Laboratory Investigation On The Behavior Of Cement Mixed Soft Clayey Soil Of Shanghai

Mixing uniformity parameter of cement and soil determines the character of cement treated soil. If the uniformity were good, so would be the character; if the uniformity were bad, the character would go bad too. A method to determine mixing uniformity is proposed by Shen Shui-Long. With this method, mixing uniformity can be determined by measuring distribution of pH value before cement treated soil hardening. However, measuring this single parameter might not evaluate comprehensive characters of cement treated soil. Therefore, based on the Shen's method, this article proposed a new method using initial pH value and initial electrical conductivity to predict final strength, to avoid inaccuracy and risks brought by Shen's method. To achieve these goals, third and forth layer of Shanghai clayey soil is used. The cement content and water content of variables, cement treated soil's pH value, electrical conductivity, hardness and strength characteristics researching tests were done. The relationships between pH value, electrical conductivity, cement content, water content, curing time and final strength were discussed. Provided experimental basis for Shanghai clayey cement treated soil. Main innovative results of this study are obtained:(1) There is a good relationship between initial electrical conductivity and final strength, which can increase the accuracy of predicting. However, due to the different salinity of different area, this relationship can not be used absolutely. Therefore, Shen's method should be invited to this predicting system, in order to control the quality of cement treated soil much better.(2) There is a good linear relationship between initial pH value and cement mixing ratio which stays on logarithm coordinate. Initial electrical conductivity also has a good linear relationship with cement mixing ratio. When importing other people's data to the relationship of initial pH value and cement mixing ratio, this good relationship maintained. In this way, the effectiveness of this method has also been proved.(3) Cement mixing ratio of variables, when measuring pH value and electrical conductivity at different water specimen mixing ratio, pH and electrical conductivity showed a logarithmic curve shape, but the magnitude of this shape in pH is smaller than the magnitude of electrical conductivity. Comparing data from cement-soil suspension water and data after centrifugation, pH value became smaller after centrifugation, but the variation maintained the same; centrifuged electrical conductivity became greater than the suspension state.(4) Shanghai clayey cement treated soil has a good logarithmic relationship between strength and hardness on logarithm coordinate. Due to the air oxidation, the hardness of out layer of soil-cement specimens is bigger than inner hardness. Comparing to Japanese cement-soil relationship between hardness and strength, the hardness of Japanese cement treated soil is bigger than Shanghai clayey cement treated soil when strength stays at low level. But with the growth of strength, the hardness of Shanghai clayey cement treated soil enhance rapidly with the increase of strength, faster than the increasing speed of Japanese cement treated soil, when the strength reaches a certain level the hardness of Shanghai clayey cement treated soil became higher than the hardness of Japanese cement treated soil.