You are spending serious money on pile foundations. You have every right to know whether the work is being done correctly. This guide is written by a specialist piling contractor and coded welder with over 20 years of experience installing bottom driven steel cased piles. We have visited other contractors' sites. We have seen the mistakes — and some of those mistakes get buried underground before the homeowner or builder knows anything is wrong.

This page explains what good work looks like, what questions to ask, and what to do if something does not seem right. You do not need technical knowledge to use it. Good contractors will welcome your interest. Bad ones will not like this page at all.

1. Weld Quality — What Good Looks Like and What to Reject

Every time your piling contractor adds a new section of steel casing — which happens multiple times on every pile — they weld the new section onto the one already in the ground. That weld is a permanent structural joint. Once the pile is driven and concreted, it will never be seen again. It needs to be right first time.

A common excuse from contractors caught with poor welds is that a good-looking weld is not necessarily a strong weld. This is not acceptable. On correctly executed steel tube casing welds, good visual appearance and structural integrity go together. If it looks wrong, ask why.

The welds shown below are our own — manual metal arc welds using 6013 rods at 3.25mm, executed to BS EN ISO 9606-1:2017 standard. In certain difficult-to-drive conditions we use ER7018 low-hydrogen rods, which produce an excellent weld but come with an important requirement: they must be stored and kept warm in a rod oven before use. Moisture in a low-hydrogen electrode causes hydrogen cracking in the weld — a serious defect that may not be visible on the surface. If your contractor is using 7018 rods, it is entirely reasonable to ask whether they are being stored correctly.

Good quality manual metal arc weld — 6013 rods, 3.25mm. Consistent bead, full fusion onto both tube sections, no porosity, slag removed before inspection.

Correct weld bead profile on a larger diameter pile casing — consistent width, full overlap on both sections, no undercut into the upper tube wall.

What a correct weld must show

• Consistent bead profile: The weld should run evenly around the full circumference of the tube with consistent width and height. Thin patches, gaps, or uneven starts and stops are signs of poor technique.
• No porosity: Porosity — holes or pitting in the weld surface — indicates gas trapped during welding, caused by contamination, damp electrodes, or incorrect technique. Any visible porosity is a defect. Do not accept it.
• No undercut into the upper tube section: The weld must not cut into the wall of the upper tube. Undercut reduces wall thickness at the joint and creates a stress concentration point — exactly where you do not want one when a pile is being hammered into the ground.
• Full overlap and fusion onto both sections: The weld must fuse onto both the upper and lower tube sections. A weld sitting predominantly on one side has not achieved full fusion and will fail under driving impact or load.
• Slag removed before inspection: Welding with coated electrodes produces slag — a protective crust over the weld as it cools. This must be chipped off and brushed before the weld is inspected. If your contractor asks you to inspect a weld through the slag, they are hiding it from you. The slag should be on the floor, not on the joint.
• No welding over slag: If a second weld pass is needed, all slag from the first pass must be removed first. Welding over trapped slag creates inclusions that significantly weaken the joint. This is basic, not advanced.

2. Alignment — Straight Piles Are Not Optional

Correctly installed bottom driven steel cased piles — straight, vertical, consistently installed. This is what a completed pile group should look like.

Every pile must start plumb and remain as straight as possible throughout driving. A bent pile carries load eccentrically, puts stress onto weld joints they were not designed for, and is far more likely to develop cracks that allow groundwater in.

Correct practice — the operator watches the tube throughout driving, monitoring alignment and movement. An operator not watching the pile during driving is not doing their job.

Your contractor should check alignment at the start of every pile and monitor it continuously during driving. If a pile starts to deviate, the correct response is to stop and assess — not to keep driving. On sites with hard upper strata over softer material below, pre-boring may be needed before driven installation begins. A competent contractor will identify this from the ground investigation data before mobilising.

Obstructions — when a pile cannot be driven straight

Occasionally a pile will hit an obstruction underground — a large stone, buried masonry, or an old foundation — and it is not always feasible to excavate, reposition, or add an additional pile. If this happens on your project, ask your contractor what they are proposing and contact your structural engineer or architect. An angled pile is not as good as a vertical one — it carries load less efficiently and introduces lateral forces into the pile head — but it can still be acceptable depending on the depth achieved and the structural loads involved. The key is that the decision is made by an engineer, not just accepted without question.

