微生物矿化风沙土强度及孔隙特性的试验研究

风沙土广泛分布于沙漠地区,其颗粒细小均匀,粒间无粘聚力,易引起风蚀形成沙尘暴的尘源.自行设计实验室制备方法及工艺,通过微生物诱导碳酸钙矿化(microbial induced calcite precipitation,MICP)技术固化沙漠风沙土.分析MICP矿化砂土试样的强度特性,以及菌液浓度,岩土基质的孔隙率及颗粒级配对MICP矿化砂土强度的影响.试验结果表明,当砂土试样的矿化时间为7天,菌液浓度OD600值在0.5～0.8之间,经MICP矿化后的风沙土其无侧限抗压强度平均值为0.66 MPa,内摩擦角平均值为36°,对运用MICP技术矿化沙漠风沙土的可行性进行了试验验证.当岩土基质具有较大的孔隙率且级配良好时,MICP矿化过程更加充分,MICP矿化砂土试样呈现出更好的强度特性.进而,利用核磁共振技术分析MICP矿化前后砂土试样的孔隙特征,测试结果显示经MICP矿化作用后试样的孔隙发育良好,孔隙半径大多分布在30μm～50μm之间,半径为100μm的孔隙提供大部分孔隙体积,且矿化作用后较未矿化前砂土试样孔隙率减小约15%.

THE STRENGTH AND POROSITY PROPERTIES OF MICP-TREATED AEOLIAN SANDY SOIL

The aeolian sandy soil is widely distributed in the desert zone.It is vulnerable to the wind erosion and serves as the dust source of the sandstorm due to its fine particles and the non-cohesion property between particles.The microbial induced calcite precipitation (MICP) is one of the bio-geotechnicai technology.This paper examines the MICP-treated aeolian sandy soil through a self-designed preparation method and process.The strength properties and their influence factors,the concentration of the bacterium,the porosity and grain distributions,are discussed.Testing results indicate that the suitable curing time for obtaining enough strength with good efficiency is 7 d for the MICP-treated sandy soil samples in this study.It is found that the MICPtreated aeolian sandy soil can have an average unconfined compress strength of 0.66 MPa and an average inner friction angle of 36° in this reasonable range of OD600 0.5～0.8.The feasibility of the MICP-treated aeolian sandy soil is verified in the application of bio-crusts in desert engineering.The pore space and the porosity of the soil matrix play an important role in the MICP process.When the soil matrix with high porosity is well-graded,the MICP-treated sandy soil samples may have a high strength.Furthermore,the pore features are tested through the nuclear magnetic resonance (NMR) technology before and after the mineralization.The results indicate that the pores are well developed after the mineralization.The radius of most pores is in the range of 30 μm to 50 μm,and the pore with radius of 100 μm offers most of pore volume.The porosity is decreased by about 15％ after the mineralization as compared with the unmineralized for the same sample.