warning was verified with a typical example. (1)The regional geo-hazards risk warning index(R)could be generalized as the product of geo-hazards potentiality parameter(Q), rainfall trigger factor(T) and vulnerability index(V). The calculation formulas of the three index(Q, T, V)were given respectively. (2)The early warning model of regional geo-hazards risk based on meteorological factor was established in Qingchuan County. According to the early warning index of regional geo-hazards, the principle dividing warning level was given. When two items of Q, T and V reached a high level(0.8) and one item reached a relative high level(0.6), it was a red alert; When two items of Q, T and V reached a relative high level(0.6) and one item reached a middle level(0.3), it was a orange alert; When one item of Q, T and V reached a relatively high level(0.6), and two items reached a middle level(0.3), it was a yellow alert. (3)Taking 26 June, 2018 as a typical example, the early warning of regional geo-hazards risk based on meteorological factor was simulated. With the actual geo-hazards, the warning effect was verified. The results showed that 94.1% of the geo-hazards were located in the warning area.
Rainfall is one of the important factors that induce geo-hazards. The early warning of regional geo-hazards based on the meteorological factor started in 2003, had achieved good results. The current early warning of regional geo-hazards are step by step from the "danger warning" to "risk warning". Early-warning model study of regional geo-hazards risk based on the meteorological factor is of great significance. This paper put forward the general model of early warning for regional geo-hazards risk based on the meteorological factor, and took a case study of Qingchuan County, Sichuan Province. Finally, the effect of the early warning was verified with a typical example. (1)The regional geo-hazards risk warning index(R)could be generalized as the product of geo-hazards potentiality parameter(Q), rainfall trigger factor(T) and vulnerability index(V). The calculation formulas of the three index(Q, T, V)were given respectively. (2)The early warning model of regional geo-hazards risk based on meteorological factor was established in Qingchuan County. According to the early warning index of regional geo-hazards, the principle dividing warning level was given. When two items of Q, T and V reached a high level(0.8) and one item reached a relative high level(0.6), it was a red alert; When two items of Q, T and V reached a relative high level(0.6) and one item reached a middle level(0.3), it was a orange alert; When one item of Q, T and V reached a relatively high level(0.6), and two items reached a middle level(0.3), it was a yellow alert. (3)Taking 26 June, 2018 as a typical example, the early warning of regional geo-hazards risk based on meteorological factor was simulated. With the actual geo-hazards, the warning effect was verified. The results showed that 94.1% of the geo-hazards were located in the warning area.
2019, 27(1): 144-151.
Tailings pond is an artificial hazard source with high potential energy. Once the dam breaks, it will surely threaten the safety of people regarding property and ecological environment of downstream. Due to the complexity of factors and the uncertainty of movement and retention in the downstream channel or site, it is difficult to predict the movement characteristics of tailings dam break. In this paper, based on the mechanics theory of continuous media and discontinuous media, considering the current ability of fluid-solid coupling numerical simulation, using the software such as Massflow, PFC3D combination UAV measurement, analysis of field investigation and verification, conduct a research of simulation study on the movement characteristics of tailings dam break. It is found that the tailings movement process is different based on PFC3D and Massflow numerical simulation. Massflow simulation results show that most of the tailings sands move along the zigzag channel downstream of the tailings pond and accumulate at the culvert where the gully meets the Zhang-Tang railway; PFC3D simulation results show that most of the tailings sands follow the tailings ponds main body towards outburst overflow, and a few enter the zigzag channel downstream. According to the research, considering the uncertainty of geological mass and movement process, it is advisable to combine two simulation methods based on different theoretical bases for the simulation of movement characteristics, and make comprehensive analysis and prediction combining with the actual situation of tailings pond.
