STUDY OF BEARING CAPACITY OF ROCKS

Abstract

Generally there has been little concern for bearing capacity and settlement of 6oundations on rocks because most of the unweathered intact rocks are stronger and less compressible than concrete. However, foundations supported by rocks also do sometimes ox mrloneebearing capacity fail-ures and settlement and therefore these possibilities must be investigated. The present study has been undertaken to investigate the validity of existing theories on the subject of bearing capacity, Synthetic samples of rock like material were used to oVl3rcome the problem of finding suitable, consistent, natural samples 6f rock. The rock samples were modelled using sand/ plaster and sand/resin mixes, in various proportions. Some actual rock samples were also tested. All the sand/plaster and sand/resin samples were cast as 15.29 cm (6") diameter 10.16 cm (411) deep cylinders while rock samples were pre-pared as cubes of 7.62 cm (3') diamensions, the indentation tests conducted on sand/plaster'and sand/resin samples in-volved `Forcing a 1.56 cm(5/8°') diameter steel die at a cons-tant displacement rate into their top surface. Rock samples were tested for ultimate failure by the same steel dio. 1 For the determination of c and PJ of the sand/plaster samples direct shear test was conducted. For this purpose samples of 6 cm x 6 cm x 2 cm dimensions were cast. Trixial tests were conducted for sand/resin and rock cores for the determination of c and 0 values. Uniaxial compression tests and Brazilian tests were also conducted, The study indicated that the Terzaghit s general failure theory, Ileyerhof's general failure theory, Davis and Booker theory over estimate the bearing capacity, while !Ieyerho?'s• cracking failure theory, Terzaghi's local failure theory, Sower's theory under estimate the bearing capacity, The Agarwal's method gives the bearing capacity values which are closer to measured values, and therefore, should. be used as a method for finding bearing capacity of rocks.