In a bauxite mining project, located near a sea shore, foundations for a 24 m deep Car Dumper Vault (CDV) was designed as partially compensated raft. Excavation and dewatering schemes were designed and constructed by another agency and it included installation of three levels of sheet piles. The scope of author’s organisation was limited to design and construction of CDV buildings only. However, when excavation reached about 23 m depth below FGL, east side of the pit was failed initiating more than 2 m of lateral displacement of the sheet piles. The excavation system was re-designed with open cut. The CDV foundation was re-designed as 800 mm dia. bored cast-in-situ piles socketted in underlying bed rock. It was estimated that two month time would be required to install required 136 nos. of piles and estimated cost would be about USD 6, 00, 000. During discussions, it was learn that 15, 000 MT of structural wide flange bearing pile section HP 360 x 133 was purchased by the Owner in 2008 for a project conceived at that time which was later abandoned. To utilize the available HP-sections as CDV foundation, corrosion tests were carried out. Installation of designed 330 nos. of H-piles was completed within one month including load tests. Total cost of installation of H-piles was about USD 2, 00, 000. Thus, the H-Pile sections helped the Owner to shorten the project schedule and reduce the project cost considerably.
Subjects: Deep excavation, compensated raft, bored piles, steel H-piles
Author: Biswajit Das, Anup Kumar Mandal, Ph.D., Suman Sen and Shuvranshu Kumar Rout