酶诱导碳酸钙沉淀技术加固TBM壁后吹填豆砾石最优配比试验及机制研究

Study on the mechanism and optimal proportioning test of pea gravel backfill behind TBM tunnel linings reinforced with enzyme-induced calcium carbonate precipitation(EICP)technology

TBM(tunnel boring machine,简称TBM)隧道中豆砾石作为管片与围岩填充层对管片承载及抗渗具有重要意义,水泥浆液流动性差,无法充满回填层进而导致壁后空洞、灌浆不密实等缺陷,酶诱导碳酸钙沉淀(enzyme-induced calcium carbonate precipitation,简称EICP)技术是作为一种环保高效的加固方法,灌浆材料均为液体具有很好的流动性和扩散性,用于豆砾石回填层灌浆施工有望解决上述问题。为实现吹填豆粒石EICP灌浆最优效果,尝试将标准砂与豆砾石共同作为回填骨料,为定量化分析二者的最优配合比,开展了不同豆砾石与砂的配合比(0.5、0.75、1.0、1.25、1.5)和不同灌浆次数(9、12、15次)的砂柱固化试验。通过无侧限抗压测试、渗透性测试、碳酸钙含量测定、超声波速测定、扫描电镜(scanning electron microscope,简称SEM)试验,从宏观和微观角度分析不同石砂配合比对EICP固化效果的影响。结果表明:EICP加固豆砾石混合砂的最优配比为1:1.5,经15次灌浆加固后,试样单轴抗压强度最高可达4.55 MPa,渗透系数达1.72×10^(-5)m/s;对于含砂量较高的试样,颗粒间孔隙易被碳酸钙晶体填充密实,碳酸钙晶体有效胶结比例较高,结石体无侧限抗压强度较高。研究成果可为EICP技术加固隧道掘进机壁后吹填豆粒石的工程应用提供理论依据。

In tunnel boring machine(TBM)tunnels,the pea gravel as a filling layer between the tunnel lining segments and surrounding rock is of significant importance for the load-bearing capacity and impermeability of the segments.Due to the poor flowability of cement slurry,it fails to adequately fill the backfill layer,resulting in defects such as voids behind the walls and inadequate grouting.Enzyme-induced calcium carbonate precipitation technology(EICP)has emerged as an environmentally friendly and efficient reinforcement method.The grouting material is liquid,exhibiting excellent fluidity and diffusivity,making it a promising solution for grouting in pea gravel backfill layers.To optimize the effectiveness of EICP grouting in pea gravel,an attempt was made to use standard sand and pea gravel as backfill aggregates.In order to quantitatively analyze the optimal mixing ratio,experiments were conducted with different ratios of pea gravel to sand(0.5,0.75,1.0,1.25,1.5)and varying grouting frequencies(9,12,15 times)in sand column solidification tests.Through unconfined compressive strength tests,permeability tests,determination of calcium carbonate content,ultrasonic velocity measurements,and scanning electron microscopy(SEM)microscopic analysis,the impact of different ratios of pea gravel to sand on the solidification effectiveness of EICP was analyzed from both macro and micro perspectives.The results indicate that the optimal ratio for EICP reinforcement of mixed pea gravel and sand is 1:1.5.After 15 grouting cycles,the uniaxial compressive strength of the specimens can reach up to 4.55 MPa,and the permeability coefficient is 1.72×10^(−5) m/s.Samples with a higher sand content exhibit a notable phenomenon where interparticle voids are readily filled and compacted by calcium carbonate crystals.This process results in a higher proportion of effective bonding among calcium carbonate crystals,consequently contributing to an elevated unconfined compressive strength of the stone body.The findings of this study can provide a theoretical basis for the engineering application of EICP technology in reinforcing TBM backfilled pea gravel.