A tunnel access shaft was required to be constructed within a geologically complex site that previously served as a sand quarry and had been backfilled with uncontrolled fill to an approximate depth of 14m.
The project requirement was to construct a Diaphragm Wall structure within the complex site conditions to form the tunnel access shaft. There were several issues with the geology on the site including uncertainty regarding the presence of inground obstructions, the stability of the fill, management of the bentonite support fluid in the ground conditions and the presence of possible asbestos containing materials.
The diaphragm wall panels were all constructed using hydraulic grabs under bentonite support fluid.
A second temporary access shaft was required to facilitate a TBM launch/retrieval using segmentally cased interlocking secant piles to enable a dry excavation to be maintained. The tight tolerances maintained on pile position and verticality is an excellent example of Wagstaff Piling’s ability to deliver challenging projects.
