Analysis of Pile Load Tests Data on Drilled Shafts in Sandy Soils of the Arabian Gulf Region Towards Assessment of Piles Load Bearing Capacity and Settlement Prediction Models
Authors: Al-Homoud A. , Tarek M.F. , Mokhtar A. 
Published: October 2008

Abstract
Several theoretical, empirical and semi-empirical methods are available in the literature to predict friction resistance, end bearing and settlement of drilled shafts in sandy soils. This study aims to assess the applicability and evaluate the accuracy of different prediction methods via comparison with data from (39) field pile load tests conducted on shafts drilled in the Arabian Gulf region. Meyerhof (1976) empirical method [1] and Vesic (1975) theoretical method [2] yielded accurate predictions for the base resistance. Burland (1973) approach [3] over predicted the skin capacities due to the uncertainty in determining the lateral earth pressure coefficient ??and the soil-pile interaction angle ?. The calculated pile settlements predicted by Vesic approach were very close to the measured values.

Introduction
Bored concrete piles are frequently used in the area of the Arabian Gulf as a safe foundation for multistory buildings. Several theoretical, empirical and semi-empirical methods are currently in use by civil engineers in region for determining the behavior of the piles without an assessment of the accuracy of prediction of these methods for the deep foundations drilled in the region. The paper presents the results carried out on (39) field pile load tests conducted onshafts drilled in the sandy soils of the Emirates accompanied with the geotechnical data on soil conditions at the sites where the piles were drilled and tested. The results obtained from the study are compared with those found in the literature, both regional and world wide. Theoretical methods developed by Vesic [2], Janbu [4] and Hansen [5] as well as the empirical approaches described by Meyerhof [1] and Reese and O'Neil [6] are used for predicting the point capacity. Results from theoretical approaches developed by Burland [3] as well as theempirical approaches described by both Vesic [7] and Meyerhof [1] for predicting the skin resistance are also presented. In settlement analysis, the approaches described by both Vesic [6] and Poulos [8] are presented and discussed, too. The fundamental equations for such methods can be referred to in Appendix A.

Review of Literature in the Region
Table 1 and Table 2 summarize the experiences and the recommendations available in the literature regarding the uplift tests and the compression tests applied on piles in the region, respectively as reported in [9]. In a study of piles drilled on the shores of the Arabian Gulf, the results of compression piles showed a predicted ultimate resistance of an average of 4228 kN/m2 with Nq=40, while the actual resistance obtained from the pile tests was 7500 kN/m2 with Nq average equals to 80. The average compression load was close to the upper end of the range of values generalized for the uncemented sands (8000 - 10 000 kN/m2) as reported in [9]. The average predicted skin friction was 13 kN/m2 for the uplift piles while the actual resistance was 15 kN/m2 with 15% as a difference. It was concluded that the new data fall within the range of values reported in the literature and that the pile capacities in the soils of the region are highly unpredictable at that time. An analysis carried out in Kuwait on short, precast concrete piles based on Meyerhoff method for layered soil profile considering standard penetration test N values [10].