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Piled Extension in Frome, Somerset
There were many challenges on this job, the customer required 4 No triangular pads, each designed with 3 No 150mm dia Steel Cased Bottom Driven, Cast In situ Piles, to extend a 3 bedroom house. The extension is to be built between the existing house, and a public footpath, which means the new extension is triangular in shape and built right up to the perimeter fence. The access to site was down the 1.2m wide footpath, where all materials and equipment had to be manoeuvred. Upon further inspection it was found that the main sewer for the houses in the vicinity, was located under the corner of the existing dwelling and travelled down through the proposed extension. Advanced Mini Piling Systems redesigned the pad positions, and contacted the local water authorities, the answer was to move one of the pads, adding an extra pile, and pre boring all the Steel Cased Bottom Driven Piles, past the depth of the main sewer pipe, relieving the pipe of any pressure from the displaced material while the Piles were being driven.
The Piles in this pad were pre bored, beyond the depth of the mains sewer and had anti heave sleeve installed, which is the cardboard tube you can around the base of the Piles. The Piles were then driven to a pre-designed set, concreted with reinforcement, and then cut down to cut off level ( CoL ).
Jurassic Coast, Contiguous Piled Wall, Branscombe, DevonProject Brief:The site is situated on the side of Branscombe cliff, in Lyme bay. The cliff is made up of three strata, Chalk, Pre-Cretaceous Upper Greensand and Mercia Mudstone with gypsum from the Triassic era. Originally Branscombe grew from mining gypsum and the property we are working on was terraced workers cottages, with the look out on the end, a coastguard station.The Jurassic coast is a world heritage site and the rock and cliff formations have been changing for millions of years, with land slip a very common problem. Only 1km down from the site is Hooken cliffs where in the 1800’s a landslip took place containing a few million tons of chalk slipping off the Triassic Mercia Mudstone, this continual changing coastline means we need to find modern answers to solve a very old problem.This project comprise of installing a Contiguous Piled Wall in front of an old coastguards lookout, the lookout which is no longer used by H M Coast guard and is now part of private home and has been converted to suit the clients needs with a large decking, cantilevered over the cliff edge. In front of the building was mass poured concrete to retain the cliff edge and support the decking, unfortunately due to weather erosion the concrete has cracked up and is slowly slipping down the cliff, leaving the footings of the old lookout exposed.In an attempt to prevent any further movement, the whole cliff has been rock anchored and netted down while works continue. With the original decking removed scaffolding had to be erected to allow for the piling rig to work in front of the building, the scaffolding had to support a 4t point load and every other support was placed on a rock anchor.The machine we used for this job is a PPS Unwin Kitten Rig which is capable of working in restricted access conditions, and very powerful and able to bore through the tough layers of limestone. The Kitten is also able to install Temporary Cased Piles, which we are using for the bearing piles 1.5m from the centre of the Contiguous Piled Wall, this places them in the middle of the scaffolding, and any spoil or concrete would fall down the cliff causing a safety hazard. Site access and weather conditions also made this a challenging job for our team, All our equipment and reinforcement had to be delivered by 7.5t lorry as roads to site were very narrow. as the winter storms of 2014, with high tides and storm force 10 and 11, for some days the wind speeds reached 90mph with driving rain on the unprotected cliff face work had to stop as just standing up became a problem. Although we were unable to work on site, we helped clear debris from the road, restaurant and secured loose boats and peoples belongings. The high tides and high winds had washed most of the service road away which leads to several beach chalets, which were also damaged, and only 25m below our site. Storm force 10 and abnormal high tides, cause major problems on the beach front.The service road and some of the chalets have been washed away. Scope of works:* Site canteen and welfare facilities provided by main contractor.* Protect all walls and drive where we are working.* All services located and isolated.* As we are working on a cliff face all safety handrails must be installed and checked.* Mobilise PPS Unwin Kitten Rig, by 7.5t lorry.* PPS Unwin Kitten Rig chained with tether while on scaffolding.* Prefabricated 6H16 – H8 helicals @ 200mm pitch, delivered to site by us.* Pile positions set out by main contractor.* Safe route for concrete deliveries planned, and lorry walked to site by banksman.
The Contiguous Piled Wall continues along the front of the garden, although here we are working in between four cantilever beams which hold the decking over the cliff, so we are installing three Piles in each section. Because the spacing between the Cantilever beams was to small, the third Pile was installed custom essays behind the face of the wall giving it the same lateral restraint.
The Contiguous Piled Wall is installed at 600mm from the centre of the piles, to the face of the Look Out, top of reinforcement is finished at 1200mm from piling platform to allow for protrusion into 600mm x 600mm R/C capping beam.
Installing 300mm dia Temporary Cased Piles here with the Kitten Rig Prevents the spoil and concrete from falling down the cliff face, and means no operatives need to come off the scaffold.
Casing is socketed into the clay to form a seal and the pile is then formed with the casings extracted straight after concreting. These piles will have pile caps formed on top of them, which will support the new decking. Site is left clean and tidy after each day, with the access to the main house kept open and the drive power washed.
Brent knoll, Somerset
To provide 220 steel cased bottom driven piles to a pre designed set, and fabricate and cast 450 x 350mm R/C beams, for a detached garage, office and utility room. The main property is located on the Somerset levels, and surrounded by land drains which prevent the main river from flooding and carry away excess water from the farm land.
When we started the project the level of the drain was 0.6m below commencing surface level, and all piles were driven to their pre designed set, and were then concreted. After waiting for the piles to cure we then proceeded to excavate for the beams, and because of the heavy rainfall the drain level rose to 0.1m below commencing surface level, which unfortunately was 0.5m above our bottom of dig, so all the beams flooded, and we were unable to continue with work until the water level of the drains fell. We returned a month later once the water level had receded, and completed excavating the ground beams, we used a mobile line pump to concrete the beams as the access to site would not allow larger vehicles onto the driveway.
Scope of works;
*Welfare facilities provided by client.
*Check for services.
*Install 220 Steel cased bottom driven piles.
*Fabricate and install steel reinforced beams.
*Pour beams with C35 concrete.
*Clear site and leave tidier then when we arrived.
Unfortunately the perimeter of the new extension, came parallel to the bank of the land drain which had been built up by the previous owners, so as soon as we disturbed the ground near the bank, it breached the drain flooding the excavated beams. Because of the abnormal weather conditions that had been taking place, the drains were full and we left site until the water level had receded and would could continue with works.
The smaller tie beams which can be seen are 350 x 350mm these will carry very little load; the one furthest away will carry the rear of the garage wall, which is timber, and closest one in the photo will support the the block and beam floor.