Load Bearing Characteristics of Bored Precast Prestressed Nodular Piles-Paper

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The paper reviews the development and performance of bored precast prestressed high-strength concrete nodular piles in Japan, focusing on the Hyper Mega (HM) method. Developed as a low-noise alternative to impact driving, HM installs piles in pre-bored holes, enlarges the pile base, and injects cement grout to improve shaft friction and end-bearing resistance. It accommodates nodular and straight piles up to 1,200 mm in diameter and can reach installation depths of 68.5 m.<br /><br />The authors describe how HM evaluates bearing resistance, including both resistance at the pile toe and friction along the grouted base. Design relationships for end bearing and shaft friction are derived from instrumented pile-loading tests in sandy, gravelly, and clayey soils. Three case studies compared measured and calculated ultimate capacities: measured values were 1.13 to 1.63 times the calculated values, indicating that the equations were conservative.<br /><br />The study also assesses load-transfer analysis using pile-shaft and pile-tip springs. The analysis reproduced the observed pile-head load–settlement relationships and axial-force distributions reasonably well, although some differences occurred, particularly at ultimate load. The authors conclude that the method provides a practical framework for estimating the axial capacity and settlement behavior of HM piles. Further testing of fully instrumented piles is recommended to strengthen the supporting dataset and improve design reliability.

Keywords

Hyper Mega method

bored precast prestressed piles

high-strength concrete

nodular piles

Japan

pile bearing resistance

end bearing

shaft friction

load-transfer analysis

pile load settlement