Accepted Article Preview
More
Accepted articles have been peer-reviewed, and will be published when volume and issue numbers are finalized. The articles are citable by DOI (Digital Object Identifier).
Current Issue
More
Others
Abstract(131)
HTML(93) 3160KB(79)
Prevention and control for mine safety is a complex systematic engineering that relates to multiple disciplines, of which the study of geological conditions and disaster mechanism is the most fundamentally important work in accident prevention and control.However, there is currently lack of a discipline or working mechanism for systematical research of safety geology.Therefore, a new cross-discipline Mine Safety Geology is proposed in this review.This paper introduces the concept, content framework, research methods, major mine safety geological issues, and risk assessment for safety geological issues in response to the needs of mine safe construction and production.Further, prospects for the key scientific problems as well as the trends for prevention and control technology that need to be solved urgently in mine safety geology are put forward.Meanwhile, this paper also briefly reviews the innovative works on mine safety geology of the main articles published in this issue with a topic of deep mine safety geology.We hope to provide a scientific support for the research on deep mine safety geology and the prevention and control of mine geological disasters Prevention and control for mine safety is a complex systematic engineering that relates to multiple disciplines, of which the study of geological conditions and disaster mechanism is the most fundamentally important work in accident prevention and control.However, there is currently lack of a discipline or working mechanism for systematical research of safety geology.Therefore, a new cross-discipline Mine Safety Geology is proposed in this review.This paper introduces the concept, content framework, research methods, major mine safety geological issues, and risk assessment for safety geological issues in response to the needs of mine safe construction and production.Further, prospects for the key scientific problems as well as the trends for prevention and control technology that need to be solved urgently in mine safety geology are put forward.Meanwhile, this paper also briefly reviews the innovative works on mine safety geology of the main articles published in this issue with a topic of deep mine safety geology.We hope to provide a scientific support for the research on deep mine safety geology and the prevention and control of mine geological disasters
With increasing coal mining depth, the rockburst risk is becoming more serious.A thorough understanding of rockburst occurrence mechanism, monitoring and prevention technology is crucial to coal mine safety.In this paper, we systematically summarized the research findings of the team, put forward the mechanismthat the superposition of static and dynamic loads causing rockburst, and accordingly subdivided the rockburst types based on the stress and energy body.We proposed the three field coupling monitoring principle for rockburst risk, including stress field, seismic field and energy field.Based on the three stress fields, we further established a multi-parameter comprehensive monitoring and pre-warning system as well as a space-temporal pre-warning model. Based on big data and cloud platform technology, we developed a cloud platform for intelligent identification and multi-parameter monitoring and pre-warning of rockburst risk.The cloud platform realized the integration of rockburst monitoring data and prevention measures information, and further improved the monitoring and pre- warning efficiency of rockburst risk.Finally, we proposed two theories, i.e., the strength weakening theory for rockburst risk reduction and the strong-soft-strong structure theory, and put forward the monitoring and prevention scheme for different rockbursts.The study results strongly promote the research of rockburst and provide significant guidance for the safety of coal mines suffering rockburst With increasing coal mining depth, the rockburst risk is becoming more serious.A thorough understanding of rockburst occurrence mechanism, monitoring and prevention technology is crucial to coal mine safety.In this paper, we systematically summarized the research findings of the team, put forward the mechanismthat the superposition of static and dynamic loads causing rockburst, and accordingly subdivided the rockburst types based on the stress and energy body.We proposed the three field coupling monitoring principle for rockburst risk, including stress field, seismic field and energy field.Based on the three stress fields, we further established a multi-parameter comprehensive monitoring and pre-warning system as well as a space-temporal pre-warning model. Based on big data and cloud platform technology, we developed a cloud platform for intelligent identification and multi-parameter monitoring and pre-warning of rockburst risk.The cloud platform realized the integration of rockburst monitoring data and prevention measures information, and further improved the monitoring and pre- warning efficiency of rockburst risk.Finally, we proposed two theories, i.e., the strength weakening theory for rockburst risk reduction and the strong-soft-strong structure theory, and put forward the monitoring and prevention scheme for different rockbursts.The study results strongly promote the research of rockburst and provide significant guidance for the safety of coal mines suffering rockburst
Rock burst and coal burst did not originally exist in nature, which were completely induced by humans'project construction such as during utilization of deep underground space and exploitation of deep mineral resources. Both of them belong to the most typical deep engineering geological hazards. For a long time, the concepts of rock burst and coal burst have been confused. This article reviewed the early research progress of rock burst and coal burst in China, and systematically analyzed the difference between them. There were fundamental differences between rock burst and coal burst in the research objects(bearing strength, energy storage and release capacity, and elastic brittleness of hard rock and coal), stress conditions(in-situ stress, disturbance stress) and boundary conditions(excavation & mining methods and procedures, disturbance range and timeliness, etc.). There were also great differences between rock burst and coal burst in the aspects of apparent phenomenon, restricted object, research object, occurrence condition, industry field, engineering construction method, engineering construction purpose, inducing mechanism, requirements and supporting principle, tendency criterion, classification type, classification grade, grade evaluation method, and so on. In conclusion, rock burst and coal burst were two kinds of parallel dynamic failure phenomena of geological body, and no subordinate relationship occurred between them. Based on the previous studies, the definition and connotation of rock burst and coal burst were given respectively. Rock burst was defined as the ejection, burst or caving phenomenon of hard rock occurring in deep buried opening(tunnel), mine roadway and pillar, accompanied by different degrees of sound. Coal burst was defined as the phenomenon that occurs in deep coal mines when coal was thrown out and releases different degrees of kinetic energy, often accompanied by vibration, loud noise, air wave or shock wave in server cases. It is suggested to replace the term "coal bump" with "coal burst" in consideration of the dynamic coal failure phenomenon and the appellative consistency. On this basis, seven viewpoints are expounded in detail in understanding the rock burst and coal burst. Finally, several key mechanisms of rock burst and coal burst were proposed from the aspects of research object, stress and boundary conditions. That is, investigations of rock burst and coal burst from the perspective of coupled static-dynamic(or dynamic-static) loading mechanics favorably agree with the full stress path of deep geological body failure, and the transformation from static state to dynamic state should be studied from the viewpoint of energy conservation. In the mechanism analysis, prediction and forecast, monitoring and early warning, regulation and control of rock burst and coal burst, the logical and dialectical relations among influencing factors should be understood scientifically. Rock burst and coal burst did not originally exist in nature, which were completely induced by humans'project construction such as during utilization of deep underground space and exploitation of deep mineral resources. Both of them belong to the most typical deep engineering geological hazards. For a long time, the concepts of rock burst and coal burst have been confused. This article reviewed the early research progress of rock burst and coal burst in China, and systematically analyzed the difference between them. There were fundamental differences between rock burst and coal burst in the research objects(bearing strength, energy storage and release capacity, and elastic brittleness of hard rock and coal), stress conditions(in-situ stress, disturbance stress) and boundary conditions(excavation & mining methods and procedures, disturbance range and timeliness, etc.). There were also great differences between rock burst and coal burst in the aspects of apparent phenomenon, restricted object, research object, occurrence condition, industry field, engineering construction method, engineering construction purpose, inducing mechanism, requirements and supporting principle, tendency criterion, classification type, classification grade, grade evaluation method, and so on. In conclusion, rock burst and coal burst were two kinds of parallel dynamic failure phenomena of geological body, and no subordinate relationship occurred between them. Based on the previous studies, the definition and connotation of rock burst and coal burst were given respectively. Rock burst was defined as the ejection, burst or caving phenomenon of hard rock occurring in deep buried opening(tunnel), mine roadway and pillar, accompanied by different degrees of sound. Coal burst was defined as the phenomenon that occurs in deep coal mines when coal was thrown out and releases different degrees of kinetic energy, often accompanied by vibration, loud noise, air wave or shock wave in server cases. It is suggested to replace the term "coal bump" with "coal burst" in consideration of the dynamic coal failure phenomenon and the appellative consistency. On this basis, seven viewpoints are expounded in detail in understanding the rock burst and coal burst. Finally, several key mechanisms of rock burst and coal burst were proposed from the aspects of research object, stress and boundary conditions. That is, investigations of rock burst and coal burst from the perspective of coupled static-dynamic(or dynamic-static) loading mechanics favorably agree with the full stress path of deep geological body failure, and the transformation from static state to dynamic state should be studied from the viewpoint of energy conservation. In the mechanism analysis, prediction and forecast, monitoring and early warning, regulation and control of rock burst and coal burst, the logical and dialectical relations among influencing factors should be understood scientifically.
The coal mining in North China type coalfield is faced with the problems of high water yield, high water pressure, complex geological structure, thin aquifuge and so on.Water disaster control faces great challenges.The identification of flowing pathway is the key problem of floor water disaster prevention.Based on the principle of microseismic monitoring, the identification method of water diversion pathway is put forward based on microseismic energy density and rock connectivity.Taking the floor water inrush monitoring project of the panel 11916 in East well of Gequan mine, Hebei province as the background, the proposed identification technology is applied.There are 1~3 dominant fissures in the collapse column area of the panel 11916 through inverting the connected flowing pathway.The fissures are verified with apparent resistivity monitoring data.The results show that, the method of characterizing the conductivity of mining induced fractures in floor strata is feasible using microseismic energy density and connectivity.This study provides a new way to promote the application of microseismic monitoring technology in floor water disaster prevention, and lays an important foundation for improving the level of floor water inrush monitoring and early warning. The coal mining in North China type coalfield is faced with the problems of high water yield, high water pressure, complex geological structure, thin aquifuge and so on.Water disaster control faces great challenges.The identification of flowing pathway is the key problem of floor water disaster prevention.Based on the principle of microseismic monitoring, the identification method of water diversion pathway is put forward based on microseismic energy density and rock connectivity.Taking the floor water inrush monitoring project of the panel 11916 in East well of Gequan mine, Hebei province as the background, the proposed identification technology is applied.There are 1~3 dominant fissures in the collapse column area of the panel 11916 through inverting the connected flowing pathway.The fissures are verified with apparent resistivity monitoring data.The results show that, the method of characterizing the conductivity of mining induced fractures in floor strata is feasible using microseismic energy density and connectivity.This study provides a new way to promote the application of microseismic monitoring technology in floor water disaster prevention, and lays an important foundation for improving the level of floor water inrush monitoring and early warning.
