Model test of the mechanism underpinning water-and-mud inrush disasters during tunnel excavation in sandstone and slate interbedded Presinian strata

Abstract

Water-and-mud inrush disasters have become a major challenge in underground engineering for the construction of tunnels in sandstone and slate interbedded Presinian strata. Disaster prediction and prevention rely in part on realistic modeling and observation of the disaster process, as well as the identification and examination of the underlying mechanisms. Based on the geological conditions and the historical records of the Xinping Tunnel on the China—Laos Railway, an engineering geological model of the water-and-mud inrush was established. A physical model test that accurately reproduced water-and-mud inrush during tunnel excavation in sandstone and slate interbedded strata was also carried out. Then, testing was conducted that examined the stress and strain, seepage pressure, and high-leakage flow of the surrounding rock. The results indicated that the water-and-mud inrush proceeded through three stages: seepage stage, high-leakage flow stage, and attenuation stage. In essence, the disaster was a catastrophic process, during which the water-resistant stratum was reduced to a critical safety thickness, a water-inrush channel formed, and the water-resistant stratum gradually failed under the influence of excavation unloading and in situ stress—seepage coupling. Parameters such as the stress and strain, seepage pressure, and flow of the surrounding rock had evident stage-related features during water-and-mud inrush, and their variation indicated the formation, development, and evolution of the disaster. As the tunnel face advanced, the trend of the stress—strain curve of the surrounding rock shifted from sluggish to rapid in its speed of increase. The characteristics of strain energy density revealed the erosion and weakening effect of groundwater on the surrounding rock. The seepage pressure and the thickness of the water-resistant stratum had a positive linear relationship, and the flow and thickness a negative linear relationship. There was a pivotal point at which the seepage pressure changed from high to low and the flow shifted from low to high. The thickness of the water-resistant stratum corresponding to the pivotal point was deemed the critical safety thickness.

摘要

目的

前震旦系砂板岩互层地层突水突泥灾害给隧道工程建设带来了巨大的困难。本文旨在通过室内模型试验，再现前震旦系砂板岩互层隧道突水突泥灾害的灾变演化过程，分析围岩应力应变、渗透压力与流量随隔水层厚度减小的变化规律，揭示砂板岩互层隧道隔水层渗透失稳突水突泥的灾变诱发机制，为突水突泥灾害的防控提供重要参考。

创新点

1. 建立了前震旦系砂板岩互层隧道突水突泥工程地质模型；2. 通过模型试验再现了前震旦系砂板岩互层隧道突水突泥灾变演化过程；3. 揭示了隔水层厚度减小过程中隧道围岩应力应变、渗流压力与流量等特征参数的变化规律。

方法

1.通过突水突泥灾害统计（图3和6）和地质结构特征（图4和5）分析，构建前震旦系砂板岩互层隧道突水突泥工程地质模型（图7）；2.通过正交试验设计和材料配比试验，研制板岩和砂岩的流固耦合相似材料（图12和13）；3.通过模型试验，再现前震旦系砂板岩互层隧道突水突泥灾变演化过程（图16）。

结论

1. 前震旦系砂板岩互层隧道突水突泥灾变演化过程可划分为渗流阶段、高涌流阶段和衰减阶段3个阶段，围岩应力应变、渗流压力与流量的变化具有阶段性特征；2. 围岩应变能密度特征揭示了地下水对围岩的侵蚀弱化作用。随着应变能密度的增大，围岩稳定性减弱，而拱顶在渗流阶段的应变能密度比拱肩高20.7%；3. 渗流压力与隔水层厚度呈线性正相关关系，流量与隔水层厚度呈线性负相关关系。特征参数突变点为隔水层劣化特征点，该点对应的隔水层厚度为临界安全厚度；4. 突水突泥本质上是在开挖卸荷和应力-渗流耦合作用下突水突泥通道的形成、隔水层厚度减小到临界厚度、隔水层逐渐丧失阻水能力的灾变过程。