Topic 3 Flashcards
design principles of retaining wall
no overturning, no sliding, no settlement, no bearing failure, no slip circle failure
failure modes for a retaining wall
slip circle, sliding, overturning, settlement, bearing capacity
functions of retaining wall
retain soil at a slope > natural angle of repose, resist pressure of retained soil and subsoil water, support vertical loads from other structure above
describe angle of repose
steepest angle relative to horizontal plane to which a material can be piled without slumping, cohesionless soils: 30 to 45. cohesion soils: 0 to 30.
types of earth pressures
active earth pressure, water pressure and passive earth pressure, ground pressure (surcharge), friction at the base, vertical load on heel due to fill and self-weight of wall
describe active case
wall moves away from soil
describe passive case
wall moves into soil
what are the effects of water on retaining walls
increase pressure on soil, reduce bearing capacity of soil, reduce frictional resistance, reduce passive pressure in front of the wall
when is proper drainage required
if water is allowed to permeate the soil behind a retaining wall, have to use highly pervious soil such as sand or gravel
why is highly impervious soil undesirable as backfill
it adds on to lateral earth pressure, difficult to drain and it is subject to swelling and shrinking
what are the types of retaining walls
gravity, cantilever, counterfort, crib, gabion, precast concrete, MSE and soil nailed
describe gravity wall
max height of 1.8m, can be constructed using semi-engineering bricks or mass concrete, natural stone can be used to 1m and they resist earth pressure due to backfill by its own weight
describe cantilever wall
designed to resist pressures by means of specially designed shapes, either precast sections or cast-in-situ and suitable for heights up to 6m
describe counterfort wall
cantilever walls with triangular beams, soil pressure is transferred to the counterfort by the wall slab and suitable for heights up to 6m
what is similar to counterfort wall
buttress wall, braces are placed on the wall face rather than along the back