ASSESSMENT OF LOADING CHARACTERISTICS OF RESIN GROUTED ROCK BOLTS UNDER DIFFERENT CONFINEMENT PRESSURE THROUGH LABORATORY AND NUMERICAL MODELLING STUDIES

Abstract

Extraction of coal pillars are extracted in a Bord and Pillar Mining Method results into creation of a large void space which is called as goaf. The overlying strata remain suspended above this goaf and usually break due to its own weight after a requisite roof span. It has been also observed during the field study that these overlying strata cave naturally due to induced stresses or sometimes allowed to fall artificially by roof blasting technique in the goaf. This caving process caused the irregular sized and shaped rock fragments to separate from the overlying strata and further disintegrates into smaller sizes by rotation and impact of the floor in the goaf. It results into an increase in the volume of the original separated/blasted rock fragments due to inefficient packing. This increase in volume of broken rock fragments compared to the original intact strata is known as bulking factor. Bulking factor decides the height of caving in the goaf during pillar extraction in any underground mining methods. Bulking factor of rock during artificial roof blasting is entirely different from the natural caving process. Previous studies found the bulking factor of different rock mass to be varying between 1.05 and 1.84. Factors like depth of cover, extraction height and density have direct influence on the rock whereas uniaxial compressive strength, modulus of elasticity and Poisson’s ratio affect indirectly on bulking factor. Bulking depends upon a number of factors during caving of overhanging roof. Strength and discontinuities in rock mass, shape and size of fragments and their packing and height of fall are some important factors which affect the caving height and subsequently in estimation of bulking factor in a rock mass. Extensive literature survey and field studies have been carried out to understand the caving angle and bulking factor for Indian coalfields. An attempt has been also made to determine the caving height using the analytical concept of bulking factor and caving angle.