Retaining Wall design | RCC Structures

How to design a retaining wall? | RCC Design

Main parts of Retaining Wall

The stem and base are the main parts of a cantilever type of retaining wall. The toe is the front portion and heel is the back portion. The stem is supported at the base and the wall tapers towards the top.

Wall Dimensions

Generally the height of the wall known and approximate dimensions are required to be assumed.

The length of the base is between 0.4 to 0.7 times the height of the wall. Toe to base ratio is 1:4. The thickness of the base slab shall be assumed to be little more than the thickness of the stem at the bottom. The minimum thickness of the stem shall be 200mm for construction purposes.

retaining wall

Earth pressure on wall

A length of one metre of the wall is considered for design.

Earth levelled up to the top of wall:

From Rankine’s theory of earth pressure

earth pressure formula - retaining walls

where,

P = total pressure on wall acting at H/3 from the base

H = total height in metres

W = weight or density of earth in kN/m3

Φ  = angle of repose of earth

Stability of retaining wall

The assumed trial section of the wall shall be checked for stability. Stability check is required for (i) overturning and (ii) sliding. In both the cases the factor of safety shall not be less than 1.5.

1. Factor of safety for overturning

(Moment due to load of wall)/(Moment due to force P) ≥ 1.5

2. Factor of safety for sliding

(Total load of wall x μ)/Force P ≥ 1.5

Read moreRetaining Wall design | RCC Structures

Bending Moment and Fixed Moment Calculations

Bending Moment and Shear Force diagrams

What is Bending Moment?

The element bends when a moment is applied to it. Every structural element has bending moment. Concept of bending moment is very important in the field of engineering especially Civil engineering and Mechanical Engineering.

Unit of measurement: Newton-metres (N-m) or pound-foot or foot-pound (ft.lb)

Bending moment is directly proportional to tensile and compressive stresses. Increase in tensile and compressive stresses results in the increase in the bending moment. These stresses also depend on the second moment of area of the cross section of the element.

What is Shear stress?

Shear stress is defined as the measure of force per unit area. Shear stress occurs in shear plane. There are many planes possible at any point in a structure which can be defined to measure stress.

Stress = Force/Unit area

Example: Bending Moment and Shear Force Calculations

Frame diagrams | Bending moment and shear force calculations
Frame diagrams | Bending moment and shear force calculations

Simply supported bending moment

Mab = wl2/8 = (22×4.14×4.14)/8

= 47.13 KN-m

Mbc = wl2/8 = (22×4.14×4.14)/8

= 47.13 KN-m

Read moreBending Moment and Fixed Moment Calculations