Lime- and Cement-Treated Sandy Lean Clay for Highway Subgrade in China

AbstractSandy lean clay (SLC) has a high content of fine sand and silt with poor compressibility and water stability. It threatens the structural stability of highways in regions where this soil type is common. Improvement of SLC for enhancing highway structural stability has attracted wide research interest. Therefore, based on a study of the basic physical-mechanical characteristics of sandy lean clay along the Puyong Expressway, the water stability of the compacted soils was investigated based on a series of indices, including cohesion, angle of internal friction, and degree of compaction. The characteristics of cement- or lime-treated soil were also studied. The results show that the water status has a great effect on the cohesion of SLC. The soaked California bearing ratio (CBR) for untreated SLC was only about 3% to 37% that of unsoaked CBR, depending on the moisture content, indicating that untreated SLC has very weak water stability. It is suggested that the water content of SLC should be controlled at a level slightly higher than the optimal moisture content (ωopt+2%) during compaction. The degree of compaction should not be used as the compaction quality control index when the subgrade is filled with SLC. CBR and other strength indicators should be used as the compaction quality control indices of SLC subgrade. Based on the results of numerical simulations using the finite-element method, improvement measures of each layer and the corresponding waterproof measures of the SLC subgrade are recommended when the embankment is 25 m thick.