# LATERAL EARTH PRESSURE AND RETAINING WALLS

## Types of Retaining Walls:

1. Gravity Retaining Walls
2. Semigravity Retaining Walls
3. Cantilever Retaining Walls
4. Counterfort Retaining Walls
5. Anchored Retaining Walls
6. Reinforced Retaining Walls
7. Slurry Walls
8. Sheet Pile Walls
9. Braced Cuts

### To Design a Retaining Wall We should Know the Following:

1- Function of Retaining Wall Different Types For Different Purposes.
2- Soil Properties
• Unit Weight
• Angle of Friction
• Cohesion C
3- Determine the Stability of The R.W.
• Sliding
• Overturning
• Bearing Capacity
• Overall Stability
4- Design The Retaining Wall Sections
• Check the Strength
• Steel Reinforcement or Steel Cross section

# LATERAL EARTH PRESSURE

1- At rest Pressure (No deformation in the Wall & No changes in Horizontal Stress)
2- Active Pressure (Deformation in the Wall& Decrease in Horizontal Stress)
3- Passive Pressure (Deformation in the Wall & Increase in Horizontal Stress)

# DESIGN OF RETAINING WALLS

1- Function of the Retaining Wall
2- Soil Properties
3- Method of Determining Lateral Earth Pressure
4- Checking the stability of the R.W.
5- Designing Cross Section of the R.W.

## LATERAL EARTH PRESSURE THEORIES

1- Coulomb's Lateral Earth Pressure Theory
2- Rankine's L.E.P
3- Culmann Method ---- Graphical
4- Poncelet Method ---- Graphical
5- Limit Analysis --- Lower and Upper bound Solution
6- Numerical Methods --- FEM & BEM

### Coulomb Earth Pressure Theory (1776)

Coulomb assumed friction between the wall and the soil.
Because of that friction

### Rankine' Earth Pressure Theory (1857)

Rankine assumed
1- Frictionless wall (Smooth) 2- Cohesionless Soil (Sand or Gravel) 3- Vertical Wall (90o with Horizontal) 4- Horizontal Backfill Surface 5- Flexible Wall

### Bell's Modification (1915)

Bell included the cohesion of the soil.
1- Active Pressure
2- Passive Pressure

## STABILITY OF RETAINING WALL

### I- Cantilever Retaining Wall

#### Use of Cantilever Retaining Walls

1- For low walls of fairly short length
Exposed height = 1 m to 3 m
Length = 40 m or less

2- Where the backfill zone is limited and or it is necessary to use the existing soil as backfill.

### Wall Stability:

The wall should be stable against:
1- Stem shear and bending due to lateral earth pressure on the stem.
2- Base shear and bending moments caused by the wall loading produced earth pressure on the wall footing.
3- Overall stability
• Sliding along the base
• Rotational stability
4- Stability against bearing capacity failure
5- Stability against excessive base settlement resulting in a large wall tilt.

## DESIGN PARAMETERS FOR DIFFERENT SOIL TYPES

### I- Sand and Gravel:

For all stages of construction and after construction use:

### II- Clay:

For cohesive soils the first three months after the construction the soil is undrained.
Therefore, the design parameters are:

### III- Silts:

Silt is in between cohesive and cohesionless soil.
The design parameters in this case can be taken as obtained from the total stress tests.
That is for the analysis of the R.W. immediately after construction.
The final active earth pressure to which the wall will be subjected can be determined from an effective stress analysis using .

SOME DESIGN CONSIDERATION

1- Rain water in tension cracks
2- Critical height for R.W. in cohesive soils
3- Choice of backfill Material

### The ideal backfill material is granular, such as gravel and clean sand with small percentage of fines.

• Clays and other fine grained oils, as well as granular soils with considerable amount of clay and silt (>15%) are not recommended as backfill material.
• Where fine soils must be used, the earth pressure should be calculated on the basis of at rest condition or higher pressure with due considerations to potential poor drainage conditions, swelling, and frost action.
• It is common to conservatively estimate the backfill parameters as and

### 4- Backfill drainage:

4.a Design of Filter Behind Retaining Walls

### 5- Effect of Construction Procedures

#### a- Compaction

* Compaction of backfill in a confined wedge behind the wall tends to increase the lateral earth pressure beyond those represented by Rankine's or Coulomb earth pressure theories.

* For guidance on lateral earth pressure computations associated with compaction of granular soil use the following methods: