This study proposes an alternative calculation mode for stresses on the slip surface(SS).The calculation of the normal stress(NS)on the SS involves examining its composition and expanding its unknown using the Taylor ...This study proposes an alternative calculation mode for stresses on the slip surface(SS).The calculation of the normal stress(NS)on the SS involves examining its composition and expanding its unknown using the Taylor series.This expansion enables the reasonable construction of a function describing the NS on the SS.Additionally,by directly incorporating the nonlinear Generalized Hoke-Brown(GHB)strength criterion and utilizing the slope factor of safety(FOS)definition,a function of the shear stress on the SS is derived.This function considers the mutual feedback mechanism between the NS and strength parameters of the SS.The stress constraints conditions are then introduced at both ends of the SS based on the spatial stress relation of one point.Determining the slope FOS and stress solution for the SS involves considering the mechanical equilibrium conditions and the stress constraint conditions satisfied by the sliding body.The proposed approach successfully simulates the tension-shear stress zone near the slope top and provides an intuitive description of the concentration effect of compression-shear stress of the SS near the slope toe.Furthermore,compared to other methods,the present method demonstrates superior processing capabilities for the embedded nonlinear GHB strength criterion.展开更多
Based on strength reduction theory,the stability numbers of shallow tunnels were investigated within the framework of upper and lower bound theorems of limit analysis. Stability solutions taking into account of water ...Based on strength reduction theory,the stability numbers of shallow tunnels were investigated within the framework of upper and lower bound theorems of limit analysis. Stability solutions taking into account of water seepage were presented and compared with those without considering seepage. The comparisons indicate that the maximum difference does not exceed 3.7%,which proves the present method credible. The results show that stability numbers of shallow tunnels considering seepage are much less than those without considering seepage,and that the difference of stability numbers between considering seepage and without considering seepage increase with increasing the depth ratio. The stability numbers decrease with increasing permeability coefficient and groundwater depth. Seepage has significant effects on the stability numbers of shallow tunnels.展开更多
Considering the rheological properties of rock and soil body,and exploiting the merit of strength reduction technique,a theory of couple analysis is brought forward on the basis of strength reduction theory and rheolo...Considering the rheological properties of rock and soil body,and exploiting the merit of strength reduction technique,a theory of couple analysis is brought forward on the basis of strength reduction theory and rheological properties.Then,the concept and the calculation procedure of the safety factor are established at different time.Making use of finite element software ANSYS,the most dangerous sliding surface of the slope can be obtained through the strength reduction technique.According to the dynamic safety factor based on rheological mechanism,a good forecasting could be presented to prevent and cure the landslide.The result shows that the couple analysis reveals the process of the slope failure with the time and the important influence on the long-term stability due to the rheological parameters.展开更多
Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only sui...Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb(EMC)strength parameters instead of the nonlinear HB strength criterion.Therefore,a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework.The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stressσ0 obtained without considering the effect of inter-slice forces,and it can satisfy all static equilibrium conditions of the sliding body,so the current method can obtain the reasonable and strict factor of safety(FOS)solutions.Compared with the results of other methods in some examples,the feasibility of the current method was verified.Meanwhile,the parametric analysis shows that the slope angleβhas an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters.Forβ≤45°,both of the results are similar,showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability,but forβ>60°,the differences of both the results are obvious,showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods,and then the current method should be used.展开更多