3. Water in the Pile — Causes, Consequences and the Only Acceptable Fix

Steel cased driven piles are designed to provide a clean, watertight bore. Water should not be present inside the casing at the point of concreting. If it is, something has gone wrong.

Why water gets in

• Failed weld: A weld with porosity, incomplete fusion, or a crack caused by driving impact will allow groundwater to enter through the casing wall. This is the most common cause and the most preventable — it comes directly back to weld quality.
• Bent or misaligned casing: A pile driven out of plumb puts lateral stress onto weld joints. Those joints can crack, opening a path for groundwater.
• Broken toe — hard over soft strata: If the site has hard upper ground over soft material below — a situation ground investigation should identify — the driving weight can punch aggressively through the hard layer and drive through the closed toe of the casing. Once the toe is broken or open, groundwater and soil enter from the bottom. This situation often means pre-boring should have been used to penetrate the hard upper layer first.
• Insufficient or wet plug: Before driving, a dry concrete plug is placed at the base of the casing to seal the toe. The plug can be driven straight away — it does not need to be left to set. However it must be the right consistency (dry mix, not wet) and the correct quantity for the pile diameter. If the plug is too small or too wet it can be driven through, leaving the base of the pile open.

Correct practice — dry mixed concrete plug prepared and ready before driving starts. The right consistency, the right quantity, placed correctly before the casing is driven. Cutting corners here is a common cause of water ingress and toe failure.

The correct remedial process when water is found:

• Pump the pile out completely — every drop removed before any concrete is placed
• Identify and address the source — failed weld, bent section, or open toe
• If the toe has failed, re-plug with dry concrete mix and allow adequate set time before further driving
• If the pile cannot be driven to the specified set after remediation, a replacement pile should be installed
• Inform your structural engineer — document what happened and what was done

4. Taking a Set — The Proof That Each Pile Is Working

Taking a set is the physical test that proves a pile has reached its specified load-bearing capacity. It is the only direct evidence available on a driven pile installation that the pile will carry the load it has been designed for.

This matters particularly because, as the structural engineer's report will note: due to the nature of the piling technique, it is not considered feasible to carry out load testing. The set is therefore not just useful — it is the sole proof of pile capacity on site. Every pile should have one.

Where the set specification comes from

The set is calculated by your structural or ground engineering specialist using a dynamic driving formula — most commonly the Olsen & Flaate modification of the Gates formula (American Society of Civil Engineers, Vol.93, Pg 279-296). The calculation uses the specific pile diameter, hammer weight, drop height, and required structural loading for your project to produce a target — a number of blows and a maximum movement in millimetres that the pile must achieve on site.

The example below is taken from a real structural engineer's report for a 220mm diameter driven pile installation:

In plain terms: for this particular project, with a 220mm pile and a 0.50 tonne hammer dropped from 2 metres, the pile must move no more than 25mm over 5 consecutive blows. The structural loading required for this project is 75kN — and when the set is correctly achieved, the calculation shows the pile is actually carrying well in excess of that, with a factor of safety of 7.9 against the minimum required of 3.0.

Your project will have its own equivalent calculation — specific to your pile diameter, hammer, structural loads and ground conditions. The set target will be different. What matters is that it exists, your contractor knows what it is, and they can demonstrate it on site.

How to approach witnessing a set

You do not need to demand to see every pile tested. A reasonable and perfectly fair request is simply: "Could I see a set on one of the piles?" Any competent contractor will be happy to demonstrate this — it takes a few minutes and gives both of you confidence the work is right. A contractor who hesitates, makes excuses, or says it is not possible is telling you something important about their confidence in their own work.

