Origins of deep fractures in glacial till: Bench-scale modelling of hydrofractures beneath a continental glacier

The presence of deep, hydraulically-conductive fractures in overconsolidated, clay-rich till aquitards increases the risk of contamination to underlying drinking water supplies and decreases the strength of the till. Despite the negative effects of these fractures, advances into detecting these fractures have not evolved from the detailed and expensive hydrogeological investigations methods from the 1970's. Determining the origins of these fractures could help in identifying regions that are likely/unlikely to be fractured. The hypothesis of this research is that the deep penetrating fractures in clay-rich till were created by hydrofracturing due to high basal water pressure beneath continental glaciers. This theory was originally proffered by Boulton and Caban (1995). Bench-scale experiments using a custom-build stainless steel fracture cell were conducted to (1) simulate the deposition and over-consolidation of till, and (2) to reproduce stresses beneath the continental glacier. The fracture cell was designed for both bench-scale experiments and future planned centrifuge modelling in Mining Engineering at Queen's University. The design required numerous design steps and revisions to conform to the centrifuge restrictions of a maximum weight of 70 kg and dimensions of 0.76 m x 0.41 m x 0.41 m. The final design incorporated the glacial and basal water pressures, while safely maximizing the volume of the cell.; Five experiments were conducted in the fracture cell on simulated till samples and produced positive results. The simulated tills had similar geotechnical consolidation and index properties such as coefficient of consolidation, water content, plastic limit, etc. to those of the till samples collected in the field. The water pressure applied in the fracture cell, which was approximately the water pressure beneath a wet bed glacier, created fractures in the till. One experiment resulted in fractures that extended up to 3.9cm below the top surface of the till, which was 32% of the column length. Therefore, under the conditions and methods used in these experiments, hydrofracturing can occur due to high water pressures under an imposed pressure. Hydrofracturing of the complete column of till did not occur. This may be due to experimental limitations such as: the small cell diameter inducing relatively large confining pressures in the cell; the upper limit on the imposed water pressure may not have been high enough; or the results may indicate that there may be more than one process that has created the deep fractures in the field. (Abstract shortened by UMI.)...