14-12-2012, 05:35 PM
Dams and reservoirs
Reservoirs and dams.ppt (Size: 9.9 MB / Downloads: 756)
Dams: types
Gravity dam: rigid monolithic structure
Trapezoidal cross section
Minimal differential movement tolerated
Dispersed moderate stress on valley floor and walls
Arch dam: high strength concrete wall
Convex faces upstream
Thin walled structure
Relatively flexible
Huge stresses imposed on valley walls and floor
Earth dams: bank or earth or rock with impermeable core
Core of clay or concrete, extended below ground
Sand or gravel drains built to cut fluid pressure
Low stress applied to valley floor and walls
Dams: forces applied
Vertical static forces
Lateral force applied by water body
Dynamic forces
wave action
overflow of water (controlled by spillway channels)
earthquakes and tremors
ice/freezing
Dams: ground improvement
Rock bolts
Rolling and preloading
compresses ground in prep for structure
improves post dam compaction
Gravity drainage and well points:
sand and gravel channels and shallow wells (for pumping) Electro-osmosis: insert conduction rods into fine grained clay-rich bedrock and have an electric field - de-waters ground via the flow of electric current
Vibroflotation
mechanical vibrating plate with load compresses low density gravels and sands
Explosives
useful in water-saturated gravel and scree – increases bulk density
Grouts
material injected into the ground
Chemical treatments
react solutions injected into ground. React with material to alter properties. NaCl solution injected into smectite-rich mud, shale etc. to alter expansivity of smectite – stabilizes ground pre-construction
Thermal treatment
Freezing with injected liquid N2 to consolidate loose ground during excavation. Heating by burning petroleum under pressure in subsurface – causes thermal metamorphism - hardens ground and cuts porosity