To obtain the distribution of in-situ stress in the peripheral exploration area of the Panji coal mine in Huainan coalfield, we used the hydraulic fracturing method and its device to test the in-situ stress in the deep exploration area of the study area.In this study, we completed the field measurement of three boreholes and 28 measuring points.The depths of the three boreholes were all over 1400 m.The maximum measuring point depth was 1460 m.Through actual measurement and analysis, we obtained the in-situ stress state and its distribution laws in the exploration area.The results show that: (1) The depth of the exploration area is within the range of 466~1460 m, the maximum horizontal principal stress is 13.62~54.58 MPa, the minimum horizontal principal stress is 11.79~37.93 MPa.The direction of the maximum horizontal principal stress is the NEE direction.The measured in-situ stress increases approximately linearly with the increase of depth.(2) The ratio of the maximum horizontal principal stress to the vertical stress in the exploration area ranges from 1.03 to 1.44, and the average ratio is 1.28, indicating that the in-situ stress state in the exploration area is dominated by horizontal stress.(3) In the area with a depth of more than 450 m, the in-situ stress field belongs to the type of tectonic stress field.With the increase of depth, the appearance of tectonic stress also increases.The measurement results can provide scientific basis for mine planning and coal mining design in the exploration area. To obtain the distribution of in-situ stress in the peripheral exploration area of the Panji coal mine in Huainan coalfield, we used the hydraulic fracturing method and its device to test the in-situ stress in the deep exploration area of the study area.In this study, we completed the field measurement of three boreholes and 28 measuring points.The depths of the three boreholes were all over 1400 m.The maximum measuring point depth was 1460 m.Through actual measurement and analysis, we obtained the in-situ stress state and its distribution laws in the exploration area.The results show that: (1) The depth of the exploration area is within the range of 466~1460 m, the maximum horizontal principal stress is 13.62~54.58 MPa, the minimum horizontal principal stress is 11.79~37.93 MPa.The direction of the maximum horizontal principal stress is the NEE direction.The measured in-situ stress increases approximately linearly with the increase of depth.(2) The ratio of the maximum horizontal principal stress to the vertical stress in the exploration area ranges from 1.03 to 1.44, and the average ratio is 1.28, indicating that the in-situ stress state in the exploration area is dominated by horizontal stress.(3) In the area with a depth of more than 450 m, the in-situ stress field belongs to the type of tectonic stress field.With the increase of depth, the appearance of tectonic stress also increases.The measurement results can provide scientific basis for mine planning and coal mining design in the exploration area.
The deformation and failure of the original geological mass can occur under the condition of coal and rock excavation, and the related physical properties (strain field, seepage field, chemical field, temperature field, geophysical field) can change accordingly. To analyze the deformation and failure mechanism in detail, it is necessary to reconstruct and invert the field source characteristics. Therefore, there is an urgent need for a high sensitivity, stable performance and distributed monitoring system for real-time dynamic monitoring of the above field source information. Based on the advantages of optical fiber sensing technology (distributed, high stability, anti electromagnetic interference, etc.), it can make up for the shortcomings of conventional resistance and vibrating wire sensors. This paper points out that it can dynamically monitor the deformation of the surrounding rock in the stope, and the massive data volume obtained can provide support for the recovery and reconstruction of the deformation field and stress field of the surrounding rock. The working principles, advantages, disadvantages and applicable conditions of fiber Bragg grating (FBG), optical time-domain reflectometer (OTDR), Brillouin optical time-domain reflectometer (BOTDR), Brillouin optical time-domain analysis (BOTDA) and Brillouin optical frequency domain analysis (BOFDA) are introduced in detail. The research progress of this technique in deformation and failure of roof and floor, abutment pressure, fault activation monitoring, stability monitoring of coal pillar and stability monitoring of grouting reinforcement of broken rock mass is described. This paper analyzes the existing problems and research hotspots of distributed fiber optic sensing (DFOS) test technology in the current research, and points out the development trend of later research. The main development directions include: (1)Research on the mechanism of rock deformation and instability and mutual feed of optical fiber data volume; (2)Research on coupling performance of optical fiber and rock mass; (3)Data visualization processing and simulation software research; (4)Research on optical fiber monitoring characterization method of rock deformation and failure; (5)Research on applicability of optical fiber for large deformation monitoring in mines; (6)Construction of multi-phase and multi field coupling monitoring system; (7)Construction of monitoring and early warning platform based on multi parameter information fusion of ground and underground integration. The related research is expected to provide reference for the transparent geology of coal mine and intelligent mining. The deformation and failure of the original geological mass can occur under the condition of coal and rock excavation, and the related physical properties (strain field, seepage field, chemical field, temperature field, geophysical field) can change accordingly. To analyze the deformation and failure mechanism in detail, it is necessary to reconstruct and invert the field source characteristics. Therefore, there is an urgent need for a high sensitivity, stable performance and distributed monitoring system for real-time dynamic monitoring of the above field source information. Based on the advantages of optical fiber sensing technology (distributed, high stability, anti electromagnetic interference, etc.), it can make up for the shortcomings of conventional resistance and vibrating wire sensors. This paper points out that it can dynamically monitor the deformation of the surrounding rock in the stope, and the massive data volume obtained can provide support for the recovery and reconstruction of the deformation field and stress field of the surrounding rock. The working principles, advantages, disadvantages and applicable conditions of fiber Bragg grating (FBG), optical time-domain reflectometer (OTDR), Brillouin optical time-domain reflectometer (BOTDR), Brillouin optical time-domain analysis (BOTDA) and Brillouin optical frequency domain analysis (BOFDA) are introduced in detail. The research progress of this technique in deformation and failure of roof and floor, abutment pressure, fault activation monitoring, stability monitoring of coal pillar and stability monitoring of grouting reinforcement of broken rock mass is described. This paper analyzes the existing problems and research hotspots of distributed fiber optic sensing (DFOS) test technology in the current research, and points out the development trend of later research. The main development directions include: (1)Research on the mechanism of rock deformation and instability and mutual feed of optical fiber data volume; (2)Research on coupling performance of optical fiber and rock mass; (3)Data visualization processing and simulation software research; (4)Research on optical fiber monitoring characterization method of rock deformation and failure; (5)Research on applicability of optical fiber for large deformation monitoring in mines; (6)Construction of multi-phase and multi field coupling monitoring system; (7)Construction of monitoring and early warning platform based on multi parameter information fusion of ground and underground integration. The related research is expected to provide reference for the transparent geology of coal mine and intelligent mining.
As the depth of coal mining increases, the water hazards in mining under the deep and complicated conditions become increasingly serious. The dynamic monitoring of roof and floor failure in the coal mining process under complex conditions is of great significance to the prediction of water inrush at the mining face and the improvement of coal mining methods. Based on the parallel electrical monitoring technology, and combining the dual-mode electrode data collection method, we monitor and research the geoelectric field characteristics of the full space of coal seam roof and floor at the coal mining face simultaneously. Additionally, we obtain the synchronous response characteristics of resistivity and self-potential of the coal seam roof and floor surrounding rock before and after the mining at the first time. Research findings are as follows. The dynamic change of the cross-hole resistivity monitoring of the roof and floor can show the dynamic variation of the inter-hole resistivity with the gradual advancement of the coal mining face. It can also demonstrate the development range of the roof and floor failure zone effectively. Besides, the degree of resistivity variations caused by the apical plate collapse is greater than the degree of resistivity change caused by the bottom plate rupture. Self-potential data can reflect the roof and floor rock and fissure expansion and closure forms, and the degree of rupture. The self-potential value of the apical plate in the study area is obviously higher than the bottom plate, and the self-potential change intensity caused by the apical plate rupture is obviously greater than the bottom plate rupture. Multi-parameters are used to synchronously and dynamically monitor the roof and floor mining damage of coal seams, which has real application value to guarantee the safe mining of the mining face. As the depth of coal mining increases, the water hazards in mining under the deep and complicated conditions become increasingly serious. The dynamic monitoring of roof and floor failure in the coal mining process under complex conditions is of great significance to the prediction of water inrush at the mining face and the improvement of coal mining methods. Based on the parallel electrical monitoring technology, and combining the dual-mode electrode data collection method, we monitor and research the geoelectric field characteristics of the full space of coal seam roof and floor at the coal mining face simultaneously. Additionally, we obtain the synchronous response characteristics of resistivity and self-potential of the coal seam roof and floor surrounding rock before and after the mining at the first time. Research findings are as follows. The dynamic change of the cross-hole resistivity monitoring of the roof and floor can show the dynamic variation of the inter-hole resistivity with the gradual advancement of the coal mining face. It can also demonstrate the development range of the roof and floor failure zone effectively. Besides, the degree of resistivity variations caused by the apical plate collapse is greater than the degree of resistivity change caused by the bottom plate rupture. Self-potential data can reflect the roof and floor rock and fissure expansion and closure forms, and the degree of rupture. The self-potential value of the apical plate in the study area is obviously higher than the bottom plate, and the self-potential change intensity caused by the apical plate rupture is obviously greater than the bottom plate rupture. Multi-parameters are used to synchronously and dynamically monitor the roof and floor mining damage of coal seams, which has real application value to guarantee the safe mining of the mining face.
