What a geotechnical surprise really costs, using a job where we had one

Every owner has heard that bad soil is expensive. Fewer have seen the arithmetic, so here it is from a real job, with the numbers we actually priced.

The finding

Borings on a 412,000 square foot distribution centre found up to eleven feet of uncontrolled fill across the northern third of the site. It was a former gravel operation, and the fill was not on any drawing we had been given.

The two options, priced

Deep foundations under the affected area came in at roughly $1.9M and ten weeks. Surcharging the north end with spoil already on site, instrumented with settlement plates, cost about $480,000 and needed seven weeks of waiting we could spend building the south end.

We surcharged. The point is not that surcharging is always right, because it is not: it needs a site with somewhere to put the load and a schedule with a piece of work that can happen elsewhere. The point is that the obvious answer was more than three times the price, and nobody would have questioned it.