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Influence of grain segregation on the behavior of sand in triaxial tests

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Journal of Mountain Science 2021年第10期18卷 2776-2790页

作者： YU Fang-wei PENG Xiong-zhi SU Li-jun 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 Department of Civil Engineering Southwest Jiaotong UniversityChengdu 610031China

As a common phenomenon in granular flow, grain segregation plays a great role in affecting the behavior of granular soil by causing a great change of grain-void distribution in granular soil. This paper presents an experimental study on the influence of grain segregation on the behavior of sand, by a number of triaxial tests to interpret the characteristic behavior, friction and dilatancy behavior, excess pore water pressure behavior and critical state behavior of sand incorporating grain segregation. An index-grain segregation index was proposed to quantify grain segregation. Grain segregation affected greatly the characteristic behavior of sand, causing the movement of void ratio-dilatancy relation of sand towards the increase of void ratio and dilatancy of sand. In the drained tests, the mobilized friction angle of sand showed a decrease followed by an increase but the mobilized dilatancy angle of sand increased, with increasing grain segregation index. An increase in grain segregation index impaired the basic friction of sand. In the undrained tests, the mobilized friction angle of sand showed an increase followed by a decrease with increasing grain segregation index. However, grain segregation caused an increase of the mobilized dilatancy of sand followed by a different development. An increase in grain segregation resulted in a higher summit of the dilatancy of sand but with a faster decrease along axial strain. In the q-p′ plane, grain segregation caused a reciprocating rotation of the dilatancy line and failure line of sand. Grain segregation resulted in enhancement of the peak-state dilatancy of sand, affecting greatly peakstate friction angle and peak-state basic friction angle of sand as well as the normalized excess pore water pressure. The excess friction angle of sand showed an increase followed by a decrease in the drained tests but increased linearly in the undrained tests, with increasing grain segregation index. The excess friction angle-over-maximum dilatancy angle of sand decreased in up conve

关键词： Critical state Dilatancy Friction Grain segregation Landslides Soil behavior triaxial tests

Influence of disturbance degree on the propped excavation stability in sandy soil in Shenyang,China

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Underground Space 2023年第3期10卷 150-165页

作者： Jiachao Dong Chen Chen Manman Dong Bo Lu Yongping Guan Wen Zhao School of Resources and Civil Engineering Northeastern UniversityShenyang 110819China Northeast Architectural Design&Research Institute Co.Ltd Shenyang 110003China Department of Engineering Management Changshu Institute of TechnologyChangshu 215500China Taizhou Transportation Investment Group Taizhou 318000China

The stability of deep excavation is often investigated through numerical simulation.However,most constitutive models cannot take into account the influence of disturbance on soil response,especially for excavations in sandy soils.In this study,the conventional Dun-can–Chang constitutive model is modified based on the data obtained from a series of triaxial consolidated drained tests on medium coarse sand with different relative densities,where all input parameters in the model are correlated with the changes in relative density due to disturbance.The modified hyperbolic model is then implemented in the general-purpose finite element code,ABAQUS.The effi-ciency of the proposed constitutive mode is demonstrated by comparing with the experimental data.Furthermore,a case study of a large-scale propped excavation for a subway station in Shenyang is analyzed through numerical calculations with the conventional Mohr–Cou-lomb model and the proposed hyperbolic model,and theoretical derivations based on the current technical code in China.It is found that the proposed approach can provide reasonable estimations compared with field measurements with a maximum error of 28%for max-imum horizontal displacement of the solider pile and of 8%for maximum ground surface settlement,whereas the other techniques over-estimate the behaviour of deep excavation significantly by more than 90%.

关键词： Propped excavation triaxial tests Constitutive model Disturbance degree Numerical analysis

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

Failure characterization of fully grouted rock bolts under triaxial testing

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第3期16卷 778-789页

作者： Hadi Nourizadeh Ali Mirzaghorbanali Mehdi Serati Elamin Mutaz Kevin McDougall Naj Aziz Centre for Future Materials(CFM) School of EngineeringUniversity of Southern QueenslandToowoombaQLD4350Australia School of Engineering University of Southern QueenslandSpringfield CentralQLD4300Australia School of Civil Engineering University of QueenslandSt LuciaQLD4072Australia School of Surveying and Build Environment University of Southern QueenslandToowoombaQLD4350Australia School of Civil Mining&Environmental EngineeringUniversity of WollongongWollongongNSW2500Australia

