Mechanically stabilized earth

Mechanically stabilized earth (MSE or reinforced soil) is soil constructed with artificial reinforcing. It can be used for retaining walls, bridge abutments, seawalls, and dikes.[1][2] Although the basic principles of MSE have 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 is the term usually used in the US to distinguish it from the trade name "Reinforced Earth". Elsewhere "reinforced soil" is the generally accepted term.

Precastconcreteretainingwall
Precast concrete retaining wall
Mechanically stabilized earth diagram
A diagram of a mechanically stabilized earth wall as it would be modeled in a finite element analysis.

Description

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.

The main advantages of MSE walls compared to conventional reinforced concrete walls are their ease of installation and quick construction. They do not require formwork or curing and each layer is structurally sound as it is laid, reducing the need for support, scaffolding or cranes. They also do not require additional work on the facing.

In addition to the flexibility of MSE walls in design and construction, seismic testing conducted on a large scale shaking table laboratory at the Japan National Institute of Agricultural Engineering (Tsukuba City), showed that modular block reinforced walls,[3] and even more so geocell retention walls,[4] retain sufficient flexibility to withstand large deformations without loss of structural integrity, and have high seismic load resistance. Highway overpasses along interstates often employ the INTER-LOK System.

History

Using straw, sticks, and branches to reinforce adobe bricks and mud dwellings has happened since the earliest part of human history, Parts of the Great Wall of China are formed as reinforced soil as are the ziggurats of the Middle East. In the 1960s French engineer Henri Vidal invented the modern form of MSE, termed Terre Armee (reinforced earth) using steel strip reinforcements. Since the 1980s the development of reinfored soil has been dramatic using a range of construction forms and reinforcements including metallic and polymeric anchors, strips and grids. The first modern forms of reinforced soil were constructed in Europe in the late 1960s. The first MSE wall in the United States was built in 1971 on State Route 39 near Los Angeles.

Reinforcement

Reinforcement placed in horizontal layers throughout the height of the wall provides the tensile strength to hold the soil together. 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 ripped, although not always, to provide added friction. There are also prefabricated pile sleeve options to reduce negative skin friction on piles embedded behind MSE bridge abutments.[5] Sometimes 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. These materials may be ribbed and are available in various sizes and strengths.[6]

For erosion control and load support the upper layer can be reinforced by geocell materials.[7]

References

  1. ^ "Mechanically Stabilized Earth Structures". Archived from the original on December 16, 2005. Retrieved 2007-01-27.
  2. ^ "Mechanically Stabilized Earth Wall Inspector's Handbook" (PDF). Florida Department of Transportation. Retrieved 2007-01-27.
  3. ^ Ling, Hoe I.; Mohri, Yoshiyuki; Leshchinsky, Dov; Burke, Christopher; Matsushima, Kenichi; Liu, Huabei (2005). "Large-Scale Shaking Table Tests on Modular-Block Reinforced Soil Retaining Walls" (PDF). Journal of Geotechnical and Geoenvironmental Engineering. 131 (4): 465–476. doi:10.1061/(ASCE)1090-0241(2005)131:4(465). ISSN 1090-0241.
  4. ^ Leshchinsky, D. (2009). "Research and Innovation: Seismic Performance of Various Geocell Earth-retention Systems" (PDF). Geosysnthetics. 27 (4): 46–52. ISSN 0882-4983.
  5. ^ "Yellow Jacket Brochure", Foundation Technologies, Inc., retrieved 2017-04-28
  6. ^ "Mechanically Stabilized Earth Walls And Reinforced Soil Slopes: Design & Construction Guidelines" (PDF). FHWA. March 2001. Retrieved 2007-08-27.
  7. ^ Jones, Colin J F P (2013). Earth Reinforcement and Soil Structures. Elsevier. p. 379. ISBN 978-1-4831-0446-1.
Alberta Highway 8

