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Earth Retaining Structures Assignment DEPT. OF CIVIL ENGINEERING TEAM MEMBERS :- 1. KUMAR AMAN 7.HRIDKAMAL BISWAS 2. SONU KUMAR 8.ANKITA DEKA 3. KAMAL SINGH 9.RAJEEV KUMAR

Design And Construction Of Cantilevered Retaining Walls

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Earth Retaining StructuresAssignment

DEPT. OF CIVIL ENGINEERINGTEAM MEMBERS :-

1. KUMAR AMAN 7.HRIDKAMAL BISWAS

2. SONU KUMAR 8.ANKITA DEKA3. KAMAL SINGH 9.RAJEEV KUMAR4. RAVINDRA VERMA 10.DHEERAJ MEENA5. VIKAS KUMAR6. NIHAL SINGH

Design And Construction Of Cantilevered Retaining Walls

RETAINING WALLS

• The structures which are constructed to retain the earth or other loose material which are unable to stand vertically by itself are called as “retaining walls”.

• They can also be used to support grounds at different levels on both sides of wall.

• The material retained by wall is called as “backfill”.

TYPES OF RETAINING WALLS

On the basis of shape & mode of resisting pressure due to backfill.

1. Gravity retaining wall2. Semi-Gravity retaining wall3. Cantilever retaining wall4. Counterfort retaining wall5. Buttress wall

1. GRAVITY RETAINING WALL

•The walls which resists the earth pressure due to backfill by its own weight.

•They are constructed with stone masonry or plain concrete.

2. SEMI-GRAVITY RETAINING WALL

• The size of section of a gravity retaining wall may be reduced if a small amount of reinforcement is provided near the back face. Such walls are known as Semi-gravity retaining wall.

3.CANTILEVER RETAINING WALL

• Cantilever retaining walls are made of reinforced cement concrete.

• The wall consist of a thin stem and a base slab cast monolithically.

4. COUNTERFORT RETAINING WALL

• Counterfort retaining walls have thin vertical slabs, known as Counterfort, spaced across the vertical stem at regular intervals. • Counterforts tie vertical stem with the base slab.

•The purpose of providing Counterfort is to reduce shear force &bending moment in the vertical stem & the base slab.

5. BUTTRESS WALL

• It is similar to the Counterfort retaining wall in which Counterfort, called as buttresses are provided on the opposite side of the backfill & act as compression struts.

MODES OF FAILURE

There are 5 types of

modes of failure

• Sliding Failure

• Overturning Failure

• Bearing capacity Failure

• Shallow shear Failure

• Deep shear Failure

Case 1

• In San Diego, California , failure in retaining wall was observed.

• The wall was constructed as a basement wall for a large building .In 1984, the building was demolished and the site was turned into a parking lot.

• The basement wall received lateral support from the foundation , a bowstring roof truss, and perpendicular building walls.

• When the building was demolished , the retaining wall became a cantilevered wall with no lateral support except from footing.

Active Earth Pressure

`

Cracks

Lateral Support

• Hence this case is remarkable case of failure of retaining wall due to reduction of lateral pressure.

• The movement of wall versus time is not at constant rate ,but rather intermittent.

• Data indicates that as the wall moves forward,cracks open up and lateral movement ceases for a while.

As Wall moves forward

Soil thrust is reduced

Takes time for soil to re-contact with back face of the

wall

Case 2

• This case study involves damage of retaining caused by Northridge earthquake(january 17 ,1994) in california.

• The magnitude of earthquake was recorded to be 6.7 in richter scale.

Factors affecting the magnitude of earthquake forces on the wall-

• Size of wall.• Distance of retaining wall from the earth

quake epicenter.• Duration of earthquake.• Mass of soil retained by wall.• Property of soil.

• In this case the EQSEARCH a computer programme was used to estimate the peak ground acceleration at that location.

• So , we can estimate the additional force exerted by earthquake.

CROSS SECTION THROUGH HOUSE

• A retaining wall was constructed near the top of the slop and the house was built in front of the wall.

• The house provides lateral support to some portion of retaining wall and those portions didn’t sustain any damage during earthquake.

• The portion of retaining wall that didn’t recieve lateral support from the house experienced tilting and cracking during Northridge earthquake .

• In this case additional earthquake force is exerted on the wall.

• Also,The affect of Northridge earthquake was to densify the backfill and increase the lateral pressure.

• So, it is a case of failure of retaining wall in which additional forces gerenated by earthquake was not considered in design.

DESIGN OF CANTILEVERED RETAINING WALLS

FACTOR OF SAFETY FOR SLIDING

• The factor of safety for sliding of the retaining wall is defined as the resisting forces divided by the driving force.

• F = (Sliding friction force + Allowable passive resultant force)/ active earth pressure resultant force

=(μW+Pp)/Pa

Where,μ = friction coefficient between the concrete foundation and bearing soil W=resultant vertical forcePp=passive resultant forcePa=active earth resultant force

Factor Of safety for Overturning

• The factor of safety for overturning of the retaining wall is calculated by taking moments about the toe of the footing .

• F = Stabilizing Moment/Overturning Moment =Wx’/(1/3)PaHWhere x’=distance from the resultant vertical force the toe of the footingPa=active earth resultant force

TYPE OF BACKFILL MATERIAL

1.) Clean granular sand or gravelBecause of the undesirable effect of clay or silt (swelling pressure on the wall , hydrostatic forces on the wall)

2.)Sometimes Soil available at site

Compaction of Backfill Material

• The best compaction equipment are small vibrator plate , such as VPG 160B and BP19/75.

• The vibrator plates effectively densify the granular backfill but do not induce high lateral loads because of their light weight.

Thank You