Case study of ground improvement at an industrial estate containing uncontrolled fill

Abstract

A proposed 1.5 hectare industrial estate in Tweed Heads, New South Wales was covered in 1.5 to 2 metres of uncontrolled fill. The site had been undeveloped for many years due to the problematic ground conditions. In order to render the site suitable for development the challenge was to engineer the site such that an allowable bearing capacity of 100 kPa was acheived. Ground improvement using impact rolling was adopted. After initial impact rolling, non-intrusive, surface wave seismic methods were used to assess the nature of the subsoil. Reliance on traditional intrusive methods alone and on a method specification was considered too risky given the variable nature of the fill material at the site that included building demolition debris and significant quantities of organic material. A seismic survey was used, using the Multi-channel Analysis of Surface Waves (MASW) method, that allowed near surface anomalies (such as zones of organic matter) to be identified and allowed correlations of seismic velocity with Young's modulus. The seismic test results generally provided good correlation with the traditional geotechnical investigation methods that were also undertaken and enabled deficient areas to be identified and reworked or excavated and replaced. The ground improvement proved successful in achieveing the required 100 kPa bearing capacity.