Advanced mini piling systems was contracted to provide piling services for a local Property development company, based in Bath; The site is at the top of Bath over looking the whole city. There are 5 plots on the site, each with a 4-5 bedroom luxury home, 3 of the plots were based on traditional foundations, because they were on the crest of the hill and based into the natural layer of brash (local stone).
The 2 remaining properties are located on the bottom of the site below the crest of the hill, and both have basements in the their designs, so the commencing surface level would be below the layer of Brash and into the fullers earth, which meant that these 2 properties would require piling, because lateral and vertical loads could not be gained via traditional strip footings.
Our engineer choose to use 220mm dia Steel cased bottom driven piles, with a 300mm thick reinforced concrete slab. One of the problems we came across while driving the piles, was that they hit softer layer of stone which made the piles bend off vertical, this happened in every location we tried; So to save the client time and money, and as the access to the site was restricted, the option for a bigger CFA rig was out of the question. The solution we came up with, was to base the piles in the soft stone, which meant they were shallower, and double up all the heavily loaded piles.
Scope of works
*Mobilise D1000H to site.
*All 220mm dia steel cased tube delivered to site in two loads.
*Install all piles to engineers specifications.
*Reinforcement for piles.
*Set up safe location for mobile boom pump.
*Concrete all piles.
The 3.0m firsts plugged up, and ready to be driven in plumb; The D1000H can lift its driving hammer over 3.0m which means the rig can drive, while other casings are being welded together which gives us a higher productivity.
We achieved very close centres to the temporary retaining wall.
All piles concreted with a mobile boom pump and a C35 pump mix.
To Provide 21 piles to rebuild a garden wall; the existing wall had fallen down due to the tree roots, and the weight of the garden it had been retaining for many years. As we were working on the party wall, permission had been granted from both sides to gain access to work. All materials and machinery would be brought through the garden, of the property at the top side of the wall, and a safe working area would be made in the garden of the bottom property.
Before work could commence trial pits had to be dug, by hand to find out where the roots of an oak tree with a TPO (Tree Preservation Order) on it were, which prevented damage to the tree roots while removing the existing wall, and while piling. The piles, beams and beam heights were determined by the location of the tree roots, the beams will bridge the roots so no piles or excavations would damage them.
Although this is not a Contiguous Piled retaining wall, which would of been more expensive, the engineer choose to design the piles to take a hollow block wall, which would be slotted onto reinforcement cast int the beam, and then filled with concrete. The piles were placed in pairs and will take lateral and vertical load, tied together with a 600×400 capping beam.
Due to ground conditions here, the decision was taken to Tremmie all piles rather than use Hollow Stem flights, as this would help to reduce mess from waste water in the cleaning process after every pile, and the clay was stiff enough to stand open while grouting.
Scope Of Works
*Site health and safety and welfare facilities provided by main contractor.
*Mobilise Kitten Piling Rig to site with grouter.
*Garden protected and ramp made to remove spoil.
*Safe working area set up for Steel fixing and use of grouter,
*All cement and sharp sand to be moved by hand to the rear of the property.
*Garden of bottom property fenced off and piling mat installed.
*Piles and pile heights set out by main contractor.
*Install all 21 piles to engineers specifications.
*Clean and clear site, demobilise rig.
All cages tied and protection boards taken up every night to prevent killing the grass.
The grout hose is placed to the bottom of the pile, which brings the water and debris out of the top, the cages are then plunged into the pile.
All piles complete and left at differing heights to allow easier cut off for the client.