| Various types of rocks and concrete are the most widely used construction materials in the field of civil engineering and construction.Concrete structures are prone to cracking in the process of use,and the appearance of cracks seriously affects the life and safety of building structures.Microbially induced carbonate precipitation（MICP）technology has been proposed to have promising applications in crack repair due to its environmental friendliness.In this paper,MICP repair of rock and concrete cracks was carried out to analyze the effects of MICP repair on rock and concrete from macroscopic physical and mechanical properties and fine microstructure studies.The tomographic images of the repaired rock specimens were obtained by CT scanning,a 3D visualization model of the fine microstructure of the rock samples was established,and the fine microstructure of the rock samples was analyzed for qualitative and quantitative characterization.The damage process of different rock samples under axial load was simulated using PFC numerical software based on the discrete unit method to analyze the fine-scale mechanical characteristics and energy changes.The main research contents and results are as follows:（1）Select Bacillus pasteurii as the experimental strain,study the effects of different conditions on its growth characteristics,urease activity and Ca CO3 yield,determine the initial p H,suitable urea,calcium source and other conditions for subsequent experiments Through extensive experimental analysis,determine the optimal MICP working temperature,p H,urea concentration and other conditions,improved perfusion process for controlling initial p H value,and lay the foundation for subsequent wide crack.（2）The effects of microorganisms on the repair of sandstone and concrete fractures were analyzed from macroscopic perspectives by NMR tests,unconfined compressive strength tests,percolation tests,and Ca CO3production rate calculations,respectively.The results showed that the cementation effect of the MICP test products in the pore structure of rock samples could effectively improve the impermeability and mechanical properties of rock samples and concrete specimens.After the microbial remediation,the porosity of rock samples decreased by 35.33%,the permeability decreased by 73.88%,and the percolation rate of concrete specimens decreased significantly.The average unconfined compressive strength of rock samples was increased from 3.915 MPa to 6.831 MPa,and the strength was restored to 46.43%of that of intact rock samples;the average unconfined compressive strength of concrete specimens was increased from 6.248 MPa to 11.953 MPa,and restored to 41.88%of the average strength of intact specimens.（3）XRD results showed that the microbially induced Ca CO3 crystals were mainly calcite and spherulite,of which spherulite accounted for 51.61%and calcite for 48.39%,and no aragonite was found.SEM revealed that in the agglomerates formed by the accumulation of a large number of Ca CO3crystals,the calcite size could reach 3 to 4 times the size of spherulite,which was favorable for cementing sand particles.（4）The pore geometry characteristics of rock samples before and after microbial restoration were analyzed based on micro-CT scanning image analysis technique with NMR T2 distribution of rock samples.The results showed that the pore distribution of the rock samples before and after restoration mainly showed a more typical three-peak structure.The volume of all types of pores decreased after restoration compared with that before restoration,but the percentage of micropores in the pores of rock samples decreased and the percentage of medium and large pores increased after restoration due to the formation of new pores when microorganisms induced Ca CO3 cemented sand particles in the fractures during the restoration process.（5）Microbially induced CaCO3 can fill pores,change the shape of pores,increase the tortuosity of connected pores,and reduce permeability.Due to the limitation of measurement principle and equipment measurement accuracy,CT scan is suitable for characterizing large pore size pores and will not miss isolated pores,but the characterization effect is poor for pores with pore size close to or smaller than voxels;NMR is suitable for characterizing small pore size pores and connected pores,and the characterization effect is poor for isolated pores.（6）By discrete element fine-scale mechanical analysis,it can be found that the repaired rock samples also have typical mechanical characteristics of geotechnical materials.The cemented sand within the fracture of the repaired rock sample increases the number of bonding and contact of the particles,and the peak cohesive energy and strain energy of the rock sample increase,and the additional cohesive force needs to be overcome during the loading and destruction of the rock sample,which is macroscopically manifested as the increase of the strength of the rock samples.91 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