Physical model test is an important method to study the roadway stability, however, it is difficult to build similar models for jointed rock mass because of long period and complicated process. To solve the technical problem, a set of physical model test methods for roadway excavation under jointed surrounding rock are proposed and the experimental procedure is introduced in detail based on typical roadway in Jinchuan mining zone. The main conclusions can be drawn as follows: (1)A mixed pouring-bricking method was proposed. Pouring was adopted in the inner ring of the model, and bricking was used in the outer ring, which can reflect the structural characteristics of jointed surrounding rocks, and improve the test efficiency; (2)A roadway excavation device based on embedded mold and spiral traction was developed independently, which can form the roadway well and slightly disturb the model; (3)The physical model built by roadway in Jinchuan mining area can truly reproduce the structural characteristics of the prototype and fully restore the excavation conditions of the roadway, which proves the higher practicability and efficiency of the method. The paper provides a technical reference for the design and production of similar model experiments. Physical model test is an important method to study the roadway stability, however, it is difficult to build similar models for jointed rock mass because of long period and complicated process. To solve the technical problem, a set of physical model test methods for roadway excavation under jointed surrounding rock are proposed and the experimental procedure is introduced in detail based on typical roadway in Jinchuan mining zone. The main conclusions can be drawn as follows: (1)A mixed pouring-bricking method was proposed. Pouring was adopted in the inner ring of the model, and bricking was used in the outer ring, which can reflect the structural characteristics of jointed surrounding rocks, and improve the test efficiency; (2)A roadway excavation device based on embedded mold and spiral traction was developed independently, which can form the roadway well and slightly disturb the model; (3)The physical model built by roadway in Jinchuan mining area can truly reproduce the structural characteristics of the prototype and fully restore the excavation conditions of the roadway, which proves the higher practicability and efficiency of the method. The paper provides a technical reference for the design and production of similar model experiments.
Excavation of roadways in deep underground can induce the sharp adjustment of stress,which can undoubtedly cause the damage of surrounding rock. Although the dynamic action of excavation lasts for a short time,the damage caused by excavation provides the basic conditions for subsequent instable failure and disaster phenomena under time-dependent deformation and engineering disturbance. In order to obtain the evolution mechanism of excavation-induced damage in deep roadways and take targeted prevention and control measures in Jinchuan mining area,the equivalent simulation method and heterogeneous model are adopted based on the actual buried depth and rock mass structure types to study excavation damage problems. The simulation results reveal the evolution process and law of excavation damage zone under different levels and rock mass structures. According to the damage and failure law of roadways in the study area,this paper puts forward five evolution models of excavation damage in deep roadways,and reveals the inducing conditions,performance characteristics,mechanical mechanisms and development trends. Relevant understanding and conclusion are expected to provide certain reference for theory and engineering practice. Excavation of roadways in deep underground can induce the sharp adjustment of stress,which can undoubtedly cause the damage of surrounding rock. Although the dynamic action of excavation lasts for a short time,the damage caused by excavation provides the basic conditions for subsequent instable failure and disaster phenomena under time-dependent deformation and engineering disturbance. In order to obtain the evolution mechanism of excavation-induced damage in deep roadways and take targeted prevention and control measures in Jinchuan mining area,the equivalent simulation method and heterogeneous model are adopted based on the actual buried depth and rock mass structure types to study excavation damage problems. The simulation results reveal the evolution process and law of excavation damage zone under different levels and rock mass structures. According to the damage and failure law of roadways in the study area,this paper puts forward five evolution models of excavation damage in deep roadways,and reveals the inducing conditions,performance characteristics,mechanical mechanisms and development trends. Relevant understanding and conclusion are expected to provide certain reference for theory and engineering practice.
This paper aims to solve the support problem of the mining roadway in the re-mined coal seam under the influence of double mining in Xuehugou Coal Mine. After field observation,the upper part of the roadway roof has the coexistence of the upper empty roadway and the coal body,which increases the difficulty of support. Through theoretical analysis and numerical simulation,the surrounding rock stability of 2-106A2 roadway is analyzed under the influence of dual mining. The original support plan is verified. The results show that the original support scheme cannot meet the stability of the roadway under this condition. The roof and the right side of the roadway are needed to be reinforced. We use numerical simulation method to analyze the stability of surrounding rock after adopting reinforcement support plan for 2-106A2 roadway. The simulation results show that the designed reinforcement plan is reasonable. In addition,the cross-point method is used to observe the deformation of surrounding rock in the 230 m section of the 2-106A2 roadway affected by the dual mining. The maximum sinking amount of the roof of the roadway is 195 mm,and the moving distances of the left and right sides are 124 mm and 265 mm respectively. The deformation of the broken zone of the roof of the roadway is well controlled,realizing safe and efficient mining of the working face. This paper aims to solve the support problem of the mining roadway in the re-mined coal seam under the influence of double mining in Xuehugou Coal Mine. After field observation,the upper part of the roadway roof has the coexistence of the upper empty roadway and the coal body,which increases the difficulty of support. Through theoretical analysis and numerical simulation,the surrounding rock stability of 2-106A2 roadway is analyzed under the influence of dual mining. The original support plan is verified. The results show that the original support scheme cannot meet the stability of the roadway under this condition. The roof and the right side of the roadway are needed to be reinforced. We use numerical simulation method to analyze the stability of surrounding rock after adopting reinforcement support plan for 2-106A2 roadway. The simulation results show that the designed reinforcement plan is reasonable. In addition,the cross-point method is used to observe the deformation of surrounding rock in the 230 m section of the 2-106A2 roadway affected by the dual mining. The maximum sinking amount of the roof of the roadway is 195 mm,and the moving distances of the left and right sides are 124 mm and 265 mm respectively. The deformation of the broken zone of the roof of the roadway is well controlled,realizing safe and efficient mining of the working face.
The abnormal geo-temperature in coal mine is a warning factor of geological disaster. Study on the hydrogeochemistry and source of geothermal water is an effective method of prevention on mine water and heat disaster. In this study,we collected 13 samples of geothermal water and 11 samples of common groundwater from draining hole at the same depth (-585m). Based on the hydrochemistry characteristics,the hydrochemical process and sources of geothermal water were analyzed. Compared with the common groundwater,geothermal water had higher content of TDS,Ca2+,Cl-. The hydrochemical facies of geothermal water were SO4 ·Cl-Ca ·Mg type in weak alkaline environment. The chemical composition of geothermal water was dominated by both ion-exchange interaction and dissolution of silicate and evaporates. The oxidation of pyrite in coal,the geothermal water possessed fine hydrodynamic condition and the more intense ion-exchange interactions are more active than those in common groundwater. The formation of geothermal water was supplied by deep Ordovician limestone water and mixed with Taiyuan limestone water through the fracture. The mixing proportion of Ordovician limestone water was higher. The outcomes of this paper can provide guidance for mine water prevention and control. The abnormal geo-temperature in coal mine is a warning factor of geological disaster. Study on the hydrogeochemistry and source of geothermal water is an effective method of prevention on mine water and heat disaster. In this study,we collected 13 samples of geothermal water and 11 samples of common groundwater from draining hole at the same depth (-585m). Based on the hydrochemistry characteristics,the hydrochemical process and sources of geothermal water were analyzed. Compared with the common groundwater,geothermal water had higher content of TDS,Ca2+,Cl-. The hydrochemical facies of geothermal water were SO4 ·Cl-Ca ·Mg type in weak alkaline environment. The chemical composition of geothermal water was dominated by both ion-exchange interaction and dissolution of silicate and evaporates. The oxidation of pyrite in coal,the geothermal water possessed fine hydrodynamic condition and the more intense ion-exchange interactions are more active than those in common groundwater. The formation of geothermal water was supplied by deep Ordovician limestone water and mixed with Taiyuan limestone water through the fracture. The mixing proportion of Ordovician limestone water was higher. The outcomes of this paper can provide guidance for mine water prevention and control.
In coal mining near the loose layer,the water-conducting fractured zone of overlying strata connected with the overlying aquifer can lead to the occurrence of roof water disaster. When other mining factors are similar,the roof overburden structure of different mining working faces can lead to the great difference in development height of water-conducting fractured zone. Therefore,17 measured data of the development height of water-conducting fractured zone in overlying strata during mining near the loose stratum in Huaibei coalfield were selected as prediction samples. The vectors of one row and two columns were selected to quantify the roof overburden structure of the mining panel near the loose layer. The five influencing factors include coal seam mining thickness,coal seam dip angle,panel length,mining depth and loose layer thickness as the input data. Combined with the five factors,the measured development height of water-conducting fractured zone was thought as the output data. Then,based on the neural network with radial basis function,a prediction model for the development height of water-conducting fractured zone during mining near the loose layer considering influence of overburden structure was established. The model was applied to the Qingdong coal mine in Huaibei coalfield. Through the verification of borehole flushing fluid leakage and borehole color TV observation,the relative error of the model prediction result is 3.3%,which is much lower than the error of 19.2% of the empirical formula calculation result in relative mining specification. This method provides theoretical support for the reasonable determination of the development height of water-conducting fractured zone during mining near loose layer. In coal mining near the loose layer,the water-conducting fractured zone of overlying strata connected with the overlying aquifer can lead to the occurrence of roof water disaster. When other mining factors are similar,the roof overburden structure of different mining working faces can lead to the great difference in development height of water-conducting fractured zone. Therefore,17 measured data of the development height of water-conducting fractured zone in overlying strata during mining near the loose stratum in Huaibei coalfield were selected as prediction samples. The vectors of one row and two columns were selected to quantify the roof overburden structure of the mining panel near the loose layer. The five influencing factors include coal seam mining thickness,coal seam dip angle,panel length,mining depth and loose layer thickness as the input data. Combined with the five factors,the measured development height of water-conducting fractured zone was thought as the output data. Then,based on the neural network with radial basis function,a prediction model for the development height of water-conducting fractured zone during mining near the loose layer considering influence of overburden structure was established. The model was applied to the Qingdong coal mine in Huaibei coalfield. Through the verification of borehole flushing fluid leakage and borehole color TV observation,the relative error of the model prediction result is 3.3%,which is much lower than the error of 19.2% of the empirical formula calculation result in relative mining specification. This method provides theoretical support for the reasonable determination of the development height of water-conducting fractured zone during mining near loose layer.
