Published on March 6, 2014
RETAINING WALL THEORY OF STRUCTURES Presented by: SHARIQUE AHMED B.Arch 3rd yr
RETAINING WALL • 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, embankments or other materials in order to hold them in a vertical position. • Retaining walls also have application in buildings and bridges such as basement, foundation wall, bridge abutment etc.
The primary geotechnical concern in design and installation of retaining walls is that the retained material is attempting to move forward and down slope due to gravity. This creates soil pressure behind the wall, which can be analysed based on the angle of internal friction (φ) and the cohesive strength (c) of the material and the amount of allowable movement of the wall. This pressure is smallest at the top and increases toward the bottom in a manner similar to hydraulic pressure, and tends to push the wall forward and overturn it. Groundwater behind the wall that is not dissipated by a drainage system causes an additional horizontal hydraulic pressure on the wall.
TYPES OF RETAINING WALLS 1. 2. 3. 4. 5. 6. 7. GRAVITY RETAINING WALL CANTILEVER RETAINING WALL COUNTERFORT RETAINING WALL BUTTRESS RETAINING WALL SHEET PILE WALLS BRIDGE RETAINING WALL MECHANICALLY STABILISED RETAINING EARTH
1.GRAVITY RETAINING WALL • A gravity wall is made of plain concrete or brick masonry. • The stability of the wall is maintained by its weight. • It is generally made up to a height of 3 m of wall.
2.CANTILEVER RETAINING WALL • It consists of a vertical wall, heal slab and a toe slab which act as cantilever beams. • Its stability is maintained by the weight of the retaining wall and the weight of the earth on the base of the retaining wall. • It is generally made when the height of the earth on the base is in the range of 3 m to 8 m.
3.COUNTERFORT RETAINING WALL height of retaining wall is more than 6-8m, it is • When the economical to tie the vertical wall with the heel slab by counter forts at some spacing. • The counterforts act as tension members to support the vertical wall and reduces bending moment in it. • It also provides support to heel slab. • Generally, counterforts are spaced at approximately one-third of the height of wall.
4. BUTTRESS RETAINING WALL • It is similar to counter fort wall except that the vertical wall is tied with the toe of the retaining wall at some spacing. • It acts as a compression member to support the vertical wall and reduces bending moment in it.
5. SHEET PILE WALLS Used to build continuous walls for waterfront structures and for temporary construction wall heights > 6 m if used with anchors. Can be made of steel, plastics, wood, pre-cast concrete. The advantages of using steel sheet-piling: 1. Provides higher resistance to driving stresses; 2. Is of an overall lighter weight; 3. Can be reused on several projects; 4. Provides a long service life above or below the water table; 5. Easy to adapt the pile length by either welding or bolting; and 6. Their joints are less apt to deform during driving
6. BRIDGE RETAINING WALL • Its behaviour is similar to that of the basement or foundation wall. • The bridge superstructure induces horizontal as well as vertical loads that alter the normal cantilever behaviour.
7.MECHANICALLY STABILISED EARTH • Mechanically stabilized earth or MSE is soil constructed with artificial reinforcing. It can be used for retaining walls, bridge abutments, dams, seawalls, and dikes. • Although the basic principles of MSE has been used throughout history, MSE was developed in its current form in the 1960s. • The reinforcing elements used can vary but include steel and geosynthetics.
MSE • Mechanically stabilized earth (MSE) retaining walls combine geosynthetic-reinforced earth layers (such as geogrids) and a fascia of geocell, wire mesh or concrete blocks to create high-strength, versatile earth retention systems. • The geogrid reinforces the soil while the fascia protects the wall face. • The versatility of MSE walls makes them suitable for a variety of applications, from road structures to golf courses.
REINFORMENT IN MSE • The reinforcement materials of MSE can vary. • Originally, long steel strips 50 to 120 mm (2 to 5 in) wide were used as reinforcement. These strips are sometimes ribbed, although not always, to provide added friction. • Steel grids or meshes are also used as reinforcement. • Several types of geosynthetics can be used including geogrids and geotextiles. The reinforcing geosynthetics can be made of high density polyethylene, polyester, and polypropylene.
EARTH PRESSURE ON RETAINING WALL Earth pressure may be calculated at the vertical section going through the heel of the wall. This is under the constraint that heel is propotional in such a way that line AC makes an angle less than or equal to n with vertical.
Advantages of retaining walls • A retaining wall provides advantages such as ▫ preventing damage by soil falling or ▫ sliding away from a foundation. ▫ This can preserve ground area on the property or even add to it.
DISADVANTAGES OF RETAINING WALLS • Vertical Cracks ▫ Vertical cracks may form in retaining walls. ▫ Some retaining walls begin developing vertical cracks, such as in poured concrete. This is often due to excessive pressure or wide changes in temperature. In order to prevent these vertical cracks, provide plenty of good drainage, which can often be expensive to accomplish. • Failing Foundation ▫ Brick retaining walls often fail under pressure. ▫ Retaining walls need extensive drainage resources to prevent moisture, but they also require a strong foundation. Some retaining walls will not be able to retain high amounts of pressure from soil, such as bricks walls. This often results in crumbling bricks or a failing foundation. • Termites ▫ Termites are sometimes found in timber retaining walls. ▫ Retaining walls also can attract termites to your property, as is often the case when timber is used as a retaining wall. Termites can nest inside rotting timber and near molded areas. Correcting this problem can be expensive, if you have to use termite monitoring and treatment devices.
