The compression and collapse behaviour of intact loess in suction-monitored triaxial apparatus

  • Dengfei Zhang
  • Jiading WangEmail author
  • Cunli Chen
  • Songhe Wang
Research Paper


Loess is susceptible to large and sudden volume reduction induced by loading or wetting. The work in this paper focused on compression and collapse behaviour of the intact loess under isotropic stress condition. To this purpose, an improved technique was introduced for the unsaturated triaxial apparatus that was capable of precise injecting know the amounts of water into the specimen, while continuously monitoring the suction. Tests were performed under two separate hydro-mechanical paths: isotropic compression at various suctions and wetting in steps at various net isotropic stresses. Experimental measurements indicated that the compression behaviour of the intact loess was highly affected by the extent of the level of the suction. The wetting-induced collapse behaviour depended on both the extent of applied net isotropic stress and the hydro-mechanical path. The collapse potential reached a maximum when the specimen was wetted at the initial yield stress. No unique of yield curve was identified from loading and wetting paths in a suction–net mean stress plane. For the same plastic volumetric strain, the suction decrease yield curve identified from wetting path appeared under the loading–collapse yield curve identified from loading path. Interestingly, the uniqueness of the yield curve was identified from loading and wetting paths in a suction–mean effective stress plane. An elastoplastic model of the intact loess under isotropic stress condition incorporating soil water retention behaviour was proposed, using the mean effective stress as constitutive stress. This model is able to reproduce the volumetric behaviour of the intact loess along constant suction paths and wetting paths quite well, using a single-valued compressibility index.


Collapse upon wetting Collapsible loess Compression deformation Elastoplastic model Yield 

List of symbols


Confining pressure


Net isotropic stress


Mean skeleton stress, or “mean effective stress”


Pore air pressure


Pore water pressure




Loss suction


Void ratio


Water content


Degree of saturation


Degree of saturation at zero suction


Entry-air value

α, n, m

Parameters of the VG model

sc0, β

Parameters for identifying the change of sc with net isotropic stress p


Yield stress at unsaturated state


Yield stress at saturated state

\(p_{\text{y}}^{{{\prime }*}}\)

Effective yield stress at unsaturated state

\(p_{\text{ref}}^{{\prime }}\)

Reference mean effective stress


Collapse suction


Total volumetric strain


Elastic volumetric strain


Plastic volumetric strain


Slope of the e–ln p curve before yielding


Slope of the e–ln p curve after yielding

\(\kappa_{\text{vs}}^{{\prime }}\)

Slope of the e–ln p′ curve before yielding

\(\lambda_{\text{vs}}^{{\prime }}\)

Slope of the e–ln p′ curve after yielding


Value of λvs at zero suction

a, b

Parameters for identifying the change of λvs with suction s

a1, b1

Parameter for identifying the change of \(\lambda_{\text{vs}}^{{\prime }}\) with suction s


Intercept of the unsaturated isotropic normal compression line in the e–ln \(p^{{\prime }} /p_{\text{ref}}^{{\prime }}\) plane


Intercept of the saturated isotropic normal compression line in the e–ln \(p^{{\prime }} /p_{\text{ref}}^{{\prime }}\) plane


Slope of the e–ln \(s^{*}\) curve after yielding

C1, C2

Parameters for identifying the change of λvp with net isotropic stress p



The National Key Research and Development Plan (2018YFC1504703), National Natural Science Foundation of China (Grant Nos. 41630639 and 51778528), the Certificate of China Postdoctoral Science Foundation Grant (2018M633559), the Key Laboratory Programme of Department of Education of Shaanxi Province of China (Grant No. 14JS063) supported the present study. The authors also want to express their deep thanks to the anonymous reviewers for their constructive comments.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Dengfei Zhang
    • 1
  • Jiading Wang
    • 1
    Email author
  • Cunli Chen
    • 2
  • Songhe Wang
    • 2
  1. 1.State Key Laboratory of Continental Dynamics, Department of GeologyNorthwest UniversityXi’anChina
  2. 2.Shaanxi Provincial Key Laboratory of Loess Mechanics and EngineeringXi’an University of TechnologyXi’anChina

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