Effect of Passive Bolt on the Anisotropic Behaviour of Synthetic Jointed Rocks

Abstract

Rock mass in the field consists of various discontinuities in the form of joints, bedding planes, faults, etc. Presence of these discontinuities makes the mass anisotropic in nature, and hence its engineering properties are direction dependent. The properties which affected most are strength and modulus. Therefore, before construction, it is mandatory to assess the strength and the modulus in each direction. However, to quantify anisotropic nature, a dimensionless parameter anisotropic ratio is used. It is defined as the ratio of maximum to minimum strength or modulus considering all the possible directions. Lesser anisotropic ratios indicate the less anisotropy in jointed rocks. If strength and modulus of rock are altered due to some reasons like installation of reinforcement, the anisotropic behaviour will also change. To assess the effect of reinforcement on the anisotropic behaviour of rock, an experimental study was performed in which passive bolts were used. Three different types of synthetic jointed rock specimens having different strength and modulus were prepared. The size of the each specimen of jointed rock was 150 mm × 150 mm × 300 mm (height). Each specimen has one smooth joint orientated between 0° and 90° with respect to the horizontal axis at an interval of 15°. Two fully grouted passive bolts of 6 mm diameter were installed at the centre of the jointed rocks. All the specimens were tested under uniaxial condition. The results indicated that the passive bolts enhanced the modulus and strength of jointed rocks and subsequently reduce the anisotropic behaviour.