Analysis On Improvement Effect Of Expansive Soil By Soil-water Characteristic Curve

Expansive soil expands and intenerates significantly after absorbing water,shrinks and cracks after losing water and deforms repeatedly, and it is typical unsaturated soil which has bad engineering properties, so light-weight structures built on them often suffered serious damage. Chemical improvement is a common treatment method in engineering, and the strength,swell-shrinking property and plasticity index etc. of soil body are usually adopted to evaluate improvement effect. In order to establish the contact between unsaturated soil theory and engineering problems, it probe into putting forward a new evaluation method, namely using soil-water characteristic curve to evaluate improvement effect of expansive soil.It has adopted lime,fly ash and RBI to improve bose expansive soil in indoor, used four mixing amount for each improver, prepared twenty soil samples for each test, conducted basic properties experiments, and obtained soil behavior change law of each soil sample before and after improvement. Contrasting existing evaluation standard, it has obtained the improvement effect of different improved soil, which can provide reference for evaluating improvement effect using soil-water characteristic curve of unsaturated soil at the same time.Dewetting soil-water characteristic curve tests of improved soil prepared simultaneously have been conducted respectively in the suction range of 5～1000KPa using pressure plate extractors. Test results have been coordinated, the soil-water characteristic curves have been drown and test data has been fitted by VG model. We can find that the correlation is very good, which shows that the test data is reasonable and credible.The results show that, the soil behavior change of lime,fly ash stabilized soil has good regularity, in which optimum water content,maximum dry density,free swelling ratio,clay content and plasticity index are decreased with the increase of improver dose, while RBI curing agent is not used to improve expansive soil. By analyzing the soil-water characteristic curve of lime,fly ash stabilized soil, we also find that the soil behavior change has good regularity. Hereby, based on unsaturated soil theory, contrasting free swelling ratio test index, it has probed into that using saturated gravity water content,air entry value,residual water content,curve slope to evaluate improvement effect of expansive soil. Further analysis and research points out that as long as three indexes among four indexes system meet the requirements can improvement effect be achieved. Among them, saturated gravity water content is essential index, and it is ok that only two indexes among the rest three meet the requirements. The results show that soil-water characteristic curve can be used to evaluate improvement effect of expansive soil. The establishment of new index system can help people to analyze engineering properties of improved expansive soil.