生物炭联合微生物矿化技术改善软土力学性能试验研究

Enhancement of shear strength of soft soil using MICP combined with biochar

【目的】实现对软土地基的绿色加固对工程建设及生态环境具有重要意义。为此,采用微生物诱导碳酸钙沉积(MICP)技术和生物炭联合固化软土。【方法】首先确定了MICP灌浆最优细菌浓度和胶结液浓度,在此基础上,研究了不同生物炭含量联合微生物矿化技术加固提升软土的抗剪强度参数。通过直剪试验,得到MICP联合生物炭固化软土的内摩擦角和黏聚力。基于扫描电子显微镜(SEM)测试、X射线衍射(XRD)和能谱试验(EDS),获得了固化软土的微观结构、矿物成分及元素分布特征。【结果】结果表明:(1)MICP能够提升软土内摩擦角和黏聚力,在最优菌液浓度OD 600=0.9,胶结液浓度为1.0 mol/L的条件下,养护28 d时,MICP固化软土的最大内摩擦角为11.3°,最大黏聚力为12.15 kPa;添加生物炭后,MICP固化软土内摩擦角和黏聚力得到显著提升,添加12%生物炭,养护28 d时,内摩擦角最大为20.8°,相应条件下的黏聚力最大值为16.61 kPa。养护周期28 d内,试样内摩擦角和黏聚力提升速率在前14 d明显高于后14 d,表明微生物矿化技术主要在养护前期发挥作用。(2)微观测试表明,经MICP处理的软土中均可观察到碳酸钙,添加生物炭后在生物炭和软土界面处观察到大量碳酸钙晶体。(3)EDS测试结果表明,土颗粒表面有明显的钙、碳和氧元素分布。【结论】研究结果证实了生物炭协同MICP技术固化软土具有可行性,为滨海软土地层的绿色加固提供了新的思路。【目的】实现对软土地基的绿色加固对工程建设及生态环境具有重要意义。【方法】采用微生物诱导碳酸钙沉积(MICP)技术和生物炭联合固化软土。首先确定了MICP灌浆最优细菌浓度和胶结液浓度,在此基础上,研究了不同生物炭含量联合微生物矿化技术加固提升软土的抗剪强度参数。通过直剪试验,得到MICP联合生物炭固化软土的内摩擦角和黏聚力。基于扫描电子显微镜(SEM)测试、X射线衍射(XRD)和能谱试验(EDS),获得了固化软土的微观结构、矿物成分及元素分布特征。【结果】结果表明:MICP能够提升软土内摩擦角和黏聚力,最优菌液浓度为OD 600=0.9,胶结液浓度为1.0 mol/L,养护28 d时,MICP固化软土的最大内摩擦角为11.3°,最大黏聚力为12.15 kPa。添加生物炭后,MICP固化软土内摩擦角和黏聚力得到显著提升。最大内摩擦角为添加12%生物炭,养护28 d时的20.8°,相应条件下的黏聚力最大值为16.61 kPa。养护周期28 d内,试样内摩擦角和黏聚力提升速率在前14 d明显高于后14 d,表明微生物矿化技术主要在养护前期发挥作用。微观测试表明:经MICP处理的软土中均可观察到碳酸钙,添加生物炭后在生物炭和软土界面处观察到大量碳酸钙晶体。EDS测试结果表明土颗粒表面有明显的钙、碳和氧元素分布。【结论】研究结果证实了生物炭协同MICP技术固化软土具有可行性,为滨海软土地层的绿色加固提供了新的思路。

[Objective]Reinforcing the soft soil foundations in an environmentally friendly way holds significant importance on engineering construction and ecological environment.Therefore,the microbially induced carbonate precipitation(MICP)combined with bio-char method was introduced to the soft soil.[Methods]The optimal concentration of bacterial solution and cementation solution of MICP-treated soft soil were determined using direct shear test.The effect of bio-char mixing ratio and curing time on the shear strength of MICP-bio-char-treated soft soil were investigated.The scanning electron microscope(SEM),X-ray diffraction(XRD)and Energy Dispersive Spectrometer(EDS)test were employed to reveal the microstructures,mineral composition and distribution characteristics of elements.[Results]The results showed that the optimal parameters for improving the strength of MICP-treated soft soil was 0.9 of OD 600 and 1.0 mol/L of cementation solution concentration,on the 28th day.In this case,the maximum values of internal friction angel and cohesion were 11.3 degrees and 12.15 kPa,respectively.Furthermore,the cohesion and internal friction angle greatly increased with the increase of bio-char mixing ratio and curing time.The optimal values of internal friction angle and cohesion were obtained when the bio-char mixing ratio was 12%and curing time was 28 days,which were 20.8 degrees and 16.61 kPa,respectively.During 28 days of curing time,the growth rates were higher within 14 days than those of later 14 days.Additionally,a large amount of calcium carbonate was observed in the MICP-treated soft soil.The calcium carbonate precipitated on the interface between bio-char and soft soil was the source of strength improvement compared with bio-char treated soft soil.Analysis of EDS indicated that there was a significant distribution of calcium,carbon,and oxygen elements on the surface of the soil sample.[Conclusion]It was demonstrated that the feasibility of bio-char combined with MICP on solidifying the soft soil.Furthermore,the findings of this study provide a new perspective for environmentally friendly reinforcement of soft soil in coastal areas.[Objective]Reinforcing the soft soil foundations in an environmentally friendly way holds significant importance on engineering construction and ecological environment.[Methods]The microbially induced carbonate precipitation(MICP)combined with biochar method was introduced to the soft soil.The biochar mixing ratio and curing time were studied using direct shear test.The microstructures,mineral composition and distribution characteristics of elements were investigated to reveal the precipitation pattern of calcium carbonate by using scanning electron microscope(SEM),X-ray diffraction(XRD)and Energy Dispersive Spectrometer(EDS)test.[Results]The result showed that the optimal parameters for improving the strength of MICP-treated soft soil was OD 600=0.9 and cementation solution concentration=1.0 mol/L.In this case,the maximum values of internal friction angel and cohesion were 11.3 degrees and 12.15 kPa,respectively,when curing time was 28 days.Furthermore,the cohesion and internal friction angle greatly increased with the increase of biochar mixing ratio and curing time.The optimal values of internal friction angle and cohesion were obtained when the biochar mixing ratio was 12%and curing time was 28 days,which were 20.8 degrees and 16.61 kPa,respectively.During 28 days of curing time,the growth rates were higher within 14 days than later 14 days.Additionally,a large amount of calcium carbonate was observed in the MICP-treated soft soil.Moreover,the calcium carbonate precipitated on the interface between bio-char and soft soil was the source of strength improvement compared with bio-char treated soft soil.Analysis of EDS indicated that there is a significant distribution of calcium,carbon,and oxygen elements on the surface of the soil sample.[Conclusion]It was demonstrated that the feasibility of biochar combined with MICP on solidifying the soft soil.Furthermore,the findings of this study provide a new perspective for environmentally friendly reinforcement of soft soil in coastal areas.