Experimental Study on the Enhancement of Waterproof Performance of Shield Tunnel Joints Using Diatomite–MICP Combined Reinforcement Technology

With the continuous development of China’s economy and technology, the number of urban transportation shield tunnels has been increasing. As tunnel depth and diameter grow, the geological conditions become increasingly complex, making leakage at segment joints of shield tunnels a more prominent issue, significantly affecting the sustainable development of urban transportation. To address the issue of water leakage, microbially induced calcium carbonate precipitation (MICP) technology offers a green and environmentally friendly solution. However, relying solely on MICP technology is insufficient to enhance the waterproofing performance of large segment joints of shield tunnel. To address this, this study proposes combining diatomite as both a carrier and filler material with MICP technology, using a diatomite–MICP composite grout to improve the waterproofing performance of tunnel segment joints. First, through laboratory macro-scale tests and micro-morphology analysis, the influence of diatomite dosage on the sealing performance of diatomite–MICP composite grout was systematically studied, and the optimal diatomite dosage was determined. Based on this, a self-developed segment joint waterproofing testing platform was adopted to conduct hydraulic tests on double-seal gasket joints, evaluating the enhancement effect of the composite grout on the overall waterproofing performance of tunnel segment joints. The results indicated that the dosage of diatomite significantly affects the sealing performance of the composite grout, with an optimal dosage of 20% by weight of the bacterial solution. At this dosage, the composite grout achieved the highest density, resulting in maximum unconfined compressive strength and shear strength, as well as the lowest permeability coefficient. The joint water pressure test confirmed that after grouting with a diatomite–MICP composite grout at the optimal dosage of 20%, the breakdown water pressures of the inner and outer seal gaskets at the segment joints reached 2011 kPa and 2019 kPa, representing increases of 15.91% and 16.64% compared to the control group without grouting. This study demonstrates the effectiveness and application potential of the green biomineralization technologies in waterproofing of shield tunnel joints.