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Shear Strength and dilatancy of Calcareous Sand in the South China Sea

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China Ocean Engineering 2022年第5期36卷 781-790页

作者： PEI Hui-min WANG Dong Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering Ocean University of ChinaQingdao 266100China Qingdao National Laboratory for Marine Science and Technology Qingdao 266100China

The shear strength and dilatancy of typical uncemented calcareous sand from the South China Sea are investigated by soil lab tests.According to drained triaxial tests at various relative densities and confining stresses,it is found that the constant volume friction angle is approximated as 39°and the traditional Bolton’s equations can be modified to estimate the peak friction angle and dilation angle.The reliability of the equation proposed for the peak friction angle is verified in terms of calcareous sands from more onshore and offshore sites worldwide,while the errors of the predicted dilation angles scatter in a relatively large range.Totally,the dilation angles of sands in the South China Sea are estimated by the equation presented with an error of±30%.The peak friction angle measured by the undrained is similar to that by the drained tests as the relative density smaller than 60%,while the former is slightly lower for denser samples.

关键词： calcareous sand triaxial tests friction angle dilatancy drained South China Sea

A generalized dilatancy angle equation of granular soil

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Journal of Mountain Science 2022年第5期19卷 1456-1463页

作者： YU Fang-wei Institute of Mountain Hazards and Environment Chinese Academy of SciencesChengdu 610041China Center for Excellence in Tibetan Plateau Earth Sciences Chinese Academy of SciencesBeijing 100101China China-Pakistan Joint Research Center on Earth Sciences CAS-HECIslamabad 45320Pakistan University of Chinese Academy of Sciences Beijing 100049China Department of Civil Engineering The University of TokyoTokyo 113-8656Japan

This paper presents a generalized dilatancy angle equation of granular soil to cover not only the drained tests but also the undrained tests by introducing a generalized structure of soil:soil skeleton formed by soil particles and the fluid in soil voids,under the assumptions of the incompressibility of soil particles and the compressibility of the fluid in soil voids.For the drained tests,the generalized dilatancy angle equation of granular soil would be degenerated to its current dilatancy angle equation.However,for the undrained tests,the generalized dilatancy angle equation of granular soil was derived with aλparameter that was related to the stress-strain state of soil and the nature of the fluid in soil voids.Theλparameter was determined by the initial dilatancy angles of granular soil at the onset of shearing on the same initial state of the soil in the drained and undrained tests.In addition,the generalized dilatancy angle equation of granular soil was verified for application in calculation of the dilatancy angles of sands in the drained and undrained tests.

关键词： Elastoplastic theory dilatancy Granular soil Sands Soil Skeleton Triaxial tests

An elasto-plastic and viscoplastic damage constitutive model for dilatancy and fracturing behavior of soft rock squeezing deformation

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Journal of Mountain Science 2022年第3期19卷 826-848页

作者： HUANG Xing LIU Quan-sheng BO Yin LIU Bin DING Zi-wei ZHANG Quan-tai State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan 430071China Key Laboratory of Geotechnical and Structural Engineering Safety of Hubei Province School of Civil EngineeringWuhan UniversityWuhan 430072China College of Energy Engineering Xi'an University of Science and TechnologyXi'an 710054China

