1.2 Preliminary site exploration
1.2.1 Desk study
Any subsurface investigation program should primarily account for the type, size and importance of the structure, the existence of any other structures that could affect or be affected by construction works, and the location of underground utilities that may interact with the project or the investigation works e.g., gas pipelines.
Before moving the testing equipment on site, or deciding on the number and depth of boreholes (or in situ tests) to be performed, a desk study is necessary for collecting and analysing all existing relevant data (Table 1.1). A review of available information prior planning a new investigation program will help establishing what to look for in the site.
or, as Glossop (1968) stated in his Rankine Lecture (FHWA, 2006):
“If you don’t know what you should be looking for in a site investigation, you are not likely to find much of value”
| Utility maps |
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|---|---|
| Aerial photographs |
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| Topographic maps |
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| Geological maps and reports |
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| Seismic hazard maps |
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| Water well logs |
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| Flood maps |
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| Geotechnical investigation reports from existing, nearby structures | … always a good point to start! |
1.2.2 Field reconnaissance visit
After the desk study, a site inspection visit will always provide valuable information regarding access of drilling and in situ testing equipment, topography, areas of active or historical landslides, nearby structures etc. A field reconnaissance visit should include, according to FHWA (2006):
- Inspection of nearby structures to determine their performance with the particular foundation type utilised. If settlement is suspected, the original structural plans should be reviewed, and the structure should be surveyed by using the original benchmark.
- For water crossings, inspection of existing foundations and of the stream banks for evidence of scour.
- Identification of the location, type and depth of any existing structures which may obstruct construction works.
- Relating site conditions with the proposed boring operations and record potential problems with utilities, site access, private property or obstructions.
A thorough site inspection is a must for planning a successful geotechnical investigation program, in order to avoid unnecessary delays and extra costs at later stages.