Based on the upper bound limit analysis theorem and the shear strength reduction technique, the equation for expressing critical limit-equilibrium state was employed to define the safety factor of a given slope and it...Based on the upper bound limit analysis theorem and the shear strength reduction technique, the equation for expressing critical limit-equilibrium state was employed to define the safety factor of a given slope and its corresponding critical failure mechanism by means of the kinematical approach of limit analysis theory. The nonlinear shear strength parameters were treated as variable parameters and a kinematically admissible failure mechanism was considered for calculation schemes. The iterative optimization method was adopted to obtain the safety factors. Case study and comparative analysis show that solutions presented here agree with available predictions when nonlinear criterion reduces to linear criterion, and the validity of present method could be illuminated. From the numerical results, it can also be seen that nonlinear parameter rn, slope foot gradient ,β, height of slope H, slope top gradient a and soil bulk density γ have significant effects on the safety factor of the slope.展开更多
For geotechnical stability analysis involving the Drucker-Prager(DP)criterion,both the c-ϕreduction scheme and the M-K reduction scheme can be utilized.With the aid of the second-order cone programming optimized finit...For geotechnical stability analysis involving the Drucker-Prager(DP)criterion,both the c-ϕreduction scheme and the M-K reduction scheme can be utilized.With the aid of the second-order cone programming optimized finite element method(FEM-SOCP),a comparison of the two strength reduction schemes for the stability analysis of a homogeneous slope and a multilayered slope is carried out.Numerical investigations disclose that the FoS results calculated by the c-ϕreduction scheme agree well with those calculated by the classical Morgenstern-Price solutions.However,the FoS results attained by the M-K reduction scheme may lead to conservative estimation of the geotechnical safety,particularly for the cases with large internal friction angles.In view of the possible big difference in stability analysis results caused by the M-K reduction scheme,the c-ϕreduction scheme is recommended for the geotechnical stability analyses involving the DP criterion.展开更多
Most of the natural and compacted fine-grained soil slopes that are in saturated or unsaturated condition undergo a large deformation prior to reaching failure conditions.Such slopes should be designed taking account ...Most of the natural and compacted fine-grained soil slopes that are in saturated or unsaturated condition undergo a large deformation prior to reaching failure conditions.Such slopes should be designed taking account of their strain-softening behavior using the residual shear strength (RSS) parameters.In this paper,the slope stability of a recently reactivated Outang landslide near the Three Gorges Dam in China is analyzed based on the RSS parameters of unsaturated soils.In addition,comparisons are provided in the FOS values of slope using both the peak shear strength (PSS) and RSS parameters.Firstly,a series of site investigations of the hydrologic and geologic conditions,ground surface displacements and cracks were described.The PSS and RSS behaviors of the sliding soils derived from a series of direct shear test results performed on saturated and unsaturated soil specimens are summarized.Secondly,a series of slope stability analysis were conducted considering the precipitation and Yangtze River water level variation within a representative period of 7 months,based on the PSS and the RSS properties.In this study,three different scenarios were considered,which include: i) considering only the precipitation with a constant water level;ii) considering only the decrease in water level without rainfall;iii) considering the combination of precipitation and decrease in water level.In each scenario,four steps were included to calculate the values of factor of safety (FOS) at different times.1) A steady-state seepage analysis was conducted with a constant total head at 525 m on the left boundary and 175 m on the slope surface below the Yangtze River water level.The initial pore water pressures were simulated in the slope under no precipitation and variation of water level.2) A specific boundary condition was applied on the slope surface to model the precipitation and Yangtze River water level variation.A transient seepage analysis was conducted to calculate pore water pressures at different times based on the initial pore water pressures.3) The FOS values at different times were calculated by the Morgenstern-Price method taking account of the variation of pore water pressures at different times,using the peak shear strength (PSS) parameters.4) The last step was repeated replacing PSS parameters with RSS parameters.The RSS parameters were lower than the peak values from laboratory’s direct shear test results for the soils in the sliding zones.The reduction in shear strength from peak to residual state under unsaturated soil condition was greater than that for a saturated soil.The FOS decreased almost linearly with time for the scenario in which only the influence of rainfall infiltration was considered.However,the total reduction in the FOS was relatively small.The FOS decreased rapidly at a linear rate with respect to time with a decrease in water level for the scenario in which Yangtze River water level decrease was considered.The FOS reached to a relatively constant value after Yangtze River water level reached the lowest value.The decrease in Yangtze River water level was the dominant factor that contributed to a reduction in the FOS.The FOS was strongly dependent on the development of the phreatic line after the Yangtze River water level reached the lowest value.The FOS calculated by RSS (i.e.FOSR) is less than unity;they were approximately 16% lower in comparison to that calculated by PSS (FOSP).If PSS parameters were used,the slope would still be stable even under the combined influence of precipitation and Yangtze River water level decrease.These results are inconsistent with the field observations.For this reason,the RSS parameters should be taken into account to evaluate reliably the slope stability of the Outang landslide.展开更多
