HOME

TheInfoList




Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to (typically a steep, near-vertical or vertical slope). They are used to bound soils between two different elevations often in areas of terrain possessing undesirable slopes or in areas where the landscape needs to be shaped severely and engineered for more specific purposes like hillside farming or roadway overpasses. A retaining wall that retains soil on the backside and water on the frontside is called a
seawall A seawall (or sea wall) is a form of coastal defence constructed where the sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers appro ...

seawall
or a bulkhead.


Definition

A wall for holding in place a mass of earth or the like, as at the edge of a terrace or excavation. A retaining wall is a structure designed and constructed to resist the lateral pressure of soil, when there is a desired change in ground elevation that exceeds the
angle of repose The angle of repose, or critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping. At this angle, the material on the slope face i ...

angle of repose
of the soil. A basement wall is thus one kind of retaining wall. But the term usually refers to a cantilever retaining wall, which is a freestanding structure without lateral support at its top. These are cantilevered from a footing and rise above the grade on one side to retain a higher level grade on the opposite side. The walls must resist the lateral pressures generated by loose soils or, in some cases,
water pressures
water pressures
. Every retaining wall supports a "wedge" of
soil Soil is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

soil
. The wedge is defined as the soil which extends beyond the failure plane of the soil type present at the wall site, and can be calculated once the
soil friction
soil friction
angle is known. As the setback of the wall increases, the size of the sliding wedge is reduced. This reduction lowers the pressure on the retaining wall. The most important consideration in proper design and installation of retaining walls is to recognize and counteract the tendency of the retained material to move downslope due to
gravity Gravity (), or gravitation, is a by which all things with or —including s, s, , and even —are attracted to (or ''gravitate'' toward) one another. , gravity gives to s, and the causes the s of the oceans. The gravitational attracti ...

gravity
. This creates
lateral earth pressure Lateral earth pressure is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , ...
behind the wall which depends on the
angle In Euclidean geometry Euclidean geometry is a mathematical system attributed to Alexandrian Greek mathematics , Greek mathematician Euclid, which he described in his textbook on geometry: the ''Euclid's Elements, Elements''. Euclid's method ...

angle
of internal
friction Friction is the force In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mass to change its velocity (e.g. moving from a Newton's first law, st ...

friction
(phi) and the cohesive strength (c) of the retained material, as well as the direction and magnitude of movement the retaining structure undergoes. Lateral earth pressures are zero at the top of the wall and – in homogenous ground – increase proportionally to a maximum value at the lowest depth. Earth pressures will push the wall forward or overturn it if not properly addressed. Also, any
groundwater Groundwater is the water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known form ...

groundwater
behind the wall that is not dissipated by a
drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural Agriculture is the practice of cultivating plants and livestock. Agr ...

drainage
system causes
hydrostatic pressure Fluid statics or hydrostatics is the branch of fluid mechanics Fluid mechanics is the branch of physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that de ...

hydrostatic pressure
on the wall. The total pressure or thrust may be assumed to act at one-third from the lowest depth for lengthwise stretches of uniform height. It is important to have proper drainage behind the wall in order to limit the pressure to the wall's design value. Drainage materials will reduce or eliminate the hydrostatic pressure and improve the stability of the material behind the wall.
Drystone Dry stone, sometimes called drystack or, in Scotland, drystane, is a building method by which structures are constructed from stones In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', (" ...

Drystone
retaining walls are normally self-draining. As an example, the
International Building Code The International Building Code (IBC) is a model building codeA model building code is a building code that is developed and maintained by a standards organization independent of the jurisdiction responsible for enacting the building code. A local ...
requires retaining walls to be designed to ensure stability against overturning, sliding, excessive
foundation Foundation may refer to: * Foundation (nonprofit), a type of charitable organization ** Foundation (United States law), a type of charitable organization in the U.S. ** Private foundation, a charitable organization that, while serving a good cause ...
pressure and water uplift; and that they be designed for a
safety factor In engineering, a factor of safety (FoS), also known as (and used interchangeably with) safety factor (SF), expresses how much stronger a system is than it needs to be for an intended load. Safety factors are often calculated using detailed analy ...
of 1.5 against lateral sliding and overturning.


Types


Gravity

Gravity walls 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. For short landscaping walls, they are often made from
mortar Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village in ...
less stone or segmental concrete units (masonry units). Dry-stacked gravity walls are somewhat flexible and do not require a rigid footing. Earlier in the 20th century, taller retaining walls were often gravity walls made from large masses of concrete or stone. Today, taller retaining walls are increasingly built as composite gravity walls such as: geosynthetics such as geocell cellular confinement earth retention or with precast facing;
gabion A gabion (from Italian Italian may refer to: * Anything of, from, or related to the country and nation of Italy ** Italians, an ethnic group or simply a citizen of the Italian Republic ** Italian language, a Romance language *** Regional Ita ...

gabion
s (stacked steel wire baskets filled with rocks); crib walls (cells built up log cabin style from precast concrete or timber and filled with granular material).


