MINESHAFT CAPPING

Client

Redrow Homes NW Ltd

Reference Contact

Wardell Armstrong (Adrian Rigby)

Contract Value

£360K

Contract Details

Probing, drilling and grouting of redundant mineshafts prior to capping with r.c. concrete slabs.

Investigate the presence of two redundant mineshafts in the footprint of a large proposed housing development and if found, to provide a concrete cap of sufficient bearing strength to withstand the proposed loading of up to 14m of engineered fill.

A series of probe investigations across the area of the site where the shafts were known to exist was undertaken and the positions and presence of both shafts was ultimately confirmed.

A bulk excavation of approximately 48,000m3 commenced down to rockhead upon which the shaft collars were exposed. The excavation was formed in the shape of a terraced bowl such that the plant and equipment used was always outside of the zone of influence of the loose fill material overlying the mineshafts.

Upon reaching rockhead, a 1m thick reinforced concrete slab was constructed over the shaft collar with sufficient bearing on all four sides to withstand the imposed loadings.

After a period during which the concrete had gained adequate strength for it to be progressively loaded, the backfilling process commenced and the whole excavation was filled with selected engineered fill, placed and compacted in layers.

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