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<\/a>Cavendish Street, Enmore NSW, June 2014<\/p><\/div>\n
It all started more than three years ago, when Marrickville Council began removing very large fig trees from the footpaths on the\u00c2\u00a0street. Although enjoyed by birds and bats, these trees broke up the paving and invaded underground pipes. I wrote a blog post <\/a>about\u00c2\u00a0local\u00c2\u00a0mourning\u00c2\u00a0when the first tree was removed.<\/p>\n ‘Tree replaced by cement!’, Cavendish Street, Enmore NSW, October 2010<\/p><\/div>\n The story resumes in April this year, and here’s how it goes. The Council excavates three huge rectangular pits in the street, digging deep down into the clay beneath the surface of the road.<\/p>\n Cavendish Street, May 2014<\/p><\/div>\n Underground infrastructure, including gas pipes, is adjusted and gravel is spread in the bottom of each hole.<\/p>\n Cavendish Street, May 2014<\/p><\/div>\n Next, a layer of large plastic cells is positioned in the pit and ‘structural soil’ is tipped in between them. Another layer of cells and soil is added, this time with a rectangular hole in the centre fenced off with plywood formwork. As I understand it, the plastic cells act as support for the roadway above; the structural soil <\/a>is a mix of gravel and loam that resists being compacted and allows tree roots to spread and grow.<\/p>\n Cavendish Street, May 2014<\/p><\/div>\n Over the soil comes a layer of geotextile then another layer of gravel.<\/p>\n Cavendish Street, May 2014<\/p><\/div>\n Concreters build retaining edges around the central tree hole to form a ‘blister’. This will prevent cars bumping into the tree trunk.<\/p>\n Cavendish Street, June 2014<\/p><\/div>\n Permeable pavers are laid. Rain falling on the road will flow towards this area of porous paving. This means that street run-off will infiltrate the tree pits instead of gushing down the gutters and into stormwater drains.<\/p>\n Within a day or so, on a nice rainy morning, advanced trees are lifted into the central hole, the formwork is removed and more soil is tipped around the large root ball. The three trees are Waterhousia floribunda<\/em> ‘Green Avenue’, a cultivar of the rainforest Weeping Lilli Pilli that is expected to grow to 16 metres.<\/p>\n<\/a><\/a><\/a><\/a><\/a><\/a>