Research On Mechanical Properties And Mechanism Of Sand Foundation Based On Microbial System

The majority of soil improvement techniques utilize mechanical energy and chemical grouting,but its high cost,high energy consumption and environmental pollution prompted the exploration of new soil treatment technology.Since the new century,the microbial induced calcium carbonate precipitation(MICP)technology based on the physics,chemistry and biology interdisciplinary has been widely valued and studied.The research results show that this technology has significant effect on improving the engineering properties of the soil(e.g.strength,stiffness,permeability and liquefaction resistance).Compared to traditional soil improvement technology,its environmental friendly characteristic in accordance with the concept of sustainable development.This paper studied on influencing factors of calcium carbonate precipitation induced by sporosarcina pasteurii,as well as the strength of grouting bio-cemented sand were studied.The microstructure of bio-cemented sand column was observed to research the mechanism of cementation.The main study contents and results were listed as follows:(1)The influencing factors of calcium carbonate deposition induced by sporosarcina pasteurii was studied and the selection of calcium source was optimized by contrast experiment.When the concentration of cementation liquid was less than1.0mol/L,the calcium carbonate production rose with the growth of concentration.However,the high concentration inhibited the urease activity and the output of calcium carbonate is reduced.The pH has little influence on microbe induced calcium carbonate when ranging from 6~9.The yield of calcium carbonate rose with the growth of temperature.(2)We took the experimental study on cementation of sand by biogrouting based on the mixed-injection method and the step-injection method.It was found that the latter mothod was more beneficial to the sand treated.The effects of sand specimens were treated by injecting a single concentration or multiple different concentrations of cementing solutions were compared.Based on the bio-treated sand unconfined compressive tests,the failure modes,calcium carbonate content and strength were analyzed.Injecting multiple different concentrations of cementing solutions can be beneficial to obtain relative high compressive strength by using less grouting times.The unconfined compressive strength of specimen is up to 10 MPa.The single and multiple different concentrations injecting methods have no pronounced effect on failure modes and calcium carbonate content.The difference in compressive strength was mainly caused by the maldistribution of calcium carbonate in the sand specimens.(3)In order to find out the the bonding methods between sand particles,the microstructures of bio-treated sand columns were examined by scanning electron microscopy(SEM).The comparison experiment of sand treatment by chemical method was carried out.Based on the experiment,it was found that microbe-induced sphere and spherical aggregates of calcium carbonate crystals around sand particles and the small size of the crystal interlocked with each other to cemented loose particles together,sand particles still retain a certain pore.The chemical formationcalcium carbonate was oblique hexahedral shape and its size was lager than microbially induced calcium carbonate.The loose particles could not be cemented by chemical method.