Surrounding rock pressure calculation based on time functions and stress release rate determination of deep soft rock tunnel: taking Zhonghe Tunnel as an example

Abstract

On the basis of the Zhonghe Tunnel project of the An-Lan Expressway, the objective of this study was to determine the appropriate method of calculating the steel arch load and stress release rate during numerical simulation. First of all, based on the monitoring results of six similar tunnel sections where the surrounding rock exerts pressure on the steel arch, using time functions, the rock pressure time history curve could be fitted, two formulas for calculating stable rock pressure in deep tunnels were compared, and the calculation model suitable for the Zhonghe Tunnel project was constructed. Then, a simulation of the Zhonghe Tunnel was performed using Flac3D, and stress release was simulated using the Mana method. By comparing the surrounding rock characteristic curves and the initial support characteristic curves under different stress release rates, the impact pattern of the stress release rate on the support load was summarized, and an appropriate excavation stress release rate was determined based on the stable rock pressure value calculation. It was found that the Zhonghe Tunnel rock pressure calculation model could better depict the change in rock pressure over time based on the empirical formula and Weibull time function. A prediction of the steel arch load of the Zhonghe Tunnel could be made using this method, and the stress release rate of the numerically simulated rock excavation was determined to be 0.5. This study thus provides a basis for the future internal force analysis and support parameter design of support systems.

Characteristics and Evolution of Tectonic Fractures in the Jurassic Lianggaoshan Formation Shale in the Northeast Sichuan Basin

“…Through the fracture cutting relationship of outcrops, cores, and sections, combined with fluid inclusions that had a uniform temperature as part of fill minerals, carbon and oxygen isotope analysis of the filler and acoustic emission stage experimental results matching the burial evolutionary history, we can determine the formation period of the fractures of the Lianggaoshan Formation in Northeast Sichuan. The first stage was the Late Yanshan-Early Himalayan tectonic movement (72~55 Ma), and the Late Cretaceous Xuefeng intracontinental orogeny system was part of the NW-trending extension deformation tectonic activity [50]. The study area was affected by far-field compressive stress and SE extrusion and structural stress, from a maximum depth to uplift and denudation; this activity formed the first phase of WNW-NNW-trending conjugate shear fractures, filler-captured fluid inclusions had normalized temperatures within 110~140 • C, and the depths of the Lianggaoshan Formation in this stage were 4223~4882 m (Figure 16).…”

Statistical Characteristics of Stress Changes in Tunnel Surrounding Rock Based on Random Discrete Variability of Geotechnical Materials

“…Chen et al [24] studied the influence of support parameters and excavation methods on statistical distribution characteristics of surrounding rock pressures in shallow buried metro tunnels. Ding et al [25] studied surrounding rock pressure calculations based on the time functions and stress release rate determination of deep soft-rock tunnels.…”