Zeen Wan

The stability of surrounding rock in operational tunnels is critically influenced by the degradation of its mechanical properties under repeated disturbances. To investigate the evolutionary patterns of mechanical performance and resistivity in surrounding rock under such conditions, this study conducted uniaxial cyclic loading–unloading experiments on limestone core samples while simultaneously monitoring resistivity. The results demonstrate a significant coupling relationship between rock pressure and resistivity: resistivity decreases with increasing pressure and increases upon unloading, exhibiting a characteristic “steep–gentle–steep” nonlinear trend. A quantitative model of the pressure-resistivity relationship was established, revealing the mechanisms behind resistivity changes from the perspectives of micro-fracture closure, propagation, and the evolution of conductive pathways. Furthermore, a three-phase rock resistivity model (rock matrix–pore water–pore gas), improved by integrating Maxwell’s conductivity formula with a series-parallel model, was developed. This model accurately reflects the influence of porosity, saturation, and volume changes on resistivity. The findings confirm that resistivity serves as a sensitive indicator for characterizing rock damage. This research provides a theoretical foundation and a novel, non-destructive technical approach for the stability monitoring and early warning of surrounding rock in operational tunnels.

Water–bearing fractures and seepage–prone zones ahead of tunnel faces may evolve rapidly under excavation–induced disturbance, making early identification and process tracking essential for risk mitigation. Cross–hole electrical resistivity tomography (ERT) is sensitive to fluid–controlled conductivity contrasts, but time–series interpretation based on independently inverted snapshots is often unreliable due to ill–posedness, noise, and temporal inconsistency. In this study, we propose an improved time–lapse ERT inversion framework for monitoring evolving water–bearing fractures ahead of tunnels. The method is formulated as a baseline–anchored, Occam–consistent difference inversion that directly estimates resistivity changes relative to an initial state, incorporating error–aware weighting of differenced data and anisotropic regularization adapted to cross–hole sensitivity, so that temporal coherence is enforced during inversion rather than through post hoc differencing. Synthetic verification is conducted using three dynamic scenarios representing horizontal, vertical, and diagonal migration of conductive water–bearing pathways between boreholes. Quantitative comparison against independent inversion across all scenarios and time steps demonstrates that the proposed framework substantially reduces the root mean square error and mean relative error of the recovered resistivity, while significantly improving the spatial correlation coefficient between the recovered and true models, with the largest improvements observed in the diagonal–migration scenario. The reconstructed change maps exhibit more compact anomaly geometry and delineate evolution corridors aligned with the prescribed trajectories, whereas independent inversion produces diffuse and epoch–dependent change patterns. These results indicate that the proposed time–lapse inversion framework provides a more reliable basis for interpreting evolving seepage–related conductive structures in tunnel–ahead investigations.

In the process of shield tunneling in clayey strata, the fine-grained clay mineral components in the soil easily adhere to the cutter plate. The clay adhering to the cutterhead and the soil compartment then solidifies and hardens, which results in the production of mud cake and clogging. At present, research on cutter plates in clayey ground is limited and has focused mostly on static tests or simplified models. There is a lack of in-depth studies on the effect of temperature on clay adhesion, which is crucial for understanding the clogging risks. In this study, we independently researched and developed a rotary adhesion tester to investigate the adhesion effect and adhesion force change in a shield cutter plate under the influence of different temperatures, water contents (ω), and clay types, revealing the change rule of the adhesion effect under the joint influence of the temperature and the consistency index (I_c). This study provides experimental evidence and an empirical model for assessing the clogging risk in shield tunneling through clay strata, offering valuable insights that support the efficient operation of earth pressure balance (EPB) shields.

Given the prevalent issue of earth pressure balance shield tunneling encountering spewing in water-rich sandy strata, a dedicated soil discharge model test system was devised. Through comprehensive tests on both unconditioned and conditioned soil under submerged conditions, this system unveiled the temporal distribution patterns of water pressure throughout the soil discharge and discharge phases. The test results show that in the case of unconditioned soil, once the water pressure within the soil chamber (Pt) surpasses 100 kPa, significant fluctuations occur upon opening the soil outlet, leading to a heightened risk of spewing. The severity of spewing can be gauged by analyzing both the average water pressure at the measurement point and the coefficient of variation in water pressure. The water pressure and water flow in the soil chamber have a great influence on the water pressure distribution in the soil discharge process. Changing the spiral speed n and soil discharge opening ratio ξ cannot restrain the spewing. For conditioned soil, individual agents like foaming agent and bentonite are prone to being washed away under high water pressure. Bentonite combined with a high molecular polymer can effectively seal the dominant flow channels within the sandy soil gap. Through the use of a shield tunnel within the Nanchang Metro, the soil conditioning system underwent renovation, introducing a spewing prevention technology employing multiple pipeline quantitative injections. This conditioning approach effectively mitigated spewing issues and enhanced soil discharge efficiency, offering valuable insights for similar engineering endeavors.

Soil conditioning technology is commonly applied to prevent mud caking and soil clogging in earth pressure balance (EPB) shield tunneling and to ensure continuous and efficient construction in highly viscous clay and weathered mudstone strata. In the note, the properties of soil conditioning agents and their interactions are investigated through a series of experimental tests and field construction applications in Changchun Metro Line 2, China. Tangential adhesion tests are carried out to learn the adhesion strength and the torque change relationship between the soil and the metal disk, by which the soil conditioning effect is evaluated. The results indicate that there is a certain interaction between the commercial foam agent and the customized anticlay agent and that the foam agent solution’s concentration and anticlay agent amount play an important role in determining the foam expansion ratio (FER) and the half-life time (HT). When the foam agent solution’s concentration is low, the anticlay agent can increase the FER and decrease the HT. When the foam agent solution’s concentration exceeds 4%, an opposite pattern is observed. It is also found that the composite application of an anticlay agent and a foam agent can significantly decrease the torque and adhesion strength of the weathered mudstone. Torque and adhesion strength can reflect the adhesion of chemically conditioned soil better than the consistency index, which has a good effect on the evaluation of unconditioned soil. Finally, field implementation indicates that mud caking and soil clogging were avoided by the application of the two conditioning agents in the EPB shield tunneling construction of Changchun Metro Line 2, China, and the thrust and torque of the shield were reduced.