EFFECT OF CEMENTED FILL ON STRENGTH OF JOINTED SPECIMEN

Abstract

ABSTRACT Several, complicated and difficult structures are constructed or in planning stages under complex geological conditions around the world. Even small variation in analysis and design can cost significantly. It is well recognized that the strength of rock masses depends upon the strain history, extent of discontinuities, orientation of plane of weakness, condition of joints, fill material in closely packed joints and extent of confinement. Several solutions are available for strength of jointed rock mass with a set of discontinuities. There is a great multiplicity in the proposed relationships for the strength of jointed rocks. In the present study, the author conceives the effect of increasing stresses to induce permanent strains. This permanent strain appears as micro crack, macro crack and fracture. A fully developed network of permanent deformations forms joint. The joint may contain deposits of hydraulic and hydrothermal origin commonly known as a fill which may have cementing tendency. The joint factor numerically captures varied engineering possibilities of joints in a rock mass. The joints grow as an effect of loading. The growth of the joints is progressive in nature. It increases the joint factor, which modify the failure stresses. After extensive experimentation significant joint properties affecting the strength of jointed rocks with unfilled joints and joints with cemented fill has been evolved. This factor is called joint modified factor in which number of joints per meter length, orientation of joints and strength along joints and strength along joints are clubbed together. As the in situ determinations of jointed rock mass is costly and time consuming attempts are being made to predict the strength and deformation of rock mass through model test under controlled laboratory conditions In the present work jointed rocks are simulated by preparing specimens of mortar and cemented joints containing PoP were created artificially by inducing paste of PoP inside the joints. The experimental investigations have been carried on PoP cemented at varied joints possibilities specimen. The specimen made of cement and standard sand in the ratio of 1:3 to simulate the rock mass. The samples were cured at the interval of 7 days to create weakly cemented rock mass and at 28 days to make a comparatively stronger rock mass. The strength changes on 7 days and 28 days are incorporated in relation to their peak compressive strength in presence of PoP cemented joints. The specimen was tested under uniaxial compression to determine the various parameters. The results have been analysed in relation to the modified joint factor Trivedi(40) and a simple empirical approach has been found to predict unconfined compressive strength of jointed rocks with PoP cemented joints. The investigation indicates that the results are in conformity with the recent analyses proposed by Trivedi [40].