Study On A Kind Of Permeability Test Technology Of Unsaturated Expansive Soil

The slope of Chengdu clay foundation pit may have deformation, softening slope, inclination of pile cantilever, even damage, the main reason is infiltration of moisture caused by rainfall.On the other hand,Chengdu clay is a kind of expansive soil and we contact mostly soil is unsaturated soil in the project.So the permeability measurement of unsaturated expansive soil is very necessary.However, a direct measurement test of unsaturated expansive soil permeability is very few and difficult at present. Therefore, this article is studied how to carry out of unsaturated expansive soil permeability test and device design.On the summary of previous experimental research,this artcle takes the instantaneous profile method as the basic test principle, try to design and improvement of the test device by consider the expansive soil’s particularity and problems of the existing test.The test device consists of the monitoring element, permeability instrument and water supply device. The selection of monitoring components are EC-5 moisture meter,MPS-2 tensiometer and EM-50 data collector.The permeameter instrument is made of stainless steel material, it has water inlet and exhaust pipe at the end, the water supply chamber is designed in the front of the soil samples chamber,the permeameter’s size is 50 cm×10 cm×10 cm, the thickness is 1cm.The water supply device is composed of the water bottle, the Mariotte bottle, water regulating pulley, water supply chamber. What’s more, the operation steps, calculation methods and matters needing attention of test are expounded in this article,therefore, a complete set of test plan is formed. On the other hand,the influence of the unsuitable test device and the improper method on the test results is also analyzed in the feasibility study of the preliminary test.This article selects unsaturated expansive soil in Chengdu area as the object of study. According to the measurement results,we can obtain the SWCC,the curve about permeability with wetting time-length, the curve about permeability with matrix suction, the curve about permeability with water saturation and so on to analyze the unsaturated expansive soil permeability in Chengdu area. The results showed that the unsaturated expansive soil permeability in Chengdu area is very weak,the orders of magnitude is roughly in between 10-10～10-11m/s; the relationship about permeability with wetting time-length, saturation, matrix suction curve is nonlinear, it is very different from the ordinary soil that the curve is the linear.In the moment of initial water entry, the permeability coefficient was from 2.88×10-10m/s to a minimum numerical value 3.19×10-11 m/s. Then,with the process of water injection, its permeability coefficient began to increase. The reason for this phenomenon may be raleted to the special characteristics of expansive soil, the soil particles was swelled and effective pore volume might be reduced when the water was absorbed.