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Subsidence Investigation Surveys

Subsidence Investigation

Since 1971, subsidence cover has been included within household insurance policies. As a result, subsidence has since become very much associated with buildings insurance claims. Subsidence, as defined within the terms of an insurance policy, usually includes heave, landslip, and water damage (typically leakage from below ground drainage or water supply services).

Ground and foundation movement and the associated damage brought about by these can affect the structure of a building.

This is, of course, by no means the only principal cause, nor the only possible cause of subsidence damage. Problems occurring through major foundation movement can also be due to a number of causes. For example, there may be adverse groundwater affects upon loose, granular or sandy soils, in which damage occurs through a landslip or retaining wall failure. Subsidence is also common in mining areas, in which collapse and movement occurs due to solution features in chalk or due to the settlement or failure of made-up ground.

We regularly advise on all aspects of subsidence, including the initial appraisal and investigation. This is followed by recommendations for the design and control and any remedial measures that need to take place.

Subsidence Insurance Claims

Due to our considerable experience of subsidence investigation, we regularly advise insurers, insurers appointed loss adjusters, and the insured regarding technical and engineering aspects of building damage and subsidence claims.

We offer advice on all aspects of insurance claims related to our expertise as consulting structural engineers.

At all key stages, it is important that we are in close communication with all respective parties. This way, we are able to find agreement going forward with any further investigations and extra works involved.

Normally, so long as the cause of damage comes within the scope of an insured event, your insurance policy will provide for the professional fees necessary for a subsidence investigation and the remedial work required thereafter; naturally, this is subject to any policy excess you may have and the particular terms of your policy.

Visual Subsidence Survey

When investigating problems pertaining to suspected subsidence, we initially carry out a specific defect survey to undertake a visual inspection to assess the extent and seriousness of any movement and damage. From this, we can then ascertain if any general conditions are prevailing that lead to probable causes.

Extent of Movement

The majority of buildings and structures are subject to some sort of movement and associated damage, but this damage is not necessarily caused by ground or foundation movement. For example, it could be caused by thermal or shrinkage movement, and therefore, not all movement requires remedial measures.

The key is to determine whether the movement and its associated damage is serious and whether it will continue to deteriorate the building.

Once we have assessed the seriousness of the movement and associated damage, we provide you with the information required to make any immediate remedial work or temporary work to maintain the safety of the building or structure.

Initial Appraisal Report

Following our initial inspection and appraisal, we provide a detailed subsidence investigation report, which includes:

● Initial reasons for the report

● General description of the building or structure

● Extent of movement and associated damage

● Initial advice and opinion upon the cause/s of the movement and its associated damage

● Further investigations including monitoring of any unnecessary movement

● Remedial measures required and if there is a need for any temporary support

● How appropriate is an insurance claim

● Summary and recommended course of action

Intrusive Subsidence Survey – Investigation and Monitoring

The subsidence investigation usually involves accurate monitoring of any movement of the building or structure. This includes precise datum monitoring of principal fractures and, where appropriate, precision level survey monitoring of datum fixed close to the foundations of the building or structure.

If we are dealing with sensitive or critical structures e.g. historic buildings or structurally suspect structures, controlled level and tilt monitoring can be used.

The monitoring of fractures doesn’t always allow for the extent or nature of the foundation movement. Therefore, a thorough investigation of the structure’s foundations and surrounding land is sometimes recommended. This can include using boreholes in adjacent ground to measure the soil parameters and water conditions, and using trial pits which expose the foundations for better inspection.

We would also need to look at the influence of environmental factors, including trees in the vicinity, types of soil (especially clay soils), and the location and condition of underground drainage. This work doesn’t always have to be invasive because there are non-invasive methods of excavation which work just as effectively.

Post – Investigation

On completion of our subsidence investigations, we provide you with an detailed report which includes:

● A brief, including instructions received.

● A general description of the state of the building or structure.

● The extent of any movement and the damage it’s causing.

● Details of investigations undertaken.

● Our opinion and advice on the cause/s of the movement and its associated damage.

● Likelihood of whether there will be any further movement or damage.

● Whether any further investigations are necessary.

● Remedial measures that are required with a full list of options.

● Insurance

● Approvals that may be required including party wall agreement where remedial work might affect adjoining properties.

● Summary and recommended course of action.

Remedial Measures

After carrying out our investigation, we are able to make the appropriate decisions regarding recommendations in respect of remedial measures required.

Underpinning and Foundation Stabilisation

Where it is considered necessary to stabilise the foundations, we could recommend underpinning foundations and ground bearing, improving the ground that the building or structure sits on, or injection grouting techniques.

There are different forms of underpinning, including the traditional mass concrete underpinning, concrete pad, reinforced concrete, or steel beams. The type of underpinning will be chosen due to all mitigating circumstances.

As with ground excavation, the impact underpinning might have on adjacent buildings or structures should be carefully considered before being implemented.

Careful consideration will need to be given to strengthening or other remedial work where ground movement that affects the building or structure is caused by slope instability, landslip, creep, or the failure of a retaining wall.

Fortunately, rather than carrying out major groundwork construction, there are many modern techniques for strengthening retaining walls or ground slopes.

Remedial Works – Design and Project Management

Once the scope of the remedial work has been agreed upon, we prepare the remedial scheme to proceed with, which includes tender and contract documents, specifications, and the necessary drawings.

The remedial scheme recommended may only be to repair damage to the building or structure, but we might also recommend foundation stabilisation, which could include underpinning, major structural repairs, injection grouting, specialist groundworks, and anchorages for retaining walls.

The remedial scheme will then be controlled through a selection of contractors which we tender for the cost analysis and building contract. This provides for necessary site inspections, contract administration, and the control of contractors’ payments until a satisfactory conclusion to the work and building contract.

On all subsidence projects, we can provide on-site control with site inspections carried out by our own resident structural engineers.

Usually, it is unlikely your insurers will agree to fund the cost of a resident engineer unless under special circumstances or your insurance claim project is large in size.