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Bored piles are reinforced concrete piles which are made into the bored hole in the ground to support the vertical structure. The hole is filled with concrete and steel reinforcement to make a pile. The bore is carried out by the drilling rigs or by hydraulic cranes. The depth of the bore piles depends on the construction and height of the vertical structure. Normally the depth of the bored piles can be up to 50 m in the ground.

Bored piles are also known as replacement piles. In Bored piles the removal of spoil forms a hole for a reinforced concrete pile which is poured in situ. The spoil is replaced by the pile, hence 'replacement' piles as opposed to displacement piles where soil is forced away by driving or screwing the pile.

Bored piling is commonly used for bridge work, tall buildings, and massive industrial complexes, all of which require deep foundations. The bored pile is also used in the difficult soil conditions. Before the start of the bored piles construction, the soil report has to be prepared. The soil report will decided the kind of technology that will be needed for the bored piles.

The biggest advantage of the bored piles is that it does not creates vibrations and noise that is generated due to traditional pile system. The other advantages of the bored piles are that the pile of variable lengths can be extended through soft, compressible, or swelling soils into suitable bearing material. Piles can be extended to depths below frost penetration and seasonal moisture variation. Large excavations and subsequent backfill are minimised in the construction of bored piles. Since the boring is done on the specific site, there is negligible disruption to the adjacent soil or structures. Also as mentioned before vibration is low therefore disturbance to adjacent piles or structures is reduced. High-capacity caissons can be constructed by expanding the base of the pile shaft up to three times the shaft diameter, thus eliminating the need for caps over groups of multiple piles. For many design situations, bored piles offer higher capacities with potentially better economics than driven piles.

Bored Piles are used for the massive construction complexes and the bridges where the load of the structures is huge. They are a commonly-used form of building foundation that provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics.

Bored piles are used primarily in cohesive subsoils for the formation of friction piles and when forming pile foundations close to existing buildings. They are popular in urban areas as there is minimal vibration, where headroom is limited, where there is no risk of heave, and if there is a need to vary the length of the piles.

In addition to their conventional use as structural foundations, bored piles have been used to construct secant or tangent pile walls for earth retention purposes, for cut-off walls for seepage control, and for slope stabilisation purposes to increase the factor of safety (FS) against sliding or overturning. 

Some of the factors affecting the selection and use of bored piles include site conditions and constraints, budgeting and scheduling concerns, presence of and depth to adequate load bearing soils/rock, environmental and noise restrictions, the magnitude of the imposed loading, reliability and risk and availability of space for construction and for the completed foundation. Especially in urban areas, environmental restrictions and noise limitations may affect the cost, productivity and foundation type/method at a particular site. In general, there seems to be increasingly tighter and more congested project sites, greater demands on drilling equipment, and alternative applications for bored piles other than for structural foundations.

Installing a bored pile starts with drilling a vertical hole into the soil, using a bored piling machine. The machine can be outfitted with specially designed drilling tools, buckets, and grabs to remove the soil and rock. Piles can be drilled to a depth of up to 60 meters and a diameter of up to 2.4 meters. The drilling process may include driving a temporary steel cylinder, or sleeve, into the soil. This remains in place in the upper portion of the hole until the pile is poured.

Once the hole is drilled, a structure of reinforcing steel rebar is built and lowered into the hole, then the hole is filled with concrete. The top of the pile may be capped with a footing or pier near ground level to support the structure above.

The type and configuration of drilling tools are chosen according to the nature and geo-mechanical characteristics of the soil to be excavated. 

An auger or a bucket can be used to bore cohesionless soil or average compacted clay. An auger consists of a central shaft with a spiral shaped flange welded around it. The cutting edges of the helical flange have wedge-shaped teeth. Augers are suitable for digging clayey or cohesionless, dry soil. In fact, if there is ground water, the excavated soil can often fall back into the hole as the tool is being lifted out. 

A bucket is made up of a hollow, cylindrical section fitted with a hatch on the bottom with a slit that is attached by a hinge to one end of the cylinder. Cutting teeth are welded onto the edge of the slit to help load the soil into the cylindrical bucket and also prevent it from falling out when the tool is withdrawn. Once the drilling tool has been brought to the surface, the hatch is unhooked from the bucket body and the soil is discharged. As it is a closed drilling tool, the bucket is ideal for digging loose, cohesionless soil or soft clay below the water table. 

A rock auger or a core barrel can be used when boring highly compacted clay or rocky soil. A rock auger uses different cutting teeth compared to a traditional auger. The teeth on a rock auger are not wedge-shaped but conical (they are also called “bullet” teeth, as they look like the streamlined tip of a bullet) with a heavy-duty metal element inserted at the top. The teeth are also housed in supports to allow them to rotate around the axle, hence wear of the cutting tip is uniform. Thanks to this configuration, rock augers are ideal for drilling highly compacted clay and soft or very weathered rocks.

When digging very hard rock formations, the most suitable drilling tool is the core barrel. A core barrel is basically a bucket without the hatch on the bottom, fitted with cutting teeth along the whole lower edge. Thanks to the special arrangement and configuration of the teeth (which can vary according to the hardness of the soil), once the rock core has entered the inner cylindrical assembly, it will not fall out as the barrel is being extracted.