表皮葡萄球菌(Staphylococcus epidermidis)X-NM1是从盐湖附近土壤中筛选出的高效碳酸盐矿化菌株,该文以滇中引水工程玉溪段剧烈砂化白云岩为例,利用表皮葡萄球菌X-NM1诱导碳酸钙沉淀技术加固剧烈砂化白云岩.通过无侧限抗压强度、碳酸钙生成含量和微观结构分析等实验,探讨不同胶结液浓度、初始相对密度以及注浆轮次等因素对加固效果的影响.实验结果表明:1)加固后样品的碳酸钙含量、干密度以及无侧限抗压强度随着胶结液浓度的增加均呈先增加后减少的趋势,最优的胶结液浓度为2 mol/L.增加注浆轮次和初始相对密度均可提高砂化白云岩柱体各项物理力学指标,注浆轮次为3轮时,样品的碳酸钙含量达29.62％,强度达7.69 MPa.2)扫描电镜(scanning electron microscope,SEM)结果显示碳酸钙晶体有效填充了 白云岩颗粒表面的孔隙,胶结了 白云岩固体颗粒,对于提高整体强度起到至关重要的作用.3)X-NM 1表皮葡萄球菌能有效诱导生成碳酸钙,对加固剧烈砂化白云岩的效果明显.
Experiment study on reinforcement of heavily sandy dolomite by micro bially induced carbonate precipitation
[Objective]Dolomite sandification is a distinctive adverse geological phenomenon in the Yuxi section of the water diversion project in central Yunnan Province.It directly or indirectly leads to water inrush,sand gush,strength reduction,collapse,and fractures.microbial-induced carbonate precipitation(MICP)is a novel and efficient soil reinforcement method,yet limited research exists on its application in sandy dolomite reinforcement.Staphylococcus epidermidis X-NM1,known for its robust calcium carbonate production ability,holds significant research value.This paper focuses on the severely sandy dolomite in the Yuxi section of the water diversion project in central Yunnan Province.It explores the application of Staphylococcus epidermidis X-NM1 in grouting reinforcement for severely sandy dolomite,studying the influence of cementing liquid concentration,grouting rounds,and initial relative density on the unconfined compressive strength of the reinforced sandy dolomite.[Methods]Staphylococcus epidermidis X-NM1 is cultured to approximately OD600=1.5,and a peristaltic pump is used for the grouting reinforcement experiment.The experiment comprised two stages:firstly,infusing two times the pore volume of bacteria solution at a grouting speed of 1.5 mL/min,and secondly,infusing two times the pore volume of cement solution at the same speed after a 12 h standing period.Three grouting rounds(1,2,3)and seven concentrations of cementation solution(0,0.25,0.50,0.75,1.00,1.50,2.00,2.50 mol/L)are set according to the experimental scheme.Three different initial relative densities(Dr=0.3,0.5,0.7)are considered.The dry density of the samples is determined using the weighing method,and the unconfined compressive strength is tested under various conditions.Finally,the calcium carbonate content of damaged samples is assessed through pickling,and the microstructure is analyzed using scanning electron microscope(SEM)to comprehensively evaluate the experimental outcomes.[Results]The calcium carbonate content,dry density,and unconfined compressive strength of the samples exhibited an initial increase followed by a decrease with the concentration of the cement solution.The optimal concentration of the cementation solution was determined to be 2.00 mol/L.Increased grouting rounds and initial relative density positively impacted the physical and mechanical properties of the sandy dolomite cylinder.With three grouting rounds,the calcium carbonate content reached 29.62％,the dry density was 2.253 g/cm3 and unconfined compressive strength reached 7.69 MPa.There was a nonlinear correlation between the unconfined compressive strength and the content of calcium carbonate.When the content of calcium carbonate was low in the early stage,the unconfined compressive strength would increase slowly.With the increasing content of calcium carbonate,the distribution was more uniform,and the cementing effect was stronger,the unconfined compressive strength value increased at a high speed.SEM results indicated effective filling of surface pores and cementation of dolomite particles by calcium carbonate crystals,crucial for enhancing overall strength.[Conclusions]Through a series of unconfined compressive strength tests,calcium carbonate content tests,dry density tests and other experiments,it is concluded that under certain conditions,Staphylococcus epidermidis X-NM1 can effectively induce calcium carbonate production,demonstrating a significant reinforcing effect on severely sandy dolomite.
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