Why Open-Ended Piles Cause Less Soil Heave

When a pile is driven close to an existing building, basement, buried pipeline or retaining wall, ground movement during installation can become an engineering concern of its own.

A closed-ended pile generally displaces soil corresponding to its full cross-sectional area as it penetrates the ground. An open-ended pile gives some of that soil a different path: it can enter the inside of the tube and form a soil plug. When the pile remains unplugged or partially plugged, less soil may be displaced into the surrounding ground, which can reduce installation-induced heave and lateral movement.

But an open-ended pile is not automatically a low-displacement pile. If a soil plug develops and moves substantially with the pile, its behaviour can become closer to that of a displacement pile.

So the real question is not simply whether the pile is open-ended. It is how the soil plug behaves during driving.

1. Why Pile Driving Can Cause Soil Heave

Any driven pile has to penetrate soil. The installation process therefore changes the volume and stress state of the ground around the pile.

With a closed-ended pile, the closed toe engages the soil across the pile’s full cross-sectional area, so the soil must be displaced around the advancing pile. Depending on the site, this can produce both vertical and lateral ground movement.

That movement may affect:

Existing foundations: ground heave or lateral movement can affect nearby footings and basement structures.

Roads and slabs: upward ground movement can cause local lifting or distortion.

Buried services: pipes, ducts and cables can be affected by lateral soil movement.

Retaining structures: ground displacement can influence loads and alignment.

Soft or sensitive soils: pile driving can also generate excess pore-water pressure and remoulding.

Excess pore-water pressure and remoulding are separate effects from installation-induced heave. The magnitude of ground movement depends on the pile geometry, installation method, soil profile and the way the soil responds around the pile.

Pile type is therefore only one part of the ground-movement assessment.

2. What an Open Toe Changes

The main difference is what happens to the soil directly beneath the pile.

A closed-ended pile generally displaces soil corresponding to its full cross-sectional area. An open-ended tubular pile allows soil to enter the tube during penetration.

Part of the soil can therefore remain inside the pile instead of being displaced entirely into the surrounding ground.

A simplified way to visualize the difference is:

Closed-ended pile
The closed toe engages the soil across the pile’s full cross-sectional area, so the soil must be displaced around the advancing pile.

Open-ended pile
Soil can enter the tube as the pile penetrates. If the pile remains unplugged or only partially plugged, less soil may be forced into the surrounding ground.

This is one reason open-ended pipe piles are considered for projects where control of installation-induced ground displacement is important.

The surrounding soil is not completely unaffected, however. The pile wall still displaces soil, and the installation response changes as the internal soil plug develops.

3. The Soil Plug: The Key to Open-Ended Pile Behaviour

The soil that enters an open-ended pile during driving is commonly referred to as the soil plug.

The plug may move relatively little compared with the pile, or it may move substantially with the pile. The installation response can therefore range from relatively low displacement to behaviour approaching that of a closed-ended displacement pile.

Engineers use different parameters and calculation methods to describe the degree of plugging. In practical terms, the important question is:

How much of the soil inside the pile moves with the pile during penetration?

An unplugged pile allows soil to continue entering the tube as the pile penetrates.

A partially plugged pile develops internal soil resistance, but the soil plug does not move fully with the pile.

A plugged pile develops sufficient internal soil resistance for the soil plug to contribute substantially to penetration resistance and move with the pile to a significant degree.

Plugging can be described using parameters such as plug length ratio (PLR), depending on the analytical or experimental method being used. In general, a lower ratio is associated with greater soil coring, while a higher ratio indicates stronger plugging.

The transition between these conditions is influenced by factors such as:

soil type and strength;

density and layering;

pile diameter and wall thickness;

pile penetration depth;

pile-soil interface friction;

driving energy and installation method; and

previous installation history.

For this reason, the plugging condition should be assessed rather than assumed from pile depth alone.

4. Why Can Open-Ended Piles Reduce Soil Heave?

The basic mechanism is a difference in soil displacement volume.

A closed-ended pile generally displaces soil corresponding to its full cross-sectional area as it penetrates.

An open-ended pile can allow part of that soil to enter the pile. When the pile remains unplugged or partially plugged, the volume of soil displaced into the surrounding ground may therefore be lower.

That can reduce:

vertical ground heave;

lateral soil displacement; and

the potential for movement of nearby structures and services.

The effect is not unlimited. As the soil plug develops, the pile can behave more like a displacement pile. A geotechnical assessment should therefore consider the expected plugging behaviour rather than assuming that an open toe alone guarantees minimal ground movement.

Open-Ended Does Not Always Mean Low-Displacement

This distinction is easy to miss.

An open-ended pile can initially behave as a relatively low-displacement pile, particularly when soil continues to enter the tube. If plugging develops strongly, however, the internal soil column can move with the pile and contribute significantly to installation resistance and ground displacement.

