The squeezing scenario in deep weak rock tunnels can hinder underground construction.However,due to the limitations of test technologies at hand,the real excavation stress path cannot be mimicked in the laboratory.Thu...The squeezing scenario in deep weak rock tunnels can hinder underground construction.However,due to the limitations of test technologies at hand,the real excavation stress path cannot be mimicked in the laboratory.Thus,the large deformation mechanism of deep weak rocks still remains unclear.For this,a true triaxial apparatus(TTA)to investigate the mechanical responses of deep weak rock under excavation stress paths in field and reveal the squeezing mechanism of deep tunnels is assembled and developed at Northeastern University,China.The apparatus can perform instantaneous unloading in s3 direction based on electromagnetism technology.In addition,uniform loading and deformation measurements can be carried out based on the proposed linked interlocking clamp and antifriction device,even if the sample has a strong dilatation deformation performance.Next,a bore trepanning is designed to capture noiseless acoustic emission(AE)signals for deep weak rock at a low threshold.Finally,two tests were are conducted using this instrument to preliminarily understand the failure and deformation features of deep weak rock based on fractured marble.The results show that the complete stressestrain curves of fractured marble have the characteristics of low strengths and large deformations,and the larger deformation and the more serious failure occur when the fractured marble enters the post-peak state after excavation.The results show that the developed apparatus is likely to be applicable for deep weak rock engineering.展开更多
Following tunnel excavation and lining completion,fractured surrounding rock deforms gradually over time;this results in a time-dependent evolution of the pressure applied to the lining structure by the surrounding ro...Following tunnel excavation and lining completion,fractured surrounding rock deforms gradually over time;this results in a time-dependent evolution of the pressure applied to the lining structure by the surrounding rock.Thus,the safety of the tunnel lining in weak strata is strongly correlated with time.In this study,we developed an analytical method for determining the time-dependent pressure in the surrounding rock and lining structure of a circular tunnel under a hydrostatic stress field.Under the proposed method,the stress–strain relationship of the fractured surrounding rock is assumed to conform to that of the Burgers viscoelastic component,and the lining structure is assumed to be an elastomer.Based on these assumptions,the viscoelastic deformation of the surrounding rock,the elastic deformation of the lining structure,and the coordinated deformation between the surrounding rock and lining structure were derived.The proposed analytical method,which employs a time-dependent safety coefficient,was subsequently used to estimate the durability of the lining structure of the Foling Tunnel in China.The derived attenuation curve of the safety coefficient with respect to time can assist engineers in predicting the remaining viable life of the lining structure.Unlike existing analytical methods,the method derived in this study considers the time dependency of the interaction between the surrounding rock and tunnel lining;hence,it is more suitable for the evaluation of lining lifetime.展开更多
Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The typ...Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The type of rock mass consisting of an interbedding of strong and weak layers poses difficulties and uncertainties for determining the RMR. For this, the present paper uses the concept of rock bolt supporting factor(RSF) for modification of RMR system to be used in such rock mass types. The proposed method also demonstrates the importance of rock bolting practice in such rock masses. The geological parameters of the Shemshak Formation of the Alborz Tunnel in Iran are used as case examples for development of the theoretical approach.展开更多
Flysch formations are generally characterised by evident heterogeneity in the presence of low strength and tectonically disturbed structures. The complexity of these geological materials demands a more specialized geo...Flysch formations are generally characterised by evident heterogeneity in the presence of low strength and tectonically disturbed structures. The complexity of these geological materials demands a more specialized geoengineering characterisation. In this regard, the paper tries to discuss the standardization of the engineering geological characteristics, the assessment of the behaviour in underground excava- tions, and the instructions-guidelines for the primary support measures for flysch layer qualitatively. In order to investigate the properties of flysch rock mass, 12 tunnels of Egnatia Highway, constructed in Northern Greece, were examined considering the data obtained from the design and construction records. Flysch formations are classified thereafter in 11 rock mass types (I-XI), according to the siltstone -sandstone proportion and their tectonic disturbance. A special geological strength index (GSI) chart for heterogeneous rock masses is used and a range of geotechnical parameters for every flysch type is presented. Standardization tunnel behaviour for every rock mass type of flysch is also presented, based on its site-specific geotechnical characteristics such as structure, intact rock strength, persistence and complexity of discontinuities. Flysch, depending on its types, can be stable even under noticeable overburden depth, and exhibit wedge sliding and wider chimney type failures or cause serious deformation even under thin cover. Squeezing can be observed under high overburden depth. The magnitude of squeezing and tunnel support requirements are also discussed for various flysch rock mass types under different overburdens. Detailed principles and guidelines for selecting immediate support mea- sures are proposed based on the principal tunnel behaviour mode and the experiences obtained from these 12 tunnels. Finally, the cost for tunnel support from these experiences is also presented.展开更多
