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Bored pile (Onshore & Offshore)
Bored pile is a cast-in-situ pile, constructed by making a cylindrical holein the ground to the required depth and subsequently filling it with reinforced concrete or other proprietary units. This type of foundation often referred as replacement pile is suitable for areas requiring minimum disturbance of ground heave and vibration,such as proximity with existing structures. Pile length and diameter (from small 0.4 m until large 2.5 m or more) can be readily varied to suit varying ground conditions, making bored piles the most commonly adopted foundation type for heavy structures. Often in bored pile constructions encounter loose and collapsible soil during drilling; as such a temporary steel casing (short or full casing system) shall be inserted into the hole, or alternatively using bentonite or polymer slurry to stabilize it from cave in. Particularly in offshore works, permanent casings are normally compulsory to construct bored piles.
One of the methods to improve the bearing capacity of bored pile is by base enlarging (under reamed) using a belling bucket to create bell shape at the base. Another method is a secondary post grouting either at the shaft or base pile, by injecting grout materials through tube a manchette after pile concreting, to spread across the soil at the shaft or base pile. Such piles can develop considerable end bearing and uplift capacity.
Piling (Onshore & Offshore)
Pile is a structural element of a deep foundation, driven into the ground to transmit surface loads to a subsurface layer or a range of depths in the soil mass. The pile material can be made out of timber, steel, reinforced and prestressed concretes. Driving piles compare to drilling shafts, is advantageous because the soil displaced by driving the piles compresses the surrounding soil (displacement pile), resulting greater friction and increasing load bearing capacity. There are commonly five types of pile driving hammer: 1) drop hammer, 2) diesel hammer (single and double acting), 3) hydraulic hammer which produces less noise and vibration than diesel, and does not emit exhaust fumes, 4) vibro hammer which best suited for sandy or gravelly soils, and 5) Jacking hammer which provides no vibration and noise nuisances and best applicable for urban areas.
Piling can be done either vertically or at an angle to the vertical (raked pile), depending on the pile driving technique. The latter is commonly adopted in offshore structures which are subjected to greater lateral loads.
Injection Pile (Micropile)
Injection pile or micropile in principal is constructed by injecting a grout materialinto the soil, after drilling a relatively small hole diameterof pile (less than 0.3 m) and forming a pregrout annulus.The action of injection will enlarge the pile hole making the pile into buldging shape like.The combination of grouting and enlargement effects will provide much improved skin friction and end bearing capacity.The capacity can be increased further by increasing the grouting pressure.The application of this pile is commonly for foundation, underpinning and anchor.
This method can be applied from soft to hard soil, and has advantages of no heavy equipments required, no vibration nuisance and veryminimum sound polution.This method is very suitable for construction with difficult access, in the sway areas, in the river or mountain, in narrow places, urban areas, between or in the houses/buildings.
Pile testing is necessary for any foundation construction to ensure the quality of the installed piles and to proof the designer’s estimate of pile capacity and settlement meet the requirements.
a) Pile driving analyzer (PDA), is a highstrain dynamic load test method (non destructive) to assess the capacity and qualityof pile, and also driving stresses and hammer energy when monitoring installation.
b) Pile integrity test (PIT), is a low stain dynamic load test method or also known low strain impact integrity test (non destructive), used for assessing the integrity of piles or shafts.
c) Pile static loading test (SLT), the most realiable method to check a pile capacity is to actually load test it. The test is simply conducted by replicating the designed actual load to the pile and analyze its performance. Three types commonly performed: axial compression, axial tension, and lateral load tests. For axial compression test, there are three methods to perfom: kentledge method, reaction pile method and bi-directional axial (O-cell) method.