Experimental Study On Mechanical Characteristics Of Fiber Reinforced MICP Treated Sand

Microbial induced calcite precipitation(MICP)has the prominent advantage of significantly improving the mechanical properties of sand soil,while MICP technology also has the obvious shortcoming of causing brittleness.In this thesis,fiber reinforcement and MICP treatment were combined to improve the mechanical properties of MICP treated sand,and a series of laboratory tests were conducted to study the influencing factors of the fiber reinforced MICP treated sand;meanwhile,an evaluation index that could accurately characterize the brittleness of MICP treated sand was presented.The main research contents are as follows.(1)Based on the consolidated drained triaxial test,the effects of the number of cementation treatments,fiber content,fiber length,and initial relative density of sample on the mechanical properties of fiber reinforced MICP treated sand were discussed.And the scanning electron microscope test was utilized to explored the internal mechanism from a microscopic view.The results show that: the number of cementation treatments and the relative density have the obvious influence rule,that is,when the number of treatments is 8times and the compaction state is slightly loose,fiber addition can improve the mechanical properties more cost-effectively;but for fiber content and fiber length,further research is needed to reveal their influences.(2)Based on the unconfined compressive test and the stereo microscope test,the effects of the fiber length and the fiber content on mechanical properties were explored from a macro and micro perspective.The results show that,when the fiber content is lower,the reinforcement effects increase with the increase of the fiber length;and in terms of higher fiber content,as the fiber length increases,the reinforcement effects is first strengthened and then weakened;while the influence law of fiber content is more unitary,as the fiber content increases,the reinforcement effects first increase and then decrease;In the scope of the study,the optimal reinforcement conditions were finally obtained as 0.3% fiber content and 20 mm fiber length.(3)With the experimental rule that the brittleness of MICP treated sand increases with the increase of treatment times,it was concluded that the ratio of elastic energy to total prepeak energy,the failure strain and the maximum average post-peak modulus have the greatest influence on the brittleness characteristics by means of correlation coefficient analysis.Moreover,an evaluation index that can characterize the brittleness of MICP treated sand with low cementation level was proposed,based on the above three parameters.It was proved by experiments that the proposed index could accurately reflect the trend that the brittleness varies with cementation level and cell pressure,and the improvement of the brittleness caused by fiber reinforcement.