The Site is located on a thick bed of clay - and the top 3m or so of this clay is expected to swell and shrink each year. To make matters worse trees were removed from the site which means that the clay can be expected to swell (heave) over the next few years as it gains moisture. The engineer deemed that a raft foundation was not suitable for the build so piles are required.

The piling solution selected is an open bored pile 300mm in diameter. The maximum service load on a pile is 170kN (equivalent to approximatly 17 tonnes). The piles were bored up to to a depth of up to 9.5m with the top 3m surrounded by a slip sleeve.

In total 33 piles were required - and up to 7 piles were bored in a day.

The two plots were leveled and the piling mat (harcore surface) was layed. If the weather had turned wet that hardcore would have been essential to work from as opposed to wet slipery clay.

The piling rig bores into the clay - each section of the auger being 1m long.

After reaching the required depth the aurgers are progresivley lifted and each auger section is removed (note the plate at the ground level ensures that the remaining auger stack within the hole does not fall to the bottom).

Once the Auger has been removed, and the depth checked, a 3m long cardboard sleeve is slid into the top of the hole. The tube is fixed to the ground so it doesn't slide to the bottom.

At the end of each day the concrete is ordered to fill the open bores and fill to just above the required level.

A 6m long 20mm diameter reinforcing steel bar is slid into the concrete and down the center of the pile with a second 6m length laped and tied to the first length and pushed all the way to the bottom of the pile.

A pile head cage is then inserted to allow 4 number 12mm reinforcing bars to protrude from the top of the pile which will eventually be bent into the ground beams.

And a video of the piling rig in action...right click here and "save link as"