So the engineering advantage is not simply:

Open end = no heave

A more accurate statement is:

Open-ended piles can reduce installation-induced ground displacement when their plugging behaviour allows soil to enter the pile rather than being displaced entirely into the surrounding ground.

5. Soil Heave Is Not the Same as Noise or Vibration

Open-ended piling does not automatically solve all the environmental effects associated with pile driving.

An open-ended pile can reduce displacement-related ground movement, but the pile-driving equipment can still generate:

noise;

vibration;

local ground acceleration; and

construction disturbance.

These are separate engineering issues.

Where nearby structures or sensitive equipment are particularly vulnerable to vibration, the installation method may need to be considered separately. Depending on the project, lower-vibration methods such as press-in piling may be evaluated instead of, or in combination with, conventional impact driving.

The practical approach is to treat soil displacement, vibration and noise as separate design and construction risks.

6. Where Are Open-Ended Piles Used?

Open-ended tubular piles can be considered in projects where installation-induced ground movement is an important constraint.

Pile selection should still be based on the complete geotechnical and structural design. Open-ended construction is not a substitute for assessing drivability, axial capacity, lateral capacity, fatigue, corrosion and installation effects.

7. Open-Ended Piles: HSS or Large-Diameter LSAW Tubulars?

Once the pile concept has been selected from a geotechnical perspective, the next question is the tubular product itself.

This is where structural hollow sections and large-diameter welded tubulars need to be distinguished.

Structural HSS

For tubular piles within a manufacturer’s structural hollow-section product range, welded CHS, SHS and RHS can be manufactured by ERW/HFW or other applicable welding routes, depending on size and product specification.

For European structural hollow sections:

EN 10219 covers cold-formed welded structural hollow sections.

EN 10210 covers hot-finished structural hollow sections.

The applicable steel grade should be selected according to the intended service conditions and project specification.

These are structural hollow-section standards, not universal piling standards. Whether an HSS product can be used as a pile depends on the project design, applicable regulations and purchaser’s specification.

A pile application may require additional requirements for drivability, weld performance, impact toughness, fatigue, dimensional tolerances and fabrication that are not established solely by the HSS product standard.

EN 10219, for example, covers cold-formed welded circular, square and rectangular structural hollow sections. Its dimensional scope is much wider than the product range of any individual manufacturer.

For this reason, a manufacturer’s actual size envelope should always be stated separately from the scope of the EN standard.

Large-Diameter LSAW Tubulars

For larger pile diameters and heavier wall thicknesses, plate-formed and longitudinally welded tubulars may be selected instead of conventional structural HSS.

For large offshore tubulars, the steel plate may be specified to an applicable offshore structural steel standard such as EN 10225, while the completed tubular is governed by the project’s fabrication, welding, inspection and design requirements.

For offshore wind support structures, DNV-ST-0126 provides requirements and guidance for structural design of wind turbine support structures and can form part of the contractual or certification framework where it is specified.

It should not, however, be treated as a universal standard for every large-diameter pile used in marine or civil engineering projects.

In other words, the product route should follow the project specification rather than being selected simply because the pile is “large.”

A Practical Product Split

The key point is simple: EN 10210 and EN 10219 define structural hollow-section products; they do not by themselves determine whether a particular section is suitable for a driven pile.

8. What Engineers Should Check Before Ordering

Choosing an open-ended pile is only the first step. The pile and installation system should be checked together.

1.Ground movement
Define acceptable movement limits for adjacent buildings, foundations, utilities and other sensitive assets.

2.Plugging behaviour
Assess whether the pile is expected to remain unplugged, partially plugged or plugged during driving. Do not assume that the same condition will apply over the full penetration depth.

3.Drivability
Check the expected driving resistance, pile stresses, hammer compatibility and potential refusal conditions.
An open-ended pile may have lower initial toe resistance when unplugged, but total driving resistance also depends on shaft resistance and the development of the soil plug.

4.Axial capacity
An open-ended pile can develop resistance from the pile wall and from the soil inside the tube. The contribution of the soil plug should be evaluated using the selected geotechnical design method.

5.Redriving
If a pile is extracted and redriven, the soil-pile interaction and plug condition may change. The installation and capacity assessment should account for the revised conditions rather than simply carrying over the original assumption.

6.Corrosion allowance
For marine or aggressive environments, establish the required corrosion allowance at the design and procurement stage. The selected wall thickness needs to reflect both structural requirements and the specified design life.

7.Inspection and documentation
NDT, weld inspection, dimensional tolerances, impact testing and inspection documents should follow the applicable product and project specification.
Where EN 10204 documentation is required, Type 3.1 is commonly specified, while Type 3.2 may be required where the purchase order calls for third-party or purchaser-witnessed inspection.

9. A Practical Checklist for Specifying Open-Ended Piles

Before sending an RFQ or pile specification, confirm the following:

Pile type: open-ended or closed-ended.

Outside diameter or section size: include the complete dimensional requirement.

