宽级配粗粒土的内部侵蚀试验及其稳定性判别

Experimental Investigation of Internal Stability of Widely Graded Coarse Granular Soil and Criteria of Internal Stability

强降雨入渗条件下宽级配粗粒土中的细颗粒会由于孔隙流体的作用发生内部侵蚀。细颗粒的运移改变了土体的微观结构,土体的水力、力学性质随之变化。利用自行研发的刚性壁渗流侵蚀实验装置,对颗粒粒径介于0.002~10 mm的9种间断及连续颗粒级配粗粒土试样进行渗流侵蚀试验,提出一种新的基于试验的内部稳定性判别标准。实验结果表明:对于宽级配粗颗粒土,内部侵蚀改变了土体的渗透系数,最终导致渗透系数下降;粗颗粒的缺失导致内部稳定性降低,渗流作用下,连续颗粒级配土也可能是内部不稳定土;侵蚀土颗粒累计质量可以度量土体内部稳定性,在容许水力梯度范围内侵蚀量超过总质量5%的土体可划分为内部不稳定土;Kezdi几何标准更适用于评价宽级配粗粒土的内部稳定性。

Fine grains within broadly graded coarse granular soils may be migrated,as a result of seepage action under intense rainfall.The migration of fines results in a change in microstructure and the consequent change in hydraulic properties and mechanical characteristics.A series of one-dimensional downward seepage tests are performed to cause internal erosion in soil samples of 9 kinds of the grain size distribution(either continuous or discontinuous),which contain grain diameter varying from 10 to 0.002mm,utilizing newly developed fixed-wall permeameter.Moreover,a new criterion for the internal stability of coarse granular soil is presented,according to testing results.The results indicate the permeability of coarse particles will be changed and end up with descent once the internal erosion takes place;the absence of coarse particles results in a decline of internal stability.Furthermore,specimens with continuous gradation may be classified as internal instable.The cumulative mass of eroded soil grains by the end of erosion seepage test can measure the internal stability of specimens tested,and the samples are classified as stable if the cumulative mass of eroded particles does not exceed 5%of the total weight of examples.Analysis based on various empirical criteria indicates Kezdi’s granulometric principle is more fitted to evaluate the internal stability of widely graded coarse granular soils than others.