The stability of room mining coal pillars during their secondary mining for recovering coal was analyzed. An analysis was performed for the damage and instability mechanism of coal pillars recovered by the caving mini...The stability of room mining coal pillars during their secondary mining for recovering coal was analyzed. An analysis was performed for the damage and instability mechanism of coal pillars recovered by the caving mining method. During the damage progression of a single room coal pillar, the shape of the stress distribution in the pillar transformed from the initial stable saddle shape to the final arch-shaped distribution of critical instability. By combining the shapes of stress distribution in the coal pillars with the ultimate strength theory, the safe-stress value of coal pillar was obtained as 11.8 MPa. The mechanism of instability of coal pillar groups recovered by the caving mining method was explained by the domino effect. Since the room coal pillars mined and recovered by the traditional caving mining method were significantly influenced by the secondary mining during recovery, the coal pillars would go through a chain-type instability failure. Because of this limitation, the method of solid backfilling was proposed for mining and recovering room coal pillars, thus changing the transfer mechanism of stress caused by the secondary mining(recovery) of coal pillars. The mechanical model of the stope in the case of backfilling and recovering room coal pillars was built. The peak stress values inside coal pillars varied with the variance of backfilling ratio when the working face was advanced by 150 m. Furthermore, when the critical backfilling ratio was 80.6%, the instability failure of coal pillars would not occur during the solid backfill mining process. By taking Bandingliang Coal Mine as an example, the coal pillars' stability of stope under this backfilling ratio was studied, and a project scheme was designed.展开更多
In the field of soil stabilization, only calcium silicate hydrate(CSH) and ettringite(AFt) as hydration products have been reported to directly contribute to the strength enhancement of the soil. A chloride dredger fi...In the field of soil stabilization, only calcium silicate hydrate(CSH) and ettringite(AFt) as hydration products have been reported to directly contribute to the strength enhancement of the soil. A chloride dredger fill, an artificial chloride saline soil, and a non-saline soil were stabilized by Portland cement(PC) and PC with Ca(OH)_2(CH) with different contents. A series of unconfined compressive strength(UCS) tests of stabilized soil specimen after curing for 7 d and 28 d were carried out, and the hydration products and microstructure of the specimens were observed by X-ray diffractometry(XRD), scanning electronic microscopy(SEM), and energy-dispersive X-ray analysis(EDXA). The results showed that the strengths of PC+CH-stabilized chloride saline soils were much higher than those of PC-stabilized soils. A new hydration product of calcium aluminate chloride hydrate, also known as Friedel's salt, appeared in the PC+CH-stabilized chloride saline soils. The solid-phase volume of Friedel's salt expanded during the formation of the hydrate; this volume filled the pores in the stabilized soil. This pore-filling effect was the most important contribution to the significantly enhanced strength of the PC+CH-stabilized chloride saline soils. On the basis of this understanding, a new optimized stabilizer was designed according to the concept that the chloride in saline soil could be utilized as a component of the stabilizer. The strength of the chloride saline soils stabilized by the optimized stabilizer was even further increased compared with that of the PC+CH-stabilized soils.展开更多
