Some recent model test results for ultimate capacity of vertical piles under axial pull in loose granular soil are presented, and the possible variation of unit uplift skin friction with the embedment depth is analyzed. Laboratory model tests were conducted in a sand box (2 ft. x 1-1/2 ft. x 2-1/2 ft.) and a modern model pile of 1 in. in diameter and 2 ft. in length was used. Silica sand was used for the tests. The model pile was placed in the test box and sand was poured and compacted in 1-in. layers to a density of 94.2 pcf. The relative density and the angle of friction for the density of compaction used were 21 percent and 31 deg. respectively. The uplift force on the pile was applied by a 1/8 - in. diam. cable attached to the center of the pile. The pile displacement during the pullout test was measured by a dial gage. The ultimate pullout load was determined from the load displacement diagrams. Tests were conducted for various depths of embedment of the pile. The laboratory test results for net ultimate uplift loads are plotted versus their corresponding embedment ratios. The results of the study have led to the conclusion that the variation of unit uplift skin friction for piles is approximately linear with depth up to a critical embedment ratio, beyond which it reaches a limiting value. For short rigid piles, the uplift capacity can be calculated by using Meyerhof's uplift coefficient. However, a conservative assumption of delta may be required. The final skin friction for tensile piles in loose granular soil used for this test program is attained at a depth of about 10-12 pile diameters. However, this may not be true for all granular soils. More test results of this type are needed to evaluate a general range for the depth of arching.

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  • Accession Number: 00127649
  • Record Type: Publication
  • Report/Paper Numbers: ASCE #11604 Proceeding
  • Files: TRIS
  • Created Date: Mar 10 1976 12:00AM