No. 10 of 19Reinforced Soil - Vertical Retaining Walls byColin Jones University of Newcastle upon Tyne

The information presented in this document has been reviewed by the Education Committee of the International Geosynthetics Society and is believed to fairly represent the current state of practice.

However, the International Geosynthetics Society does not accept any liability arising in any way from use of the information presented.

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Basic Principles : Reinforced SoilSoil is strong in compression (when confined) but weak in tension

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19.bin

Soil is strong in compression (when confined) but weak in tension. Resistance to tensile strain in the soil can be provided by reinforcement. The interaction between the reinforcement and the soil is by friction or interlock (in case of grids).

Basic Principles of Reinforced SoilResistance to tensile strain can be provided by reinforcement

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20.bin

When soil and the reinforcement are effectively connected, the strain in the soil is the same as the strain in the reinforcement, providing a classic example of strain compatibility.

Basic Principles of Reinforced SoilInteraction between reinforcement and soil is by friction or mechanical interlock

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21.bin

Strain compatibility is a fundamental concept; when applied to reinforce soil it implies that the stiffness of the reinforcement influences the strain in the reinforced soil and also that the properties of the soil and the stress state of the soil influence the behaviour, Jones (1996).

Basic Principles of Reinforced SoilFor reinforced soil to work, the soil and reinforcement must STRAINIn a stable structure the strain in the soil and reinforcement are equal (i.e. there is strain compatibility)The strain in the reinforced soil is influenced by:

The stiffness of the reinforcementProperties of the soilThe stress state of the soil

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Why Construct Reinforced Soil Walls?They are economic and offer technological benefits

University of NewcastleReinforced soil provides technical and economic benefits.

Why Construct Reinforced Soil Walls?They can be constructed on poor/weak foundations or in difficult terrain

University of NewcastleFrom a technical aspect reinforced soil walls produce solutions which are not possible in other modes/materials and also produce more economical solutions to conventional structures, both with regard to materials and labour.

Why Construct Reinforced Soil Walls?Reinforced soil structures are fully compatible with modern design philosophies such as integral bridges

Reinforced soil walls can withstand earthquakes

University of NewcastleReinforced soil is particularly beneficial for structures constructed on poor/weak foundations which would require piled foundations or some other method to improve the bearing capacity of the soil. Reinforced soil structures are fully compatible with modern design philosophies, for example reinforced soil abutments are regularly used in the design of integral bridges.

Reinforced soil walls have been shown to be particularly suitable for construction in seismic regions, notably the Kobe earthquake in Japan and the 1996 earthquake in California.

Types of StructureReinforced soil walls are defined as vertical structures if they are steeper than 80. They are used to form:

University of NewcastleReinforced soil walls are defined as vertical structures if they are steeper than 80o. They are used for all forms of structures including:

Types of StructureConventional retaining walls

University of NewcastleConventional retaining walls

Types of StructureWalls in difficult terrain

University of NewcastleRetaining structures in difficult terrain (on steep slopes) or to construct terraces

Types of StructureBridge abutments

University of NewcastleBridge abutments

Types of StructureTemporary works

University of NewcastleIndustrial structures including temporary works

Types of StructureIndustrial structures

University of NewcastleEnhancing/improving existing infrastructure

(i.e. widening railway embankments without the need for additional land)

Main Elements of Reinforced Soil WallsReinforced soil walls consist of three main elements:

SoilReinforcementFacing

University of NewcastleReinforced soil retaining walls consist of three main elements:

soil, reinforcement and facing

The nature of the soil used influences the behaviour of the wall.

A wide range of fill can be used although fine grained purely cohesive material is not usually used in vertical structures. Good cohesionless soil with a high shearing resistance () will produce a very stable structure.

Main Elements of Reinforced Soil WallsA wide range of soil/fill can be used. The ideal fill is a cohesionless material with a high shearing resistance

University of NewcastleGeosynthetic reinforcement is available in a range of forms including strips, grids and sheets. Most geosynthetic reinforcements are proprietary products which have been subjected to extensive testing. A number have been awarded certificates by

Main Elements of Reinforced Soil WallsReinforcement can take a number of forms including:

University of Newcastleinternational/national testing agencies (i.e. Agrment Board in UK, BAM in Germany).

