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PageSubject

االهداء2

3introduction

4Definition of retaining walls

4Function of retaining walls

4Angle of repose

5Types of retaining walls

5Typical dimentions of different types of retaining

walls

6Retaining walls terminology

7Detailed explanation of the types of retaining walls

14Provisions for Joints in the Construction of Walls

15Drainage system of retaining walls

16Factors and considerations in the design of retaining

walls

16Forces acting on a retaining wall

19stability of retaining walls

23case study 1

26case study 2

27References

اهداء إلى من أضاء بعلمه عقل غيره

 أو بدد بالجواب الصحيح حيرة سائليه

 فأظهر بسماحته تواضع العلماء

وبرحابته سماحة العارفين

نتقدم نحن الطالب : حسين االسطة , ماهر عطاونة و عبد السالم قباجة... بأهداء هذا العمل المتواضع الى الدكتور نبيل الجوالني

متمنين من الله ان نكون حققنا الهدف المرجو من هذا البحث ... من... معلموات بحثية وخطوات بحث علمي

شاكرين له حسن التعاون وعدم البخل في مد يد المساعدة

Introduction

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When we choose retaining walls to be our project in foundation foundation engineering course we choose it because of its importance in construction world ,,, and it is very interesting topic

In this project we will talk about some important parts of retaining walls ,We will start from definition , Function of retaining walls , Angle of repose , Types of retaining walls , Typical dimentions of different types of retaining walls , Retaining walls terminology , Detailed explanation of the types of retaining walls , Provisions for Joints in the Construction of Walls , Drainage system of retaining walls , Factors and considerations in the design of retaining walls , Forces acting on a retaining wall , stability of retaining walls

At the end of project we will take two case study about retaining walls

Retaining walls

• What is the retaining walls ?

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 of the

soil .

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•what is the Function of retaining wall ?

The basic function of a retaining wall is to retain soil at a slope which is greater than it would normally assume , The natural slope taken up by any soil is called its angle of repose .

• what is the angle of repose ?

The natural slope taken up by any soil is called its angle of repose and is measured in relation ship to the horizontal , it is the wedge of soil resting on this upper plane of the angle of repose which a retaining wall has to support .

• types of retaining walls

There’s many types of retaining walls every one has a different structure from others …

And there’s the types

1. Gravity retaining wall2. Cantilevered retaining wall3. Counterfort retaining wall4. Precast concrete retaining wall5. Precast concrete crib retaining wall6. Sheet pile wall

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• Typical dimentions of different types of retaining walls

• Retaining walls terminology

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Surcharge : any loading from above the soil line upon earth being supported by a retaining wall

Rear face : Side of the retaining wall which is in the direction of the soil

Front face : Side of the retaining wall which is in opposite direction of the soil

Stem : the inner part of retaining wall Battered face : the sloped face of retaining wall

Retained earth : the earth which retained on retaining wall

Straight or vertical face : the outer part of retaining wall which is in the free

Drainage hole : hole which mad ein the retaining wall to drain water

• Detailed explanation of the types of retaining walls

I. Gravity retaining wall

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Gravity retaining walls depend on their own weight and any soil resting on the concrete in resisting lateral earth forces. They are generally economical up to 10 feet in height for cast concrete structures. Usually are sufficiently massive to be unreinforced. Monolithic cast walls are generally formed on site. and specialized form of gravity walls is a semi-gravity retaining wall. These have some tension reinforcing steel included so as to minimize the thickness of the wall without requiring extensive reinforcement. They are a blend of the gravity wall and the cantilever wall designs

II. Cantilevered retaining wall

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Cantilever retaining walls are constructed of reinforced concrete. They consist of a relatively thin stem and a base slab. The base is also divided into two parts, the heel and toe. The heel is the part of the base under the backfill.The toe is the other part of the base Use much less concrete than monolithic gravity walls, but require more design and careful construction. Generally economical up to about 25 ft. in height. Can be precast in a factory or formed on site.

III. Counterfort retaining wall

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Counterfort retaining walls are similar to cantilever walls except they have thin vertical concrete webs at regular intervals along the backside of the wall. These webs are known as counterforts the counterforts tie the slab and base together, and the purpose of them is to reduce the shear forces and bending moments imposed on the wall by the soil. A secondary effect is to increase the weight of the wall from the added concrete. Can be precast or formed on site. Counterfort retaining walls are more economical than cantilever walls for heights above 25 ft.

IV. Precast concrete retaining wall

It has four types …

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Bolt down Quick to install and extremely stable, these precast retaining walls are bolted to a concrete foundation slab and require no additional fixing or support. This makes them ideal for situations in which there is no framework.

