Super Strength Pile
SS Pile or Super strength pile is a type of precast concrete piles, which mean the SS pile will be produced in the factory and delivered to construction site if there is a need. SS Pile is slightly different compare with other concrete piles, SS Pile has a widen radius and it can supports more loads from structures with fewer number of points. There is two types of stressing of tendons, which is post-tensioning and pre-tensioning, while SS Pile is using prestressing or pre-tensioning. Pile which uses prestressing is to strengthen the strengh of pile, or prevent crack and improves its’ strength so that the pile can carries more load.
Procedure and Sketch of How To Produce Super Strength Pile (SS Pile)
1) PC Bar Cutting and Heading
2) Cage Forming
3) Joints Setting
4) Concrete Placing
5) Concrete Batching
These are all the steps of how to produce a SS Pile. All the procedures must be followed exactly and done it clean and neat. Safety protection must be carried on for workers who involved in the process of producing SS Pile. After the SS Pile has been done, it will be handled and stored in the factory or yard and ready for delivery.
Pile can be done in precast or cast-in-situ, cash-in-situ pile which is casted on the site, while precast pile is casted in the factory and deliver to construction site. This article will be teaching you how to handle and store the precast pile after it has been casted in the factory. Basically this article is writing about handling and storing hollow section pile such as Super Strength Pile (SS Pile). It has several steps need to be followed.
Procedures Of Handling and Storing Piles
1) Two point lifting position to be pitched at 0.2 x L distance from the pile ends (Diagram 1a as above). Alternatively, lifting from the pile ends is to be executed with the following controls :-
i) No jerking movements by the crane.
ii) Crane must be stationary.
iii) Vertical lifting rate at slower pace.
iv) Boom of crane to be swung at minimum rate of movement.
v) Piles are to be carried one at a time.
vi) Wire ropes are to be capable of carrying the load.
vii) Free rotation of the top swivel is to be ensured (Diagram 2 as above).
viii) Wire ropes are to be inclined at least 45 degree acute angle with the pile body. (Diagram 2 as above)
ix) Only PPDC verified / authorized hooks are to be used.
x) Two flat M.S. plate hooks are to be used at cross fin shoe ends or circular / torus hooks for conical shoe ends.
xi) Stoppers are to be put at both sides of the piles and fastened to be ground. (Diagram 1b as above)
2) Lifting from one end for pitching is at 0.2 x L. Pile is to be fastened in such a way to prevent slipping (multiple loop grip tie) with the following controls :-
i) No dragging along ground.
ii) Lifting rate at slower pace.
iii) Lifting piles from the ground is to be done at the open-ends with “C” hook.
iv) Nothing must be below the pile at transfer.
3) Refer to diagram 1a and 1b above for storage details.
i) Piles are preferably to be stored according to their respective lengths.
ii) Spacers of 2″ x 4″ hardwoods are to be placed at 0.2 x L from both ends of the piles and in between the 2 layers of piles.
iii) Preferably the ground is levelled and compacted with a 100mm thick bed of 20mm aggregates.
SS Pile and also known as Super Strength Pile has higher strength to carry higher loads of building with lesser pile point, it saves the cost and more economic. Contractor like to use this piling method on those high building and large structure. There is few steps to install or drive the SS piles, it’s economic piling method but it takes time to install as well. Every types of piles have their own pile driving procedure, so the pile driving method is slight different compare with the piling driving procedure for normal spun pile or bored pile. Piling machine used is different as well.
How To Install Super Strength Pile or SS Pile
1) Driving of Piles
Place the cushion, helmet and gammer on the pile head with adequate alignment. Check verticality of the pile to BS 8004 requirements. After several blows, check pile location and alignment again. Concentricity of driving equipment and pile shall be maintained at all times.
When driving to soft ground, adjust the hammer drop so as not to induce excessive tensile stress in the pile. Driving should proceed without interruption until the pile reaches the expected depth or blow count (ie. penetration mm/10 blows).
2) Joint Welding
When a pile has been driven close to the ground level and an extension is required, the driving must be immediately stopped. Joint plates are to be cleaned thoroughly from mud, dust, oil and other residues detrimental to the welding. Cleaning can be done by using wire brush and some solvents in between runs of weld.
