Natural geological structures in rock(e.g.,joints,weakness planes,defects)play a vital role in the stability of tunnels and underground operations during construction.We investigated the failure characteristics of a d...Natural geological structures in rock(e.g.,joints,weakness planes,defects)play a vital role in the stability of tunnels and underground operations during construction.We investigated the failure characteristics of a deep circular tunnel in a rock mass with multiple weakness planes using a 2D combined finite element method/discrete element method(FEM/DEM).Conventional triaxial compression tests were performed on typical hard rock(marble)specimens under a range of confinement stress conditions to validate the rationale and accuracy of the proposed numerical approach.Parametric analysis was subsequently conducted to investigate the influence of inclination angle,and length on the crack propagation behavior,failure mode,energy evolution,and displacement distribution of the surrounding rock.The results show that the inclination angle strongly affects tunnel stability,and the failure intensity and damage range increase with increasing inclination angle and then decrease.The dynamic disasters are more likely with increasing weak plane length.Shearing and sliding along multiple weak planes are also consistently accompanied by kinetic energy fluctuations and surges after unloading,which implies a potentially violent dynamic response around a deeply-buried tunnel.Interactions between slabbing and shearing near the excavation boundaries are also discussed.The results presented here provide important insight into deep tunnel failure in hard rock influenced by both unloading disturbance and tectonic activation.展开更多
Since collapse of horizontal wellbore through long brittle shale interval is a major problem,the occurrence characteristics of weak planes were analyzed according to outcrop,core,and SEM and FMI data of shale rocks.A ...Since collapse of horizontal wellbore through long brittle shale interval is a major problem,the occurrence characteristics of weak planes were analyzed according to outcrop,core,and SEM and FMI data of shale rocks.A strength analysis method was developed for shale rocks with multiple weak planes based on weak-plane strength theory.An analysis was also conducted of the strength characteristics of shale rocks with uniform distribution of multiple weak planes.A collapse pressure prediction model for horizontal wells in shale formation with multiple weak planes was established,which takes into consideration the occurrence of each weak plane,wellbore stress condition,borehole azimuth,and in-situ stress azimuth.Finally,a case study of a horizontal shale gas well in southern Sichuan Basin was conducted.The results show that the intersection angle between the shale bedding plane and the structural fracture is generally large(nearly orthogonal);with the increase of weak plane number,the strength of rock mass declines sharply and is more heavily influenced by weak planes;when there are more than four weak planes,the rock strength tends to be isotropic and the whole strength of rock mass is greatly weakened,significantly increasing the risk of wellbore collapse.With the increase of weak plane number,the drillingfluid density(collapse pressure)to keep borehole stability goes up gradually.For instance,the collapse pressure is 1.04 g/cm^(3) when there are no weak planes,and 1.55 g/cm^(3) when there is one weak plane,and 1.84 g/cm^(3) when there are two weak planes.The collapse pressure prediction model for horizontal wells proposed in this paper presented results in better agreement with those in actual situation.This model,more accurate and practical than traditional models,can effectively improve the accuracy of wellbore collapse pressure prediction of horizontal shale gas wells.展开更多
The finite element analysis(FEA) technology by hydraulic-mechanical-chemical-damage(HMCD) coupling is proposed in this paper for inclined wellbore stability analysis of water-sensitive and laminated rock, developed ba...The finite element analysis(FEA) technology by hydraulic-mechanical-chemical-damage(HMCD) coupling is proposed in this paper for inclined wellbore stability analysis of water-sensitive and laminated rock, developed basing on the recently established FEA technology for transversely isotropic rock with hydraulic-mechanical-damage(HMD) coupling. The chemical activity of the drilling fluid is considered as phenomenological hydration behavior, the moisture content and parameters of rock considering hydration could be determined with time. The finite element(FE) solutions of numerical wellbore model considering the chemical activity of drilling fluid, damage tensor calculation and weak plane strength criterion for transversely isotropic rock are developed for researching the wellbore failure characteristics and computing the time-dependent collapse and fracture pressure of laminated rock as shale reservoirs. A three-dimensional FE model and elastic solid deformation and seepage flow coupled equations are developed, and the damage tensor calculation technology for transversely isotropic rock are realized by introducing effect of the hydration and the stress state under the current load. The proposed method utilizing weak plane strength criterion fully reflects the strength parameters in rock matrix and weak plane. To the end, an effective and reliable numerically three-step FEA strategy is well established for wellbore stability analysis. Numerical examples are given to show that the proposed method can establish efficient and applicable FE model and be suitable for analyzing the timedependsolutions of pore pressure and stresses, and the evolution region considering the hydration surrounding wellbore,furthermore to compute the collapse cycling time and the safe mud weight for collapse and fracture pressure of transversely isotropic rock.展开更多
