This paper analyzes the significance of anti-seepage design and summarizes the common technology of anti-seepage design, and studies how to do a good job of anti-seepage design. Through the research, it can help the d...This paper analyzes the significance of anti-seepage design and summarizes the common technology of anti-seepage design, and studies how to do a good job of anti-seepage design. Through the research, it can help the designers to better grasp the key points of dam seepage design and prolong the service life of the dam.展开更多
High-capacity, post-tensioned anchors have found wide-spread use, originally in initial dam design and construction, and more recently in the strengthening and rehabilitation of concrete dams to meet modern design and...High-capacity, post-tensioned anchors have found wide-spread use, originally in initial dam design and construction, and more recently in the strengthening and rehabilitation of concrete dams to meet modern design and safety standards. Despite the advances that have been made in rock mechanics and rock engineering during the last 80 years in which post-tensioned anchors have been used in dam en- gineering, some aspects of the rock engineering design of high-capacity rock anchors for dams have changed relatively little over the last 30 or 40 years. This applies, in particular, to the calculations usually carried out to establish the grouted embedment lengths required for deep, post-tensioned anchors. These calculations usually make simplified assumptions about the distribution and values of rock-grout interface shear strengths, the shape of the volume of rock likely to be involved in uplift failure under the influence of a system of post-tensioned anchors, and the mechanism of that failure. The resulting designs are generally conservative. It is concluded that these aspects of the rock engineering design of large, post- tensioned rock anchors for dams can be significantly improved by making greater use of modern, comprehensive, numerical analyses in conjunction with three-dimensional （3D） models of the rock mass structure, realistic rock and rock mass properties, and the results of prototype anchor tests in the rock mass concerned.展开更多
Characterizing the permeability variation in fractured rocks is important in various subsurface applications,but how the permeability evolves in the foundation rocks of high dams during operation remains poorly unders...Characterizing the permeability variation in fractured rocks is important in various subsurface applications,but how the permeability evolves in the foundation rocks of high dams during operation remains poorly understood.This permeability change is commonly evidenced by a continuous decrease in the amount of discharge(especially for dams on sediment-laden rivers),and can be attributed to fracture clogging and/or hydromechanical coupling.In this study,the permeability evolution of fractured rocks at a high arch dam foundation during operationwas evaluated by inverse modeling based on the field timeseries data of both pore pressure and discharge.A procedure combining orthogonal design,transient flow modeling,artificial neural network,and genetic algorithm was adopted to efficiently estimate the hydraulic conductivity values in each annual cycle after initial reservoir filling.The inverse results show that the permeability of the dam foundation rocks follows an exponential decay annually during operation(i.e.K/K0=0.97e^(-0.59t)+0.03),with good agreement between field observations and numerical simulations.The significance of the obtained permeability decay function was manifested by an assessment of the long-term seepage control performance and groundwater flow behaviors at the dam site.The proposed formula is also of merit for characterizing the permeability change in riverbed rocks induced by sediment transport and deposition.展开更多
An overview of the GeoSafe 2016 Symposium topic is provided using the example of large concrete dams for purposes of illustration.It is essential that the risks associated with large dams be evaluated rigorously and m...An overview of the GeoSafe 2016 Symposium topic is provided using the example of large concrete dams for purposes of illustration.It is essential that the risks associated with large dams be evaluated rigorously and managed proactively at all stages of their lives so that the risk of failure remains As Low As Reasonably Practicable(ALARP).Rock engineering features of large concrete dams that require particular attention,assessment and monitoring during the investigation,design,construction,initial filling,inservice operation,and subsequent repair and upgrade stages of the lives of concrete dams are identified and illustrated by examples from recorded experiences.A number of major concrete dam failures,including that of the St.Francis dam,California,U.S.A.,in 1928,have led to significant developments in rock mechanics and rock engineering knowledge and techniques,as well as in dam design and review processes.More recent advances include a range of analytical,numerical modelling,probabilistic,reliability,failure mode and risk assessment approaches.展开更多
Siltation gradient and siltation length are important parameters for designing gravity check dams for debris flows,which directly affect the accuracy of estimates of interception capacity.At present,siltation gradient...Siltation gradient and siltation length are important parameters for designing gravity check dams for debris flows,which directly affect the accuracy of estimates of interception capacity.At present,siltation gradient calculations are based primarily on empirical values,and range from 0.4 to 0.95 times the channel slope coefficient.The middle reaches of the Bailong River are one of the four areas in China that are most severely affected by debris flow hazards.Gravity dams are widely employed in this mountainous area.However,field studies of their capacity are lacking.In this paper,the operations of check dams were investigated.Based on field investigation results and theoretical analysis,calculations for siltation gradient,siltation length,and dam storage capacity are established.The impact of debris flow density,channel slope,and particle size weight percentages are discussed.The calculations show that the theoretical values for siltation gradient are consistent with measured values with 83.6% accuracy;and theoretical values of siltation length are consistent with measured values with 91.6% accuracy.The results of this research are an important reference for optimal height and spacing of dams,estimation of dam storage capacity,and disaster prevention.展开更多
