Ziade v Woollahra Council & Anor unreported CA40457/93 28 April 1994 at p 6

At the base of the subsurface profiles very low to low strength shale and very low strength mudstone was encountered.

The report states "(i)t is understood that the proposed development comprises the construction of a split level residence with minimum disturbance of natural ground, and with foundations taken to rock".

"Based on the above investigation, the risk of slope instability on the site has been reassessed to one of medium risk, and the lot is considered suitable for residential development following the guidelines for hillside development in Table 2 attached" and the listed specific geotechnical constraints.

• House foundations to be socketed at least 300 mm into intact, tightly jointed rock (an allowable bearing pressure of 400 kPa is appropriate).

• No fill should be imported onto the site, and any filling arising from on-site excavation should be supported by an engineered retaining wall.

• Temporary excavations up to 2.5m high may be battered no steeper than 1.5:1V for soil and 0.5H:1V for rock, with all excavations to be permanently supported by a retaining wall.

• Retaining walls must be founded in rock and include subsoil drainage pipes and aggregate and have a defined outlet into the stormwater system.

• Retaining walls and foundations should be designed to allow for the lateral load arising from soil creep on the steep slopes, and also hydrostatic loads arising from potential groundwater sources not drained by subsoil drains.

• Stormwater runoff and roofwater must be collected and discharged clear of the site.

• The surface interceptor drain upslope of the site must be maintained in good working order and the neighbouring residents and council may be required to assist with this maintenance.

• Development of the site should ensure that the irregularities in slope profile resulting from previous development are remediated and supported, and that every opportunity to improve subsurface and surface drainage is taken as a means of reducing the risk of future slope instability. Similarly existing excavations and fills should be supported by engineered retaining walls to be constructed as part of the site development.

Alexander Welham, the author of the report, has explained to the Court that the description of the proposed development was based on a sketch plan shown to him by the respondent and discussions he had with Dr Falamaki prior to preparing the report. He says that the recommendations contained in the report enabled the construction of the residence without the extreme excavation which has since taken place. Further, if the respondent had not found the subsurface condition exposed by the test pits, the proper course of action would have been to confer again with the geotechnical consultant for advice as to how the development could proceed. Finally, he told the Court that the extent of excavation which has been carried out has significantly increased the risk of instability of the land and adjoining land.

Dr Falamaki made the following observation in a letter which accompanied the structural plans lodged with the council on 22 October 1996:-

... an examination of the Geotechnical report indicates that the location of solid bed rock with a strength of at least 400 kPa, in most places is at a depth of at least 3.5 meters. Therefore, it was decided to perform the excavation in few stages, and after completion of each stage, construct a temporary retaining structure, using DUCKBILL, or any other similar earth anchorage system, to stabilise the soil.

Mr Stone says that the respondent either misunderstood or misinterpreted the Coffey definition of rock quality needed for support purposes. In his opinion, the requirement for "intact tightly jointed" material "with an allowable bearing pressure of 400 kPa" means rock which is not a floater, has closed joints, but need only have a strength equivalent to a "very stiff/hard" soil.

Mr Hargreaves inspected the site on 23 April 1997 at the request of the respondent. He also viewed the approved plans, the Coffey Report dated 30 October 1995 and the Longmac Report dated 21 April 1997.

His conclusions directed to Dr Falamaki may be summarised as follows:-

1. Arter Avenue is one of the most challenging areas for building in Australia.

2. He expressed surprise at the Coffey risk classification of "medium".

3. He would have discouraged such an extensive cut.

5. He was surprised at the lack of fretting or debris from the face.

6. Assuming the respondent's calculations to be correct, and after recognising the innovative method, he approved the proposal by the respondent to:-

c) Resist the earth pressures via a series of beams and braces which will (without affecting the dwelling's integrity) transmit these forces to the concrete pad footings which are founded in bedrock.

Subsequently, on 29 May 1997, he furnished supplementary advice recommending additional precautions to be taken to ensure any workmen are not exposed to risks greater than normally expected.

Finally, after receiving a copy of a report by Peter John Yttrup, a consulting structural and geotechnical engineer engaged by the respondent, Mr Hargreaves settled upon three practical options to resolve the situation. These include the use of shotcreting as specified by Mr Yttrup, or to increase the bracing within the structure if the structural integrity is not sufficient to resist the calculated loadings. The third option was a hybrid solution of the first two options, where the sides of the excavations are retained by shotcreting and the rear of the excavation by the structure itself.

Peter Tobin is a geotechnical engineer employed in the Works Division of the council.