The stability of a gravity dam against sliding along deep-seated weak planes is a universal and important problem encountered in the construction of dams.There is no recommended method for stability analysis of the da...The stability of a gravity dam against sliding along deep-seated weak planes is a universal and important problem encountered in the construction of dams.There is no recommended method for stability analysis of the dam on deep-seated weak planes under earthquake condition in Chinese design codes.Taking Tingzikou dam as an example,the research in this paper is focused on searching a proper way to evaluate the seismic safety of the dam against sliding along deep-seated weak planes and the probable failure modes of dam on deep-seated weak planes during earthquake.It is concluded that there are two probable failure modes of the dam along the main weak geological planes in the foundation.In the first mode,the concrete tooth under the dam will be cut and then the dam together with part foundation will slide along the muddy layer;in the second mode,the dam together with part foundation will glide along the path consist of the weak rock layer under the tooth and the muddy layer downstream the tooth.While there is no geological structure planes to form the second slip surface,the intersection of the main and the second slip surface is 40 to 80 m downstream from dam toe,and the angle between the second slip surface and the horizontal plane probably be 25 to 45 degrees.展开更多
In this paper,an elasto-plastic constitutive model is employed to capture the shear failure that may occur in a rock mass presenting mechanical discontinuities,such as faults,fractures,bedding planes or other planar w...In this paper,an elasto-plastic constitutive model is employed to capture the shear failure that may occur in a rock mass presenting mechanical discontinuities,such as faults,fractures,bedding planes or other planar weak structures.The failure may occur in two modes:a sliding failure on the weak plane or an intrinsic failure of the rock mass.The rock matrix is expected to behave elastically or fail in a brittle manner,being represented by a non-associated Mohr-Coulomb behavior,while the sliding failure is represented by the evaluation of the Coulomb criterion on an explicitly defined plane.Failure may furthermore affect the hydraulic properties of the rock mass:the shearing of the weakness plane may create a transmissive fluid pathway.Verification of the mechanical submodel is conducted by comparison with an analytical solution,while the coupled hydro-mechanical behavior is validated with field data and will be applied within a model and code validation initiative.The work presented here aims at documenting the progress in code development,while accurate match of the field data with the numerical results is current work in progress.展开更多
For the plane curves Γ,the maximal operator associated to it is defined by Mf(x)=sup|∫f(x-Γ(t))(r^(-1)t)r^(-1)dt| where is a Schwartz function.For a certain class of curves in R^2,M is shown to bounded on (H(R^2)...For the plane curves Γ,the maximal operator associated to it is defined by Mf(x)=sup|∫f(x-Γ(t))(r^(-1)t)r^(-1)dt| where is a Schwartz function.For a certain class of curves in R^2,M is shown to bounded on (H(R^2),Weak L^1(R^2).This extends the theorem of Stein & Wainger and the theo- rem of Weinberg.展开更多
针对纹理稀疏及光照变化的室内场景下,仅基于单一点特征的视觉同时定位与建图(Simultaneous Localization and Mapping,SLAM)算法位姿估计精度低甚至完全失效的问题,结合稳定性更强的线、面特征,提出了一种基于点线面特征的位姿解耦RGBD...针对纹理稀疏及光照变化的室内场景下,仅基于单一点特征的视觉同时定位与建图(Simultaneous Localization and Mapping,SLAM)算法位姿估计精度低甚至完全失效的问题,结合稳定性更强的线、面特征,提出了一种基于点线面特征的位姿解耦RGBD-SLAM系统。充分利用不同特征的互补优势和场景的结构化特性,采用位姿解耦估计的思想,通过曼哈顿世界假设实现无漂移的旋转估计,并最小化多特征联合误差函数估计平移,从而减小了传统SLAM系统采用逐帧跟踪的位姿估计方式带来的累积误差影响,提高了系统的位姿估计精度,并据此构建了环境信息丰富的点线面结构地图。实验结果表明,所提SLAM系统在ICL-NUIM数据集的8个子序列中,平均绝对轨迹精度相较于ORBSLAM2,PL-SLAM和SP-SLAM分别提升了54.5%,23.5%和28.3%;在TUM RGBD数据集的11个子序列中,分别提升了33.9%,26.2%和11.7%,表现出更优的全局定位性能和更强的系统鲁棒性;且所构建的点线面结构地图能够更好地描述环境。展开更多
基金Projects(52004143,51774194)supported by the National Natural Science Foundation of ChinaProject(2020M670781)supported by the China Postdoctoral Science Foundation+2 种基金Project(SKLGDUEK2021)supported by the State Key Laboratory for GeoMechanics and Deep Underground Engineering,ChinaProject(U1806208)supported by the NSFC-Shandong Joint Fund,ChinaProject(2018GSF117023)supported by the Key Research and Development Program of Shandong Province,China。
