Structural foundation or deep foundation is a type of foundation that is used to transferring the structural loads in to the subsoil. These are several ways of transferring structural loads into the subsoil on sites where ground conditions are unfavourable. The bearing capacity of the subsoil can be increased by ground improvement techniques such as :
replacement of non-load bearing layers of soil close to the surface.
soil consolidation using pre-loading or vertical drains.
soil compaction using grout injection; deep vibration or stone columns.
Alternatively, structural loads can be transferred to stronger competent strata at depth by the use of :
bored piles
diaphragm wall elements
mixed in place (MIP) piles
piles reinforced by steel bars
vibrated concrete columns
Technical literature on all these special alternative construction techniques is available on request from foundation contractor. There are several ways to build structural foundation or deep foundation, they are retaining wall and bored piles.
Retaining Wall
Retaining wall is a type of structural foundation or deep foundation, which is used to transfer the structural into the subsoil. The problem of providing stable retaining structures close to existing buildings or of constructing watertight excavation pits can be solved in a number of ways. However, the most appropriate solution is almost always the installation of a bored pile retaining wall.
Bored Piles
In general bored piles offer the most economical foundation as they can be constructed in a wide choice of diameters, typically ranging from 300mm to 1800mm, and to depths of up to 70m at rakes of up to 1:4. They can thus be tailored precisely to the particular requirements of the building or excavation. This flexibility means that bored piles can provide solid foundation elements suitable for almost all site conditions.
* Friction Pile
* End Bearing Pile
Bored piles can be classified into two main groups, according to their load bearing behaviour: friction piles, which transfer loads mainly by frictional resistance along the shaft; and endbearing piles in which load is primarily transferred to the surrounding soil of through the pile base. Depending on the structural requirements, bored piles may be constructed singly, in groups or as walls using secant, contiguous or king piles, with or without infill.
* Single Piles
Usually bored pile is used for those tall buildings or massive industrial complexes, which require foundations which can bear the load of thousands of tons, most probably in unstable or difficult soil conditions. The method of drilling bored pile is different from RC Square pile or spun pile which are using driving method, the piling machine to be used will be different too. Bored piling works required specialist bored piling contractor to follow up instead of hiring general piling contractor. There is a simple step-by-step method on how to drill the bored pile in construction site.
How To Drill Bored Pile
1) Adjust the piling machine on the pile axis and haul with the auger to the drilling place.
2) Start drilling until the auger is filled.
3) Return from the drilling level to the top of the pile hole.
4) Swing to the uploading area.
5) Unload the dirt in the unloading area.
6) Swing back to the top of the hole.
7) Repeat steps 2 to 7 until the pile is completely drilled. Relocated the machine and start steps 1 to 8.
8 ) Start erecting rebar cage using a crane.
9) Use funnel for dry method and tremie for wet method. Start pouring the concrete and finish the pile.
Bored pile is another type of reinforced concrete pile which is used to support high building which has heavy vertical load. Bored pile is a cast-in-place concrete pile where the bored piles have to be cast on construction site, while other concrete piles like Spun Pile and Reinforced Concrete Square Pile are precast concrete pile which they’re cast in the factory.
Normally bored piling has be to carried on those tall buildings or massive industrial complexes, which require foundations which can bear the load of thousands of tons, most probably in unstable or difficult soil conditions. Bored piling is cast by using bored piling machine which has specially designed drilling tools, buckets and grabs, it’s used to remove the soil and rock. Normally it can be drilling into 50metres depth of soil. The advantage of bored piling is its’ drilling method, little vibration and lower noise level.
The drilling method is depending on the condition of soil, piling contractor has to do soil investigation and decide which drilling technology has to be carried on. Piling contractor decide the correct drilling technology and minimize disturbance of the surrounding soil. For cohesionless soils such as sands, gravels, silts etc, whether it’s under the water table or not, the pile bore hole must be supported using steel casing or stabilizing muds such as bentonite suspension. After these, reinforcement bar will be put into the bore hole and concrete will be poured into the bore hole.
Bored piling is popular to be used in construction as a foundation especially for bridge work and tall building as well. Bored piling work has to be done by specialist bored piling contractor, normal piling contractor can’t be done without experience and knowledge about bored piles.
