Uplift Performance of Anchor Plates Embedded in Cement-Stabilized Backfill

A series of pullout tests is presented in this paper and is used to identify the kinematics of failure and the uplift response of circular anchor plates embedded in sand-cement stabilized layers at distinct normalized embedment depths ($\mathit{H}/\mathit{D}$), where $\mathit{H}$ is the thickness of the treated layer and $\mathit{D}$ is the diameter of the anchor plates. Experimental results show that the uplift capacity of anchor plates embedded in sand backfill layers increases considerably after mixing 3% cement with the backfill material. Distinct failure mechanisms observed for anchor plates embedded in both sand and cement-stabilized backfills are shown to be a function of $\mathit{H}/\mathit{D}$. The addition of cement to the sand backfill leads to an increase in uplift capacity of 9 times for an $\mathit{H}/\mathit{D}$ ratio of 1.0 and of 13 times for an $\mathit{H}/\mathit{D}$ ratio of 2.0. For sand backfill with $\mathit{H}/\mathit{D}=1.0$, the failure surface had a truncated cone shape with a vertical inclination of 22°, whereas for $\mathit{H}/\mathit{D}$ of 1.5 and 2.0, radial cracking was observed, and final failure surfaces had inclinations of 26 and 30°, respectively. Pullout of anchor plates in cement-stabilized backfills at $\mathit{H}/\mathit{D}$ ratios ranging from 1.0 to 2.0 exhibit two distinct characteristics: (a) a linear elastic deformation response at small pullout displacements and (b) a later stage where radial fracturing of the stabilized backfill leads to hardening just prior to failure. Radial cracks starting at the top of the layer near the center of the anchor plates start to propagate only at about 90% of the final uplift failure load, irrespective of $\mathit{H}/\mathit{D}$.