Confining stresses serve as a pivotal determinant in shaping the behavior of grouted rock bolts.Nonetheless,prior investigations have oversimplified the three-dimensional stress state,primarily assuming hydrostatic stress conditions.Under these conditions,it is assumed that the intermediate principal stress(σ_(2))equals the minimum principal stress(σ_(3)).This assumption overlooks the potential variations in magnitudes of in situ stress conditions along all three directions near an underground opening where a rock bolt is installed.In this study,a series of push tests was meticulously conducted under triaxial conditions.These tests involved applying non-uniform confining stresses(σ_(2)≠σ_(3))to cubic specimens,aiming to unveil the previously overlooked influence of intermediate principal stresses on the strength properties of rock bolts.The results show that as the confining stresses increase from zero to higher levels,the pre-failure behavior changes from linear to nonlinear forms,resulting in an increase in initial stiffness from 2.08 kN/mm to 32.51 kN/mm.The load-displacement curves further illuminate distinct post-failure behavior at elevated levels of confining stresses,characterized by enhanced stiffness.Notably,the peak load capacity ranged from 27.9 kN to 46.5 kN as confining stresses advanced from σ_(2)=σ_(3)=0 to σ_(2)=20 MPa and σ_(3)=10 MPa.Additionally,the outcomes highlight an influence of confining stress on the lateral deformation of samples.Lower levels of confinement prompt overall dilation in lateral deformation,while higher confinements maintain a state of shrinkage.Furthermore,diverse failure modes have been identified,intricately tied to the arrangement of confining stresses.Lower confinements tend to induce a splitting mode of failure,whereas higher loads bring about a shift towards a pure interfacial shear-off and shear-crushed failure mechanism.

关键词： Rock bolts Bolt-grout interface Bond strength Push test triaxial tests

Effect of insoluble materials on the volumetric behavior of rock salt

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第1期13卷 84-97页

作者： Mejda Azabou Ahmed Rouabhi Laura Blanco-Martìn MINES ParisTech PSL Research UniversityCentre de Géosciences35 rue St HonoréFontainebleau77300France

This paper focuses on the presence of nodules of insoluble materials within salt specimens,and their effect on the volumetric strain measurements and the dilatancy phenomenon.We analyzed experimental results of over 120 conventional triaxial compression tests,and found that in 20%of the cases,the volumetric strain measurements were atypical.We also noted that the natural variability of the specimens can lead to a non-negligible data scattering in the volumetric strain measurements when different specimens are subjected to the same test.This is expected given the small magnitude of those strains,but it occasionally implies that the corresponding specimens are not representative of the volumetric behavior of the studied rock.In order to understand these results,we numerically investigated salt specimens modeled as halite matrices with inclusions of impurities.Simulations of triaxial compression tests on these structures proved that such heterogeneities can induce dilatancy,and their presence can lead to the appearance of tensile zones which is physically translated into a micro-cracking activity.The modeling approach is validated as the patterns displayed in the numerical results are identical to that in the laboratory.It was then employed to explain the observed irregularities in experimental results.We studied the natural variability effect as well and proposed a methodology to overcome the issue of specimen representativity from both deviatoric and volumetric perspectives.

关键词： Rock salt Dilatancy Material heterogeneity Natural variability triaxial tests Virtual laboratory

Influence of particle breakage on the isotropic compressibility of sands

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Journal of Mountain Science 2022年第7期19卷 2086-2099页

作者： YU Fang-wei SU Li-jun PENG Xiong-zhi Institute of Mountain Hazards and Environment Chinese Academy of SciencesChengdu610299China Center for Excellence in Tibetan Plateau Earth Sciences Chinese Academy of SciencesBeijing100101China China-Pakistan Joint Research Center on Earth Sciences Islamabad45320Pakistan University of Chinese Academy of Sciences Beijing100049China Department of Civil Engineering The University of TokyoTokyo113-8656Japan Department of Civil Engineering Southwest Jiaotong UniversityChengdu610031China

