Complies with the standards for technical backfill foundations

Q. Can you provide some background on the type of work NHBC and LQS do?

NHBC is best known as the leading warranty provider for new build homes in Great Britain. But probably a lesser known fact is that we are an independent, not-for-profit distribution company. So there are no shareholders, which puts us in an excellent position to spend profits on developing new products and services that support the sector and ultimately protect homeowners. The theme of the whole company is that quality is very important, and we try to benchmark what is good.

LQS is part of NHBC’s services portfolio. We are not a supervisory authority and we work with information that is available and provided to us. We work collaboratively with the wider project team with a focus on ensuring the performance of the scheme over the life of homes. We work on a wide range of projects across the UK, including infilled open pit mines, former power stations, docklands and coal mines with complex industrial histories.

We assess the locations in a pre-development phase. We provide technical advice as to whether the work carried out or proposed is acceptable to NHBC. We then highlight specific technical issues that must be resolved to obtain the NHBC warranty.

The service itself provides a path to warranty. And part of the reason for that is that normally, on an annual basis, about 40% of NHBC’s portfolio is on previously developed land. So we understand that early involvement is critical to raising standards and protecting homeowners.

We are a pre-registration service typically carried out by landowners, developers or other parties involved in transferring land into residential-led markets. The service then reduces the risks from contaminated or geotechnically challenging sites by identifying hazards early and controlling them. It then removes uncertainty about whether these projects will continue for future housing projects.

One of the advantages of those offering the services is that the land whose risks are mitigated generally has a higher value and offers a greater return on investment. It also reduces the risk of delays in the development phase and the likelihood of future significant abnormal costs.

We always assign a specialist geotechnical and geoenvironmental engineer to each of our projects, with the aim of trying to ensure that the proposed foundations are suitable for both purposes and provide a holistic approach.

Q. What are NHBC Standards?

If you register your plot for NHBC warranty, it is a requirement that the work has been carried out in accordance with NHBC standards.

The NHBC Standards are a volume that is produced and updated annually.

The standards – and any adjustments we make – are based on a review of claims history, feedback from construction customers and the industry, and key themes and current topics for the housing market.

What LQS is generally working on is chapter four, which contains subchapters on different types of foundations, ground improvement techniques, land quality and building near trees.

Our standards are used by a wide range of people. The on-site homebuilder can look up and see exactly what to do, while geotechnical professionals use it when trying to decide what they need for their foundation or for building near trees.

Q. What prompted the creation of the new technical backfill chapter and what does it cover?

As part of that body of work on foundation standards, one of the key questions was: What does NHBC think about engineering backfilling?

There are different ideas about what NHBC’s preference is. So what we wanted to do was provide guidance and clarify what we’re looking for in terms of technical fill.

There is a strong desire within the industry for clear guidance on this and in line with this is the fact that we see a wide variety of quality works – sometimes of excellent quality, but sometimes the works are designed and implemented by humans. with limited or no experience with geotechnical engineering. In addition, specifications may be lacking in detail or appropriate for the end use, and often verification reports are very unclear and, again, not focused on what the end use is.

The aim of this new chapter within the standards is to provide a risk-based and highly pragmatic approach that promotes good practice. It’s nothing new for experienced geotechnical engineers.

In this new chapter we outline an approach to what we need from initial research through to the development of the defined strategy, the implementation of that strategy and then verification.

It very closely aligns the quality of the earthwork with the foundation solutions that are acceptable. It clearly defines that if your earthworks meet these specific criteria, you have these foundation options.

One of the other reasons why it is relevant now is that, with an emphasis on sustainability, projects aim to reuse locally sourced materials rather than importing them. How do you deal with this and ensure that it is still suitable for residential construction, and what foundation options are acceptable?

Q. Which parties will benefit most from the information?

The chapter contains a lot of detail about which materials are suitable and which are not, but there is already good guidance available. BRE has done a lot of work building on the fill, so we are not reinventing the wheel, but what we are doing is clearly identifying what needs to happen at each stage to promote good practice and maintain that quality.

The standards are used by multiple parties, which makes it a quite difficult document. It is not a technical article that is only read by consultants. It may also be read by a housebuilder who has carried out a small scheme where they are just raising the levels for flooding, as opposed to a consultant who is planning to carry out a scheme on a former surface site with 60 meters of infill . .

So in terms of width it is a difficult animal to manage. It is about providing guidance and signposts that show what the performance standard should be.

In preparation for the new chapter, we have collaborated with the industry on a number of different points.

LQS, together with NHBC’s standards, innovation and research department, have consulted with house builders, developers, consultants, earthmoving companies and geotechnical laboratories.

Q. What message would you like to share with our geotechnical readership?

The standards and the new chapter explain what we should all do; it’s nothing new. It just reminds people what good practice is and the need to demonstrate compliance and performance.

I think the lack of interpretation we see in many reports is surprising. So you can have the best data in the world, but you have to demonstrate compliance and use the information you have, rather than saying it’s all in an appendix.