Cast in These L-shaped walls are manufactured with reinforcement bar protruding from the toe of the unit so they can be incorporated into the concrete floor slab. This will achieve a retaining wall structure but there is no toe above ground: ideal for storage bays where buckets and machinery are being used.

Heavy duty Our bolt down and cast in precast walls are ideal for most projects. However, some jobs come along that require a higher

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specification. This is when we recommend our heavy duty retaining wall which has been designed to reach 4000mm in height and cope with excessive loads and additional surcharges. They can be manufactured with a variety of reinforcement patterns and tend to be a more cost-effective solution than casting a wall on site.

Freestanding These units are ideal for a wide range of industries, offering an adaptable option for grain stores, recycling centres and slurry stores to name a few. With built in recesses for forklifting, they’re ideal for creating adjustable storage bays without the need for foundation work.

V. Precast concrete crib retaining wall

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CONCRIB Retaining Walls are low cost, of open web construction and can be quickly and inexpensively erected. They can be used almost anywhere a retaining wall is needed – driveways, building sites, garden areas, and when planted out will add beauty and value to your property they are gravity retaining walls constructed from interlocking precast concrete components, filled with free draining material and earth backfill, eliminating the hazards of hydrostatic pressure building up behind the wall.

VI. Sheet pile wall

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Sheet piling is an earth retention and excavation support technique that retains soil, using steel sheet sections with interlocking edges. Sheet piles are installed in sequence to design depth along the planned excavation perimeter or seawall alignment. The interlocked sheet piles form a wall for permanent or temporary lateral earth support with reduced groundwater inflow. Anchors can be included to provide additional lateral support if required

Sheet pile walls have been used to support excavations for below grade parking structures, basements, pump houses, and foundations, construct cofferdams, and to construct seawalls and bulkheads. Permanent steel sheet piles are designed to provide a long service life.

Vibratory hammers are used to install sheet piles. If soils are too hard or dense, an impact hammer can be used to complete the installation. At certain sites where vibrations are a concern, the sheets can be hydraulically pushed into the ground

Sheet piles are also a sustainable option since recycled steel is used in their construction, and the piles can often be reused.

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• Provisions for Joints in the Construction of Walls

Cast concrete retaining walls may be constructed with any or all of the following joints:

Construction Joints:

These are vertical or horizontal joints that are used between two successive pours of concrete. Keys are used to increase the shear resistance at the joint. If keys are not used, the surface of the first pour is cleaned and roughened before the next placement of concrete. Keys are almost always formed in the base to give the stem added sliding resistance. The base is formed first, and the stem constructed afterwards

Contraction Joints:

These are vertical joints or grooves formed or cut into the wall that allows the concrete to shrink without noticeable harm. Contraction joints are usually about 0.25 inches wide and about ½ to ¾ inch deep, and are provided at intervals of not exceeding 30 feet.

Expansion Joints:

Vertical expansion joints are incorporated into the wall to account for expansion due to temperature changes. These joints may be filled with flexible joint fillers. Greased steel dowels are often cast horizontally into the wall to tie adjacent sections together. Expansion joints should be located at intervals up to 90 feet.

• Drainage system of retaining walls

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Backfill Drainage of Retaining Walls

One area that can be commonly overlooked, or at least underestimated, is the necessity to drain the backfill of rainwater and/or groundwater. Hydrostatic pressure can cause or induce retaining wall failure, or at least damage.     Drainage of water as a result of rainfall or other wet conditions is very important to the stability of a retaining wall. Without proper drainage the backfill can become saturated, which has the dual impact of increasing the pressure on the wall and lessening the resistance of the backfill material to sliding. Granular backfill material offers the benefits of good drainage, easy compaction, and increased sliding resistance.

Drainage systems usually utilize weep holes and drainage lines.

  Weep holes actually penetrate the retaining wall and drain the area immediately behind the wall. Weep holes should have a minimum diameter so as to permit free drainage; for large walls, 4 inch weep holes are common. Adequate spacing between weep holes allows uniform drainage from behind the wall. Weep holes should always have some kind of filter material between the wall and the backfill to prevent fines migration, weep hole clogging, and loss of backfill and caving. Drainage lines are often perforated and wrapped in geo textile or buried in a granular filter bed, and serve to carry water to the weep holes from areas deeper within the backfill.

