Building work in Wigan often turns on what lies beneath the surface. Much of the borough sits on a former coalfield, so construction services here — from extensions to new-build housing and commercial units — frequently begin with checks for old workings, made ground and unstable fill before any foundation design is settled.
Why the ground beneath Wigan needs attention
Wigan was at the heart of the Lancashire Coalfield. Decades of deep and shallow mining left a legacy of disused shafts, collapsed workings and altered ground across areas such as Ince, Hindley, Platt Bridge and Aspull.
That history matters because it affects how the ground behaves under load. Shallow workings can collapse and create subsidence at the surface, while old shafts may be poorly recorded or capped to standards that no longer satisfy current guidance.
"Made ground" is also common — soil that has been deposited or reworked by people rather than laid down naturally. Around former collieries, spoil tips and infilled clay pits, the ground may contain ash, slag, brick rubble and other fill of variable strength. This can settle unevenly and is rarely suitable to build on without investigation.
Coal Authority searches and identifying made ground
Building work in Wigan often turns on what lies beneath the surface.
Most projects in a former-coalfield area start with a Coal Authority search. This is a report that shows whether a site falls within a "Development High Risk Area" and flags recorded mine entries, past workings and any reported subsidence nearby.
A standard search will not tell you everything. Records from early mining are patchy, so a clear report does not guarantee clear ground. Where the search raises concerns, a Coal Mining Risk Assessment is usually expected as part of a planning application, and the Coal Authority may need to issue a permit before any drilling or work near a mine entry takes place.
Identifying made ground typically involves a ground investigation — physical testing of the site rather than desk study alone. This can include:
- Trial pits dug by an excavator to expose the soil profile and any buried fill;
- Boreholes drilled to reach competent natural ground and to probe for voids or workings;
- Laboratory testing of soil samples for strength and for contaminants linked to industrial use.
A geotechnical engineer interprets these results and advises what the ground can support. In Wigan, contamination and mining risk often need to be considered together, since former industrial sites may carry both.
Matching foundations to unstable ground
Foundation choice follows the investigation, not the other way round. Where competent ground is shallow, a simple strip or trench-fill foundation may be enough. Where made ground is deep or workings lie below, more substantial solutions are common.
Deep foundations transfer building loads past weak material to firmer strata below. Piled foundations are the usual approach — concrete or steel piles driven or bored into the ground, tied together by a reinforced concrete ground beam or raft. For lighter loads, mini-piling is sometimes used because the rigs are smaller and suit constrained sites.
Old shafts and shallow workings may require grouting, where a cement-based mix is pumped underground to fill voids and stabilise the ground before building. The right method depends entirely on what the site investigation reveals, so it is worth asking a structural or geotechnical engineer to set the foundation design rather than relying on assumptions.
Brick terrace renovation across Wigan's older streets brings its own questions. Many terraces predate modern foundations and sit on shallow footings. Before extending or underpinning, it helps to understand whether existing movement reflects normal age-related settlement or active subsidence linked to the ground below. A survey of existing cracking, drainage and footings can clarify this before further work is committed to.
In short, the sensible order in a former-coalfield area is search, investigate, then design — with each step informing the next.
Reviewed: June 2026