The damage
18The applicant's case is based on a report prepared for them by Mr Don Katauskas, a Consulting Geotechnical Engineer, and dated 27 January 2014.
19The wall is part single, part double brick that forms the eastern boundary of the applicant's property. The fence comprises panels between brick columns. The inner side of the wall is faced with sandstone tiles. The Norfolk Island Pine is growing behind an engineered retaining wall to the east. Between the respondent's retaining wall and the applicant's wall is a concrete path. The original soil level at the base of the tree is about 1m above the path; due to fill associated with the construction of a pool on the respondent's property, the new soil level is about 1.5m above the path. The pathway is on the respondent's property however it provides a right of way for pedestrian access to a number of nearby properties. There are a number of services beneath the path including sewerage, drainage and communications.
20According to Mr Katauskas, the southern end of the most southern panel of the wall has rotated by approximately 5 degrees. There is a displacement and separation of about 30mm between the top of the panel and the adjoining column. There are a number of cracks in the mortar between the two lowest courses of sandstone tiles on the inside of the wall. In addition to the damaged wall, there is movement and cracking in the stairs that lead from a gate in the wall onto the applicant's property. The gate sticks and has been adjusted on several occasions. The damaged structures are within about 2m of the tree.
21Mr Katauskas is of the strongly held opinion that roots from the Norfolk Island Pine have caused the damage and he states:
Because of the dynamic and increasing pressures exerted by the continuously growing tree, in my opinion there can be no effective permanent solution to restricting pressures on any structures within the zone of influence of the tree and its roots.
The damage to the walls and walkway are continuing, and addressing this will ultimately require drastic and expensive remedial measures.
The only long-term solution to this situation is to remove the tree.
22Mr Katauskas also raises concerns about the long-term adequacy of the new retaining wall as he states that the soldier piles are displaced from vertical and the timber infill is rigid and immovable. In his view, this indicates that the new retaining wall is under some stress.
23Both Mr MacLeod and Mr Katauskas have visited the site on several occasions and have prepared reports on the integrity of the original retaining wall. Mr Katauskas has inspected the site on a number of occasions, the first being 3 March 2009, then 22 February 2011, 6 December 2013 and then 10 January 2014. As part of his earlier investigations, Mr Katauskas made several bore holes into the pathway and near the tree to determine the nature of, and depth to, the underlying bedrock.
24Similarly Mr MacLeod inspected the site on 18 August 2008 and 13 January 2009. In January 2010 he reviewed a number of reports in response to the DA. On 27 February 2014, Mr MacLeod reinspected the retaining wall for the purpose of this hearing. He also reviewed Mr Katauskas' 27 January 2014 report.
25In response to Mr Katauskas' latest report, Mr Macleod states that Mr Katauskas has provided no evidence, for example by way of test pits in the pathway, to support his opinion that roots are impinging on the wall's footings, thus creating the rotation. In Mr MacLeod's opinion, the wall is constructed in un-reinforced brick masonry and is acting as a retaining wall, something it is not designed to be. In his view, normal soil pressures could cause such rotations without any roots. In regards to the new retaining wall, Mr MacLeod considers the slight displacement to be within normal tolerances and given the natures of construction, the slight displacement has no bearing on structural adequacy. In his opinion there is no need to remove the tree.
26Mr MacLeod's report also includes calculations on static loading of the tree in regards to its likely failure. As this element of the application is no longer pressed, expert evidence relating to this aspect is not considered in this judgment.
27In response to Mr MacLeod's opinion regarding soil pressure as a likely cause of rotation, Mr Katauskas [in Exhibit B] states that the applicant's wall is founded on sandstone bedrock at the foot of a sandstone ledge; the wall incorporates other garden beds and is effectively buttressed by the steps; and there is inadequate soil volume behind the wall to cause pressure. He reiterates his opinion that the damage can only be attributed to root expansion causing uplift and horizontal pressures against the wall.
28During the hearing, the location and extent of the damage was inspected and Mr Katauskas' summary of it confirmed. The pathway between the relevant walls was noted to be in relatively fair to poor condition. There were many patches of different materials, some much older than others. There was a drain inlet close to the rotated pillar. Some minor cracking of the path was noted between the corner of the retaining wall and the pillar/gate, but no lifting of any significance.
29The engineers' oral evidence supported their written opinions. Mr MacLeod stated that if roots were present he would expect to see an uplift of the paving. Mr Katauskas said that there is always a reason for a crack in a structure and in this case it is because of a root/s from the tree.
30When asked, the engineers agreed that the damage to date could be considered 'severe' in accordance with the relevant standard; that is, the crack is wide enough to be in that category. However, the damage is essentially cosmetic and not structurally significant. However, Mr Katauskas pressed his assertion that unless the tree is removed, the damage will worsen. The engineers also agreed that some additional movement of structures near gates was possible and that the loading on the wall created by the sandstone tiles could have an effect; in Mr Katauskas' view the effect would be negligible, Mr MacLeod considered the effect would be minor.
31Ms Hobley indicated a woody root at the base of the retaining wall, and based on photographs she had seen of the exposed roots when the old wall was removed, opined that this root was a likely cause of the damage given its direction of growth. Mr Home stated that the root had been dead for some time. This was confirmed on site.
32On the basis of Mr Katauskas' and Ms Hobley's assumptions that roots were the cause of the damage to the wall and stairs, the experts were asked to consider what, if any, alternatives to tree removal there might be.
33Mr MacLeod suggested that if roots were confirmed, a root barrier could be installed close to the applicant's wall in order to prevent future damage. The wall could then be repaired by retrofitting ties between the pillar/pier and the brick panel.
34The arborists agreed that a root barrier would be feasible but varied slightly in their opinion as to where it should be located. It was also agreed that any proposed root barrier would necessitate an exploratory trench to identify the size and location of any roots that may be present and then determine whether cutting the roots would have any unreasonable impact on tree health or stability.