Pullout Tests of Piles in Sand

Abstract

Three pullout tests on two instrumented 24-in. -diameter, steel-pipe piles were performed in a deep sand deposit at Mustang Island, Tex., to determine the tension capacity of a pile and to assess the effects of lateral loading on pullout resistance. Test equipment and procedures are described and results of strain data and load vs pile-top movement are presented. Skin friction parameters are determined from these results. Introduction Pullout tests on open-steel pipe piles in sand were run at Pullout tests on open-steel pipe piles in sand were run at the Shell Oil Co. Tank Battery on Mustang Island, Tex. The map in Fig. 1 indicates the test site. About 5 ft of fill was excavated at the site so that the water table would be at ground surface. Two instrumented test piles were driven and pullout tests were performed before and after lateral loading. Test Equipment and Test Piles Test Setup and Test Piles The test setup and test piles are shown in Fig. 2. Two reaction beams, one on each side of the test pile, rested on timber mats. Two hydraulic jacks with pumping units and pressure gauges rested on the reaction beams. A 10-ft pressure gauges rested on the reaction beams. A 10-ft section of 24-in.-diameter pile was specially made and welded to the top of the test pile. Two small-diameter piles were driven to support deflection gauges used to piles were driven to support deflection gauges used to measure movement of the pile top. Cables from deflection and strain gauges were run from the pile to the instrumentation system housed in a van parked beside the excavated area. Two test piles were manufactured from seamless steel pipe (ASTM A-53, Grade B) with 24-in. OD. The wall pipe (ASTM A-53, Grade B) with 24-in. OD. The wall was 3/8-in. thick and weighed 94.6 lb/ft. The piles were composed of a 10-ft loading section, a 32-ft instrumented section, and 38-ft anchor section (Fig. 2). The instrumented section was sealed off by diaphragms at the top and bottom of the section to prevent moisture from damaging the strain gauges. Wires from these gauges were passed through pressure-packing glands in the diaphragm at the top of the instrumented section. Each pile had 40 strain gauges - 34 active and 6 unstrained dummies. The 120-ohm strain gauges were 0.50- x 0.50-in. metal foil. Strain-gauge spacing in the 32-ft section is indicated in Fig. 2. Both test piles were driven with a Delmag-12 diesel hammer. The 38-ft open-ended, uninstrumented section was driven until its top was about 3 ft above the soil surface. Next, the soil plug inside the section was augered out completely to keep it from driving against the diaphragm in the bottom of the 32-ft instrumented section. After welding the 32-ft section to the 38-ft section, driving was resumed and the pile was driven to grade, with the pile flange approximately I ft above the soil surface. The pile was embedded 69 ft. Measurement of Load, Strain, and Deflection During the pullout tests, readings were taken of the applied load, the deflection of the top of the pile, and the axial strain along the pile. The applied load was obtained by reading bourdon-tube pressure gauges that measured the hydraulic pressure in the jacks. The pile deflection was obtained from dial indicators and by use of lineardisplacement transducers. Output from the displacement transducers and from strain gauges was recorded with a digital recording system. JPT P. 343