Demolition of Elisabeth House, St Peters Square, Manchester City CouncilConnell Brothers were appointed as demolition contractors for the demolition of Elisabeth House in the centre of Manchester.
The building was located adjacent to the war memorial and the central library. The building comprised several retail units on the ground floor with office accommodation to the upper floors and three basement areas.
The building was 7 storey high with a 4 storey podium comprising a reinforced concrete frame on a rectangular grid with an internal light well forming a ground floor car park. From the first floor the building cantilevered out beyond the structural frame. The floors comprised one-way spanning troughs with integral reinforced concrete spine beams spanning in both grid directions between columns. From the absence of shear walls it was assumed that the building gained its structural strength from frame action.
A hoarding was constructed around the building encompassing a road to the rear of the building. The building was then clad in scaffold with monaflex sheeting to enable floor by floor demolition to be carried out.
During the scaffolding works asbestos containing material were removed from throughout the building by Connell Brothers in house Asbestos Removal Specialists. The building was soft stripped with the central light well being used as a drop zone. The internal car park and light well was utilised to position skips within the footprint of the building for waste removal, reducing the amount of space needed externally and thus reducing the impact on city centre traffic.
An investigation into the existing structure was carried out on site to enable a full propping scheme to be developed to allow mini-excavators to be placed on the floors to carry out the floor by floor demolition.
Once the propping had been completed a mobile crane was brought to site and the mini-excavators were lifted onto the roof of the 7 storey building to commence the floor by floor demolition. Concurrent with this work was the removal of a section of the 4 storey structure to the rear by the use of a high reach excavator. Due to the nature of the building structure demolition had to be undertaken carefully to ensure that sufficient structure was maintained to balance the cantilevered floors. Arrisings from the demolition works were removed from the building via an internal drop zone formed by the removal of lift shafts. Floor by floor demolition continued down the main tower section of the building until roof level of the lower sections was reached. From this point floor by floor demolition was undertaken to the entire remaining structure.
Initially the concrete arrisings were removed from site to a local recycling facility. Sufficient arrisings were retained to be crushed to a 6F2 specification for use in the formation of the piling mat.
Following the demolition to ground floor level the ground floor slab and identified foundations were removed. The below ground construction comprised raft foundations bearing on stiff clay. The raft foundations were within the building line and columns cantilevered out from the base to the building line, the columns being tied back with ground beams. In areas of basement construction the raft foundation forms the basement slab.
Prior to removing the ground floor slabs to the basement areas an investigation into the construction of the perimeter retaining walls was undertaken by drilling out core samples to determine if temporary wall supports would be required. Analysis of the cores and construction drawings determined that the retaining walls were of sufficient strength to not require additional support. During this time Connell Brothers were able to accommodate the site investigation works without disrupting the progress of the works. The slabs above the basements were then removed and a bulk excavation undertaken to formation level for construction of a piling mat.
Identified sections of basement walls and ground beams were removed and the perimeter of the excavation battered back with the basements being backfilled with site won 6F2. A geotextile membrane was laid on the formation level and the 6F2 placed in compacted layers to form the piling mat and the access ramp to ground level for the piling equipment.
Following the formation of the piling mat the perimeter hoarding was re-aligned to accommodate the piling contractor.
This challenging city centre project was completed ahead of schedule and without incident. The close working relationship between the Client and Connell Brothers enabled changes to the specification to be carried out without disrupting the overall programme. Working together as a team enabled any problems arrising throughout the works, such as unknown foundations, to be rapidly addressed and solutions found in a timely manner minimising any impact on the overall project.