Experimental Study On Mechanical Properties Of Remolded Mudstone Reinforced By Cement Based On MICP Method

With population growth and economic and social development,the demand for civilian infrastructure has increased dramatically.However,poorly-stabilized mudstone layers are often encountered during new construction,highway foundation construction,and coal mining,which affects people’s lives.At present,China’s current application of mudstone foundation improvement technology mainly includes two types,one is chemical improvement by adding Portland cement,lime,fly ash,etc.The other is physical improvement by adding green sand,gravel,etc.Obviously,the traditional foundation improvement technology is not easy to control and has a great impact on the surrounding environment.Therefore,a new type of mudstone improvement technology is urgently needed to meet the actual engineering needs.Microbial induced calcium carbonate precipitation（MICP）is a method of applying biomineralization technology in soil microscopy to soil consolidation.This technology has many unmatched advantages such as easy control,simple mechanism,and environmental friendliness.Based on the MICP method,this paper mainly remolds mudstone by cementing with microorganisms（Sporosarcina pasteurii）.During the laboratory test,a series of tests including microbial activation culture,scanning electron microscope,direct shear,consolidation,calcium carbonate pickling,and disintegration of mudstone in aqueous solution were carried out.Firstly,the effects of sample particle size,preparation method,and MICP treatment method on calcium carbonate precipitates were studied,and the feasibility of the MICP method for the stability of mudstones was discussed.Finally,the effects of nutrient salt concentration on the mechanical properties,calcium carbonate content and microstructure of cemented samples were analyzed to provide data support for the new mudstone improvement technology.The main research results of this article are:（1）Calcite carbonate crystals can be formed in the sample by soaking the bacteria solution once under the same concentration of nutrient salt（0.5mol/L）.Crystals are deposited at the contact of particles or pores to form a"cementation bridge",which produces a cementation effect and enhances the mechanical properties of the sample.Under different vertical pressures,the strength of cemented specimens gradually increased to a stable value,which was characterized by strain hardening,and the cohesion and internal friction angle increased by 288%and 8.66%,respectively.（2）The comparative test analysis of the disintegration of mudstone in aqueous solution before and after cementation shows that the application of MICP method to the remolded mudstone sample has significant cementation effect,and it shows an improvement in softening performance in the macroscopic view.（3）Under the same reaction conditions（same time and volume）,as the nutrient concentration increases,the shear strength and porosity ratio increase first and then decrease.When the nutrient salt concentration reached 0.5mol/L,the shear strength and porosity were the largest.At this time,the sample cohesion and internal friction angle were 15.5kPa and 18.83°.（4）The content of calcium carbonate increased with the increase of nutrient salt concentration.When the nutrient salt concentration reached 0.7mol/L,the average calcium carbonate content of the sample increased less.The uniformity of the distribution of calcium carbonate crystals is convex with the change of nutrient salt concentration from low to high.The strength of the cemented sample depends on the amount of CaCO₃ crystals produced and their distribution.