纤维加筋微生物固化砂土的力学特性

微生物固化能有效提高砂土的强度,但同样会导致土体破坏时呈现明显的脆性。为了平衡微生物固化砂土脆性破坏的不利影响,提出纤维加筋与微生物固化相结合的改性方法,即将质量分数为0%,0.05%,0.15%,0.25%和0.30%的聚丙烯纤维与石英砂均匀混合,然后基于微生物诱导碳酸钙沉积(MICP)技术对土样进行固化,并开展了一系列无侧限抗压试验,同时采用酸洗法测定了各组试样中的碳酸钙含量,进一步分析了试样的微观结构及纤维–土颗粒之间的界面作用特征。结果表明:①在微生物固化砂土中掺入纤维,能极大提高土样的无侧限抗压强度和残余强度,并能显著改善土样破坏时的韧性;②纤维掺量对微生物固化砂土的力学特性有重要影响,无侧限抗压强度随纤维掺量总体上呈先增加后减小的趋势,最优纤维掺量为0.15%,峰后残余强度与纤维掺量呈单调正相关关系;③纤维加筋使微生物固化砂土的峰后应力–应变曲线呈阶梯式下降模式,局部存在波浪式起伏特征;④纤维加筋能够提高微生物诱导碳酸钙的沉积效率和产量,与此同时,碳酸钙的胶结作用对纤维加筋效果具有促进作用。纤维加筋技术与MICP技术相结合能够实现优势互补,对提高工程结构的安全性与稳定性具有积极意义。

Mechanical behavior of microbial-induced calcite precipitation (MICP)-treated soil with fiber reinforcement

Microbial cementation can effectively improve the strength of soil, but it can also lead to the obvious brittleness at soil failure. In order to balance the adverse effect of brittleness of the bio-cemented soil, a modified method of combining the fiber reinforcement with the microbial cementation is suggested. The polypropylene fibers, with mass fraction of 0%, 0.05%, 0.15%, 0.25% and 0.30%, are uniformly mixed with silica sand, then the soil samples are bio-cemented based on microbial-induced calcite precipitation (MICP). A series of unconfined compression tests are also carried out, the calcium carbonate content in each group is determined by acid pickling, and the morphological structure of fiber surfaces in soil matrix is characterized by using the scanning electron microscopy (SEM). The result shows that: (1) The fiber reinforcement can greatly improve the unconfined compressive strength and residual strength of soil samples, and can significantly improve the toughness of soil failure. (2) The fiber content has important influence on the mechanical properties of bio-cemented soil. The unconfined compressive strength with fiber content shows a trend of decrease after the first increase in general, the optimal fiber content is 0.15%, and the residual strength after peak is monotonically related with the fiber content. (3) The stress-strain curve of the microorganism solidified sandy soil is in a step-down mode, and the wave type relief features are locally exhibited. (4) The fiber reinforcement can improve the precipitation efficiency and yield of microbial-induced calcite, and at the same time, the bio-cementation effect of the calcium carbonate can promote the effect of fiber reinforcement. The combination of fiber reinforcement technology and MICP technology can realize complementary advantages, which has positive significance for improving the safety and stability of construction.