Weak rock zone (soft interlayer, fault zone and soft rock) is the highlight of large-scale geological engineering research. It is an important boundary for analysis of rock mass stability. Weak rock zone has been form...Weak rock zone (soft interlayer, fault zone and soft rock) is the highlight of large-scale geological engineering research. It is an important boundary for analysis of rock mass stability. Weak rock zone has been formed in a long geological period, and in this period, various rocks have undergone long-term consolidation of geostatic stress and tectonic stress; therefore, under in-situ conditions, their density and modulus of deformation are relatively high. Due to its fragmentary nature, once being exposed to the earth's surface, the structure of weak rock zone will soon be loosened, its density will be reduced, and its modulus of deformation will also be reduced significantly. Generally, weak rock zone can be found in large construction projects, especially in the dam foundation rocks of hydropower stations. These rocks cannot be eliminated completely by excavation. Furthermore, all tests nowadays are carried out after the exposure of weak rock zone, modulus of deformation under in-situ conditions cannot be revealed. In this paper, a test method explored by the authors has been introduced. This method is a whole multilayered medium deformation method. It is unnecessary to eliminate the relatively complete rocks covering on weak rock zone. A theoretical formula to obtain the modulus of deformation in various mediums has also been introduced. On-site comparative trials and indoor deformation modulus tests under equivalent density conditions have been carried out. We adopted several methods for the prediction researches of the deformation modulus of weak rock zone under in-situ conditions, and revealed a fact that under in-situ conditions, the deformation modulus of weak rock zone are several times higher than the test results obtained after the exposure. In a perspective of geological engineering, the research findings have fundamentally changed peoples' concepts on the deformation modulus of weak rock zone, provided important theories and methods for precise definition of deformation modulus of deep weak rock zone under cap rock conditions, as well as for reasonable engineering applications.展开更多
Estimating weak rock mass modulus has historically proven difficult although this mechanical property is an important input to many types of geotechnical analyses. An empirical database of weak rock mass modulus with ...Estimating weak rock mass modulus has historically proven difficult although this mechanical property is an important input to many types of geotechnical analyses. An empirical database of weak rock mass modulus with associated detailed geotechnical parameters was assembled from plate loading tests performed at underground mines in Nevada, the Bakhtiary Dam project, and Portugues Dam project. The database was used to assess the accuracy of published single-variate models and to develop a multivariate model for predicting in-situ weak rock mass modulus when limited geotechnical data are available.Only two of the published models were adequate for predicting modulus of weak rock masses over limited ranges of alteration intensities, and none of the models provided good estimates of modulus over a range of geotechnical properties. In light of this shortcoming, a multivariate model was developed from the weak rock mass modulus dataset, and the new model is exponential in form and has the following independent variables:(1) average block size or joint spacing,(2) field estimated rock strength,(3) discontinuity roughness, and(4) discontinuity infilling hardness. The multivariate model provided better estimates of modulus for both hard-blocky rock masses and intensely-altered rock masses.展开更多
Based on an engineering background of a deep tunneling in weak rocks, the numerical modeling is used to compare different support schemes of tunnel at great depth in this paper. Focused on the general behaviors of wea...Based on an engineering background of a deep tunneling in weak rocks, the numerical modeling is used to compare different support schemes of tunnel at great depth in this paper. Focused on the general behaviors of weak rocks at great depth, a tunneling scheme with rock bolting and steel fibre reinforced sprayed concrete is proposed. This scheme is practiced successfully at a deep tunnel in weak rocks in Coal Mine No 10 of Hebi Coal Mining Administration.展开更多
Slacking experiments were performed on the red beds weak rock from vicinity of Changsha. Grain size distribution of the slacking rock was tested periodically during the experiments, which can be used to describe the p...Slacking experiments were performed on the red beds weak rock from vicinity of Changsha. Grain size distribution of the slacking rock was tested periodically during the experiments, which can be used to describe the physical transition of red beds weak rock during slacking process. According to the similar characters of many attributions such as environmental moisture, mineralogical composition, grain size and other factors between big rocks before slacking and its slacked product, the self-similar property of big rock and the small one can be induced. Fractal concept was introduced to construct the slacking model of red beds weak rock. Combining the supposed relationship of time for slacking and grain size of weak rock, the mathematic simulation of slacking process of red beds weak rock was conducted. To simplify the parameters back calculation, the fractal model proposed by Tyler and Wheatcraft was introduced to describe the characters of grain size distribution variation. The results show that the fractal dimension calculated from simulation data meet experiments data closely, which proves that the mathematic simulation method is reasonable and the parameters determination method is effective.展开更多
