Monitoring of Tunnel Rock Mass Deformations During Provisional Support Stage: A Case Study

Abstract

The present study evaluates on site the effects of provisional support on the rate of deformation (convergence) of clay-stone of a twin-tube tunnel. The combination of shotcrete, steel lattice, steel retaining, pre-supporting iron bar and Rock bolts can act as structural support in the form of provisional support for new or existing tunnels. Applications of provisional supports as confinement mechanisms to decrease the capacity of convergence can be helpful for distressed rock mass during tunnels digging. Real-size and real-time field monitoring over a period of approximately one (01) year was carried out with a Tachometer “Leica, TS 09” and 3D Displacement Monitoring Objectives fixed on the top heading and on the invert/bench. Wherefore; a sketch of the same cross-section of the tunnel was used in order to define the deformations of the rock mass of the tunnel measured in 3D in successive periods in all directions along the weak rock mass of the fourth class (IV) after the installation of the provisional support. The study shows good results in terms of deformation of the rock mass of the tunnel and satisfactory stability in terms of confinement. Consequently; it was noticed, that there is a relation between the deformations (convergence) in the two tubes along tunnel - when the deformation of the left tube increases the deformation of the right tube decreases -, and that the deformation of the tunnel is a deformation overall of the rock mass and it is the same along the tunnel relative to its rock mass. It can be concluded that there is a reciprocal effect between the two tunnel tubes, which can be considered as a conservation principle of the rock mass.

Internal and External Collapse Analysis of Twin-Tubes Tunnel in the Initial Support Stage

“…The rock mass along the tunnel axis (Figure 2) were classified into different categories based on Geo-mechanical classification system also called Rock mass rating (RMR-system) [26]. The used physical and geotechnical properties of rock mass along the tunnel alignment were already determined by H. Khelalfa et al [27,28].…”

Study on the Synergistic Effect of Primary Support and Surrounding Rock of Large Buried Depth Tunnel in Soft and Fractured Strata

“…P Oreste et al [14] proposed an analysis method for reverse engineering reliable rock mass parameters under probabilistic background. H Khelalfa et al [15] conducted a study on monitoring the deformation of surrounding rock during the temporary support stage after tunnel excavation through a case study.…”