In-Situ Pile Segment Model Experiments at Empire, Louisiana

Abstract

Fourteen experiments were conducted at Empire, La. using instrumented pile simulation probes to measure lateral pressures and t-z behavior at various times and under a variety of loadings. Three of the fourteen were conducted at the same depth in parallel bore holes and enable comparisons of the effects of two diameters and two end conditions. A detailed presentation of the three sets of results leads to an improved understanding of the significant mechanisms and processes involved in the axial-load behavior of long offshore piles. Introduction Two types of instrumented probes have been developed to model segments of long flexible piles. The probes are instrumented to determine in situ the significant soil response parameters under a variety of static and cyclic loading conditions (Refs 1 and 2). The resulting data provide a basis for more rational and reliable axial pile design methods. Experiments have included consideration of the effects on axial pile capacity of diameter, wall thickness, and setup or consolidation time, plus the effects of displacement and load history, and cyclic degradation. In 1975 a series of tests on four 50-ft-long pipe piles 14 inches in diameter were performed at Empire, Louisiana for Chevron Oil Field Research Company (Refs 3 and 4). Test depths ranged from 115 to 360 ft. In April, 1984, fourteen experiments were performed with the instrumented model segment probes at the same site. Test depths ranged from 120 to 250 feet, covering the depths reported for Chevron's piles 1 and 2. Eight of the experiments were in a normally consolidated clay from 120 to 160 feet. The locations of the borings in which the experiments were performed are shown in Fig 1. Also shown are the locations of earlier work at the site, including the original pile tests by TERA, soil borings made by McClelland Engineers, proprietary CPT and pyrometer work done by Fugro Gulf, and experiments with the PLS probe done by the Massachusetts Institute of Technology (Ref 5). OBJECITVES The research program was originally proposed as a fundamental study of the response of a normally consolidated clay to a pile under a variety of loading conditions, including comparisons with the Chevron pile tests. The probes have been successfully deployed at the onshore and offshore sites of three instrumented large-scale pile load tests and at two onshore sites for which parallel large-diameter pile load test data are not available. The scope included examination of open and plugged end conditions, effects of diameter on setup and shear transfer, degradation under one-way and two-way cyclic loading, and the effects of loading rate on shear-displacement behavior

Numerical Procedure for Predicting Pile Capacity—Setup/Freeze

“…Pile installation causes changes in the stresses and pore water pressures in the soil around the pile. Field measurements (17)(18)(19)21) of in situ stresses during and just after pile installation demonstrated that the effective radial stress state reached by the soil at the pile interface is very low. The HiSS-δ * 2i model (2,6) was developed, based on the nonassociative anisotropic HiSS-δ * 2 model (32), to characterize soil behavior at the pile-soil interface as well as at the far field.…”

“…Subsequently, numerical and analytical methods (12)(13)(14) were developed to study pile behavior using cavity expansion methods and constitutive models to characterize the soil. Instrumented piles, pile models, and pile segment models were fabricated to conduct experimental studies and to verify numerical methods (3,(15)(16)(17)(18)(19)(20)(21)(22). The results of these studies demonstrated the importance of the effective stress state in the soil around the pile in evaluating pile shaft-soil behavior.…”

“…Many investigators (16,18,21,(23)(24)(25) studied the increase of pile capacity with time after pile installation. During these experimental field studies, the changes in soil properties and the changes in stresses and pore water pressures during the life stages of the pile were monitored.…”