Engineering geological map and site investigation

Topographic map

A topographic map shows the shape and relief of the ground surface using contour lines, and also natural and man-made features such as rivers, roads, settlements and vegetation, drawn to scale. It shows the surface only, not the rocks beneath.

Aerial photograph

An aerial photograph is a photograph of the ground taken from an aircraft (or drone) with the camera pointing vertically or obliquely downward. Overlapping pairs viewed under a stereoscope give a 3-D view. They are used to identify rock units, lineaments, faults, landslides, drainage patterns and land use, and to prepare base maps.

Engineering geological map

An engineering geological map is a map, made on a topographic base, that shows rock and soil types, their engineering properties, geological structures (dip, strike, folds, faults, joints), weathering, groundwater, slope stability, hazards and construction material sources, for use in civil engineering projects.

Importance for site investigation

1. Shows the distribution and nature of foundation rocks and soils at one glance.
2. Helps to compare alternative sites or alignments quickly and cheaply.
3. Identifies hazards such as landslides, active faults, unstable slopes, swelling soil and flood zones.
4. Guides the planning of boreholes, trenches and geophysical lines, so that investigation is placed where it is needed.
5. Shows groundwater conditions, springs and seepage areas.
6. Locates sources of construction material.
7. Helps design slope cuts, foundations, tunnel support and drainage.
8. Serves as a permanent record for later stages and maintenance.