Bored piers and screw piles both carry a structure down to competent material, and the choice between them is settled by load, site classification, access and program. Bored piers are cast in situ reinforced concrete, drilled and poured on site. Screw piles are galvanised steel shafts with helical plates, wound into the ground under hydraulic torque. 

Neither is universally better. This guide is written for the builder or developer holding a geotechnical report, and it covers what actually decides the method on a Melbourne site, including the factors the rest of the search results skip: site classification, spoil, and program days.

What Are Bored Piers?

A bored pier is a reinforced concrete column cast in place in a drilled shaft. The rig augers to the specified depth, a reinforcement cage is lowered in, and concrete is placed to form a continuous pier from founding level to the pier head, where it connects to the footing, slab or capping beam above. Capacity comes from end bearing at the base, skin friction along the shaft, or both.

Two consequences follow from casting concrete in the ground, and both hit a build program: the pier must cure before it takes load, and the drilled material has to go somewhere. Our guide on when bored piers are the right call on a Melbourne site covers what pushes a design towards piers.

The installation sequence:

1. Set out against the engineer's drawings and located services.
2. Drill to specified depth and diameter, logging the material encountered.
3. Clean the base and confirm founding material against the geotechnical report.
4. Lower the reinforcement cage, setting cover and level.
5. Place concrete and finish the pier head.
6. Cure before follow-on trades load the pier.

What Are Screw Piles?

A screw pile is a galvanised steel shaft fitted with one or more helical plates, wound into the ground by a hydraulic torque head mounted on an excavator or dedicated rig. The plates pull the shaft down as they rotate, and the pile advances until installation torque reaches the value correlated to the required capacity. They are also sold as helical piles or screw piers.

What decides when a screw pile suits a site:

• No spoil. The helix displaces soil rather than removing it, so there is nothing to stockpile, classify or cart off.
• Immediate load capability. No concrete to cure, so the pile takes load once installed and capped.
• Torque correlated verification. Capacity is inferred from recorded installation torque, pile by pile.
• Low vibration. The pile is rotated in rather than driven, which matters next to existing structures.
• Compact plant. Excavator-mounted torque heads reach sites a piling rig cannot.
• Steel in the ground. Corrosion protection is a design input, usually galvanising plus a durability allowance.

Urban Pour installs bored piers and structural piling. This comparison is written neutrally, and where screw piles are the better answer, that is what this article says.

Bored Piers vs Screw Piles at a Glance

Start With Your Site Classification

The soil report classification is the input every Victorian builder already holds, and it is the sensible starting point. The Building and Plumbing Commission (Victorian Building Authority) sets out the site classification scheme used across Victoria, running from Class A, non-reactive sand and rock sites with little or no ground movement, through S for slightly reactive clay, M for moderate reactive clay or silt, H1 and H2 for highly and very highly reactive clay, E for extremely reactive, and P for soft soil, varying depths of fill and sites subject to abnormal moisture conditions.

What the classification changes:

• Class A and S sites rarely force a deep foundation at all. Where piers or piles appear, load or slope is driving it, not reactivity.
• Class M through E sites mean seasonal moisture movement in reactive clay, so the design generally needs to found below that movement zone, pushing depth up.
• Class P sites are where the method conversation gets real. Fill of unknown depth and abnormal moisture conditions mean nothing can be assumed, and both methods are candidates.

The classification informs the conversation, it does not settle it. As the Commission puts it, an endorsed building engineer designs the footings of a house to suit the classification of the soil and likely movement. The engineer's design governs method, depth and capacity.

Melbourne Ground Conditions and What They Change

The same design brief resolves differently across Melbourne because the ground changes so much across the metropolitan area. Resources Victoria records that around 400 volcanoes produced extensive basalt flows across western Victoria, forming a veneer generally less than 50 metres thick. West and north-west of the city, competent rock can appear at workable depth, but also unpredictably as floaters and weathered zones above sound basalt.