The disaster caused by water inrush from bed separation has a serious impact on the safety of coal mine production. It is important to clarify the research status of its water inrush mechanism and prevention and pre-control technology to promote the process of coal mine safety construction. This paper systematically summarizes and discusses the research progress in three aspects: dynamic development mechanism of water inrush mechanism from bed separation,the prediction and pre-control technology. With the advancing process of the working panel,the bed separation presents the characteristics of dynamic development. When the bed separation of a certain layer has one or more of the three power sources which include stable confined space,stable supply water source,sufficient duration of bed separation space and water inrush pathway,there is the possibility of water inrush disaster. We carry out the treatment of disaster caused by bed separation water from two folds of prevention and pre-control. The prevention measures include building the prediction model of bed separation development based on the theory of transferring beam structure,key strata and rock beam curvature,and changing the overlying strata movement by adjusting the mining speed,cutting height and using green mining technology. The pre-control measures include the layout of geological boreholes for drainage,borehole cutting off and so on. Finally,we point out the problems that need to be solved in the current research process. The water logging detection technology is not accurate enough. The advanced drainage technology system is not perfect. Then we look forward to the new research directions of optical fiber detection,joint pre-control of water pumping (water depressurization,water blocking),non-destructive mining and so on. The disaster caused by water inrush from bed separation has a serious impact on the safety of coal mine production. It is important to clarify the research status of its water inrush mechanism and prevention and pre-control technology to promote the process of coal mine safety construction. This paper systematically summarizes and discusses the research progress in three aspects: dynamic development mechanism of water inrush mechanism from bed separation,the prediction and pre-control technology. With the advancing process of the working panel,the bed separation presents the characteristics of dynamic development. When the bed separation of a certain layer has one or more of the three power sources which include stable confined space,stable supply water source,sufficient duration of bed separation space and water inrush pathway,there is the possibility of water inrush disaster. We carry out the treatment of disaster caused by bed separation water from two folds of prevention and pre-control. The prevention measures include building the prediction model of bed separation development based on the theory of transferring beam structure,key strata and rock beam curvature,and changing the overlying strata movement by adjusting the mining speed,cutting height and using green mining technology. The pre-control measures include the layout of geological boreholes for drainage,borehole cutting off and so on. Finally,we point out the problems that need to be solved in the current research process. The water logging detection technology is not accurate enough. The advanced drainage technology system is not perfect. Then we look forward to the new research directions of optical fiber detection,joint pre-control of water pumping (water depressurization,water blocking),non-destructive mining and so on.
With the shift of coal seam mining from deep to shallow,the water-bearing bodies of huge thick loose layers covering the coal seams have become a safety hazard that cannot be ignored in Huainan mine area. So the safety evaluation of reserved coal pillars is particularly important. This paper takes the Kouzidong mine as an example,presents the comprehensive and systematic collection and collation of geological and hydrogeological data revealed by long-term observation of mine water dynamics and underground mining works in Kouzidong mine in recent years. It uses the numerical simulation and theoretical analysis methods and obtained the following findings. (1)Based on the borehole column diagram of the classic block section in the mine area,a FLAC3D based mechanical model is established to simulate the workface retrieval by step. The displacement cloud diagram,maximum principal stress diagram and plastic damage diagram are observed and analyzed to recognize the mining overburden damage law. The height of the hydraulic fracture zone is about 56.6 m. The hydraulic fracture zone cannot be developed to the height of the aquifer. (2)According to the hydrogeological data of Kouzidong mine,a hydrogeological model based on GMS(Groundwater Modeling System) is established. The bending deformation of the overburden rock caused by mining lead to the changes in its vertical permeability coefficient and hydraulic gradient. The stress effect of mining on the model in FLAC3D is used as the basis. The stress magnitude is transformed into the vertical permeability coefficient of the bending zone as a variable reflected in the GMS model. The accuracy of the model is checked and the changes in the seepage field before and after mining is observed. It is found that the changes in the seepage field are very small,which also ensures the safety of leaving the coal pillars. (3)The control factors of water gushing sand is analyzed. The mine pumping test data is used. The iterative calculation program is developed using computer. The two critical hydraulic gradients(Jcr) are calculated as follows: Jcr for the fourth aquifer=1.66 and Jcr for the red layer=1.62. The critical head height of each point takes the value range of 10 to 25 m and is far less than the actual water level. These values are used as a basis for the evaluation of resistance to permeability damage. At present,when mining coal seams under water-bearing seams,the factors for setting up waterproof coal pillars mainly include mining height,seam inclination,roof lithology and its mechanical properties. The hydraulic properties of water-bearing seams and their changes after the change of seepage field are not taken into consideration. The above-mentioned properties of bedrock weathering layers are also not taken into consideration. This paper provides a scientific method and basis for evaluating the safety of coal pillars. With the shift of coal seam mining from deep to shallow,the water-bearing bodies of huge thick loose layers covering the coal seams have become a safety hazard that cannot be ignored in Huainan mine area. So the safety evaluation of reserved coal pillars is particularly important. This paper takes the Kouzidong mine as an example,presents the comprehensive and systematic collection and collation of geological and hydrogeological data revealed by long-term observation of mine water dynamics and underground mining works in Kouzidong mine in recent years. It uses the numerical simulation and theoretical analysis methods and obtained the following findings. (1)Based on the borehole column diagram of the classic block section in the mine area,a FLAC3D based mechanical model is established to simulate the workface retrieval by step. The displacement cloud diagram,maximum principal stress diagram and plastic damage diagram are observed and analyzed to recognize the mining overburden damage law. The height of the hydraulic fracture zone is about 56.6 m. The hydraulic fracture zone cannot be developed to the height of the aquifer. (2)According to the hydrogeological data of Kouzidong mine,a hydrogeological model based on GMS(Groundwater Modeling System) is established. The bending deformation of the overburden rock caused by mining lead to the changes in its vertical permeability coefficient and hydraulic gradient. The stress effect of mining on the model in FLAC3D is used as the basis. The stress magnitude is transformed into the vertical permeability coefficient of the bending zone as a variable reflected in the GMS model. The accuracy of the model is checked and the changes in the seepage field before and after mining is observed. It is found that the changes in the seepage field are very small,which also ensures the safety of leaving the coal pillars. (3)The control factors of water gushing sand is analyzed. The mine pumping test data is used. The iterative calculation program is developed using computer. The two critical hydraulic gradients(Jcr) are calculated as follows: Jcr for the fourth aquifer=1.66 and Jcr for the red layer=1.62. The critical head height of each point takes the value range of 10 to 25 m and is far less than the actual water level. These values are used as a basis for the evaluation of resistance to permeability damage. At present,when mining coal seams under water-bearing seams,the factors for setting up waterproof coal pillars mainly include mining height,seam inclination,roof lithology and its mechanical properties. The hydraulic properties of water-bearing seams and their changes after the change of seepage field are not taken into consideration. The above-mentioned properties of bedrock weathering layers are also not taken into consideration. This paper provides a scientific method and basis for evaluating the safety of coal pillars.
Based on the theory of the hydrogeochemistry,the hydrochemistry and environmental isotope basic eigenvalues of different aquifers overlying the coal seam in the Yushen mining areas were established. On this basis,the mine water sources of shallow buried mines,mid-deep buried mines,and deep buried mines were identified combined with the hydrogeological structures and heights of water conducting fracture zone of typical mines. Results showed that,the hydrochemical types and environmental isotope values of different aquifers overlying the coal seam were obviously different affected by the water-rock reactions and hydrodynamic condition. With the increase of the buried depth of coal seam,the salinity of mine water showed a significant increasing trend,while the δD and δ18 O of mine water showed a decreasing trend. And then the source of mine water for coal mines of different buried depth coal seam was identified by applying comprehensive hydrochemistry and stable isotope. It was considered that the mine water for shallow buried coal mines was a mixture of the groundwater for the Jurassic sandstone aquifer and the Quaternary loose aquifer. And the mine water for deep and mid-deep buried coal mines mainly came from the Jurassic sandstone aquifer. Based on the theory of the hydrogeochemistry,the hydrochemistry and environmental isotope basic eigenvalues of different aquifers overlying the coal seam in the Yushen mining areas were established. On this basis,the mine water sources of shallow buried mines,mid-deep buried mines,and deep buried mines were identified combined with the hydrogeological structures and heights of water conducting fracture zone of typical mines. Results showed that,the hydrochemical types and environmental isotope values of different aquifers overlying the coal seam were obviously different affected by the water-rock reactions and hydrodynamic condition. With the increase of the buried depth of coal seam,the salinity of mine water showed a significant increasing trend,while the δD and δ18 O of mine water showed a decreasing trend. And then the source of mine water for coal mines of different buried depth coal seam was identified by applying comprehensive hydrochemistry and stable isotope. It was considered that the mine water for shallow buried coal mines was a mixture of the groundwater for the Jurassic sandstone aquifer and the Quaternary loose aquifer. And the mine water for deep and mid-deep buried coal mines mainly came from the Jurassic sandstone aquifer.
Loose rock mass is a kind of common rock mass structure in mining,tunnel,underground space and other projects. It has the characteristics of low strength and poor stability. Grouting reconstruction is one of the important technologies to enhance its integrity and strength in site. To meet the special needs of the plugging project of the main ore pass with large-scale collapse under the condition of full rocks in Hebei provincial Xingshan Iron Mine,the concept of the controllable grouting of cement-sodium silicate slurry in the large loose rock mass is adopted. Based on the experimental study of cement-sodium silicate slurry grouting in the large volume loose rock mass,the grouting process was divided into the following five stages. They are vertical dominant seepage with macrovoid,circumjacent seepage with macrovoid,superior seepage stone,splitting and seepage of the first layer and splitting and seepage of the nth layer. According to the spatiotemporal propagation of slurry,the controllable grouting problem was divided into the one-dimensional vertical dominant seepage of cement-sodium silicate slurry and the circumferential spatiotemporal diffusion of single-stage grouting. and the mechanism of its occurrence was revealed that there is an exponential function with base e between the diffusion distance and the time of the one-dimensional vertical dominant seepage of cement-silicate slurry in the loose rock mass. On the basis of the above experimental results,the technology of the controllable grouting of cement-silicate slurry in the loose rock mass was applied to the plugging project of the main ore pass fully filled with large-scale collapsed rocks in the Xingshan Iron Mine,and good engineering performance were achieved. Loose rock mass is a kind of common rock mass structure in mining,tunnel,underground space and other projects. It has the characteristics of low strength and poor stability. Grouting reconstruction is one of the important technologies to enhance its integrity and strength in site. To meet the special needs of the plugging project of the main ore pass with large-scale collapse under the condition of full rocks in Hebei provincial Xingshan Iron Mine,the concept of the controllable grouting of cement-sodium silicate slurry in the large loose rock mass is adopted. Based on the experimental study of cement-sodium silicate slurry grouting in the large volume loose rock mass,the grouting process was divided into the following five stages. They are vertical dominant seepage with macrovoid,circumjacent seepage with macrovoid,superior seepage stone,splitting and seepage of the first layer and splitting and seepage of the nth layer. According to the spatiotemporal propagation of slurry,the controllable grouting problem was divided into the one-dimensional vertical dominant seepage of cement-sodium silicate slurry and the circumferential spatiotemporal diffusion of single-stage grouting. and the mechanism of its occurrence was revealed that there is an exponential function with base e between the diffusion distance and the time of the one-dimensional vertical dominant seepage of cement-silicate slurry in the loose rock mass. On the basis of the above experimental results,the technology of the controllable grouting of cement-silicate slurry in the loose rock mass was applied to the plugging project of the main ore pass fully filled with large-scale collapsed rocks in the Xingshan Iron Mine,and good engineering performance were achieved.
