Strengthening sandy soils by microbial methods

Some contemporary methods and materials are available in geotechnical engineering to improve the engineering performance of soils. Bacterial calcium carbonate cementation could be an innovative application by bonding at the particle contacts and increasing the shear strength. Bacteria type is the most effective factor on the calcium carbonate precipitation while incubation time, concentration, and pH were minor effects. The increasing urea concentration reduces the amorphous phase and increases the crystalline phase with vaterite. Meanwhile, the increasing incubation time is very effective transforming the vaterite crystals to calcite. Paenibacillus favisporus U3 forms the maximum calcium carbonate precipitation among the tested ones, and it is utilized for the geotechnical studies. The unit weights of the samples are not changed noticeably by the bacterial procedure. The uniaxial compressive strength of the tested core samples are varying in a quite large range from 66.8 to 204.1 kPa. The young modulus of the treated samples reaches up to 89.4MPa. The Vp and Vs sonic velocity values rise up to 985 and 443 m/s, respectively. The images prove the homogeneous distribution of bacterial carbonate cement material among the soil grains, and it fills the gaps up to 0.5 mm size. The improvement provided by the bacterial treatment is sufficient to support the project loads in very large areas like transportation projects and factory sites. The method can be employed in the associated geotechnical engineering applications.