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The two types of wall (bolted and berlinese) are built to retain soil from excavation, and possibly provide a sealing and foundations for a structure.
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In this technique, parts of the retaining wall (soldier piles, cast-in-place or precast columns) taking the passive earth pressure (at the toe) and the active earth pressure (multiple tie-backs or struts) are built before excavation commences.
When these are in place, excavation proceeds in stages (one to a few metres deep, depending on the stand-up time of the soil). Struts or ground anchors are immediately installed on the soldiers previously built, and sheeting is placed against the exposed soil faces.
Several stages of excavation may be necessary (there are cases of six rows of tie-backs). The sheeting spanning between the soldiers may be made of precast concrete slabs, wood timbers, steel beams or shotcrete.
The generic name of Berlin wall comes from the fact that the technique has been widely used in that city. There, the soldiers were steel beams, usually installed in boreholes a few metres apart. The system was mostly used as a temporary support of excavations.
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Berliner walls
Definition:
consistent wall of::
profiled vertical (piles or metal section)
wood shielding, prédalles or shotcrete
Characteristics:
only retained ground
only possible if the water level is lower than the level of earthwork
ground must have temporary cohesion to excavate and place the shielding.
without anchoring, displacement at the head considerable (plusieures cm) necessary pourque the passive resistance is formed.
possible ground excavation depending on the technique
Scope of application:
ground reserve (without sheet of water on the height of excavation
economic solution
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The soldier pile wall is a temporary or permanent retaining wall commonly
used for excavations in urban areas.
The method consists of :
Drilling regularly spaced boreholes in which metal beams are sunk
Installing cladding (wood, shotcrete, steel plates) between the beams as the excavation
progresses
The stability of the retaining wall is temporarily provided by struts or anchors except in shallow
excavations where the wall may be self-supporting.
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Diaphragm walls are walls produced in soil with so-called cast-in-place concrete, which can reach high depths. The walls are built with a low noise and vibration method; its thickness depends on the structural usage and the equipment used. Diaphragm walls have small deformations, and are therefore mainly used in inner-city foundations as retaining wall. Due to their relatively high water tightness they are also suitable as external wall for the future structure. In special cases, individual diaphragm wall elements are applied for foundations.
Cut-off walls seal dams and retain landfill sites, tank storages or other industrial plants that may jeopardize the ground water.
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Drainage is often a satisfactory solution for stabilizing landslides.
It is usually done by digging a network of ditches or by drilling drain-holes.
Drainage ditches have the advantage that they systematically capture every single ingress of water but they are limited to a few metres depth.
Sub-horizontal drains capture incidental arrivals of water but in a random manner.
The drainage trench using biodegradable mud and placed upstream or in a landslide provides continuous capture, like the classic drainage trench, but at larger depth (deeper than 20 m on some civil works completed as of today).
The traditional drainage trench is constructed by excavating and backfilling with gravel successive panel elements which are connected together as the site moves onward. To achieve this, a temporary shuttering is placed at the end of Panel N when excavation is completed, enabling the filling of Panel N. This is then used to retain Panel N while Panel N + 1 is excavated.
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Trench Grates
The Webforge range of AS3996 strength class compliant fabricated trench grates provides the following benefits:
- Extended life from hot dip galvanising.
-High hydraulic efficiencies due to maximum waterway created by narrow load bars.
- Bicycle and pedestrian safety due to cross rods at 100mm centres.
- Simple speedy installation as the 2m long torsionally rigid frame can be cast in with grates removed.
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Keller Ground Engineering offers the widest range of anchorage systems available in the UK. As one of the world's leading ground anchorage contractors, Keller has unrivalled experience in designing and installing anchorage systems for a wide variety of construction projects, including dams, ports and harbours, deep basements, roads and bridges, slope stabilisation schemes etc.
Through innovative engineering, Keller has developed installation techniques and systems to enhance the available frictional and cohesive capacity of the soil. This ensures that the anchorages installed are not only extremely efficient in utilising ground strength, but also provide an economic solution. This applies to most ground conditions from granular soils through mixed to cohesive soils and in all rock types.
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The MANTA RAY ® anchoring range was designed for use in places where great strength is needed.
MANTA RAY ® devices are currently being used in civil engineering, military engineering, sub-marine operations, etc.
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The STING RAY ® anchoring range was designed for use in places where great strength is needed or in soils whose retention capacity.
STING RAY ® devices are currently being used in civil engineering, military engineering, sub-marine operations, etc.
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Tie rods are structural elements undergoing traction and suitable for conveying loads to soil depths.
Tie rods are made of an active part, the bond length, and a passive part, that transfers the stresses from the anchoring head placed on the anchor wall to the soil. Tie rods can be grouted either by low pressure or by high pressure, while, with reference to their duration in time, they can be divided into temporary and permanent tie rods.
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Ground anchors are structural elements where a grout body is produced in the subsoil by injecting grouting mortar around the rear part of a steel tendon. The grout body is connected by way of the steel tendon and the anchor head to the structure or the rock section to be anchored.
Any load to be taken up by the grouted anchor is passed into the subsoil not over the entire length of the anchor but only in the area of the grout body. The steel tendon section where the anchor is free to expand is the free tendon length.