Wall thickness: include both nominal wall and any required corrosion allowance.

Pile length: state total length, individual pile length or required splices.

Steel grade: specify the required grade and impact temperature where applicable.

Product standard: identify EN 10210, EN 10219 or another governing standard as required by the project.

Geotechnical information: provide the soil profile and design assumptions needed to assess plugging and drivability.

Installation method: impact driving, vibratory driving, press-in piling or another specified method.

Inspection: define NDT and inspection-document requirements.

Certification: state whether EN 10204 Type 3.1, Type 3.2 or another inspection regime is required.

Corrosion protection: define corrosion allowance or coating requirements based on the design environment.

Project-specific offshore requirements: identify any applicable DNV, EN, IEC or owner specifications.

Where applicable, CE marking and EN 1090 requirements should also be confirmed against the intended structural use and project specification rather than assumed for every European project.

10. The Main Engineering Takeaway

The reason open-ended piles can reduce soil heave is straightforward:

They can allow part of the soil displaced by pile penetration to enter the pile rather than displacing soil corresponding to the full pile cross-sectional area into the surrounding ground.

The benefit depends on the plugging condition. An unplugged or partially plugged pile may behave as a lower-displacement pile, while stronger plugging can increase both installation resistance and ground displacement.

For projects near buildings, buried services, tunnels, quay walls or other sensitive structures, the key design question is therefore not simply whether the pile is open-ended, but how the soil plug is expected to behave during installation.

Frequently Asked Questions

Q:What is an open-ended pile?
A:An open-ended pile is a tubular pile with an open toe. During driving, soil can enter the inside of the tube and form a soil plug rather than being displaced entirely around the outside of the pile.

Q:How does an open-ended pile reduce soil heave?
A:When the pile remains unplugged or partially plugged, some of the soil enters the tube instead of being displaced into the surrounding ground. This can reduce installation-induced soil displacement and associated heave compared with a fully displacement pile.

Q:Does an open-ended pile always cause less soil movement?
A:No. The amount of ground movement depends on the soil, pile geometry, installation method and plugging condition. If the soil plug develops strongly and moves with the pile, the installation response can approach that of a displacement pile.

Q:What is a soil plug?
A:A soil plug is the column of soil that enters and becomes retained inside an open-ended pile during penetration. Its behaviour depends on the interaction between the soil and the inside wall of the pile.

Q:What is the difference between plugged and unplugged piles?
A:An unplugged pile allows soil to enter the tube as penetration continues. A plugged pile develops sufficient internal soil resistance for the soil plug to contribute substantially to penetration resistance and move with the pile to a significant degree. Partially plugged behaviour lies between these conditions.

Q:Do open-ended piles reduce noise and vibration?
A:Not necessarily. Open-ended piles can reduce displacement-related ground movement, but pile-driving equipment can still generate significant noise and vibration. If vibration is a project constraint, the installation method needs to be assessed separately.

Q:Are open-ended piles suitable near existing buildings?
A:They can be considered where control of ground movement is important. However, the actual reduction in heave and lateral displacement needs to be assessed for the specific soil profile, pile geometry and installation method.

Q:Can ERW/HFW steel tubes be used as open-ended piles?
A:Depending on size, wall thickness, steel grade and project requirements, welded ERW/HFW tubular products—including open-ended pipe piles—may be considered for piling applications. EN 10219 covers cold-formed welded structural hollow sections, while EN 10210 covers hot-finished structural hollow sections. Neither standard should be treated as a universal piling design standard.

Q:What standards can apply to tubular piles?
A:The governing standard depends on the pile product and project. Structural hollow sections may be specified to EN 10210 or EN 10219. Large-diameter welded tubulars may use project-specified plate and fabrication requirements, including offshore structural steel requirements where applicable. Offshore wind support structures may also be subject to DNV-ST-0126 when that standard is part of the project or certification basis.

Q:Is EN 10225 a piling standard?
A:No. EN 10225 is associated with structural steel products for offshore structures. If EN 10225 material is used for a welded tubular pile, the complete pile specification still needs to address fabrication, welding, inspection, dimensions and project-specific requirements.

Q:Do open-ended piles reduce driving energy compared with closed-ended piles?
A:An unplugged open-ended pile can require less driving energy initially because its toe resistance may be lower than that of an equivalent closed-ended pile. However, total driving resistance depends on shaft resistance and the development of a soil plug. As plugging increases, the required driving effort may also increase.

Q:When should I monitor or clean out the soil plug during installation?
A:Monitoring can be particularly important for long piles, large diameters, and dense or layered soils where plugging may become significant.
Sudden increases in driving resistance, reduced penetration per blow, or changes in hammer performance can provide indications of changing pile-soil interaction. In some projects, plug monitoring, inspection or removal may be specified as part of the installation procedure.
Any decision to remove soil from inside the pile should follow the project’s geotechnical and installation requirements, because changing the plug condition can also change driving resistance and pile behaviour.

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