含碎石芯软黏土复合试样大三轴试验研究

Study on Large Triaxial Test of Soft Clay Composite Samples with Gravel Core

以拟建的某水电站碎石桩地基处理为背景,研发了能提高重塑软黏土固结效率、减小试样扰动的含碎石芯软黏土复合试样的室内试验制样方法,开展了不同围压和碎石芯置换率的复合试样室内大三轴试验研究.研究表明,复合试样在较小围压下表现出应变硬化特性,在较高围压下则基本呈现软化特征,且碎石置换率越小,软化特征越明显,相同围压时,复合试样的初始变形模量随试样面积置换率的增大而增大;在高围压和低置换率时,软黏土碎石芯复合试样的剪切破坏面明显,在低围压和高置换率时,复合试样中部出现较明显的鼓胀现象,碎石芯最大鼓胀量总体随着围压和置换率的提高而增大.规范方法高估了复合试样(地基)的内摩擦角,面积置换率越大,规范计算值与试验结果的差值越大.高围压下传统应力叠加法高估了软黏土振冲置换碎石桩复合地基的承载能力,低估了复合地基的沉降,置换率越高,相同轴向应变时与复合试样大三轴试验的偏应力误差越大.

Taking the foundation treatment of gravel pile in a proposed hydropower station as the background,an indoor experimental sample preparation method of soft clay composite samples with gravel core was developed,which can improve the consolidation efficiency of remolded soft clay and reduce the disturbance of the samples.The large triaxial tests of composite samples with different confining pressures and gravel core replacement rates were carried out.The results show that composite specimens exhibit strain hardening characteristics under small confining pressures,while they generally exhibit softening characteristics under high confining pressures,and the softening characteristics are more pronounced with a smaller gravel replacement rate.At the same confining pressure,the initial deformation modulus of the composite specimen increases with the increase of the sample area replacement rate.At high confining pressure and low replacement rate,the shear failure surface of the soft clay gravel core composite sample is obvious.At low confining pressure and high replacement rate,there is a more obvious bulging phenomenon in the middle of the composite sample.The maximum bulge amount of the gravel core generally increases with the increase of confining pressure and replacement rate.The current code method overestimates the internal friction angle of the composite specimen(foundation),and the larger the area replacement rate,the greater the difference between the calculated values and the experimental results.Under high confining pressures,the traditional stress superposition method overestimates the bearing capacity of the soft clay vibroflotation replacement gravel pile composite foundation and underestimates the settlement of the composite foundation.The higher the replacement rate,the greater the deviation stress error between the stress superposition method and the large triaxial test of the composite sample.