Settlement Ratio of Pile Groups in Sandy Soils from Field Load Tests
by Y. Xu, (Res. Asst., Dept. of Civ. Engrg., The Hong Kong Univ. of Sci. and Technol., Clear Water Bay, Hong Kong. Email: xuyao@ust.hk) and L. M. Zhang, (corresponding author), M.ASCE, (Assoc. Prof., Dept. of Civ. Engrg., The Hong Kong Univ. of Sci. and Technol., Clear Water Bay, Hong Kong Email: cezhangl@ust.hk)
Journal of Geotechnical and Geoenvironmental Engineering, Vol. 133, No. 8, August 2007, pp. 10481054, (doi: http://dx.doi.org/10.1061/(ASCE)10900241(2007)133:8(1048))
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Document type: 
Technical Note 
Discussion: 
by William J. Neely, P.E. Email: wneely@reinforcedearth.com (See full record)

Closure:  (See full record)

Abstract: 
This note studies settlement ratio, R_{s}, of pile groups in sandy soils, defined as the ratio of the settlement of a pile group to that of a single pile at the same average load per pile. 31 cases of field pilegroup load tests and the corresponding field singlepile load tests were collected for this study. More than onehalf of the cases consist of 3diameter spaced, 9pile groups. Based on the field test data, statistical analyses of R_{s} at different load levels were conducted for pile groups with capground contact (PGCs) and pile groups with freestanding caps (PGFs), respectively. The mean of R_{s} decreases with the load level for both PGCs and PGFs, whereas the coefficient of variation of R_{s} increases with the load level. The influence of capground contact on R_{s} does not appear to be significant based on a comparison of the mean R_{s} values of these PGCs and PGFs. In addition, a comparative study on R_{s} and group resistance ratio R_{s}, which is defined as the ratio of the average resistance of a pile in a group to that of a single pile at the same settlement, was conducted to clarify possible misunderstanding between R_{s}and pile group efficiency factor η for driven pile groups in sandy soils. The value of R_{s} compares settlement at the working load and is often larger than unity. The value of η compares failure loads, which occur at different settlements for pile groups and their respective single piles. η is usually larger than unity due to soil densification and additional contributions from the capground contact for PGCs. 
