Preparation and components of EG map

An engineering geological map is a special-purpose map that shows the geology of an area (rock and soil types, structures, groundwater, geomorphology and hazards) in terms of its behaviour and suitability for civil engineering works such as dams, tunnels, roads and bridges.

Preparation

1. Desk study: collect topographic sheets, geological maps, aerial photos/satellite images and old reports; decide scale (1:50,000 for regional, 1:5,000 to 1:1,000 for a site).
2. Base map: enlarge or prepare a topographic base map with contours and coordinates.
3. Field mapping: traverse the area, record lithology, contacts, strike and dip, joints, faults, folds, weathering grade, springs, slope condition, landslides and erosion.
4. Sub-surface data: add data from test pits, trenches, drill holes, geophysical surveys and tunnel/adit logs.
5. Laboratory/field tests: rock and soil strength, permeability, rock mass classification (RMR, Q).
6. Compilation: transfer all data to the base map, draw boundaries, then add cross-sections and engineering zoning.
7. Interpretation and report: classify the ground into engineering units and give recommendations.

Components

• Topographic base (contours, rivers, roads, settlements, north arrow)
• Lithological units with age, grain size, hardness and weathering
• Structural data: strike/dip symbols, joints, faults, folds, shear zones
• Soil/overburden type and thickness
• Hydrogeology: springs, water table, seepage zones
• Geomorphology and hazards: landslides, rock falls, flood limits, active faults
• Engineering classification/zoning of rock mass and sites (good, fair, poor)
• Legend, scale, title, cross-sections and explanatory notes