Particle breakage is a theme of great focus on affecting the behavior of granular soil.This paper presents an experimental investigation on the influence of particle breakage on the isotropic compressibility of the precrushed sands using a number of drained isotropic consolidation tests.Particle breakage resulted in movement of the compression lines followed by the rebound lines towards a decrease in the void ratio,implying that particle breakage caused a more contractive soil.Particle breakage impaired the bulk deformation modulus by increasing the compression coefficient for the compression behavior of the precrushed sands,but showed a complex effect on the bulk deformation modulus and rebound coefficient for the rebound behavior of the precrushed sands.However,particle breakage caused an increase in the compression indexes of the precrushed sands but showed a complex effect on the rebound indexes of the precrushed sands.In the e-p’plane and the e-logp’plane,the compression lines and rebound lines of the precrushed sands were curved.A generalized model was proposed to straighten the compression and rebound lines of the precrushed sands in the e-(p’p_(a))^(α) plane.Particle breakage resulted in a general rotation and translation of the linear compression and rebound lines of the precrushed sands in the e-(p’p_(a))^(α)plane.The critical state line and isotropic consolidation line on the loosest state of silica sand no.5 were curved in the e-logp’plane but straightened in the e-p’^(α=0.7) plane.In the e-p’^(α=0.7 )plane,a reasonable linear critical state line of silica sand no.5 was proposed by adjusting it to match the isotropic consolidation line on the loosest state.

关键词： Compression Isotropic consolidation Particle breakage Rebound Sands triaxial tests

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

Cyclic deformation behaviour of natural K_0-consolidated soft clay under different stress paths

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Journal of Central South University 2015年第12期22卷 4828-4836页

作者：孙磊蔡袁强谷川王军郭林 Research Center of Coastal and Urban Geotechnical Engineering Zhejiang University College of Architecture and Civil Engineering Wenzhou University

Characteristic of cyclic loading due to passing wheels is associated with one-way loading without stress reversal,which includes a simultaneous cyclic variation of vertical normal stress and horizontal normal stress lasting for a long period of time and generally takes place in partially-drained conditions.Therefore,it is of great practical relevance to study the deformation behaviour according to the characteristic of traffic loading.In this work,a series of one-way stress-controlled cyclic triaxial tests with a simultaneous variation of the vertical and horizontal stress components during cyclic loading were conducted to investigate the deformation behaviour of natural K_0-consolidated soft clay in partially-drained conditions.Test results demonstrate that not only the deviator part of the stress rules accumulation but also the volumetric part significantly contributes.While the deviator part of the stress amplitude is held constant,the increase amplitude of cyclic confining pressure will promote the development of both permanent volumetric strain and axial strain significantly.Furthermore,the effects of cyclic confining pressure on the deformation of natural K_0-consolidated soft clay was quantified.Finally,an empirical formula for permanent axial strain considering the effects of cyclic confining pressure was proposed which can be used for feasibility studies or for the preliminary design of foundations on K_0-consolidated soft clay subjected to traffic loading.

关键词： cyclic loads triaxial tests natural soft clay soil deformation

A DUAL-SURFACE DAMAGE MODEL AND EVALUATION FOR NATURAL SOILS WITHIN THE THERMOMECHANICAL FRAMEWORK

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Acta Mechanica Solida Sinica 2008年第1期21卷 85-94页

作者： Xuan Guo Chenggang Zhao Dajun Yuan Mengshu Wang Tunnel and Underground of Engineering Experienmental Research Center Beijing Jiaotong University Beijing 100044 China School of Civil Engineering ＆ Architecture Beijing Jiaotong University Beijing 100044 China

Naturally deposited or residual soils exhibit more complicated behavior than remolded clays. A dual-surface damage model for structured soils is developed based on the thermodynamics framework established in our first paper. The shift stresses and the transformation between the generalized dissipative stress space and actual stress space are established following a systematic procedure. The corresponding constitutive behavior of the proposed model is determined, which reflects the internal structural configuration and damage behavior for geomaterials. Four evolution variables κj^i（i=D, R;j=V, S） and the basic parameters λ, s, v and e0 are introduced to account for the progressive loss of internal structure for natural clays. A series of fully triaxial tests and isotropic compression tests are performed for structured and reconstituted samples of Beijing and Zhengzhou natural clays. The validation of the proposed model is examined by comparing the numerical results with the experimental data.

关键词： dual-surface damage model triaxial tests structured soils thermomechanical approach compressibility