Soft rock squeezing deformation mainly consists of pre-peak damage-dilatancy and post-peak fracture-bulking at the excavation unloading instant,and creep-dilatancy caused by time-dependent damage and fracturing.Based on the classic elastoplastic and Perzyna over-stress viscoplastic theories,as well as triaxial unloading confining pressure test and triaxial unloading creep test results,an elastoplastic and viscoplastic damage constitutive model is established for the short-and long-term dilatancy and fracturing behavior of soft rock squeezing deformation.Firstly,the criteria for each deformation and failure stage are expressed as a linear function of confining pressure.Secondly,the total damage evolution equation considering time-dependent damage is proposed,including the initial damage produced at the excavation instant,in which the damage variable increases exponentially with the lateral strain,and creep damage.Thirdly,a transient five-stages elasto-plastic constitutive equation for the short-term deformation after excavation that comprised of elasticity,pre-peak damage-dilatancy,post-peak brittle-drop,linear strain-softening,and residual perfectly-plastic regimes is developed based on incremental elasto-plastic theory and the nonassociated flow rule.Fourthly,regarding the timedependent properties of soft rock,based on the Perzyna viscoplastic over-stress theory,a viscoplastic damage model is set up to capture creep damage and dilatancy behavior.Viscoplastic strain is produced when the stress exceeds the initial static yield surface fs;the distance between the static yield surface fs and the dynamic yield surface fd determines the viscoplastic strain rate.Finally,the established constitutive model is numerically implemented and field applied to the-848 m belt conveyer haulage roadway of Huainan Panyidong Coal Mine.Laboratory test results and in-situ monitoring results validate the rationality of the established constitutive model.The presented model takes both the transient and time-dependent damage and fracturi

关键词： Soft rock Squeezing deformation Damage dilatancy Fracturing Elasto-plastic and viscoplastic damage constitutive model

Experimental investigation on dilatancy behavior of water-saturated sandstone

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International Journal of Mining Science and Technology 2018年第2期28卷 323-329页

作者： Jiangyu Wu Meimei Feng Bangyong Yu Wenli Zhang Xiaoyan Ni Guansheng Han State Key Laboratory for Geomechanics & Deep Underground Engineering China University of Mining & Technology School of Mechanics & Civil Engineering China University of Mining & Technology Institute of Construction Engineering Technology Changzhou Vocational Institute of Engineering

It is important to study the dilatancy property of water-saturated rock for understanding the engineering behavior of loaded rock mass. This study carried out the uniaxial and triaxial compressive experiments on the water-saturated red sandstone, analyzed the influences of confining pressure and pore pressure on dilatancy property of water-saturated rock, and discussed the reasonable basis of the stress of dilatancy onset as a strength design parameter of rock engineering, finally established the prediction model of the stress of dilatancy onset under the impacts of confining pressure and pore pressure. The results show that the strength parameters(the stress of dilatancy onset and peak strength) and deformation parameters(axial strain and circumferential strain) of water-saturated sandstone increase with the confining pressure, and the relations can be fitted with a positive linear function. The cohesion and internal friction angle obtained from the stress of dilatancy onset decrease by 11.57% and 7.33%, respectively, when compared with those obtained from the peak strength. The strength parameters and deformation parameters of water-saturated sandstone decrease basically with the increase of pore pressure, in which the relations between strength parameters or axial strain and pore pressure can be fitted with a negative linear function. However, the relation between the peak circumferential strain and the pore pressure should be characterized by a negative exponential function, and the circumferential strain at dilatancy onset isn't affected by the pore pressure.

关键词： Rock mechanics dilatancy behavior Confining pressure Pore pressure Water-saturated

dilatancy equation of rockfill material under the true triaxial stress condition

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Science China(Technological Sciences) 2011年第S1期54卷 175-184页

作者： XIAO Yang 1,2,LIU HanLong 1,2,ZHU JunGao 1,2 & SHI WeiCheng 1,3 1 Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering,Hohai University,Nanjing 210098,China 2 Geotechnical Research Institute,Hohai University,Nanjing 210098,China 3 School of Civil Engineering and Architecture,Changzhou Institute of Technology,Changzhou 213002,China Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai University Nanjing China Geotechnical Research Institute Hohai University Nanjing China School of Civil Engineering and Architecture Changzhou Institute of Technology Changzhou China

Rockfill material is widely used for construction of high rockfill dam due to its facility,economical cost,high strength and effective aseismatic property.It is provoked profoundly to propose a suitable constitutive model for a better application of this material.The dilatancy equation of rockfill material plays a significant role in the constitutive model.For the sake of simplicity,a dilatancy equation is established by the linear least square method on the basis of the rearranged data of rockfill material in the true triaxial tests.Based on the fact that the rearranged data at different initial confining pressures are aligned in a narrow band,the dilatancy behavior of rockfill material is independent of the initial confining pressure.However,different from the initial confining pressure,both the intermediate principal stress ratio and the specimen density exhibit a remarkable influence on the dilatancy behaviors of rockfill material.Furthermore,the predictions of the proposed dilatancy equation are in a good agreement with the rearranged test data of rockfill material at different specimen densities and stress paths.

