Geotechnical advice ought to be obtained whenever there are proposals to construct substantial structures and / or undertake earthworks. Further, whenever building works are planned in areas identified as having some ‘geotechnical hazard’ [e.g. landslip, rockfall, shrink/swell soils, etc.], it is essential to obtain appropriate geotechnical advice before the detailed planning stage, and preferably at the ‘feasibility’ stage.
Local Councils also often request geotechnical reports to accompany Development Applications [sometimes called a ‘DA’] for new construction or major renovations.
Commonly, the types of development that require geotechnical advice include:
The scope and extent of geotechnical advice & reports also varies considerably, with the typical geotechnical study ranging from an initial inspection and on-site advice, to an extended investigation over many weeks and a voluminous report.
It is also important to recognise that the geotechnical report for a Local Council is a very specific thing and has to cover a number of ‘site specific’ and ‘development consent’ issues for a Council. Some Councils [e.g. Pittwater north of Sydney] also require very onerous statements [and associated implied legal responsibilities] on the author of a report submitted to the Council.
NO
As with any profession, there a number of areas of ‘specialisation’ within the geotechnical engineering field and some persons [e.g. engineering geologists] who sometimes call themselves ‘geotechnical engineers’, are in fact not engineers at all.
Broadly, geotechnical engineers fall into two categories:
Typically, normal geotechnical engineers undertake site drilling, testing and ‘site investigation’ reporting; these geotechnical engineers also commonly own their own drilling equipment and have a laboratory for undertaking soil tests. In many respects, this group of geotechnical engineers provide standard advice to their clients in relation to ground conditions.
Typically, specialist geotechnical engineers focus on the ‘engineering’ aspects of geotechnical & ground engineering and specialise in the planning, assessment and analysis of a site’s problems. This group of engineers usually have in-house design staff, prepare plans and specifications for ground engineering works and employ drillers / testing laboratories on a sub-contract basis.
In both of the categories described above, there are geotechnical engineers who have a particular knowledge of certain areas of ground engineering such as shrink / swell [or reactive] soils, land slope stability, reinforced soil structures, anchors & rock bolts, piling, etc.
‘Normal’ geotechnical engineers, are usually those with limited specialist training & experience, and undertake work in accordance with ‘standard’ procedures established over many years. Engineers of this type usually have:
The services a ‘Normal’ geotechnical engineer are also usually limited to:
‘Specialist’ geotechnical engineers are those geotechnical engineers who have specialist training & have extensive experience in their particular field.
Specialist geotechnical engineers can carry out all of the ‘normal’ geotechnical engineering tasks, but also have:
Some specialist geotechnical engineers also work in the field of forensic engineering, and are often called on to serve on professional review bodies, standards committees, etc.
The answer to this question relates to the geotechnical engineering services / tasks that are required for a particular project.
Whilst in general terms it can be said that if the matter is ‘routine’, then an normal geotechnical engineer will suffice; however, should the matter require investigation of the ‘cause’ of damage, design issues, the planning of remedial works, slope stability, etc., then it would normally be prudent to seek out the more specialist engineer.
Also, where litigation is contemplated [viz: a forensic engineer is needed] it is usually essential to engage a specialist engineer who has the additional understanding and knowledge of:
The problems that can arise on a site as a result of geotechnical issues largely depends on the topography and underlying geology of the area. As a general rule, there are more extensive geotechnical stability issues on sloping sites than on ‘flat’ sites.
On sloping sites, important geotechnical matters relate to issues such as:
On ‘flat’ sites, the problems that relate to geotechnical issues are more commonly:
Yes
Geotechnical failures are in fact a very common type of failure, with major risks [to both property and life] arising from the inadequate management of the geotechnical issues on a site.
