Grouped Pipe Pile Foundations for Massive Tidal Barrage Structure Anchored to Granite Layer-PPT Presentation

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The March 11, 2011 earthquake and tsunami devastated Miyako, Japan. Existing river levees settled due to liquefaction and were overtopped, causing major flooding downtown. In response, a new floodgate was planned at the mouth of the Hei River to protect the area from flood levels up to T.P. 10.4 m.<br /><br />The floodgate is 164.4 m wide and has four gates. Its foundations were designed to resist horizontal forces and extend through sand and gravel into granite. The project used 1,000 mm-diameter pipe piles, generally spaced 2.5 diameters apart. In total, 272 piles were installed, with lengths ranging from 6 to 26 m; some longer piles required on-site splicing.<br /><br />Piles were installed using the Gyropress method, which rotates and presses pipe piles into hard ground, including rock. Skip-lock attachments enabled closely spaced installation. The work encountered a granite obstruction during pre-drilling, which was resolved by dislodging the rock. Construction was carried out in phases, including temporary cofferdams; after the first phase, the navigation channel was relocated through the completed section.<br /><br />The project demonstrates that pipe piles can provide reliable foundations for floodgates and other in-water structures, and that Gyropress can install them efficiently into rock at close spacing.

Keywords

Miyako earthquake

tsunami

floodgate

Hei River

liquefaction

pipe piles

Gyropress method

granite foundation

cofferdam

flood protection