The Stress Concentration Ratio of Stone Columns under Confined Condition

Abstract

This paper is focused towards investigating the stress concentration ratio ( n ) on stone columns of different backfill materials under confined conditions. Various backfill material modified by sand, lime and cement were used. The backfill materials used are crushed stone crushed stone with 50% sand, crushed stone with 5 and 10 % dry lime, and crushed stone with 2.5 and 5 % cement. The investigation was carried out using model tests of stone column performed inside cylindrical container of 300 mm in diameter and 350 mm in height. The undrained shear strength of the soil prepared in the containers ranged from 5.5 to 13.5 kPa. The results revealed that the values of stress concentration ratio ( n ), ranges from 4 for columns with crushed stone as backfill material, to 7.6 for columns with crushed stone stabilized with 5% cement. The presence of dry lime did not show any significant increase in the stress concentration. In general, it is found that the value of stress concentration ratio ( n ) increases with decreasing the shear strength of surrounding soil from 5.5 to 13.5 kPa. It is found also that the stress concentration ratio ( n ) increases when the total stress was held constant and with increasing the time at different rates depending on the type of the backfill material.