Lecture 2 - Geotechnical Engineering contd...
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What long term bolt and dowel stabilisation techniques are there? How are they achieved?
Bolts, dowels, anchors - transfer load from unstable exterior to confined inferior Rock bolts - steel bars drilled in holes fixed at inner end by resin or expansive shell, tensioned, increase normal stress across joints Grouped dowels, steel bars drilled in holes through joints providing direct shear resistance
How can are soil and rock anchors used to stabilise slope long term?
Rock and soil anchors - tensioned steel cables drilled into rock soil, drill rod removed, cable grouped into position, cable tensioned, locked on plate
Name one kind of rock anchor
Duckbill rock anchor
What is shotcrete? Why is it unpopular?
Shotcrete is a long term stabilisation technique whereby concrete is sprayed onto slope Unpopular as ugly
What do baboons provide? Give two advantages
Provide toe stabilisation Cheap and simple
Give examples of retaining structures
Cribs, mechanically stabilised walls and sheet piles
How does gradient of slope effect choice of method for stabilising embankments and cuttings
Embankments used up to 45 degree slope >45 degrees reinforced with geotextiles If near vertical then retaining structures used
What are embankments generally composed of?
Material from cuttings
What is the different purposes of basal geotextiles and synthetic soil cells?
Basal geotextiles - prevents settlement Synthetic soil cell - prevents failure
How is blasting carried out? What are the key controls?
• Face survey • Drilling of shot holes • Checking holes • Charging with explosives and stemming top • Detonating the explosives • Shotpile ready for loading Key controls are rock strength and fracture state
What is the disadvantages of production blasting?
Untidy, less stable slope
What is the pro and con of pre-split blasting?
Pro: Controlled, more stable slope Con: Unnatural appearance
What is ripping?
Mechanical excavation by steel Tyne mounted on bulldozer
What three factors influence tunnels?
Rock type Nature of bedding, fractures Orientation of bedding, fractures