Experimental Study On Expansive Soil Modified With Cement

Expansive soil as one of typical unsaturated soil, it is a great harm to water conservancy project and highway engineering because of its characteristic that expands when sucking water and contracts when losing water. Expansive soil problem is very hard to prevent, it has been paid high attention all over the world. Expansive soil problem has been a great harm to South-to-North Water Diversion Project, because of expansive soil problem the channel will break and collapse, so how to prevent expansive soil problem is very important. Chemistry modified expansive soil has been a usual way to deal with expansive problem because of its good cost performance. Modified expansive soil with cement is a good way to deal with expansive soil problem and because cement has little pollution to water, it do a better job than lime and fly-ash in expansive soil channel project.With the research object of expansive soil in Nanyang intermingled by cement and by the physical experiments, it is found out that using cement to modify expansive soil has effect on the character of expansion and contraction. In order to find out the best cement content, physical experiments with different cement content were carry out. Expansive soil as one of unsaturated soil, its strength is not only depends on cohesion and friction angle but also suction. In order to find out the effect of suction to the strength of expansive soil and the difference between expansive soil to modified expansive soil, unsaturated direct shear experiments were carry out in the control of different vertical pressure and suction. By the results of the experiments above, main research findings can be obtained as follows:1. The free expansion efficiency and contraction coefficient of expansive soil are reduced by intermingle cement. The rseults shows that the expansion efficiency of middle expansion soil reduce up to 28% and the expansion efficiency of weak expansion soil reduce up to 17%. The contraction coefficient of middle expansive soil reduces up to 0.3.2. Increase the content of cement will improve the modified effect,but as the content of cement reach to a certain degree,there is no more change of modified effect.The experiment result shows that the best cement content of middle expansive soil is 6% and the best cement content of weak expansive soil is 4%.3. The strength of expansive soil is improved a lot by intermingle cement. The peak value of shear strength can be found out clearly in experiments of expansive soil modified by cement that do not appear in the experiments of expansive soil. The main strength of expansive soil modified by cement is consist of cohesion and friction angle and cement frame, only a little strength is consist of suction,but suction play an important role in the strength of expansive soil.During shear process expansive soil modified by cement expand because of the cement frame make the soil more dense,but the expansive soil contract during shear process.