The Jianpudong No. 4 tunnel is a shallow tunnel, which belongs to Shaoshan County scenic highway in Hunan province, China and whose surrounding rock is weak. According to its characteristics, the field monitoring test...The Jianpudong No. 4 tunnel is a shallow tunnel, which belongs to Shaoshan County scenic highway in Hunan province, China and whose surrounding rock is weak. According to its characteristics, the field monitoring tests and numerical analysis were done. The mechanical characteristics of shallow tunnels under weak surrounding rock and the stress-strain rule of surrounding rock and support were analyzed. The numerical analysis results show that the settlement caused by upper bench excavating accounts for 44% of the total settlement, and the settlement caused by tunnel upper bench supporting accounts for 56% of the total settlement. The maximum axial force of shotcrete lining is 177.2 k N, which locates in hance under the secondary lining. The maximum moment of shotcrete lining is 5.08 k N·m, which locates in the arch foot. The stress curve of steel arch has three obvious stages during the tunnel construction. The maximum axial force of steel arch is 297.4 k N, which locates in tunnel vault. The axial forces of steel arch are respectively 23.5 k N and-21.8 k N, which is influenced by eccentric compression of shallow tunnel and locates in hance. The results show that there is larger earth pressure in tunnel vault which is most unfavorable position of steel arch. Therefore, the advance support should be strengthened in tunnel vault during construction process.展开更多
In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation.The dynami...In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation.The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads.展开更多
The application of destressing method can change the distribution patterns of the stress field in the weak rock surrounding openings, locate the openings in the zone of low stress level, thus improve their loading and...The application of destressing method can change the distribution patterns of the stress field in the weak rock surrounding openings, locate the openings in the zone of low stress level, thus improve their loading and maintaining conditions. Such method is considered as a new way of opening maintenance in weak rock and has caused extensive interests in mining industry both at home and abroad. The results of theoretic research and lab experiments of utilizing topdestresslng trough to maintain the opening affected by mining activities in weak rock, as well as its practical application in a coal mine are introduced in this paper. The research results indicate that the deformation and floor heaving of the opening in weak rock can be effectively controlled, and long-term stability of the opening can be realized by applying destressing method as long as the destressing plan and concerned parameters are carefully determined.展开更多
Considering the heterogeneity of geomechanical materials, seismicity during brittle rock failure under compressive loading on the sample with an original weak zone is simulated by using rock failure process analysis c...Considering the heterogeneity of geomechanical materials, seismicity during brittle rock failure under compressive loading on the sample with an original weak zone is simulated by using rock failure process analysis code (RFPA2D). The run-through process of weak zone, the forming of new fault and associated micro-seismicities are studied. The modeling demonstrates the total process of source development of earthquake from deformation, micro-failure to collapse and the behavior of temporal-spatial distribution of micro-seismicities. The stress, strain and the temporal-spatial distribution of micro-seismicities life-likely portrayed the phenomena of localization and temporal-spatial transitions, which is similar to those observed in our real crust. Also, the results obtained in simulations are in agreement with or similar to the reported experimental observations.展开更多
The cause and mechanism of fly rock in geological condition of weak intercalation are analyzed.According to the features of fly rock caused by weak intercalation,the differences of fly rock caused in weak intercalatio...The cause and mechanism of fly rock in geological condition of weak intercalation are analyzed.According to the features of fly rock caused by weak intercalation,the differences of fly rock caused in weak intercalation and general condition are distinguished.Specific to complicated circumstance of weak intercalation and town,the control measures of fly rock are given.With project examples,the control measures are scientific and rational,and have important project value.展开更多
