Design of a Permeable Concrete Block Retaining Wall

Design of a Permeable

Concrete Block Retaining WallPresenter: Cosmo Farinola – Cardno

Introduction

Presentation overview

What is a permeable

concrete block retaining

wall?

Details of permeable

concrete blocks

Designing a permeable

concrete block retaining

wall

Massbloc wall projects

Questions

What is a Permeable Concrete Block Retaining wall

Consists of large permeable precast concrete blocks that interlock to create a gravity retaining wall structure

The system was originally developed in New Zealand in the early 1980’s and was launched by Rocla in Australia in 2002 as the Rocla MassBloc retaining wall system

The blocks have been used in bridge abutments, road embankments, highway stabilization and general retaining walls up to 6.0m in height

The blocks are laid without mortar and are interlocked by a nib at the base of each standard block

Cardno was engaged by Rocla to prepare design and construction details and has an ongoing relationship

Details of a permeable concrete block wall

Large concrete blocks that are

1000mm high x 1190mm wide x

900mm deep

The base unit forms the bottom

row of the wall and has no nib and

a block weighs 1.7tonne

The standard unit has a nib (170

wide) at the bottom of the block

that overhangs the block below

resulting in the interlocking. A

standard unit weighs 1.9tonne

Blocks can be manufactured with

varying height and width up to the

above stated dimensions and a

variety of colours


Blocks are unreinforced and are

supplied with a 5.0 tonne lifting

anchor

The wall steps back 170mm for

each metre height due to the nib

interlocking

Solid blocks (20MPa) are also

available for load bearing

applications


Walls can be constructed with a 90

degree maximum change in

direction using half blocks


Walls can also be constructed to a

curvature or radius


The permeability of the block

unit and mortar free joints

assists in relieving water

pressure from behind the

wall but as with all good

retaining wall construction

practice it is recommended

that adequate drainage is

provided to the rear of the

wall

Designing a Permeable Concrete Block Retaining Wall

A Massbloc retaining wall is a gravity wall designed in accordance with the requirements of AS4678-2002 Earth Retaining Structures and AS1170.0 & AS1170.1 -2002 Loading Codes

The wall is generally designed using Coulomb Theory and is checked for overturning, sliding, bearing and global stability.

Loads to be resisted by the wall generally consist of horizontal earth or water pressures and vertical surcharge loading to the rear of the wall, if applicable.

The parameters required to carry out the design normally consist of the following:

I. Backfill material

II. Total wall height

III. Maximum backfill slope

IV. Wall classification in accordance with AS4678-2002

V. Maximum surcharge loading

VI. Subground bearing pressure

VII. Φ = internal friction angle of soil

VIII. C = characteristic cohesion of soil.


Depending on the location and use of the wall it may also be required to be

designed for Earthquake forces

A computer program has been developed by Cardno for Rocla for the design of

Massbloc retaining walls and is able to be downloaded for free from the Rocla

website. The program utilizes the above parameters.

The computer program has a maximum wall height of 6.0m and wall heights

greater than 6.0m will need to be checked by using first principles.

No fines concrete (concrete without fine aggregate) can also be used as backfill

material to increase the depth of the wall and allow for greater retaining height

provided the usual checks are carried out.

Massbloc Wall Projects

• Blayney Bridge

Abutment


• Mining application


• Lake Eacham,

Cairns


• Mt Hotham Ski fields


• Hunter Expressway

• Note solid blocks

Questions?

Design of a Permeable Concrete Block Retaining Wall

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