| In the geotechnical engineering field,many new materials have showed up to solve some weakness and problems of concrete materials.The strength and deformation of sand have always been the focus of research all the time.This paper proposes a new technology for microbial induced calcium carbonate precipitation to strengthen sand.This novel method of improving sand is not harmful to the environment,and it has been foreign scholars’ research hotspots in recent years.In this paper,a series of tests are carried out around the technology of MICP consolidation of sand,including one-dimensional compression test and triaxial consolidation drainage test.The main point is to study the factor of gradation on the compression and shear properties of MICP-treated sand.Its main contents include:(1)In order to study the influence of the compression characteristics of the graded MCP-reinforced sand,four sets of different grades of sand(Cu=1.1,2,5,10)were designed for one-dimensional compression test.The test results show that:(1).the same Under the stress level and calcium carbonate content,the smaller the unevenness coefficient of the sample,the smaller the strain experienced,the smaller the compressibility and the higher the strength of the sample.(2).Under the same stress level,the MICP strengthened specimen and the unreinforced test Compared with the sample,the compression is smaller and the strength is higher.(2)In order to study the effect of MICP calcium carbonate cementation on sand particle breakage,the fracture characteristics of sand with cu=1.8 under three different degrees of reinforcement and three different stresses were designed.The microscopic behavior of particle breakage was studied by SEM image.The results obtained from the study are as follows:(1).At the same stress level,the amount of particle breakage decreases with the increase of calcium carbonate content;(2)the precipitation of calcium carbonate cement in the MICP-reinforced sample has an inhibitory effect on particle breakage;The three functions of cementation precipitation during the loading process:(a)during the loading process,the calcium carbonate between the particles and the surface of the particles has a good protective effect on the surface of the particles,thereby delaying the cracking;(b)carbonation between the particles Calcium absorbs energy during disintegration;(c)Disintegrated calcium carbonate can be used to fill voids between sand particles,which can also act as a buffer for sand particles during loading;4sem images show higher stress It will lead to a larger amount of fracture,which proves that calcium carbonate cementation can indeed inhibit the occurrence of particle breakage.(3)In order to reveal the influence of the shear characteristics of the graded MCP-reinforced sand,four different grades of sand(Cu=1.1,2,5,10)were designed,three different degrees of reinforcement,and the test was triaxially fixed.The undrained study shows that:(1).Under the same confining pressure and calcium carbonate content,the smaller the unevenness coefficient of the sample,the larger the peak(residual)deviatoric stress,the larger the dilatancy of the sample,and the final volume expansion.The larger the amount;the higher the calcium carbonate content at the same confining pressure and Cu,the larger the peak(residual)deviator stress of the sample,the larger the dilatancy of the sample,and the larger the final volume expansion.(2).Under the same level,the higher the calcium carbonate content of the sample,the smaller the strain experienced by the sample reaching the peak deviatoric stress,and the more obvious the stress softening phenomenon of the sample;the same level of calcium carbonate content of the sample High,the peak mean effective stress,peak stress ratio,residual mean effective stress,and residual stress ratio of the sample are larger;(3).It can be seen from the curve fitting that the peak stress and residual stress of the sample and the calcium carbonate content are the same.There is a good linear relationship between them. |
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