ADVANCEMENTS IN RETAINING WALL
MSE Precast Panel Retaining Wall • Reinforced Earth retaining walls are coherent gravity structures consisting of alternating layers of granular backfill and high-strength, inextensible discrete steel strip soil reinforcement with a modular precast concrete facing. • They are used extensively in highway projects for retaining walls and bridge abutments, in seawalls, dams, bulk storage facilities, and in supporting various types of railway transit.
Retained Earth – MSE Precast Panel Retaining Wall • Retained Earth retaining walls are coherent gravity structures consisting of alternating layers of granular backfill and high-strength, inextensible, highadherence welded wire bar mat soil reinforcement with a modular precast concrete facing. • They are used extensively in highway projects for retaining walls and bridge abutments, in seawalls, dams, bulk storage facilities, and in supporting various types of railway transit.
Terratrel– MSE Wire Faced Retaining Wall • Terratrel is a wire-faced MSE wall system that combines the technology of Reinforced Earth and Retained Earth with the economy of wire facing. • The system provides a cost-effective alternative for wall applications where aesthetics are not critical, a temporary retaining structure is required or differential and overall settlement exceeds the limits for a one-stage precast panel MSE wall. • The Terratrel system can be designed to utilize discrete steel strip, welded wire bar mat or high-tenacity polyester based geostrap soil reinforcements.
GeoMega– MSE Precast Panel Retaining Wall • GeoMega retaining walls are coherent gravity structures consisting of alternating layers of granular backfill and a hightenacity polyester based geostrap soil reinforcement with a modular precast concrete facing. • The Omega strip consists of high tenacity polyester fibers encased in a polyethylene sheath which makes it ideal for use in the construction of walls in where sea water or other chemically aggressive environments preclude the use of galvanized steel soil reinforcements.
Piano Wall – MSE Precast Retaining Wall with Traffic Barrier • Piano Wall is a MSE wall system which combines the technology of a Reinforced Earth retaining wall topped with an integral traffic barrier in a single engineered unit. • This unique solution was developed for projects that require a Jersey-type traffic barrier atop a five- to ten-foot high Reinforced Earth retaining wall. • It is ideal for projects requiring low-height grade separations adjacent to bi-level roadways.
TechWall - Precast Counterfort Retaining Wall • TechWall is a full height panel which combines a precast counterfort and wall facing into one unit. • When the traditional design advantages and benefits of a typical counterfort retaining wall are recommended due to items such as a severe right-of-way restriction, large utility conflict, construction in cut conditions, and roadway widening TechWall is an effective solution which encompasses the quality and efficiency of precast concrete.
Fanwall - Noisewall / Protective Barrier • Fanwall is a precast modular permanent barrier wall system which can be a freestanding trapezoidal structure or where right-of-way is minimal, a post and panel alternative is available. • A unique, rotatable and interlocking connection system and limitless architectural finishes makes Fanwall extremely versatile. • This engineered barrier wall system is available for nearly every noise or security problem found in the transportation, utility, industrial, and commercial markets.
RE/Tension - Precast Counterfort Retaining Wall • RE/Tension consists of integral precast box attached to the back of a standard MSE wall facing panel, the box serves as a form for a cast-in-place concrete counterfort. • This system is ideally suited for retaining walls with right-ofway constraints, large utility conflicts and full or partial rock cut situations. • Since the facing is comprised of standard MSE wall panels the RE/Tension system can be easily combined with a Reinforced Earth retaining wall within the same structure, while maintaining an identical aesthetic appearance.
ADVANTAGES OF MECHANICALLY STABILISED RETAINING WALLS • • • • • • • • • • • • • • • • Simple construction. The use of heavy equipment is reduced. More land is available for construction. Faster construction than traditional concrete walls. Do not require specialized labor. Reduces the need for wall finishing. Less site prep is needed. Can be built in confined areas or areas where a concrete wall is almost impossible to be constructed. Reduces the need for additional land acquisition process. Mechanically Stabilized Earth walls are susceptible to elastic deformation. High seismic load resistance. MSE walls can be used as tall structures, exceeding more than 60 feet of wall height. Can be combined with other products. Various shapes and forms can be made. Excavation works for footings are reduced. Can be built on poor soil areas.
DISADVANTAGES OF MSE • Require a relatively large space behind the wall or outward face to obtain enoughwall width for internal and external stability. • MSEW require select granular fill. (At sites where there is a lack of granular soils,the cost of importing suitable fill material may render the system uneconomical). • Requirements for RSS are typically less restrictive. • Suitable design criteria are required to address corrosion of steel reinforcingelements, deterioration of certain types of exposed facing elements such asgeosynthetics by ultra violet rays, and potential degradation of polymer reinforcementin the ground. • Since design and construction practice of all reinforced systems are still evolving,specifications and contracting practices have not been fully standardized.
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