Remediation of Deep Uncontrolled Fill using Dynamic Compaction

Abstract

This thesis examines the geotechnical remediation of a backfilled quarry for residential and commercial development. The study involved two parts: the characterisation and settlement characteristics of the uncontrolled fill; and the implementation of dynamic compaction. The first part focuses on the mechanism and magnitude of settlement of the fill, in particular, collapse settlement. The results of a study are presented quantifying the magnitude of the collapse with respect to the density ratio of the soil. The results enable a detailed understanding of the mechanism involved in collapse of uncontrolled fill. Also presented are relationships between in situ wet density and collapse strain. These relationships are used to quantify the amount of collapse strain within the fill, from which the ground surface settlement profile can be calculated. A process for compacting the fill (Dynamic Compaction, or DC) was adopted to mitigate the potential of collapse settlement and is focus of the second part of the thesis. The results of full scale trials using DC are presented that quantify the effects of changing the grid spacing and number of blows forming part of the DC process. Based on the trials, new relationships are presented for assessing the effect of DC and designing the number of blows and grid spacing. Literature on DC is primarily focused on the settlement resulting from DC; however none of the literature presents information about the heave that also occurs. The depth and extent of the heave have been quantified, and modified bearing capacity theory has been used to estimate the heave resulting from DC. Historical relationships have been presented for the depth and magnitude of settlement resulting from DC. Based on the results of the trials, amendments to previously established relationships are provided to increase the knowledge in the field of DC.