Bored piles are widely used in Malaysia because they can:
Malaysian bored-pile design commonly considers information obtained from soil investigation, including Standard Penetration Test results, groundwater conditions, rock levels and the characteristics of the soils or rock encountered. Rock-socketed bored piles are also frequently used where suitable bedrock is reachable.
Every bored-pile project is different. The appropriate pile diameter, depth, reinforcement, construction method, borehole-support system and testing requirements must be determined by the project’s geotechnical and structural engineers.
2. How Bored Piles Transfer Loads
3. Bored Pile Construction Sequence
4. Steel Casing and Drilling Fluid
5. Typical Bored Pile Diameters and Depths
6. Bored Piles in Soil and Rock-Socketed Bored Piles
7. Advantages and Limitations of Bored Piles
8. Quality Control and Testing
9. Common Bored Pile Construction Problems
10. Frequently Asked Questions About Bored Piles
A bored pile is a cast-in-place reinforced concrete foundation constructed by removing soil or rock to create a cylindrical borehole in the ground.
It is may also be commonly described as:
The term replacement pile is used because the soil or rock occupying the pile location is removed and replaced with reinforced concrete. This differs from a displacement pile, such as a driven reinforced concrete pile, which pushes the surrounding soil aside as it enters the ground.
A typical bored pile consists of:
The pile receives loads from the structure above and transfers them into the surrounding ground. Depending on the design and ground conditions, the load may be resisted through friction or adhesion along the pile shaft, bearing resistance at the pile base, resistance within a rock socket, or a combination of these mechanisms.
Bored piles may be used for:
They are particularly useful where the structural loads are too high for shallow pad or raft foundations, or where compressible surface soils would result in excessive settlement.
The completed pile may look simple, but successful bored-pile construction requires coordinated control of:
A problem at any stage can affect pile quality and structural performance. For this reason, bored piling should be undertaken by an experienced specialist contractor working under an approved method statement and appropriate engineering supervision.
A bored pile transfers structural loads from the building or structure into the ground through several resistance mechanisms.
The principal mechanisms are:
For most buildings, the primary design concern is the pile’s ability to carry vertical compression loads while keeping settlement within acceptable limits.
Shaft resistance develops along the external surface of the pile where the concrete interacts with the surrounding soil or rock.
As the structure applies load to the pile head, a small amount of downward pile movement mobilises friction or adhesion along the pile shaft. The surrounding ground resists this movement and carries part of the structural load.
The amount of shaft resistance depends on factors including:
A long pile passing through competent residual soil may obtain a substantial proportion of its capacity from shaft resistance, even when it eventually terminates in a stronger bearing layer.
Instrumented bored-pile studies in Malaysian Old Alluvium have shown that, for some long piles, shaft resistance carried most of the working load while base resistance made a relatively small contribution at normal working-load levels. This does not apply to every pile, but it demonstrates why pile behaviour must be assessed using project-specific ground information rather than assuming that all loads reach the pile toe.
Base resistance develops beneath the toe of the pile.
When the pile moves downward, the material below the pile base resists penetration. Strong dense soil or competent rock can provide significant end-bearing capacity.
The theoretical base resistance may be high, particularly for large-diameter piles. However, its reliable mobilisation depends on:
Loose soil, rock cuttings, contaminated drilling fluid or sediment left at the bottom of the bore can form a compressible layer beneath the pile. This may reduce effective base resistance and increase settlement.
For this reason, Malaysian bored-pile practice may place greater reliance on shaft resistance unless the pile base can be adequately inspected, cleaned, verified and tested. The adopted design approach remains the responsibility of the geotechnical designer.
Most bored piles behave through a combination of shaft and base resistance.
The load does not instantly travel to the bottom. It is progressively transferred from the pile into the surrounding ground along the pile length. The proportion carried by the shaft and base changes as pile movement increases.
At relatively small working-load movements, shaft resistance may dominate. As the applied load and settlement increase, more base resistance may be mobilised.
Engineers therefore assess both:
A pile that has a high theoretical ultimate capacity may still be unsuitable if it settles excessively under service conditions.
Bored piles may also be designed to resist horizontal forces and bending moments generated by:
Lateral resistance is provided by interaction between the pile and the surrounding ground, together with the structural bending stiffness of the reinforced concrete pile.
Tension and uplift resistance
Where a foundation is subjected to uplift, the pile may act as a tension element.
Examples include:
In such cases, the reinforcement must be detailed to transfer tensile force through the pile, pile cap and supporting structure. Shaft resistance generally provides much of the geotechnical uplift resistance.
The precise construction method depends on the pile design, ground conditions, groundwater, access and equipment available. A typical rotary bored-pile sequence is described below.
A bored-piling rig is a large and heavy item of construction equipment. It must operate on a properly designed, prepared and maintained working platform.
