Client: St George South London plc
Value of contract: £72,700
These stability works by the McArdle Group at St George Wharf in Vauxhall, London SW8, involved a 17-metre stretch of the existing river wall in order to provide a structural no-fines concrete thickening to the wall during the construction of the Tower at the site.
There were several constraints to the construction of the wall strengthening:
- No vessels were permitted to berth against the river wall during the duration of the works
- No additional lateral loading from the river side of the wall was permitted
- Surcharge loading was not permitted to exceed 10Kn/m2 within 10m of the rear of the river wall
- The hydrostatic imbalance between the river level and the water levels within the exposed foundation had to be controlled to restrict head differences to no more than 2m
- Before any excavation, surveys needed to be carried out to establish the presence of all services and likelihood of unexploded ordnance
- All exposed steelwork / ties / rails exposed within the excavation had be brought to the engineer’s immediate attention to advise on removal strategy. This steelwork would then need to be removed following the engineer’s inspection
- The maximum excavation length was 3m long and no other excavation could be carried out within 6m. Therefore the work was planned so that the 17m of wall was split into seven bays of either 2m or 3m bays to satisfy these requirements
- Muck excavated from the installation of the strengthening was stockpiled and removed following WAC testing to determine the classification of the material. This was carried out using our own road lorries. Inert material was retained on site and used as backfill to the no-fines concrete strengthening works
The works by the McArdle Group consisted of a reduced dig, installation of dowel bars and a mass concrete fill. H16 dowel bars 1400mm long were installed to a depth of 600mm into the rear of the existing river wall with Hilti HY System. The Dowel Bars were placed at 1000mm centres vertically and 1000mm centres horizontally as a maximum.
We used trench sheets to support the sides of the excavation and to give support to the shuttering plywood at either end of the concrete pour.
Works had to be undertaken at low tide – we obtained details of the low tide times from the Port Of London Authority.Various method statements and risk assessments were developed during the progress of the works.
The works were completed in three weeks instead of the four that we were allowed and the contract was completed within budget.