On 24 April 1997, Mr Tobin was requested by Mr Lett, Manager Health and Building, to comment on the geotechnical report by Mr Hargreaves. Mr Tobin recommended that a letter be addressed to Dr Falamaki requiring submission of a structural design based on geotechnical advice for the provision of temporary support and further structural design, again based on geotechnical advice, detailing permanent structures. This advice was not acted upon and no letter was written at that time in those terms.

The purpose of the work undertaken by Mr Stone, and the subject of his report to the council dated 21 April 1997, is to advise on the stability conditions of the work and on any action necessary in the short term. Mr Stone stated that he understood the excavation was contrary to the building approval. Development plans were not reviewed and no geotechnical documentation was considered.

He recommended that a rock fill buttress be used to infill the base cut and provide passive support to the exposed cut.

After a meeting with council officers on 1 May 1997, Mr Stone expressed general agreement with comments made by Mr Tobin and inquired regarding measures and contingency actions planned for slope support in case of extended rain disrupting the work and increasing the threat of instability. He also raised questions regarding safety during construction, details for backfill and geometry of the structure.

Dennis Thomas is a consulting structural and civil engineer who is retained by the applicant to review the plans and specifications prepared by Dr Falamaki for the structure currently being erected at 12 Arter Avenue. Mr Thomas asserts that the structure differs in significant respects from the plans approved by the applicant and it has not been constructed in a proper and workman like manner.

He analysed the structure using the Spacegass computer program which analyses loads and forces on structures and checks that members are adequate to support or resist those loads and forces. His analysis indicated that, applying the information provided by the respondent and his consultant, the structure would fail and be substantially damaged.

It became clear, during the cross examination of Mr Thomas, that many critical factors had not been taken into account and that accordingly the results cannot be relied upon. His evidence has done nothing to persuade the Court that removal of the structure is necessary.

Contrary to the views expressed by others, including Mr Hargreaves and Mr Yttrup, that the design for the proposed structure was not unusual, Mr Thomas insisted that the proposed building is a prototype and that as a result there must be some doubt as to whether the structure or any part of it complies with the relevant codes and standards. It became apparent, while Mr Thomas was in the witness box, that he did not understand the concept and had therefore failed to consider technical elements of the design which provided the essential bracing and support by transferring the loads to the base of the columns through a steel buttress frame.

After having heard all of the evidence, the Court agrees with the respondent's consulting structural and geotechnical engineer, Mr Yttrup, that the calculations by Mr Thomas are essentially useless. The failure by Mr Thomas to provide an explanation of his assumptions and details behind his computer model leaves fundamental questions unresolved. Mr Thomas based his comments on a three dimensional structural model which ignored the role of the action of the floor diaphragm and sheer walls.

Either Mr Thomas was complicitous in a deliberate attempt by the council to forestall the construction of the building to which it had given approval, or the task was beyond his professional expertise. In any event, the evidence of the respondent's witnesses is to be preferred.

Mr Yttrup wrote to Dr Falamaki making comments, opinions and recommendations following a site inspection on 10 November 1997.

He suggested that, with the benefit of hindsight, the building approval issued by the applicant council should never have been granted in a landslip sensitive site without detailed geotechnical appraisal and justification. However, he recognised in principle that the proposed structure can resist the earth loads from the potential landslip above the site, but the structure has to be completed before it can provide the needed ground support. He recommended that vertical retaining walls should be installed, effectively drained and backfilled with compacted material to introduce ground support as quickly as possible.

The observations by Mr Yttrup in respect of the analytical approach taken by Mr Thomas have been referred to.

Mr Yttrup had been requested earlier to assist Dr Falamaki to review the calculations made by Mr Thomas. The lack of response to requests for further information directed to Mr Thomas through the council's solicitors meant that Mr Yttrup was not able to review the calculations. When that information was still unavailable in December 1997, he was highly critical of Mr Thomas. It appeared to Mr Yttrup that Mr Thomas had analysed a different structure to either the original structure, designed by the respondent and approved by council, or an alternative conceptual design discussed with Mr Thomas in May 1997.

In the opinion of Mr Yttrup, the exchange of correspondence between the council at the behest of Mr Thomas and the respondent shows that Mr Thomas is an inexperienced structural analyst and that the failure to provide a legible wire diagram, an explanation of his assumptions, and the philosophy or details behind his computer model makes it impossible to examine his findings.

Ultimately, Mr McEwen conceded on behalf of the council that the analysis undertaken by Mr Thomas is incapable of proving that the structure will fail because that analysis omitted to take into account all relevant structural elements. Mr McEwen made it plain that the concession is not to be construed as conceding the structure is sound.

In his oral evidence, Mr Yttrup told the Court that the approach taken by the respondent in respect of the subject hillside site was absolutely valid. He agreed with the Coffey assessment that before excavation took place, the risk of landslip was properly assessed as moderate, although the issue is not free from doubt.

