Many construction methods have been developed to create hydraulic barriers to depths of 30 to 50 meters, but few have been proposed for depths on the order of 500 meters. For these deep hydraulic barriers, most methods are potentially feasible for soil but not for hard rock. In the course of researching methods of isolating large subterranean blocks of oil shale, the authors have developed a wax thermal permeation method for constructing hydraulic barriers in rock to depths of over 500 meters in competent or even fractured rock as well as soil. The technology is similar to freeze wall methods, but produces a permanent barrier; and is potentially applicable in both dry and water saturated formations. Like freeze wall barriers, the wax thermal permeation method utilizes a large number of vertical or horizontal boreholes around the perimeter to be contained. However, instead of cooling the boreholes, they are heated. After heating these boreholes, a specially formulated molten wax based grout is pumped into the boreholes where it seals fractures and also permeates radially outward to form a series of columns of wax-impregnated rock. Rows of overlapping columns can then form a durable hydraulic barrier. These barriers can also be angled above a geologic repository to help prevent influx of water due to atypical rainfall events. Applications of the technique to constructing containment structures around existing shallow waste burial sites and water shutoff for mining are also described.
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