Alberta Provincial Highway No. 8, commonly referred to as Highway 8, is a highway in Southern Alberta that connects Highway 22 in Rocky View County just north of Redwood Meadows to Deerfoot Trail (Highway 2) in Calgary. In Rocky View County, the highway initially parallels the Elbow River before entering Calgary where it becomes a heavily travelled expressway known as Glenmore Trail, named after the reservoir which it crosses. Glenmore Trail is a busy freeway between Richard Street in southwest Calgary to Ogden Road in the southeast, carrying nearly 160,000 vehicles per weekday at its busiest point placing it second only to Deerfoot Trail as the busiest road in Western Canada. East of Deerfoot Trail, Glenmore Trail continues east providing a key link to Stoney Trail, after which traffic levels decrease and it becomes Highway 560 en route to Langdon.

Borehole

A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water, other liquids (such as petroleum) or gases (such as natural gas), as part of a geotechnical investigation, environmental site assessment, mineral exploration, temperature measurement, as a pilot hole for installing piers or underground utilities, for geothermal installations, or for underground storage of unwanted substances, e.g. in carbon capture and storage.

Clay

Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz (SiO2), metal oxides (Al2O3 , MgO etc.) and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, and become hard, brittle and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red.

Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. There is, however, some overlap in particle size and other physical properties. The distinction between silt and clay varies by discipline. Geologists and soil scientists usually consider the separation to occur at a particle size of 2 µm (clays being finer than silts), sedimentologists often use 4–5 μm, and colloid chemists use 1 μm. Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg limits. ISO 14688 grades clay particles as being smaller than 2 μm and silt particles as being larger.

Mixtures of sand, silt and less than 40% clay are called loam. Loam makes good soil and is used as a building material.

Earth structure

An earth structure is a building or other structure made largely from soil. Since soil is a widely available material, it has been used in construction since prehistoric times.

It may be combined with other materials, compressed and/or baked to add strength.

Soil is still an economical material for many applications, and may have low environmental impact both during and after construction.

Earth structure materials may be as simple as mud, or mud mixed with straw to make cob. Sturdy dwellings may be also built from sod or turf. Soil may be stabilized by the addition of lime or cement, and may be compacted into rammed earth. Construction is faster with pre-formed adobe or mudbricks, compressed earth blocks, earthbags or fired clay bricks.Types of earth structure include earth shelters, where a dwelling is wholly or partly embedded in the ground or encased in soil. Native American earth lodges are examples. Wattle and daub houses use a "wattle" of poles interwoven with sticks to provide stability for mud walls. Sod houses were built on the northwest coast of Europe, and later by European settlers on the North American prairies. Adobe or mud-brick buildings are built around the world and include houses, apartment buildings, mosques and churches. Fujian Tulous are large fortified rammed earth buildings in southeastern China that shelter as many as 80 families. Other types of earth structure include mounds and pyramids used for religious purposes, levees, mechanically stabilized earth retaining walls, forts, trenches and embankment dams.

Geologic hazards

A geologic hazard is one of several types of adverse geologic conditions capable of causing damage or loss of property and life. These hazards consist of sudden phenomena and slow phenomena:

Sudden phenomena include:

avalanches (snow, rock, or air & snow) and its runout

earthquakes and earthquake-triggered phenomena such as tsunamis

forest fires (espec. in Mediterranean areas) leading to deforestation

geomagnetic storms

ice jams (Eisstoß) on rivers or glacial lake outburst floods below a glacier

landslide (lateral displacement of earth materials on a slope or hillside)

mudflows (avalanche-like muddy flow of soft/wet soil and sediment materials, narrow landslides)

pyroclastic flows

rock falls, rock slides, (rock avalanche) and debris flows

torrents (flash floods, rapid floods or heavy current creeks with irregular course)

volcanic eruptions, lahars and ash falls.Gradual or slow phenomena include:

alluvial fans (e.g. at the exit of canyons or side valleys)

caldera development (volcanoes)

geyser deposits

ground settlement due to consolidation of compressible soils or due to collapseable soils (see also compaction)

ground subsidence, sags and sinkholes

liquefaction (settlement of the ground in areas underlain by loose saturated sand/silt during an earthquake event)

sand dune migration

shoreline and stream erosion

thermal springsSometime the hazard is instigated by man through the careless location of developments or construction in which the conditions were not taken into account.

