Pile Tests, Low-Sill Structure, Old River, Louisiana

A comprehensive pile testing program was undertaken at the site for the low-sill structure for control of the Old River, Louisiana. The object of the program was to determine the required type, size, and length of piles necessary to carry the design compression and tension loading without any significant movement of the structure. Information regarding the driving of displacement and nondisplacement types of piles was also desired. Fourteen-inch H-piles and pipe piles ranging from 16 in. to 20 in. in diameter were driven and tested. The details of the loading arrangement and test procedures are described. Because from 50 ft to 60 ft of alternating strata of silty sands, sandy silts, and clay overlie the sand beneath the structure, both the total bearing capacity and the bearing capacity of only the section of the piles penetrating into the sand were measured. The lo ad carried by that section was computed from strain measurements that were made on rods attached at different points along the pile. After the compression tests were completed, the piles were allowed to rest and tension tests were performed on all piles but one.

From the pile-load tests, either 20-in. steel-pipe piles, 20-in. precast-concrete piles, or 14-in., 73-lb-per-ft, steel H-beam piles, with respective penetrations of 15 ft, 12 ft, and 27 ft into sand, were considered satisfactory for carrying the design load of 100 tons in compression and 40 tons in tension, with an ample factor of safety against both detrimental settlement and sudden plunging. The estimated average unit skin friction in the silts was 0.64 ton per sq ft for the piles tested in compression and 0.26 ton per sq ft for the piles tested in tension. The average angle of internal friction of the sand, which was computed from bearing-capacity formulas and the maximum load carried in the pile tip, was 33°. The strain-rod installation proved to be satisfactory and reliable in determining the distribution of applied load in the silt and sand strata.