关键词： rockfill material dilatancy equation true triaxial test density stress path initial confining pressure

The role of dilatancy in shallow overburden tunneling

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Underground Space 2019年第3期4卷 181-200页

作者： Muhammad Shehzad Khalid Mamoru Kikumoto Ying Cui Kiyoshi Kishid Department of Urban Management Kyoto UniversityNishikyo-KuKyoto 615-8540Japan Department of Civil Engineering Yokohama National UniversityYokohamaKanagawa 240-8501Japan

The mechanical behavior of sandy ground during shallow circular tunneling is explored for various overburden heights H(=0.5D,1.0D,1.5D and 2.0D;D is the diameter of the tunnel)and various dilatancy coefficients(w//=0,1/3,1/2,and 1;/and w are the internal friction angle and dilation angle,respectively)through finite difference analyses.The ground is modeled as a linear elastic-perfectly plastic material that employs the Mohr-Coulomb yield criterion and obeys the non-associated flow rule.The ground reaction curve is applied in conjunction with the stress path as a conceptual tool for interpreting the mechanical response of the ground to tunneling.It is revealed that,at a certain relaxation value,a yield zone develops during tunneling and extends to the surface.This relaxation value increases with increases in the overburden and w//values for the cases of less shallow tunnels(i.e.,H=1.0D,1.5D and 2.0D),while for the shallowest case(H=0.5D),the extent of the yield zone to the ground surface is not sensitive to the w//value.The shear strain due to tunneling also increases with an increase in the w//value.Moreover,the w//value affects the radial displacement and the surface settlement due to tunneling.The magnitudes of the surface settlement and the radial displacement at the tunnel crown both decrease with an increase in the w//value.The relative difference in the displacement at the tunnel crown between the upper bound and lower bound values,w//(at the last computed stage),increases with an increase in the overburden height.It is recommended,therefore,that careful consideration be given to the dilatancy angle in the case of relatively less shallow tunnels.

关键词： Shallow tunnels dilatancy Overburden Ground reaction curve Stress path

Stress dilatancy analysis of shallow tunnels subjected to unsymmetrical pressure

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Journal of Central South University 2008年第S2期15卷 28-33页

作者：杨小礼王金明 School of Civil and Architectural Engineering Central South University

Numerical simulation using finite differential code was conducted for the single line railway and four-lane road shallow tunnels subjected to unsymmetrical pressure. The mechanical behavior of weak rock mass was studied considering the influences of stress dilatancy on the failure mechanisms, and the results of numerical simulation were compared with the analytical solutions in specifications. The results show that the dilatancy angle has great influences on the surrounding rock displacement and the shape of failure face for the shallow tunnels. When the dilatancy angle equals zero, the failure face of the surrounding rock forms and extends to the ground surface. With the dilatancy angle increasing, the loose region decreases gradually, and failure surface discontinues. When the dilatancy angle equals the friction angle, the loose region is only distributed in a small range around the crown and sidewalls. On the side of smaller buried depth, the difference of break angle between numerical simulation and the code is less than 10% for single line railway tunnels with the dilatancy angle of zero. However, for the four-lane road tunnels, the difference reaches 20.8%. On the side of larger buried depth, the break angles are smaller than those by the code, the difference reaches 16.8% for single line railway tunnels, and 13.8% for four-lane road tunnels. With the dilatancy angle increasing, especially the dilatancy angle approximating to internal friction angle, it is on safe side to calculate the break angle using the analytical solution method of specifications. Therefore, the influence of stress dilatancy should be considered while determining the failure mechanisms of shallow tunnels subjected to unsymmetrical pressure in weak rocks.

