Retaining Wall Flashcards
a structure that holds or retains material (usually soil) behind it
retaining wall
types of materials that can be used to create retaining walls
- concrete blocks
- poured concrete
- treated timbers
- rocks or boulders
2 classification of earth-retaining structures
(1) externally stabilized systems
(2) internally stabilized systems
2 types of externally stabilized systems
(1) in-situ walls
(2) gravity walls
4 examples of in-situ walls
(1) sheet pile
(2) soldier pile
(3) cast in-situ
(4) soil cement
7 examples of gravity walls
(1) massive
(2) cantilever
(3) counterfort and buttress
(4) gabion
(5) crib
(6) bin
(7) cellular cofferdam
2 types of internally stabilized systems
(1) reinforced soils
(2) in-situ reinforcement
2 examples of reinforced soils
(1) reinforced earth
(2) geotextile
2 examples of in-situ reinforcement
(1) soil nailing
(2) reticulated micropiles
4 different types of retaining wall
(1) gravity wall
(2) piling wall
(3) cantilever wall
(4) anchored wall
a type of retaining wall that depend on their mass (stone, concrete or other heavy material) to resist pressure from behind and may have a ‘batter’ setback to improve stability by leaning back toward the retained soil
gravity walls
for short landscaping walls, they are often made from mortarless stone or segmental concrete units (masonry units)
gravity walls
3 kinds of gravity walls
(1) concrete cast
(2) segmental
(3) gabion walls
these are constructed of reinforced concrete
cantilever retaining walls
they consist of a relatively thin stem and a base slab; the base is also divided into two parts, the heel and toe, in which the heel is the part of the base under the backfill
cantilever retaining walls
2 kinds of cantilever retaining walls
(1) cast-in-place
(2) precast
a kind of piling walls that is usually used in soft soil and tight spaces
sheet pile retaining walls
these are made out of steel, vinyl or wood planks which are driven into the ground
sheet pile walls
for a quick estimate in piling walls, the material is usually driven _____ above ground, _____ below ground, but this may be altered depending on the environment
1/3; 2/3
this kind of pile retaining walls are built by assembling a sequence of bored piles, proceeded by excavating away the excess soil
bored pile retaining walls
this construction technique tends to be employed in scenarios where sheet piling is a valid construction solution, but where the vibration or noise levels generated by a pile driver are not acceptable
bored pile wall
3 kinds of piling walls
(1) sheet pile
(2) soldier beam
(3) pier and concrete panel
this type of retaining wall can be constructed in any of the aforementioned styles but also includes additional strength using cables or other stays anchored in the rock or soil behind it
anchored walls
these are stabilizing structures that are used for holding back earth
retaining wall
7 uses of retaining wall
(1) improve property’s appearance
(2) create a flat area
(3) make a slope useful
(4) provide handicapped accessibility
(5) improve site drainage
(6) hold back water
(7) simplify maintenance
6 things to consider in wall selection
(1) wall type (vary depending on the client)
(2) highway sector
(3) required right of way (ROW) for construction
(4) performance issues (settlement, lateral movement, and water tightness)
(5) cost, aesthetics, and environment
(6) durability and maintenance requirements
4 things to consider in designing or selecting retaining walls
(1) type of material being retained
(2) surcharge loads
(3) type of retaining wall that would work best for the scenario
(4) ground condition (soil shear strength, ground water table, site slopes, necessary fill, and necessary cut)
this is the most simple retaining wall
gravity walls
it is generally trapezoidal constructed of mass concrete
gravity walls
it relies on self weight to resist overturning and sliding
gravity walls
its typical heights 3 to 10 feet
gravity walls
2 advantages of gravity walls
(1) cheap and simple to build – particularly suitable for remote areas (such as mountains) where they can be built from locally available materials
(2) when constructed from natural materials can look attractive
3 disadvantages of gravity walls
(1) limited to about 5m height (wall becomes too big for higher walls)
(2) space needed behind wall for construction and backfilling
(3) not suitable for soft soils due bearing failure
it generally consists of steel reinforced concrete stem and base
cantilever walls
relies on weight of soil above base to resist overturning and
sliding
cantilever walls
the vertical ‘stem’ of the wall acts like a cantilever structure to support the lateral earth pressure on the back of the wall
cantilever walls
its typical heights of 6 to 30 feet
cantilever walls
2 advantages of cantilever walls
(1) take up small space with much of structure below ground
(2) no specialist equipment required – standard reinforced concrete skills required for construction
4 disadvantages of cantilever walls
(1) prone to sliding failure – often require propping
(2) space required behind wall for construction and backfilling
(3) height limited to about 6m.