In recent years,many experts and scholars have carried out theoretical and experimental research on the mechanism of additional stress in shaft lining and the corresponding eliminating methods. On the basis of these researches,this paper proposes the strata settlement coordination method,analyzes the mechanism of the proposed method,carries out an experimental study on the change of additional stress in shaft lining in the soil layer,as well as analyzes the effectiveness of the proposed method while it is used in eliminating the additional stress. By setting different isolation coordination conditions,the proposed method acquires the stress variation of shaft lining and the settlement deformation of soil surface in the strata settlement process. In the experiment,there are sudden increases in the vertical strain of the shaft lining. The first group without isolation coordination body,the sudden increase values are obviously higher than the latter three groups. In addition,the settlement of the ground surface in the process of strata subsidence can be decreased using the method of stratum settlement deformation. The proposed method can decrease the sudden increase values and the steady values of shaft lining vertical strain effectively. In the meantime,the horizontal strain of cylinder can keep steady. Therefore,the proposed method can be developed to be a potentially effective approach for prevent and control lining failure of coal mine shaft. In recent years,many experts and scholars have carried out theoretical and experimental research on the mechanism of additional stress in shaft lining and the corresponding eliminating methods. On the basis of these researches,this paper proposes the strata settlement coordination method,analyzes the mechanism of the proposed method,carries out an experimental study on the change of additional stress in shaft lining in the soil layer,as well as analyzes the effectiveness of the proposed method while it is used in eliminating the additional stress. By setting different isolation coordination conditions,the proposed method acquires the stress variation of shaft lining and the settlement deformation of soil surface in the strata settlement process. In the experiment,there are sudden increases in the vertical strain of the shaft lining. The first group without isolation coordination body,the sudden increase values are obviously higher than the latter three groups. In addition,the settlement of the ground surface in the process of strata subsidence can be decreased using the method of stratum settlement deformation. The proposed method can decrease the sudden increase values and the steady values of shaft lining vertical strain effectively. In the meantime,the horizontal strain of cylinder can keep steady. Therefore,the proposed method can be developed to be a potentially effective approach for prevent and control lining failure of coal mine shaft.
This paper presents an approach of combining fractal geometry theory and UDEC discrete element numerical simulation method to study the fractal evolution law of mining-induced fracture of overburden rock. It can be applied to quantitatively evaluate development characteristics of mining fracture network in weakly consolidated overburden under the high-intensity mining in the western mining area. The research result indicates the following findings. The development and expansion of overlying rock fractures have good self-similarity under high-intensity mining conditions and the fractal dimension is between 0.461 and 1.488. The law of evolution can be divided into four stages including the dimensionality rapidly increasing stage,quickly reducing stage,stable stage,and periodically varying stage. In addition,the fractal dimension at each stage and the number of mining meet the logarithmic relationship,linear relationship and quadratic function relationship,respectively. With slice mining in huge coal stratum,the fitting curve of fractal dimension shows a high degree of similarity,has a certain periodicity,and shows a power function relationship. The research results provide scientific basis and technical reference for safe mining in western mining area and protection of water resources. This paper presents an approach of combining fractal geometry theory and UDEC discrete element numerical simulation method to study the fractal evolution law of mining-induced fracture of overburden rock. It can be applied to quantitatively evaluate development characteristics of mining fracture network in weakly consolidated overburden under the high-intensity mining in the western mining area. The research result indicates the following findings. The development and expansion of overlying rock fractures have good self-similarity under high-intensity mining conditions and the fractal dimension is between 0.461 and 1.488. The law of evolution can be divided into four stages including the dimensionality rapidly increasing stage,quickly reducing stage,stable stage,and periodically varying stage. In addition,the fractal dimension at each stage and the number of mining meet the logarithmic relationship,linear relationship and quadratic function relationship,respectively. With slice mining in huge coal stratum,the fitting curve of fractal dimension shows a high degree of similarity,has a certain periodicity,and shows a power function relationship. The research results provide scientific basis and technical reference for safe mining in western mining area and protection of water resources.
Based on PIV technology,the single-through fractured rock mass specimens were prefabricated by similar materials and compression-shear failure tests were carried out to explore the influence of fracture aperture on the strength,deformation and failure process. The results show that: (1)When the initial fracture occurs,the stress of the test group with different fracture apertures decreases obviously. The plastic deformation of the hinged part of the fractured rock mass increases with the increase of the aperture. The characteristic stress value of the rock mass specimen decreases; (2)The fracture aperture affects the proportion of the deformation of the fracture and the hinge part in the total deformation of the specimen,thereby affecting the axial peak strain and the lateral peak strain of the fractured specimen. The larger the fracture aperture is,the smaller the axial peak strain and the lateral peak strain of the fractured specimen are; (3)By PIV monitoring,it is found that the initial fracture position of the specimen transfers from the middle and lower parts to the middle and upper parts with the increase of aperture degree. The specimen gradually changes from tensile shear composite failure to single shear failure; (4)Through the analysis of displacement contour pictures,it is found that the surface of the specimen needs to reach the displacement threshold k to produce cracks,and the increase of the prefabricated crack aperture will reduce the displacement threshold k of the specimen. The results provide basis for the investigation of the mechanism of water and sand mixture inrush in deep mines. Based on PIV technology,the single-through fractured rock mass specimens were prefabricated by similar materials and compression-shear failure tests were carried out to explore the influence of fracture aperture on the strength,deformation and failure process. The results show that: (1)When the initial fracture occurs,the stress of the test group with different fracture apertures decreases obviously. The plastic deformation of the hinged part of the fractured rock mass increases with the increase of the aperture. The characteristic stress value of the rock mass specimen decreases; (2)The fracture aperture affects the proportion of the deformation of the fracture and the hinge part in the total deformation of the specimen,thereby affecting the axial peak strain and the lateral peak strain of the fractured specimen. The larger the fracture aperture is,the smaller the axial peak strain and the lateral peak strain of the fractured specimen are; (3)By PIV monitoring,it is found that the initial fracture position of the specimen transfers from the middle and lower parts to the middle and upper parts with the increase of aperture degree. The specimen gradually changes from tensile shear composite failure to single shear failure; (4)Through the analysis of displacement contour pictures,it is found that the surface of the specimen needs to reach the displacement threshold k to produce cracks,and the increase of the prefabricated crack aperture will reduce the displacement threshold k of the specimen. The results provide basis for the investigation of the mechanism of water and sand mixture inrush in deep mines.
The disturbance between workface mining and roadway extraction is the main key factor that inducing rockburst disasters in the coal mines. The deep area is disturbed by large roadway deformation besides rockburst. Aiming to solve this common technical challenge,this paper proposes the linear roof cutting technology. Based on the key strata theory,firstly we analyze the structure characteristics of the key strata of inclined coal seam and reveal that the spatial occurrence of the key block B is critical for rockburst and surrounding rock control. Then the optimal fracture line of key block B of the inclined coal seam is suggested. Using the COMSOL software we simulate the rules of stress distribution after blasting with different charge diameters. The results show that the stress peak exponentially attenuates,and the fracturing area is positively correlated with the charge diameter in a power function. The fitting formula for the fracture zone under different charge diameters is obtained. Take the tensile strength of the roof rock as the index value,the optimal distance corresponding to the charge diameter can be determined. We design different in-situ schemes based on the geological conditions. The field experiments verify that the linear roof cutting technology has a significant effect on rockburst prevention and roadway protection,comparing to the traditional deep hole roof blasting since the crack can be penetrated between two adjacent blasting holes. So,the most important parameter for roof cutting is the distance of blasting holes. Through the displacement observation and microseismic monitoring,it is shown that the linear roof cutting technology can effectively reduce the deformation of the surrounding rock of the gob-side roadway,and at the same time reduce the rockburst of the working face. Field practice has verified the theoretical and simulation results,and provides a valuable reference for similar engineering. The disturbance between workface mining and roadway extraction is the main key factor that inducing rockburst disasters in the coal mines. The deep area is disturbed by large roadway deformation besides rockburst. Aiming to solve this common technical challenge,this paper proposes the linear roof cutting technology. Based on the key strata theory,firstly we analyze the structure characteristics of the key strata of inclined coal seam and reveal that the spatial occurrence of the key block B is critical for rockburst and surrounding rock control. Then the optimal fracture line of key block B of the inclined coal seam is suggested. Using the COMSOL software we simulate the rules of stress distribution after blasting with different charge diameters. The results show that the stress peak exponentially attenuates,and the fracturing area is positively correlated with the charge diameter in a power function. The fitting formula for the fracture zone under different charge diameters is obtained. Take the tensile strength of the roof rock as the index value,the optimal distance corresponding to the charge diameter can be determined. We design different in-situ schemes based on the geological conditions. The field experiments verify that the linear roof cutting technology has a significant effect on rockburst prevention and roadway protection,comparing to the traditional deep hole roof blasting since the crack can be penetrated between two adjacent blasting holes. So,the most important parameter for roof cutting is the distance of blasting holes. Through the displacement observation and microseismic monitoring,it is shown that the linear roof cutting technology can effectively reduce the deformation of the surrounding rock of the gob-side roadway,and at the same time reduce the rockburst of the working face. Field practice has verified the theoretical and simulation results,and provides a valuable reference for similar engineering.