The platform must be able to support:
An inadequate platform can result in excessive settlement, tilting or instability of the rig. Platform condition also affects the ability to maintain pile position and verticality.
Access routes, overhead restrictions, underground utilities, drainage and working space should be reviewed before mobilisation.
The pile centre is established based on the approved pile-layout drawings.
Setting-out controls may include:
The piling rig is aligned over the pile position, and the drilling mast is checked for verticality before boring begins.
Accurate setting out is important because significant pile-position errors can affect the pile cap, column alignment and load distribution. Malaysian bored-piling specifications commonly require installation records and as-built survey verification after completion.
A temporary steel casing is often installed through the upper soil layers.
The casing can:
The casing may be installed by the rotary rig, casing oscillator, casing rotator, vibro hammer or another approved method, depending on the project.
Some stable ground conditions may allow an open or dry bore below the casing. Unstable ground may require deeper casing, full-length casing, or casing used together with stabilising fluid.
The pile shaft is excavated using drilling tools selected for the ground conditions.
Common tools include:
The rig advances the borehole while excavated material is brought to the surface and removed.
The drilling team should observe and record the materials encountered. Changes in soil, obstructions, groundwater, cavities, loss of drilling fluid and the depth at which rock is encountered can all influence the construction process and pile acceptance.
The actual ground conditions should be compared with the available soil-investigation information. Significant discrepancies should be brought to the attention of the project engineer.
Where the ground cannot remain open safely, the borehole is supported using:
The objective is to prevent the borehole wall from collapsing or excessive soil from entering the excavation.
The drilling fluid level is normally maintained above the groundwater level to provide stabilising pressure against the sides of the bore. Its properties must be monitored because fluid that is too heavily contaminated, too thin, too thick or incorrectly mixed may not perform as intended.
The pile is advanced to its intended termination depth.
Depending on the design, it may:
The pile should not be terminated merely because a predetermined drawing depth has been reached if the actual founding conditions differ materially from those assumed in the design.
The final depth and any required rock-socket length should be verified in accordance with the approved method statement, drawings and engineer’s requirements.
After reaching the required depth, loose material and drilling debris are removed from the base.
Cleaning may involve:
Before concreting, checks may include:
This is one of the most important stages of bored-pile construction. Loose sediment or contaminated fluid at the base can restrict concrete flow and adversely affect the completed pile.
A prefabricated steel reinforcement cage is lifted and lowered into the borehole.
The cage typically includes:
Large or deep cages may be fabricated in sections and joined while being lowered into the pile.
The cage must be sufficiently rigid to avoid excessive deformation during lifting. It should be positioned at the correct level and adequately centralised to maintain concrete cover.
Where cross-hole sonic logging is required, access tubes are secured to the cage before installation and protected against damage or blockage.
Concrete is commonly placed using a tremie pipe, particularly where water or drilling fluid remains in the bore.
The tremie is lowered to the bottom of the borehole. Concrete is introduced through the pipe so that fresh concrete rises from the bottom upward.
During concreting:
Concrete should not simply be allowed to fall through water or drilling fluid, as this may cause segregation, washing out, contamination and discontinuities.
The concrete must have appropriate strength, workability, cohesiveness and retention of workability for the selected placement method. Project specifications may set particular requirements for slump, concrete grade, cement content, delivery time and testing.
Temporary casing is usually removed while the concrete remains workable.
Casing extraction must be coordinated with the concrete level so that:
Concrete is normally placed above the final pile cut-off level. This additional concrete, known as overcast, allows contaminated or weak concrete at the top to be removed later.
After the concrete has gained sufficient strength, the pile head is broken down to the specified cut-off level and prepared for connection to the pile cap or structure.
G&P’s Malaysian bored-piling specification, for example, requires concrete to be finished above cut-off so that the retained pile concrete is homogeneous and free of laitance or other deleterious material. The precise overcast requirement remains project-specific.
Temporary casing is a cylindrical steel tube installed into the ground before or during drilling.
It is commonly used to support:
Temporary casing can also provide a positive guide for the drilling tool and improve control of the pile position.
The required casing length is not necessarily the same for every pile. It may vary across a site according to:
Where a discrete unstable layer exists at depth, special measures may be necessary. These can include longer casing, double casing, full-length casing or changes to the drilling method.
In certain conditions, the casing may be left permanently in the ground.
Permanent casing may be considered where:
Permanent casing adds material and installation cost and must be incorporated into the design and construction method.
Bentonite is a clay-based material mixed with water to produce a thixotropic support fluid.
When properly prepared and maintained, it can:
The fluid is circulated, cleaned or replaced as necessary. Before concreting, excessive suspended sand and debris must be removed.
Common control parameters include:
The acceptance values depend on the project specification and the stage at which the fluid is tested. Malaysian specifications may require sampling near the base of the bore before concreting because conditions at the bottom can differ significantly from conditions at the surface.
