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RETAINING WALLS-TAIYABA RASHIDF/O ARCHITECTURE & EKISTICSJAMIA MILLIA ISLAMIANEW DELHI
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RETAINING WALLS
• Retaining walls are used to retain earth or other materials which have the tendency to slide and repose at a particular inclination.
• They provide lateral support to the earthfill, embankment or other materials in order to hold them in a vertical position.
• Types:Gravity retaining wallCantilever retaining wallCounterfort retaining wallButtress retaining wallBasement/foundation wallBridge abutment
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GRAVITY RETAINING WALL• Made of plain concrete or brick masonry.
• Stability of wall is maintained by its weight.
• Generally made up to a height of 3m of wall.
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CANTILEVER RETAINING WALL
• Consists of a vertical wall, heal slab & toe slab which act as cantilever beams.
• Stability maintained by weight of retaining wall & weight of earth on the base of retaining wall.
• Height ranges from 3m to 8m.
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COUNTERFORT RETAINING WALL
• Height ranges from 6m to 8m.
• More economical to tie the vertical wall with the heel slab by counterforts at some spacing.
• Acts as tension member to support vertical wall & reduces bending moment.
• Supports the heel slab & reduces bending moment.
• Spacing: 1/3rd the height of wall.
• Stability maintained by weight of earth on base & by self-weight.
• More widely used as it is hidden beneath the retained materials.
• Has a clean, uncluttered face for more efficient use of space in front of wall.
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COUNTERFORT RETAINING WALL
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BUTTRESS RETAINING WALL
• Similar to the counterfort wall.
• Vertical wall is tied with toe of retaining wall at some spacing.
• Acts as compression member to support vertical wall & reduces its bending moment.
• Supports toe slab & reduces its bending moment.
• Spacing: 1/3rd the height of the wall.
• Buttress as compression member is more economical than a tension counterfort.
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BUTTRESS RETAINING WALL
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BASEMENT/FOUNDATION WALL
• Restrained at the bottom by basement floor slab & at the top by the first floor slab.
• Subjected to:Lateral earth pressure exerted by
earth fillVertical load from superstructure.
• Lateral support is provided by basement floor & first floor slabs.
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BRIDGE ABUTMENT• Behaviour similar to basement or
foundation wall.
• Superstructure induces horizontal & vertical loads that alter the normal cantilever behaviour.
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BRIDGE TERMINOLOGY
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FORCES ON RETAINING WALLS
• Self-weight
• Weight of soil above foundation base
• Earth pressure
• Surcharge i.e., forces due to loads on earth surface
• Soil reactions on footing
• Friction on footing due to sliding
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CONSTRUCTION METHODS
• A concrete retaining wall
• An interlocking block retaining wall
• A Wood retaining wall
• An Insulated Concrete Form retaining wall or ICF retaining wall
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SLOPE STABILITY• The field of slope stability encompasses the analysis of static and
dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock.
SIMPLE SLOPE SLIP SECTION
SLOPE WITH ERODING RIVER & SWIMMING POOL
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SLOPE STABILITY
• If the forces available to resist movement are greater than the forces driving movement, the slope is considered stable.
• Factor of safety=Forces resisting movement /Forces driving movement.
• In earthquake-prone areas, the analysis is typically run for static conditions and pseudo-static conditions, where the seismic forces from an earthquake are assumed to add static loads to the analysis.
• METHOD OF SLICES
• BISHOP’S METHOD
• SARMA METHOD
• LORIMER'S METHOD
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• Method for analysing the stability of a slope in two dimensions.
• The sliding mass above the failure surface is divided into a number of slices.
• The forces acting on each slice are obtained by considering the mechanical equilibrium for the slices.
SLOPE STABILITY-ANALYSIS METHODSMETHOD OF
SLICES
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• Proposed by Alan W. Bishop.
• Method for calculating the stability of slopes.
• An extension of the Method of Slices.
