CONSTRUCTION PROBLEMS ON M25(A10-M11) CONTRACT 1

This section of motorway on the North East quadrant of M25 has a very high structural content and includes a cut and cover tunnel 650 m long. The paper describes how the contractor dealt with the general problems of access, programme and construction sequences arising from the location in a heavily-built up urban area, together with certain specific problems. The contract entailed construction of large diaphragm wall panels for both the outer walls of the tunnel and the retaining walls to the east approach. In contrast the retaining walls to the west approach were high modulus steel sheet piles. A large control complex and drainage sump 16 m deep was built adjacent to the tunnel with the excavation stages controlled by the construction of in-situ concrete ring beams. In addition the reinforced earth walls either side of the railway bridge involved the largest area of such walls constructed in the UK. (TRRL)