A considerable amount of tunnelling has been going on in India for various projects such as hydroelectric power, irrigation, roads and railways. Most of these projects are located in Himalayas, far away from the urban...A considerable amount of tunnelling has been going on in India for various projects such as hydroelectric power, irrigation, roads and railways. Most of these projects are located in Himalayas, far away from the urban areas. Tunnelling through weak and jointed rock masses such as the one in the Himalayas is a challenging task for the planners, designers, engineers and geologists because of high overburden, thickly vegetated surface, weak, poor and fragile rocks and highly varying geology with the presence of numerous small and big shear zones, faults, etc. Due to these reasons, various tunnelling problems have been faced in the past and are still being encountered. Failures and the problems may be regarded as challenges and opportunities for generating new knowledge base and thereby increasing self-reliance in tunnelling. The experiences of Himalayan tunnelling through weak and fragile rocks covering varying and mixed geology, understanding on tunnelling in squeezing ground conditions and applicability of TBM in Himalayas are presented. It has also been highlighted that the probe holes planning, drilling and monitoring shall be followed seriously to reduce the geological surprises.展开更多
According to the structural characteristics of gently inclined thin layer rock mass in which lots of weak interlayer existed,the concept of gently inclined thin layer weakness structure was proposed.If single-borehole...According to the structural characteristics of gently inclined thin layer rock mass in which lots of weak interlayer existed,the concept of gently inclined thin layer weakness structure was proposed.If single-borehole measuring method of the acoustic along the conventional arrangement mode was used in measuring the broken rock zone in this structure,the change of the relationship curves (Vp-L) between acoustic p-wave velocity (Vp) and borehole depth (L) would present the irregular feature due to the mechanical characteristics of layered rock mass and harmful effects of weak interlayers,and the scope of broken rock zone couldn't be defined quickly.Based on the analysis of the me- chanical characteristics of layered rock mass,the propagation rule of acoustic and distri- butions characteristics of plastic zone and slip zone in layered rock mass,new arrange- ment mode of acoustic measuring boreholes for broken rock zone in gently inclined thin layer weakness structure was proposed.Namely,the measuring boreholes in two sides were parallel to the strata,the measuring boreholes in the roof and floor perpendicular to the strata.Besides the controlling depth of the measuring boreholes in the scope of the large plastic zones or the large slip zones should be increased.Engineering example showed that new acoustic measuring boreholes arrangement mode had the better appli- cability and could determine the scope of the broken rock zone in the gently inclined thin layer weakness structure quickly.展开更多
基金the financial support from the 111 Project(Grant No.B17009)the Liao Ning Revitalization Talents Program(Grant No.XLYCYSZX1902).
文摘The squeezing scenario in deep weak rock tunnels can hinder underground construction.However,due to the limitations of test technologies at hand,the real excavation stress path cannot be mimicked in the laboratory.Thus,the large deformation mechanism of deep weak rocks still remains unclear.For this,a true triaxial apparatus(TTA)to investigate the mechanical responses of deep weak rock under excavation stress paths in field and reveal the squeezing mechanism of deep tunnels is assembled and developed at Northeastern University,China.The apparatus can perform instantaneous unloading in s3 direction based on electromagnetism technology.In addition,uniform loading and deformation measurements can be carried out based on the proposed linked interlocking clamp and antifriction device,even if the sample has a strong dilatation deformation performance.Next,a bore trepanning is designed to capture noiseless acoustic emission(AE)signals for deep weak rock at a low threshold.Finally,two tests were are conducted using this instrument to preliminarily understand the failure and deformation features of deep weak rock based on fractured marble.The results show that the complete stressestrain curves of fractured marble have the characteristics of low strengths and large deformations,and the larger deformation and the more serious failure occur when the fractured marble enters the post-peak state after excavation.The results show that the developed apparatus is likely to be applicable for deep weak rock engineering.
基金supported by the National Natural Science Foundation of China(Nos.71631007 and 71771020)。
文摘Following tunnel excavation and lining completion,fractured surrounding rock deforms gradually over time;this results in a time-dependent evolution of the pressure applied to the lining structure by the surrounding rock.Thus,the safety of the tunnel lining in weak strata is strongly correlated with time.In this study,we developed an analytical method for determining the time-dependent pressure in the surrounding rock and lining structure of a circular tunnel under a hydrostatic stress field.Under the proposed method,the stress–strain relationship of the fractured surrounding rock is assumed to conform to that of the Burgers viscoelastic component,and the lining structure is assumed to be an elastomer.Based on these assumptions,the viscoelastic deformation of the surrounding rock,the elastic deformation of the lining structure,and the coordinated deformation between the surrounding rock and lining structure were derived.The proposed analytical method,which employs a time-dependent safety coefficient,was subsequently used to estimate the durability of the lining structure of the Foling Tunnel in China.The derived attenuation curve of the safety coefficient with respect to time can assist engineers in predicting the remaining viable life of the lining structure.Unlike existing analytical methods,the method derived in this study considers the time dependency of the interaction between the surrounding rock and tunnel lining;hence,it is more suitable for the evaluation of lining lifetime.