文摘Natural geological structures in rock(e.g.,joints,weakness planes,defects)play a vital role in the stability of tunnels and underground operations during construction.We investigated the failure characteristics of a deep circular tunnel in a rock mass with multiple weakness planes using a 2D combined finite element method/discrete element method(FEM/DEM).Conventional triaxial compression tests were performed on typical hard rock(marble)specimens under a range of confinement stress conditions to validate the rationale and accuracy of the proposed numerical approach.Parametric analysis was subsequently conducted to investigate the influence of inclination angle,and length on the crack propagation behavior,failure mode,energy evolution,and displacement distribution of the surrounding rock.The results show that the inclination angle strongly affects tunnel stability,and the failure intensity and damage range increase with increasing inclination angle and then decrease.The dynamic disasters are more likely with increasing weak plane length.Shearing and sliding along multiple weak planes are also consistently accompanied by kinetic energy fluctuations and surges after unloading,which implies a potentially violent dynamic response around a deeply-buried tunnel.Interactions between slabbing and shearing near the excavation boundaries are also discussed.The results presented here provide important insight into deep tunnel failure in hard rock influenced by both unloading disturbance and tectonic activation.
文摘Since collapse of horizontal wellbore through long brittle shale interval is a major problem,the occurrence characteristics of weak planes were analyzed according to outcrop,core,and SEM and FMI data of shale rocks.A strength analysis method was developed for shale rocks with multiple weak planes based on weak-plane strength theory.An analysis was also conducted of the strength characteristics of shale rocks with uniform distribution of multiple weak planes.A collapse pressure prediction model for horizontal wells in shale formation with multiple weak planes was established,which takes into consideration the occurrence of each weak plane,wellbore stress condition,borehole azimuth,and in-situ stress azimuth.Finally,a case study of a horizontal shale gas well in southern Sichuan Basin was conducted.The results show that the intersection angle between the shale bedding plane and the structural fracture is generally large(nearly orthogonal);with the increase of weak plane number,the strength of rock mass declines sharply and is more heavily influenced by weak planes;when there are more than four weak planes,the rock strength tends to be isotropic and the whole strength of rock mass is greatly weakened,significantly increasing the risk of wellbore collapse.With the increase of weak plane number,the drillingfluid density(collapse pressure)to keep borehole stability goes up gradually.For instance,the collapse pressure is 1.04 g/cm^(3) when there are no weak planes,and 1.55 g/cm^(3) when there is one weak plane,and 1.84 g/cm^(3) when there are two weak planes.The collapse pressure prediction model for horizontal wells proposed in this paper presented results in better agreement with those in actual situation.This model,more accurate and practical than traditional models,can effectively improve the accuracy of wellbore collapse pressure prediction of horizontal shale gas wells.
基金supported by the National Natural Science Foundation of China(Grant Nos.11372157,11302115&51608301)the Doctoral Fund of Ministry of Education of China(Grant No.20120002110075)+1 种基金the Foundation for the Author of National Excellent Doctoral Dissertation of China(Grant No.201326)the China Postdoctoral Science Foundation(Grant No.2015M571030)
文摘The finite element analysis(FEA) technology by hydraulic-mechanical-chemical-damage(HMCD) coupling is proposed in this paper for inclined wellbore stability analysis of water-sensitive and laminated rock, developed basing on the recently established FEA technology for transversely isotropic rock with hydraulic-mechanical-damage(HMD) coupling. The chemical activity of the drilling fluid is considered as phenomenological hydration behavior, the moisture content and parameters of rock considering hydration could be determined with time. The finite element(FE) solutions of numerical wellbore model considering the chemical activity of drilling fluid, damage tensor calculation and weak plane strength criterion for transversely isotropic rock are developed for researching the wellbore failure characteristics and computing the time-dependent collapse and fracture pressure of laminated rock as shale reservoirs. A three-dimensional FE model and elastic solid deformation and seepage flow coupled equations are developed, and the damage tensor calculation technology for transversely isotropic rock are realized by introducing effect of the hydration and the stress state under the current load. The proposed method utilizing weak plane strength criterion fully reflects the strength parameters in rock matrix and weak plane. To the end, an effective and reliable numerically three-step FEA strategy is well established for wellbore stability analysis. Numerical examples are given to show that the proposed method can establish efficient and applicable FE model and be suitable for analyzing the timedependsolutions of pore pressure and stresses, and the evolution region considering the hydration surrounding wellbore,furthermore to compute the collapse cycling time and the safe mud weight for collapse and fracture pressure of transversely isotropic rock.
