HKIE TRANSACTIONS 2018, VOL. 25, NO. 3, 153–164 https://doi.org/10.1080/1023697X.2018.1499446 Practical shotcrete rock reinforcement for hard rock openings Keith W K Kong Black & Veatch Hong Kong Limited, Hong Kong, People’s Republic of China ABSTRACT Conventional cast in-situ concrete linings are a costly, time consuming activity and environ- mentally unfriendly solution for supporting hard rock excavations because concrete linings are unable to utilise the inherent strength of the rock. In evidence, by the application of confining pressure via pattern bolts suffices to improve the strength of the rockmass at the underground opening (i.e. cavern or tunnel). In the implementation of this measure, the rock arch formed by the tunnel roof and walls is considered to be a supporting arch capable of sustaining a thrust at the arch ends. However, a potential rock wedge failure, of comparatively small size, is highly probable and may occur between rock bolts. To deal with this issue, shotcrete linings will then be introduced to act as thin “protective skin” liners to support the rock surface with performance similar to a reinforced concrete slab. A detailed discussion of these combination measures, so called “shotcrete rock reinforcement” (SRR), including analysis of the strengthened rock arch and the design of shotcrete linings’ structural capacity according to Eurocodes for hard rock underground openings are presented in the paper together with numerical modelling to check against the boundary deformation of openings. Key issues of the constructability of SRR are also discussed. ARTICLE HISTORY Received 4 July 2017 Accepted 4 June 2018 KEYWORDS Excavation; failure; reinforcement; rockmass; support 1. Introduction With the continuous demand for usable land to accom- modate infrastructures in highly urbanised places such as Hong Kong, the need for sub-terranean solutions such as underground openings in rock including tun- nels and caverns is evident. Many of these underground openings may be used for storage, transporting per- sonnel, conveying materials and supplies, civil facilities, etc. Based on their function and service life time, these openings must be “sustainably” designed with ade- quate factor of safety and constructed with proper work sequence. In terms of sustainable solutions for open- ings in jointed hard rock, rock reinforcement approach is one of the underground rock-support methods and strategies. In short, rock reinforcement is a means of conserving or improving the overall rockmass proper- ties from within the rockmass by techniques such as rock bolts, cable bolts and ground anchors. It is no doubt that rock supports adopting conven- tional cast in-situ concrete lining is an expensive and time-consuming activity for rock caverns and tunnels, and are considered inefficient for supporting hard rock excavations. Hudson and Harrison [1] and Kong and Garshol [2] advised that concrete linings are unable to utilise the inherent strength of the rock, particularly for strong rock with very poor quality of rockmass or better rock in terms of Q-value [3] Q ≥ 0.1. Acknowledged by Kong and Garshol [2], detailed rock reinforcement design comprising rock bolt and shotcrete for underground openings has been provided. However, some specific details of design and construc- tion that have not been discussed in their paper will be further elaborated in the following sections. In addi- tion, the numerical modelling to check against the boundary deformation of openings is utilised in order to obtain a complete picture for the design so that mon- itoring strategy for construction can be implemented. 2. Rock reinforcement 2.1. Rock load According to the classical assumption made by Terzaghi [4], the rock load factors were estimated from a 5.5 m wide steel-arch which supported rail/road tunnel in the Alps during the late 1920s. The rock load factors con- sidered the structural discontinuities of the rockmasses and classified them qualitatively into nine categories for non-squeezing rock, squeezing rock and swelling rock. Kong and Garshol [2] made a short summary based on the findings and studies from Barton et al. [3], Ver- man [5] and Goel et al. [6] that Terzaghi’s rock load class (modified by Deere et al. [7]) had found limitations as summarised below: (i) Terzaghi’s method provides reasonable support pressure for small tunnels (tunnel span of B < 6 m). (ii) It provides over-safe estimates for large tunnels and caverns (with span/diameter of 6 m to 14 m); and CONTACT Keith W K Kong [email protected] © 2018 The Hong Kong Institution of Engineers
Practical shotcrete rock reinforcement for hard rock openings
Jun 15, 2023
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
