Design alternatives

How to Design retaining block walls

Terraforce retaining blocks can be used either as part of a gravity system or as the fascia of a geosynthetic reinforced segmental retaining wall structure, or as a fascia for a cement stabilized backfill. Download the Recommended specifications on the downloads page.

Gravity retaining | Reinforced retaining | Design tables | Submission sheet | Test results

Gravity retaining walls

Gravity retaining walls rely on their self-weight to resist lateral earth pressure, and such walls have been in use for centuries. In a gravity system the Terraforce masonry units can be stacked several courses deep to provide support to the forces imposed by the retained soil; the weight and geometry of the stacked units prevent the constructed wall from sliding on its base or at an intermediate height, toppling over, or rotating out of position.

 Light gravity wall  Heavy gravity wall
Light gravity wall
Heavy gravity wall

Design tables for single skin walls

Information relating to the design of single-block-width gravity retaining walls will be given in these design charts for Terraforce blocks. Designs which feature multiple rows of blocks should be prepared on a site specific basis by an experienced professional engineer.

Click in the boxes below for the Design Tables of the different Terraforce blocks (in various sizes):

S10 L11 L12 L13 L15 L15IT L18 L22 Terralite 4×4 Multi

Confirm availability of products with your local supplier.

Contact us for a copy of the I.C.B.O. Evaluation Report

Reinforced retaining walls

top of page

Sometimes the complexity or wall height required for certain installations require retaining walls that are reinforced by either geofabric material or, in really tough cases, concrete-filled doubleskin layers of blocks.

Gravity retaining | Reinforced retaining | Design tables | Submission sheet | Test results

1. Geosynthetic reinforced soil segmental retaining walls

Geosynthetic reinforced soil segmental retaining walls

Geosynthetic reinforced soil segmental retaining walls utilize reinforcing sheets of geogrid or suitable woven geotextile which are attached to the fascia and are embedded in a body of engineered fill.

The integrated nature of the fascia and the abutting large body of reinforced soil thereby supports the applied earth forces. In this case the “gravity” component of the retaining wall is provided by the reinforced soil mass, which acts as a monolithic unit.

Geosynthetic reinforced soil segmental retaining walls

By virtue of their inherent flexibility, such walls are able to accommodate movement and some settlement without suffering distress. This makes the system particularly suitable for construction on (engineered) filled ground or in areas which may be prone to settlement effects. Also, the cost and difficulty of construction of such retaining walls is minimized as the need to provide full frost wall foundations can be waived in many circumstances.

The maximum wall heights for a single skin, mass gravity, block retaining wall system - with additional geogrid reinforcement

The maximum wall heights (in block height, metres, feet) for a single skin, mass gravity, block retaining wall system – with additional geogrid reinforcement
Geosynthetic reinforced soil segmental retaining walls
 Geosynthetic reinforced soil segmental retaining walls

The publication “Terraforce-design and installation manual for Geosynthetic Reinforced Soil Applications” by Colin Alston and Dr Richard Bathurst contains 24 design charts that cover a wide variety of situations. Request a copy from your nearest supplier. See case studies for examples.

2. Reinforced concrete-filled segmental retaining walls

 Retaining walls with reinforced concrete infill or stabilised backfill

Occasionally severe space limitations dictate the use of a double skin of Terraforce blocks in combination with reinforced concrete infill or stabilised backfill.

This type of installation, while similar in nature to conventional reinforced concrete/masonry retaining walls, offers a number of added advantages:

  • Ease and speed of construction – no shuttering and less specialised construction skills required.
  • Aesthetic appeal – choose between split face blocks or smooth moulded appearance. It is even possible to retain a degree of plantibility in some cases.
Retaining walls with reinforced concrete infill or stabilised backfill

Design procedures are the same as those employed for traditional reinforced masonry retaining walls.

Submission sheet for mass gravity retaining walls  top of page

To download updated versions in PDF format:

Submission sheet for gravity walls
Submission sheet for reinforced walls

Gravity retaining | Reinforced retaining | Design tables | Submission sheet | Test results
Retaining wall detail / Submission sheet
Blocks   Wall   Foundation
Block Type   Height (H)   Type  
Height (h)   Tilt angle (ß)   l1  
Width (B)   Surface angle (i)   l2  
Offset (x)
(set back)
  Height of keys (Hk)   l3  
Keys per m2   Keyless height (Ho)   d1  
layer width (c)
  Surcharge (kN/m2)   d2  
Title: TERRAFORCE retaining wall detail
Designed: Checked:
Drawn: Date:


  • Retaining wall to be constructed of Terraforce precast concrete blocks. (Type as indicated.)
  • Blocks placed as shown and to be filled with well tamped topsoil.
  • For walls retaining clay or shale, provide a free draining sand layer behind wall. Backfill to be well rammed in 150mm layers.
  • Drainage outlet pipes to be provided at toe of slope and to be capped with geotextile.
  • Stormwater cut-off drain is to be provided above the wall where necessary.
  • Ground under all bases to be of approved granular material well compacted prior to constructing base.
  • The engineer is to be notified of any variations of levels or dimensions shown.
  • Minimum concrete strength for concrete foundations to be 20MPa at 28 days (to be designed accordingly).
  • Shear keys with a minimum design shear stress of 0,3N/mm² are to be installed as indicated. i.e. 75 x 75 mm 1:4 cement or crusher-sand mortar or 40mm H.D.P.E Class 6 pipe sections.
  • No services or trenches permitted immediately in front of the retaining wall.
  • Maximum superimposed loading as indicated behind wall (surcharge).
  • Concrete keys to be class 1 mortar or 15Mpa concrete.
  • Please refer to the Terraforce construction manual and the guide to Terraforce L13 retaining walls for further detalls.
  • The Terraforce block retaining wall design spreadsheet can also be used to assist in the design process.

References and test results 

top of page

Gravity retaining | Reinforced retaining | Submission sheet | Test results
  • Guide to the design of Terraforce retaining walls, Oct. 1992 by W G Technau of Hawkins, Hawkins & Osborn. Rivonia, South Africa.
  • Guidelines for the use of the Terraforce retaining wall design spreadsheet, Nov. 1994 by G Bentel of Steffen, Robertson & Kirsten.  Technology Park, W Australia.
  • Terraforce, the living retaining wall system: Design and installation manual for geosynthetic reinforced soil applications, Feb. 1996 by Dr Richard J Bathurst of Royal Military College, Kingston, Ontario and Colin Alston of Alston Associates Inc., Markham, Ontario, Canada.
  • Terraforce design manual for Boral Besser Masonry Ltd, Oct. 1997 by Andrew Shirley of Shirley Consulting Eng. Sydney, Australia.
  • Crushing tests of blocks subject to line loading, July 1998 by Damon Clark Associates. Durban, South Africa.
  • Connection tests and interface shear tests, Nov. 1998 and Feb. 1999 by Dr Richard J Bathurst of Royal Military College. Kingston, Canada.

All information is given in good faith without warranty and no liability is accepted. Sole responsibility rests with the user who must ensure that a professional engineer is engaged to design and supervise the installation. The proprietary products and trademarks described herein are registered. All rights and copyright belong to Terraforce (Pty) Ltd.

Print Friendly, PDF & Email

Comments are closed.