Topic 3 Flashcards

1
Q

design principles of retaining wall

A

no overturning, no sliding, no settlement, no bearing failure, no slip circle failure

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2
Q

failure modes for a retaining wall

A

slip circle, sliding, overturning, settlement, bearing capacity

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3
Q

functions of retaining wall

A

retain soil at a slope > natural angle of repose, resist pressure of retained soil and subsoil water, support vertical loads from other structure above

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4
Q

describe angle of repose

A

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.

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5
Q

types of earth pressures

A

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

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6
Q

describe active case

A

wall moves away from soil

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7
Q

describe passive case

A

wall moves into soil

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8
Q

what are the effects of water on retaining walls

A

increase pressure on soil, reduce bearing capacity of soil, reduce frictional resistance, reduce passive pressure in front of the wall

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9
Q

when is proper drainage required

A

if water is allowed to permeate the soil behind a retaining wall, have to use highly pervious soil such as sand or gravel

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10
Q

why is highly impervious soil undesirable as backfill

A

it adds on to lateral earth pressure, difficult to drain and it is subject to swelling and shrinking

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11
Q

what are the types of retaining walls

A

gravity, cantilever, counterfort, crib, gabion, precast concrete, MSE and soil nailed

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12
Q

describe gravity wall

A

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

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13
Q

describe cantilever wall

A

designed to resist pressures by means of specially designed shapes, either precast sections or cast-in-situ and suitable for heights up to 6m

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14
Q

describe counterfort wall

A

cantilever walls with triangular beams, soil pressure is transferred to the counterfort by the wall slab and suitable for heights up to 6m

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15
Q

what is similar to counterfort wall

A

buttress wall, braces are placed on the wall face rather than along the back

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16
Q

describe precast concrete wall

A

can be erected on a foundation as permanent retaining wall, lifting holes are provided which can be utilised for fixing

17
Q

what are the advantages of precast concrete wall

A

reduction in time by eliminating curing period, cost of formwork, time to erect and dismantle the temporary forms

18
Q

describe gabion wall

A

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

19
Q

why is gabion advantageous over rigid structures

A

they can conform to ground movement, dissipate energy from flowing water and drain freely

20
Q

describe crib wall

A

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

21
Q

describe MSE wall

A

soil constructed with artificial reinforcing that are sometimes ribbed for friction such as steel or aluminium strips, steel grids or mesh or fabric

22
Q

what are the stages in installing an MSE wall

A

erection of facial panel - filling of backfill - placement of reinforcement - filling of backfill - erection of next facial panel - repeat until wall is completed

23
Q

describe soil nailed walls

A

used to stabilise natural slopes or excavations and maximum depth for each stage of excavation depends on the soil type and slope inclination

24
Q

how does soil nailed walls work

A

nails develop tension as the ground deforms laterally in response to ongoing excavation

25
Q

what are the factors to be considered in the
construction of retaining walls

A

retention of soil during construction, control of ground water, the actual constructional form and materials to be used, backfilling the structure