Thompson v City of Canada Bay Council

[2004] NSWLEC 506

Land and Environment Court

of New South Wales

CITATION:	Thompson v City of Canada Bay Council [2004] NSWLEC 506
PARTIES:	Mark Thompson (Appl) City of Canada Bay Council (Resp)
FILE NUMBER(S):	11595 of 2003
CORAM:	McClellan CJ
KEY ISSUES:	Appeal :- Council order requiring repair or structural alteration of a retaining wall How to classify the wall Structural stability of the wall
LEGISLATION CITED:
CASES CITED:
DATES OF HEARING:	2 July 2004
DATE OF JUDGMENT:	09/08/2004
LEGAL REPRESENTATIVES:	D Miller (Appl) PricewaterhouseCoopers Legal (Sol - Appl) I Hemmings (Resp) Maddocks (Sol - Resp)

JUDGMENT:

THE LAND AND
ENVIRONMENT COURT
OF NEW SOUTH WALES

McCLELLAN J

WEDNESDAY 8 SEPTEMBER 2004

11595/03 THOMPSON v CANADA BAY CITY COUNCIL

JUDGMENT

1 HIS HONOUR: This is an appeal against s 121B Order No 4 issued by the Council on 24 November 2003, requiring the repair or making of structural alterations to a retaining wall at 49 The Esplanade, Drummoyne. The terms of the order are:

"1. To repair or make such structural alterations to the wall and paling fence (located on top of the wall) to the rear of the property separating No's 49 and 50 The Esplanade so as to make the wall comply with relevant standards, in particular:

1.1 AS 4678-2002 "Earth Retaining Structures", and
1.2 AS 3700-2001 "Masonry Structures".

2. To prepare and submit to the Council, within 2 weeks from the date of this Order, particulars of the work proposed to be executed to satisfy this Order (including the repairs and structural alterations to the wall) so as to make the wall structurally sound and comply with relevant standards, including those described above. Such particulars are to be prepared by a practising structural engineer."

2 I have been assisted by Commissioner Hussey in the resolution of the matter. We had a view of the site.

3 The retaining wall is situated wholly within No 49 and adjacent to the common boundary with No 50, which is the lower property. It is approximately 15.4m long and varies in height from about 300mm to 1800mm. It is constructed of various materials comprising a sandstone and brick base, besser-block wall mid-section, and paling fence on top.

4 The owner of No 49, Mr M Thompson, stated that he has occupied his property since 1994. He says the back yard level of his property is much the same level now as it was in 1994, although in 1996 the back room of his house was demolished and alterations undertaken. This involved some work in the back yard, which involved the removal of one course of the besser-blocks. Otherwise, the retaining wall was unaffected.

5 Concern about the adequacy of the retaining wall arose in 2002 when the owners of No 50 submitted a development application to demolish the existing house on their property and subsequently construct a new house, together with a lap pool, adjacent to the retaining wall. A boundary setback of approximately 900 mm was proposed.

6 On 21 August 2002, the Council granted consent (DA 357/2002) to the application subject to conditions.

7 Condition 17 provided:

"Support for Neighbouring Buildings:
If an excavation associated with the demolition or construction of a building extends below the level of the base of the footings of a building on an adjoining allotment of land, the person causing the excavation shall comply with the requirements of clause 78F of the Environmental Planning and Assessment (Amendment) Regulation 1998 details shall be submitted prior to the issue of a Construction Certificate where applicable."

8 Condition 28 also required that a dilapidation report be prepared, although this condition was subsequently modified.

9 The development application was accompanied by a report from consulting engineers Jeffery & Katauskas Pty Ltd, which referred to the existing sandstone block retaining wall and indicated that it appeared to be in good condition. However, these engineers recommended further investigation work to assess the geometry of the wall and determine whether underpinning to rock and/or provision of lateral supports by dowels would be required.

10 In anticipation of commencement of the development, one of the owners of No 50, Mr Dal Cin, arranged for Astroc Structural Engineering (Astroc) to enter the properties to undertake a dilapidation survey. In the course of this inspection, Astroc formed the opinion that the retaining wall was not sound and advised the Council accordingly.

11 On 19 November 2002, the respondent issued the Notice of Proposed Order for the wall repairs relying, as I understand the position, on the Astroc report. On 21 November 2002, the owners of No 50 lodged a Notice of Commencement of Building Works.

12 As the building works involved the removal of some natural soil from around the base of the retaining wall and then further excavation for services and the pool, Mr Dal Cin arranged for the construction of 4 piers and connecting beams to underpin and support the wall during the excavation works.

The evidence

13 Following the making of the s 121B Order, a number of engineering investigations were undertaken. Reports were obtained on the Council's behalf from Mr S Hamilton, consulting engineer of Richard Harris Moretti Engineers, and Mr R Ottaviano, consulting structural engineer of Astroc Engineers.

14 For the applicant, investigations were undertaken by Mr M Lawrie, consulting structural engineer of Montego Cay Pty Ltd, and Mr D Dickson, consulting geotechnical engineer of Dickson & Associates Pty Ltd.

