Piled foundations and pathways for ground gas migration in the UK

Abstract

Piled foundations are commonly thought to create preferential pathways for ground gas migration. This view is often held without consideration of site-specific ground conditions, pile type or source of gas. There are currently no published data that quantify the effects of piles on gas flow from the ground. Both contaminated water and gas are fluids that for the purposes of this paper can be modelled using the standard equations of fluid flow. Therefore, the available research on the risk of piles increasing the permeability of the surrounding ground with respect to contaminated water can also be applied to gas flow. This paper discusses the different types of pile construction commonly used in the UK and how each may, or may not, influence gas migration. Understanding ground conditions is critical to assessing whether a preferential pathway will form. This paper looks at the available evidence on the influence of piles on the permeability of the surrounding ground. Even if it is considered possible that a preferential pathway could develop, the influence on the gas risk will depend on the number of piles, gas pressure and horizontal permeability. A significant effect is possible only where gas is under pressure and/or the piles are very closely spaced.