Synthetic or natural polymer systems may be used as an alternative to bentonite on suitable projects.
Potential benefits include:
However, polymer performance is sensitive to:
Neither bentonite nor polymer should be treated as a material that can simply be mixed and left uncontrolled. The support-fluid system must be designed, tested and managed throughout the operation.
Poor drilling-fluid control can contribute to:
The contractor should maintain records of fluid type, test results, fluid losses, desanding and corrective actions. Waste fluid must also be contained and disposed of according to applicable project and regulatory requirements.
Bored piles can be constructed in many diameters and to substantial depths.
There is no single standard size suitable for all projects. The selected diameter and length depend on:
For conventional building and infrastructure work, bored-pile diameters commonly include sizes such as:
Smaller or larger diameters may be used where required.
Specialist large-diameter bored piles can exceed 2 metres in diameter. Keller states that its bored piles can be constructed in typical diameters of up to approximately 2.4 metres, although actual contractor capabilities and project limits vary.
Increasing the pile diameter provides:
However, a larger diameter also usually means:
The most economical solution is not automatically the largest pile. In some projects, a greater number of smaller piles may be preferable. In others, fewer large-diameter piles may simplify the pile-cap arrangement and reduce congestion.
Bored piles may extend from relatively moderate depths to more than 60 metres. Greater depths are possible with suitable equipment and construction planning.
Pile depth is governed mainly by the level at which the required capacity and settlement performance can be achieved.
A pile may need to pass through:
Two piles of the same diameter can therefore have very different lengths, reinforcement requirements and construction risks.
Pile diameter, length and capacity interact.
For example:
The final pile schedule should be based on engineering design supported by an adequate ground investigation and, where required, preliminary or verification load testing.
Bored piles can obtain support from soil, rock or a combination of both.
The distinction is important because soil piles and rock-socketed piles may require different drilling tools, termination criteria, inspection methods and design assumptions.
A soil-founded bored pile remains predominantly within soil and derives capacity from:
Typical soil formations may include:
For Malaysian projects, SPT results are frequently used as one input when estimating bored-pile shaft and base resistance in soil. However, design should not be based on SPT values alone without considering geology, groundwater, soil description, construction effects and applicable design methods.
Long soil piles may carry substantial loads through shaft resistance. This can make them effective even when competent rock is too deep to reach economically.
The performance of a soil pile is affected by how the bore is constructed. Excessive disturbance, prolonged exposure, loss of ground or poorly controlled drilling fluid can change the condition of the pile-soil interface.
A bored pile may terminate in a dense or very stiff soil layer intended to provide base resistance.
For reliable performance, the founding layer must be:
The pile base must also be properly cleaned. Even a strong bearing layer cannot perform as intended if loose cuttings remain between the concrete pile and the founding material.
Rock-socketed bored piles
A rock-socketed bored pile extends into rock for a specified depth.
Its resistance may be developed through:
Rock sockets are commonly considered where competent rock is found at an economically reachable depth and high pile capacities are required. Gue & Partners’ Malaysian guide describes rock-socketed bored piles as common in local practice where suitable bedrock is accessible.
Constructing a rock socket normally requires tools such as:
Rock-socket drilling is generally slower than soil excavation and causes greater wear to tools and equipment.
Rock quality can vary considerably.
The design and construction team may need to consider:
A shallow socket in strong, continuous rock may behave differently from a longer socket through fractured or weathered material.
Limestone can present particular construction challenges because of karstic features such as:
A bore may encounter apparently competent rock at one level while an adjacent pile encounters a cavity or much deeper rock.
In such conditions, the piling method may require:
The required rock-socket depth should not be selected as a universal rule. It must reflect the load, rock mass, pile diameter, design method, construction quality and project specification.
Bored piles offer significant advantages, but they are not the best foundation solution for every site.
Large-diameter bored piles can carry substantial axial loads. Their diameter, depth, reinforcement and founding condition can be adjusted to suit heavily loaded buildings and infrastructure.
Bored piles can be constructed in multiple diameters rather than being limited to a small number of manufactured pile sections.
This gives designers flexibility to optimise:
Modern rotary piling equipment can construct deep piles through multiple ground layers and into rock.
Because the soil is drilled and removed rather than displaced by impact driving, bored piling generally produces less vibration than driven piling.
This can be important near:
Bored-pile rigs still create machinery, excavation and handling noise, but they avoid the repeated impact associated with drop-hammer or some driven-piling systems.
This can make bored piling more suitable for certain urban or noise-sensitive sites.
Appropriate drilling tools can penetrate hard layers, weathered rock and some obstructions that may cause refusal or damage to driven piles.
The reinforcement cage can be designed to accommodate:
Drilling spoil provides additional information about the materials encountered. While this does not replace a proper soil investigation, it helps the site team compare actual conditions with the expected ground profile.