Tailings pond is an artificial hazard source with high potential energy. Once the dam breaks, it will surely threaten the safety of people regarding property and ecological environment of downstream. Due to the complexity of factors and the uncertainty of movement and retention in the downstream channel or site, it is difficult to predict the movement characteristics of tailings dam break. In this paper, based on the mechanics theory of continuous media and discontinuous media, considering the current ability of fluid-solid coupling numerical simulation, using the software such as Massflow, PFC3D combination UAV measurement, analysis of field investigation and verification, conduct a research of simulation study on the movement characteristics of tailings dam break. It is found that the tailings movement process is different based on PFC3D and Massflow numerical simulation. Massflow simulation results show that most of the tailings sands move along the zigzag channel downstream of the tailings pond and accumulate at the culvert where the gully meets the Zhang-Tang railway; PFC3D simulation results show that most of the tailings sands follow the tailings ponds main body towards outburst overflow, and a few enter the zigzag channel downstream. According to the research, considering the uncertainty of geological mass and movement process, it is advisable to combine two simulation methods based on different theoretical bases for the simulation of movement characteristics, and make comprehensive analysis and prediction combining with the actual situation of tailings pond.
2019, 27(1): 152-161.
As a kind of common nature disaster, acid rain will not only pollute and damage the environment, but also trigger the failure of rock and soil mass such as slope collapse, while scholars study less on the latter. The failure of slope of mafic igneous/ultramafic igneous rocks is not unusual in the acid rain area, but the specific mechanism of instability remains to be studied by considering the acid rain effects. In this paper, gabbro samples from a cutting slope in Ya'an city of typical acid rain area were processed, and the simulated acid rain treatment of pH 3.0 in the laboratory was carried out. The shear strength parameters of structural plane of samples before and after the action of acid rain were compared by direct shear tests. Then the slope stability before and after the action of acid rain was studied and evaluated. The result shows that the slope stability decreases with the increase of acid rain duration. In order to obtain the internal reasons of acid rain significantly weakening the slope stability, samples before and after the action of acid rain were tested by X-ray Diffraction(XRD), Polarizing Microscope and Scanning Electron Microscope(SEM). The results indicate that the mechanism of acid rain weakening on the gabbro slope is mainly reflected in two aspects. Part of the chain silicate mineral(pyroxene) and the framework silicate mineral(calcic plagioclase) convert into layered silicate minerals(chlorite, illite and kaolinite) under acidic conditions, which is inferred to be one of the major causes of the decrease of the shear strength parameters. With soluble salts and part of clay minerals being gradually dissolved and removed out by acid rain, cracks gradually grow and propagate on the structural plane of samples. Newly formed cracks leading to the less effective shear area of structural plane probably also accelerates the reduction of strength. Conclusion of this paper may be taken as references for the stability analysis of rock slopes in acid rain area and their reinforcement design methods.
As a kind of common nature disaster, acid rain will not only pollute and damage the environment, but also trigger the failure of rock and soil mass such as slope collapse, while scholars study less on the latter. The failure of slope of mafic igneous/ultramafic igneous rocks is not unusual in the acid rain area, but the specific mechanism of instability remains to be studied by considering the acid rain effects. In this paper, gabbro samples from a cutting slope in Ya'an city of typical acid rain area were processed, and the simulated acid rain treatment of pH 3.0 in the laboratory was carried out. The shear strength parameters of structural plane of samples before and after the action of acid rain were compared by direct shear tests. Then the slope stability before and after the action of acid rain was studied and evaluated. The result shows that the slope stability decreases with the increase of acid rain duration. In order to obtain the internal reasons of acid rain significantly weakening the slope stability, samples before and after the action of acid rain were tested by X-ray Diffraction(XRD), Polarizing Microscope and Scanning Electron Microscope(SEM). The results indicate that the mechanism of acid rain weakening on the gabbro slope is mainly reflected in two aspects. Part of the chain silicate mineral(pyroxene) and the framework silicate mineral(calcic plagioclase) convert into layered silicate minerals(chlorite, illite and kaolinite) under acidic conditions, which is inferred to be one of the major causes of the decrease of the shear strength parameters. With soluble salts and part of clay minerals being gradually dissolved and removed out by acid rain, cracks gradually grow and propagate on the structural plane of samples. Newly formed cracks leading to the less effective shear area of structural plane probably also accelerates the reduction of strength. Conclusion of this paper may be taken as references for the stability analysis of rock slopes in acid rain area and their reinforcement design methods.