The core of strength reduction method(SRM) involves finding a critical strength curve that happens to make the slope globally fail and a definition of factor of safety(FOS). A new double reduction method, including a ...The core of strength reduction method(SRM) involves finding a critical strength curve that happens to make the slope globally fail and a definition of factor of safety(FOS). A new double reduction method, including a detailed calculation procedure and a definition of FOS for slope stability was developed based on the understanding of SRM. When constructing the new definition of FOS, efforts were made to make sure that it has concise physical meanings and fully reflects the shear strength of the slope. Two examples, slopes A and B with the slope angles of 63° and 34° respectively, were given to verify the method presented. It is found that, for these two slopes, the FOSs from original strength reduction method are respectively 1.5% and 38% higher than those from double reduction method. It is also found that the double reduction method predicts a deeper potential slide line and a larger slide mass. These results show that on one hand, the double reduction method is comparative to the traditional methods and is reasonable, and on the other hand, the original strength reduction method may overestimate the safety of a slope. The method presented is advised to be considered as an additional option in the practical slope stability evaluations although more useful experience is required.展开更多
The factor of safety of mechanically stabilized earth(MSE) structures can be analyzed either using limit equilibrium method(LEM) or strength reduction method(SRM) in finite element/difference method. In LEM, the stren...The factor of safety of mechanically stabilized earth(MSE) structures can be analyzed either using limit equilibrium method(LEM) or strength reduction method(SRM) in finite element/difference method. In LEM, the strengths of the reinforcement members and soils are reduced with the same factor. While using the SRM, only soil strength is reduced during the calculation of the factor of safety. This causes inconsistence in calculating the factor of safety of the MSE structures. To overcome this, an iteration method is proposed to consider the strength reduction of the reinforcements in SRM. The method is demonstrated by using PLAXIS, a finite element software. The results show that the factor of safety converges after a few iterations. The reduction of strength has different effects on the factor of safety depending on the properties of the reinforcements and the soil, and failure modes.展开更多
随着我国山区高速公路建设的不断推进,弃渣场地的稳定性及致灾机制成为工程建设评估的重要因素之一。为了实现弃渣场的稳定性、失稳灾害动力学全过程的分析,基于面向GPU并行高性能计算软件CoSim中的物质点法(material point method,简称...随着我国山区高速公路建设的不断推进,弃渣场地的稳定性及致灾机制成为工程建设评估的重要因素之一。为了实现弃渣场的稳定性、失稳灾害动力学全过程的分析,基于面向GPU并行高性能计算软件CoSim中的物质点法(material point method,简称MPM),引入强度折减法(strength reduction method,简称SRM)开展相关研究工作。为了验证算法的合理性,以典型均质边坡为例,采用基于MPM的强度折减法与极限平衡法(limit equilibrium method,简称LEM)进行了对比,表明两者无论在稳定系数Fs还是在潜在滑动面上均具有良好的一致性。在此基础上,以云南某高速公路弃渣场降雨诱发失稳灾害为例,对其在天然工况和暴雨工况下稳定性和失稳过程进行了分析。结果表明,该弃渣场边坡在天然状态下处于稳定状态,而在暴雨工况下会发生失稳和大变形滑动;数值模拟和现场调查结果吻合较好,表明了提出的方法在弃渣场边坡稳定性与大变形失稳动力学分析中有强大的优势,可以实现斜坡的“稳定性→大变形→流动→堆积”的全过程分析。展开更多
基金Project(52278380)supported by the National Natural Science Foundation of ChinaProject(2023JJ30670)supported by the National Science Foundation of and Technology Major Project of Hunan Province,China。
文摘This study proposes an alternative calculation mode for stresses on the slip surface(SS).The calculation of the normal stress(NS)on the SS involves examining its composition and expanding its unknown using the Taylor series.This expansion enables the reasonable construction of a function describing the NS on the SS.Additionally,by directly incorporating the nonlinear Generalized Hoke-Brown(GHB)strength criterion and utilizing the slope factor of safety(FOS)definition,a function of the shear stress on the SS is derived.This function considers the mutual feedback mechanism between the NS and strength parameters of the SS.The stress constraints conditions are then introduced at both ends of the SS based on the spatial stress relation of one point.Determining the slope FOS and stress solution for the SS involves considering the mechanical equilibrium conditions and the stress constraint conditions satisfied by the sliding body.The proposed approach successfully simulates the tension-shear stress zone near the slope top and provides an intuitive description of the concentration effect of compression-shear stress of the SS near the slope toe.Furthermore,compared to other methods,the present method demonstrates superior processing capabilities for the embedded nonlinear GHB strength criterion.
基金Project(200550) supported by the Foundation for the Author of National Excellent Doctoral Dissertation of ChinaProject(09JJ1008) supported by Hunan Provincial Natural Science Foundation of ChinaProject(200631878557) supported by West Traffic of Science and Technology of China
文摘Based on strength reduction theory,the stability numbers of shallow tunnels were investigated within the framework of upper and lower bound theorems of limit analysis. Stability solutions taking into account of water seepage were presented and compared with those without considering seepage. The comparisons indicate that the maximum difference does not exceed 3.7%,which proves the present method credible. The results show that stability numbers of shallow tunnels considering seepage are much less than those without considering seepage,and that the difference of stability numbers between considering seepage and without considering seepage increase with increasing the depth ratio. The stability numbers decrease with increasing permeability coefficient and groundwater depth. Seepage has significant effects on the stability numbers of shallow tunnels.
