An enormous number of Victorian residential soil reports have incorrectly understated minimum founding depths and related requirements, resulting in the failure of thousands of slabs.

A headline in The Age last year read “Thousands of suburban home owners facing financial ruin.” This referred to an official report on the failure of mainly waffle pod slabs to stay within permitted flexure limits in the western and northern suburbs of Melbourne, and the effects of that failure have been devastating.

Although owners and builders could have demanded a second soil report for any new home project and the building surveyors could have required more information via a more stringent soil test (that may have resulted in a stronger slab or bored pier construction based on that report), this obviously has not happened for possibly more than 10,000 Victorian new home owners.

The local councils are not required to become involved, merely acting as filing clerks for the documentation for future use by subsequent owners. It’s a pity, because local building surveyors often have ready access to vital knowledge that could have helped avoid many a slab failure.

So it’s up to those involved with the house projects, prior to commencement of construction: the soil report writers, structural engineers, building surveyors, and possibly the builders, draftspersons, architects, and even owners, to ensure that the most informed soil report possible is carried out, particularly in light of the fact that we have had a recent record 14-year drought.

For many a housing project, vital information was actually obtainable if just one of the aforementioned people had cared enough to ferret it out.

I inspected a slab in Melbourne’s outer north west where the slab was over 90 millimetres out-of-level. The builder has since been permitted to install substantial bolstering of the slab and improve drainage, rather than everyone going to VCAT. The jury’s out as to whether what has been done will be enough.

After a little delving, it was eventually discovered that a map had actually been available, and it showed where large trees (about 1.2 metres in diameter) had existed just a few years prior to the development of the estate. One of these trees had existed within the house envelope, and its absence caused considerable heave (swelling due to extra-dry soil regaining its moisture, the causes of which are often difficult to pin-point) past the limits set out in the soil report due to the prolonged 14-year drought in Melbourne just ending when the house was built.

There was also a retained tree, and it caused excessive settlement to both slab and the few supporting piers provided to the edge of the slab nearest the tree, proving that the original classification was wrong and/or that any extra requirements or recommendations were inadequate. Amongst other things, Appendix D of the Code AS2870 had been ignored.

Another excessively distorted unit in Melbourne’s outer east resulted from combined excessive (65 millimetre) settlement/heave due to inadequate allowance for the effects of large removed trees and a row of retained trees.

This demonstrates negligence on the part of one or more of the soil engineer, structural engineer and relevant building surveyor – those who should have known better and who were actually required to expect dire situations where (highly) reactive clay soils are concerned, especially when the ground had been dried by a record drought and/or significant trees, past or present.

What a fiasco! What a tragedy!  

But just what were the specific details of the scenario that basically caused soil report writers to fail in their duty to classify the soil correctly and fail to provide sufficient extra requirements (as distinct from recommendations), so that the structural engineers would design adequate concrete slabs for the sites on which the houses were to be built, particularly in the NW Melbourne volcanic plains and similar problem soil areas?

There were two pertinent codes involved with soil reports:

  • Residential Slabs and Footings – Construction AS2870 – 1996 (since revised), and
  • The Building Code of Australia (BCA).

According to AS2870, the basic requirements for soil classifications are:

  1. Normal weather conditions must prevail
  2. A history of unaltered drainage must be the go
  3. Rows or groups of trees or large trees (on or in the immediate vicinity of the block of land), must not remain and must not have been recently removed

Otherwise further vital information must be sought.

According to the BCA from 1996 onward (at clause P2.1(b) (xiii)), the effects of shrinkage and swelling of soil ‘must’ be considered.

Therefore (it is implied), further vital information must be sought. Pretty simple, really!

But in possibly tens of thousands of instances it appears these codes were used without that information being obtained or Appendix D being consulted, because by doing that, those slabs would have resulted in greater measures being taken, albeit at considerably greater expense.

The obtaining of the cheapest quotes for soil reports seems to have led to many soil report writers to taking the easy path, Clause 2.2.1(b) in AS2870, whereby the characteristic surface movement estimation methodology could (they thought), serve as a shortcut to the consulting of Appendix D of AS2870.

Classifications were basically downgraded by ignoring the basics of these codes, leading to this enormous tragedy. Owners (who were kept in the dark) signed the contracts, and project after project sailed along unobstructed by bored piers, stronger slabs and re-vamped finance. Those involved with the process of ascertaining the correct soil classification all had a job.

