Enriched finite element procedures for analyzing decoupled bolts installed in rock mass



Numerical procedures are developed to analyze interaction between fully grouted bolts and rock mass using ‘enriched finite element method (EFEM)’. A solid element intersected by a rock bolt along any arbitrary direction is termed as ‘enriched’ element. The nodes of an enriched element have additional degrees of freedom for determining displacements, stresses developed in the bolt rod. The stiffness of the enriched element is formulated based on properties of rock mass, bolt rod and grout, orientation of the bolt and borehole diameter. Decoupling at grout–bolt interface and elasto-plastic behavior of rock mass have also been incorporated into the EFEM procedures. The results of this method are compared with analytical pull-out test results presented by Li and Stillborg (Int. J. Rock Mech. Min. Sci. 1999; 36:1013–1029). In addition, a numerical example of a bolted tunnel is provided to demonstrate the efficacy of the proposed method for practical applications. Copyright © 2010 John Wiley & Sons, Ltd.