Rock bolt is one of the main supporting members in recent tunnel construction. There are two opinions for using the rock bolt in weak ground, which can be assumed to be continuum ground; rock bolt is effective for weak ground, and rock bolt is almost no effect for weak ground. To understand the effect of rock bolt in weak ground, theoretical solutions are derived. In the solutions, ground is assumed as an elastic infinite thick plate with a circular hole. Rock bolt is assumed as an elastic finite cylinder. Full-bond between the ground and the bolt is assumed. Each solution for ground and rock bolt is expressed by summation of the deformations modes. Substructure method and the point matching method are used to derive the solutions that consider ground and bolt interaction. Numerical results show that the area of the influence of the rock bolt is limited. Moreover, shear stress is larger than axial compressional stress around the rock bolt. Rock bolt have probably little effect on preventing the expansion of plastic region and is little effect for weak ground.
Rock bolts belong to the main support means in tunnel construction, and their functional concepts and effects depend on the type of bolts and geological condition. Rock bolts have been widely used for a long period. However, controversial opinions can be found about the effectiveness of rock bolts in weak ground (continuum ground); rock bolt is effective for weak ground, and rock bolt is almost no effect for weak ground.
The objective of this paper is to improve understanding about a rock bolt support for weak ground. Theoretical solutions rigorously considering the mutual interaction between a rock bolt and the surrounding ground are derived. These solutions are based on two-dimensional axisymmetric elasticity (Chandrashekhara and Muthanna, 1978; Meleshko, 2003; Meleshko and Tokovyy, 2013). The substructure method and the point matching method are used to derive the solution considering the ground-rock bolt interaction.