Overcoming inclusions within Diaphragm Walls at Cambridge Heath Shaft Whitechapel
Summary
This paper discusses how the Whitechapel Project Team overcame issues regarding the inclusion of foreign material in the Diaphragm Wall panels at Cambridge Heath Shaft, Whitechapel Crossrail station. The shaft is circular in shape and formed of Diaphragm Walls with an internal diameter of 28.0 m and a depth of 32 m. It functions as an intervention and evacuation shaft, also housing railway plant.
On excavation of the shaft two significant Diaphragm Wall inclusions were found. The first comprising a significant vertical strip of foreign material within the Diaphragm Wall and the second significant areas of weak rubble presumably from the made ground at the top of the panel. The repair had to consider the stability of the shaft during the works and this paper describes how this was ensured. The Project Team comprising Crossrail, the Diaphragm Wall contractor (C511), the Station Contractor (C512) and the Designer (C140) worked together to ensure the repair works were safely undertaken without affecting construction programme.
As the inclusions were discovered when the shaft was only partially excavated the Project Team also needed to consider the potential impact on the shaft if they were found to continue below formation level beyond a depth that could be repaired and thus their possible permanent incorporation into the works. Analysis and design work was therefore also undertaken to develop a minimum acceptable repair strategy for this case.
Consideration is also given to the cause of the inclusions and whether it is possible in future to take additional precautions to avoid their occurrence.