Design table creator for single skin Terraforce walls. Use this interactive excel sheet to work out the design values – number of blocks, wall height and recommended setback – for Terraforce blocks.
Please ensure that the supplier of the Terraforce blocks is a reputable, licensed manufacturer, and is able/willing to provide design information or can refer you to a qualified engineer.
Download the Excel Design Sheet here:
Once the Excel Sheet has downloaded, save the file by selecting file/save as to your computer and you will be able to use the highlighted fields as drop downs to select you block size and fill.
These design tables are intended to assist in estimating the cost of proposed gravity retaining walls to be built with Terraforce blocks and to confirm the viability of such undertaking. Your local engineer will be able to either verify the table creator values or will be able to produce a more accurate cross section. The table creator does is not a design tool an does not eliminate the need to seek the advice of a competent person who understands the principles of retaining wall design.
For a reasonable fee, TERRASAFE DESIGN can assist in providing a pertinent design. We can also arrange for a quotation by an experienced installer or for supervision by an engineering professional in some areas.
For the design of composite Terraforce walls, i.e. structures with mechanically stabilised backfill or with additional stability requirements, – double block rows, cement stabilised backfill or reinforced concrete infill, etc., please go to MAXIWALL PRO design program or contact TERRASAFE DESIGN.
Minimum CRB block wall requirements & quality assurance during manufacture.
The production of Terraforce concrete retaining blocks must adhere to local and international standards. The blocks have been extensively laboratory tested, locally and internationally and have been evaluated by reputable accreditations agencies.
Our minimum standard is mostly based on the following codes.
- SANS 207: 2011 and SANS 508/2006
- CMA manuals
- BS 8006-1
- ASTM-D6916-18 and ASTM-C 90
- ICB 1802 and ICB 1805.4.1 + 2 (International Building Code)
Licensed manufacturers must adhere to our minimum standard and regular compressive strength tests must be conducted. Weight and dimensional tolerances must be complied with as part of our quality assurance programme.
————————————————————————————————————————————-A WORD OF CAUTION
Avoid disappointment and take note of these possible shortfalls.
Please ensure that the supplier of the Terraforce blocks is a reputable, licensed manufacturer, and is able/willing to provide design information or can refer you to a qualified engineer. Also appoint a competent designer with experience and Professional Indemnity Insurance cover.
- Insufficient constructed mass due to no or negligible design input, use of incorrect block size/infill material, incorrectly conveyed site information or poor drawings/specifications.
- Saturated backfill due to a lack of storm water control above the wall. Inadequate sub-soil drainage.
- Design angle and height exceeded due to a lack of supervision during construction. Unauthorised changes to the wall details.
- Settlement of backfill due to substandard material, inadequate compaction, backfill erosion or lack of supervision during placement of backfill.
- Undermining caused by excavation close to wall foundations.
- Excessive loading above the wall, not accounted for in the original design.
- Limited bearing capacity due to poor or saturated founding conditions or no foundation at all.
- Incorrect selection of supplementary reinforcement, choice of inadequate geo-grid. Poor connection between blocks and geo-grid. Inadequate concrete or reinforced concrete infill or alternatively cement stabilised backfill.
- Linear cracking of blocks due to excessive lateral earth pressure or poor quality of blocks.
- Non-adherence to local OHS Act – (Occupational Health and Safety Act).
Although every reasonable effort has been made to ensure that the technical information and the design procedure presented in this guide are correct, neither Terraforce CC. and any supplier of the product, nor their consultants, who have contributed to the preparation of these guidelines, will be held liable for any loss or damage, either direct or consequential, arising from any failure of installations constructed with Terraforce precast concrete blocks.
As with any structure, the design of Terraforce projects should only be undertaken by suitably qualified and experienced designers with due cognisance being taken of the specific geotechnical conditions and vital soil parameters pertaining to the site.
Steps to follow for a professional end-result.
