There exist within the boundaries of the Shire of Northam areas of cohesive (clay) and other suspect soils, which require specific and specialised design of proposed buildings by a qualified structural engineer.
The applicant should when submitting plans satisfy the Council’s requirements in regards to the structural integrity and design of the buildings. This can be achieved by a site visit by an engineer to test the site for the particular characteristic of the soil.
To assist in helping applicants understand potential problem areas, the following list of ground surface indicators in this pamphlet have been formulated to allow an understanding of why a qualified engineer is required as a part of your plan submission to the Council.
INDICATORS
1. Where the site is subject to any easement and there has been or will be an excavation for the provision or services or utilities, (e.g. sewer, pipelines, gas mains) marker posts or an inspection cover is present at or adjacent to the site.
2. The presence of fill of unknown quality or suspect construction at the proposed building site.
3. Evidence of soft compressible material such as peat, diatomaceous earth or organic soil occurring on the site.
4. Signs of distress or cracking in any structures at the site or adjacent sites.
5. A site to be permanently damp or that has visible springs with the water having a strong yellow brown to red brown colour or is muddy.
6. Tall or large trees, or grass bush, in a regular or linear pattern. Lush vegetation existing next to stunted growth. The presence of reeds or rushes.
7. An average slope of ground steeper than 1 (vertical) to 2.5 (horizontal).
8. A building plan that shows that the site topography will need to be modified in order to accommodate the building such that
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(i) Fill is to be placed to a maximum depth greater than 1.5m.
(ii) The site will be cut to a depth exceeding 1.5m at the deepest portion.
9. Erosion of gullies or field tunnels on the site. The presence of land slide scars or other signs of recent movement. A site that has signs of clay mixed with rock.

10. A building location over or adjacent to a non-cohesive granular soil (clean sand) that records a blow count less than four per 300mm using a Standard Perth
Penetrometer.
11. A building location over or adjacent to a cohesive soil (clay) which may be moulded by strong finger pressure, or less.
Note: Most cohesive soils when dry (i.e. exposed to the atmosphere during dry or hot weather) will pass this test. Accordingly, this test may be valid only to the soil immediately after excavation from a depth greater than one metre. If there is any doubt experienced professional advice should be obtained.
12. A top soil dark red in colour or black top soil over red sub soil.
13. Clay from the site that has a smooth greasy feel when wetted and cracks on drying. A pattern of cracking in the ground. A poorly drained surface.
14. If in any pits or cuttings, clays are visible when there is present-
(i) a yellow orange and grey mottle
(ii) a medium to dark grey and black clay
(iii) a grey green clay under red soil
(iv) brown and red brown clays
15. The presence of dark or coloured rock
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(i) scattered on the grounds surface
(ii) present at the base of large trees
16. The presence of outcrops of dark coloured rock.
The above list is not conclusive and whilst indicative of problem ground conditions, the applicant should take note of any other evidence which may suggest the need for further site investigation. For all new dwellings and large concrete pad construction an engineer stamp and signature must be on all plans and specifications.