ABSTRACT
Deep cement mixing (DCM) pile has been widely used to improve the engineering properties of soft clay layer. The DCM pile can effectively reduce settlements of full-scale embankments by studies of Bergado et al. (1999) and Lai et al. (2006) whereas the practice research work by Petchgate et al. (2003a, b; 2004) showed that DCM pile has low strength and stiffness and this kind of pile may lead to low bearing capacity and large settlement (Wu et al., 2005). Consequently, DCM pile is not suitable for medium or high design load constructions (Dong et al., 2004). Hence, a new composite structure of DCM with a concrete core has been introduced. This is called stiffened deep cement mixing (SDCM) pile which employs a concrete plug at the center of DCM as shown in Figure 1. The concrete plug or concrete pile having higher strength and stiffness serves to resist compression stress along the pile shaft and takes most of the load and gradually transmits it to the soil-cement through the interface between the concrete core pile and cementadmixed clay. Therefore, the interface shear strength between the concrete pile and cement-admixed clay must be strong enough to develop the necessary load transfer mechanism. A series of pile load tests have been conducted to investigate the behavior of SDCM piles in China by Dong et al. (2004), Wu et al. (2005), and Zheng et al. (2005). Most of the test results were only bearing capacities of SDCM piles.
