Analysis on Uplift Bearing Mechanisms and Failure Modes of Anchor Bolts in Hard Rock Foundation

To study the uplift bearing mechanisms and failure modes of anchor bolt foundations in rock, considering the influence of buried depths and diameters of anchor bolts, and concrete curing ages, 24 anchor bolt loading tests in the field were conducted on hard granite sites. By distributed optical fiber sensing technology, strain tests were performed on 7 anchor bolts of those specimens, the load transfer mechanisms, load-bearing performance influencing factors, and failure modes and characteristics of the anchor bolts were analyzed. To anchor bolts with large diameters and deep embedded depths in rock foundation, the curves between uplift forces and displacements appeared a hardening trend, the failure mode was mainly the yielding of anchor bars. To anchor bolts with small diameters and shallow embedded depths in rock foundation, the curves between uplift forces and displacements of anchor bolts were a softening type, and the failure mainly occurred in interfaces between anchor bars and concrete, between anchor bolts and the rock masses and in shallow bedrock, they were mainly shear composite failure. To anchor bolts in rock, whose the effective anchor depth was less than 1.6 m, the mean bond strength between anchor bars and fine aggregate concrete was 2.82 MPa, and the shear strength of the interface between concrete and hard granite was not less than 1.89 MPa, the ultimate uplift bearing capacity was significantly influenced by the critical depth-to-diameter ratio, however the concrete cured more than 5 days had a little influence on the ultimate uplift bearing capacity.