Coal geology is a subject that applies the theories and methods of geology and geochemistry to study the material composition,genesis,physical and chemical properties,spatial distribution of coal seam,coal measure,and its associated mineral resources. In the background of the ecological civilization and green development advocating by China and achievement carbon peak before 2030,the research focus of coal geology is changing gradually. Based on the statistical analysis of the articles published in the Journal of International Journal of Coal Geology from 2016 to 2020,the development process of Coal Geology in China is expressed in this paper. The current research hotspots of the Coal Geology is discussed,and the possible development direction of Coal Geology in the future is put forward. The results show that the most paper is published by Chinese scholars,accounting for 27.4%,followed by the United States and Australia. According to the first author's organization,the China University of Mining and Technology(Beijing),the University of Queensland,and the China University of Geosciences(Beijing) are the three institutions of highest numbers of papers. According to the research content,coal petrology and organic geochemistry have the largest number of papers,accounting for 31.3%.They are the research hotspots in the past five years. They are followed by minerals,trace elements,and geochemistry of coal and coal measure gas. It is predicted that there will be more and more researches on coal clean utilization in the future,and the cross subjects related to coal geology will also develop rapidly. Coal geology is a subject that applies the theories and methods of geology and geochemistry to study the material composition,genesis,physical and chemical properties,spatial distribution of coal seam,coal measure,and its associated mineral resources. In the background of the ecological civilization and green development advocating by China and achievement carbon peak before 2030,the research focus of coal geology is changing gradually. Based on the statistical analysis of the articles published in the Journal of International Journal of Coal Geology from 2016 to 2020,the development process of Coal Geology in China is expressed in this paper. The current research hotspots of the Coal Geology is discussed,and the possible development direction of Coal Geology in the future is put forward. The results show that the most paper is published by Chinese scholars,accounting for 27.4%,followed by the United States and Australia. According to the first author's organization,the China University of Mining and Technology(Beijing),the University of Queensland,and the China University of Geosciences(Beijing) are the three institutions of highest numbers of papers. According to the research content,coal petrology and organic geochemistry have the largest number of papers,accounting for 31.3%.They are the research hotspots in the past five years. They are followed by minerals,trace elements,and geochemistry of coal and coal measure gas. It is predicted that there will be more and more researches on coal clean utilization in the future,and the cross subjects related to coal geology will also develop rapidly.
The midpoint density of joint traces at outcrop is an important index for identifying the distribution characteristics of joint. However,the calculated results of midpoint density generally contain censoring,size and orientation biases,because of the factors including the limited size of outcrop or survey window,the difference in trace-length and the variation of the included angle between the outcrop and the joint. Therefore,we firstly present the conventional methods of correcting the censoring,size and orientation biases,and then propose a new method of correcting the above biases by importing the correction coefficient of orientation bias into the end-point estimator. We systematically test the proposed method by generating a 3D discrete joint network model and calculating the midpoint densities of joint traces from survey windows with different orientations,sizes and shapes. Finally,we use the proposed method to estimate the midpoint density of joint traces at a real outcrop,located at the entrance of the Beishan Exploration Tunnel(BET) in Gansu Province,China. The calculation example and the case study indicate that the proposed method is effective in correcting the censoring,size and orientation biases. The proposed method provides a reliable tool to estimate the density of joint randomly distributed in rock mass. The midpoint density of joint traces at outcrop is an important index for identifying the distribution characteristics of joint. However,the calculated results of midpoint density generally contain censoring,size and orientation biases,because of the factors including the limited size of outcrop or survey window,the difference in trace-length and the variation of the included angle between the outcrop and the joint. Therefore,we firstly present the conventional methods of correcting the censoring,size and orientation biases,and then propose a new method of correcting the above biases by importing the correction coefficient of orientation bias into the end-point estimator. We systematically test the proposed method by generating a 3D discrete joint network model and calculating the midpoint densities of joint traces from survey windows with different orientations,sizes and shapes. Finally,we use the proposed method to estimate the midpoint density of joint traces at a real outcrop,located at the entrance of the Beishan Exploration Tunnel(BET) in Gansu Province,China. The calculation example and the case study indicate that the proposed method is effective in correcting the censoring,size and orientation biases. The proposed method provides a reliable tool to estimate the density of joint randomly distributed in rock mass.
ynsedimentary fault is the most basic geological tectonic type of sedimentary basin. It controls the spatial distribution,geometric shape,internal sedimentation,and oil and gas reservoir distribution of the basin. According to advances of home and abroad,we summarize and discuss the research status of synsedimentary fault from the aspects of characteristics and classification,secondary structures,research methods,genesis,and evolution theory. We believe that the fine detection,quantitative evaluation,and high-precision simulation of synsedimentary fault are the key points of future research. Based on the development characteristics of some structural ground fissures and the characteristics of synsedimentary faults,we propose the concept of synsedimentary ground fissures. Taking Xi'an ground fissures as an example,we expound the characteristics of the synsedimentary ground fissure,and point out that the research on the development mode,formation mechanism,fracture propagation effect and influence zone width of the ground fissure is the direction of the tectonic ground fissure research in the future. ynsedimentary fault is the most basic geological tectonic type of sedimentary basin. It controls the spatial distribution,geometric shape,internal sedimentation,and oil and gas reservoir distribution of the basin. According to advances of home and abroad,we summarize and discuss the research status of synsedimentary fault from the aspects of characteristics and classification,secondary structures,research methods,genesis,and evolution theory. We believe that the fine detection,quantitative evaluation,and high-precision simulation of synsedimentary fault are the key points of future research. Based on the development characteristics of some structural ground fissures and the characteristics of synsedimentary faults,we propose the concept of synsedimentary ground fissures. Taking Xi'an ground fissures as an example,we expound the characteristics of the synsedimentary ground fissure,and point out that the research on the development mode,formation mechanism,fracture propagation effect and influence zone width of the ground fissure is the direction of the tectonic ground fissure research in the future.
In the evening of February 7,2018,a deadly ground collapse of a metro tunnel under construction occurred in Foshan,Guangdong Province,China. The accident caused 11 deaths,8 injuries,1 missing person,and direct economic loss of more than 53 million yuan. In order to understand the mechanism of this collapse,it is necessary to examine the deformation characteristics of the ground before and after the event. Compared with the ground-based observation techniques,the synthetic aperture radar (SAR) interferometry technique has demonstrated its potential for monitoring the collapse sinkholes due to the advantages of covering large areas,mapping of high-density spatial and historical ground deformation. Therefore,using the 56 Sentinel-1A spanning from 2017-03 to 2019-01,we obtain the spatial-temporal deformation information of the study area by using Small Baseline Subset SAR Interferometry(SBAS-InSAR) techniques. It is found that continuous ground subsidence occurred in the collapse area and its adjacent areas,and the deformation rate reached more than 30·a-1,while areas far away from the sinkhole was mostly stable. In order to further verify the reliability of the deformation and analyze the connection between the land subsidence and the collapse,we carry out a field survey and a detailed analysis of the deformation characteristics near the collapse area,and find uneven ground subsidence in the sinkhole and its adjacent areas. The maximum subsidence at the collapse site was nearly 37 mm over the past year of collapse accident. What's more,accelerated subsidence appeared one month before the collapse accident,which was related to the metro construction disturbance. Meanwhile,based on the local geological data and accident investigation report,it is considered that the collapse accident was caused by the water supply pipeline damage and the poor engineering geological environment at the accident site. In the end,we reasonably deduce the mechanism of collapse formation: due to the uneven settlement of the mucky soil under the water supply pipeline,the distribution of bearing capacity of mucky soil to the water supply pipeline was also uneven. The water leakage in the pipeline saturated the stratum,weakened the mechanical properties of the mucky soil layer,and the Metro construction disturbance increased the deformation of the saturated soil layer and pipeline leakage,and the water penetrated down to the fine sand layer below the shield machine tail. With the increase of water content,the bearing capacity of the fine sand layer was reduced,which led to the subsidence of the shield machine tail and the cracks in the pipe segments that had not reached the freezing point,and the shield machine tail was permeable with water and sand. But the builders failed to plug the leak,and the flooding became more severe. The sand layer under the shield machine quickly drained away,resulting in the downward displacement and deformation of the shield machine. After the tunnel structure was damaged,a huge amount of sediment suddenly poured into the tunnel,and caused a rapid impact of air waves in the limited space of the tunnel,which eventually led to the tunnel and the ground collapse. The results can provide theoretical basis for the collapse monitoring and early warning of shield tunneling in the future. In the evening of February 7,2018,a deadly ground collapse of a metro tunnel under construction occurred in Foshan,Guangdong Province,China. The accident caused 11 deaths,8 injuries,1 missing person,and direct economic loss of more than 53 million yuan. In order to understand the mechanism of this collapse,it is necessary to examine the deformation characteristics of the ground before and after the event. Compared with the ground-based observation techniques,the synthetic aperture radar (SAR) interferometry technique has demonstrated its potential for monitoring the collapse sinkholes due to the advantages of covering large areas,mapping of high-density spatial and historical ground deformation. Therefore,using the 56 Sentinel-1A spanning from 2017-03 to 2019-01,we obtain the spatial-temporal deformation information of the study area by using Small Baseline Subset SAR Interferometry(SBAS-InSAR) techniques. It is found that continuous ground subsidence occurred in the collapse area and its adjacent areas,and the deformation rate reached more than 30·a-1,while areas far away from the sinkhole was mostly stable. In order to further verify the reliability of the deformation and analyze the connection between the land subsidence and the collapse,we carry out a field survey and a detailed analysis of the deformation characteristics near the collapse area,and find uneven ground subsidence in the sinkhole and its adjacent areas. The maximum subsidence at the collapse site was nearly 37 mm over the past year of collapse accident. What's more,accelerated subsidence appeared one month before the collapse accident,which was related to the metro construction disturbance. Meanwhile,based on the local geological data and accident investigation report,it is considered that the collapse accident was caused by the water supply pipeline damage and the poor engineering geological environment at the accident site. In the end,we reasonably deduce the mechanism of collapse formation: due to the uneven settlement of the mucky soil under the water supply pipeline,the distribution of bearing capacity of mucky soil to the water supply pipeline was also uneven. The water leakage in the pipeline saturated the stratum,weakened the mechanical properties of the mucky soil layer,and the Metro construction disturbance increased the deformation of the saturated soil layer and pipeline leakage,and the water penetrated down to the fine sand layer below the shield machine tail. With the increase of water content,the bearing capacity of the fine sand layer was reduced,which led to the subsidence of the shield machine tail and the cracks in the pipe segments that had not reached the freezing point,and the shield machine tail was permeable with water and sand. But the builders failed to plug the leak,and the flooding became more severe. The sand layer under the shield machine quickly drained away,resulting in the downward displacement and deformation of the shield machine. After the tunnel structure was damaged,a huge amount of sediment suddenly poured into the tunnel,and caused a rapid impact of air waves in the limited space of the tunnel,which eventually led to the tunnel and the ground collapse. The results can provide theoretical basis for the collapse monitoring and early warning of shield tunneling in the future.