文摘Rock mass classification systems are the very important part for underground projects and rock mass rating(RMR) is one of the most commonly applied classification systems in numerous civil and mining projects. The type of rock mass consisting of an interbedding of strong and weak layers poses difficulties and uncertainties for determining the RMR. For this, the present paper uses the concept of rock bolt supporting factor(RSF) for modification of RMR system to be used in such rock mass types. The proposed method also demonstrates the importance of rock bolting practice in such rock masses. The geological parameters of the Shemshak Formation of the Alborz Tunnel in Iran are used as case examples for development of the theoretical approach.
文摘Flysch formations are generally characterised by evident heterogeneity in the presence of low strength and tectonically disturbed structures. The complexity of these geological materials demands a more specialized geoengineering characterisation. In this regard, the paper tries to discuss the standardization of the engineering geological characteristics, the assessment of the behaviour in underground excava- tions, and the instructions-guidelines for the primary support measures for flysch layer qualitatively. In order to investigate the properties of flysch rock mass, 12 tunnels of Egnatia Highway, constructed in Northern Greece, were examined considering the data obtained from the design and construction records. Flysch formations are classified thereafter in 11 rock mass types (I-XI), according to the siltstone -sandstone proportion and their tectonic disturbance. A special geological strength index (GSI) chart for heterogeneous rock masses is used and a range of geotechnical parameters for every flysch type is presented. Standardization tunnel behaviour for every rock mass type of flysch is also presented, based on its site-specific geotechnical characteristics such as structure, intact rock strength, persistence and complexity of discontinuities. Flysch, depending on its types, can be stable even under noticeable overburden depth, and exhibit wedge sliding and wider chimney type failures or cause serious deformation even under thin cover. Squeezing can be observed under high overburden depth. The magnitude of squeezing and tunnel support requirements are also discussed for various flysch rock mass types under different overburdens. Detailed principles and guidelines for selecting immediate support mea- sures are proposed based on the principal tunnel behaviour mode and the experiences obtained from these 12 tunnels. Finally, the cost for tunnel support from these experiences is also presented.
文摘Weak rock zone (soft interlayer, fault zone and soft rock) is the highlight of large-scale geological engineering research. It is an important boundary for analysis of rock mass stability. Weak rock zone has been formed in a long geological period, and in this period, various rocks have undergone long-term consolidation of geostatic stress and tectonic stress; therefore, under in-situ conditions, their density and modulus of deformation are relatively high. Due to its fragmentary nature, once being exposed to the earth's surface, the structure of weak rock zone will soon be loosened, its density will be reduced, and its modulus of deformation will also be reduced significantly. Generally, weak rock zone can be found in large construction projects, especially in the dam foundation rocks of hydropower stations. These rocks cannot be eliminated completely by excavation. Furthermore, all tests nowadays are carried out after the exposure of weak rock zone, modulus of deformation under in-situ conditions cannot be revealed. In this paper, a test method explored by the authors has been introduced. This method is a whole multilayered medium deformation method. It is unnecessary to eliminate the relatively complete rocks covering on weak rock zone. A theoretical formula to obtain the modulus of deformation in various mediums has also been introduced. On-site comparative trials and indoor deformation modulus tests under equivalent density conditions have been carried out. We adopted several methods for the prediction researches of the deformation modulus of weak rock zone under in-situ conditions, and revealed a fact that under in-situ conditions, the deformation modulus of weak rock zone are several times higher than the test results obtained after the exposure. In a perspective of geological engineering, the research findings have fundamentally changed peoples' concepts on the deformation modulus of weak rock zone, provided important theories and methods for precise definition of deformation modulus of deep weak rock zone under cap rock conditions, as well as for reasonable engineering applications.
