In general bored piles and hand-dug caisson considered as the most economical foundation amongst all types of deep foundation. Similar to micro pile, bored pile/hand-dug caisson are a cast in-situ concrete pile. Bored pile can be constructed in a wide choice of diameters, typically ranging from 350mm to 1800mm, and to depths of up to 100m at rakes of up to 1:4. Whereas hand-dug caisson often constructed in larger diameter greater than 900mm at confined/constraint spaced. One of the advantages that made bored pile/hand-dug caisson popular type of deep foundations is that they can be tailored to particular requirements of the building or deep excavation. According to their load bearing behavior, bored pile/hand-dug caisson are categorised into two main groups namely, friction piles, (i.e. transfer loads mainly by frictional resistance along the shaft) and end-bearing piles (i.e. load is primarily transferred to the surrounding soil of through the pile base). Bored piles/hand-dug caisson may be constructed singly, in groups or as walls using secant, contiguous or king piles, with or without infill based on the structural requirements. In Malaysia bored piling and hand-dug caisson are very popular type of pile in the construction of many tall buildings and bridges that require withstanding/bearing load of thousands of tons. Bored piling is cast by using bored piling machine that has specially designed drilling tools, buckets and grabs.

 

Temporary casing with combination of auger is sometime used to drilling and remove the surface loose soil. The bucket type of drilling tools is used to obtain more vertical and cylindrical shape of bored pile. Depending on the type of hard stratum, generally it can be drilling into 50 metres depth of soil. As most of the drilling method involves less vibration, it is a very suitable type of foundation to minimise noise pollution. Although many piling contractor may assume as it is one of the simplest type of foundation, to decide on the type of drilling tools to be used for a specific subsurface condition required more knowledge in geotechnical engineering. In fact this is one of the advantages that Zeox has acquired over the years, where with experienced engineers, the correct drilling technology by ensuring less disturbance of the surrounding soil is easily decided after immediate study. To prevent the drilled/bored hole from collapsing, it must be supported by either using steel casing or stabilizing muds such as bentonite suspension especially in cohesionless soils such as sands, gravels, silts etc. When steel casings is used temporarily, it is important to ensure the thickness of wall is thick enough to allow multiple uses, in addition a thicker collars is made on the top of casing for easy handling when driving using vibro hammers and the internal diameter is slightly larger than bored piles’ nominal diameter, to allow easy passage of drilling tools. However when permanent casings is required then sufficient thickness to drive in the casing is enough. Upon desired depth is achieved, reinforcement in form of rebar cages usually are prefabricated in segments with sufficient length and is enable to lift using crane. Splicing of rebar cages can be done by lap splice, welded lap splice or mechanical threaded couplers but staggering lapping is recommended. The concrete casting is done by pouring concrete with the design strength and slump as required, through watertight segmental Tremie Pipes, starting from the pile bottom and letting the tremie pipe bottom end remain at least 2 meters submerged in concrete until the completion of pouring. This method while ensure the pile is free from any cold joint, the final quality of cast concrete will be better.