Cantilevered

Cantilevered retaining walls are made from an internal stem of steel-reinforced, cast-in-place concrete or mortared masonry (often in the shape of an inverted T). These walls cantilever loads (like a
beam Beam may refer to: Streams of particles or energy *Light beam, or beam of light, a directional projection of light energy **Laser beam *Particle beam, a stream of charged or neutral particles **Charged particle beam, a spatially localized group ...
) to a large, structural footing, converting horizontal pressures from behind the wall to vertical pressures on the ground below. Sometimes cantilevered walls are buttressed on the front, or include a counterfort on the back, to improve their strength resisting high loads. Buttresses are short
wing wall A wing wall (also "wingwall" or "wing-wall") is a smaller wall A wall is a structure and a surface that defines an area; carries a load; provides security, Shelter in place, shelter, or soundproofing; or, is decorative. There are many kinds of ...
s at right angles to the main trend of the wall. These walls require rigid concrete footings below seasonal frost depth. This type of wall uses much less material than a traditional gravity wall.


Diaphragm wall

Diaphragm walls are a type of retaining walls that are very stiff and generally watertight. Diaphragm walls are expensive walls, but they save time and space, and hence are used in urban constructions.


Sheet piling

Sheet pile retaining walls are usually used in soft soil and tight spaces. Sheet pile walls are driven into the ground and are composed of a variety of material including steel, vinyl, aluminum, fiberglass or wood planks. For a quick estimate the material is usually driven 1/3 above ground, 2/3 below ground, but this may be altered depending on the environment. Taller sheet pile walls will need a tie-back
anchor An anchor is a device, normally made of metal, used to connect a Watercraft, vessel to the Seabed, bed of a body of water to prevent the craft from drifting due to Leeway, wind or Ocean current, current. The word derives from Latin ''ancora'' ...
, or "dead-man" placed in the soil a distance behind the face of the wall, that is tied to the wall, usually by a cable or a rod. Anchors are then placed behind the potential failure plane in the soil.


Bored pile

Bored pile retaining walls are built by assembling a sequence of
bored pile , United States. , Florida Florida (, ) is a U.S. state, state located in the Southeastern United States, Southeastern region of the United States. With a population of over 21million, Florida is the List of states and territories of the ...
s, followed by excavating away the excess soil. Depending on the project, the bored pile retaining wall may include a series of
earth anchor An earth anchor is a device designed to support structures, most commonly used in geotechnical#REDIRECT geotechnical engineering#REDIRECT geotechnical engineering {{Redirect category shell, 1= {{R from other capitalisation ... {{Redirect cat ...
s, reinforcing beams, soil improvement operations and
shotcrete Shotcrete, gunite (), or sprayed concrete is concrete Concrete is a composed of fine and coarse bonded together with a fluid (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world a ...
reinforcement layer. 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 A pile driver is a heavy-duty tool used to drive piling, piles into soil to build piers, bridges, cofferdams, and other "pole" supported structures, and patterns of pilings as part of permanent deep foundations for buildings or other structures ...

pile driver
are not acceptable.


Anchored

An anchored 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. Usually driven into the material with boring, anchors are then expanded at the end of the cable, either by mechanical means or often by injecting pressurized concrete, which expands to form a bulb in the soil. Technically complex, this method is very useful where high loads are expected, or where the wall itself has to be slender and would otherwise be too weak.


Alternative retaining techniques


Soil nailing

Soil nailing is a technique in which soil slopes,
excavations In archaeology, excavation is the exposure, processing and recording of archaeological remains. An excavation site or "dig" is the area being studied. These locations range from one to several areas at a time during a project and can be condu ...
or retaining walls are reinforced by the insertion of relatively slender elements – normally steel reinforcing bars. The bars are usually installed into a pre-drilled hole and then
grout Grout is a dense fluid which is used to fill gaps or used as reinforcement in existing structures. Grout is generally a mixture of water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main c ...
ed into place or drilled and grouted simultaneously. They are usually installed untensioned at a slight downward inclination. A rigid or flexible facing (often sprayed concrete) or isolated soil nail heads may be used at the surface.


Soil-strengthened

A number of systems exist that do not consist of just the wall, but reduce the earth pressure acting directly on the wall. These are usually used in combination with one of the other wall types, though some may only use it as facing, ''i.e.'', for visual purposes.