(4) not suitable for soft soils due bearing failure
these also support lateral earth pressures by acting as cantilever structures; but instead of fixity for the cantilever coming from a rigid base, it comes from the passive lateral earth pressure in front of the wall
embedded cantilever walls
they are quick to install and can be installed in difficult site conditions, such as on soft ground or under water; they are installed in flat ground before excavation in front of the wall; they require special equipment for installation which can make them expensive
embedded cantilever walls
the walls can be constructed of driven steel sheet piles, reinforced concrete bored piles or reinforced concrete diaphragm walls
embedded cantilever walls
5 advantages of piling walls
(1) narrow walls which take up little space
(2) can be installed up to the site boundary with little or no space required behind the wall for construction – this is particularly advantageous in built-up areas
(3) installed quickly and early in construction and wall can form both temporary and permanent support to excavation
(4) no restriction on height of wall
(5) can be installed in weak ground
3 disadvantages of piling walls
(1) expensive option (for short walls)
(2) specialized skills and equipment are required for their installation
(3) vibrations and noise can be issues for neighboring properties
7 advantages of anchored walls
(1) very versatile in design options
(2) install easily
(3) materials are readily available
(4) can be used to create high, curved or shaped walls
(5) interlocking walls possible
(6) DIY applications for homeowners
(7) can be built in confined areas
3 disadvantages of anchored walls
(1) quality control is critical on the anchorage capacity
(2) MSE and SRW require proper reinforcement orientations and locations
(3) require proper drainage
for stability, a retaining wall should satisfy the 6 conditions:
(1) external stability check
(2) sliding
(3) overturning
(4) bearing capacity
(5) global stability
(6) settlement
3 failure modes of gravity walls
(1) over-turning
(2) sliding
(3) bearing failure
remedy for over-turning in gravity walls
increase weight of wall or widen base
remedy for sliding in gravity walls
increase weight of wall or widen base
remedy for bearing failure in gravity walls
widen base or reduce weight of wall if possible
4 failure modes of reinforced concrete cantilever walls
(1) over-turning
(2) sliding
(3) bearing failure
(4) internal failure in structures
remedy for over-turning in reinforced concrete cantilever walls
increase size of base (heel and toe)
remedy for sliding in reinforced concrete cantilever walls
increase size of key
remedy for bearing failure in reinforced concrete cantilever walls
increase size of base (heel and toe)
remedy for internal failure in structure in reinforced concrete cantilever walls
increase reinforcement in structure
3 failure modes of embedded cantilever walls (piling walls)
(1) passive failure
(2) bearing failure
(3) internal failure in wall
remedy for passive failure in embedded cantilever walls (piling walls)
increase embedment depth or add props to support wall
remedy for bearing failure in embedded cantilever walls (piling walls)
increase embedment depth of wall
remedy for internal failure in embedded cantilever walls (piling walls)
increase strength of wall section
5 internal stability of anchored walls
(1) tensile resistance
(2) pullout resistance
(3) face element
(4) face element connection
(5) MSEW reinforcement
4 potential external failure mechanisms for a mechanically stabilized earth (MSE) wall
(1) sliding
(2) overturning (eccentricity)
(3) bearing capacity
(4) deep seated stability (rotational)
typical factors of safety for external stability
- sliding — F.S > 1.5
- limiting eccentricity — e < B/6
- overturning — FS > 2.0
