Laboratory Test Study On The Behavior Of Cement Mixed Soft Clayey Soil Of Shanghai

In nowadays, cement-mixed soil improvement technology has been applied in coastal region widely. A series of technical and economic effects have been obtained. All of these are due to its good performance, extensive material resource, and cheap price. The study measures pH value of soil-cement admixture before hardening and unconfined compression strength (qu) after curing in laboratory first. The relationship between pH value and qu are analyzed. Consequently, a new method on quality check of soil-cement mixed piles is proposed. In addition, the mixing energy affects the mixing uniformity. The relationship between energy consuming and unconfined compression strength was obtained through test. Moreover, energy consumption factors are analyzed. Based on the research work of this study, following new findings are obtained:(1) From measurement on pH value and unconfined compression strength of four kinds soft clay (clay, silty clay, mucky clay and mucky silty clay) in Shanghai, it was found that pH value of soil-cement admixture increases with the increase of curing time. In the prophase of curing (7d preceding), the lower the cement content is, the sooner the increasing velocity of pH value is. After the period, increasing velocity becomes consistent. qu increases with the increase of curing time. The higher the cement content is, the longer the steady time is.(2) There exists a critical initial pH value. When below the critical value, unconfined compression strength increases slowly; by contraries, if initial pH value exceeds the critical value, qu increases rapidly. The critical value will be different due to the variance of soil characters. When the cement ratio comes to a certain value, its influence on pH value becomes smaller and the increase of qu also being slower.(3) During the mixing, energy consumption depends on the mixing method, cement content, mixing velocity, rate of penetration, mixing time and so on. The consumed energy increases with the increase of mixing time. In static mixing, it increases linearly. The higher the cement content is, the larger energy consumed. The reason is that the higher the cement content is, the longer the steady time with the same quantity of soil is, accordingly, the larger the consumed mixing energy is.(4) There exists a critical value on the relationship between unconfined compression strength (qu) and consumed mixing energy (E). When below the critical value, qu increases remarkably with the increase of E. However, when E exceeds the critical value, there is no obvious change of qu. It is to say that after mixing for a period of time, continuous mixing contributes quite small to the unconfined compression strength.