高分解度泥炭土直剪抗剪强度特性及机理

Shear strength properties and mechanisms of peaty soil with high degree of decomposition in direct shear tests

基于大量室内压缩-直剪联合试验结果,系统分析了取自昆明市和大理市3个不同场地典型高分解度泥炭土的直剪抗剪强度特性及机理。试验结果表明：固结快剪、快剪和慢剪所得泥炭土的剪应力～剪切位移关系曲线表现出不同的形态;固结快剪和慢剪时,随着法向应力的增大,剪切变形从塑性变形转变为弹塑性变形为主;不同法向应力下,快剪的剪切变形均以塑性变形为主。高分解度泥炭土抗剪强度包线近似为相交的2段不同斜率的直线;固结快剪和慢剪抗剪强度包线转折点对应的法向应力σs约为200 k Pa,快剪时σs约为100 k Pa。通过分析泥炭土固结压缩变形特性并建立压缩-剪切微结构模型,分析了其抗剪强度来源及演化机理。机理分析表明：随着法向应力增大,高分解度泥炭土经历了从多孔隙状态至相对密实状态的转变,导致其抗剪强度及抗剪强度参数发生相应改变。

Based on the results of a large number of laboratory compression-direct shear combined tests,the shear strength properties and mechanisms of typical peaty soil with a high degree of decomposition,sampled from three different sites in Kunming and Dali cities,were analyzed. The test results demonstrate the following： the shear stress-shear displacement curves of peaty soil showed different shapes in the consolidated quick shear test,quick shear test,and slow shear test; with the increase of the normal stress,the shear deformation changed from plastic deformation to elastic-plastic deformation in the consolidated quick shear and slow shear tests; the shear deformation in the quick shear test showed mainly the plastic deformation under different normal stresses; the shear strength envelopes of peaty soil with a high degree of decompression were,basically,two intersecting polygonal lines with different slopes; the normal stress（ σs） corresponding to the break point of shear strength envelopes was about200 k Pa in the consolidated quick shear test and slow shear test,and the value was about 100 k Pa in the quick shear test. Based on analysis of the compression deformation of peaty soil,the evolution mechanisms of the shear strength were further analyzed by means of establishing compression-shear microstructural models for peaty soil. Weconclude that the increasing normal stress causes peaty soil to change from a porous state to a relatively densified state,leading to changes in the shear strength and the shear strength parameters.