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In this section you will find:


Caisson shaft units can be supplied with diameters of 2100mm up to 4000mm. Caissons are manufactured in accordance with the requirements of BS EN 1917, and have Kitemark certification where relevant to the scope of BS5911 (2100mm – 3000mm diameters). However 3600mm and 4000mm diameters remain operative within the scope of the ISO9001 accredited Quality Management System.

Open Caisson-sinking techniques permit a shaft structure to be progressively sunk, either under its own weight or with the aid of Caisson jacks, in a controlled manner from the surface to a predetermined depth. Caisson shafts are constructed using a metal cutter ring and base section with rings being added on top as excavation proceeds. The technique is suited to shaft construction through weak soils, high-plasticity clays, silts, sands and gravels; particularly below the water table.

Smoothbore Shaft and Tunnel Segments

Each size is specifically designed to meet the tunnelling industry’s exacting and varied needs, recognising the key criteria as being strength, stability and the capability of performing in all types of ground conditions.

Design features: 
All rings, with the exception of the cutter choker comprise of ordinary segments and two top segments. The top segments have one tapered cross joint in order that they can be installed with an EPDM gasket. The cutter choker comprises of ordinary segments.

All segmental rings are supplied with a factory fitted EPDM gasket as the primary sealing system is immediate upon build.

Cross joint connections are made using a spear bolt passing through a pocket in one segment and a plastic socket in the adjacent segment. Circle joint connections are made using a T bolt passing through a hole in one segment and into a T box in the adjacent segment. Bolts are designed to fully compress the gasket. All connections are sheradised. (Other finishes to fittings, including galvanised, are available on request.)

Ring types:
Segmental ring types are front or back bolted:
1. Standard rings
2. Corbel rings
3. Recessed rings (standard, choker or cutter choker)
4. Choker rings
5. Combined cutter choker rings.

Mix and reinforcement:
Each segment is wet cast to achieve a smooth internal finish. The concrete mix provides a Design Chemical Class 4 (DC4) with a minimum 28 day characteristic strength of 55 N/mm2 . Alternative mixes are available. The segments are reinforced with either a reinforcing cage or structural synthetic and steel fibres to suit both design and customer requirements.

Build methods:
The segmental rings are suitable for underpinning, caisson and chimney construction methods.

We offer both Trapezoidal and Expanded Segmental Smoothbore tunnel linings, designed to provide durability, speed and ease of installation intunnel construction. Trapezoidal tunnel linings are developed to work alongside technologically advanced tunnel boring machines, with linings designed and manufactured to suit exacting project requirements. Tunnel segments can be modified to suit a variety of joint fixings, segment thickness and tunnel diameters. The latest manufacturing techniques incorporate steel fibre dosing to guarantee a high quality, reliable product. The wedge shape design of individual segments eliminates the requirement for a special closure segment.

Shaft Cover and Landing Slabs

Mix and reinforcement 
Slab sections are wet cast in fabricated steel moulds and steel cage reinforced. The concrete mix design is to a standard characteristic strength of 55N/mm2 at 28 days. Alternative mixes are available.

Design features
Design and detailing may be undertaken to the customers design specification. Reinforced concrete cover slabs are generally designed to withstand loads in accordance with the recommendations of British Standard 5400:Part 2 and BD37/01, generally 30 units of Type HB loading, together with the load associated with overburden. Cover slabs can be designed to withstand 45 units of Type HB loading, or loadingspecific to contract. In non-trafficked areas, the slabs may be designed for notional superimposed loads. Landing slabs are designed to an imposed load of 5kN/m2.

Lifting and handling 
Depending on lifting requirements on site, we are able to supply fitted lifting loops or cast in sockets and spherical head lifting anchors.

Quality standards
Shaft Cover Slabs and Landing Slabs are manufactured in accordance with quality management system, BSI accredited to BS EN 9001.

Jacking Pipes 

Jacking Pipes enable pipe installation where the opening of trenches is neither practical nor cost effective. Jacking pipes are made from dense, durable, steel cage reinforced, sulphate resistant concrete having a minimum strength of 50N/mm2 Features include: Self-lubricating joint gasket (Lamell type F-146), Built-in handling system with an extensive range to suit most machines and shields.

They are manufactured in accordance with BS EN 1916 and BS 5911-1 and certified by Quality Assessment under the Kitemark Scheme and BS EN ISO 9001

For more information Download a PDF of the Tunnelling section of our Utilities Guide here.