文摘Considering the rheological properties of rock and soil body,and exploiting the merit of strength reduction technique,a theory of couple analysis is brought forward on the basis of strength reduction theory and rheological properties.Then,the concept and the calculation procedure of the safety factor are established at different time.Making use of finite element software ANSYS,the most dangerous sliding surface of the slope can be obtained through the strength reduction technique.According to the dynamic safety factor based on rheological mechanism,a good forecasting could be presented to prevent and cure the landslide.The result shows that the couple analysis reveals the process of the slope failure with the time and the important influence on the long-term stability due to the rheological parameters.
基金Project(2015M580702)supported by China Postdoctoral Science FoundationProject(51608541)supported by the National Natural Science Foundation of ChinaProject(2014122066)supported by the Guizhou Provincial Department of Transportation Foundation,China
文摘Hoek–Brown(HB)strength criterion can reflect rock’s inherent failure nature,so it is more suitable for analyzing the stability of rock slopes.However,the traditional limit equilibrium methods are at present only suitable for analyzing the rock slope stability using the linear equivalent Mohr–Coulomb(EMC)strength parameters instead of the nonlinear HB strength criterion.Therefore,a new method derived to analyze directly the rock slope stability using the nonlinear HB strength criterion for arbitrary curve slip surface was described in the limit equilibrium framework.The current method was established based on certain assumptions concerning the stresses on the slip surface through amending the initial normal stressσ0 obtained without considering the effect of inter-slice forces,and it can satisfy all static equilibrium conditions of the sliding body,so the current method can obtain the reasonable and strict factor of safety(FOS)solutions.Compared with the results of other methods in some examples,the feasibility of the current method was verified.Meanwhile,the parametric analysis shows that the slope angleβhas an important influence on the difference of the results obtained using the nonlinear HB strength criterion and its linear EMC strength parameters.Forβ≤45°,both of the results are similar,showing the traditional limit equilibrium methods using the linear EMC strength parameters and the current method are all suitable to analyze rock slope stability,but forβ>60°,the differences of both the results are obvious,showing the actual slope stability state can not be reflected in the traditional limit equilibrium methods,and then the current method should be used.
基金Project(2006318802111) supported by West Traffic Construction Science and Technology of ChinaProject(2008yb004) supported by Excellent Doctorate Dissertations of Central South University, China Project(2008G032-3) supported by Key Item of Science and Technology Research of Railway Ministry of China
文摘Based on the upper bound limit analysis theorem and the shear strength reduction technique, the equation for expressing critical limit-equilibrium state was employed to define the safety factor of a given slope and its corresponding critical failure mechanism by means of the kinematical approach of limit analysis theory. The nonlinear shear strength parameters were treated as variable parameters and a kinematically admissible failure mechanism was considered for calculation schemes. The iterative optimization method was adopted to obtain the safety factors. Case study and comparative analysis show that solutions presented here agree with available predictions when nonlinear criterion reduces to linear criterion, and the validity of present method could be illuminated. From the numerical results, it can also be seen that nonlinear parameter rn, slope foot gradient ,β, height of slope H, slope top gradient a and soil bulk density γ have significant effects on the safety factor of the slope.
基金Projects(42002277,41972279,41772291)supported by the National Natural Science Foundation of ChinaProjects(2020M680321,2021T140046)supported by the China Postdoctoral Science Foundation+1 种基金Projects(2020-zz-081,2021-PC-003)supported by the Beijing Postdoctoral Research Foundation,ChinaProject(X21074)supported by the Fundamental Research Funds for Beijing University of Civil Engineering and Architecture,China。
文摘For geotechnical stability analysis involving the Drucker-Prager(DP)criterion,both the c-ϕreduction scheme and the M-K reduction scheme can be utilized.With the aid of the second-order cone programming optimized finite element method(FEM-SOCP),a comparison of the two strength reduction schemes for the stability analysis of a homogeneous slope and a multilayered slope is carried out.Numerical investigations disclose that the FoS results calculated by the c-ϕreduction scheme agree well with those calculated by the classical Morgenstern-Price solutions.However,the FoS results attained by the M-K reduction scheme may lead to conservative estimation of the geotechnical safety,particularly for the cases with large internal friction angles.In view of the possible big difference in stability analysis results caused by the M-K reduction scheme,the c-ϕreduction scheme is recommended for the geotechnical stability analyses involving the DP criterion.