文摘The stability of a gravity dam against sliding along deep-seated weak planes is a universal and important problem encountered in the construction of dams.There is no recommended method for stability analysis of the dam on deep-seated weak planes under earthquake condition in Chinese design codes.Taking Tingzikou dam as an example,the research in this paper is focused on searching a proper way to evaluate the seismic safety of the dam against sliding along deep-seated weak planes and the probable failure modes of dam on deep-seated weak planes during earthquake.It is concluded that there are two probable failure modes of the dam along the main weak geological planes in the foundation.In the first mode,the concrete tooth under the dam will be cut and then the dam together with part foundation will slide along the muddy layer;in the second mode,the dam together with part foundation will glide along the path consist of the weak rock layer under the tooth and the muddy layer downstream the tooth.While there is no geological structure planes to form the second slip surface,the intersection of the main and the second slip surface is 40 to 80 m downstream from dam toe,and the angle between the second slip surface and the horizontal plane probably be 25 to 45 degrees.
基金the DECOVALEX-2019 funding organisations of Andra,BGR/UFZ,CNSC,US DOE,ENSI,JAEA,IRSN,KAERI,NWMO,RWM,SURAO,SSM and Taipower for their financial and technical support of the work described in this paper。
文摘In this paper,an elasto-plastic constitutive model is employed to capture the shear failure that may occur in a rock mass presenting mechanical discontinuities,such as faults,fractures,bedding planes or other planar weak structures.The failure may occur in two modes:a sliding failure on the weak plane or an intrinsic failure of the rock mass.The rock matrix is expected to behave elastically or fail in a brittle manner,being represented by a non-associated Mohr-Coulomb behavior,while the sliding failure is represented by the evaluation of the Coulomb criterion on an explicitly defined plane.Failure may furthermore affect the hydraulic properties of the rock mass:the shearing of the weakness plane may create a transmissive fluid pathway.Verification of the mechanical submodel is conducted by comparison with an analytical solution,while the coupled hydro-mechanical behavior is validated with field data and will be applied within a model and code validation initiative.The work presented here aims at documenting the progress in code development,while accurate match of the field data with the numerical results is current work in progress.
文摘For the plane curves Γ,the maximal operator associated to it is defined by Mf(x)=sup|∫f(x-Γ(t))(r^(-1)t)r^(-1)dt| where is a Schwartz function.For a certain class of curves in R^2,M is shown to bounded on (H(R^2),Weak L^1(R^2).This extends the theorem of Stein & Wainger and the theo- rem of Weinberg.
文摘针对纹理稀疏及光照变化的室内场景下,仅基于单一点特征的视觉同时定位与建图(Simultaneous Localization and Mapping,SLAM)算法位姿估计精度低甚至完全失效的问题,结合稳定性更强的线、面特征,提出了一种基于点线面特征的位姿解耦RGBD-SLAM系统。充分利用不同特征的互补优势和场景的结构化特性,采用位姿解耦估计的思想,通过曼哈顿世界假设实现无漂移的旋转估计,并最小化多特征联合误差函数估计平移,从而减小了传统SLAM系统采用逐帧跟踪的位姿估计方式带来的累积误差影响,提高了系统的位姿估计精度,并据此构建了环境信息丰富的点线面结构地图。实验结果表明,所提SLAM系统在ICL-NUIM数据集的8个子序列中,平均绝对轨迹精度相较于ORBSLAM2,PL-SLAM和SP-SLAM分别提升了54.5%,23.5%和28.3%;在TUM RGBD数据集的11个子序列中,分别提升了33.9%,26.2%和11.7%,表现出更优的全局定位性能和更强的系统鲁棒性;且所构建的点线面结构地图能够更好地描述环境。