Through the Melbourne Zone, the same source describes shallow to deep marine sedimentation continuing through the Silurian and Early Devonian, the origin of the siltstones and sandstones under much of the inner and eastern suburbs. Depth to competent material varies over short distances, so refusal risk and depth variability are worth pricing rather than assuming.

The Six Factors That Decide the Method

Run these in order against your site. In most cases the answer falls out in the first three.

1. Design Load and Depth to Competent Material

High compressive loads and deep founding levels favour bored piers, because capacity scales with diameter and depth and a pier can be socketed into rock. Screw piles carry light to moderate loads efficiently, and heavier loads mean more piles or larger helices, which has a ceiling on a constrained footprint.

2. Site Classification and Soil Reactivity

Deep reactive profiles and Class P conditions generally suit cast in situ piers, because founding material can be inspected directly at the base of an open shaft. If you are also weighing driven options, how driven piling compares with bored piers covers that side of the decision.

3. Site Access, Headroom and Rig Footprint

A piling rig needs room to track, set up and be serviced, and a bored pier also needs a concrete truck within reach or a pump set up. Low headroom, narrow side access and battle-axe blocks push towards screw piles, which install from smaller plant and extend in short sections. On infill sites this overturns more design assumptions than any other factor.

4. Adjacent Structures, Vibration and Noise

Neither method drives a pile with a hammer, so both are comparatively kind to neighbours. The adjacency question for bored piers is the open shaft and its zone of influence beside existing footings. WorkSafe Victoria's compliance code for excavation work, published 19 December 2019, sets out the duties applying to excavation and how to reduce the risk of ground collapse.

5. Spoil Volume, Classification and Disposal

Every bored pier produces a shaft volume of spoil that must be brought up, stockpiled, classified and carted away. On a tight metropolitan site with no stockpile area, that is a logistics problem before it is a cost problem: truck movements, traffic management and disposal to a facility that accepts the classified material. Screw piles displace soil instead, so the line disappears.

6. Program and Time to Load

This is where the word "faster" earns its meaning. A screw pile takes load as soon as it is installed and capped, so following trades proceed the same week. A bored pier requires cure before loading, so the sequence carries fixed dead time. On a staged development where pile caps, ground beams and frame queue behind the piers, those days are money.

When Bored Piers Are the Wrong Choice

Bored piers are what Urban Pour installs, and there are still sites where they are the wrong call:

• Severely restricted access. If a rig and a concrete truck or pump cannot reach the pier locations, the method is fighting the site.
• Low headroom. Working under an existing structure or overhead services leaves no room to raise an auger or a cage.
• Prohibitive spoil disposal. No stockpile area, contaminated ground, or restrictions on truck movements.
• Programs that cannot absorb cure time. Where the critical path runs through the foundations with no parallel work available.
• The engineer has specified otherwise. That ends the discussion.

When Screw Piles Are the Wrong Choice

The counter case is just as real, and worth knowing before a screw pile quote gets accepted on price alone:

• Rock and obstruction refusal. Buried rubble, floaters or shallow rock can stop a pile before design torque, leaving capacity unproven.
• Very high compressive loads. A large diameter pier socketed into competent material carries them with fewer elements.
• Aggressive or contaminated ground. Corrosive soils and low resistivity make steel durability a problem over the design life.
• Deep founding through poor material. Long steel shafts through soft ground bring buckling and lateral capacity into the design.
• The engineer has specified cast in situ concrete. Same rule, in reverse.

What Drives the Cost of Each Method

Both methods are quoted, not priced from a table, and the honest answer to "which is cheaper" depends on which drivers your site activates.

