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Geology for dam and bridge sites

Short answer

For dams: strong, massive rock, narrow valley, watertight, upstream dipping beds, stable abutments, no active faults, nearby materials. For bridges: sound rock or dense gravel at shallow depth; straight, narrow, stable channel reach; stable banks; no faults; consider scour depth and liquefaction.

Write the geological considerations that should be taken in selection of dam site and bridge site.

Dam site

  1. Foundation rock: strong, sound, massive, little weathered (granite, gneiss, quartzite); avoid weak shale, phyllite and soft soil.
  2. Structure: avoid faults, shear zones, closely jointed rock and unfavourable bedding dip; upstream dip is preferable.
  3. Watertightness: no cavernous limestone, open joints or permeable gravel; plan for grouting.
  4. Abutments: stable and free from landslides; adequate rock cover.
  5. Valley shape: narrow with sound rock at shallow depth.
  6. Seismicity: no active faults near the site.
  7. Reservoir: watertight, stable rim, low sedimentation.
  8. Materials: aggregates, clay and sand nearby.

Bridge site

  1. Foundation: sound rock or dense gravel at shallow depth for piers and abutments; avoid thick soft clay and loose sand.
  2. River channel: straight, narrow, stable reach; avoid bends, braided reaches, confluences and fast-shifting channels; estimate scour depth and maximum flood level.
  3. Structure: avoid faults and weak shear zones; stable bedding.
  4. Banks and abutment slopes: no landslides, rock fall or active erosion.
  5. Groundwater: affects excavation of foundations.
  6. Seismic hazard, liquefaction of sandy soil.
  7. Approach roads on stable ground; construction materials and access.

Investigation by mapping, core drilling at piers and abutments, geophysics and in-situ tests supports both selections.

✓ Answer checked by Claude Opus 5.5 (high effort)

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