Gabion meshes

This type of soil strengthening, often also used without an outside wall, consists of
wire A wire is a single usually cylindrical A cylinder (from ) has traditionally been a Solid geometry, three-dimensional solid, one of the most basic of curvilinear geometric shapes. Geometrically, it can be considered as a Prism (geometry), p ...

wire
mesh A mesh is a barrier made of connected strands of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearan ...

mesh
"boxes", which are filled with roughly cut stone or other material. The mesh cages reduce some internal movement and forces, and also reduce erosive forces. Gabion walls are free-draining retaining structures and as such are often built in locations where ground water is present. However, management and control of the ground water in and around all retaining walls is important.


Mechanical stabilization

Mechanically stabilized earth, also called MSE, is soil constructed with artificial reinforcing via layered horizontal mats (
geosynthetics Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve civil engineering Civil engineering is a professional engineering Regulation and licensure in engineering is established by ...
) fixed at their ends. These mats provide added internal shear resistance beyond that of simple gravity wall structures. Other options include steel straps, also layered. This type of soil strengthening usually needs outer facing walls (S.R.W.'s – Segmental Retaining Walls) to affix the layers to and vice versa. The wall face is often of precast concrete units that can tolerate some differential movement. The reinforced soil's mass, along with the facing, then acts as an improved gravity wall. The reinforced mass must be built large enough to retain the pressures from the soil behind it. Gravity walls usually must be a minimum of 50 to 60 percent as deep or thick as the height of the wall, and may have to be larger if there is a slope or surcharge on the wall. Cellular confinement systems (geocells) are also used for steep earth stabilization in gravity and reinforced retaining walls with geogrids. Geocell retaining walls are structurally stable under self- weight and externally imposed loads, while the flexibility of the structure offers very high seismic resistance. The outer fascia cells of the wall can be planted with vegetation to create a
green wall A green wall is a vertical built structure intentionally covered by vegetation. Green walls include a vertically applied growth medium such as soil, substitute substrate, or hydroculture felt; as well as an integrated hydration and fertigation ...
.


See also

*
Civil engineering Civil engineering is a professional engineering Regulation and licensure in engineering is established by various jurisdictions of the world to encourage public welfare, safety, well-being and other interests of the general public and to defin ...
*
Direct shear test A direct shear test is a laboratory or field test used by geotechnical engineers to measure the shear strength In engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, i ...
*
Earthquake engineering Earthquake engineering is an interdisciplinary Interdisciplinarity or interdisciplinary studies involves the combination of two or more academic disciplines into one activity (e.g., a research project). It draws knowledge from several other ...
*
Flying arch A flying arch is a form of arch bridge An arch bridge is a bridge with abutment in Yass, New South Wales Yass is a town in the Southern Tablelands of New South Wales, Australia in Yass Valley Council. The name appears to have been deriv ...
*
Foundation (engineering) In engineering, a foundation is the element of a structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements tha ...
*
Geotechnical engineering Geotechnical engineering, also known as geotechnics, is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective e ...
*
Landslide mitigation Landslide mitigation refers to several man-made activities on grade (slope), slopes with the goal of lessening the effect of landslides. Landslides can be triggered by many, sometimes wikt:concomitant, concomitant causes. In addition to shallow e ...
*
Lateral earth pressure Lateral earth pressure is the pressure Pressure (symbol: ''p'' or ''P'') is the force In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mas ...
*
Revetment Revetments in stream restoration Stream restoration or river restoration, also sometimes referred to as river reclamation, is work conducted to improve the environmental health of a river A river is a natural flowing watercourse, usually ...

Revetment
*
Seawall A seawall (or sea wall) is a form of coastal defence constructed where the sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers appro ...

Seawall
*
Slope stability analysis Slope stability analysis is a static or dynamic, analytical or empirical method to evaluate the stability of earth and rock-fill dams, embankments, excavated slopes, and natural slopes in soil and rock. Slope stability refers to the condition of in ...
*
Structural engineering Structural engineering is a sub-discipline of civil engineering Civil engineering is a professional engineering Regulation and licensure in engineering is established by various jurisdictions of the world to encourage public welfare, safety ...
* Terraced wall *
Trench shield Trench shields (also called trench boxes or trench sheets) are steel or aluminum structures used for protecting utility workers while performing their duties within a trench and avoid Cave-in (excavation), cave-ins. They are customarily construc ...
*
Trench shoring Trench shoring is the process of bracing the walls of a trench A trench is a type of excavation or depression in the ground that is generally deeper than it is wide (as opposed to a wider gully A gully is a landform A landform is a natu ...


References


Further reading

*Bowles, J.,(1968). Foundation Analysis and Design, McGraw-Hill Book Company, New York *Ching, F. D., Faia., R., S., & Winkel, P. (2006). Building Codes Illustrated: A Guide to Understanding the 2006 International *Crosbie, M. & Watson, D. (Eds.). (2005). Time-Saver Standards for Architectural Design. New York, NY: McGraw-Hill. {{DEFAULTSORT:Retaining Wall Geotechnical shoring structures Types of wall