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Geology A2 - Engineering Geology 1 (Landslip and slumping hazards and road…

- - - - Natural aggregate:
        
        Sand and gravel mainly extracted from recent Quaternary river, glacio-fluvial and shallow marine deposits.
        
        Beds should be thick (no lateral/vertical variation) to give a consistent product.
        
        Sand and gravel must be clean with no impurities.
      - Crushed rock aggregate:
        
        Mainly used for roadstone.
        
        Hard rocks crushed for aggregate include many igneous rocks, gneiss, limestone and greywacke, along with industrial waste such as furnace slag.
    - - Crushed aggregate mixed with bitumen used to surface roads.
        Roads are constructed in layers with a base-course overlain by a top wearing-course.
        Aggregate must be:
        
        Strong with high impact and crushing strength.
        
        Resistant to abrasion and mechanical weathering.
        
        Impermeable and resistant to chemical corrosion.
        
        Skid resistant.
        
        Bonds to bitumen well.
    - - Bricks:
        
        Made from clay, mudstone and shale.
        
        Different compositions produce different coloured and types of bricks.
        
        Clay moulded into required shape then fired at high temps in a kiln.
        
        Thick beds with constant compositions are required.
    - - Cement made from a mixture of crushed limestone and chalk, mixed with some clay or shale.
        Limestone provides calcium carbonate and clay provides silica and alumina.
        Mixture roasted in rotary kiln at about 1500°C and 5% gypsum is added to prevent cement setting too quickly.
        Concrete made by mixing cement with sand and gravel or crushed rock.
    - - Common building stones include limestone, sandstone, granite and marble.
        Building stone must be:
        
        Competent with high load-bearing strength.
        
        Well jointed.
        
        Attractive in appearance.
        
        Occur in thick, uniform units with few structures or weakness*.
        
        Impermeable and resistant to mechanical and chemical weathering.
  - - - Development of coastal 'super-quarries:
        
        Rock easily transported by ship.
        
        Often situated in Areas of Outstanding Natural Beauty.
      - Offshore dredging for marine aggregates:
        
        Disrupts marine ecosystems.
        
        Alters the sea floor shape.
        
        Changes current patterns increasing coastal erosion in certain places.
- - - - Flooding of land for reservoir
        
        Loss of agricultural land or villages.
        
        Relocation.
        
        Loss of archaeological sites.
        
        Decaying vegetation in flooded forests release carbon dioxide and methane.
        
        Damage to aquatic ecosystems
        
        Due to changes in water depth, temperature and dissolve oxygen content downstream.
        
        Prevent migration routes.
        
        Silting of the reservoir
        
        Starves downstream of sediment.
        
        Released water contains little sediment as its trapped.
        
        Risk of downstream flooding
        
        Water amount needed to be released calculated to avoid overflow.
        
        Unexpected weather events risks overflow.
    - - Poor choice of site
        poor design, construction or maintenance
        Extreme weather conditions
    - - Weight of dam and reservoir water may lead to earthquakes as crust adjusts to additional load.
        Infiltrating water increases pore fluid pressure in rocks so they become saturated and more liable to fail.
        Water acts as a lubricant, making fault planes more likely to slip.
  - - - Dams and Reservoirs are built for variety of reasons
        Effects of dam building can have large consequences beyond national borders creating issues for neighbouring countries.
        Benefits of dams and reservoirs:
        
        Water supply.
        
        Hydroelectric power.
        
        Flood protection.
        
        Reclamation of wetlands.
        
        Improve navigations.
        
        Dam - A structure that holds back water.
        Reservoir - A body of water behind a dam wall.
        Hydroelectric power - Releasing water stored behind a dam to turn a turbine to generate electricity.
    - - General conditions
        
        Lack of seismic and volcanic activity
        
        Earthquakes may cause dam failure.
        
        Volcanic eruptions may fill the reservoir with pyroclastics or lava.
        
        Stable valley sides
        
        If beds dip towards the reservoir, landslips may occur (especially if competent, permeable rocks are interbedded with incompetent, impermeable rocks).
        
        High river catchment
        
        Requires sufficient rainfall and an underlying impermeable rock to promote surface runoff collection.
        
        Important that there are no exposed mineral veins containing toxic elements open to the reservoir.
        
        Ideally rivers should have low sediment loads to avoid fast siltation.
      - Foundations
        
        Underlying rock should be:
        
        Strong and competent with high load-bearing strength.
        
        Impermeable.
        
        Uniform.
        
        Low weathering depth.
        
        Low effects from previous human activity.
        
        Rock should be a crystalline igneous or metamorphic rock or cemented sedimentary rock.
      - Attitude of the strata
        
        Beds that are horizontal or dip upstream provide stable foundations.
        Beds dipping downstream are unstable. Potential for leakage and slippage along bedding planes that may lead to dam collapse.
      - Geological structures
        
        Structure presence can cause problems:
        Faults
        
        Zones of permeability and weakness.
        
        May have different rock types either side.
        
        Weight may reactivate old faults increasing seismic activity.
        
        Joints
        
        Zones of permeability that cause leakage.
        
        Often more closely spaced than faults.
        
        Anticlines
        
        Make unstable foundations because slippage can occur along bedding planes on the fold limbs.
        
        Tension joints on the crest of the anticline may allow water leakage from the reservoir.
        
        Synclines
        
        Stable but water can bypass the dam through permeable beds.
    - - Two main types of dam:
        Embankment dams
        
        Clay core held in place with piles of rock or earth.
        
        Built in broad, shallow valleys.
        
        Dam weight spread over wide area.
        
        Foundation doesn't need to be strong but requires large quantities of fill material.
        
        Masonry and concrete dams
        
        Can be arch, buttress or gravity dams.
        
        Needs cement and aggregate supply to make concrete.
    - - Ground improvement strategies used to prevent leakage include:
        Grouting
        
        Holes drilled into rock and liquid cement pumped in.
        
        Cement fills pore spaces, joints and fissures.
        
        Reduces permeability and increases rock strength.
        
        Clay or plastic lining
        
        Prior to filling, reservoir lined with an impermeable material.
        
        Prevents water leakage into underlying rock.
        
        Cut off curtain
        
        Impermeable barrier constructed as an extension below the dam.
        
        Cut off curtains particularly effective preventing leakage from dams situated on synclines.
        
        Further benefit of strengthening foundations and preventing slippage of beds downstream.
- - - - Rock type
        
        How competent and strong a rock is.
        
        The permeability and porosity of a rock.
        
        Presence of geological structures (and the dip) in a rock.
        
        The amount of wreathing occurred to a rock.
        
        Slope angle
        
        Depends on the maximum slope angle of a rock type.
        
        The steeper the gradient of a slope in a particular material, the more likely it is to fail.
        
        Water
        
        Mass movements often occur after heavy rainfall or snow melt.
        
        Water adds weight to rock increasing pore fluid pressure acting as a lubricant, resulting in friction and cohesion loss.