Effects Of Clay’s Content On Mechanical Properties Of Sand With Microbially Induced Calcite Precipitation

Microbially induced calcite precipitation（MICP）is a new type of soil reinforcement technology with sustainable development,low energy consumption,less pollution and excellent performance.Microbial solidification technology is the use of urease produced by microorganisms to metabolize urea to produce ammonium and carbonate ions.The surface of the bacterial cell wall bears a large amount of negative charge,adsorbs cations such as calcium ions in the solution,and hydrolyzes the carbonate ions produced by urea with urease.In combination,a calcium carbonate precipitate is formed with the microorganism as the center,and the precipitate can bind the loose sand particles into a whole,thereby improving the strength of the soil body.As the object to be improved,the characteristics of the sand particles have an important influence on the improvement effect of the soil.This article analyzes the curing effect through penetration test,porosity test,dry density test,water absorption test,calcium carbonate content test,unconfined compressive strength test,consolidated undrained test,scanning electron microscope and X-ray diffraction test.The effects of particle gradation and clay content on the mechanical properties of microbial solidified sand were discussed.The mechanism of the influence of the characteristics of sand on microbial solidification was analyzed,which provided a certain reference for expanding the range of soil suitable for microbial solidification technology.The research results of this article are as follows:（1）Particle grading is an important factor that affects the curing effect of microorganisms.Good particle grading sand has a more significant curing effect than poor particle grading sand.Sand with good particle gradation has a better ratio of coarse and fine particles,which can provide more deposition sites conducive to the generation of calcium carbonate.The calcium carbonate generated is more evenly distributed,which improves the overall strength of the sample.Combined with microscopic test results,the pores in the sand column of well-graded sand can provide better living space for microorganisms and provide more locations for"effectively deposited calcium",so that calcium carbonate induced by microorganisms The internal distribution of the sand column is more uniform,the"structure"of the sand sample after curing is stronger,and the strength characteristics are better.（2）Under a certain confining pressure,as the content of clay particles increases,the thickness of the soil matrix film gradually increases,and t he shear strength of the sand-clay particle mixture decreases accordingly.With the increase of the clay content,the internal friction angle of the sample decreases with the increase of the clay content,and the cohesive force increases with the increase of the clay content.（3）After the sand with different clay content is treated with MICP,its calcium carbonate content,permeability coefficient,porosity,and water absorption are different,but the curing effect is best when the clay content is 9%.Lower clay content can be tter improve the microbial solidification effect;improve the unconfined compressive strength and failure strain of the sand column.The results of the CU test show that the internal friction angle and cohesion tend to increase first and then decrease with the increase of the content of the clay particles,mainly because the lower content of the clay particles can enhance the mechanical interaction between the particles Intensity（4）After MICP treatment,there are three main contact methods between sand-clay particles-Ca CO₃:clay particles contact with calcium carbonate,sand particles contact with calcium carbonate,and clay particles contact with sand particles.When the content of clay particles is small,the clay particles mainly play a filling role.Th e contact mode between sand-clay particles-Ca CO₃ is mainly the contact of sand particles with calcium carbonate and the contact of clay particles with calcium carbonate.At this time,the contact mode between sand-clay particles-Ca CO₃ is mainly based on the contact between clay particles and calcium carbonate and between clay particles and sand particles.The higher content of clay particles will cause the sand particles to be wrapped by the clay particles,preventing the contact between calcium carbonate a nd the sand particles.The generated calcium carbonate mainly adheres to the clay particles,and the adhesion between the clay particles and the sand particles the force is very small.When the sample is subjected to external force,because the sand partic les are wrapped by the clay particles,the slip damage between the clay particles and the sand particles occurs first,reducing the strength of the sample.