retaining wall design video

The things you need

to be aware of

BASICS

Retaining Wall Design

Scope - Cantilever and gravity retaining wall types

Cantilever – King Post Cantilever - Precast L shape Cantilever - Reinforced Block Cantilever - Reinforced Block

Gravity – Masonry Gravity – Criblock Gravity – Concrete Block Gravity – Gabion Basket

Retaining wall design codes of practice – BS 8002 :1994

Retaining wall are designed by structural engineers who are experienced in structural design of concrete, masonry, steel and structures.

They use the site investigation information about the soil types to carry out their design.

Retaining wall design and failure types

Overturning – The material being retained creates a force (moment) that causes toppling of the wall. The weight of a retaining wall resists this moment.

Bearing capacity – The weight of the wall and earth is supported by the ground beneath. The ground bearing capacity needs to be checked to ensure any settlement is within limits.

Sliding – The retaining earth creates a horizontal force that can cause the retaining wall to slide. This is resisted by the friction between the wall and earth beneath, and the embedment of the wall.

Stability – The earth around the wall requires adequate strength to avoid an overall slip failure.

Shear – The blocks and masonry can shear at the base or on courses.

A simple demonstration to understand overturning and slip

Site investigation made simple

• Site investigation bore holes• Site investigation trial holes• Site investigation desk top study• Site investigation contractors

The structural engineer needs ground information before a design can be carried out

What is a site investigation?

Site investigation is required to determine the engineering properties of soil and rock and how they will interact with a planned retaining wall. The purpose of site investigation is to establish parameters for foundation and retaining wall structural design.

There are a variety of techniques and procedures that may be used, and each consultant may adopt a different approach for any particular project. However, it is typical for the investigation to be carried out as a phased exercise, generally comprising:

Phase 1 — desk studyPhase 2 — intrusive investigationPhase 3 — remediation strategyPhase 4 — validation

The output is a borehole log and report

A bore hole log shows you the ground strata.

Each layer is recorded for the depth and type of soil.

Tests are carried out on the soil during the drilling process to determine the soil strength.

A report is then prepared for the structural engineer.

What is a trial pit?

Trial pits are used to recover large bulk samples of soil or where thorough visual examination of the strata is required.

The principal advantage of this method compared with light-cable percussion drilling or window sampling is the relative speed with which the work can be carried out.

The pit can be excavated by machine or by hand.

The soil at the formation level of the retaining wall can be checked for bearing capacity.

Bore hole data – British Geological Survey

https://www.bgs.ac.uk/

Geotechnical site investigation contractors

Case study – Project in Cumbria for a new hotel

The ground bearing pressure of this project was 100 kPa.

The width of the foundation was increased to allow for the low ground bearing pressure.

You can also see the ground above the wall has a 30 degree slope adding a surcharge load.

A design example

Case Study – Somerset - Design Summary

Design output

Conclusion

Retaining walls must be designed by a structural engineer using soil information

from a geotechnical engineer to ensure the retaining wall will not fail in the future.

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