INCREMENTAL GROWTH OF A SHALLOW HYDRAULIC FRACTURE AT A WASTE REMEDIATION SITE, OAKBROOK, ILLINOIS FROM INVERSION OF ELEVATION CHANGES

Elastic dislocation theory in a half-space is used together with a geophysical inverse technique to determine the geometry and incremental growth of a shallow (approximately 3 m) hydraulic fracture designed for facilitating remediation of contaminated unconsolidated sediments at Oakbrook, Illinois using the elevation changes monitored during the experiment. It is determined that the hydrofracture strikes N69-degrees-E and dips 25-degrees-NW, matching well with the observations throughout the split spoon sampling following the experiment. The fracture opening is highly non-uniform. The fracture front propagated at a varying speed. The growth rate of the hydrofracture decreases with time, indicating an essentially stable fracturing process. The resolving power of the data is closely dependent on the distribution of the observation stations. Sources near the observation stations are better resolved, both in length and amplitude, than are those away from the stations. the resolution length is in the order of 1-2 m.