Pile founding level optimisation
An innovative design approach for the foundation of the Hong Kong-Zhuhai-Macao Bridge Passenger Clearance Building has resulted significant material savings and CO2 emission reduction.
The boundary crossing facility is to be located on an artificial island of about 150 hectares reclaimed from the open waters off the northeast of the Hong Kong International Airport (HKIA). The Passenger Clearance Building is the largest among all the structures on the artificial island
Golder was retained by the contractor joint venture to review the pile design.
The Hong Kong code of practice for foundations provides strict requirements for piles founding in rock, where a minimum Total Core Recovery of 85% has to be achieved along the rock socket and 5m below the pile base to achieve the Cat1c category. If lower core recovery is identified from predrills, standard practice in Hong Kong is to lower the toe level until the criteria are met. This practice may significantly increase the rock excavation requirements and pile length in order to meet code requirements, while providing only marginal engineering and stability benefits in some cases.
Golder developed two ways to pre-agree changes from the conforming design level criterion to a rational design method and demonstrate that sufficient bearing capacity is achieved under certain conditions even though the Cat1c requirements are not met.
Savings for the project include:
- 24 piles;
- 20% of rock drilling;
- Approximately 50-100 rig working days;
- 63 tonnes of reinforcement and 560m³ of concrete; and
- Approximately 400 tonnes of carbon dioxide emissions.
Golder worked with the engineer and the project owner, the Highways Department, to obtain approval for the rational design method to recognise and realise these cost and resource savings.
In 2017, the project gained an energy and environmental merit award from the CIMIC group (our client). These awards recognise innovation that serves to continually improve their business leading safer, more efficient projects, and giving them a competitive edge.