Analytical Models to Estimate the Time Dependent Increase in Pile Capacity (Pile Set-Up)

This paper presents the analyses of twelve prestressed concrete (PSC) instrumented test piles that were driven in different locations of Louisiana in order to develop analytical models to estimate the increase in pile capacity with time or pile set-up. The twelve test piles were driven mainly in cohesive soils. Detailed soil characterizations including laboratory and in-situ tests were conducted to determine the different soil properties. The test piles were instrumented with vibrating wire strain gauges, piezometers and pressure cells. Several static load tests (SLT) and dynamic load tests (DLT) were conducted on each test pile at different times after end of driving (EOD) to quantify the magnitude and rate of set-up. Measurements of load tests confirmed that pile capacity increases almost linearly with the logarithm of time elapsed after EOD. Case Pile Wave Analysis Program (CAPWAP) were performed on the restrikes data and were used along with the load distribution plots from the SLTs to evaluate the increase of skin friction capacity of individual soil layers along the length of the piles. The logarithmic set-up parameter "A" for unit skin friction was calculated of the 70 individual clayey soil layers, and were correlated with different soil properties. Nonlinear multivariable regression analyses were performed and three different empirical models are proposed to predict the pile set-up parameter "A" as a function of soil properties.