Pishasandstone is a kind of special rock widely distributed in the middle and upperreaches of the Yellow River

which is composed of sand shale and argillaceoussandstone. Due to the low diagenetic degree

the poor cementation between sandgrains

the low structural strength

and containing a large number of clayminerals

its anti-weathering ability is weak. Pisha sandstone becomes sand when encountering wind and becomes mud whenencountering water

which is an important source of "sediment deliveryinto the Yellow River". Based on microbially induced carbonateprecipitation (MICP) technology

the weathered Pisha sandstone soil was improved and reinforced. Aiming to obtain good strengthof improved soil samples and combine with the analysis of physical propertiesand pore structure

the optimal scheme design of improvement for the soilscontaining many fine-grained soils was carried out. Under 12 workingconditions

the artificial control with crystal forms

crystal morphology

andcrystal size were carried out through three experimentalcontrol factors: the concentration of the bacterial solution

the dosage ratioof bacterial solution to calcium source solution

and the molar ratio ofcalcium to urea. The results show that when the urea consumption was 0.4 mol

using the test scheme that the bacterial solution concentration OD was 1.2

the ratio of bacterial solution to calcium source solution was 1:20

and the ratio of calcium to ureawas 1:1

it is found that the calcium carbonate crystal induced by microorganisms wasdeposited in the form of "20−30 μm calcite-vateriteaggregates". These aggregates were filled in the pores of the weatheredPisha sandstone soil to increase the soil compactness

and therefore the sample porosity was reduced by62.4%

enhancing the corrosion resistance. The improved soil also showed goodstrength characteristics with 1 MPa of unconfined compressive strength.Due to the filling and cementation of this calcium carbonate crystal

thestrength remained 43.6% after being saturated with water

which solved theproblem of the soil collapsing in water. The research results expand theapplication of MICP technology in the reinforcement of mixed soil with a largeamount of fine-grained soil and provide a theoretical and experimental basisfor the engineering application of the improvement of weathered Pisha sandstonesoil.