• By making some simplifying assumptions, the problem becomes statically determinate and suitable for hand calculations.
• Forces on the sides of each slice are horizontal
• The method has been shown to produce factor of safety values within a few percent of the "correct" values.
SLOPE STABILITY-ANALYSIS METHODSBISHOP’S
METHOD
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• c’= effective cohesion
• ’= angle of internal friction
• b= width of slice
• w= weight of each slice
• u= water pressure at base of each slice
SLOPE STABILITY-ANALYSIS METHODSBISHOP’S
METHOD
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• Proposed by Sarawa K. Sarma
• A Limit equilibrium technique used to assess the stability of slopes under seismic conditions.
• May also be used for static conditions if the value of the horizontal load is taken as zero.
• Can analyse a wide range of slope failures as it may accommodate a multi-wedge failure mechanism and therefore it is not restricted to planar or circular failure surfaces.
• May provide information about the factor of safety or about the critical acceleration required to cause collapse.
SLOPE STABILITY-ANALYSIS METHODS
SARMA METHOD
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• Developed in the 1930s by Gerhardt Lorimer.
• A technique for evaluating slope stability in cohesive soils.
• Differs from Bishop's Method in that it uses a clothoid slip surface in place of a circle.
• This mode of failure was determined experimentally to account for effects of particle cementation.
SLOPE STABILITY-ANALYSIS METHODS
LORIMER'S METHOD
A CLOTHOID OR EULER SPIRAL
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REINFORCED EARTH
• Also called Mechanically Stabilized Earth or MSE.
• Soil constructed with artificial reinforcing.
• Can be used for retaining walls, bridge abutments, dams, seawalls, and dikes.
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REINFORCED EARTH• MSE walls stabilize unstable slopes and retain the soil on steep slopes and
under crest loads.
• The wall face is often of precast, segmental blocks, panels or geocells that can tolerate some differential movement.
• The walls are infilled with granular soil, with or without reinforcement, while retaining the backfill soil.
• Reinforced walls utilize horizontal layers typically of geogrids.
• The reinforced soil mass, along with the facing, forms the wall.
• In many types of MSE’s, each vertical fascia row is inset, thereby providing individual cells that can be infilled with topsoil and planted with vegetation to create a green wall.
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• Ease of installation.
• Quick construction.
• Do not require formwork or curing and each layer is structurally sound as it is laid, reducing the need for support, scaffolding or cranes.
• Do not require additional work on the facing.
• Retain sufficient flexibility to withstand large deformations without loss of structural integrity, and have high seismic load resistance.
REINFORCED EARTHADVANTAGES
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GEOSYNTHETIC MATERIALS• Polymeric products used to solve civil
engineering problems.
• Includes eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosynthetic clay liners, geofoam, geocells and geocomposites.
• Suitable for use in the ground where high levels of durability are required.
• Can also be used in exposed applications.
• Available in a wide range of forms and materials, each to suit a slightly different end use.
Geocells
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GEOSYNTHETIC MATERIALS
GEOSYNTHETIC REINFORCED STRUCTURES
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GEOGRID• Geosynthetic material used to reinforce soils.
• Used to reinforce retaining walls, as well as subbases or subsoils below roads or structures.
• Soil pulls apart under tension. Compared to soil, geogrids are strong in tension.
• Transfer forces to a larger area of soil.
• Made of polymer materials, such as polyester, polyethylene or polyproylene.
• Woven or knitted from yarns, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material, then stretched into a grid.
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GEOCELLS• Also called Cellular Confinement
Systems.
• Used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention.
• Typically made with ultrasonically-welded high-density polyethylene (HDPE) or Novel Polymeric Alloy strips that are expanded on-site.
• Creates a stiff mattress or slab to distribute the load over a wider area.
• Reduces punching of soft soil.
• Increases shear resistance and bearing capacity.
• Decreases deformation.
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THANK YOU
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