Stability Evaluation of TBM Pilot Tunnels to Rear Blasting Using the Protection Shield

Suk-Min Kong,Seung-Bo Shim,Sang-Il Choi,Dong-Wook Oh,Seong-Won Lee,Hana Lee

doi:10.3390/app11041759

Abstract

Recent studies have increasingly investigated construction methods for tunnel excavation because of growing underground space development. Although the New Austrian tunneling method (NATM)—a representative tunnel excavation method—can be applied to various ground conditions, as well as having good constructability and economic feasibility, it suffers from problems such as vibration and noise. By contrast, excavation using a tunnel boring machine (TBM)—a representative mechanized construction method—affords advantages such as stable excavation, minimized ground and environmental damage, noise, and vibration. However, it cannot be applied easily to various ground conditions, and it suffers from problems such as high construction costs and delays owing to equipment defects. Therefore, the simultaneous pilot tunnel excavation using the TBM—which affords advantages such as constructability, economic feasibility, and minimized noise and vibration—and rear enlargement blasting using NATM was investigated in this study. A protection shield was installed to minimize accidents occurring from equipment defects (a disadvantage of TBM) and analyze the decrease in the effect of NATM blasting, which depends on the use of the protection shield and the separation distance through 3D numerical analysis.

Highlights

Underground space development has attracted increased interest
Advancements have been made in mechanized construction, including tunnel boring machines (TBM) and ground reinforcement technology, and excavation methods that are advantageous in terms of economic feasibility and constructability have been developed
The vibration velocity decreased by 36.02%, 49.29%, 58.86%, and 65.85% as the separation distance between the blasting point and the protection shield was increased to 2 m, 4 m, 8 m, and 20 m, respectively, in the case of using a protection shield compared to the case of not using a protection shield (Figure 7)

Summary

Introduction

Underground space development has attracted increased interest. Advancements have been made in mechanized construction, including tunnel boring machines (TBM) and ground reinforcement technology, and excavation methods that are advantageous in terms of economic feasibility and constructability have been developed. The simultaneous excavation method, which uses a TBM pilot and New Austrian tunneling method (NATM) enlargement, involves excavating a pilot tunnel with a smalldiameter TBM before excavating the full face of the tunnel without producing large disturbances in the surrounding rock mass. There are advantages to investigating, analyzing, and evaluating the ground conditions in advance before performing the main NATM enlargement excavation; simultaneously, the blasting vibration greatly reduces because the center-cut blasting that produces a large vibration can be avoided (Figure 1). Economic efficiency increases because the construction period is shortened by appropriately controlling the pre-excavation and using a TBM with a high excavation speed and enlargement blasting/excavation stages

Objectives

Results

Conclusion