15 One of the primary debates in the proceedings has been how to classify the retaining wall and its ability to support any imposed loading. The concern arises due to the uncertainty expressed by the engineers as to whether the retaining wall was adequately designed as a mass sandstone gravity wall or as a cantilevered retaining wall.

16 Mr Hamilton gave evidence that he undertook site inspections and reviewed the available structural engineers' details. He concluded that the structural stability of the wall was questionable because there is no evidence of substantial reinforced concrete footing supporting the blockwork wall, there is uncertainty about vertical reinforcement in the wall and details of its embedment into bedrock, and there are no details about the encasement of any reinforcement, which poses questions of durability in what he believes to be a high risk corrosion environment.

17 Mr Hamilton's position is generally consistent with Mr Ottavianos' opinion. From his observations of a test pit behind the retaining wall, Mr Ottavianos says that the wall has not been built directly on rock. Instead, he considers it is bearing on a sandy clay foundation, which makes it structurally unstable and liable to "catastrophic failure".

18 Mr Lawrie also investigated the condition of the retaining wall and engaged Mr Dickson to assist in understanding of the stability of the existing wall. Mr Dickson found that:

"The wall is drained with several 50mm black polyethylene 'agg-drain' pipes protruding from the face at the lower intersection of the wall. The wall has been laid with roded mortar joints and the blocks have been filled with concrete. There are no visible signs of distress, movement, settlement, cracking or any other visible signs that the wall has moved in the past."

19 Mr Dickson also undertook a stability risk assessment of the retaining wall. From this he found that the site meets the acceptable/tolerable risk requirements (as defined by AGS 2000) for Category LOW.

20 He concluded that:

"the wall is stable and that the wall will remain stable so long as its support (foundation) is not removed or the drainage impeded."

21 Mr Lawrie also asked Mr Dickson to undertake further detailed geotechnical investigations so as to gain an understanding of the way in which the wall was constructed and enable an assessment of its performance to date. This investigation involved using dynamic cone penetrometer test probes to identify and characterise the backfill, residual soils and sandstone bedrock behind the wall. The soil moisture was also observed from the condition of the rods on withdrawal and observations were made of the surrounding soil type, geomorphology, the shape of local landforms and observed drainage characteristics.

22 From this investigation, Mr Dickson concluded that the wall is made up of 3 construction types all with very different properties and performance criteria. This includes an original wall, now only 300 to 400 mm high and forming the base of the existing wall, which comprises dry stacked sandstone blocks. Next there is the brick masonry wall, between 1 and 3 courses of brick and used as a levelling course beneath the concrete block work. On top of this is 190 mm concrete block work, which appears to be filled with concrete grout and reinforced in accordance with details consistent with Concrete and Masonry Association 1976 MA101.

23 By application of the dynamic cone penetrometer survey analysis, various wall design scenarios were modelled and tested. These design tests take into account the total heights of the wall as being load bearing with differing fill heights for the sections. Mr Dickson says that it is apparent that the footing for the wall must incorporate some form of cantilever reinforcing either cast in the concrete at the base of the wall or drilled into the sandstone under the footing base, because from the design assessment, crack widths and wall distortion would be much wider in the event that steel was not present.

24 From this analysis, Mr Dickson concluded that:

"the wall is a faced gravity wall, reinforced with S16 bars at 400 centres in the vertical and horizontal. Further it is our opinion that the wall acts as a gravity wall in preference to a cantilever wall. It is also our opinion that the fill is made up of sandstone cobbles, boulders and rubble with a sandy matrix probably of residual soils from the Hawkesbury sandstone. The boulders and sandstone near the base of the wall are most likely bound by concrete, some of which is visible in the exposed section of the wall foundations."

25 Mr Lawrie has reviewed the dynamic cone penetrometer survey analysis and supports Mr Dickson's conclusion that the wall is stable and remains structurally sound.

Conclusions

26 In order that the Court could assess the conflicting positions, evidence was taken concurrently from the experts. Although Mr Hamilton did not dispute the findings of the dynamic cone penetrometer testing, he still considered that this alone was not sufficient to allow the formation of a substantive opinion on the method of construction of the existing retaining wall.

27 I am satisfied that a comprehensive site investigation has been undertaken by Mr Dickson with the dynamic cone penetrometer testing and his review of local conditions. I accept his conclusion and that of Mr Lawrie that the existing retaining wall is stable and that it is in a low risk category of failure.

28 This position was confirmed on the view, where an examination of the wall revealed only minimal shrinkage cracking and no indication of any movement in the wall. Neither Mr Hamilton nor Mr Ottaviano could explain why the retaining wall showed no sign of movement let alone failure, which I am satisfied would now be present if the wall, as constructed, had any problems.

29 Accordingly, I am satisfied that the wall is structurally sound even though it does not comply with all aspects of the designated Australian Standards. There is nothing in the evidence which persuades me that the Council's notice was justified.

30 Accordingly, I make the following orders:

1. Appeal upheld.

2. The s 121B Order made by the Council is revoked.

31 I will hear the parties in relation to costs or compensation.

**********