基金funded by the National Institute of Occupational Safety and Health through research contract 200-2011-39965(Principal Investigator Dr.Kallu)University of Nevada,Reno,NV
文摘Estimating weak rock mass modulus has historically proven difficult although this mechanical property is an important input to many types of geotechnical analyses. An empirical database of weak rock mass modulus with associated detailed geotechnical parameters was assembled from plate loading tests performed at underground mines in Nevada, the Bakhtiary Dam project, and Portugues Dam project. The database was used to assess the accuracy of published single-variate models and to develop a multivariate model for predicting in-situ weak rock mass modulus when limited geotechnical data are available.Only two of the published models were adequate for predicting modulus of weak rock masses over limited ranges of alteration intensities, and none of the models provided good estimates of modulus over a range of geotechnical properties. In light of this shortcoming, a multivariate model was developed from the weak rock mass modulus dataset, and the new model is exponential in form and has the following independent variables:(1) average block size or joint spacing,(2) field estimated rock strength,(3) discontinuity roughness, and(4) discontinuity infilling hardness. The multivariate model provided better estimates of modulus for both hard-blocky rock masses and intensely-altered rock masses.
文摘Based on an engineering background of a deep tunneling in weak rocks, the numerical modeling is used to compare different support schemes of tunnel at great depth in this paper. Focused on the general behaviors of weak rocks at great depth, a tunneling scheme with rock bolting and steel fibre reinforced sprayed concrete is proposed. This scheme is practiced successfully at a deep tunnel in weak rocks in Coal Mine No 10 of Hebi Coal Mining Administration.
基金Project (95-05-01-45) supported by the Ministry of Communications of China
文摘Slacking experiments were performed on the red beds weak rock from vicinity of Changsha. Grain size distribution of the slacking rock was tested periodically during the experiments, which can be used to describe the physical transition of red beds weak rock during slacking process. According to the similar characters of many attributions such as environmental moisture, mineralogical composition, grain size and other factors between big rocks before slacking and its slacked product, the self-similar property of big rock and the small one can be induced. Fractal concept was introduced to construct the slacking model of red beds weak rock. Combining the supposed relationship of time for slacking and grain size of weak rock, the mathematic simulation of slacking process of red beds weak rock was conducted. To simplify the parameters back calculation, the fractal model proposed by Tyler and Wheatcraft was introduced to describe the characters of grain size distribution variation. The results show that the fractal dimension calculated from simulation data meet experiments data closely, which proves that the mathematic simulation method is reasonable and the parameters determination method is effective.
基金Projects(51408060,51208063)supported by the National Natural Science Foundation of China
文摘The Jianpudong No. 4 tunnel is a shallow tunnel, which belongs to Shaoshan County scenic highway in Hunan province, China and whose surrounding rock is weak. According to its characteristics, the field monitoring tests and numerical analysis were done. The mechanical characteristics of shallow tunnels under weak surrounding rock and the stress-strain rule of surrounding rock and support were analyzed. The numerical analysis results show that the settlement caused by upper bench excavating accounts for 44% of the total settlement, and the settlement caused by tunnel upper bench supporting accounts for 56% of the total settlement. The maximum axial force of shotcrete lining is 177.2 k N, which locates in hance under the secondary lining. The maximum moment of shotcrete lining is 5.08 k N·m, which locates in the arch foot. The stress curve of steel arch has three obvious stages during the tunnel construction. The maximum axial force of steel arch is 297.4 k N, which locates in tunnel vault. The axial forces of steel arch are respectively 23.5 k N and-21.8 k N, which is influenced by eccentric compression of shallow tunnel and locates in hance. The results show that there is larger earth pressure in tunnel vault which is most unfavorable position of steel arch. Therefore, the advance support should be strengthened in tunnel vault during construction process.
基金financially supported by the Research and Innovation Team of Chengdu University of TechnologyProject of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Grant No. SKLGP2013Z002)
文摘In order to investigate the effect of a weak intercalation on slope stability, a large-scale shaking table model test was conducted to study the dynamic response of rock slope models with weak intercalation.The dynamic response of the prototype slopes were studied in laboratory with the consideration of law of similitude. The initiation failure was observed in the rock slope model with a counter-tilt thin-weak intercalation firstly, not in the slope model with a horizontal thin-weak intercalation. Furthermore, it was interesting that the fracture site is shifted from crest top to the slope surface near the weak intercalation, which is different with the location of failure position in a normal layered slope. We also discussed the effect of the dip angle and the thickness of weak intercalation on the failure mechanism and instability mode of the layered rock slope. From the experimental result, it was noted that the stability of the slope with a counter-tilt weak intercalation could be worse than that of the other slopes under seismic excitation. The findings showed the difference of failure in slopes with a horizontal and counter weak intercalation, and implicated the further evaluation of failure of layered slopes caused by seismic loads.
