CIVIL ENGINEERING
Civil engineering projects involve
 Construction
 Excavation
 Remedial work
All these involve interaction with the natural environment.
Civil engineering should avoid problems of
 Instability
 Interference with the hydrological regime (groundwater)
Before major engineering works can be carried out, the site has to be investigated.
What types of site investigation can be carried out?
1
Type of investigation/how carried out
Use OS maps
2
Use geological maps
3
Use geophysical surveys
4
Drilling
5
Trial excavations
6
Modelling
7
Use a geologist
Use & value of investigation
STAGES IN SITE INVESTIGATION
(See ‘Foundations of Engineering Geology pp. 38 – 43)
SEQUENCE OF STAGES
Initial Stage
 Desk study of available data
 Site visit and visual assessment
 Preliminary report and fieldwork plan
Main Stage
 Fieldwork
Geological mapping if necessary
Geophysical survey if appropriate
Trial pits, trenches and boreholes
 Laboratory testing, mainly of soils
 Final report
Review Stage
 Monitoring during excavation and construction
DESK STUDY
a) Geological maps and records
 BGS maps and reports
 Borehole logs
 Mining records
b) Topographical maps – comparing older ones with more recent ones shows mines and
quarries, past land use, changes in coastline etc
c) Photogeology – aerial photos may show rock types and natural and man-made
features. Heat sensitive satellite imagery is important in locating natural resources.
FIELDWORK
GEOPHYSICAL SURVEYS
 Seismic surveys – shock waves produced by explosions, hammer blows etc are
refracted or reflected on geological boundaries. Small geophones record wave arrivals
 Magnetic surveys – record changes and distortions in the earth’s magnetic field. Used
to detect old mineshafts.
 Gravity surveys – record variations in the earth’s gravity – used to detect negative
anomalies, which may indicate a mine or cave, or low density rock.
 Electromagnetic surveys – measures conductivity in rocks – useful for finding water
(high conductivity). Also helps to decide nature of rock – clay and basalt have much
higher conductivity than sandstone or limestone.
BOREHOLE SURVEYS
 percussion drilling
 rotary drilling
 rock probing
A log is kept of the samples, to record
 type
 thickness
 depth
 permeability
 strength
 quality