Gravel

Gravel is a loose aggregation of rock fragments. Gravel is classified by particle size range and includes size classes from granule- to boulder-sized fragments. In the Udden-Wentworth scale gravel is categorized into granular gravel (2 to 4 mm or 0.079 to 0.157 in) and pebble gravel (4 to 64 mm or 0.2 to 2.5 in). ISO 14688 grades gravels as fine, medium, and coarse with ranges 2 mm to 6.3 mm to 20 mm to 63 mm. One cubic metre of gravel typically weighs about 1,800 kg (or a cubic yard weighs about 3,000 pounds).

Gravel is an important commercial product, with a number of applications. Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or asphalt; Russia alone has over 400,000 km (250,000 mi) of gravel roads. Both sand and small gravel are also important for the manufacture of concrete.

Henri Vidal (engineer)

Henri Vidal (b 1924 in Draguignan) is a French civil engineer, known for the invention, in 1963 of Terre Armée or reinforced earth also known as Mechanically stabilized earth.

Vidal entered the École Polytechnique in 1944 and graduated from the École Nationale des Ponts et Chaussées in 1949. Vidal had the hope of becoming an architect, and so he enrolled at the fine arts school, École des Beaux-Arts de Paris while continuing to work as an engineer in the maintenance department Électricité de France.After graduating from the École des Beaux-Arts de Paris in 1961, he opened an architectural practice the same year, while continuing to work as an engineer at Fougerolles. As an architect, he collaborated with Yves Bayard to design the Musée d'art moderne et d'art contemporain in Nice.After five years of establishing the theory for his process and of experiments on scale models, he filed the patent for reinforced earth in 1963.

Natchez silt loam

In 1988, the Professional Soil Classifiers Association of Mississippi selected Natchez silt loam soil to represent the soil resources of the State. These soils exist on 171,559 acres (0.56% of state) of landscape in Mississippi.

Permeability (earth sciences)

Permeability in fluid mechanics and the earth sciences (commonly symbolized as k) is a measure of the ability of a porous material (often, a rock or an unconsolidated material) to allow fluids to pass through it.

The permeability of a medium is related to the porosity, but also to the shapes of the pores in the medium and their level of connectedness.

Response spectrum

A response spectrum is a plot of the peak or steady-state response (displacement, velocity or acceleration) of a series of oscillators of varying natural frequency, that are forced into motion by the same base vibration or shock. The resulting plot can then be used to pick off the response of any linear system, given its natural frequency of oscillation. One such use is in assessing the peak response of buildings to earthquakes. The science of strong ground motion may use some values from the ground response spectrum (calculated from recordings of surface ground motion from seismographs) for correlation with seismic damage.

If the input used in calculating a response spectrum is steady-state periodic, then the steady-state result is recorded. Damping must be present, or else the response will be infinite. For transient input (such as seismic ground motion), the peak response is reported. Some level of damping is generally assumed, but a value will be obtained even with no damping.

Response spectra can also be used in assessing the response of linear systems with multiple modes of oscillation (multi-degree of freedom systems), although they are only accurate for low levels of damping. Modal analysis is performed to identify the modes, and the response in that mode can be picked from the response spectrum. These peak responses are then combined to estimate a total response. A typical combination method is the square root of the sum of the squares (SRSS) if the modal frequencies are not close. The result is typically different from that which would be calculated directly from an input, since phase information is lost in the process of generating the response spectrum.

