Challenges in the Construction of Deep Rock Socketed Pile for Urban Infrastructure
摘要
Pile drilling in rock is a challenging job in the foundation industry. The challenge refers to the selection of appropriate construction methodology which includes the type of drilling, rig machine, and drilling tool. The selection is greatly dictated by characteristics of pile, job site condition, and features of rock layer such as depth, type, strength, and its variation within the project site boundary. This paper discusses the challenges involved and effective methodology adopted in rock socketed piling for a top-down construction of urban underground infrastructure. The subsurface condition of the site includes silty sand and clayey soil layers varying from 21 to 24 m depth below ground level and followed by highly weathered to fresh Charnockite rock. The top-down construction method requires 1.5 and 2.2 m diameter pile and steel plunged-in column to be terminated at a depth of 32.5 to 34.5 m below ground level. The conventional methodology of rock drilling with rotary piling rig was found to be less productive, and highly time- and cost-consuming. Hence, a methodology comprised of soil drilling using rotary piling rig and followed by rock drilling using Reverse Circulation Drilling (RCD) rig was adopted. The application RCD in onshore project site requires effective planning of resources such as RCD assembly, steel liner, and adequate water supply. Accordingly, the onshore RCD methodology was framed with temporary liner and closed water circulation system considering water scarcity in urban location. The new methodology involving onshore RCD application reduced piling time through increased penetration rate in rock and ensured completion of piling job on time.