2019, 27(1): 162-169.
The karst water mixed with infitrated river water shows high Na, Cl and O-18 values and can be used to indicate the distribution of the infiltrated river water in karst aquifers. Individual flow path for three recharge sources was identified in the Xishan karst aquifer in Beijing, China using hydrochemical and isotopic methods. The recharge of rainfall in the Junzhuang area had two flow routes:one flows eastwards to the Yongfengtun; another flows southeastwards along east of the Yongding fault. The recharge of rainfall in Tanzhesi area flows along north of the Babaoshan fault northeastwards Sijiqing. The Yongdingriver infiltrates in the Junzhuang area and flows along the Yongding fault in the direction of southeast and turns to the diction of northeast near Gucheng, along a buried fault which is revealed this time. River water plays an important role in recharge to the karst aquifer and can be used to restore depleted karst flow systems by increasing the flow and infiltration of river water.
The karst water mixed with infitrated river water shows high Na, Cl and O-18 values and can be used to indicate the distribution of the infiltrated river water in karst aquifers. Individual flow path for three recharge sources was identified in the Xishan karst aquifer in Beijing, China using hydrochemical and isotopic methods. The recharge of rainfall in the Junzhuang area had two flow routes:one flows eastwards to the Yongfengtun; another flows southeastwards along east of the Yongding fault. The recharge of rainfall in Tanzhesi area flows along north of the Babaoshan fault northeastwards Sijiqing. The Yongdingriver infiltrates in the Junzhuang area and flows along the Yongding fault in the direction of southeast and turns to the diction of northeast near Gucheng, along a buried fault which is revealed this time. River water plays an important role in recharge to the karst aquifer and can be used to restore depleted karst flow systems by increasing the flow and infiltration of river water.
2019, 27(1): 170-177.
Environmental issues caused by hydraulic fracturing and wastewater reinjection during shale gas development have been paid more attention to. Because there are a wide variety of pollutants of the hydraulic fracturing, it is necessary to determine sensitive monitoring indicators for potential pollution tracing. This study takes the Jiaoshiba as an example, and has established the baseline values of groundwater environment(including water chemistry, isotopes and dissolved gas). Shallow groundwater is the typical karst water with TDS between 146 and 402 mg·L-1, belonging to HCO3-Ca·Mg water chemistry type. The groundwater samples are in the range of young groundwater(the contained 3H and 14C close to 100 pmC). The mass concentrations for CH4 of all groundwater samples are less than 0.01 mg·L-1 and the volumetric concentrations in dissolved gas of groundwater are less than 0.006 4%. The δ13C-CH4 values for dissolved methane in groundwater are lower than-50‰, suggesting biogenic origin. The TDS of the shale water in the Jisoshiba shale gas field is about twice that of the seawater, but it shows the genesis of atmospheric origin, which is significantly distinguished from the shale water in North America that originates from the seawater(or evaporated seawater). According to the differences of hydrogeochemical characteristics between shale water and shallow groundwater, the framework for determining sensitive monitoring indicators has been established. In the Jiaoshiba gas field, the sensitive indicators have included 7 items. The potential groundwater contamination processes due to shale gas development are mainly from stray natural gas and dissolved solid constituents. For the contamination of stray gas, end-members have been established by the use of methane and noble gas(3He/4He) to identify gas contamination. The contamination from dissolved constituents can be identified by the determined sensitive indicators based on the baseline values of shallow groundwater. This study may hold great significance for the groundwater protection of shale gas development in China and contribute to the improvement of monitoring groundwater environment and tracing potential contamination during shale gas development.