文摘The application of destressing method can change the distribution patterns of the stress field in the weak rock surrounding openings, locate the openings in the zone of low stress level, thus improve their loading and maintaining conditions. Such method is considered as a new way of opening maintenance in weak rock and has caused extensive interests in mining industry both at home and abroad. The results of theoretic research and lab experiments of utilizing topdestresslng trough to maintain the opening affected by mining activities in weak rock, as well as its practical application in a coal mine are introduced in this paper. The research results indicate that the deformation and floor heaving of the opening in weak rock can be effectively controlled, and long-term stability of the opening can be realized by applying destressing method as long as the destressing plan and concerned parameters are carefully determined.
基金The Development Program on National Key Basic Researches under the Project Mechanism and Prediction of Continental Strong Earthquakes (G19980407) State Natural Science Foundation (49974009).
文摘Considering the heterogeneity of geomechanical materials, seismicity during brittle rock failure under compressive loading on the sample with an original weak zone is simulated by using rock failure process analysis code (RFPA2D). The run-through process of weak zone, the forming of new fault and associated micro-seismicities are studied. The modeling demonstrates the total process of source development of earthquake from deformation, micro-failure to collapse and the behavior of temporal-spatial distribution of micro-seismicities. The stress, strain and the temporal-spatial distribution of micro-seismicities life-likely portrayed the phenomena of localization and temporal-spatial transitions, which is similar to those observed in our real crust. Also, the results obtained in simulations are in agreement with or similar to the reported experimental observations.
文摘The cause and mechanism of fly rock in geological condition of weak intercalation are analyzed.According to the features of fly rock caused by weak intercalation,the differences of fly rock caused in weak intercalation and general condition are distinguished.Specific to complicated circumstance of weak intercalation and town,the control measures of fly rock are given.With project examples,the control measures are scientific and rational,and have important project value.
文摘A considerable amount of tunnelling has been going on in India for various projects such as hydroelectric power, irrigation, roads and railways. Most of these projects are located in Himalayas, far away from the urban areas. Tunnelling through weak and jointed rock masses such as the one in the Himalayas is a challenging task for the planners, designers, engineers and geologists because of high overburden, thickly vegetated surface, weak, poor and fragile rocks and highly varying geology with the presence of numerous small and big shear zones, faults, etc. Due to these reasons, various tunnelling problems have been faced in the past and are still being encountered. Failures and the problems may be regarded as challenges and opportunities for generating new knowledge base and thereby increasing self-reliance in tunnelling. The experiences of Himalayan tunnelling through weak and fragile rocks covering varying and mixed geology, understanding on tunnelling in squeezing ground conditions and applicability of TBM in Himalayas are presented. It has also been highlighted that the probe holes planning, drilling and monitoring shall be followed seriously to reduce the geological surprises.
基金the National Natural Science Foundation of China(50490274)National Key Project of Scientific and Technical Supporting Programs of China(2006BAB02A02)Guangxi University Research Foundation(X061068)
文摘According to the structural characteristics of gently inclined thin layer rock mass in which lots of weak interlayer existed,the concept of gently inclined thin layer weakness structure was proposed.If single-borehole measuring method of the acoustic along the conventional arrangement mode was used in measuring the broken rock zone in this structure,the change of the relationship curves (Vp-L) between acoustic p-wave velocity (Vp) and borehole depth (L) would present the irregular feature due to the mechanical characteristics of layered rock mass and harmful effects of weak interlayers,and the scope of broken rock zone couldn't be defined quickly.Based on the analysis of the me- chanical characteristics of layered rock mass,the propagation rule of acoustic and distri- butions characteristics of plastic zone and slip zone in layered rock mass,new arrange- ment mode of acoustic measuring boreholes for broken rock zone in gently inclined thin layer weakness structure was proposed.Namely,the measuring boreholes in two sides were parallel to the strata,the measuring boreholes in the roof and floor perpendicular to the strata.Besides the controlling depth of the measuring boreholes in the scope of the large plastic zones or the large slip zones should be increased.Engineering example showed that new acoustic measuring boreholes arrangement mode had the better appli- cability and could determine the scope of the broken rock zone in the gently inclined thin layer weakness structure quickly.