Discrete element simulations of one-dimensional compression of breakable granular assemblies were performed to investigate the capability of the exponential compression equation suggested by Bauer.The relationship bet...Discrete element simulations of one-dimensional compression of breakable granular assemblies were performed to investigate the capability of the exponential compression equation suggested by Bauer.The relationship between the so-called solid hardness and the particle strength was studied so as to provide a physical background for the introduction of a time-dependent solid hardness.A hyperbolic flow rule,describing the relationship between the inclination of the strain path and the stress ratio during wetting,was proposed based on typical triaxial wetting experiments on two different rockfill materials.The flow rule was then extended and incorporated into the transformed stress based hypoplastic model to capture the direction of creep strains.Meanwhile,a new density factor was introduced to the extended model to take into account the dependence of the magnitude of creep strains on the packing density.The stiffness tensor given by the extended model was discussed and the flowchart for the integration of the constitutive equation was designed.The extended model was then embedded into a finite element program and used to simulate the triaxial compression and wetting experiments performed on the aforementioned rockfill materials.Good agreement between the model predictions and the measured results lends sufficient credibility to the extended model in reproducing the stress-stain behaviour under loading and the creep behaviour during wetting.The extended model and the finite element program were also used to investigate the deformation behaviour of an earth-rock dam at the end of construction and during first impounding.The familiar phenomena such as the wetting induced settlement of the upstream shell and the movement of the dam crest towards the upstream were successfully captured by the numerical model,which confirms the feasibility of applying the extended model to dam engineering in the future.展开更多
In this study,data-driven methods(DDMs)including different kinds of group method of data handling(GMDH)hybrid models with particle swarm optimization(PSO)and Henry gas solubility optimization(HGSO)methods,and simple e...In this study,data-driven methods(DDMs)including different kinds of group method of data handling(GMDH)hybrid models with particle swarm optimization(PSO)and Henry gas solubility optimization(HGSO)methods,and simple equations methods were applied to simulate the maximum hydro-suction dredging depth(h_(s)).Sixty-seven experiments were conducted under different hydraulic conditions to measure the h_(s).Also,33 data samples from three previous studies were used.The model input variables consisted of pipeline diameter(d),the distance between the pipe inlet and sediment level(Z),the velocity of flow passing through the pipeline(u_(0)),the water head(H),and the medium size of particles(D_(50)).Data-driven simulation results indicated that the HGSO algorithm accurately trains the GMDH methods better than the PSO algorithm,whereas the PSO algorithm trained simple simulation equations more precisely.Among all used DDMs,the integrative GMDH-HGSO algorithm provided the highest accuracy(RMSE=7.086 mm).The results also showed that the integrative GMDHs enhance the accuracy of polynomial GMDHs by∼14.65%(based on the RMSE).展开更多
文摘This paper analyzes the significance of anti-seepage design and summarizes the common technology of anti-seepage design, and studies how to do a good job of anti-seepage design. Through the research, it can help the designers to better grasp the key points of dam seepage design and prolong the service life of the dam.
文摘High-capacity, post-tensioned anchors have found wide-spread use, originally in initial dam design and construction, and more recently in the strengthening and rehabilitation of concrete dams to meet modern design and safety standards. Despite the advances that have been made in rock mechanics and rock engineering during the last 80 years in which post-tensioned anchors have been used in dam en- gineering, some aspects of the rock engineering design of high-capacity rock anchors for dams have changed relatively little over the last 30 or 40 years. This applies, in particular, to the calculations usually carried out to establish the grouted embedment lengths required for deep, post-tensioned anchors. These calculations usually make simplified assumptions about the distribution and values of rock-grout interface shear strengths, the shape of the volume of rock likely to be involved in uplift failure under the influence of a system of post-tensioned anchors, and the mechanism of that failure. The resulting designs are generally conservative. It is concluded that these aspects of the rock engineering design of large, post- tensioned rock anchors for dams can be significantly improved by making greater use of modern, comprehensive, numerical analyses in conjunction with three-dimensional （3D） models of the rock mass structure, realistic rock and rock mass properties, and the results of prototype anchor tests in the rock mass concerned.
基金The financial supports from the National Key R&D Program of China(Grant No.2018YFC0407001)the National Natural Science Foundation of China(Grant No.51925906)the Research Program of China Three Gorges Corporation(Grant No.XLD/2119)are gratefully acknowledged.
文摘Characterizing the permeability variation in fractured rocks is important in various subsurface applications,but how the permeability evolves in the foundation rocks of high dams during operation remains poorly understood.This permeability change is commonly evidenced by a continuous decrease in the amount of discharge(especially for dams on sediment-laden rivers),and can be attributed to fracture clogging and/or hydromechanical coupling.In this study,the permeability evolution of fractured rocks at a high arch dam foundation during operationwas evaluated by inverse modeling based on the field timeseries data of both pore pressure and discharge.A procedure combining orthogonal design,transient flow modeling,artificial neural network,and genetic algorithm was adopted to efficiently estimate the hydraulic conductivity values in each annual cycle after initial reservoir filling.The inverse results show that the permeability of the dam foundation rocks follows an exponential decay annually during operation(i.e.K/K0=0.97e^(-0.59t)+0.03),with good agreement between field observations and numerical simulations.The significance of the obtained permeability decay function was manifested by an assessment of the long-term seepage control performance and groundwater flow behaviors at the dam site.The proposed formula is also of merit for characterizing the permeability change in riverbed rocks induced by sediment transport and deposition.
