Soil Types in Stonnington
District Overview
The southern boundary of the municipal district of Stonnington is located 1.5 kilometres (at the west) and 9 kilometres (at the east) from Port Phillip Bay. The northern municipal boundary is the middle of the Yarra River at the east and its tributory, Gardiners Creek at the West.
For a link to geographical maps showing the land in and around Stonnington go to the following Department of Primary Industries webpage or the Geoscience Australia website. The 145o longitudinal meridian passes through the suburb of Prahran at the western end of Stonnington.
Soil Types in Detail
Most of Stonnington has a sandy topsoil (Tertiary 'Brighton Group' sediments) underneath which, at depths usually ranging from 600mm to 1.2m, are seams of firm clay having a mottled red and grey colour. This material is not highly reactive. Sometimes clay and sand are intermixed to considerable depths.
Land around the Yarra River and Gardiners Creek contains deep seams of pale grey/ochre Silurian mudstone (the 'Melbourne Formation'), visible in the gorge around the north of South Yarra and Toorak or buried just below the ground surface where the hills extend down to Toorak Road. This material often requires machinery to be excavated but forms a very good foundation.
In pockets of Windsor and Armadale, especially near Dandenong Road, there are areas of sub-surface water evident when the soil is dug to about 300mm below the ground surface. Buildings founded in this soil appear generally unaffected by ground moisture or reactivity. Foundation excavations, however, should make allowance for difficulties in forming neat trenches and holes due to the sand collapsing in on itself, especially during rainy weather.
In parts of Windsor and Prahran building excavations have revealed clean, dry, white sand, probably being the remains of ancient beaches and dunes. At the western end of Prahran and South Yarra excavations have struck ancient creek beds with worn river stones.
The highly reactive (swelling with moisture) basaltic clays and stone 'floaters' of extrusive volcanic origin found in the northern suburbs of Melbourne are not found in Stonnington.
Throughout the district the typical soil classification under Australian Standard 2870.1 (Residential slabs and footings - Construction) is usually Class M (moderately reactive) due to the clay seams usually found by soil tests. Please note, however, that this comment must not be taken as reliable data for the purposes of building work at a specific site. We recommend that reports or other data be obtained.
Human disturbance
Excavations, particularly in areas developed in the 19th century, are likely to encounter disturbed soil with fill and discarded material (eg bones, bricks, coal, metal remnants etc). Occasionally footings of old building structures, not removed in the course of earlier demolition, may be uncovered.
Areas adjoining railway lines may be significantly filled with spoil from the railway cuttings which was sometimes mounded to form embankments, subsequently built over.
There are large underground drains following old watercourses in the low-lying areas to the north of the district. Most run under roads but, in a some areas, they run under private land. Proper building preparation such as investigation of the land title and, where applicable, a soil report should identify if these will be an issue.
The main drains are:
- the Chadstone and Murrumbeena main drains draining to Gardiners Creek bordering the Malvern East golf course
- the Prahran main drain leading to outfalls into the Yarra River near the Chapel Street bridge and
- its diversionary outfall line under Como Park, South Yarra.
We recommend all excavations for the footings of buildings should reach undisturbed soil unless there is an engineer designed alternative to suit the circumstances.