Around eight years ago a developer excavated to a depth of 2-3m along this property's border and built a dry stone wall with boulders. The excavation was close to, but not on the shared boundary. This was to provide a flat area for the house he was renovating. Since then, the house has changed owners a few times, the last is recent. In one place, the cut was within 2.5m of a sizeable gum, which now seems to have developed a slight lean away from the cut. It is a long boundary of around twenty fence panels. My property, timber on brick piers plus some on slab, is on the high side of the cut with the nearest to the boundary being about 2.5m. The problem to address is that the soil is eroding from immediately under the fence and the adjoining soil level in my yard appears to have dropped by 300mm or more, tapering off to around 2m from the fence line. The soil is a mix of loam and clay shale under (my uneducated assessment). There is a 'spongey' feel near to the fence in some places. Ordinarily, if the problem was lesser I might just mount a line of 200mm high H4 sleepers along the fence and fill on my side. However, I do not want to be inheriting an expensive 'shared' retaining wall problem in the future. How to resolve?
Trees may be assigned Tree protection zones (TPZ) and Structural root zones. The TPZ is determined by multiplying the trunk diameter of the tree at breast height, 1.4 metres from ground level, by 12. A 10% encroachment on one side of this zone is acceptable without investigation into root distribution or offset of the lost area. Section 3.2 of the Australian Standard AS4970 – 2009 Protection of Trees on Development Sites states that the TPZ of Palms, other monocots, cycads and tree ferns should not be less than 1 m outside the crown projection. It may be that the wall was too close to the tree, breaching AS4970. It may have been badly engineered or backfill was not compacted enough. If a causal relationship can be established between the erosion, spongy soil and the retaining wall, then the current owner appears to have inherited a problem. An engineering or other specialist report may be advised. If the ground is subsiding then this is a serious matter that needs to be resolved. Keep the neighbour informed about matters. If nothing else it will condition the neighbour to potential actions and costs.
Many thanks for your reply. I suspect that the dry boulder wall was a run of boulders too low (ran out of rocks?) and /or that retaining wall fabric was installed sloppily or is absent. How to find a suitable engineer? Would any civil engineer do? Surveyor as well? Then convey the gist of the report/s to the (absentee*) neighbour? I would prefer to avoid legal conflict if possible, although I must protect my rights.
I have no idea if an engineer is needed, or what sort. Some sort of expert is needed. You could start by asking structural engineers and soil testers if this lies within their expertise. When doing this sort of exercise I write down what I want done and sending possible contractors the same information. At this stage I suggest giving the suburb but not the address. The less people that know the address the better. The suburb is needed as the contractor may be in Brisbane and you are in Cairns. I've seen this! I may look for tiler Hawthorn (a Melbourne suburb) and get a list including tilers from 200 kilometres away. The tiler websites give no clue about where they are based. Not good. Avoiding legal conflict is good. Keeping the neighbours informed and slowly moving towards a new wall or whatever is far better than sending them advice that the wall is kaput and needs to replaced ASAP, cost around $8000. If they can be gently led to understand that the wretched problem is not of their making and that it has to be fixed or your house will fall down is easier. They will also understand that it is their problem too. As soon as you know what sort of expert to engage and have a short list, go to the neighbour and ask them if the one you like is okay. This makes them part of the decision, and it will later be hard for them to be critical of the report. This aspect cannot be stressed too much. Quite often people are more annoyed about not being consulted than the result, and they take that annoyance out by criticising the result. Say that you will be paying for the engineer or expert. It is arguable that as the problem is caused by the wall the neighbour should pay. But what if the neighbour delays and your house falls over? Also, by paying for the report you can later say that the cost has been shared somewhat. Due to the potential very costly harm I'm inclined to move quickly on this.
Burramys Thank you. Most appreciated. Hoping to be back to you in due course to report some progress on this.