The same general bored-piling process can be adapted to form:
Much of the completed pile is underground and cannot be directly inspected after concreting.
Performance depends on controlling:
Bored piling produces soil, slurry, rock cuttings and sometimes contaminated material that must be stored, transported and disposed of properly.
Urban sites may have limited room for spoil-handling operations.
Once concreting begins, continuous placement is generally required.
Disruption caused by:
can create serious construction risk.
Conventional bored piling requires adequate:
Sites with very restricted access or low headroom may require micropiles, mini-piles or specialised low-headroom equipment instead.
Unstable, water-bearing or highly permeable ground can require extensive casing and drilling-fluid support.
Hard rock, boulders, obstructions and heavily reinforced old foundations can significantly reduce production and increase tool wear.
Ground loss or overbreak can increase the actual concrete volume. This is especially relevant in loose zones, cavities, fill and fractured formations.
Large or highly loaded piles may require:
These measures improve confidence but must be included in the programme and budget.
Depending on the ground, loads and site constraints, alternatives may include:
Foundation selection should compare whole-project cost and risk rather than only the price per metre of pile.
Quality control for bored piling begins before the first pile is drilled and continues until the piles have been accepted.
A comprehensive quality-assurance system should address materials, equipment, personnel, installation records, inspection and testing.
Before piling begins, the contractor may be required to submit:
The method statement should reflect the actual ground conditions and equipment proposed rather than being a generic document.
Checks should confirm:
Pile position and verticality tolerances should follow the project specification. Deviations can affect the structural design of the pile cap and may require engineering review.
A record should be maintained for each pile.
Information may include:
Detailed records help engineers assess whether the pile was installed as intended and identify patterns across the site. Malaysian specifications commonly require unexpected conditions, cavities, drilling-fluid losses, concrete quantities and installation times to be recorded.
Before reinforcement and concrete placement, the bore may be checked for:
Inspection methods vary with the project and may include weighted tapes, sampling devices, callipers, sonic measurements or borehole-camera systems.
Where support fluid is used, testing may be performed:
Parameters can include:
The objective is not merely to complete a test sheet. The results should demonstrate that the fluid can stabilise the bore while allowing concrete to displace it effectively.
The cage should be checked for:
The cage should remain stable during lifting, lowering and concreting.
Concrete controls may include:
Actual concrete volume is compared with the theoretical pile volume.
A moderate increase may be expected due to casing dimensions or minor overbreak. A sudden or very large increase may indicate ground loss, a cavity or bore enlargement. An unexpectedly low volume may indicate an incorrect depth reading, obstruction, necking or another issue requiring investigation.
Important controls include:
The tremie should not be lifted out of the fresh concrete during placement. Loss of embedment can allow water, slurry or soil to enter the concrete column and create a discontinuity.
Low-strain integrity testing, sometimes called PIT or sonic-echo testing, uses a small impact at the pile head and measures the reflected stress wave.
It can help identify major changes such as:
It is a useful screening test but has limitations. Interpretation may be affected by pile length, diameter, soil damping, pile-head condition and reinforcement. It does not directly prove the pile’s load capacity.
Cross-hole sonic logging uses access tubes installed within the reinforcement cage.
A transmitter and receiver are lowered through water-filled tubes, and ultrasonic signals pass through the concrete between them.
The test can help identify zones of:
It is particularly useful for large-diameter piles where low-strain testing may provide limited resolution.
The number and arrangement of tubes should be established before cage fabrication. Malaysian specifications may require sonic-logging tubes at selected piles or more widely, depending on the project.
A static load test applies a controlled load to the pile and measures displacement.
It is one of the most direct methods of assessing pile behaviour under axial loading.
The reaction may be provided by:
The test can provide information on:
Instrumentation may also be installed to measure how the load is distributed along the pile shaft and base.
Depending on the project, testing may also include:
No single test detects every possible defect or proves every aspect of performance. The testing programme should combine appropriate methods based on pile size, risk, ground conditions and structural importance.
A successful bored-pile foundation depends on more than selecting a pile diameter from a drawing.
The construction team must understand:
Shinei Geotechnique provides specialist geotechnical and foundation-construction services for projects in Malaysia.
We can review the proposed bored-piling works together with the project owner, consultant, main contractor or tendering team to understand the practical construction requirements and identify issues that may affect method, equipment, cost or programme.
Planning a bored-pile project or preparing a tender?
Send us the available:
Our team can review the information and discuss an appropriate way forward.
Contact Shinei Geotechnique to discuss your bored-pile foundation requirements.
Ir Tan Chin Shu is a Geotechnical Engineer with over 40 years’ experience in the foundation and geotechnical engineering industry. He is the founding Director of Shinei Geotechnique, a specialist contractor in Malaysia.
