Effective heave pressures beneath restrained basement slabs

In basement excavations it is common practice to employ ground-bearing slabs that are restrained from significant vertical movement by piles or surrounding retaining walls. For the structural design of these slabs, it is necessary to assess the upward pressure, known as heave pressure, from the ground beneath the slab that will develop in the long term. This paper examines two different processes in current use for the calculation of long-term heave pressures beneath basement slabs, concluding that one of them is fundamentally flawed. For a very simple situation, it is shown that the final effective heave pressure is largely independent of the magnitude of ground stiffness, but is significantly dependent on other properties of ground behaviour. Estimation of long-term heave pressures is very difficult and field observations of long-term heave pressures and groundwater pressures at the time slabs are constructed are very much needed.