关键词： stress dilatancy shallow tunnel failure mechanism unsymmetrical pressure

Prediction of fracture and dilatancy in granite using acoustic emission signal cloud

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第5期13卷 1059-1077页

作者： Dongjie Xue Lan Lu Lie Gao Lele Lu Cheng Chen School of Mechanics and Civil Engineering China University of Mining and TechnologyBeijing100083China State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing UniversityChongqing400030China Key Laboratory of Safety and High-efficiency Coal Mining Anhui University of Science and TechnologyHuainan232001China

The invisibility of fracture network evolution in the rock under triaxial compression seriously restricts the correlation modeling between dilatancy behavior and fracture interconnectivity.The key to solving such a challenge is strongly dependent on the accurate modeling of the spatial correlation in fracture network,which could be indirectly re-constructed by the acoustic emission(AE)signal cloud.Considering the interaction of local fractures,a cube cluster approach is established to describe the spatial correlation.The evolutional cube clusters effectively present the geometric characteristics induced by the increasing dilatancy of fracture.Two descriptors(i.***.three-axis length sum and pore fraction)are introduced to correlate cluster model with dilatancy behavior.Most fitting results support the linear correlation between two descriptors and volumetric strain,which verifies the sensitiveness of the cube cluster model to dilatancy.More importantly,by the statistical analysis of cluster structure,the cluster model shows the potential of calculating fracture angle.Moreover,a comparison between dilatancybased damage and porosity-based damage is made not to prove the best but provide an AE-based prediction of local damage evolution.Finally,four classical models for calculating fracture angle are compared.The deviations prove the huge difficulty of describing the development of the fracture network uniquely dependent on a fracture angle.The proximity of measured angle and cluster-based angle supports the effectiveness of predication by the cube cluster approach.

关键词： Fracture network Acoustic emission(AE) Spatial correlation dilatancy Damage Fracture angle

Strength and dilatancy behaviors of deep sands in Shanghai with a focus on grain size and shape effect

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第6期12卷 1214-1225页

作者： Bandana Tiwaria Guanlin Ye Mingguang Li Usama Khalid Santosh Kumar Yadav Department of Civil Engineering and State Key Laboratory of Ocean Engineering Shanghai Jiao Tong UniversityShanghai200240China Department of Civil Engineering IOEPulchowk CampusTribhuvan UniversityLalitpur44700Nepal

With rapid development of infrastructures like tunnels and open excavations in Shanghai,investigations on deeper soils have become critically important.Most of the existing laboratory works were focused on the clayey strata up to Layer 6 in Shanghai,i.***.at depth of up to 40 m.In this paper,Layers 7,9,and 11,which were mostly formed of sandy soils at depth of up to 150 m,were experimentally investigated with respect to physico-mechanical behaviors.The stressestrain behaviors were analyzed by the consolidated drained/undrained(CD/CU)triaxial tests under monotonic loading.One-dimensional(1D)oedometer tests were performed to investigate the consolidation properties of the sandy soils.Specimens were prepared at three different relative densities for each layer.Also,the micro-images and particle size analyzers were used to analyze the shape and size of the sand grains.The influences of grain size,density,and angularity on the stressestrain behaviors and compressibility were also studied.Compared to the other layers,Layer 11 had the smallest mean grain size(D50),highest compressibility,and lowest shear strength.In contrast,Layer 9 had the largest mean grain size,lowest compressibility,and highest shear strength.Layer 7 was of intermediate mean grain size,exhibiting more compressibility and less shear strength than that of Layer 9.Also,the critical state parameters and maximum dilatancy rate of different layers were discussed.

关键词： Deep sands in Shanghai Laboratory tests Shear strength dilatancy Relative density