考虑膨胀土超固结性的渗透特性试验研究

Experimental study on permeability characteristics of over-consolidated expansive soil

膨胀土是一种具有显微裂隙构造的超固结黏土,其渗透特性对卸荷工程稳定性的影响不容忽视,而膨胀土的裂隙性与超固结性息息相关,在研究膨胀土的渗透特性中引入超固结性,对于有效地进行膨胀土边坡设计及治理等十分必要。本文通过不同卸荷水平下的三轴渗透试验,研究超固结比以及不同固结方式(K_(0)固结和等压固结)对膨胀土渗透特性的影响,通过对比卸荷前后的渗透系数变化得到卸荷对原状土渗透特性的影响机制。进行不同水力梯度下的常水头渗透试验,得到原状膨胀土渗透系数与水力梯度间的关系曲线,对比应力作用下和无应力作用下原状土的渗透性规律,从而反映出应力作用对膨胀土渗透特性的影响。试验结果表明:超固结比越大,土体密实程度增大,渗透系数降低。相同轴向应力下,等压固结的土样渗透系数均比K_(0)固结的要大。轴向应力较小时,两种固结状态下的渗透系数非常接近,主要是受到试样内存在的裂隙的控制,随着轴向压力的增大,K_(0)固结土样更为致密,其渗透系数比等压固结状态下低。

Expansive soil is the over-consolidated clay with micro-fracture structure,the influence of permeability characteristics on the stability of unloading engineering cannot be ignored,and the fractures of expansive soil are closely related to the over-consolidation feature.Therefore,it is essential to consider the over-consolidation feature in the permeability characteristics for designing and treating expansive soil slopes.This article studies the influences of over-consolidation ratio and different consolidation methods(K_(0) consolidation and isotropic consolidation)on the permeability characteristics of expansive soil through triaxial permeability tests at different unloading levels.By comparing the changes in permeability coefficient before and after unloading,the mechanism of unloading on the permeability characteristics of undisturbed soil is obtained.The fixed water head permeability tests of undisturbed expansive soil under different hydraulic gradients are conducted,and the relationship between the permeability coefficient and hydraulic gradient is obtained.By comparing the permeability laws of soil under the unstressed state and stress state,the influence of stress on the permeability characteristics of expansive soil is reflected.The test results show that the larger the over-consolidation ratio,the higher the soil compaction degree and the lower the permeability coefficient.The permeability coefficient of isotropic consolidation soil is higher than that of K_(0) consolidation soil under the same axial stress.When the axial stress is small,the permeability coefficients of the two consolidation states are very close,mainly controlled by the cracks in the sample.With the increase of axial pressure,the soil under K_(0) consolidation state become denser,and their permeability coefficient is lower than that under isotropic consolidation state.