文摘Most of the natural and compacted fine-grained soil slopes that are in saturated or unsaturated condition undergo a large deformation prior to reaching failure conditions.Such slopes should be designed taking account of their strain-softening behavior using the residual shear strength (RSS) parameters.In this paper,the slope stability of a recently reactivated Outang landslide near the Three Gorges Dam in China is analyzed based on the RSS parameters of unsaturated soils.In addition,comparisons are provided in the FOS values of slope using both the peak shear strength (PSS) and RSS parameters.Firstly,a series of site investigations of the hydrologic and geologic conditions,ground surface displacements and cracks were described.The PSS and RSS behaviors of the sliding soils derived from a series of direct shear test results performed on saturated and unsaturated soil specimens are summarized.Secondly,a series of slope stability analysis were conducted considering the precipitation and Yangtze River water level variation within a representative period of 7 months,based on the PSS and the RSS properties.In this study,three different scenarios were considered,which include: i) considering only the precipitation with a constant water level;ii) considering only the decrease in water level without rainfall;iii) considering the combination of precipitation and decrease in water level.In each scenario,four steps were included to calculate the values of factor of safety (FOS) at different times.1) A steady-state seepage analysis was conducted with a constant total head at 525 m on the left boundary and 175 m on the slope surface below the Yangtze River water level.The initial pore water pressures were simulated in the slope under no precipitation and variation of water level.2) A specific boundary condition was applied on the slope surface to model the precipitation and Yangtze River water level variation.A transient seepage analysis was conducted to calculate pore water pressures at different times based on the initial pore water pressures.3) The FOS values at different times were calculated by the Morgenstern-Price method taking account of the variation of pore water pressures at different times,using the peak shear strength (PSS) parameters.4) The last step was repeated replacing PSS parameters with RSS parameters.The RSS parameters were lower than the peak values from laboratory’s direct shear test results for the soils in the sliding zones.The reduction in shear strength from peak to residual state under unsaturated soil condition was greater than that for a saturated soil.The FOS decreased almost linearly with time for the scenario in which only the influence of rainfall infiltration was considered.However,the total reduction in the FOS was relatively small.The FOS decreased rapidly at a linear rate with respect to time with a decrease in water level for the scenario in which Yangtze River water level decrease was considered.The FOS reached to a relatively constant value after Yangtze River water level reached the lowest value.The decrease in Yangtze River water level was the dominant factor that contributed to a reduction in the FOS.The FOS was strongly dependent on the development of the phreatic line after the Yangtze River water level reached the lowest value.The FOS calculated by RSS (i.e.FOSR) is less than unity;they were approximately 16% lower in comparison to that calculated by PSS (FOSP).If PSS parameters were used,the slope would still be stable even under the combined influence of precipitation and Yangtze River water level decrease.These results are inconsistent with the field observations.For this reason,the RSS parameters should be taken into account to evaluate reliably the slope stability of the Outang landslide.