文摘An overview of the GeoSafe 2016 Symposium topic is provided using the example of large concrete dams for purposes of illustration.It is essential that the risks associated with large dams be evaluated rigorously and managed proactively at all stages of their lives so that the risk of failure remains As Low As Reasonably Practicable(ALARP).Rock engineering features of large concrete dams that require particular attention,assessment and monitoring during the investigation,design,construction,initial filling,inservice operation,and subsequent repair and upgrade stages of the lives of concrete dams are identified and illustrated by examples from recorded experiences.A number of major concrete dam failures,including that of the St.Francis dam,California,U.S.A.,in 1928,have led to significant developments in rock mechanics and rock engineering knowledge and techniques,as well as in dam design and review processes.More recent advances include a range of analytical,numerical modelling,probabilistic,reliability,failure mode and risk assessment approaches.
基金sponsored by the National Science and Technology Support Program (2014BAL05B01)STS Project of the Chinese Academy of Science (KFJ-EW-STS-094)Scientific Project of Department of land and resources of Sichuan Province (KJ-2015-18)
文摘Siltation gradient and siltation length are important parameters for designing gravity check dams for debris flows,which directly affect the accuracy of estimates of interception capacity.At present,siltation gradient calculations are based primarily on empirical values,and range from 0.4 to 0.95 times the channel slope coefficient.The middle reaches of the Bailong River are one of the four areas in China that are most severely affected by debris flow hazards.Gravity dams are widely employed in this mountainous area.However,field studies of their capacity are lacking.In this paper,the operations of check dams were investigated.Based on field investigation results and theoretical analysis,calculations for siltation gradient,siltation length,and dam storage capacity are established.The impact of debris flow density,channel slope,and particle size weight percentages are discussed.The calculations show that the theoretical values for siltation gradient are consistent with measured values with 83.6% accuracy;and theoretical values of siltation length are consistent with measured values with 91.6% accuracy.The results of this research are an important reference for optimal height and spacing of dams,estimation of dam storage capacity,and disaster prevention.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51179059,90815024)the Fund for Young Scientists in Nanjing Hydraulic Research Institute (Grant No. Y312004)
文摘Discrete element simulations of one-dimensional compression of breakable granular assemblies were performed to investigate the capability of the exponential compression equation suggested by Bauer.The relationship between the so-called solid hardness and the particle strength was studied so as to provide a physical background for the introduction of a time-dependent solid hardness.A hyperbolic flow rule,describing the relationship between the inclination of the strain path and the stress ratio during wetting,was proposed based on typical triaxial wetting experiments on two different rockfill materials.The flow rule was then extended and incorporated into the transformed stress based hypoplastic model to capture the direction of creep strains.Meanwhile,a new density factor was introduced to the extended model to take into account the dependence of the magnitude of creep strains on the packing density.The stiffness tensor given by the extended model was discussed and the flowchart for the integration of the constitutive equation was designed.The extended model was then embedded into a finite element program and used to simulate the triaxial compression and wetting experiments performed on the aforementioned rockfill materials.Good agreement between the model predictions and the measured results lends sufficient credibility to the extended model in reproducing the stress-stain behaviour under loading and the creep behaviour during wetting.The extended model and the finite element program were also used to investigate the deformation behaviour of an earth-rock dam at the end of construction and during first impounding.The familiar phenomena such as the wetting induced settlement of the upstream shell and the movement of the dam crest towards the upstream were successfully captured by the numerical model,which confirms the feasibility of applying the extended model to dam engineering in the future.
文摘In this study,data-driven methods(DDMs)including different kinds of group method of data handling(GMDH)hybrid models with particle swarm optimization(PSO)and Henry gas solubility optimization(HGSO)methods,and simple equations methods were applied to simulate the maximum hydro-suction dredging depth(h_(s)).Sixty-seven experiments were conducted under different hydraulic conditions to measure the h_(s).Also,33 data samples from three previous studies were used.The model input variables consisted of pipeline diameter(d),the distance between the pipe inlet and sediment level(Z),the velocity of flow passing through the pipeline(u_(0)),the water head(H),and the medium size of particles(D_(50)).Data-driven simulation results indicated that the HGSO algorithm accurately trains the GMDH methods better than the PSO algorithm,whereas the PSO algorithm trained simple simulation equations more precisely.Among all used DDMs,the integrative GMDH-HGSO algorithm provided the highest accuracy(RMSE=7.086 mm).The results also showed that the integrative GMDHs enhance the accuracy of polynomial GMDHs by∼14.65%(based on the RMSE).
