Abstract
The poor impermeability of fractured rock induced by excavation and construction is improved through the application of microbial-induced calcite precipitation (MICP), but it is difficult to monitor and evaluate the permeability reduction under a confining pressure and fracture aperture. For this, the grouting ratio, permeability, and electrochemical impedance of fractured rock with MICP grouting were experimented with, considering the effects of fracture aperture and confining pressure. The equivalent circuit model of grouting-fractured rock is presented, and the corresponding ratio of the electrical resistivity and cross-sectional area of the grouted fracture ( ρ / S ) is indicated by an electrochemical impedance spectroscope (EIS). The relationships of the permeability coefficient, the ρ / S , and the grouting ratio are analysed. The experimental results show that the Darcy permeability coefficient of fractured rock with MICP grouting is reduced by an order of magnitude of 3 to 4. As fracture aperture ranged from 1.28 to 2.56 mm and grouting rate was 0.003 ml/s, the Darcy permeability coefficient decreased with an increase in confining pressure. The grouting ratio and fracture aperture also decreased with a reduction in ρ / S . The results also showed that the permeability reduction of MICP correspondingly increased in these conditions. What is more, the Darcy permeability coefficient of fractured rock grouted by MICP and its permeability reduction may be well predicted by confining pressure and ρ / S . This study provides a new EIS method for predicting the reduction in permeability of MICP grouting-fractured rock and further enriches the application of MICP and EIS techniques in impermeable rock engineering.
Highlights
The poor impermeability performance of fractured rock induced by excavation and construction seriously influences the safety of underground engineering projects such as subways and tunnels [1]
The Microbial-induced calcite precipitation (MICP) technique was applied to the cementation of sands, to enhance bearing capacity and liquefaction resistance, the sequestration of carbon, soil erosion control, groundwater flow control, and the remediation of soil and groundwater impacted by metals [7]
It shows that the seepage quantities of fractured rocks with and without MICP linearly increase with increasing time
Summary
The poor impermeability performance of fractured rock induced by excavation and construction seriously influences the safety of underground engineering projects such as subways and tunnels [1]. Poor impermeability performance is effectively improved by traditional cement-based grouting [2, 3] and polymer grouting [4, 5]. Microbial-induced calcite precipitation (MICP) was elucidated by Mitchell and Santamaria in the 1990s [6] and is a new microbial grouting technique. MICP has low viscosity and grouting pressure, and enables fluid transportation over a longer distance with intrusion into smaller cracks [15, 16]. MICP has some advantages for environmental protection, such as a moderate pH, small shrinkage, and no release of heavy ions or toxic ions [17, 18]
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