Load-Testing Program to Evaluate Pile-Setup Behavior for Individual Soil Layers and Correlation of Setup with Soil Properties

摘要

Six instrumented static-load test piles driven at four different locations along the LA-1 highway alignment in coastal Louisiana provided the opportunity to study the soil-setup behavior in relation to the soil properties. The instrumented piles consisted of six square prestressed-concrete (PSC) test piles of different sizes and different lengths. Both soil boring and piezocone penetration tests (PCPT) were conducted at each test-pile location to characterize the subsurface soil conditions. The testing program consisted of performing dynamic-load tests (DLTs) at predetermined time intervals, followed by one static-load test (SLT) at the end. These piles were instrumented with vibrating-wire sister-bar strain gauges along their length. Case pile-wave analyses were performed on the DLT data to calculate the soil-resistance distributions along test piles. Design parameters such as the adhesion factor a and the effective stress coefficient β were also backcalculated. The a values ranged from 0.68 to 1.78, and the (3 values ranged from 0.11 to 0.32. The load test results showed that the shaft resistances increased significantly with time, while the toe resistances remained almost constant with time for all test piles. The rates of setup parameter A for individual soil layers were calculated using the unit shaft resistances. The resulting average A values for clayey and sandy soils were 0.36 and 0.16, respectively. The setup parameters of individual soil layers were correlated with soil properties, which showed that the A parameter decreases with increasing undrained shear strength (S_u) and increases with increasing plasticity index (PI) for clayey soil layers. A nonlinear regression model based on undrained shear strength and plasticity index was developed and proven to be applicable to other sites as well.