Installation Time of Ground Support during Tunnel Excavation: A Novel Graph Methodology
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pISSN 1226-7988, eISSN 1976-3808 www.springer.com/12205
DOI 10.1007/s12205-020-1079-x
Tunnel Engineering
Installation Time of Ground Support during Tunnel Excavation: A Novel Graph Methodology Kai Su
a,b,c
, Yan-Jun Zhang
a
, Jin-Peng Cui
d
, and Cong-An Li
e
a
State Key Laboratory of Water Resource and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China Key Laboratory of Rock Mechanics in Hydraulic Structural Engineering, Ministry of Education, Wuhan University, Wuhan 430072, China c Hubei Provincial Key Lab of Water System Science for Sponge City Construction, Wuhan University, Wuhan 430072, China d Changjiang Institute of Survey, Planning, Design and Research, Wuhan 430015, China e Huadong Enineering Corporation Limited, Power China Group, Hangzhou 310014, China b
ARTICLE HISTORY
ABSTRACT
Received 18 June 2019 Revised 1st 11 May 2020 Revised 2nd 11 July 2020 Accepted 27 July 2020 Published Online 2 October 2020
Installation time of ground support in many caverns excavation is mainly based on analytical and empirical method, instead of the robust numerical simulations. A novel graph method is proposed to determine the installation time of the support upon finite difference method (FDM) simulation. A three dimensional numerical model for the diversion tunnel of Guandi hydropower station is developed. The curve d-r between the convergence d and the excavation unloading rate r is built up upon one-step excavation simulation. Meanwhile, the curve d-l between d and the distance from the tunnel face l, is established via the step-by-step simulation. Using the dimensionless convergence λ instead of d in both curve d-r and curve dl, curve λ-r and curve λ-l can be yielded to achieve the composite graph r-λ-l. When r = r0, l can be chose as l0 along the identical λ in the comprehensive graph r-λ-l, where r0 is the excavation unloading rate at the critical plastic state and l0 is the distance from the tunnel face to the support installation location. The proposed graph method is demonstrated to meet well with common sense upon the diversion tunnel of Guandi hydropower station and can be conveniently realized in other engineering practice.
KEYWORDS Tunnel excavation Ground support Numerical simulation FDM Graph method
1. Introduction Generally, the stability of an underground engineering in rock is deteriorated during excavation in the presence of embedded faults, joints and weak rock mass, as well as the complex tectonic stress and high in-situ stress level. And more than 80% of the damage occurs within a short period after excavation. For drill and blast excavation, ground support, generally including bolts and shotcrete, is commonly installed after the round being shot and mucked out before drilling, loading, and blasting of the next round. The most purpose of ground support is to stabilize the rock mass, preserve the tunnel after excavation and provide worker safety against possible damage, such as rock burst or collapse (Son and Cording, 2007; Mason and Stacey, 2008). According to the
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