The loess joints with various variety and angles are important factors affecting the mechanical properties of loess. To investigate the influences of loess joints on mechanical properties of loess,uniaxial and triaxial compressive strength tests of loess samples with joints were carried out. The influence of joints angle on shear failure modes,strength and deformation characteristics of loess were analyzed. The result shows that the shear failure modes of the joint specimens can be divided into two types: intersecting of shear failure plane and joint,and paralleling of shear failure plane to joint. Under pressure,wing cracks and secondary cracks initiate continuously at joints tip,which are easy to expand into shear fracture planes. The anti-deformation of the specimen is weaken by joints. The stress-strain curves of the specimen under uniaxial compression present strain softening phenomenon. The deformation modulus at the yield stage and the shear failure displacement of specimens are reduced by joints,which accelerates the shear failure process of the specimen. The shear strength of loess is reduced significantly by joints. The peak strength and residual strength first decrease and then increase with the joints angle,but the variation range decreases with the increasing confining pressure. The cohesion of specimen changes with joints angle more sensitively. The shear strength of specimen is the lowest when the joint angle is 60°. When the joints angle is closer to the shear failure angle of the loess specimen,the joints are easier to expand into the shear failure planes,the anti-deformation of the specimen becomes worsen,the deterioration of the strength becomes more obvious,and the shear failure of the specimen occurs easier. The research results provide a reference for revealing the mechanism of deterioration of loess joints on promoting loess slope sliding. The loess joints with various variety and angles are important factors affecting the mechanical properties of loess. To investigate the influences of loess joints on mechanical properties of loess,uniaxial and triaxial compressive strength tests of loess samples with joints were carried out. The influence of joints angle on shear failure modes,strength and deformation characteristics of loess were analyzed. The result shows that the shear failure modes of the joint specimens can be divided into two types: intersecting of shear failure plane and joint,and paralleling of shear failure plane to joint. Under pressure,wing cracks and secondary cracks initiate continuously at joints tip,which are easy to expand into shear fracture planes. The anti-deformation of the specimen is weaken by joints. The stress-strain curves of the specimen under uniaxial compression present strain softening phenomenon. The deformation modulus at the yield stage and the shear failure displacement of specimens are reduced by joints,which accelerates the shear failure process of the specimen. The shear strength of loess is reduced significantly by joints. The peak strength and residual strength first decrease and then increase with the joints angle,but the variation range decreases with the increasing confining pressure. The cohesion of specimen changes with joints angle more sensitively. The shear strength of specimen is the lowest when the joint angle is 60°. When the joints angle is closer to the shear failure angle of the loess specimen,the joints are easier to expand into the shear failure planes,the anti-deformation of the specimen becomes worsen,the deterioration of the strength becomes more obvious,and the shear failure of the specimen occurs easier. The research results provide a reference for revealing the mechanism of deterioration of loess joints on promoting loess slope sliding.
The climate of the Mogao Grottoes is dry,so the earthen plaster of murals in the caves are in the state of low moisture content and high suction. This state of soil is greatly affected by the humidity in the cave environment. To further understand the characteristics of suction variation and the property of adsorbed moisture in earthen plaster under the influence of relative humidity in cave environment,we tested the soil-water characteristic curves at high suction range of different kinds of earthen plasters in Mogao Grottoes through vapor adsorption process,then calculated and analyzed the variation characteristics of different types of suction caused by Vander Waals force and capillary condensation respectively according to the test results. Meanwhile,we also tested the soil-water characteristic curves of plaster samples with different contents of NaCl and discuss the osmotic suction during moisture adsorption process. In addition,we utilized thermogravimetric to test and analyze the features of the moisture which adsorbed by earthen plaster under the action of Vander Waals force and capillary condensation. The results show the follows. Most matric suction in earthen plaster still comes from capillary condensation during the moisture adsorption process. The van der Waals forces between soil particles can provide obvious suction only in the case of very low moisture content. Significant osmotic suction can be present during the moisture adsorption process of earthen plaster only when environmental humidity is greater than the deliquescence relative humidity of the soluble salt in earthen plaster. Most moisture adsorbed by plaster is in the form of loose bound water. The critical moisture content of loose bound water increases with the Dengban soil content in earthen plaster. These findings can offer data and theoretical basis for the research of mechanism of mural damage with the participation of moisture and the water vapor transport in plaster. The climate of the Mogao Grottoes is dry,so the earthen plaster of murals in the caves are in the state of low moisture content and high suction. This state of soil is greatly affected by the humidity in the cave environment. To further understand the characteristics of suction variation and the property of adsorbed moisture in earthen plaster under the influence of relative humidity in cave environment,we tested the soil-water characteristic curves at high suction range of different kinds of earthen plasters in Mogao Grottoes through vapor adsorption process,then calculated and analyzed the variation characteristics of different types of suction caused by Vander Waals force and capillary condensation respectively according to the test results. Meanwhile,we also tested the soil-water characteristic curves of plaster samples with different contents of NaCl and discuss the osmotic suction during moisture adsorption process. In addition,we utilized thermogravimetric to test and analyze the features of the moisture which adsorbed by earthen plaster under the action of Vander Waals force and capillary condensation. The results show the follows. Most matric suction in earthen plaster still comes from capillary condensation during the moisture adsorption process. The van der Waals forces between soil particles can provide obvious suction only in the case of very low moisture content. Significant osmotic suction can be present during the moisture adsorption process of earthen plaster only when environmental humidity is greater than the deliquescence relative humidity of the soluble salt in earthen plaster. Most moisture adsorbed by plaster is in the form of loose bound water. The critical moisture content of loose bound water increases with the Dengban soil content in earthen plaster. These findings can offer data and theoretical basis for the research of mechanism of mural damage with the participation of moisture and the water vapor transport in plaster.
Loess is a porous,weakly cemented loose sediments with typical open structure. The mechanical characteristics of loess are typically the macro reflection of its deformation and failure in microstructure. To reveal the mechanical behavior of loess,it is necessary to start from the microstructure of loess since the material composition and microstructure characteristics are controlled by its special aeolian genesis. Based on this,a method to simulate the process of loess deposition and construct its initial structure model is proposed. In order to generate the microstructure model formed by the loess deposition process and simulate the deformation,firstly,the particle group of loess before deposition is generated by Monte Carlo method on the basis of determining the morphology of loess particles. Then the discontinuous deformation analysis method(DDA) is adopted to establish the structure model of loess and to simulate the falling process of loess particles considering the collision force and friction force between particles. From the model,three pore types and four major contact structures can be identified. The consolidation test of the loess initial structure model under different pressures is carried out. The radial distribution function is obtained by selecting particles from different parts. It microscopically illustrates that the macropores and open structures of the loess can be destroyed first during the compression process. The numerical results are compared with the results of physical model test under the same conditions. The results show that the trend of the e-lgp compression curve of the numerical simulation and the physical model test is about the same,indicating that the proposed method is feasible. This method provides a basis for further microscopic analysis of loess mechanical behavior. Loess is a porous,weakly cemented loose sediments with typical open structure. The mechanical characteristics of loess are typically the macro reflection of its deformation and failure in microstructure. To reveal the mechanical behavior of loess,it is necessary to start from the microstructure of loess since the material composition and microstructure characteristics are controlled by its special aeolian genesis. Based on this,a method to simulate the process of loess deposition and construct its initial structure model is proposed. In order to generate the microstructure model formed by the loess deposition process and simulate the deformation,firstly,the particle group of loess before deposition is generated by Monte Carlo method on the basis of determining the morphology of loess particles. Then the discontinuous deformation analysis method(DDA) is adopted to establish the structure model of loess and to simulate the falling process of loess particles considering the collision force and friction force between particles. From the model,three pore types and four major contact structures can be identified. The consolidation test of the loess initial structure model under different pressures is carried out. The radial distribution function is obtained by selecting particles from different parts. It microscopically illustrates that the macropores and open structures of the loess can be destroyed first during the compression process. The numerical results are compared with the results of physical model test under the same conditions. The results show that the trend of the e-lgp compression curve of the numerical simulation and the physical model test is about the same,indicating that the proposed method is feasible. This method provides a basis for further microscopic analysis of loess mechanical behavior.
Ningde City is located in the north of Fujian Province. Its soft clay has typical sedimentary characteristics of Quaternary soft clay in Northeast Fujian,and its unique sedimentary environment makes it different from the traditional Zhejiang-Fujian coastal soft clay in physical and mechanical properties. Based on the geological survey,including in-situ and laboratory geotechnical tests surrounding Sanduao,the sedimentary characteristics,physical and mechanical properties of the soft clay in Ningde are systematically investigated. It is found that the clay has the characteristics of high compressibility,high liquid limit and high sensitivity,and is vulnerable to be disturbed. Attention should be paid to the loss of strength in engineering construction and evolution of infrastructure disaster. The abundant diatom with flourishing pores and strong hydrophilicity is the reason of the high specific surface area and its structural characteristics. These two remarkable features distinguish Ningde soft soil from other traditional soft clays. Ningde City is located in the north of Fujian Province. Its soft clay has typical sedimentary characteristics of Quaternary soft clay in Northeast Fujian,and its unique sedimentary environment makes it different from the traditional Zhejiang-Fujian coastal soft clay in physical and mechanical properties. Based on the geological survey,including in-situ and laboratory geotechnical tests surrounding Sanduao,the sedimentary characteristics,physical and mechanical properties of the soft clay in Ningde are systematically investigated. It is found that the clay has the characteristics of high compressibility,high liquid limit and high sensitivity,and is vulnerable to be disturbed. Attention should be paid to the loss of strength in engineering construction and evolution of infrastructure disaster. The abundant diatom with flourishing pores and strong hydrophilicity is the reason of the high specific surface area and its structural characteristics. These two remarkable features distinguish Ningde soft soil from other traditional soft clays.
