砂-黏土混合物高压压实性能试验研究

Experimental investigations on compaction properties of sand-clay mixture at high pressure

利用自行设计高压固结仪对5种不同含砂率的饱和砂-黏土混合物开展一系列高压压缩试验,研究砂-黏土混合物压缩性和渗透性演化规律及其对矿物组分的依赖性。试验结果表明,饱和砂-黏土混合物的孔隙比-压力(e-lgP)曲线随着含砂率增高呈现出指数函数模式向双曲线函数模式转化,而e-P曲线在压力高于8.1 MPa则呈线性变化,其斜率依赖于含砂率。最优含砂率随固结压力的增大而逐渐从75%移向30%。不同含砂率的砂-黏土混合物的孔隙率、固结压力和含砂率存在统一的幂函数关系。渗透系数与含砂率有关,渗透系数与孔隙率符合指数函数关系。从砂-黏土混合物骨架结构和孔隙类型的角度出发,从本质上分析含砂率、固结压力对混合物压缩性和渗透性的作用规律。结合SEM微细观结构观测结果,验证砂-黏土混合物骨架结构与含砂率之间的相关性。

In this study, we perform a series of oedometric tests on saturated sand-clay mixtures with five different sand contents at high pressure using a self-designed high-pressure oedometer. The evolutions of compressibility and permeability and their dependency on mineralogical compositions during compaction process were investigated. Experimental results showed that the compression curve(e-lg P) of the saturated sand-clay mixtures transfers from an exponential function to a hyperbolic function with the increase of sand content. However, the compression curve(e-P) plotted in normal coordinates presents a linear evolution for all the sand-clay mixtures when the consolidation pressure is above 8.1 MPa, and its slope depends on sand content. The concept of optimum sand content is used to describe the minimum void ratio at a certain value of consolidation pressure. The optimum sand content varied continuously from 75% to 30% following the increase of consolidation pressure. Furthermore, it was founded that the relationship among void ratio, consolidation pressure and sand content follows the uniform power function for all the mixtures studied. An exponential correlation is proposed to describe the correlation between the permeability coefficient and void ratio, which can further reveal the influence of sand content on hydraulic conductivity. Overall, the effects of consolidation pressure and sand content on the compressibility and permeability of the sand-clay mixtures were analyzed from the perspectives of skeleton structure and pore features of sand-clay mixture. The correlation between the skeleton structure and sand content of sand-clay mixtures was further confirmed by SEM microphotograph observations.