Water Jetting to Mitigate Defects in Drilled Shafts

A laboratory investigation was designed to examine the effectiveness of water jetting as a means of removing anomalous (deleterious) material from drilled shafts. One objective of the investigation was to establish relationships between jetting parameters and the removal of common anomalous materials, including low-strength concrete, slurry-mixed concrete, grout, and clay soil. The experimental work consisted of blasting test specimens of anomalous material with water by using rotary jets, nozzles, pumping equipment, and testing procedures in current construction practice. During testing, erosion levels and rates were measured as a function of jetting pressure and standoff distance for specimens with compressive strengths ranging between approximately 5 and 6,500 pounds per square inch (psi). Erosion levels, erosion rates, and water-jetting effectiveness were found to correlate with the compressive strength of the anomalous material. Reinforcing steel bars in a drilled shaft influenced erosion levels and water-jetting effectiveness locally by interfering with the jet path. For jetting pressures around 10,000 to 11,000 psi, erosion was observed to a radial distance of approximately 12 in. from the axis of the water jet for the weakest specimen. The erosion distances observed during the investigation were less than half of the maximum design spacing typically used for drilled shaft access tubes installed for nondestructive testing.