Mr Yttrup does not agree that the structure should be regarded as a prototype or "showcase" because, as a structure, it is a normal structure following engineering principle and is not particularly novel. He did agree however, that the classification of the site by Coffey was conditional upon the adoption of hillside management techniques which had not occurred.

Condition 6 must be construed in the context of the plans approved and the whole of the Coffey report. Specific constraints are nominated in the body of the report. Mr McEwen has not been able to show, in so far as the work has progressed to date, that any particular listed constraint has not been satisfied. Although the house foundations are apparently socketed into the bedrock, the council's argument is that the profiles disclosed in the test pits show that appropriate material was available at a depth of down to 2.9 metres. It was therefore not in accordance with the Coffey report to take the excavation beyond that depth.

The architectural plans lodged with the building application show two small areas of cut with the building resting at approximately ground level at the western extremity and on shallow fill at the lowest eastern extremity. The deepest proposed cut scales at just over two metres. Even allowing for the lack of detail provided by the architectural plans, it is not possible to construe those plans as contemplating an excavation to seven metres.

Mr Welham proceeded with his investigation on the basis of a sketch plan shown to him by Dr Falamaki and discussions with him prior to preparing the report. The description of the proposed development in the report is consistent with the building shown in the plans lodged with and approved by council in 1995. The report clearly addresses a proposed split level residence with minimum disturbance of natural ground.

When Dr Falamaki cross examined Mr Welham, it became clear that Dr Falamaki had concentrated on finding bedrock to found the slabs and beams. Mr Welham countered that very low to low strength rock investigated from the test pits was sufficient to withstand the load. In other words, the material that was there was suitable for the building Dr Falamaki was proposing at the time.

Notwithstanding the approval given by council to the structural plans on 23 October 1996, what is now on the site contrasts in significant and material respects from the proposal considered as the basis for the Coffey report. The siting of the building within the site and the extent of excavation departs substantially from the 1995 approved plans.

Prudence dictates that if Dr Falamaki did not encounter satisfactory material to bed the foundations as contemplated by the Coffey report, then he should have referred the matter back to Coffey for further geotechnical advice.

It therefore must follow that the structure has been erected otherwise than in accordance with the Coffey report. The consequence is that the respondent has not complied with the recommendations of the geotechnical engineer's report as required by condition 6 of the building approval.

The council file contains an A4 size copy of a foundation plan and details approved on 23 October 1996. It is alleged by the council that the specifications on that plan are indecipherable. The Court agrees. However, Dr Falamaki produced an A3 size copy of the same plan duly stamped with the approval dated 23 October 1996. The council accepts that the dimensions and specification on the copy of the plan held by the respondent are readable and show levels consistent with those actually achieved by the excavation.

The council can offer no explanation for the reduced copy being the only copy of the relevant plan held by it. The officer who gave the approval was not called. Dr Falamaki denied that he obtained the full size stamped copy now held by him at a subsequent time. He maintains that an A3 size copy was lodged for approval on 22 October and cannot explain why the council copy is in reduced form. The Court accepts Dr Falamaki's evidence that a full copy was lodged and approved by the council. The council was therefore in a position to appreciate that when it approved the plans on 23 October 1996, it was acknowledging that the excavation would be greater than that shown on the plans approved on 8 December 1995 in response to the application for the building approval.

The purpose of structural plans is to provide engineering and other details to prove stability and strength of construction sufficient to support the approved structure. They cannot modify the building approval in any material respect.

The approval of structural plans which are inconsistent with an approved building plan cannot have the effect of amending the original building approval unless they are lodged for the latter purpose.

No application to amend the approval given in 1995 has ever been made. It was necessary for the respondent to make a separate application to council in order to obtain authority to carry out the works in a manner different to that disclosed by the approved plans and otherwise than in accordance with the recommendations in the Coffey report.

However, in the circumstances, it was not unreasonable for Dr Falamaki to assume, contrary to law, that he had received the appropriate approval of the council to proceed to excavate the site down to the levels shown in the plans approved on 23 October 1996.

Even though a council may not have a duty to check that structural plans conform with approved building plans (see obiter remarks of Meagher JA in Ziade v Woollahra Council & Anor unreported CA40457/93 28 April 1994 at p 6), the council was careless in the way in which it approved the plans in October 1996. This lack of care was compounded during 1997 by the subsequent inspection and approval of the pad footings in February 1997 and the delay until April before it demanded a stop to work. The inability of Mr Thomas to proceed with a helpful analysis has contributed to further delays and exposure to risk of damage to property and persons. Fortunately no actual damage has occurred.

This is a case where the council has proved its case to the point where it is entitled to the declaration and other relief claimed but, in the circumstances, the Court should exercise its wide discretion not to make any such declaration or order (Warringah Shire Council v Sedevcic (1987) 10 NSWLR 335 (CA)).

