Study on the Control of Underground Rivers by Reverse Faults in Tunnel Site and Selection of Tunnel Elevation

Abstract

Along with the need for western economic development, the number of long tunnel projects which go through mountains is constantly on the rise. In the process of construction, various disaster-causing structures are frequently exposed, which leads to many geological disasters. The traditional idea is that the reverse fault is not easily developed for an underground river, which means that the tunnel elevation design is not considered adequately. When some tunnels cross the bottom of the river, the fractures near the fault between the underground river and the excavation space may be activated and then evolve into channels, causing serious water inrush accidents during construction and operation processes. Taking the Qiyueshan Tunnel site as an example, on the premise of the anatomy of the control mechanism of the reverse fault on the development of the underground river, based on the multiperiod typical structural traces of the tunnel and surface outcrop, it was found that stratifications, dip joints, transverse joints, and tension joints of good aperture grade are important control factors. The cut block easily loses its stability and provides space for karst development, while intermittent uplifting of regional structures provides hydrodynamic conditions for the development of the underground river, causing the hydraulic gradient to be inconsistent in the overall underground river. Finally, the rainwater dynamic monitoring and tracer connectivity are data that can be fully utilized to demonstrate that a reverse fracture can control the development of the underground river. The authors further considered the effect of the vertical zoning of the fault structure and the excavation disturbance, and, drawing on the experience of the relative location of the same site in the same field, put forward the suggestion that the construction of the follow-up tunnel in the study area should be slightly higher than the elevation of the underground river. The research results can provide useful reference for similar engineering problems in the future.

Developments in 3D Visualisation of the Rail Tunnel Subsurface for Inspection and Monitoring

“…Culverts-Small passages allowing watercourses to pass under railway tracks, including underground rivers [235]. Old masonry culverts particularly can be weakened by solution and hydraulic action resulting in partial section collapse, deforming the railbed above and causing water backlog which floods tunnels.…”

Hydraulic Behavior of Karst Aquifers

“…Groundwater inrush is a typical hydrologic natural hazard connected with mining activities. Groundwater inrush hazards from a grouted karst collapse pillar in longwall mining were investigated by Ma et al [17]. The karst collapse pillar represents a common geological structure in northern China coalfields, often acting as an important groundwater inrush pathway in underground mining as it contains a significant number of granular rocks, which can easily migrate under high hydraulic pressure.…”

“…A mechanical model with a floor-pillar-roof system was established, followed by a numerical model to evaluate the continuous instability and groundwater inrush risk. The criteria for the system stability assessment were defined based on comparison of the collective energy and stiffness in the floor-pillar-roof system [17], aimed at eliminating groundwater inrush hazards in coal mines which, in the past, were responsible for casualties in the hundreds of miners.…”

Identification and Treatment of Collapse and Mud Inrush Caused by Deep Karst Trough in Tunnels

“…The related disasters are mainly characterized by climatic instantaneous discharge of water and mud inrush, with great suddenness, high frequency, and great severity [29]. The scale of water inrush caused by underground rivers is large, and the disaster is catastrophic because underground rivers are rich in water sources and greatly affected by rainfall [30]. Li et al [31] studied the major water and mud inrush disasters in Lingjiao Tunnel and concluded that the water-bearing and mud-filled structure was the fracture-induced karstified zone rather than the main fault area.…”