The Channel Tunnel rail link between Britain and France is getting its shape and finish from reinforced concrete. Most of the concrete is in the form of precast reinforced segments. The curved segments are lifted and erected against the tunnel walls as the boring machines advance. Two casting factories, one at each end of the tunnel, provide the precast segments. The British factory will produce about 500,000 segments. The French factory will produce about 240,000 segments. The two factories are making different types of segments because the rock conditions are different at each end of the tunnel.
TWO MANUFACTURING METHODS USED
On the French side the chalk is fractured, so the 3- to 8-ton segments are of the bolted type with neoprene gaskets that keep the lining watertight. On the British side the better-quality chalk allows the segments to be erected directly against the tunnel's walls. The segments are a nonbolted expanded ring design. The 5-foot wide ring of eight segments is held in compression by a wedge-shaped key driven home as the last segment of each ring is positioned.
SHOTCRETE PROVIDES THE FINISHING TOUCH
The inside of the tunnel is to be lined with dry-mix shotcrete. Wire mesh and open design steel arches (called lattice girders) provide reinforcement in the shotcrete.