The breach occurred as a consequence of the failure by Dr Falamaki to properly understand the definition of rock and the categorisation of material identified by the Coffey report as being suitable as a bed for foundation. Although the actions taken by him have created a critical situation, they were nevertheless done in good faith, notwithstanding submissions made by the council to the contrary.

The public duty of the council to ensure that the building is ultimately constructed in a safe manner can be achieved by requiring certification of the engineering specification for the structure. Mr Yttrup accepts that a house with the proposed configuration could be safely built on the site while maintaining the excavation.

The development is already static in the sense that the breach can only be remedied at great cost and inconvenience.

Having heard all the expert evidence, the Court is satisfied that the structure can be completed in a way which ensures the appropriate loads are supported and the site is made safe from landslip.

A suggested form of certification was put to Mr Yttrup by Mr McEwen. Mr Yttrup acknowledged that an acceptable certification was contained in the draft submitted but he preferred that it go further. He expressed a need for it to extend to the structural system. He was given the opportunity to draft what he considered to be a suitable form of certification. Dr Falamaki agrees that, if given the opportunity, he can provide certification in the form preferred by Mr Yttrup within a short time.

The excavation has already withstood the ravages of weather and erosion for over twelve months without showing signs of deterioration or collapse. The experts are agreed that the excavation cannot be left in its present condition for an extended period. The Court is prepared to exercise its discretion in favour of the respondent, provided that certification is provided in the form approved by Mr Yttrup within three months from this date.

The making of final orders will be deferred until 30 September 1998 to allow Dr Falamaki the opportunity to obtain acceptable certification.

The application will be dismissed if, before 30 September, the respondent furnishes to the council a design certification by Peter John Yttrup, or such alternative structural engineer who is acceptable to council, other than Dennis Thomas, in the following form:-

That the structure and associated retaining system and details have been designed to support the adjacent land to a level of risk of landslip equivalent to the current condition of "medium risk" in terms of the AGS Guidelines.

The building shall have a performance expectation similar to normal residential building construction.

The structural system shall comply with relevant design codes.

In the meantime, each party will be granted liberty to apply on two days notice.

The exercise of the Court's discretion in favour of the respondent is a factor in any litigation where relief is claimed in the form of mandatory or restraining orders.

The council approached the problem of the erection of the building otherwise than in accordance with the building approval on a practical basis, namely, that if the respondent could satisfy it that the building could be sound and secure against the effect of landslip, the work might proceed to completion. Notwithstanding directions by various Judges during the interlocutory stages of the proceedings, the council failed to provide answers to questions raised by the respondent or to furnish essential particulars of the modelling undertaken on council's behalf. The fact that Dr Falamaki has been frustrated in his attempts to satisfy the council, its experts and its officers in this respect is in large part a consequence of its own procrastination due mainly to the failure to obtain competent advice.

The Court has nevertheless found that Dr Falamaki was primarily the cause of his own dilemma by not complying with the requirements of the Coffey report and by building a structure which is inconsistent with the approved plans.

Mr McEwen submitted that this might be an appropriate case where each party be ordered to pay its own costs. Both parties came to the hearing seeking resolution of a dispute which they have not been able to resolve by negotiation. Although it might be argued the council initially overreacted by commencing the litigation when it did, the Court recognises that, prima facie, having regard to the history of landslip in the area, there was, at all relevant times, a potential for serious landslip to occur. It is fortuitous that nothing of the sort occurred. This, in part, is due to protective works put in place by the respondent, including the use of tarpaulins to protect the face of the cut from the elements. Notwithstanding that the responsible officer or officers of council were found to be careless in their approach up to April 1997, the situation at that time called for an effective response.

I agree with Mr McEwen that, in the circumstances, it is appropriate that each party pay their own costs. This will mean, in Dr Falamaki's case, that, he will be responsible only for the expenses incurred by his expert witnesses. This is a just result, because in the end those witnesses have been able to persuade the Court that Dr Falamaki should be allowed the opportunity to proceed with his building work, notwithstanding the established breach of the law, subject to a condition of certification. However, the question of costs will be formally reserved. It is appropriate for the certification to be furnished before Dr Falamaki is finally relieved of liability for payment of the council's costs.

1. Matter 40091 of 1997 is adjourned to 9.30am 30 September 1998 for the purpose of making final orders.

3. Either party has liberty to apply on two days notice.

DISCLAIMER - Every effort has been made to comply with suppression orders or statutory provisions prohibiting publication that may apply to this judgment or decision. The onus remains on any person using material in the judgment or decision to ensure that the intended use of that material does not breach any such order or provision. Further enquiries may be directed to the Registry of the Court or Tribunal in which it was generated.