Part 2 – Earthworks and Land Stability
2.5 Technical Responsibilities
Where any urban land subdivision or development involves carrying out bulk earthworks, or the assessment of slope stability, or the detailed evaluation of the suitability of natural ground for the foundations of buildings, streets, services or other works, then a geotechnical engineer shall be appointed by the developer to carry out the following functions:
- Prior to detailed planning of any development, to undertake a site inspection and such investigations of subsurface conditions as may be required.
- To review the drawings and specifications defining the earthworks proposed, and submit a written report to the Council on foundation and stability aspects and any proposed departures from this Manual and associated standards.
2.5.1 Preliminary Site Evaluation
Prior to any detailed planning or design, the Developer or geotechnical engineer, as applicable, shall undertake a preliminary evaluation of the general nature and character of the site in sufficient detail to determine the likely requirements for earthworks or the need for further investigations into the suitability of foundation conditions, or both, and the stability of the natural ground. The preliminary evaluations should be carried out in the context of the total surroundings of the site. In simple cases a visual appraisal may be sufficient. In other cases, depending on the nature of the project, its locality, the scale of development proposed and individual site characteristics, particular attention may need to be given to the following matters, which should normally be considered prior to preparing a scheme of subdivision or development.
It is important to identify the existing natural drainage pattern of any area and to locate natural springs or seepage.
Where any natural drainage paths are to be interfered with or altered by earthworks, appropriate measures should be taken to ensure that sufficient adequate alternative drainage facilities are provided.
b) Slope Stability
Some natural slopes exist in a state of marginal stability and relatively minor works such as trenching, excavation for streets or building platforms, removal of scrub and vegetation, or the erection of buildings, can lead to failure. Signs of instability include cracked or hummocky surfaces, crescent shaped depressions, crooked fences, trees or power poles leaning uphill or downhill, uneven surfaces, swamps or wet ground in elevated positions, plants such as rushes growing on a slope or water seeping from the ground.
c) Foundation Stability
A study of the general topography of the site and its surroundings may indicate areas which have previously been built up as a result of natural ground movement or by the deliberate placing of fill material. Unless such fill has been placed and compacted under proper control, long-term differential settlement could occur causing damage to superimposed structures, roads, services or other subdivision works.
2.5.2 Specialists Services
Where a soils report is required, then prior to or at the time of applying for a subdivision or development consent, the developer shall submit to Council a written report from a geotechnical engineer setting out the particulars of any investigations carried out. The report should include details of contours, natural features and modifications proposed thereto, and include a statement from the geotechnical engineer as to the suitability of the land for subdivision or development, with details of any special conditions that should be imposed.
Note: A suitable format for this statement of opinion is included within the MPDC Infrastructure Code of Practice.