On this website, you can access the details & photographs of some of the failures in which the firm has been involved. [link]
The firm is has also provided advice on a number of major geotechnical failures in the last 2 to 3 years, as well as being aware of a number of failure / problems on which the firm has not advised. Some of these are as follows:
It is also noted that the firm is aware of many other ‘much less major’ geotechnical failures in the last 5 years that have caused extensive structure damage; the majority of these failures could have been avoided if proper planning & advice was obtained from the start of a project.
Usually yes, and particularly when the project designers / builder / client are willing to listen to, and faithfully implement appropriate geotechnical advice during the planning & construction stages of the work.
Conversely, when the relevant geotechnical engineering issues are not well understood by the design & construction team, failures often occur.
It is also essential during the construction phase of a project that persons experienced in geotechnical matters review the construction. It is also the firm’s experience that if the construction work is not regularly inspected, then the likelihood of failure is greatly increased.
The scope and extent of all advice, including geotechnical advice, depends on what your needs are, and the nature of the problem you are seeking to resolve. In the geotechnical field, this usually means how ‘geotechnically complex’ is the site.
As such, the content of a geotechnical report will generally only be as much as is necessary to satisfy a client’s instructions / request.
In addition, as different engineers will often perceive things differently, the extent / detail of advice provided on the requested issues may be very different, and largely depend on the level of experience of the individual / company preparing the report.
For example, a report requested to only address site stability issues may offer little, or no guidance on the essential design parameters for building works on the site.
In general terms there are three broad groups of geotechnical investigations & reports:
A geotechnical site inspections is usually a detailed ‘walk-over’ type of site inspection by an experienced geotechnical engineer. The inspection is typically limited to about 1 or 2 hours site time, and is commonly required for specific reasons such as meetings / client consultations, checking of construction items, etc.
When a site meeting does not take place and the inspection lasts for more than about 2 hours, geotechnical mapping [usually to scale] and some limited subsurface exploration [by hand tools] is commonly carried out.
Note: Some consulting firms collect extensive documentation during a site inspection, whereas other firms may not.
The documentation of this type of inspection would normally be limited to site notes and photographs and a short report largely determined on the basis of the engineer’s experience and initial opinions.
Site Inspections can also include, if more site time is spent:
A site investigation is usually a much more extended investigation of a site conditions and usually intended to obtain a significant amount of information and determine the relevant geotechnical matters.
Typically a site investigation follows a Site Inspection; it is also usually unwise to undertake a site investigation without a preceding site inspection.
The timeframe for site investigations may be a full day, or even multiple days, during which extended investigations, measurements, testing or drilling of the site sub-strata is required.
A site investigation also usually requires sub-contractors such as drillers, surveyors, laboratory personnel, labourers, etc., with the engineer’s duties being supervising site staff and recording the various field test results.
In short, a comprehensive investigation is a more extended version of a site investigation with the following work / investigations being added to the typical site investigation list:
Normally, a comprehensive investigation report is required in a forensic study.
SCE suggest that a client should provide the engineer with as much information as possible at the enquiry stage. For new building developments, the information that will assist SCE in preparing a fee proposal might include:
An enquirer who has carefully researched the site information and understands the scope of the report they require, will also be in a better position to make a meaningful assessment of the quotes from different consultants.
On the basis of the firm’s experience, the most effective ‘least cost’ way of proceeding with a development is to:
The firm also considers that whilst the above method will probably result in larger ‘geotechnical costs’, the resultant design and construction will most probably be more economic and relevant to the site conditions, with the later construction issues / cost over-runs being less.
Yes
This is because the firm’s experience is that:
Yes
In most cases, there will be a need for ongoing geotechnical advice throughout the course of a project. Further, the requirements of most Councils / Private Certifiers are such that a geotechnical consultant usually needs to verify and ‘sign off’ the geotechnical aspects of the construction.
Where the certification mentioned above is required, the geotechnical engineer must be involved during the construction stage to verify and advise on the construction.
Note: Whilst SCE has a policy of not relying on the observations of others before assembling / issuing a certificate, some consultants are prepared to ‘certify’ construction on the basis of documents supplied by others.