Road, dam and foundation site geology

Geological considerations for road site

• Stable slopes with strong rock; avoid landslides, steep weak slopes, and old debris.
• Favourable structure: beds dipping into the hill; avoid faults, shears and daylighting joints.
• Avoid wet, swampy ground and springs; limit stream crossings; stay above flood level.
• Materials (aggregate, borrow) along route.

Geological considerations for dam site

• Sound, strong, massive foundation rock with low weathering; narrow valley.
• No active faults, shear zones or highly jointed zones.
• Watertight foundation and rim; no solution cavities.
• Stable abutments and favourable dip (upstream); materials nearby.

Investigation of foundation site for a building

• Desk study and surface mapping of the site.
• Test pits and boreholes (to a depth of at least 1.5-2 times the footing width B below foundation level) to find soil/rock type, thickness, water table.
• SPT, plate load test, soil samples for laboratory tests (bearing capacity, settlement).
• Look for fill, soft clay, expansive soil, liquefiable sand, slope stability.

Investigation of foundation site for a bridge

• Mapping of both banks and the river; scour and flood study.
• Boreholes at each pier and abutment, with core drilling 3 m into sound rock; SPT in soil.
• Geophysics (seismic refraction/resistivity) across the river.
• Lab tests for bearing capacity and foundation depth below scour level.