Experimental Study on the Shear Strength Characteristics of Cement Soil-Concrete Interface Under Varying Scale Tests

Stiffened deep cement mixing (SDCM) pile is a new type of composited pile comprised of two interfaces. As the main part of the pile contacting with the surrounding soil and transmitting the load, the interface is particularly critical to the overall bearing capacity. Thus, to figure out the failure mechanism and characteristics of the cement soil-concrete interface, a series of large-scale shear tests, along with corresponding unconfined compressive tests and direct shear tests, were specifically conducted. Three stages of failure process of the cement soil-concrete interface were proposed. Bonding shear strength, peak shear strength and residual shear strength of cement soil-concrete interface were correspondingly analyzed. The results indicated that shear strength of the interface increases with the age and cement mixing ratio, and decreases with the increase of water-cement ratio. Besides, shear strength of the cement soil-concrete interface is positively related to both unconfined compressive strength and shear strength of the cement soil. There exists a clear positive linear correlation between the interface shear strength and unconfined compressive strength or shear strength of the cement soil under the same age. Further analysis with additional experimental data is expected to elucidate their specific contributions to interface strength at different stages.