Experimental Study on Strength and Dry–Wet Cycle Characteristics of South China Coastal Soft Soil Solidified by Cement Collaborating Sand Particles

To study the influence of sand particles on the strength and dry–wet cycle characteristics of cement-solidified South China coastal soft clay, a series of cement-solidified South China coastal soft clay samples with different contents and sizes of sand particles were prepared, and unconfined compression strength (UCS) tests, dry–wet cycle tests under seawater and freshwater conditions, scanning electron microscopy tests, and X-ray diffraction tests were carried out. The test results show that the UCS of cement–sand-solidified soil (CS-SS) samples at 7, 14 and 28 d increase as sand particle content increases, and their 28 d strength increase as sand particle size decreases; the average mass loss rate of sand–cement samples ranges from 14% to 61%. The properties of strength and dry–wet cycle durability improve as the sand particle content increases and the sand particle size decreases. Moreover, the anti-dry–wet cycle ability of samples under freshwater conditions is better than those under seawater conditions. The scanning electron microscopy (SEM), X-ray diffraction (XRD), and ion chromatography test results show that the stiffness replacement effect (the high stiffness of sand particles replaces the low stiffness of soft clay), the interface cementation effect between the sand particles and cemented soil, and the microcrack expansion-obstructing effects of sand particles contribute to the improvement of the strength and dry–wet cycle durability of cement–sand solidified South China coastal soft clay.