How did this happen?

There are basically two paths soil report writers can take to assess the classification of house sites, but due to abnormal moisture conditions in reactive clay soils (M,H,E) each of these paths still required the soil report writers to seek out the aforesaid information plus consult Appendix D of code AS2870 for minimum founding depths plus personally assess whether the soil immediately footings had been excavated prior to the placement of underlays and reinforcement.

One of the paths to a soil classification, where the surface movement factor is estimated appears to be permitted to bypass all other requirements of AS2870 whilst ignoring the basics of the code, clauses 1.3.2 and 1.3.3. But for virtually all sites west of Melbourne, this was not an option.

Reactive clay sites with abnormal moisture were to be classified P (P meaning problem), and thus had to comply with clause 2.4.4 of the Code AS2870. Soil report writers were therefore required to consult Appendix D anyway; and reports required (as opposed to recommended) greater founding depths as a result. For P soils, the footings or slabs had to be structural-engineer-designed as well.

But even with all those safeguards in place, relevant building surveyors did not make a stand and question the shortcut approach of the soil report writers who were asked to report for less than half of what the cost should have been. And the structural engineers who designed the slabs, trained in the basics of civil engineering, were surely also required to know the basics of code AS2870, and that at least ‘P’ classification was required for these sites due to the long-term drought issue alone.

So why did no authority or the Institute of Engineers or the Building Surveyors Board ring the alarm bells? And when the code was revised, why was there no public forum for this enormous problem?

In 2012, when the 14-year drought was ending, the code AS2870 was finally overhauled, despite many slabs distorting excessively for years prior to that.

Extra classifications were made available to choose from: H1, H2, H3 (instead of just H). Further requirements for reinforcement in slab designs were implemented. It all sounds good!

But will these revisions be sufficient to prevent people from taking shortcuts in future? Does the revised Code AS2870 ensure that soil report writers can no longer ignore Appendix D and the rules for P class sites? Either way, I hope they have mentioned heave and (long-term) droughts this time too.

There will still be many more tragedies to play out just from the pool of houses already built, but will the saga continue unabated?

Let’s think ahead in future and not bury our heads in the relatively young volcanic loam.

  • Mark,
    A good description of the problem and what to look out for.
    But it will be more interesting to see what responsible builders, agencies and industry associations will do. Compromised foundations do not bode well for buildings supposed to last at least 50 years. This stuff compromises the industry's public standing and confidence in what our industry does.
    If this situation is as you report the strongest demonstrable action should be taken to remediate these faults. Construction progress payments are made for work completed in accordance with the contract (and not otherwise). Making wrongful claims has no defence in ignorance, it is also fraud. It has been interesting to see that the US False Claims Act has recently been mentioned in regards to whistleblowing in such circumstances in an Australian context.
    It is long overdue. Will be interesting to see how any Australian company falsely supplying goods to the US may fare in the new Free Trade World.

  • That this was allowed to happen at all was disgraceful.

    The bottom line of all this was that despite several parties being in a position to act, nobody did anything. At the end, in this case the consumer is the one who finally suffers and has to pay for the damage done by others.

    This would not be acceptable in any other industry, and should not be acceptable in the building industry.

    • Yes indeed Richard,

      What has stopped (and what is still stopping) meaningful reform from happening is what the governments need to get onto, or the industry will remain a joke… and I'm not talking about just a small percentage of its operators at fault as so many people in the industry do.

  • Where are Slater & Gordon?? They (or similar) legal companies should be making a killing. Hefty financial penalties soon exert enough pressure to force changes.

  • Concrete flimsy raft slabs are used because its cheap. Using a concreter and a plumber and you are at floor level. Concrete raft slabs are primarily used for temporary buildings with a service of life of no more than 25 years. Up to now most parts of brick veneer houses had a similar life expectancy.
    Wealthy people demolish ordinary 25 year old houses and build again rather than adding to a second rate structure. In reactive soils concrete raft slabs are not a suitable system; apart from the problem of the quality of concrete. Their is no tolerance to anything unusal creating a problem.
    I only use concrete raft slabs for temporary unit developments in areas that I know the buildings will be demolished soon as the land is too valuable for the current underdevelopment and to please Councils push to keep floors no more than 150mm above ground level.
    Soil test prices have more than doubled in five years, and, they are far more restrictive as what you can do with them. The professional soil engineer I use is open to discussions and most times he is right. In many cases my local knowlegde leads me to specify footings at a greater depth than the soil engineers originaly specified. I do tell the clients they will have more soil removal and more concrete; but to remember the whole investment will be sitting on the footings. Often a Class P site can be changed to Class A by going a little deeper. A stable base often costs very little.
    The house building industry is tied into the concrete raft floor systems in every way. We no longer have the brains of CSIRO to come to the party and find an alternative. Any change doubles the cost of building. Any part of building requiring thinking starts a new and expensive process.