Environmental issues caused by hydraulic fracturing and wastewater reinjection during shale gas development have been paid more attention to. Because there are a wide variety of pollutants of the hydraulic fracturing, it is necessary to determine sensitive monitoring indicators for potential pollution tracing. This study takes the Jiaoshiba as an example, and has established the baseline values of groundwater environment(including water chemistry, isotopes and dissolved gas). Shallow groundwater is the typical karst water with TDS between 146 and 402 mg·L-1, belonging to HCO3-Ca·Mg water chemistry type. The groundwater samples are in the range of young groundwater(the contained 3H and 14C close to 100 pmC). The mass concentrations for CH4 of all groundwater samples are less than 0.01 mg·L-1 and the volumetric concentrations in dissolved gas of groundwater are less than 0.006 4%. The δ13C-CH4 values for dissolved methane in groundwater are lower than-50‰, suggesting biogenic origin. The TDS of the shale water in the Jisoshiba shale gas field is about twice that of the seawater, but it shows the genesis of atmospheric origin, which is significantly distinguished from the shale water in North America that originates from the seawater(or evaporated seawater). According to the differences of hydrogeochemical characteristics between shale water and shallow groundwater, the framework for determining sensitive monitoring indicators has been established. In the Jiaoshiba gas field, the sensitive indicators have included 7 items. The potential groundwater contamination processes due to shale gas development are mainly from stray natural gas and dissolved solid constituents. For the contamination of stray gas, end-members have been established by the use of methane and noble gas(3He/4He) to identify gas contamination. The contamination from dissolved constituents can be identified by the determined sensitive indicators based on the baseline values of shallow groundwater. This study may hold great significance for the groundwater protection of shale gas development in China and contribute to the improvement of monitoring groundwater environment and tracing potential contamination during shale gas development.
2019, 27(1): 184-194.
This is a summary of the 2018 annual symposium of engineering geology in Xi'an. The conference gathered nearly 1, 500 delegates with the theme of "the Belt and Road and the coordinated development of the ecological environment". Through 17 special invited lectures, 24 keynote speeches, 283 group reports and the papers published in the proceedings, this conference reflected 10 aspects on the theoretical accumulation and academic achievements of engineering geology in China for several decades, including the development of the discipline system, geotechnical engineering geology, geohazard and engineering geodynamics, marine and urban engineering geology, internationalization of engineering geology, developments of engineering geology technology, significant works in major projects and constructions of technical standard system. Based on the conference theme, technology innovation, discipline distribution and globalization opportunities, this paper demonstrated the ideas of engineering geology in the new era. And also, it put forward new development missions for the comprehensive application of national strategy of engineering geology.
This is a summary of the 2018 annual symposium of engineering geology in Xi'an. The conference gathered nearly 1, 500 delegates with the theme of "the Belt and Road and the coordinated development of the ecological environment". Through 17 special invited lectures, 24 keynote speeches, 283 group reports and the papers published in the proceedings, this conference reflected 10 aspects on the theoretical accumulation and academic achievements of engineering geology in China for several decades, including the development of the discipline system, geotechnical engineering geology, geohazard and engineering geodynamics, marine and urban engineering geology, internationalization of engineering geology, developments of engineering geology technology, significant works in major projects and constructions of technical standard system. Based on the conference theme, technology innovation, discipline distribution and globalization opportunities, this paper demonstrated the ideas of engineering geology in the new era. And also, it put forward new development missions for the comprehensive application of national strategy of engineering geology.
2019, 27(1): 202-207.
Coral reef is a kind of special geotechnical medium. From the perspective of engineering geology, it can be divided into two types:coral sandstone and coral reef limestone. This paper reviews the basic history of coral reef research for 30 years, focusing on the exploration and research results of the static mechanical properties, dynamic properties, low particle strength and other special mechanical properties of the coral sand soil and the engineering properties of the pile foundation. Taking the development and construction of coral reef islands in the South China Sea as a guide, more research scholars are called upon to join the research team of coral reefs to jointly promote the development of coral reef engineering geology.