- Decide what you want to achieve, possibly with a layout sketch and a cross section drawing. Select from www.terraforce.com, click on our products, the block of your choice. Please ensure that your local supplier stocks or produces your selection, click on Terraforce suppliers.
- Contact your local supplier for prices and a reference to recommended installers with experience in the construction of Terraforce retaining walls. For installation instructions, click on (link to installation instructions and videos)
- Ensure that, a proper design has been prepared, to submit to your local municipality, as approval may be required. Some installations are deemed pure landscaping measures and would not require the submission of plans. Confirm with the local authority, what their regulations are. Should your recommended or preferred installer not be able to assist in these questions, find a new one.
- During the construction phase, ensure that the designer of the approved plans, or his representative, visits the site to ensure that his specifications are met.
- After completion of the wall, obtain a completion certificate as prescribed by SANS 10400 Form 4 or other local regulations (if required) and hand it to the building inspector.
- Please ensure that the supplier of the Terraforce blocks is a reputable, licensed manufacturer, and is able/willing to provide design information or can refer you to a qualified engineer.
Information required by the designer to conduct his task without wasting time on clarifying site specific details, or on the desired appearance of the wall.
A cross section sketch, or multiple cross sections if the wall has varying heights (in 1m height intervals), showing the following information.
- Height of wall and inclination of the fascia, in degrees. Walls at say 65 degree inclination are more cost effective than steep walls at say 85 degrees. Alternatively a completed Terraforce questionnaire for gravity, composite or terraced walls should be submitted. (link to three forms)
- Type of native soil found on site, at foundation level and on the slope to be retained. Photos may help the designer to assess site conditions. A geotechnical report and/or density tests, if available is a great help.
- Is the ground behind the wall level or is it rising further? Photos will help, if the designer is unable to visit the site.
- Indicate any surcharge loading, such as a building or a driveway, above the wall and indicate the distance between the load and the top of wall.
- Steep and high wall often need to have geogrid reinforcing incorporated into the backfill for stability. Indicate the space available behind the block fascia and the cut face to incorporate such measures. Provide the designer with information pertaining to the type of geogrid that is available in your country.
- Any ground water visible? The most common cause for failure of retaining walls is the build-up of pore water pressure in the retained soil. Trapped water needs to escape via an agricultural drain, through spaced outlets.
- Is there a possibility of surface water above the wall to drain towards the wall? Ideally all surface water needs to be directed away from the wall and is not allowed to spill over the walls. Drainage recommendations to be followed diligently.
- Any information on previous proposed designs involving other methods.
- Appoint an experienced contractor/installer, even if his rates are higher than those offered by others who possibly lack the necessary know-how or commitment.
- Ensure that a qualified professional is in charge to supervise the installation, to sign of the completion certificate to be handed to the building inspector.
- Always appoint a competent designer with experience and who has public liability and professional indemnity insurance cover.
Contractor check list.
Materials utilized on site:
- All materials intended to be utilized in the construction of the wall, to be submitted to the Engineer for approval, prior to utilization.
- DPC density test results to be recorded and approved.
- Placed on site concrete to be strictly to specification.
- Location plan for testing sites to be provided.
- Notify Engineer of tests to be conducted for oversight where required.
- Ensure that CRB’s (concrete retaining blocks) on site are to specified strength and size.
- Follow installation instructions provided by Terraforce.
- If specified, submit sample and spec-sheet of geogrid/geofabric.
- Install geogrid/geofabric to protrude slightly beyond the blocks for inspection, to be trimmed off after final structural inspection.
- Setting out of foundation and profile of the wall, preferably to be undertaken in the presence of client or his engineer.
- Proposed wall position to be clearly marked and confirmed in writing, with a photo record to avoid unnecessary disputes.
- Always ensure that the supplier of your Terraforce blocks is reputable and a licensed manufacturer, able and willing to provide adequate design back-up or who can refer you to qualified engineer.