Abstract: Pisha sandstone is a kind of special rock widely distributed in the middle and upper reaches of the Yellow River, which is composed of sand shale and argillaceous sandstone. Due to the low diagenetic degree, the poor cementation between sand grains, the low structural strength, and containing a large number of clay minerals, its anti-weathering ability is weak. Pisha sandstone becomes sand when encountering wind and becomes mud when encountering water, which is an important source of "sediment delivery into the Yellow River". Based on microbially induced carbonate precipitation (MICP) technology, the weathered Pisha sandstone soil was improved and reinforced. Aiming to obtain good strength of improved soil samples and combine with the analysis of physical properties and pore structure, the optimal scheme design of improvement for the soils containing many fine-grained soils was carried out. Under 12 working conditions, the artificial control with crystal forms, crystal morphology, and crystal size were carried out through three experimental control factors: the concentration of the bacterial solution, the dosage ratio of bacterial solution to calcium source solution, and the molar ratio of calcium to urea. The results show that when the urea consumption was 0.4 mol, using the test scheme that the bacterial solution concentration OD₆₀₀ was 1.2, the ratio of bacterial solution to calcium source solution was 1:20, and the ratio of calcium to urea was 1:1, it is found that the calcium carbonate crystal induced by microorganisms was deposited in the form of "20−30 μm calcite-vaterite aggregates". These aggregates were filled in the pores of the weathered Pisha sandstone soil to increase the soil compactness, and therefore the sample porosity was reduced by 62.4%, enhancing the corrosion resistance. The improved soil also showed good strength characteristics with 1 MPa of unconfined compressive strength. Due to the filling and cementation of this calcium carbonate crystal, the strength remained 43.6% after being saturated with water, which solved the problem of the soil collapsing in water. The research results expand the application of MICP technology in the reinforcement of mixed soil with a large amount of fine-grained soil and provide a theoretical and experimental basis for the engineering application of the improvement of weathered Pisha sandstone soil.

Key words: Pisha sandstone, MICP technology, crystal regulation, pore characteristics