Characterization of model uncertainty in predicting axial resistance of piles driven into clay

Abstract

This paper summarizes 239 static load tests to evaluate the performance of four static design methods for axial resistance of driven piles in clay. The methods are ISO 19901-4:2016, SHANSEP, ICP-05, and NGI-05. The database is categorized into four groups depending on the load type (compression or uplift) and pile tip condition (open or closed end). The model uncertainty in resistance prediction is quantified as a ratio between measured and calculated resistance, which is called a model factor. The measured resistance is interpreted as a load producing a settlement level of 10% pile diameter. Database studies show that the four methods present a similar accuracy, where the mean and coefficient of variation (COV) of the model factor are around 1 and 0.3, respectively. The COV values are smaller than those for driven piles in sand available in literature. The model statistics determined from the database are applicable to a simplified or full probabilistic form of reliability-based design (RBD) of driven piles in clay. As an illustration, the resistance factors in load and resistance factor design (LRFD, a simplified form of RBD) are calibrated by Monte Carlo simulations.

Bayesian Estimation of Resistance Factor for Bored Piles Based on Load Test Database

“…e model factor is frequently represented as the ratio of the measured capacity to calculated capacity [1,7,8]:…”

“…where λ is model factor of pile capacity; Q m is the measured pile capacity; and Q p is the calculated pile capacity. Numerous investigations show that model factor is a random variable and obeys log-normal distribution [1,2,7,10,13,14].…”

“…e resistance factor is calculated incorporating in reliability analysis methods based on pile load test data [7,8]. Enough-accuracy in situ data are necessary to calculate resistance factor of bored piles.…”

“…However, it is difficult to collect accuracy in situ data to calculate reliability index and resistance factor because of various uncertainties, for example, parameter uncertainty, calculation model uncertainty, testing random error, and systematic error. A large number of investigations are carried out to calibrate resistance factor of driven piles [7][8][9][10][11][12][13][14][15][16], and significant achievements have been developed. However, few investigations about resistance factor of bored piles have been reported.…”

Analytical Solution for Estimating Bearing Capacity of a Closed Soil Plug: Verification Using An On-Site Static Pile Test

“…Numerous research have been conducted related to formation of soil plugs in open-ended piles from various perspectives such as, (1) Parameters in the dynamic process of forming soil plugs, such as the diameter of the pile [7], the penetration method [8], the penetration speed [9,10] and the condition of the soil layer [11,12]; (2) IFR (incremental filling ratio) [13] and (3) Dynamic effects [14] through the analysis of parameters to more accurately calculate the effects of soil plugs. At the same time, more experimental methods such as centrifuge test [15], model test research [16][17][18], and field test [19][20][21][22] are also adopted to study the soil plug effect. The scale model test and centrifugal test are affected by the particle size, and there are two obvious defects.…”