• The plug must not go in before the set is shown: The concrete plug at the base of the casing must not be placed before the set is demonstrated. If the plug goes in first, the measured driving resistance comes partly from the plug compressing — not the pile bearing on the ground. This gives a false result. It happens. Watch for it.
• Watch for movement at the top of the pile: When the hammer drops, you should see a small, measurable movement at the top of the visible casing. This confirms the driving energy is travelling the full length of the pile to the toe. If there is no movement at all, either the pile has achieved genuine refusal in very hard rock — or the base has failed. If the toe has gone or a weld has cracked near the bottom, the energy is absorbed at the failure point. The pile shows apparent refusal but is bearing on nothing. A small elastic reaction in the casing above ground is what you are looking for.
• Ask to see a set before you pay: Set records are typically provided after the client has paid for the work. A more practical approach is to ask to see a set being taken on at least one pile before you make final payment. This is a completely reasonable request — and any competent contractor will be happy to oblige. If they are not, that tells you something important.

5. The Concrete Pour — Getting the Final Stage Right

The concrete pour is the last stage of pile installation. Everything done correctly up to this point can be undermined by a poor pour.

No water before concreting

Any water inside the casing must be pumped out completely before concrete is placed. Water cannot escape from a sealed steel casing once concreting begins. Any remaining water will be trapped in the finished pile, diluting the mix and potentially creating voids or weak zones within the shaft. There is no acceptable reason to concrete over standing water in a pile.

Concrete consistency

• Too dry: A stiff mix will not flow properly around the reinforcement cage, leaving voids in the finished shaft.
• Too wet: An overly wet mix has too high a water-to-cement ratio, reducing compressive strength and risking segregation within the pile.
• Correct: The mix should be workable — flowing freely under its own weight — but not sloppy. A designed mix to the structural engineer's specification, placed and rodded correctly, is what the job requires.

If bars are being adjusted during or after the pour

This is not always a problem — there are legitimate reasons to reposition a reinforcement cage. But if you see bars being forced into partially set concrete, or the cage adjusted after the pour without a clear explanation, ask the question. You are entitled to a straightforward answer.

Your On-Site Checklist

Take this with you when your piling contractor is on site. You do not need any technical knowledge — just ask the questions and watch the responses.

What to Do If You Have Concerns

• Stop the work: You are the client. If something does not look right, you are entitled to ask the contractor to pause and explain before proceeding.
• Document everything: Take photos. Note the time, date, pile number, and what you observed. This matters if a dispute arises later.
• Contact your structural engineer: They have the authority and knowledge to determine whether work meets specification. Call them.
• Request set records in writing: Set records — blow count, drop height, and measured movement for every pile — are typically provided after payment. Ask to see a set demonstrated on at least one pile before you pay. A competent contractor will have no hesitation.
• Consider independent integrity testing: If you believe piles have been installed incorrectly, non-destructive integrity testing can assess whether finished piles have voids or structural defects without excavating. Your structural engineer can arrange this.

Why We Wrote This Page

We have visited other contractors' sites. We have seen welds with porosity that would fail a basic visual inspection. We have seen piles concreted over standing water. We have seen contractors who could not produce set records when asked. And we have seen homeowners and builders left with defective foundations they knew nothing about until problems appeared long after the contractor had gone.

The piling industry has no mandatory licensing or minimum competency standard for operatives. Anyone can buy or hire a rig and start installing pile foundations. Some of those companies appear prominently in Google search results. That does not mean they know what they are doing.

The standards described on this page are not exceptional. They are what any competent piling contractor should deliver as a matter of course. If yours cannot — or will not — you now know what to do about it.

Our Steel Cased Driven Piling Services

If you are looking for a contractor who works to the standards described on this page — and can prove it — we would be happy to discuss your project.

• Bottom Driven Steel Cased Piles — our primary specialism, installed across South West England and the Midlands since 2005
• Bored Piles — low-vibration alternative where ground conditions suit an auger method
• Piled Foundations — complete foundation packages including ground beams and capping beams
• Screw Piles — fast installation with immediate load capacity for lightweight structures
• Basement Construction & Piled Retaining Walls — specialist below-ground solutions
• Areas We Cover — South West England and the Midlands including Somerset, Bristol, Gloucestershire, Wiltshire, Devon, Dorset and Hampshire