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
describe precast concrete wall
can be erected on a foundation as permanent retaining wall, lifting holes are provided which can be utilised for fixing
what are the advantages of precast concrete wall
reduction in time by eliminating curing period, cost of formwork, time to erect and dismantle the temporary forms
describe gabion wall
constructed by filling wire baskets with broken stone across, battered wall face, either with a stepped face or back and suitable for heights up to 10m
why is gabion advantageous over rigid structures
they can conform to ground movement, dissipate energy from flowing water and drain freely
describe crib wall
rear edges of crib act as anchorage system for the front which contains granular fill, suitable for heights up to 5m and for greater heights, width can be doubled or tripled
describe MSE wall
soil constructed with artificial reinforcing that are sometimes ribbed for friction such as steel or aluminium strips, steel grids or mesh or fabric
what are the stages in installing an MSE wall
erection of facial panel - filling of backfill - placement of reinforcement - filling of backfill - erection of next facial panel - repeat until wall is completed
describe soil nailed walls
used to stabilise natural slopes or excavations and maximum depth for each stage of excavation depends on the soil type and slope inclination
how does soil nailed walls work
nails develop tension as the ground deforms laterally in response to ongoing excavation
what are the factors to be considered in the
construction of retaining walls
retention of soil during construction, control of ground water, the actual constructional form and materials to be used, backfilling the structure
