Existing Foundation Trial pits

In addition to assessing the suitability of existing foundations for extensions and subsidence prevention, our trial pit service is also instrumental in identifying crucial construction details, particularly when it comes to drainage systems. Clients often require this information for build-over agreements as mandated by local water authorities. Understanding the relationship between drainage pipes and foundations is essential for ensuring compliance with regulations and preserving the integrity of both the property and public infrastructure.

Finally, clients who suspect subsidence in their property often turn to our trial pit service to evaluate whether the foundation has been designed to an adequate standard. Subsidence can result in significant structural damage and costly repairs, making it crucial to address this issue promptly. Our comprehensive assessments not only identify potential causes of subsidence but also offer guidance on appropriate remedial measures. By choosing our services, clients benefit from the peace of mind that comes with knowing their property is safe, secure, and compliant with building regulations.

how it works

Safe digging practices

Prior to any excavation, we use Cable Avoidance Tools to establish the location of nearby underground services as they may be in the way (water, gas, electricity, etc.) and we want to avoid any service strike.
Once this condition has been satisfied, trial pits can usually be safely excavated to a depth of about 1.2m using hand tools, assuming the sides of the trial pit are stable.
If services are found, we excavate alongside them, rather than directly above. The final exposure of the service will be carried out by horizontal digging as the force applied to insulated hand tools can be controlled more effectively.

We bag & tag soil samples

The works are generally undertaken by a two-man crew and completed within a single working day.
Subsoil samples are taken by hand augured boreholes or by window sampling techniques and are taken to a laboratory for subsequent testing.
The details of the foundations and the strata are noted and recorded to be included within our factual report.

Factual Reporting

Upon completion of the site works, the information gained is then compiled into a factual detailed report. This includes photographs, soil strata logs, shear vane readings, a CAD layout plan and a CAD profile section for each pit we dug. This is forwarded to our clients to implement in their design process. We can e-transmit attachments or overlay them directly on to your AutoCAD.

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Call us now for an enquiry. Clever Works Ltd – Drainage & Subsidence Investigation

01932 961 864

Commonly asked questions

What is subsidence?

Subsidence is the gradual sinking or downward settling of the ground, which can cause damage to buildings and structures. It is often the result of changes in the soil composition or underground conditions, such as soil shrinkage, erosion, or groundwater level fluctuations.

What causes subsidence?

Several factors can contribute to subsidence, including:

Soil type (e.g., clay soils are more prone to shrinkage and swelling)
Tree roots that extract moisture from the soil, causing shrinkage
Leaking drains or water mains that wash away or soften the ground
Inadequately discharged stormwater runoff#
Poorly designed structures
Mining activities or underground excavations

What are the common signs of subsidence?

Some common signs of subsidence include:

Cracks in walls, especially diagonal cracks that widen towards the top
Sticking doors and windows due to shifted frames
Sloping floors or uneven surfaces
Separation of walls from adjacent structures or gaps in brickwork

Can a trial pit help establish if I have subsidence?

Yes, a trial pit can serve as a reliable indicator of potential subsidence risks. By exposing the foundation and revealing its construction, a trial pit can help assess structural integrity. Although factors such as site geology and vegetation may contribute to subsidence, a properly designed structure tailored to site-specific conditions (including foundation depth) will continue to perform effectively.

By incorporating site-specific information about nearby trees, drainage, and design criteria from the NHBC Guide Chapter 4.2, foundations can be designed and specified to an appropriate depth to mitigate subsidence risks. Unfortunately, an incorrectly designed or poorly constructed foundation may not adequately protect against subsidence. Thus, conducting a trial pit excavation can help eliminate at least one potential cause from the list of possible factors contributing to subsidence.

How can subsidence be prevented or minimized?

To prevent or minimize subsidence, consider the following steps:

Ensure proper drainage systems are in place to prevent water accumulation
Avoid planting large trees near buildings or remove existing ones
Regularly inspect and maintain underground pipes and utilities
Consult an engineer for appropriate foundation design and construction techniques

What should I do if I suspect subsidence in my property?

A: If you suspect subsidence in your property, take the following steps:

Document the signs of damage (e.g., photographs)
Consult a surveyor for a professional assessment
Notify your insurance company, as subsidence may be covered under your policy
Implement the necessary remedial measures as advised by experts

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CONTACT

01932 544 095
hello@clever-works.co.uk