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• Factors and considerations in the design of retaining walls could be :

Nature & type of soil Height of water table Subsoil water movements Type of wall Material used in the construction of the wall

•Forces acting on a retaining wall : The designer is mainly concerned with the effect of two forms of earth pressure- active & passive , and there is a third type of pressure it called pressure at rest this type will not affect the retaining wall .

1. Pressure at rest : When the soil behind the wall is prevented from lateral movement (towards or away from soil) of wall, the pressure is known as earth pressure at rest this is the case when wall has a considerable rigidity Basement walls generally fall in this category.

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2. Active earth pressure :

If a retaining wall is allowed to move away from the soil accompanied by a lateral soil expansion, the earth pressure decreases with the increasing expansion a shear failure of the soil is resulted with any further expansion and a sliding wedge tends to move forward and downward. The earth pressure associated with this state of failure is the minimum pressure and is known as active earth pressure.

3. Passive earth pressure

If a retaining wall is allowed to move towards the soil accompanied by a lateral soil compression, the earth pressure increases with the increasing compression in the soil.

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• diagrams of forces acting on a retaining wall

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• stability of retaining walls :

The overall stability of a retaining wall is governed by the action and reaction of a number of loads , Excessive SETTLEMENT may occur if weak soil layer is located below the foundation within 1.5 times foundation width

Deep seated shear failure may occur if there is a weak soil layer below the foundation within a depth of about 1.5 times width of foundation , The failure surface may be assumed to have cylindrical shape and critical failure surface for sliding may be determined through analysis , For back fill with its slope less than 10º, the critical sliding surface may be assumed to pass through heel of the retaining wall .

There is five Modes of failure :

Sliding Failure Overturning Failure Bearing capacity Failure Shallow shear Failure Deep shear Failure

1. Sliding Failure

Sliding failure is nothing but sliding of wall away from backfill when there is shearing failure at the base of wall

The Factor of safety against sliding is,

< 1.5

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µ = coefficient of friction = tan δ

vertical & horizontal components of resultant R of weight of wall &

earth pressure

2. Overturning failure

Overturning failure is rotation of wall about its toe due to exceeding of moment caused due to overturning forces to resisting forces

The Factor of safety against overturning is given by

< 1.5 - 2.0

Where :

= sum of resisting moment about toe

= sum of overturning moment about toe

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3. Bearing capacity failure

The pressure exerted by resultant vertical force at toe of wall must no exceed the allowable bearing capacity of the soil , the pressure distribution is assumed to be linear

The maximum pressure is given by :

The Factor of safety against bearing failure is :

< 3.0Where : qna = allowable bearing pressure

4. Shallow shear failure

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This type of failure occurs along a cylindrical surface ABC passing through the heel of retaining wall , the failure takes place because of excessive shear stresses along the cylindrical surface within the soil mass , and the FOS against horizontal sliding is lower than that for shallow shear failure however, FOS against sliding is greater than 1.5, shallow shear failure is not likely to occur .

5. Deep shear failure

This type of slope failure occurs along a cylindrical surface ABC ABC as Shown in the photo down when there is a weak layer of soil under the wall

at a depth of about 1.5 times ht. of wall . The critical failure surface is found by trial & error method For the backfills

having slope i less than 10º , it has been seen that critical failure surfaceDEF passes through the edge of heel slab as shown in the down fig In this condition possibility of excessive settlement should also be checked

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• case study

1. Retaining wall collapse at castle village on 12th may 2005

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The castle village is located in historic Washington heights section of Manhattan. The wall is owned by Castle village owner’s corporation. Five buildings, 575 unit co-operative housing complex is located on the top of hill

behind the wall. On Thursday, May 12, 2005 at approx 4:00 pm, a portion of a 65 foot high stone

retaining wall on side of bluff rising above Hudson river suddenly collapsed. About 10 minutes later second larger collapse followed as 150 feet section of 800

foot long wall and covered Henry Hudson parkway. Fortunately, there were no deaths or even injuries

The collapse was cause of structural failure resulting from increased pressure developed behind the wall due to build up of ground water throughout the years.

Langan Engg. & Environmental services was the firm inspecting, evaluating and making recommendations about & repair certain areas of retaining walls.

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The retaining wall has moved about 2 feet from its initial position when it was constructed.

Hence this case is remarkable case of sliding of retaining wall.

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2. Retaining wall failure in Austria on 30th October 2012

The landslide triggered due snow melt caused this retaining wall failure.

It was due to overturning of wall due to excessive overturning moment caused by pressure generated by snow melt.

It fell on the carriageway & Unfortunately it fell onto a truck, killing the driver.

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References

http://www.wikipedia.org http://www.slideshare.net

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