A facing is required with vertical reinforced soil retaining walls. The facing can take a number of forms, ranging from elemental, modular or full height. Facings are a key element in the appearance of the structure and aesthetic considerations are an important feature of modern reinforced soil walls.

Main Elements of Reinforced Soil WallsStrips

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Main Elements of Reinforced Soil WallsGrids

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Main Elements of Reinforced Soil WallsSheets

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Main Elements of Reinforced Soil WallsAnchors

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Design of Reinforced Soil WallsWalls are designed to produce stability against:

An ultimate limit stateA serviceability limit state

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Design of Reinforced Soil WallsFailure mechanisms of reinforced soil can be identified as limit modes covering:

(a)Sliding failure(b)Bearing failure(c)Reinforcement rupture(d)Reinforcement pullout(e)Slip/wedge failure(f)Rotation and settlement

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Construction of Reinforced Soil WallsA basic property of reinforced soil is that some strain must occur before the soil and the reinforcement can interactAll reinforced soil structures move (strain) during construction and construction techniques reflect this flexibility

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Construction of Reinforced Soil WallsThere are three construction techniques:

Wraparound (concertina)Elemental (telescopic)Full height (sliding)

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Main Elements of Reinforced Soil Walls : Concertina

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Main Elements of Reinforced Soil Walls

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Main Elements of Reinforced Soil Walls : Sliding

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ConstructionConstruction of a reinforced soil structure is a sequential operation:

Construction is always at ground levelConstruction is in lifts; the fill is usually placed in 300 mm layers and compacted

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ConstructionCompaction of the fill is essential. Without compaction the strain of the structure may be excessive and the reinforcement forces may increase

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ConstructionReinforcement is laid on compacted fill and loose fill placed on top (no construction plant should run over the reinforcement)

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FacingA wide range of facings are available. They must be structurally adequate, durable and have aesthetic appeal. Different forms include:

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Facingsoft facing

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Facingfull height units

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23.bin

Facingelemental units

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ConclusionReinforced soil retaining walls are technologically advanced structures which are robust and economic. They are simple to construct even in difficult terrain and can provide alternative solutions in a wide range of applications.

University of Newcastle

Soil is strong in compression (when confined) but weak in tension. Resistance to tensile strain in the soil can be provided by reinforcement. The interaction between the reinforcement and the soil is by friction or interlock (in case of grids).When soil and the reinforcement are effectively connected, the strain in the soil is the same as the strain in the reinforcement, providing a classic example of strain compatibility.Strain compatibility is a fundamental concept; when applied to reinforce soil it implies that the stiffness of the reinforcement influences the strain in the reinforced soil and also that the properties of the soil and the stress state of the soil influence the behaviour, Jones (1996).

Reinforced soil provides technical and economic benefits.From a technical aspect reinforced soil walls produce solutions which are not possible in other modes/materials and also produce more economical solutions to conventional structures, both with regard to materials and labour.Reinforced soil is particularly beneficial for structures constructed on poor/weak foundations which would require piled foundations or some other method to improve the bearing capacity of the soil. Reinforced soil structures are fully compatible with modern design philosophies, for example reinforced soil abutments are regularly used in the design of integral bridges.

Reinforced soil walls have been shown to be particularly suitable for construction in seismic regions, notably the Kobe earthquake in Japan and the 1996 earthquake in California.Reinforced soil walls are defined as vertical structures if they are steeper than 80o. They are used for all forms of structures including:Conventional retaining walls

Retaining structures in difficult terrain (on steep slopes) or to construct terraces

Bridge abutments

Industrial structures including temporary works

Enhancing/improving existing infrastructure

(i.e. widening railway embankments without the need for additional land)

Reinforced soil retaining walls consist of three main elements:

soil, reinforcement and facing

The nature of the soil used influences the behaviour of the wall.

A wide range of fill can be used although fine grained purely cohesive material is not usually used in vertical structures. Good cohesionless soil with a high shearing resistance () will produce a very stable structure.

Geosynthetic reinforcement is available in a range of forms including strips, grids and sheets. Most geosynthetic reinforcements are proprietary products which have been subjected to extensive testing. A number have been awarded certificates byinternational/national testing agencies (i.e. Agrment Board in UK, BAM in Germany).

A facing is required with vertical reinforced soil retaining walls. The facing can take a number of forms, ranging from elemental, modular or full height. Facings are a key element in the appearance of the structure and aesthetic considerations are an important feature of modern reinforced soil walls.