• Title/Summary/Keyword: cavity expansion

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Undrained solution for cavity expansion in strength degradation and tresca soils

  • Li, Chao;Zou, Jin-feng;Sheng, Yu-ming
    • Geomechanics and Engineering
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    • v.21 no.6
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    • pp.527-536
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    • 2020
  • An elastic-plastic solution for cavity expansion problem considering strength degradation, undrained condition and initial anisotropic in-situ stress is established based on the Tresca yield criterion and cavity expansion theory. Assumptions of large-strain for plastic region and small-strain for elastic region are adopted, respectively. The initial in-situ stress state of natural soil mass may be anisotropic caused by consolidation history, and the strength degradation of soil mass is caused by structural damage of soil mass in the process of loading analysis (cavity expansion process). Finally, the published solutions are conducted to verify the suitability of this elastic-plastic solution, and the parametric studies are investigated in order to the significance of this study for in-situ soil test.

Experimental Study on Road-Subsidence Characteristics in Unsaturated Sandy Soils (불포화 사질토의 도로함몰 특성에 관한 실험적 연구)

  • Kweon, Gichul
    • International Journal of Highway Engineering
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    • v.20 no.1
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    • pp.19-25
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    • 2018
  • PURPOSES : The purpose of this study is to identify the road-subsidence mechanism in unsaturated sandy soils. METHODS : A series of soil chamber tests were conducted under various conditions. RESULTS : The cavity-expansion characteristics in unsaturated sandy soils due to seepage were affected by the outlet size, seepage intensity, relative density, and fine content. CONCLUSIONS : In unsaturated sandy soils, the cavity-expansion speed was affected by the outlet size, relative density, seepage intensity, and clay content; however, the cavity-expansion shape was very similar. As the outlet size and seepage intensity increased, the cavity-expansion speed increased. As the relative density increased, the cavity-expansion speed increased because of a sudden decrease in shear strength, resulting from the increased saturation (reduction of matric suction). The cavity expanded faster with the increasing clay content, up to a certain threshold. It expanded at a slower rate once it passed the threshold. Finally, it reached a stable state where the cavity did not expand due to seepage.

Created cavity expansion solution in anisotropic and drained condition based on Cam-Clay model

  • Li, Chao;Zoua, Jin-Feng
    • Geomechanics and Engineering
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    • v.19 no.2
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    • pp.141-151
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    • 2019
  • A novel theoretical solution is presented for created (zero initial radius) cavity expansion problem based on CamClay model and considers the effect of initial anisotropic in-situ stress and drained conditions. Here the strain of this theoretical solution is small deformation in elastic region and large deformation in plastic region. The works for cylindrical and spherical cavities expanding in drained condition from zero initial radius are investigated. Most of the conventional solutions were based on the isotropic and undrained condition, however, the initial stress state of natural soil mass is anisotropy by soil deposition history, and drained cavity expansion calculation is closer to actual engineering in permeable soil mass. Finally, the parametric study is presented in order to the engineering significance of this work.

Elasto-plastic solution for cavity expansion problem in anisotropic and drained soil mass

  • Li, Chao;Zou, Jin-feng;Li, Liang
    • Geomechanics and Engineering
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    • v.19 no.6
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    • pp.513-522
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    • 2019
  • This study presents an elasto-plastic (EP) solution for drained cavity expansion on the basis of unified strength failure criterion and considers the influence of initial stress state. Because of the influence of initial consolidation of soil mass, the initial stress may be anisotropic in the natural soil mass. In addition, the undrained hypothesis is usually used in the calculation of cavity expansion problem, but most of the cases are in the drained situation in practical engineering. Eventually, the published solution and the presented solution are compared to verify the suitability of the study.

A numerical stepwise approach for cavity expansion problem in strain-softening rock or soil mass

  • Zou, Jin-Feng;Yang, Tao;Ling, Wang;Guo, Wujun;Huang, Faling
    • Geomechanics and Engineering
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    • v.18 no.3
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    • pp.225-234
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    • 2019
  • A numerical stepwise approach for cavity expansion problem in strain-softening rock or soil mass is investigated, which is compatible with Mohr-Coulomb and generalized Hoek-Brown failure criteria. Based on finite difference method, plastic region is divided into a finite number of concentric rings whose thicknesses are determined internally to satisfy the equilibrium and compatibility equations, the material parameters of the rock or soil mass are assumed to be the same in each ring. For the strain-softening behavior, the strength parameters are assumed to be a linear function of deviatoric plastic strain (${\gamma}p^*$) for each ring. Increments of stress and strain for each ring are calculated with the finite difference method. Assumptions of large-strain for soil mass and small-strain for rock mass are adopted, respectively. A new numerical stepwise approach for limited pressure and plastic radius are obtained. Comparisons are conducted to validate the correctness of the proposed approach with Vesic's solution (1972). The results show that the perfectly elasto-plastic model may underestimate the displacement and stresses in cavity expansion than strain-softening coefficient considered. The results of limit expansion pressure based on the generalised H-B failure criterion are less than those obtained based on the M-C failure criterion.