基金Project(2014ZDPY02)supported by the Fundamental Research Funds for the Central Universities
文摘The stability of room mining coal pillars during their secondary mining for recovering coal was analyzed. An analysis was performed for the damage and instability mechanism of coal pillars recovered by the caving mining method. During the damage progression of a single room coal pillar, the shape of the stress distribution in the pillar transformed from the initial stable saddle shape to the final arch-shaped distribution of critical instability. By combining the shapes of stress distribution in the coal pillars with the ultimate strength theory, the safe-stress value of coal pillar was obtained as 11.8 MPa. The mechanism of instability of coal pillar groups recovered by the caving mining method was explained by the domino effect. Since the room coal pillars mined and recovered by the traditional caving mining method were significantly influenced by the secondary mining during recovery, the coal pillars would go through a chain-type instability failure. Because of this limitation, the method of solid backfilling was proposed for mining and recovering room coal pillars, thus changing the transfer mechanism of stress caused by the secondary mining(recovery) of coal pillars. The mechanical model of the stope in the case of backfilling and recovering room coal pillars was built. The peak stress values inside coal pillars varied with the variance of backfilling ratio when the working face was advanced by 150 m. Furthermore, when the critical backfilling ratio was 80.6%, the instability failure of coal pillars would not occur during the solid backfill mining process. By taking Bandingliang Coal Mine as an example, the coal pillars' stability of stope under this backfilling ratio was studied, and a project scheme was designed.
基金Project(51008007)supported by the National Natural Science Foundation of ChinaProject(2013318J01100)supported by the Science and Technology Project of Ministry of Communications,China
文摘In the field of soil stabilization, only calcium silicate hydrate(CSH) and ettringite(AFt) as hydration products have been reported to directly contribute to the strength enhancement of the soil. A chloride dredger fill, an artificial chloride saline soil, and a non-saline soil were stabilized by Portland cement(PC) and PC with Ca(OH)_2(CH) with different contents. A series of unconfined compressive strength(UCS) tests of stabilized soil specimen after curing for 7 d and 28 d were carried out, and the hydration products and microstructure of the specimens were observed by X-ray diffractometry(XRD), scanning electronic microscopy(SEM), and energy-dispersive X-ray analysis(EDXA). The results showed that the strengths of PC+CH-stabilized chloride saline soils were much higher than those of PC-stabilized soils. A new hydration product of calcium aluminate chloride hydrate, also known as Friedel's salt, appeared in the PC+CH-stabilized chloride saline soils. The solid-phase volume of Friedel's salt expanded during the formation of the hydrate; this volume filled the pores in the stabilized soil. This pore-filling effect was the most important contribution to the significantly enhanced strength of the PC+CH-stabilized chloride saline soils. On the basis of this understanding, a new optimized stabilizer was designed according to the concept that the chloride in saline soil could be utilized as a component of the stabilizer. The strength of the chloride saline soils stabilized by the optimized stabilizer was even further increased compared with that of the PC+CH-stabilized soils.
基金Project(11102218) supported by the National Natural Science Foundation of China
文摘The core of strength reduction method(SRM) involves finding a critical strength curve that happens to make the slope globally fail and a definition of factor of safety(FOS). A new double reduction method, including a detailed calculation procedure and a definition of FOS for slope stability was developed based on the understanding of SRM. When constructing the new definition of FOS, efforts were made to make sure that it has concise physical meanings and fully reflects the shear strength of the slope. Two examples, slopes A and B with the slope angles of 63° and 34° respectively, were given to verify the method presented. It is found that, for these two slopes, the FOSs from original strength reduction method are respectively 1.5% and 38% higher than those from double reduction method. It is also found that the double reduction method predicts a deeper potential slide line and a larger slide mass. These results show that on one hand, the double reduction method is comparative to the traditional methods and is reasonable, and on the other hand, the original strength reduction method may overestimate the safety of a slope. The method presented is advised to be considered as an additional option in the practical slope stability evaluations although more useful experience is required.
基金Project(41072200)supported by the National Natural Science Foundation of ChinaProject(14PJD032)supported by the Shanghai Pujiang Program,China
文摘The factor of safety of mechanically stabilized earth(MSE) structures can be analyzed either using limit equilibrium method(LEM) or strength reduction method(SRM) in finite element/difference method. In LEM, the strengths of the reinforcement members and soils are reduced with the same factor. While using the SRM, only soil strength is reduced during the calculation of the factor of safety. This causes inconsistence in calculating the factor of safety of the MSE structures. To overcome this, an iteration method is proposed to consider the strength reduction of the reinforcements in SRM. The method is demonstrated by using PLAXIS, a finite element software. The results show that the factor of safety converges after a few iterations. The reduction of strength has different effects on the factor of safety depending on the properties of the reinforcements and the soil, and failure modes.
