Experimental Study On The Cracking Law Of Filling Expansive Soil Under Different Working Conditions

Swell-shrink characteristics, fissures and over-consolidation are the three maincharacteristics of expansive soil, among which fissures are the key factors for "everycut will slip, every embankment will collapse" of the expansive soil subgrade. As aresult, to clarify the law of the cracking of expansive soil has an important theoreticalsignificance and engineering value. In previous studies, the affects of fissures to soilstrength, deformation and stability of expansive soil slope were theoretically analyzed,and the simulation tests were aiming at the saturated mud, which had a certain gapwhile being compared with the practical engineering. In this paper, the simulationtests were carried out based on the actual situation of expansive soil filling in highway,the emergency and development laws of the fissures in filling under the differentstates of compactness, dry-wet circle number, with and without the reinforcementmaterials are studied.To ensure the research can be carried out smoothly, the program of the indoorsimulation tests are designed carefully, and the matching test equipment is producedspecifically, which is also the largest size in the same testing by now. The analyticalmethods and the definition of fissure rate are determined, and then the conventionalsoil properties tests of Baise expansive soil are carried out to obtain the necessaryparameters for analyzing the development of fissures.The existing processing technology to obtain the fissures in the soil and thegraph imagery processing function of MATLAB7.0 are comprehensively analyzed,and integrates innovation, the fissures analysis method with four steps of image grayprocessing, image enhancement, image binary and pixel-counting is established, thenthe continuous, dynamic, nondestructive and quantitative observation and statistics ofthe cracking processing of expansive soil can be realized with the MATLAB.According to the existing program of the simulation tests, specimens of 4 kindsof compactness are prepared, and 0～4 times of dry-wet cycling are set, 39 groups ofsimulation tests of unreinforced and reinforced expansive soil specimens arecompleted to obtain the cracking law of filling expansive soil under different workingconditions: the first dry-wet cycling has the most significant effect on thedevelopment of fissures, the width and depth of the fissures increase rapidly, and thefollowing dry-wet cycles also increase the fissure rate, but the effect is less; as the moisture content decreases, the fissure rate increases with a law of "three stages";the fissure rate decreases with the increase of the compactness; reinforced can inhibitthe development of fissures in the expansive soil.The conclusions in the paper can be as the basis and reference for not only thefurther study of the fissures in expansive soil, but also the interpret and improve ofthe new treating technology of the expansive soil subgrade.