(a) The moisture content of the site at the start of the construction is unknown. Mr Cheenikal assumed (page 237 of exhibit A) that the soil was dry before construction started:
9.2.11 Refer to point 8.34 [of Mr Speechley's report, exhibit 9]. As noted in the point, the building pad was left for 6 to 7 weeks during the period September to October 2002 (6 to 7 weeks period). I agree that the building pad could have significantly dried out during this period. A contractor should provide adequate cover for the fill or cut platform by spreading topsoil or providing other cover to maintain the soil moisture of the building platform. The builder should also moisture condition the near surface soils and then re-compact the surface immediately prior to the construction of slab and footings. I understand that this procedure was not followed in the site and the footings and slab were constructed on top of the dry loose soils. I consider that it is likely that the dry fill materials absorbed moisture during the following winter wet season until it reached equilibrium moisture conditions. This could have caused the uplift of the dwelling, predominantly in the fill area. The natural soils on the western cut area may have been less impacted by the soil moisture variation due to factors such as permeability.
(b) Both Mr Cheenikal and Mr Speechley (exhibit 5), who did have that history, assumed that the pad was substantially dry when construction started:
8.3.4 … There is no data on what condition the soils were in just prior to pouring the slab. It is possible that they may have been quite dry if there had been no rain for some time. Mr Wheeler states in Point 12 of his Affidavit that he inspected the block on or about 25 September and the building pad had been completed. I have checked the rainfall records provided to me by the Bureau of Meteorology from their registered Station Number 72150 (a copy of the rainfall records from January 2002 to 14 March 2008 is attached as Appendix D). The rainfall records show that there was very little rainfall from 26 September 2002 through to 24 November 2002 (a period of more than 8 weeks). There were only four days where rainfall was recorded and these rainfalls were all less than 0.5mm. Therefore we suspect that the building pad had probably dried out significantly during the 6 to 7 week period.
(c) Mr Carter explained (in exhibit 6) that after preparation the site was left for a period whilst they were awaiting approvals to begin construction:
20 After the 2 days of watering the site was given time to consolidate in accordance with my usual practice. In this case I believe it was left to consolidate for 6 to 7 weeks whilst we waited for the construction certificate to issue. That certificate was issued by WWCC on 21 October 2002.
(d) In the ordinary course of things, the site might be expected to dry out in that period, as was assumed by both Mr Cheenikal and Mr Speechley. However, the plaintiff's evidence raised doubts about the degree to which the site had dried out before construction. The plaintiffs' witness, Mr Livingstone Jones (page 76 of exhibit A), confirmed that the site was watered using a sprinkler; and that Mr Carter drove his vehicle on the site. The watering was sufficient to cause Mr Carter to bog his vehicle on the site. According to Mr Livingstone Jones (page 76 of exhibit A), 'a short time later' [than] Mr Carter bogged his vehicle on the site, Mr Livingstone Jones observed that the 'house slab had been poured and finished' and Mr Livingstone Jones recalled 'thinking that this was strange as it was only several days earlier that Mr Carter had bogged his car on the block.'
(e) Mr Cheenikal was not told that the site had been watered, and said that this was something he would have taken into account in forming his opinions. Mr Cheenikal opined that water ingress had caused the heave, and that the dryness of the soil at construction was thus causal, saying (page 233 of exhibit A) that:
9.2.11 … I consider that it is likely that the dry fill materials absorbed moisture during the following winter wet season until it reached equilibrium moisture conditions. This could have caused the uplift of the dwelling predominantly in the fill area. The natural soils on the western cut area may have been less impacted by the soil moisture variation due to factors such as permeability.
(f) Mr Cheenikal's opinion was offered (page 237-238 of exhibit A) on the basis that:
9.2.11 … the building pad was left for 6 to 7 weeks during the period September to October 2002 (6 to 7 weeks period). I agree that the building pad could have significantly dried out during this period. A contractor should provide adequate cover for the fill or cut platform by spreading topsoil or providing other cover to maintain the soil moisture of the building platform. The builder should also moisture condition the near surface soils and then re-compact the surface immediately prior to the construction of slab and footings. I understand that this procedure was not followed in the site and the footings and slab were constructed on top of the dry loose soils …
(g) The significance of Mr Livingstone Jones' observations about site watering and a bogged vehicle were not explored in the evidence. They do little more than make it difficult to form any view about the degree to which the site had dried out between site preparation and start of construction, and add confusion.
