Experimental study of dynamic performance of loose sandy soil improved with micro-Organisms

Abstract

Due to the increasing number of construction projects, various methods, including more environmentally friendly methods, are used to increase the strength and bearing capacity of soil. Bio-cementation method is one of the newest methods that uses bacteria to form calcium carbonate crystals to make high-strength Metamorphic products. This process can stabilize the soil without breaking the original structure. One of these processes, which are common in nature, is the microbiological deposition of calcium carbonate by enzymatic hydrolysis of urea. Due to the size of soil grains and the size of bacteria used in sediment production, these bacteria will be able to produce sediment in silty, clay and sandy soils that form a wide range of soils. In this research, the effect of microbially induced carbonate precipitation (MICP) on the cyclic properties (liquefaction resistance, secant shear modulus and damping ratio) of loose sand is investigated via performing cyclic triaxial tests. Results revealed that carbonate precipitation could significantly increase the liquefaction resistance of Nikabad sand. So that the required cycles to reach the liquefaction criteria was increased from 6 for unstabilized sand to 97 (at cyclic stress ratio (CSR) of 0.2) for 4 times grouted carbonate precipitated sand. Also, this value was increased to 127 for 6 times grouted carbonate precipitated sand. Moreover, test findings show that CSR has an important effect on liquefaction resistance such that, the number of cycles leading to liquefaction decreased from 127 to 46 with the increase of CSR from 0.2 to 0.3 for 6 times grouted carbonate precipitated sand. Due to the carbonate precipitation, the secant shear modulus of sand increased by up to 67 %, and also the damping ratio of sand increased by up to 50 %