| Microbial induced carbonate precipitation(MICP)can significantly improve the strength and other engineering mechanical properties of calcareous sand.However,the high strength dispersion,significant brittleness under high cementation level and unclear mechanism of strength growth should be paid much more attention.In this thesis,MICP treatment and rubber reinforcement were used to treat the calcareous sand,aiming to investigate the strength and deformation characteristics of bio-cemented calcareous sand and rubber reinforced bio-cemented calcareous sand through conducting a series of unconfined compressive strength(UCS)test and triaxial consolidation drainage(CD)test.Moreover,scanning electron microscopy(SEM)was adopted to observe the microstructure of the MICP-treated samples.Based on the results analysis at macro-and micro-scale,the mechanisms of strength improvement and rubber reinforcement were revealed.The main research contents and conclusions are as follows:(1)Calcareous sand with three different particle size distributions were adopted to study the influence of particle size and cementation level on the unconfined compressive strength and its dispersion of MICP-treated calcareous sand.According to the SEM observation,the mechanism of strength improvement was discussed.The results show that the strength of bio-cemented calcareous sand increases with the increase of cementation level,but the increasing dispersion of strength.The strength dispersion is mainly caused by the difference in the calcareous sand skeleton and the uniformity of calcium carbonate distribution.(2)MICP treatment was used to treat the calcareous sand,aiming to investigate the shear strength parameters and shear deformation characteristics of bio-cemented calcareous sand with different cementation levels through conducting the CD test of the treated sand.In the meantime,the internal mechanism of strength improvement of bio-cemented calcareous sand was further discussed on the basis of SEM test results.The results show that the shear strength of bio-cemented calcareous sand is mainly determined by the cementation of calcium carbonate crystals and the encapsulation of calcium carbonate crystal “shell”.With the increase of cementation level,the brittleness of bio-cemented calcareous sand is more obvious;the internal friction angle increases first and then decreases,while the cohesion increases in the form of curve.(3)Due to the brittle behavior of the highly treated calcareous sand,MICP treatment and rubber reinforcement were introduced to treat the calcareous sand,aiming to investigate the shear strength and deformation characteristics of rubber reinforced bio-cemented calcareous sand with the considerations of different cementation levels and rubber content.Based on the results of CD test and SEM observation,the mechanism of rubber reinforcement was revealed.The results show that as the rubber content increases,the cohesion of the rubber reinforced bio-cemented calcareous sand decreases in the form of curve,while the internal friction angle decreases approximately linear.The brittleness of bio-cemented calcareous sand can be improved with the increasing rubber content.However,the weak cementation interface is introduced at the presence of rubber,resulting in the loss of strength. |
