OasisLMS

Abstract: This paper presents the results of tension proof tests on rock anchors for underground excavations in Manhattan Schist at 63rd Street Station and 86th Street Station for the Second Avenue Subway Phase 1 expansion in New York City. A total of 23 tied-back rock anchors, 4 rock dowels and 2 prestressed toe anchors in rock were tested. Back-analysis of the test results was performed to investigate the development of bond resistance in the rock. The results were correlated with rock mass properties characterized by borings located within the vicinity of the excavations, with particular focus on site-specific geological features that may influence anchor performance. Rock mass strength was determined using the relationships proposed by Zhang (2010) and Brown and Hoek (1988) based on rock quality designation (RQD) and rock mass rating (RMR) respectively. The RMR approach, which accounts for RQD, joint properties and water conditions, produced less scatter for rock mass strength than using RQD alone. The equation for grout-rock bond resistance proposed by Horvath and Kenny (1979) for small diameter rock-socketed drilled shafts and anchors is recommended, with modifications for improved quantification of rock mass strength using RMR. This paper highlights the influence of geological features on grout-rock interface bond resistance and provides new insights for rock anchor design.

Dr. Chu Ho

Annual Conference Proceedings