In Qinghai,the loess is widely distributed and coal reserves are rich. Rapid consumption of coal resources leads to increased production of fly ash. Therefore,many scholars have studied fly ash as a cementitious material and added it to cement soil. The shear strength of fly ash cement soil is poor. At the same time,due to the problems of loess collapsibility,the strength of fly ash cement soil can rapidly decrease. This paper aims at the influence of different curing ages on the shear strength of fly ash cement soil. It carries out unconsolidated and undrained triaxial shear tests to analyze the effect of curing age on fly ash cement soil from the perspective of macro mechanics. It combines with SEM test and XRD test to analyze the internal structure and material composition of the specimen from a microscopic perspective. Experimental results show that: from a macro perspective,the overall stress-strain curve of fly ash cement soil shows strain softening. The shear strength of the sample gradually increases with the increase of curing age and the shear strength is the largest at the 28 days. Simultaneously,due to the increase of the curing age,the mutual chemical reactions between the substances in the sample can continue. The longer the curing age of the sample,the stronger the cementation between the substances inside the sample,which can cause the internal friction angle and cohesive force of the sample to gradually increase. From a micro perspective,with the extension of curing time,the crystalline material (Ettringite) and gelling material (C-S-H gel) generated inside the sample can fill the large pores inside the sample. These materials can adhere to each other,and cause the sample to become denser and the shear strength increases. This paper provides a test basis for the shear strength of solidified loess with fly ash and other materials,offers reference for the application of industrial by-products such as fly ash in engineering,and has reference significance for the utilization of fly ash and environmental protection. In Qinghai,the loess is widely distributed and coal reserves are rich. Rapid consumption of coal resources leads to increased production of fly ash. Therefore,many scholars have studied fly ash as a cementitious material and added it to cement soil. The shear strength of fly ash cement soil is poor. At the same time,due to the problems of loess collapsibility,the strength of fly ash cement soil can rapidly decrease. This paper aims at the influence of different curing ages on the shear strength of fly ash cement soil. It carries out unconsolidated and undrained triaxial shear tests to analyze the effect of curing age on fly ash cement soil from the perspective of macro mechanics. It combines with SEM test and XRD test to analyze the internal structure and material composition of the specimen from a microscopic perspective. Experimental results show that: from a macro perspective,the overall stress-strain curve of fly ash cement soil shows strain softening. The shear strength of the sample gradually increases with the increase of curing age and the shear strength is the largest at the 28 days. Simultaneously,due to the increase of the curing age,the mutual chemical reactions between the substances in the sample can continue. The longer the curing age of the sample,the stronger the cementation between the substances inside the sample,which can cause the internal friction angle and cohesive force of the sample to gradually increase. From a micro perspective,with the extension of curing time,the crystalline material (Ettringite) and gelling material (C-S-H gel) generated inside the sample can fill the large pores inside the sample. These materials can adhere to each other,and cause the sample to become denser and the shear strength increases. This paper provides a test basis for the shear strength of solidified loess with fly ash and other materials,offers reference for the application of industrial by-products such as fly ash in engineering,and has reference significance for the utilization of fly ash and environmental protection.
Contamination of heavy metal always leads to the change of engineering characteristics of soil. In order to discuss the influence of Cu(Ⅱ) on the expansion and shrinkage characteristics of expansive clay,we used CuSO4 solution with concentration of 2.5 g·L-1,5.0 g·L-1,10 g·L-1 and deionized water to soak samples made of expansive clay. Then,we conducted series of expansion and shrinkage experiments to investigated expansion and shrinkage characteristics. We tried to use Does Response model to fit the deformation process of expansion and shrinkage. Through experiment of Malvern laser particle size,we analyzed the particle size distribution of expansive clay before and after contamination. The results show that rapid growth,variable deceleration and slow growth stages constitute the non-load expansion deformation process,and slow shrinkage,rapid shrinkage and stable stages constitute the shrinkage process. The deformation process of expansion can be described in sections by Does Response model and power function,while the process of shrinkage can be just described by Does Response model. The expansive rate,water absorption quality,shrinking rate and vertical shrinkage rate of expansive clay increase with the increase of Cu(Ⅱ) concentration. However,the loss water content of expansive clay does not change with the increase of concentration. With the increase of Cu(Ⅱ) concentration,peak value of particle size distribution at 80 μm disappeared,and the peak value at 47 μm change into a value representing smaller particle size. It is proof that the cement dissolves gradually,which causing the decomposition of some large particles of expansive clay. Thus,specific surface area of expansive clay increases and the area of water film attached to the surface of clay particles also increase. As a result,water-absorbent capacity enhances. This brings about higher expansion and shrinkage of expansive clay in high concentration environment. Contamination of heavy metal always leads to the change of engineering characteristics of soil. In order to discuss the influence of Cu(Ⅱ) on the expansion and shrinkage characteristics of expansive clay,we used CuSO4 solution with concentration of 2.5 g·L-1,5.0 g·L-1,10 g·L-1 and deionized water to soak samples made of expansive clay. Then,we conducted series of expansion and shrinkage experiments to investigated expansion and shrinkage characteristics. We tried to use Does Response model to fit the deformation process of expansion and shrinkage. Through experiment of Malvern laser particle size,we analyzed the particle size distribution of expansive clay before and after contamination. The results show that rapid growth,variable deceleration and slow growth stages constitute the non-load expansion deformation process,and slow shrinkage,rapid shrinkage and stable stages constitute the shrinkage process. The deformation process of expansion can be described in sections by Does Response model and power function,while the process of shrinkage can be just described by Does Response model. The expansive rate,water absorption quality,shrinking rate and vertical shrinkage rate of expansive clay increase with the increase of Cu(Ⅱ) concentration. However,the loss water content of expansive clay does not change with the increase of concentration. With the increase of Cu(Ⅱ) concentration,peak value of particle size distribution at 80 μm disappeared,and the peak value at 47 μm change into a value representing smaller particle size. It is proof that the cement dissolves gradually,which causing the decomposition of some large particles of expansive clay. Thus,specific surface area of expansive clay increases and the area of water film attached to the surface of clay particles also increase. As a result,water-absorbent capacity enhances. This brings about higher expansion and shrinkage of expansive clay in high concentration environment.
In order to explore the improvement effect of nano-SiO2 and lime on silt in the Yellow River flood area,a series of tests including compaction test,unconfined compressive strength test,scanning electron microscope test and XRF test were conducted. This paper aims to study the effects of nano-SiO2 and lime content on the compaction characteristics,compressive strength,water stability of silt. The microstructure and improved mechanism of the stabilized silt were analyzed. The results show that the maximum dry density and the optimum water content of the stabilized silt increase with the addition of nano-SiO2 content. The addition of lime in the nano-SiO2 stabilized silt reduces the maximum dry density,but increases the optimal water content. The combined improvement effect of nano-SiO2 and lime is better than that of nano-SiO2 alone. The unconfined compressive strength,cohesion and angle of internal friction increase most significantly. Compared with pure soil and nano-SiO2 stabilized silt,the water stability of nano-SiO2-lime stabilized silt is significantly improved. In the nano-SiO2 stabilized silt,the nano-SiO2 mainly serves to fill the pores between the soil particles. The combined application of nano-SiO2 and lime can form cementing material in the silt,play a role of bonding and filling,and greatly improve the strength of the silt. In order to explore the improvement effect of nano-SiO2 and lime on silt in the Yellow River flood area,a series of tests including compaction test,unconfined compressive strength test,scanning electron microscope test and XRF test were conducted. This paper aims to study the effects of nano-SiO2 and lime content on the compaction characteristics,compressive strength,water stability of silt. The microstructure and improved mechanism of the stabilized silt were analyzed. The results show that the maximum dry density and the optimum water content of the stabilized silt increase with the addition of nano-SiO2 content. The addition of lime in the nano-SiO2 stabilized silt reduces the maximum dry density,but increases the optimal water content. The combined improvement effect of nano-SiO2 and lime is better than that of nano-SiO2 alone. The unconfined compressive strength,cohesion and angle of internal friction increase most significantly. Compared with pure soil and nano-SiO2 stabilized silt,the water stability of nano-SiO2-lime stabilized silt is significantly improved. In the nano-SiO2 stabilized silt,the nano-SiO2 mainly serves to fill the pores between the soil particles. The combined application of nano-SiO2 and lime can form cementing material in the silt,play a role of bonding and filling,and greatly improve the strength of the silt.
Widely distributed in the coastal areas of the Beibu Gulf,the structural clay of the Zhanjiang Group poses significant challenges to engineering practice due to its high thixotropy. To reveal the way that the factors of water content,void ratio and sensitivity can affect thixotropy,we conducted a series of tests examining how these physico-mechanical properties of the clay along with its thixotropy changed over time after disturbing the clay samples and putting them to stand. Test results show that: (1)higher water content leads to greater thixotropic strength growth by the end of the standing period,with the thixotropic strength growth rate being high in the early stage of standing and low in the late stage; (2)void ratio presents insignificant correlation with thixotropic strength growth during the early standing stage while,during the late stage,a higher void ratio is associated with considerably smaller growth in thixotropic strength as well as a lower growth rate; and (3)higher sensitivity leads to greater thixotropic strength. Widely distributed in the coastal areas of the Beibu Gulf,the structural clay of the Zhanjiang Group poses significant challenges to engineering practice due to its high thixotropy. To reveal the way that the factors of water content,void ratio and sensitivity can affect thixotropy,we conducted a series of tests examining how these physico-mechanical properties of the clay along with its thixotropy changed over time after disturbing the clay samples and putting them to stand. Test results show that: (1)higher water content leads to greater thixotropic strength growth by the end of the standing period,with the thixotropic strength growth rate being high in the early stage of standing and low in the late stage; (2)void ratio presents insignificant correlation with thixotropic strength growth during the early standing stage while,during the late stage,a higher void ratio is associated with considerably smaller growth in thixotropic strength as well as a lower growth rate; and (3)higher sensitivity leads to greater thixotropic strength.