Bored piles are cast in place cylindrical piles excavated either by use of rotary equipment operated augers , buckets, under static drilling fluid or large drill bit (for hard rock) with reverse circulation, with chisel grab and casing oscillator for bouldery ground, with large diameter DTH hammers and compressed air (drilled piles), among others.
Most common large diameter bored piles, are installed through an overburden of cohesive or cohesionless soil strata, with or without water tale, down to firmer ground, to achieve the design bearing capacity by skin friction, base bearing or both, to serve as foundation piles for residential, commercial, institutional buildings, industrial complexes or infrastructures.
Bored piles installed in common soil with the presence of water table, generally require the use of a short temporary steel casing and a drilling fluid as static suspension to provide support to the surrounding soil while excavating the pile and until complete backfill of the pile excavation with concrete, in order to prevent cave-in of the excavation and destabilizing the surrounding soil formation.
The preparation and handling by most effective drilling fluid, Bentonite Mud, is a sophisticated technology by itself and requires a complete set up of dedicated equipment and (basic) field laboratory.
The most common diameters of bored piles range from 0.6 meter to 2.0 m meters, likewise length can range from few meter to sixty or more meters, depending upon design loads and soil parameters.
Classification of piles with respect to load transmission and functional behavior
• End bearing piles (point bearing piles)
• Friction piles (cohesion piles)
• Combination of friction and cohesion piles
Classification of pile with respect to type of material
• Composite piles
Classification of pile with respect to effect on the soil
A simplified division into driven or bored piles is often employed.
• Foundation elements for carrying vertical building loads
• Foundation elements for retaining walls
• Temporary building pit walls
• Components of the final structure
• Protection against uplift and for taking up tension loads
• Slope security
Quality Assurance/Quality Control
Quality control criteria for piles are developed using the framework of acceptance-sampling analysis based on the statistical data of static and dynamic load tests. The static and dynamic load tests are often carried out for quality control and verification of load-carrying capacity of driven piles. The number of load tests and the acceptance criterion of measured capacities are discussed in this technical note. The relationship between the number of load tests and the criterion on acceptance of measured capacity is elucidated. It is shown that the measured capacity required to assure adequate quality control decreases with an increase in the number of load tests. Either the number of load tests or the target measured capacity or both needs to be increased in order to obtain a higher target reliability index. The number of load tests associated with the acceptance criteria of the measured capacities is recommended in this technical note for the static and dynamic pile test methods to achieve different levels of reliability.
Benefits of Bored Piles
• Length can be readily varied to suit varying ground conditions.
• Soil removed in boring can be inspected and if necessary sampled or in- situ test made.
• Can be installed in very large diameters.
• End enlargement up to two or three diameters are possible in clays.
• Material of piles is not dependent on handling or driving conditions.
• Can be installed in very long lengths.
• Can be installed with out appreciable noise or vibrations.
• Can be installed in conditions of very low headroom.
• No risk of ground heave.
Back to page