Site investigation - Geotechnical Investigation and Design Tables - page 2

1.2 Geotechnical requirements for the different
project phases

•

The geotechnical study involves phasing of the study to get the maximum
benefit. The benefits ( 20% per phase) are approximately evenly distributed

throughout the lifecycle of the project.

∼

•

Traditionally (currently in most projects), most of the geotechnical effort ( > 90%)

and costs are in the investigation and construction phases.

•

The detailed investigation may make some of the preliminary investigation data
redundant. Iteration is also part of optimisation of geotechnical investigations.

•

The geotechnical input at any stage has a different type of benefit. The Quality
Assurance (QA) benefit during construction, is as important as optimising the
location of the development correctly in the desktop study. The volume of testing
as part of QA, may be significant and has not been included in the Table. The
Table considers the Monitoring/Instrumentation as the engineering input and not
the testing (QA) input.

•

The observational approach during construction may allow reduced factors of
safety to be applied and so reduce the overall project costs. That approach may
also be required near critical areas without any reduction in factors of safety.

Table 1.2 Geotechnical requirements.

Geotechnical Key Model Relative (100% total) Key data Comments

Study

Effort Benefit

Desktop Geological

<

5%

∼

20% Geological setting, Minor SI costs

study model existing data, (site reconnaissance)

site history, with significant

aerial photographs planning benefits.

and terrain
assessment.

Definition 5% 20% Justify investigation Safety plans and

< ∼

of needs requirements and services checks.

anticipated costs. Physical, environmental

and allowable
site access.

Preliminary Geological and 15% 20% Depth, thickness Planning/Preliminary ∼

investigation geotechnical and composition Investigation of

model of soils and 20% of planned ∼

strata. detailed site

investigation.

Detailed site Geotechnical 75% 20% Quantitative, and Laboratory analysis of

∼

investigation model characterisation of 20% of detailed

critical or founding soil profile.

strata.

Monitoring/ 10% 20% Instrumentation Confirms models < ∼

Inspection as required. adopted or

QA testing. requirements to adjust

assumptions. Increased
effort for observational
design approach.