Designing foundations on silty soil

Restrictive design criteria

Our challenge on a recent industrial project was to design the foundation for a piece of heavy press equipment, which had to meet extremely stringent soil settlement criteria. The vertical displacement of the foundation was limited to 2 mm, whereas in current practice, geotechnical reports define the soil bearing capacity as being limited to a settlement of around 25 mm.

Often enough, in such situations, a design engineer's reflex is to propose deep foundations like piles. Although we studied this option for our project, it wasn't chosen because of financial (high cost of bored piles) and technical reasons (settlement in excess of 2 mm, which would have been difficult to adhere to with driven piles).

Moreover, it wasn't technically feasible to design a foundation with these constraints. The only possible solutions were to change the location of the foundation or to reinforce the existing soil. Since this was an expansion project for an existing plant, changing the location wasn't an option.

A highly specialized technique

The ground reinforcement technique is based on highly specialized know-how and, as a result, isn't often used in mainstream construction. In fact, this type of expertise is more complementary to the services that consulting engineering firms offer.

In this project, this type of expertise was used to provide controlled modulus columns (CMC) with onsite monitoring (see Figure 1).

We enlisted the services of an expert in the field, and they proposed an innovative approach that would allow us to work efficiently, minimizing laborious and iterative calculations.

Over the following months, as we carried out preloading and CMC strength tests in situ, measurements would demonstrate that, after the actual equipment loads were applied to the reinforced soil, the resulting deformations were similar to the results of theoretical calculations.

A productive collaboration

This project is a prime example of BBA's collaboration with a firm that specializes in reinforcement solutions to meet the challenges posed by silty soils.

It's important to know which firms can offer proven, tailor-made solutions for foundations on silty soils or in other structural sectors. Trust us with your projects!