A Model Test and the Ultimate Capacity Analysis of Multi-Underreamed Anchors in Silty Clay

Multi-underreamed anchors (MUAs) are widely used in areas with soft soils owing to their high ultimate capacity. To explore the bearing mechanism of MUAs in soft soil, this paper performs a model test of MUAs in silty clay and draws the following conclusions. With an increase in the underream number of MUAs, the ultimate capacity of the anchors significantly increases. The strength of MUAs develops faster and more efficiently than that of non-underreamed anchors but is lost faster after the load reaches its peak value. There are two failure modes of MUAs, namely arch-shaped and cylindrical failure modes. Both of them involve three processes: initial cracking, crack deflection, and crack penetration. The ultimate capacity of ground anchors is composed of end and side bearing capacity. For MUAs, both the side and end resistance effects are improved. Owing to the superposition of the two kinds of effects, the ultimate capacity of MUAs is higher than that of non-underreamed anchors.