Why geotechnical investigations use boreholes
Investigation boreholes provide a practical way to observe subsurface materials at selected locations and depths. Depending on the project scope, recovered soil or rock samples and field observations can help interpret fill, natural soils, weathered material and possible founding conditions.
Boreholes are one potential component of a geotechnical investigation; the appropriate methodology, number of locations and depth depend on the proposed development and the engineering questions being assessed.
How borehole locations and depths are selected
A residential dwelling, retaining structure, basement and commercial development may require different investigation layouts. Existing buildings, proposed structural footprints, changes in ground level and the likely depth of relevant ground conditions influence scope.
Ground variability means results from one investigation location cannot automatically be assumed to represent an entire site. Underground service clearance, equipment access and safe working conditions must be considered before fieldwork.
Sampling, reporting and practical limitations
Selected soil samples can help describe subsurface conditions and, where included in the agreed scope, support relevant laboratory testing. Field logs and engineering interpretation should identify the observations relevant to the proposed development.
Drilling refusal, variable rock, groundwater, access limitations and local subsurface changes may affect what can be observed. The completed assessment should explain the practical limitations of the investigation rather than treating isolated boreholes as a guarantee of uniform conditions.
Common questions
Borehole drilling and soil sampling: common questions
How many geotechnical boreholes does a Sydney project need?+
There is no universal number. Borehole locations and depths depend on the proposed development, site variability, engineering risks and agreed investigation scope.
Do all geotechnical investigations include laboratory testing?+
No. Laboratory testing is included when the project requirements and ground conditions justify it within the agreed scope.
Can a neighbouring borehole replace an assessment of my site?+
Neighbouring information may provide useful background but does not automatically represent the conditions or development requirements of your individual site.
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Send the site address, proposed works, current plans and any request from your builder, engineer, council or certifier. Sydney Geotechnical will review the information and confirm an appropriate scope and fee.
This guide provides general information only and is not a substitute for investigation, engineering advice, footing design or approval advice for a particular property. Project requirements and ground conditions must be assessed site by site.
