Review on the End Bearing Capacity of Large Diameter Bored Piles founded on Meta-sedimentary Rock in Hong Kong

The HKSAR Government has introduced the Northern Metropolis Development Strategy to transform the northern part of Hong Kong into a metropolitan area for living, working, and traveling. Covering 30,000 hectares, it includes districts like Yuen Long, Tin Shui Wai, Fanling, and Sheung Shui. The strategy aims to increase land availability, improve transport infrastructure, and develop housing, industries, and community facilities. The government has prioritized the Northern Metropolis in its strategic development plans, emphasizing an "industry-driven and infrastructure-led" approach to integrate it with the nation's overall development. Meta-sedimentary bedrock formations are not uncommon in the Northern Metropolis. A review of the allowable end bearing capacity of this bedrock has been conducted in this paper. The Code of Practice for Foundation 2017 specifies the allowable end bearing capacities for various types of rocks and soils in Hong Kong. For Grade III meta-sedimentary rock, it is limited to 3,000kPa, while for granitic and volcanic bedrock, it has been upgraded to 7,500kPa. To study the behaviour of piles founded on Grade III meta-sedimentary rock, two bored piles were tested each under a load three times the design working load. The test results showed maximum mobilized end bearing pressures exceeds 15,000kPa (i.e. with a factor of safety of 3, the allowable bearing pressure is greater than 5,000kPa). These findings provide valuable insights into pile behavior on meta-sedimentary rock in the Northern Metropolis, suggesting efficient and economical foundation design can be achievable in the new development areas.