微生物诱导碳酸钙沉积固化三峡库区黏性紫色土试验研究OA北大核心CSTPCD

Three Gorges Reservoir Area is prone to natural disasters;microbial induced carbonate precipitation(MICP)is a soil consolidation technique with the advantages of low energy consumption,less pollution and great sustainability.The clayey purple soil is the main soil type in the Three Gorges Reservoir Area with small soil pores,and the effect of MICP on its reinforcement is unclear.in this study,the MICP-cured soil specimens,which conformed of different Bacillus bacterium concentrations(OD600=0,0.5,1.0,1.5)and curing fluid concentrations(0,0.5,1.0,1.5 and 2.0 mol/L)were subjected to unconsolidated undrained triaxial shear tests to examine the stress-strain relationship,elastic modulus and shear strength index(cohesion and internal friction angle)while their microstructures were analyzed by SEM tests.The results indicated that the shear strength,elastic modulus and cohesion increased and then decreased with the increase of the bacterium concentration or the curing fluid concentration under the same curing fluid concentration or the same bacterium concentration.The best combination existed when bacterium concentration is OD600=1.0 and the concentration of cement solution is 1.5 mol/L.The average internal friction angle was characterized as increase followed by decrease with the increase of curing fluid concentration,the highest value of internal friction angle was obtained at the bacterium concentration with OD600=0.5 or OD600=1.0 under the same curing fluid concentration.Compared with no treatment,the maximum values of the cured specimens were increased by 62.59%,50.18%,119.50%,and 10.33%(226.00 kPa,6.44 MPa,48.30 kPa and 26.70°),respectively.The SEM revealed that the MICP-reinforced purple soil formed a large number of spherical and flaky calcium carbonate crystals,which distributed on the surface and in the interstices of soil particles.The crystals present on the surface of soil particles increased the surface roughness and soil particle size,which in turn increased the friction angle of the soil,while the crystals present in the interstices of soil particles produced cementation,contributing to the cohesion.The MICP can effectively improve the strength of cohesive purple soil,and the optimal reinforce performance occurred at the combination of the bacterium concentration with OD600=1.0 and curing fluid concentrations with 1.5 mol/L.