Flowable fill was used to strengthen the soft soil surrounding piles and behind the pile cap. The flowable fill placed beneath the pile cap surrounding the piles showed no appreciable increase in lateral resistance, this was partially due to the fact that the flowable fill placed had an unconfined compressive strength of 30 psi. Flowable fill was also used to replace a 12 ft wide, 6 ft thick, and 6 ft deep zone consisting of an average 475 psf clay that was adjacent to a 9-pile group in 3x3 pile configuration capped with a 9 ft x 9 ft x 2.5 ft, 5000 psi concrete cap. The flowable fill placed behind the pile cap had an unconfined compressive strength of about 137 psi. Lateral load testing of the pile foundation was then undertaken. The results of this testing were compared with similar testing performed on the same foundation with native soil conditions. The lateral resistance of the native soil was 282 kips at 1.5 inches of displacement, and the total lateral resistance of the pile foundation with flowable fill placed behind the pile cap was increased by about 53% or 150 kips. Of the 150 kips, 90% to 100% can be attributed to the increased passive force on the face of the flowable fill zone and shearing of the base and sides denoting that the flowable fill zone behaved as a rigid block. The long term strength of the flowable fill when water is allowed to flow over it is still in question. Samples of the 137 psi flowable fill were cured in a fog room for 700 days and showed a 56% decrease in their unconfined compressive strength. Any increase in lateral strength from the flowable fill would be compromised over a period of time less than 700 days. Site specific characteristics concerning water flow would need to be evaluated to determine if flowable fill would be an acceptable material to increase the lateral resistance of a pile group.



College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering



Date Submitted


Document Type





flowable fill, controlled low strength material, lateral resistance