A similarity solution for undrained expansion of a cylindrical cavity in K0-consolidated anisotropic soils

  • Wang, You;Lin, Lin;Li, Jingpei
    • Geomechanics and Engineering
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    • v.25 no.4
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    • pp.303-315
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    • 2021
  • A rigorous and generic similarity solution is developed for assessment of the undrained expansion responses of a cylindrical cavity expansion in K0-consolidated anisotropic soils. A K0-consolidated anisotropic modified Cam-clay (K0-AMCC) model that can represent the initial stress anisotropy and the effects of stress-induced anisotropy is used to model the soil behaviors during cavity expansion. All the seven basic unknowns, the three stress components, the pore water pressure, the particle velocity, the specific volume and the hardening parameter, are reduced to the functions of a dimensionless radial coordinate and are taken as coupled variables to formulate the problem. The governing equations are formulated by making use of the equilibrium equation, the constitutive equation, the consistency condition, the continuity condition and the undrained condition, which are then solved as an initial value problem. The proposed rigorous similarity solution is compared with some well-documented rigorous solutions to validate the solution and to highlight the special expansion responses in anisotropic soils. The results reveal that the present solution can yield more predictions for cavity expansion problems in soils with initial anisotropic stresses.

End Bearing Capacity of a Single Pile in Cohesionless Soils using Cavity Expansion Concept (공동확장개념에 의한 사질토에서의 말뚝의 선단지지각 해석)

  • 이명환
    • Geotechnical Engineering
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    • v.5 no.1
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    • pp.35-46
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    • 1989
  • To analyse the end bearing capacity of a single pile in cohesionless soils, the mode of deformation due to a pile penetration has been intestigated through model pile penetration tests using acetone hardening and resin impregnation technique. A new mode of deformation has been assumed from the experimental results and a new solution compeying with the theory of spherical cal.its expansion has been proposed. The end bearing capacity according to the proposed solution is expressed as the product of the limit spherical cavity expansion pressure multiplied by a col.relation factor. The results has been compared with other solutions based on the theory of cavity expansion. From the comparison, the proposed solution is expected to provide a way to solve the problem of pile bearing capacity prediction based on the theory of cavity expansion which often has been criticized as giving higher value of pile bearing capacity than the actual value.

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A Study on Consolidation Characteristics at Sand Pile Adjacent Ground by Cavity Expansion Theory (공동확장이론에 의한 Sand Pile 주변지반에서의 압밀특성에 관한 연구)

  • 천병식;여유현
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.231-238
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    • 2000
  • Sand piling method is one of the most widely used methods to improve soft soils. There are several methods to install sand piles, but driven pile method is considered as one of the easiest method. This method simply pushes down the sand piles into soft soils, so that the excess pore pressure would be generated if the soil is saturated. This pore pressure acts as consolidation load. If the amount of sand pile induced pore pressure can be predicted in reasonable ways, the effects of sand piling to improve soft soils would be predicted, and the height of preload can be reduced. In this article, sand pile induced excess pressure was predicted by cavity expansion theory, and the predicted values were compared with the field measured values. The results showed fair agreements between the measured and the predicted excess pore pressure.

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A new approach for the cylindrical cavity expansion problem incorporating deformation dependent of intermediate principal stress

  • Zou, Jin-Feng;Xia, Ming-yao
    • Geomechanics and Engineering
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    • v.12 no.3
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    • pp.347-360
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    • 2017
  • The problem of cylindrical cavity expansion incorporating deformation dependent of intermediate principal stress in rock or soil mass is investigated in the paper. Assumptions that the initial axial total strain is a non-zero constant and the axial plastic strain is not zero are defined to obtain the numerical solution of strain which incorporates deformation-dependent intermediate principal stress. The numerical solution of plastic strains are achieved by the 3-D plastic potential functions based on the M-C and generalized H-B failure criteria, respectively. The intermediate principal stress is derived with the Hook's law and plastic strains. Solution of limited expansion pressure, stress and strain during cylindrical cavity expanding are given and the corresponding calculation approaches are also presented, which the axial stress and strain are incorporated. Validation of the proposed approach is conducted by the published results.

Evaluation on Cavity Expansion under Pavement based on Groundwater Injection test (지하수 주입실험을 통한 도로노면 하부의 공동 확장 평가)

  • Park, Jeong-Jun;You, Seung-Kyong;Hong, Gigwon
    • Journal of the Korean Geosynthetics Society
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    • v.18 no.3
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    • pp.79-88
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    • 2019
  • This study described a results of groundwater injection test in cavity, in order to evaluate characteristics of cavity expansion under pavement. That is, groundwater amount proportional to the cavity volume was injected into the generated cavity step by step, and then the cavity with the changed size was monitored as the injected groundwater was drained. The test result showed that the cavity volume by groundwater injection increased, and then it converged or decreased. This means that some of the relaxation soil around the cavity collapsed, and the fine-grained soils in some soils filled the void in the surrounding soils when the cavity is expanded by groundwater injection. The volume change and expansion characteristics of the cavity according to the groundwater injection step were analyzed. The result showed that the cavity extended laterally. Therefore, it was found that the cavity expansion is caused by the repetition of the relaxation soil collapse due to the groundwater flow and the loss of the collapsed soil below the cavity.