It acts like a spring which can be pretensioned to the structure against the subsoil. Grouted anchors are subjected to tension only. Their load capacity is checked by pre-tensioning.
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Definition:
an axial element is placed in a seal and borehole in the ground by injection. By friction the load is transmitted towards the ground. The ties are pressurized, the nails are passive.
Characteristics:
strands of prestressed or bars of steel or lost borehole tubes: section and characteristic of steel are determined by the fourniceurs (EP Diwidag, Ischebeck, Fressinet)
provisional and final ties (different protector from corrosion)
gravitating injection, IGU (injection total to unitair) and IRS (injection repetitive and selective)
possibility of exécutioncomplètement dismountable
give the responsability max to be taken again is determined by the characteristic of ground and the type of injection (gravitating, IGU, IRS)
Scope of application:
reserve of pressure earth and water, macadam binding
resumption of the tractive efforts on the constructions requested by the water uplift
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Earth or rock anchors generally consist of steel elements (bars or strands) grouted in a drilled hole. The bars or strands are subsequently tensioned. This provides lateral or vertical force to resist movement of a retaining structure. Anchors are often used for excavation support, or as a part of permanent retaining walls, or to resist up-lift forces on foundations. Rembco uses rock anchors to stabilize slopes and walls, provide tiebacks for bridges, stabilize dams, and secure caisson bottoms.
Anchors and bolts can have very high load capacities. over 25 years, Rembco has installed many different sizes and lengths. The largest had a working load of 1,000 kips.
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Ground anchors have been used for years in civil engineering works to ensure the stability of embankment sheet pile walls.
The first bored and pre-stressed ground anchors, however, only appeared some fifty years ago.
The ground anchor is a tensioned device used to stabilise the
construction to which it is fixed in loose or rocky soil.
The pre-stressed anchor rod combines two totally different specialties :
-geological knowledge of the ground
-pre-stressing of the steel
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Definition:
reinforcement of the cut ground progressively of its excavation by the installation of passive bars. To prevent that the ground does not run out between the bars a facing generally made up one places of a treuillis and a shotcrete
Characteristics:
excavation in phases (1 with 1.5m excavation, installation of the nails, shotcrete, excavation 1 with 1.5m, installation of the nails, etc)
displacement minimal at the head of the wall is equal to 2promille height of the maximum excavation. Displacement is inevitable to introduce friction into the passive nails.
without vibrations
method calculated like wall of weight (standard "Clouterre")
Scope of application:
reinforcement of the existing taluds
realization of the higher and/or stiffer slopes
limited to the sites except ground water
unusable in grounds non-cohesive short-term
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The nailed retaining wall is the archetype of light, flexible shoring combined with the terrain.
This shoring relies essentially on the stabilising capacity of the nails combined with a containment skin in shotcrete.
Excavation is performed in successive top down stages with immediate implementation of the nails and shotcrete.
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A ground anchor transmits the tensile forces applied to it to a competent stratum.
It consists of three parts:
- The head, transmitting the anchor force to the structure via the bearing plate.
- The free length of tendon, from the head to the near end of the anchorage.
- The grouted anchorage, which is the length of tendon by which the tensile force is transmitted to the surrounding ground through the intermediary of the grout.
There are "active" and "passive" soil anchors:
A passive soil anchor is tensioned as the structure itself applies load to it. It does not usually have a free length of tendon (it is grouted over its whole length).
An active soil anchor is pretensioned before it takes up the load, which is a means of limiting deformation.
Anchor capacity ranges from a few tonnes to 1,500 tonnes. The usual range is 20-200 tonnes.
Overall length is specific to each project, ranging from 10 to more than 60 metres. They are commonly 15-25 metres long.
Tendons are usually of the type used in structural prestressing, or similar.
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Definition:
walls in piles either independent, or tangent, or secant.
The piles can be installed according to the techniques following:
piles independent: all techniques
piles tangent: CFA, GCV, GCV lambda, drilled piles of large diameter, piles double rotation
secant piles: drilled piles of large diameter, piles doubles rotation
Characteristics:
piles independent and tangent: only retained ground. Level of water must be lower than the level of excavation
secant piles: reserve of water and grounds
secant piles: traditionally only one pile out of two is armed (pious sécundaires)
considerable bearing load
no the horizontal reinforcement, it is necessary to envisage a beam of distribution
Scope of application:
when should be crossed obstacles (masoneries, rocks, concrete)
excavations of irregular size (walls in piles are more adaptable than slurry trench walls)
excavations of limited size.
cilindric rigidity in excavations circular limits the quantity of steel
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The name refers to a cast in place wall, excavated with conventional equipment under bentonite slurry. Subsequent concreting is done with a deformable, watertight, plastic concrete, composed of 100-200 kg/m3 cement, 1,800-2,000 kg/m3 well graded aggregate and 30-40 kg/m3 bentonite. Typical wall thickness is 0.6 m. Installation is done by alternate panels and stop-end tubes are used.
This method allows to install very deep walls (50 m or more), but for very large depths, wall thickness should be increased to 1 or 1.2 m in order to reduce the risk of gaps near panel joints which may be caused by deviations.
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Special foundations: slurry-trenches, ground anchors...
