Research On The Physical And Mechanical Properties Of Microbially Solidified Sand Based On Particle Shape And Particle Size

Microbial Induced Calcium carbonate Precipitation(MICP)technology is a new,natural and environmentally friendly foundation treatment method that can improve the mechanical properties of cured soils by inducing calcium carbonate precipitation to cement loose sand and soil into a single unit,effectively enhancing the strength of the soil.It can effectively improve the mechanical properties of the cured soil and has a good application prospect.However,the MICP technology has problems in practical engineering applications,such as poor homogeneity of the sand and soil,and obvious brittleness when damaged.In order to better exploit the advantages of microbial reinforcement of sandy soils,it is proposed that the optimum particle shape and particle size for microbial reinforcement of sandy soils should be exploited by taking advantage of the characteristics of the sandy soil itself,such as the shape and particle size of sandy soil particles.At this stage,most of the research is on the environment and concentration of microbial solution in the process of microbial reinforcement,but the research on particle size and particle shape is still in a blank stage.This paper is a study of the effect of particle shape and particle size on the physical and mechanical properties of microbially reinforced sand,Sporosarcina pasteurii was used for reinforcement,and three materials,namely calcareous sand,silica sand and glass beads,were selected and sieved to obtain a particle size range of 0.15mm-0.28 mm,0.28mm-0.75 mm,0.4mm-0.9mm and 0.9mm-2mm.different number of rounds of grout reinforcement.Preliminary structural characteristics were observed in microstructure by optical microscope and electron microscope,and the two physical property indices of calcium carbonate content and water absorption test and four mechanical property indices of unconfined compressive strength(UCS)and dynamic strain,dynamic pore pressure and dynamic strength were combined to provide a comprehensive analysis of the characteristics of MICP reinforced sandy soil with different particle shapes and different particle sizes,and to provide a practical application for subsequent engineering The main findings of this paper are as follows.The main findings of this paper are as follows.(1)The fine microscopic test shows that: the glass beads appear round,and the overall occlusion force and internal friction are lower than those of silica sand and calcareous sand.As the particle size of calcareous sand increases,the cementation effect of calcium carbonate between calcareous sand particles gradually decreases,and calcium carbonate only adheres to the surface of the sand particles but does not effectively connect the sand particles.(2)The calcium carbonate content test shows that when the shape of the particles is round,it is not conducive to the attachment of bacteria on the surface of the particles,resulting in a low calcium carbonate crystal content of the specimen.As the average particle size of the sand particles in the specimen increased,the calcium carbonate content of the specimen showed a significant downward trend,and the overall performance showed that the sand soil particle gradation could produce a high calcium carbonate content when it was within the easy liquefaction zone.(3)The water absorption test shows that when the particle shape is round,it increases the inter-particle space,which makes the water absorption rate of the specimen increase.As the particle size of calcareous sand increases,the water absorption rate of the specimen also gradually increases,showing an increasing trend.(4)The unconfined compressive strength test shows that the unconfined compressive strength decreases with the increase of the shape parameter RS and the increase of the particle size of calcareous sand.The particle shape and particle size lead to a decrease in the calcium carbonate content of the specimen,which directly leads to a decrease in the dry density and unconfined compressive strength of the specimen and an increase in the water absorption,thus reducing the reinforcement effect.(5)The unidirectional vibration triaxial test showed that the dynamic strength of MICPreinforced specimens with different particle shapes decreased with increasing particle shape parameters,and the closer the particle shape was to a circle,the worse the MICP reinforcement effect.The dynamic strength of the MICP-reinforced specimens decreased with increasing particle size for different particle sizes,and the larger the particle size of the calcareous sand,the worse the MICP-reinforcement effect.The larger particle size makes the specimen too porous during microbial reinforcement,bacteria and cementation fluid cannot be well retained inside the specimen,too little calcium carbonate precipitation is generated,and the interparticle cementation is weak,which ultimately leads to a weaker resistance of the sand to dynamic loading.