Results of Static Loading Tests on Single Piles and on Pile-Supported LPG Tanks

Abstract

Full-scale static loading tests on eight single test piles and hydrotests on two 50-m diameter tanks supported on 849 piles intended for storing refrigerated gas were performed at Cai Mep Industrial Park approximately 90 km southeast of Ho Chi Minh City, Vietnam. The test piles were precast concrete piles installed through 21 m of soft clay into dense sand to about 45 m depth below ground surface. Four piles were installed by driving and four by jacking. The maximum pile test loads were 3000 kN, which was well below any ultimate resistance, but showed that the tank-foundation piles (to be installed by jacking) could expect to shorten about 3 mm for the 750-kN working load. Each tank was hydro-tested to 636-MN maximum service load, which load was held constant for 1 week, while monitoring the tank settlement at benchmarks placed along the tank perimeters. The records showed the tank perimeters to settle about 15 mm in addition to an about 3-mm pile shortening. Back-analysis of the tank foundation modeled as flexible equivalent rafts at the pile toe level showed that the settlement of the tank center was about three times larger than that of the perimeter. Analysis of long-term settlements indicated that, under service loading, the tank perimeters and centers will settle an additional about 100 mm and 300 mm, respectively. Due to a 3 m thick fill placed over the site causing the clay to consolidate, the ground surface is expected to settle more than 1 m over the long-term. The general subsidence will affect the perimeter piles and transfer load to the interior piles. However, because the pile neutral plane is located in the sand below the clay, downdrag is not an issue for the piled foundation. The drag force will be well below the limit of the pile axial structural strength.