Lateral load tests were performed on a full-scale pile cap in clay before and after construction of eight 1.5 m diameter jet grout columns to a depth of 3 m around the pile group. Jet grouting with a cement content of about 400 kg/m3 (20% by weight) increased the average compressive strength of a soft, plastic clay from 40 to 60 kPa to an average of 4500 kPa. The lateral resistance was increased by 2200 kN or 177% and the initial stiffness was increased by 400%. About 65% of the increased resistance could be accounted for by passive pressure and side/base shear on the jet grout mass; however, the remaining 35% increase must be due to the interaction between the piles and the strengthened soil. Jet grouting provides a method to significantly increase the lateral resistance of pile group foundations at costs much lower than typical structural approaches.
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