Experiences in Drivability Analysis, Testing of Open-Ended Steel Pipe Piles and Drilled Shafts at Dahej LNG Project, India

Abstract

APDPPL has constructed a coal terminal at Dahej, India. The 670-m off-shore jetty head is connected to land with 1170-m pile-supported trestle followed by 1200-m rubble mounted bund. The original plan was to construct the jetty head and approach trestle with 1200-mm concrete bored piles. However, due to site constraints, high tidal variation and to ensure timely completion, it was decided to change the jetty head piles to steel pipe piles at the jobsite. The pile diameter selected was 1422 mm and design done as per API RP2A method. The thickness of the pipe varied from 22 to 38 mm. The piles were generally planned for up to 30 m penetration into seabed and the maximum working load varied from 3228 to 5223 kN. It was required to select a hammer to drive the piles to the required depth. Options were generally limited to Delmag D100-13 or D150-42 hammer due to commercial considerations. A GRLWEAP was performed to evaluate the suitability of the hammer for driving the pile. Both the drivability and bearing graph analysis were done, and also checks were done using soil static analysis. Based on the finding, the Delmag D100-13 hammer was selected and the piles were successfully driven to the required penetration. HSDPTs were performed at EOID with 2 restrikes to confirm the long-term pile capacities due to set-up. The results gave enough confidence about the pile capacity and hammer capability to drive all the piles. Static load testing was eliminated at the project site. 10% of the steel piles, 5% bored piles and 20% integrity tests were done at the jobsite. The entire job was successfully completed, and the berths are in operation currently. The case study is an excellent example of using combination of GRLWEAP, static analysis and HSDPT towards successful completion of the entire job.