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Technical paper: Entrance lock strengthening at Rosyth Royal Dockyard using rock anchorages

Scott Hunter, Graduate Engineer, Kvarner Cementation Foundations. This paper was first published in GE’s June 1998 edition.

Introduction

The entrance lock at Rosyth was constructed between 1908 and 1914 under threat of the First World War. Many of the Royal Navy’s ships and submarines have since passed through the entrance lock, which forms a link from the River Forth to the non-tidal dockyard basin.

Eighty years on the Navy has vacated the dockyard. However, the entrance lock remains under its jurisdiction, its use primarily as a contingency facility for works carried out on nuclear class submarines. The dock is 259m long, 34m wide and 20m deep. It is sealed by removable, floating caissons.

The original construction was carried out by blasting a channel through a Dolerite island, Dhu Crag, on which the entrance lock was constructed. The blast material was used as aggregate for the mass concrete walls forming the dock. The structure, even by today’s standards was an impressive feat of engineering. However today’ requirements are very different to those of the early 1900s. Nuclear regulations now require that the structure is strengthened primarily to increase its capacity to withstand seismic activity. After assessing various alternatives, the project designers recommended an anchorage option, which consisted essentially of pinning the dock to the underlying bedrock, thus increasing its effective mass, and therefore its resistance to seismic disturbance.

A Kvaerner Construction Group joint venture tendered for this contract, comprising Kvaerner Construction and Kva.rner Cementation Foundations. The advantages of the Kvaerner JV was that a project specific team was identified at an early stage. This ensured that any duplication of overheads and potential confrontation, prevalent with main contractor-subcontractor relationships, was reduced to a minimum. This paper describes the design, fabrication and construction phase of the contract. 

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