  • As a former civil contractor I am always bemused by the subgrade preparation for individual new residential constructions. How many times do you see the small drott or a mini excavator and the pad cut to level and the only compaction the subgrade receives is with the small machine's tracks. It is particularly significant where cut/fill is involved and where differential settlements must occur. The writer is absolutely correct particularly in relation to highly reactive clays. I have seen movements of up to 100mm in pipework around dwellings caused by significant periods of wet and dry. Preparation for commercial dwellings is significantly more controlled so why not residential. There must be someone that signs off on the control of the subgrade preparation. Geotechnical supervision of this would add to cost but the lack of it is false economy.

  • Great article Mark, building today is about profit, get in and out as quick as possible and if the customer has any problems, the legal profession and associated jurisdictions protect the builders profit.
    I am from a family of self employed builders,, third generation, and from a young age assisted my dad in all aspects of building, my dad had 'pride of workmanship' which I have inherited.
    Reading your article nothing surprises me, I was told the integrity of the building starts at ground level.
    I remember most home dad built had packing sand compacted by machine under them which the raft slab rested on. this slab had beams with steel mesh in them and sheet mesh on top, in some case two layers of mesh.
    it didn't matter what soil type was under the sand, because the slab rested on that sand, clay soil types that formed large cracks during dry periods, then contract when wet the sand formed a cushion to avoid slab damage. Where there was any filed land or areas where trees were removed these had sand, and occasionally rock , extremely packed first.
    Then came along the enforcement of the supporting beams going down to a firm soil type, the packing sand remained. However in really bad soggy clay soil types the expansion, contraction still occurred, and the pressure tended at times to fracture the beams and the connecting slab.
    Then came along waffle pads, a cheaper quicker alternative to sand packing, BUT NO STRUCTURAL INTERNAL BEAMS WITH STEEL. Your picture says it all, NO INTERNAL BEAMS, one layer of steel mesh when probably two were required. Then the concreters adding water to the concrete mix changing the specification so the narrow spaces between the waffle pods can be filled easily which without steel are virtually useless.
    Who's to blame the builders, for pressuring the trades for a cheaper price, because these people have guaranteed ongoing work. The consumer relies on the building to do their job and provide them with a product that will stand the test of time because most consumers take 20 – 30 years before they own their homes, DO THE BUILDERS CARE? NO. LOOK AT THE 10,000 HOMES OR SO THAT HAVE 'SLAB HEEVE'.

  • Mark, this is an excellent expose exposing the tricksters’ sting and how the web of deceit works so wonderfully well. It is long overdue. As you have highlighted, the soil test is the key a – geotechnical engineer produces false reports on soil classification, with the engineers and building surveyors all happy to sign off and accommodate the builder! In our case, the house was built on footings, not a slab. The site was, is and always will be a 'P', or PROBLEM site. But the geotech builder's buddy 'engineered' a false classification – decided to lie and claim it as an M site! The engineer and surveyor were willing to collaborate and accommodate the 'builder'. Hence, our major foundation problems, the most serious among the countless other major defects and amounting to a $300,000 monetary loss – and much other loss.

    In fact, I now know that even without visiting the site, engineers can distinguish the classification of all sites – a computer program accurately identifies the soil type at each site location – at the click of a button! But under the current ‘building fraud’ arrangements orchestrated by the vested interests to advantage the cowboys – and approved by the senior bureaucrats who are meant to regulate, enforce compliance and protect owners – builders have been allowed to 'legally' extort money from owners. Thus, they have been enabled to execute what is literally ‘legalized robbery’! This is not simply unconscionable conduct – but outright criminal conduct kept secret, and supported by successive Governments for decades. It is now time to stop these lawbreakers. Time to force the delinquents to depart ‘building’. Time to end our current consumer catastrophe. And time to reclaim our stolen 'consumer rights'!

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