The main limitation of response spectra is that they are only universally applicable for linear systems. Response spectra can be generated for non-linear systems, but are only applicable to systems with the same non-linearity, although attempts have been made to develop non-linear seismic design spectra with wider structural application. The results of this cannot be directly combined for multi-mode response.

Retaining wall

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 or a bulkhead.

Seismoelectrical method

The seismoelectrical method (which is different from the electroseismic physical principle) is based on the generation of electromagnetic fields in soils and rocks by seismic waves. This technique is still under development and in the future it may have applications like detecting and characterizing fluids in the underground by their electrical properties, among others, usually related to fluids (porosity, transmissivity, physical properties).

Silt

Silt is granular material of a size between sand and clay, whose mineral origin is quartz and feldspar. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water (also known as a suspended load) and soil in a body of water such as a river. It may also exist as soil deposited at the bottom of a water body, like mudflows from landslides. Silt has a moderate specific area with a typically non-sticky, plastic feel. Silt usually has a floury feel when dry, and a slippery feel when wet. Silt can be visually observed with a hand lens, exhibiting a sparkly appearance. It also can be felt by the tongue as granular when placed on the front teeth (even when mixed with clay particles).

Specific storage

In the field of hydrogeology, storage properties are physical properties that characterize the capacity of an aquifer to release groundwater. These properties are storativity (S), specific storage (Ss) and specific yield (Sy).

They are often determined using some combination of field tests (e.g., aquifer tests) and laboratory tests on aquifer material samples. Recently, these properties have been also determined using remote sensing data derived from Interferometric synthetic-aperture radar.

SuperRedTan Interchange

The SuperRedTan Interchange is a symmetrical four-level freeway interchange in eastern Mesa, Arizona. Completed in 2007, the interchange provides access between U.S. Route 60 and Loop 202. It is fully directional, meaning that a motorist traveling towards the interchange in any direction can exit onto either direction of the intersecting freeway. The interchange is said to be the first in the Valley of the Sun to include design icons on the support columns in addition to the retaining walls. There are no HOV connections at this time, although they are planned in the future.

Thixotropy

Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick or viscous under static conditions will flow (become thin, less viscous) over time when shaken, agitated, sheared or otherwise stressed (time dependent viscosity). They then take a fixed time to return to a more viscous state.

Some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity; the longer the fluid undergoes shear stress, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a steep change in shear rate. Some thixotropic fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others such as yogurt take much longer and can become nearly solid. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Thixotropy arises because particles or structured solutes require time to organize. An excellent overview of thixotropy has been provided by Mewis and Wagner.Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Fluids which exhibit this property are sometimes called rheopectic. Anti-thixotropic fluids are less well documented than thixotropic fluids.

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, or ditch), and narrow compared with its length (as opposed to a simple hole).In geology, trenches are created as a result of erosion by rivers or by geological movement of tectonic plates. In the civil engineering field, trenches are often created to install underground infrastructure or utilities (such as gas mains, water mains or telephone lines), or later to access these installations. Trenches have also often been dug for military defensive purposes. In archaeology, the "trench method" is used for searching and excavating ancient ruins or to dig into strata of sedimented material.

Void ratio

The void ratio of a mixture is the ratio of the volume of voids to volume of solids.

It is a dimensionless quantity in materials science, and is closely related to porosity as follows:

and

where is void ratio, is porosity, VV is the volume of void-space (such as fluids), VS is the volume of solids, and VT is the total or bulk volume. This figure is relevant in composites, in mining (particular with regard to the properties of tailings), and in soil science. In geotechnical engineering, it is considered as one of the state variables of soils and represented by the symbol e.

Note that in geotechnical engineering, the symbol usually represents the angle of shearing resistance, a shear strength (soil) parameter. Because of this, the equation is usually rewritten using for porosity:

and

where is void ratio, is porosity, VV is the volume of void-space (air and water), VS is the volume of solids, and VT is the total or bulk volume.

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