Regulated by RICS
Subsidence Investigation Surveys
Subsidence – Background Information
Since 1971 subsidence cover has been included within household insurance policies. This is the major reason for Subsidence in the interim years becoming very much associated with buildings insurance claims.
Subsidence as defined within the terms of an insurance policy is usually associated with and 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 are what can affect the structure of a building
This is, of course, by no means the only principal cause, nor the only possible cause in subsidence damage, problems occurring through major foundation movement can also be due to other causes, for example: there may be adverse groundwater affects upon loose or granular / sandy soils, damage can occur through a landslip or retaining wall failure, there may be subsidence due to a property being in a mining area, collapse and movement can happen due to solution features in chalk or due to settlement or failure of made-up ground.
We regularly advise upon all aspects of subsidence, including the initial appraisal and investigation, we follow this up with recommendations for the design and control and any remedial measures.
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 or structure damage and or subsidence claims.
We are able to offer advice upon all aspects of insurance claims within 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 when it comes to 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.
Subsidence Surveys - Visual Subsidence Survey
When we are requested to investigate problems pertaining to suspected subsidence, we would initially carry out 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 a little associated damage, this damage is not necessarily caused by ground or foundation movement, for example, it could be caused by thermal or shrinkage movement. Therefore not all movement requires remedial measures.
The main thing is to determine whether the movement and its associated damage is serious or not and whether it will continue to cause the building or structure to deteriorate.
Once we have assessed the seriousness of the movement and damage associated with it, we would provided you with the information required on whether you need to take 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 would normally provide a detailed subsidence investigation report, which would include:
- Initial reasons for the report
- General description of the building or structure
- Extent of movement and its associated damage
- Initial advice and opinion upon the cause/s of the movement and its associated damage
- Further investigations include monitoring of any unnecessary movement
- Remedial measures required and if there is 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 to 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 building or structures 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, the types of soil, especially clay soils and the location and condition of below ground drainage. This work doesn’t always have to be invasive because there are non-invasive ways of carrying out excavation work.
On completion of our subsidence investigations we would provide you with an appropriately well detailed report, which would include:
- 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 advise upon 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
- Approvals that may be required including party wall agreement where remedial work might affect adjoining properties
- Summary and recommended course of action
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 building or structure foundations, we could recommend the underpinning of the foundations and ground bearing, or to improve the ground that the building or structure sit on, injection grouting techniques may be necessary.
There are different forms of underpinning, including the traditional mass concrete underpinning, concrete pad or reinforced concrete or steel beams. The type of underpinning that is chosen will be done so due to all mitigating circumstances.
As with ground excavation the effect your underpinning might have upon 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 there are many modern techniques for retaining wall or ground slopes strengthening, rather than carrying out major ground work reconstruction.
Remedial Works - Design and Project Management
Once the scope of the remedial work has been agreed upon, we can prepare the remedial scheme to go forward with including: tender and contract documents, specifications and the necessary drawings.
The remedial scheme recommended may only be repair to the damage of the building or structure. But it might also be that we recommend foundation stabilisation, which could include underpinning, major structural repairs, injection grouting, specialist ground-works and anchorages for retaining walls.
The remedial scheme would then be controlled through a selection of contractors which we would have tendered for the cost analysis and the building contract, this would provide for necessary site inspections, contract administration and the control of contractors payments until a satisfactory conclusion to the work and the building contract.
On all subsidence projects we can provide on site control with site inspections carried out by our own resident structural engineer.
Usually when it comes to insurance claim projects, that is unless these are of large size or there are special circumstances, it is unlikely your Insurers will agree to fund the cost of a resident engineer.