寒区湿地软土抗剪强度特征试验研究

Experimental Study on Shear Strength Characteristics of Soft Soil on Wetland in Cold Regions

针对寒区湿地公路软土地基在路堤填筑分级加载作用下的稳定性问题,为采用理论计算方法研究寒区湿地软土地基稳定性提供必要的计算参数,采集原状土,对寒区湿地两层软土进行三轴试验和直剪试验。研究寒区湿地软土在5个不同固结压力和3个不同固结度下主应力差与轴向应变关系的变化,以及5个不同固结压力和6个固结度下抗剪强度指标和抗剪强度的变化。试验结果表明:采用不排水剪,第1层软土的应力-应变关系呈现典型的加工硬化特征,第2层软土的则接近于理想塑性。在相同的应变下,随着固结压力和固结度的增加偏应力逐渐增大;抗剪强度随固结压力和固结度的增加而增大。粘聚力c在固结度U<20%时,随固结度的增加而减小;固结度U>20%,总体上随固结度的增加而增大。内摩擦角φ随着固结度的增大有所增加,但规律性不很明显。

To solve the problem of stability of soft soil foundation of highway on wetland in cold regions under incremental loading during construction of subgrade or embankment and to provide necessary parameters for study on stability of soft soil foundation on wetland in cold regions by theoretical calculation method, undisturbed soil samples were collected and triaxial test and direct shear test were carried out for two-layer soft soil of wetland in cold regions to study the change of relation between the main stress difference and axial strain under five different consolidation pressures and three different degrees of consolidation as well as the change of shear strength indexes and shear strength under five different consolidation pressures and six different degrees of consolidation. The results of triaxial test show that （ 1 ） in undrained shear test, the relation between stress and strain of the first layer of soft soil appears in typical work hardening characteristic, while the relation between stress and strain of the second layer of soft soil is similar to perfect plasticity; （2） under a fixed strain, deviatoric stress increases gradually with increase of consolidation pressure and degree of consolidation. The results of direct shear test show that （ 1 ） shear strength increases with increase of consolidation pressure and degree of consolidation; （2） cohesive force c decreases with increase of degree of consolidation when degree of consolidation U is less than 20% but generally increases with increase of degree of consolidation when degree of consolidation U is larger than 20%; （3） the internal friction angle ψ increases a little bit with increase of degree of consolidation, but the law of change is not obvious.