(h) The plaintiffs' case is that the construction site had dried out. However, Mr Livingstone Jones says that 'only several days' before the slab was poured, the soil was 'very soft and wet' (page 76 of exhibit A). If that (unchallenged) recollection/opinion be right, doubt must attend the assumption that the site had dried out before the slab was poured. That has implication for expert opinion rested upon that assumption, as said in Makita (Australia) Pty Ltd v Sprowles [[2001] NSWCA 305; (2001) 52 NSWLR 705].
64 The basal principle is that what an expert gives is an opinion based on facts. Because of that, the expert must either prove by admissible means the facts on which the opinion is based, or state explicitly the assumptions as to fact on which the opinion is based. If other admissible evidence establishes that the matters assumed are 'sufficiently like' the matters established 'to render the opinion of the expert of any value', even though they may not correspond 'with complete precision', the opinion will be admissible and material: … One of the reasons why the facts proved must correlate to some degree with those assumed is that the expert's conclusion must have some rational relationship with the facts proved.
(i) Mr Speechley identified the complexity when shown Mr Livingstone Jones' affidavit:
A. Well, what it says is what the vehicle got bogged. I'm not quite sure what bogged means, whether it was bogged as in it went down, or whether, you know, wheels are spinning. So I don't really know there. What it does tell me about, [paragraph] four [of Mr Livingstone Jones' affidavit, page 76 of exhibit A], is that quite possibly the fill soils weren't dry just before the slab was laid.
(j) Mr Speechley explained that certain tests might permit opinions to be formed to ascertain the effect upon the construction of the moisture content at the time of construction, but that he had not done these:
[HER HONOUR ?]: At the end of the day, Mr Loughnan I think is going to submit that if it had been done right, X would have happened. What actually happened was Y happened and the difference is the problem.
HER HONOUR: Is that a short way of putting it, Mr Loughnan?
LOUGHNAN: There will be many submissions, but that's a fair one to make, your Honour.
HER HONOUR Q: How do I know what the gap was?
A. I'm not sure, to be honest. It's a difficult concept, because there's a lot of factors involved, and the easiest way is to look at a ratio type of thing. We could look at the moisture contents of the actual soils, which we have moisture content data from Aitken Rowe. We could look at the liquid limit and the plastic limit, which is approximately equal to that optimum moisture content, and we could do it on a ratio type basis. But it would involve a lot of looking at the various samples and so forth.
Q. You've not done that?
A. I haven't done that, no.
Q. Is it in Mr Coffey's report?
A. I don't think so.
(k) Mr Cheenikal did not undertake testing of the requisite type. The significance of the moisture content or degree of drying out of the construction site remains conjecture, as does the actual moisture content at the relevant time; but the cross-examination of Mr Speechley was inconsistent with Mr Cheenikal's assumption that the site had dried out before construction:
Q. Let me put it this way, Mr Speechley. If this is true, if this vehicle got bogged several days before the slab was laid, shouldn't that have sent off some warning bells for the defendant in this case?
A. Well, yeah, if it was bogged and it sunk down into the ground, I agree, it would have been indicative of the soil's being wet and probably poorly compacted.
(l) Mr Kennard noted that the slab might have settled if it was too moist (page 93 of exhibit A):
- The site has reportedly been prepared by constant watering and then left to consolidate for 6 to 7 weeks. In item 8.3.4 it is suspected that the building pad had probably dried out significantly during the 6 to 7 week period. If the pad had not dried out, and subsequently dried out after pouring of the slab, then settlement would almost certainly have occurred.
(m) However, the slab has not settled (putting aside differential settlement). It heaved" (Judgment pp 71-3).