A new tunnel roof support system with specific reference to the Brovello Tunnel

Abstract

Recent practical and technical developments in traditional geotechnical and foundation engineering techniques have opened the way to new applications and opportunities for contractors, and more efficient and cost-effective solutions for clients. In the UK contractors have traditionally lagged behind their continental colleagues because of the contractual procedures which have prevented the client, contractor and engineer from working more closely together at the design stage of projects. In addition, the fact that many of the new techniques have been entirely developed by specialist contractors has meant that many consultants have been unaware or unsure of such techniques and their application. The Brovello Tunnel is an example where extreme limitations on the allowable settlement have necessitated specialist expertise not available internally within the client or main contractors' organizations. Potential subcontractors were therefore asked to make their own independent assessment of the ground conditions and submit proposals for a design and build agreement with the main contractor and client. In the light of the sensitivity of the site to settlement, the subcontract was awarded to the subcontractor whose scheme was considered to most significantly reduce the risk of settlement. The approved scheme involved a combination of conventional minipiling and ground anchoring techniques, subvertical and inclined jet mix columns for block ground stabilization and subhorizontal jet mix columns for tunnel roof support. The combination of these techniques has provided a degree of support which could not have been guaranteed by traditional ground stabilization or construction techniques.