Coral reef is a kind of special geotechnical medium. From the perspective of engineering geology, it can be divided into two types:coral sandstone and coral reef limestone. This paper reviews the basic history of coral reef research for 30 years, focusing on the exploration and research results of the static mechanical properties, dynamic properties, low particle strength and other special mechanical properties of the coral sand soil and the engineering properties of the pile foundation. Taking the development and construction of coral reef islands in the South China Sea as a guide, more research scholars are called upon to join the research team of coral reefs to jointly promote the development of coral reef engineering geology.
2019, 27(1): 208-218.
The NSFC proposals and grants of engineering geology in 2018 were analyzed. The number of proposals declined, mainly due to the decline in the number of applications for Young Scientists Fund and Major Program. The number of applications for Key Program and General Program remained stable, and the number of applications for Excellent Young Scientists Fund increased significantly in this year. The peer-review referees well handled the peer-review scale on the proposals. The age structure of applicants for General Program tends to be younger, and that for the Youth Scientists Fund is reasonable. Applicants for Key Program are still dominated by scientists born in the 1960s, while the number of scientists born in the 1970s is increasing and gradually being funded. The applicants of engineering geology has been funded in several different project types, showing increasing competitiveness.
The NSFC proposals and grants of engineering geology in 2018 were analyzed. The number of proposals declined, mainly due to the decline in the number of applications for Young Scientists Fund and Major Program. The number of applications for Key Program and General Program remained stable, and the number of applications for Excellent Young Scientists Fund increased significantly in this year. The peer-review referees well handled the peer-review scale on the proposals. The age structure of applicants for General Program tends to be younger, and that for the Youth Scientists Fund is reasonable. Applicants for Key Program are still dominated by scientists born in the 1960s, while the number of scientists born in the 1970s is increasing and gradually being funded. The applicants of engineering geology has been funded in several different project types, showing increasing competitiveness.
2019, 27(1): 178-183.
Exploitation with reinjection is thought to be one of the most effective ways to keep reservoir pressure and mitigate water table decrease, which it's widely encouraged. Reinjection with water from other sources is proposed for carbonate reservoir that is easily to inject. This paper discusses the possibility of reinjection with untreated lake water and geochemical responses of carbonate reservoir based on water-rock interactions experiments for dolomite reservoir of Wumishan Group in Donglihu Area, Tianjin. Results show that after reactions with dolomite, TDS of reacted water decreases indicating that precipitation occurs and the precipitates amounts to 142.6 mg·L-1, which is equal to 0.09%increase in mineral quality. At the initial stage, plagioclase dissolves and alkaline metals like K、Ca、Na, SiO2 and Al-bearing compositions were released, leading to oversaturation and precipitations of dolomite, calcite and K-feldspar. With the progresses of reactions, incongruent dissolution causes part of the dolomite dissolves while calcite keeps precipitating. Illite precipitates and its effects on reservoir structure depend on its shape. Based on the experimental data, it's concluded that the dolomite reservoir will slightly be affected by reinjection of lake water and it's still a good way to explore sustainable developments for geothermal exploitation.
Exploitation with reinjection is thought to be one of the most effective ways to keep reservoir pressure and mitigate water table decrease, which it's widely encouraged. Reinjection with water from other sources is proposed for carbonate reservoir that is easily to inject. This paper discusses the possibility of reinjection with untreated lake water and geochemical responses of carbonate reservoir based on water-rock interactions experiments for dolomite reservoir of Wumishan Group in Donglihu Area, Tianjin. Results show that after reactions with dolomite, TDS of reacted water decreases indicating that precipitation occurs and the precipitates amounts to 142.6 mg·L-1, which is equal to 0.09%increase in mineral quality. At the initial stage, plagioclase dissolves and alkaline metals like K、Ca、Na, SiO2 and Al-bearing compositions were released, leading to oversaturation and precipitations of dolomite, calcite and K-feldspar. With the progresses of reactions, incongruent dissolution causes part of the dolomite dissolves while calcite keeps precipitating. Illite precipitates and its effects on reservoir structure depend on its shape. Based on the experimental data, it's concluded that the dolomite reservoir will slightly be affected by reinjection of lake water and it's still a good way to explore sustainable developments for geothermal exploitation.
2019, 27(1): 195-201.
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