Effect of Microbial Stabilization on the Unconfined Compressive Strength and Bearing Capacity of Weak Soils

Abstract

Weak soils comprise of saturated clays, fine silts and loose sand. These soils are susceptible to failure and pose problems of stability. Therefore, the aim of this study was to study the strength behaviour of weak soil treated with different optical densities (0.4 and 1.5) of a microbe Bacillus pasteurii along with a binding solution of urea and calcium chloride at two different molarities of 0.5 and 1.0 by unconfined compressive strength and plate load tests. The soil specimens of 38-mm and 70-mm diameter treated with microbe Bacillus were also cured for 7 days and subjected to unconfined compressive strength (UCS) tests. Plate load tests were performed at the top of the treated soil on a 0.3-m2 model footing in a 1-m3 test tank to simulate field conditions. The experimental test results showed that the UCS values of treated soil specimen increased by 3 times for 38-mm diameter samples and 3.5 times for 70-mm diameter samples respectively. Similarly, plate load test results showed that there was significant enhancement (2 times) in the bearing capacity of treated soil. The improvement was attributed to the formation of calcium carbonate (CaCO3) precipitation by microbial stabilization of weak soils and with curing period. The x-ray diffraction, energy dispersive x-ray spectroscopy tests and the scanning electron microscopy micrographs also confirmed the formation of CaCO3, which binds the stabilized soil particles and increases flocculation. Thus, the key purpose of this study was to balance out weak soils and utilize them for a variety of field applications as a construction material.