Bored pier cost drivers:

• Pier diameter and design depth, setting concrete and steel quantities
• Rig mobilisation and standing time
• Spoil volume, disposal classification and cart-away distance
• Concrete supply, and pump hire where trucks cannot reach
• Reinforcement cage fabrication
• Program days lost to cure

Screw pile cost drivers:

• Steel tonnage, shaft diameter and helix configuration
• Pile count required to meet the design load
• Galvanising and any additional corrosion allowance
• Rig or torque head mobilisation
• Refusal risk, and remediating piles that do not reach design torque

The method that looks cheaper on a quote comparison is frequently not the cheaper method delivered. A screw pile solution that saves on spoil can lose the saving to pile count on a heavily loaded footprint, and a pier solution that prices well per pier can absorb the difference in truck movements. Price the whole sequence, not the pier. Urban Pour publishes no rates:

Where Underpinning Fits

Both methods appear in underpinning and remedial work, where an existing structure is showing movement and needs new support taken down to competent material. It is a different problem from new build foundation selection, because the work happens around and under a structure that is already there, already loaded, and often already damaged.

That constraint changes what drives the method. Access beneath the existing footing, headroom, the condition of that footing, and the structure's tolerance of further movement all outrank the factors that decide a greenfield job. Underpinning is designed by an engineer against a specific structure and cause of movement, never selected from a comparison table.

How the Decision Actually Gets Made

The sequence on a real project is short, and the contractor is not at the top of it:

1. Geotechnical investigation. Boreholes or test pits establish the profile, depth to competent material and site classification.
2. Engineer's design. The structural engineer sets method, capacity, depth and pile type against design loads and the soil report. AS 2159 covers piling design and installation, and AS 2870 covers residential slabs and footings.
3. Constructability review. Access, rig selection, spoil handling, service clearances and program sequencing get tested against the design, with any issue referred back to the engineer.
4. Installation and verification. Founding material inspected for piers, torque recorded for screw piles.
5. Engineer sign-off before load. Follow-on trades proceed once the foundations are accepted.

Where the design lands on cast in situ concrete, piling and bored piers in Melbourne is the work itself: drilling, cages, pours and pier heads to specification.

Ready to Get the Foundations Right?

Get the geotechnical investigation done, let the engineer specify, then test the design against your access, spoil handling and program before pricing the job. Those three factors decide more foundation methods than any comparison table does. Urban Pour installs piling and bored piers across Melbourne. Talk to the team about your site and you will get a straight answer on whether bored piers suit it.

Frequently Asked Questions

1. Are screw piles cheaper than bored piers?

Neither method is reliably cheaper, and any answer offering a figure is guessing at your site. Screw piles avoid spoil disposal and cure time, two of the largest cost drivers on a bored pier job. Bored piers carry high loads with fewer elements, which wins on a heavily loaded footprint.

2. What are the disadvantages of screw piles?

Refusal risk and load ceiling are the main disadvantages. A pile hitting rock or buried obstruction before design torque has not proven its capacity and needs remediation. Very high compressive loads require more piles or larger helices, which can outgrow a constrained footprint. Steel durability in aggressive ground is a further constraint.

3. What are the disadvantages of bored piers?

Spoil and cure time are the main disadvantages. Every pier generates a shaft volume of material that must be classified, stockpiled and removed, which is a logistics problem on tight sites. Concrete must cure before the pier takes load, putting fixed dead time into the program.

4. How deep should bored piers be?

Depth is set by the engineer against the geotechnical report and the design load, not by a rule of thumb. The pier must found in competent material and, on reactive clay sites, below the zone of seasonal moisture movement. Because that depth varies across Melbourne, neighbouring sites can carry very different pier schedules.

5. Can bored piers be used on sloping sites?

Yes, and slope is a common reason a design moves to piers. Piers take load through variable surface material down to consistent founding material, avoiding the differential settlement a shallow footing risks on a slope. Rig and concrete access becomes the practical question, along with any retention required during the works.

6. Do bored piers need to be inspected before the pour?

Yes. Founding material at the base of the shaft is checked against the geotechnical report, and the cage, its cover and its level are confirmed before concrete is placed. Once poured, none of it can be verified visually. Inspection requirements sit in the engineer's specification.

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