Good foundations form both the figurative and literal basis of any successful and cost effective new structure. The importance of getting your foundations right cannot be overstated, and it is often this aspect of a build that imposes the highest level of risk with respect to cost, programme, and liability to the designers, construction team, and client.

Robust and efficient foundation design costs will generally be a fraction of the cost of the physical works, and by investing in a smart design, significant cost and programme savings will likely be realised on a project.

The Chicken And Egg

The traditional approach to foundation investigation and design is that two separate companies, one specialising in geotechnical engineering, and another in structural engineering, will do their own assessment to form the basis of a foundation design. Often this can lead to a “chicken and egg” type situation – the geotechnical engineers can’t always determine the most suitable and efficient investigation works until they know the configuration, type and performance criteria required from the superstructure.

Whereas, the structural engineers will need to rely on the geotechnical report/recommendations in order to design the foundations and the associated superstructure.

This typically involves the geotechnical engineering company carrying out site specific testing, then producing a geotechnical report with foundation recommendations, to suit a foundation configuration they believe may be used. This can, in some cases, result in foundation designs which are conservative, as the performance requirements of the structure, and imposed loads are not clearly defined at the time the geotechnical report is written. Therefore, conservative estimate/assumptions can be made, which can result in more robust (and expensive) foundation systems being nominated.

The architect and/or structural engineer will then often take the proposed foundation recommendations from the geotechnical report, and design the structure based on these. For example, the number of storeys, cladding system, floor type, size of openings, will all likely be influenced by the site-specific ground conditions and foundation system.

Ideally the geotechnical engineers should work closely and collaborate with the structural engineer, and also the architect, from an early stage in the project, and as the project progresses, as this will enable these key parties to work together. This will ensure that the foundation system is suitable for the site conditions and is likely to be more cost effective than alternative options (which are not borne out of the same design process).

Working Together Cuts Costs

Working for a multidisciplinary engineering and surveying firm, we find enormous benefits in having the ability for our geotechnical and structural teams being able to work together, under the same roof, particularly from the early stages of the project. This results in efficient and appropriate foundation designs, which are tailored not only to the site conditions, but also the structural requirements. In this way, we are often able to save our clients significant and very real costs, by providing foundation solutions which are not overly conservative.

For example, we were recently asked to provide a structural design for a new detached shed structure (Importance Level 1 structure). The previous design (provided by others) indicated that the structure required to be supported on piled foundations.

However, we were able to undertake our own geotechnical assessment for the site, with knowledge of the proposed structure and the performance requirements (as required by the NZ Building Code). We were able to come up with an alternative foundation design solution, which involved a shallow foundation system. This resulted in a significant cost saving for the client, for the foundation construction.

If you are planning on undertaking a building development, it is important to get sound geotechnical and structural engineering advise (preferably from a company which offers both services), so as to ensure the foundation system, as designed, is suitable for the site conditions. This could save you money in the long run, on foundation construction costs.