Three guide plates at 120 angle to each other are set up on the driven pile before the extension pile is being lowered to sit concentrically over it. The two piles will be alligned automatically. Welders should be qualified to BS 4872 welding test.
Welding is performed by means of either manual or semi-automatic arc welding. For manual welding, electrodes should be selected carefully and conform to type E41 of BS 5135 as a minimum or higher if deemed necessary. Semi-automatic welding should be non-gas shield arc welding.
Throat depth should be filled with more than two layers of welding materials and slag removed in between layers. Metal oxide paint can be applied as an anticorrosion measure. The welding must be checked before driving proceeds.
3) Driving Equipment
SS Piles are usually installed by percussion method. In certain cases where underground obstructions such as large boulders are encountered, special shoes (i.e. conical, oslo point or pipe shoe) or pre-augering may be necessary. The driving hammer type (hydraulic or diesel) and size must be carefully selected to install the piles successfully without any damage to the pile itself (BS 8004). Two plumb guides at right angles to each other are normally used to ensure verticality of the pile during driving. Spirit levels and theodolites have also been proven useful.
4) Helmet and Cushioning
Correct helmet dimensions is critical in curbing the vibration and/or movement of the pile head hence maintaining fixity and eccentricity of hammer to pile.
The inner diameter of the helmet should have a small but not larger than 30mm clearance over the outside diameter of the pile which needs to be wedged tight. The hammer ram must be kept concentric with the pile head to minimize secondary stresses arising from the piling activity.
Adequate timber cushioning is also very significant as it ensures uniform transmission of driving energy. Thickness of cushion is a minimum of 100mm for hard wood for 300mm Ø to 400mm Ø piles and a minimum of 150mm for larger sizes. Since stiffness of the cushioning material increases with repeated compaction.
5) Set Criterion
A pile is considered set when the calculated set criterion is met (penetration mm/10blows) or the required penetration depth reached. Bearing capacity of the pile can then be further checked with a load test after
the pore water pressure has dissipated. PDA and driving formulae checks are also useful.
6) Pile Head Preparation
Piles should be cut using a diamond cutter. Hacking is not recommended as it will generate micro cracks in the concrete. Pile Anchorage Details show suggested anchorage reinforcement. However, reinforcement may be redesigned to cater for individual project specifications.
Super Strength Pile or SS pile is another type of piling which has higher strength and able to carry more loads from any structure with fewer number of points. Most probably SS piles are made of prestressed or spun concrete. SS piles are constructed in round and hollow in cross section and have the lengths up to 12 metres. SS Piles have a nominal bearing capacity in the range 1690 kN to 3500 kN. Of course, SS Pile has its’ own piling machine and it’s slightly different compare to other piling machine.
Features Of Super Strength Pile
Being economical is the basic consideration of every piling contractor. With the wide variety of sizes to choose from, SS Piles allow for optimum selection of sizes, wall thicknesses and lengths to meet contractor’s requirement. In additional to that, the higher strength also means that contract will need fewer number of points to cater for a designed column load.
2) High Concrete Strength
Owing to the Autoclave curing technology and high compaction induced by the centrifugal process, SS Piles are able to achieve concrete compressive strength of more than 78.48Mpa within a time frame of 24 hours. Coupled with SS Piles’ hollow circular cross-sections and prestressing, contractor will have piles with high resistance to bending. Higher concrete compressive strengths also allow SS Piles to be driven hard into rigid bearing strata to attain higher bearing capacity per pile point.
The carefully monitored spinning process which gradually induces a force equivalent to 35 times that of gravity will lower the water to cement ratio further thus increasing the concrete density greatly.
Though the high temperature and pressure of the Autoclave curing technology, the calcium silicate hydrate in the high-density concrete will stabilize and form crystals of tobermorite. Permeability is then reduced. Low permeability also means high resistance to internal steel reinforcement, making the concrete exceedingly durable.
Utilizing SS Piles in extremely corrosive marine condition can also be considered as the low permeability will prevent sulfate and also hinder the more vigorous chloride attack.
4) Consistent High Quality
The quality control team rigorously inspects in-coming raw materials to ensure their compliance with governing standards. An exemplary quality control program including periodical samplings and testings, is conducted constantly to guarantee optimum performance of the SS Piles.