Ground heave and subsidence: managing construction risk from the ground up

Hotter, drier periods and changing rainfall patterns are increasing the practical importance of shrink-swell ground movement. For developers, contractors and consultants, the legal issue is not simply whether movement occurs, but whether the risk was properly investigated, allocated, designed for and managed through the project documents and site records.

In their article, ‘Shallow Geohazards,’ The British Geological Survey said, “Shrink–swell, or expansive, soils are one of the most costly and globally widespread geological hazards, with costs estimated to run into several billion pounds annually.”

Why ground movement creates construction claims

Clay-rich soils change volume as their moisture content changes. Drying can cause shrinkage and settlement or subsidence; rehydration can cause swelling and heave. Vegetation, tree removal, drainage changes, leaking services and the timing of foundation construction can all affect moisture content. The resulting movement may damage foundations, superstructure, drainage, and external works.

From a disputes perspective, cracking is only the symptom. The key questions are usually:

• what mechanism caused the movement;

• whether it was foreseeable from the available ground and vegetation information;

• whether the design allowed for it;

• whether the works complied with the design and specification; and

• whether the proposed remedial scheme is reasonable and proportionate.

Do not assume the contractor automatically carries the risk

Risk allocation depends on the contract. A statement that the contractor “always” bears the risk of ground conditions is too broad. The position may turn on the procurement route, the site-information provisions, design responsibility, express ground-risk clauses, and the mechanisms governing instructions, variations, and extensions of time.

On a traditional project, the employer’s geotechnical and structural design team may retain significant responsibility for site investigation and foundation design. The contractor remains responsible for workmanship, compliance with the design and any contractual duty to warn. Under design and build procurement, the contractor may assume wider responsibility for completing or adopting the design and satisfying performance requirements, but the precise wording still matters.

When a potential problem is identified, the first legal review should therefore include:

1. the building contract, amendments, employer’s requirements, and contractor’s proposals;

2. the geotechnical report, desk study, trial-pit, and borehole information;

3. foundation drawings, calculations, and design-change records;

4. tree surveys, arboricultural information, and records of removed or historic vegetation;

5. risk registers, tender qualifications, and site-information disclaimers;

6. inspection records, requests for information, photographs, and as-built information; and

7. notice provisions for ground conditions, compensation events, variations, delay, loss, and expense.

Where liability may fall

Practical risk management and evidence

Legal and technical risk management should operate together from the outset. Responsibility for site investigation, interpretation of ground information and foundation design should be clearly allocated. Assumptions about soil plasticity, groundwater, vegetation, tree removal, and drainage should be identified and recorded. The building contract, consultant appointments, warranties, and insurance arrangements should be checked to ensure that design and ground-condition risks are allocated consistently. There should also be a clear mechanism for dealing with unforeseen or inaccurately described ground conditions.

Where movement is suspected, early preservation of evidence is important. Ground-movement disputes are often expert-led, so parties should consider involving a geotechnical engineer, structural engineer and, where vegetation is relevant, an arboricultural expert. Depending on the circumstances, practical steps may include:

1. preserving geotechnical information, including trial-pit and borehole records, soil samples, and laboratory testing;

2. recording crack patterns, levels, and movement over time, using an agreed monitoring protocol where appropriate;

3. investigating drains and water services where leakage may be a potential cause;

4. retaining relevant vegetation-management, tree-removal, and site records;

5. preserving foundation drawings, design changes, inspection records, photographs and as-built information;

6. giving contractual and insurance notifications promptly and reserving rights before intrusive investigations or remedial works;

7. giving potentially responsible parties an opportunity to attend inspections and testing, where appropriate; and

8. keeping the proposed remedial solution, costs, and any temporary works under review as the technical evidence develops.

The important point from a construction law perspective is that the technical investigation should not take place in isolation. The contract, design responsibility, notification requirements, and potential claims against other members of the project team should be reviewed alongside the technical evidence, particularly before destructive investigations or remedial works alter the available evidence.

How we can help

Our construction team advises developers, contractors, consultants, owners and insurers on ground-condition and foundation disputes. Our advice covers contractual risk allocation, Defective Premises Act claims, expert evidence, limitation, insurance notifications, adjudication, mediation, and court proceedings.

If you are dealing with cracking, subsidence, or heave on a live or completed project, an early, coordinated legal and technical review can preserve the evidence and avoid the loss of contractual or insurance rights. It can also ensure that any investigation or remedial proposal is proportionate to the developing evidence.