PURPOSE OF WORKS
As part of the development of the Ba Son Shipyard Line 1 Metro Station in Ho Chi Minh City, Bauer Vietnam were approach to undertake emergency works to close a defective Diaphragm wall constructed by Others.
CONSTRUCTION WORKS & SPECIAL FEATURES
To ensure pile integrity in the variable soil conditions, the bored piles were installed with 8m of temporary casing and bentonite support fluids batched on site. The bored piles were installed to 42m depth with grout tubes and access pipes for later Construction Quality Assurance testing.
It became apparent immediately why the Diaphragm wall works by Others had experienced such difficulties upon the project. The site was underlain by extensive obstructions with limestone boulders, structural steel, rail sleepers, steel rebar as well as miscellaneous objects recovered during the works. The excavation of the station box measures 15m in depth and was being constructed in a bottom up sequence with extensive temporary propping.
CONCEPT AND DESIGN
The design called for a contiguous 1.2m diameter piled retaining wall to be installed to 41m depth. These piles were designed to close a large gap in the existing diaphragm retaining wall. The piles would be temporarily propped during basement excavation but required considerable volumes of additional steel to be fixed at 12-14m depth. This steel would be mechanically interfaced to the station box’s sub-basement floor slab.
Do to extensive obstructions that became apparent during the works; Bauer recommended design changes that enabled a considerable saving to the follow on ground improvement work by Others.
Throughout modern history the site had been used as a ship yard. The ground conditions were highly variable and consisting of backfill and alluvial deposits. The soil profiles indicated soft Clay to 12m depth over soft Clay with leases of sand to 32m depth where hard Clay was encountered. Given the close proximity to the tidal Sai Gon River; the phreatic surface varied in depth from 1.0m below ground level.
Great care was required to ensure that the pile bore neither collapsed nor deflected from the intended verticality. Quality control management was adopted with every pile surveyed using a Koden machine before concreting commenced.
The client was so happy with Bauer Vietnam’s work, we were asked to undertake King Post piling also.