Dynamic Characteristics Of Cement Improved Expansive Soil Under Dry-Wet Cycling

By conducting laboratory soil test, dry-wet cycling test and dynamic tri-axial test, this thesis studies the basic physical parameters of cement improved expansive soil, unimproved expansive soil, remolded expansive soil and cement remolded expansive soil. It also analyzes the dynamic characteristics of these four kinds of soil under different confining pressures and influences. The main research contents and results are as follows:The thesis makes a comparative analysis of the basic physical parameters of natural, unimproved and cement improved expansive soils through laboratory soil test. A great difference amount the basic physical parameters of the four kinds of soil, which mainly reflects in grain composition, water ratio limit and free swelling ratio, is discovered. Cement improved expansive soil shares better grain composition than natural and cement remolded expansive soils; while liquid limit, plasticity index and free swelling ratio of cement improved expansive soil are poorer than the other two.Dry-wet cycling tests are conducted for the four kinds of soils which are divided into 3 different groups of dry-wet circle. Dynamic tri-axial tests are implemented for the four types of soils, from which the curves of the four kinds of soils’dynamic stress σd, dynamic modulus Ed, and damping ratio λ versus dynamic strain εd under 3 kinds of confining pressure conditions are obtained. By the means of Origin software and based on y=1/a+bx, values of those soils a and b are calculated and the fitting of relation curve Ed-εd is finished.Through the analysis of the influences of times of dry-wet cycling, vibration times, on-site embankment soil and remolded soil in the lab test on dynamic properties of expansive soil, the results show that, the increasing times of dry-wet cycling would reduce the intensity and stiffness of soil and raise its hysteresis; increasing vibration times decreases soil stiffness and improves hysteresis; the addition of cement improves expansive soil’s intensity and stiffness, as well as the resistant performance of expansive soil to dry-wet cycle in intensity, stiffness and hysteresis, and reduces hysteresis; the intensity and stiffness of on-site embankment soil are better than remolded soil in the lab test, and the former is stronger than the later inresistant to dry-wet cycle in intensity; the hysteresis of on-site embankment soil under cyclic dynamic loading is better than remolded soil in the lab, and the former is stronger than the later in resistance to dry-wet cycling in hysteresis.