Building in Wigan often means working over former mining ground, so most projects start with checks that would be unnecessary elsewhere. Much of the borough sits on the Lancashire Coalfield, and the legacy of shafts, shallow workings and disturbed ground shapes how foundations are designed and what risk assessments a project needs before work begins.
How does Wigan's mining past affect building?
Wigan was a major coal-mining area for generations, and that history left a complicated layer beneath the surface. Old shafts, shallow seams worked close to ground level, and the spoil left behind all influence how stable a site is today. A site that looks ordinary can sit above voids or backfilled workings that affect how it bears weight.
This matters across the full range of local projects — house extensions in areas like Hindley and Ashton-in-Makerfield, new-build housing on reclaimed colliery land, and commercial development near the town centre. The Coal Authority records mining features across the borough, and that information feeds into the early stages of most schemes.
Coal mining risk assessments explained
Building in Wigan often means working over former mining ground, so most projects start with checks that would be unnecessary elsewhere.
A coal mining risk assessment is a report that identifies whether a site has been affected by past mining and what that means for building on it. It draws on records of shafts, recorded workings, mine entries and ground stability, then sets out the level of risk and any further investigation needed.
For sites in defined mining areas, this assessment is often expected as part of a planning application. The process typically runs as follows:
- A desk study reviews Coal Authority records and historical maps for the site.
- If risks are flagged, intrusive investigation — boreholes or trial pits — confirms ground conditions.
- The findings inform whether remediation, such as grouting old voids, is required before construction.
You should ask whether your site falls within a Coal Authority Development High Risk Area, as this determines how much investigation a planning authority will look for.
Designing foundations for variable ground
Former mining ground rarely behaves uniformly, so foundation design responds to what the ground investigation finds rather than a standard approach. Where workings or voids sit close to the surface, engineers may specify deeper or reinforced foundations to span weaker zones and reduce the risk of settlement.
Common responses on Wigan sites include reinforced raft foundations that spread load across a slab, piled foundations that transfer weight to firmer strata below, and ground improvement to strengthen the layer beneath a building. A structural engineer will base the choice on borehole data, the depth of any workings, and the loads the structure will carry.
For a domestic extension, the design might be modest — but even small projects can need adjusting where shallow mine workings are recorded nearby. Building control officers will want to see that foundations suit the proven ground conditions.
Building on made ground
Made ground is soil that has been placed or disturbed by human activity rather than laid down naturally. Across the former coalfield this often means colliery spoil, demolition rubble, or material used to level and reclaim old industrial sites. It varies in depth and composition, and can settle unevenly or contain contaminants.
Because made ground is unpredictable, a project usually needs investigation to establish how thick it is and whether firmer natural ground lies beneath. Where made ground is shallow, foundations may simply be taken down to undisturbed strata. Where it is deep, piling or ground improvement becomes more likely.
Contamination is a related concern on reclaimed land, and a contaminated land assessment may sit alongside the mining and ground reports. Together these checks give a planning authority and building control the evidence that a Wigan site can be built on safely.