Potential for Hydraulic Fracture when Drilling in Dams and Levees

Abstract Hydraulic fracturing of embankment dams or levees and their soil foundations is a real concern when invasive techniques are used for investigation and remediation. Methods using water, drilling mud, compressed air, and grout have resulted in fracturing of the embankments or foundations as evidenced by cracking, loss of circulation, connections to other borings, and blowouts on embankment slopes. Numerous incidents have been documented in the literature, but many more undocumented cases are likely to have occurred. To predict the occurrence of hydraulic fracture, a practical model required by U.S. Army Corps of Engineers regulations was compared to laboratory and field data. The model requires estimation of the total minor principal stress and the undrained shear strength of the soil. Methods for estimating these parameters are discussed. Pressure measurement and comparison to the correct limiting pressures, in terms of total stress, are critical factors in the evaluation of hydraulic fracture potential and the potential to damage underground structures. Decisions to drill into dams and levees should be made only after proper evaluation of the risk. Drilling techniques that do not require fluids should be used when possible. If fluids are required, then pressures should be limited to gravity. If higher pressures must be used, then the pressures must be measured, and efforts must be made to keep them below the estimated threshold for hydraulic fracture.