Deep Foundations Penetrating Mineral Sealing Barriers: Impacts on Hydraulic Flow and Contaminant Transport

Abstract

Redevelopment of closed landfills and brownfield sites is a beneficial goal. Regulatory concerns have been raised that pile foundations might transmit contaminants from polluted upper layers to clean lower aquifers when penetrating a sealing barrier. Current solutions include isolating the pile by casing and sealing with grout. In this investigation the contaminant transport associated with piles that are not hydraulically isolated was investigated. For conduit formation (development of flow paths near and at the pile soil interface) and wicking transport (flow through the pile material itself), large-scale laboratory tests were set up. Herein, clay barriers were fully penetrated by piles and were subjected to permeant for more than 170 days. Four types of piles (wood and steel) were tested simultaneously. Due to the unique test setup, the flow characteristics in the areas near and distant to the pile were measured. Possible side effects during the laboratory tests were double checked by using FE software. Numerical modeling of the laboratory setup showed that horizontal flow was negligible. Flow along the pile soil interface can be minimized using appropriate pile shapes. Large displacement piles were shown to have the ability of developing sufficient soil pressure for sealing any surrounding conduits. Combining the "right" shape with an impermeable pile material makes a pile usable in a safe manner without the additional costly sealing.