Questions and Answers

1. Where can Terraforce blocks be purchased? Top of page

Our licensees can be found in various locations on 5 continents. Go to the - where to buy -  section on our website to see their contact details and a list of our products that they make.

2. What are the main differences between Terraforce blocks and other systems?

There are many different types of segmented concrete retaining blocks on offer, worldwide. From heavy solid cast concrete blocks to medium or small solid pressed concrete blocks, via medium to small hollow blocks like the Terraforce range with a closed vertical surface. These are available in most parts of the world while in some developing nations there are also a few open-face systems available. Terraforce combines more advantages than any of the other systems: relatively light weight for transport, interlocking on both planes – horizontally and vertically, reversible to display smooth round-face or split straight-face, fully plant supportive, has closed vertical surface structure
for proper compaction of backfill and prevention of backfill erosion, wall angle can vary to suit site conditions, can be filled with soil, gravel or concrete as designed by the engineer.

3. Are all retaining systems plant supportive? Top of page

No, solid block systems are not plant supportive and open face systems are plantable to a degree although excessive evaporation in these would require an increased input of irrigation water that will possibly increase backfill erosion. Terraforce blocks have an open horizontal surface structure, can be fully filled with garden soil and will allow root systems and irrigation water to penetrate deep into the installation. A continued aesthetic value is thus ensured.

4. What is the difference between open-face and closed-face retaining systems?

Apart from what has been said under question 3, it can be stated that the main differences, as we see it, are as follows: Closed-face systems (meaning the vertical face) generally require more blocks per square metre of wall, all fully filled as specified and are thus heavier than open-face systems. Further compaction of the backfill is easier in closed systems and the backfill will retain it’s integrity, which is not always the case in open systems. Since, as far as we know, the pullout resistance of  geogrids that have been clamped between blocks, has never been tested in open systems, we can only state that Terraforce blocks performed in this test with results that are above industry standards. It also appears that a test to determine the full block crushing resistance, of some open-face systems has yet to be devised.

5. How does this difference affect long-term integrity of a wall? Top of page

Apart from the lesser constructed mass, generally, the long term integrity of drainage layer and backfill to open walls, remains a contentious issue. We are of the opinion that erosion of the backfill will occur over time.

6. To suit site requirements, what design options are available? Top of page

We can reaffirm that Terraforce remains unsurpassed in terms of versatility. Sections – planning alternatives – and – design alternatives – on our website deals with these issues.

7. Is Terraforce a truly one block system? Top of page

Once you have chosen your Terraforce block, you can do most features that are normally required with that one block. Occasionally you may have to cut blocks to form sharp corners or to match up to existing buildings. Go to – details – on our website.

8. How should I make my choices? Top of page

Our blocks are available in different sizes to suit varying requirements. Your local supplier will gladly assist you in making the right choice. He will also refer you to an engineer where the need arises. Test results and evaluation reports are available on request.

9. What kind of foundation needs to be provided? Top of page

Ultimately your engineer will make that decision, especially for walls above 1,6m ( 5ft ). Low walls can often be built on a compacted gravel foundation. In some instances even high walls can be built on a gravel foundations, provided the walls are of the composite type. ( walls with geosynthetic reinforcing of the backfill ) If the foundation has been specified as concrete, the first row of blocks should be set in mortar to facilitate levelling of blocks.

10. At what inclination and to what height can my wall be built? Top of page

As a rule of thumb, it is safe to say that the cost of a wall goes up, as it is planned to be steeper and higher. Low to medium walls at shallow inclinations can be built very cost-effectively as normal gravity walls that are stable by virtue of their self-weight. As height and/or inclination increases, it becomes necessary to reinforce the wall by various means and consequently the cost increases as well. Terraforce walls have been built to heights approaching 20m ( 60ft ) at an inclination of 70 deg. and vertically up to 6m ( 18ft ).

11. What kind of infill do I need for the blocks? Top of page

The blocks should be filled with material as specified by the engineer. Garden soil, clean sand, gravel or concrete ( reinforced if needed ). Low garden walls that are meant to be plant supportive, should be filled with the best garden soil available.

12. Does the block infill improve stability, and if so, how? Top of page

Gravel is heavier than garden soil and will also interlock the blocks better on the vertical plane, thus gravel infill improves stability considerably.

13. How do Terraforce blocks interlock? Top of page

On the horizontal plane, the blocks interlock via the convex and concave shape of blocks that interact with one another. On the vertical plane, interlocking strength is gained by the block infill which functions like a interlocking core. Infill materials such as coarse gravel or concrete obviously have a higher core strength than sand or garden soil. No pins or interlocking lips are involved, that interfere with versatility in alignment and inclination.
( near vertical to 55 deg. )

14. Do the blocks have to be packed staggered like brickwork? Top of page

Although this is standard practice, it is not a requirement and stack bond is also allowed. Our engineers agree that the integrity of a wall is not affected by switching from stagger bond to stack bond as often happens on sites where the extreme Terraforce versatility is applied to create meanders at varying wall inclinations.

15. Is there a minimum radius for tight curves within a wall? Top of page

Although very tight curves can be packed, especially with the smaller blocks, it is recommended that smaller curves than 500mm ( 1,5ft ) should be avoided. Right angle corners can be created by cutting interacting blocks with an angle grinder to suit.

16. Does the choice between round face and straight face influence stability?

No, stability is not affected. However poor construction techniques and cost-saving manoeuvres will. Ensure to have suitably experienced workmen on site.

17. Can Terraforce blocks be dismantled and re-used? Top of page

Yes, they can, and on many occasions the blocks have been used for temporary installations.

18. Can Terraforce be installed by keen do-it-yourselfers? Top of page

Some of our award winning installations have been built by home owners, one of whom likened this construction method to therapy for the soul. He created the most intricate details, with one block type, and thoroughly enjoyed it.

19. Do I need mortar for the installation? Top of page

No, mortar is not required except when you want to level the first row of blocks on a concrete foundation.

20. Do I need a geo-fabric filter hehind my Terraforce wall? Top of page

Since Terraforce is a system with a closed vertical surface structure, a filter membrane is not normally required. There are exceptions such as when very fine sand is used as backfill or when a high water table in present behind the wall. This will be decided by the engineer.

21. How can I create steps within the wall? Top of page

Steps can be built by simply reversing the standard Terraforce retainer blocks that you are using so that the flat area is facing forward. Alternatively, for a more up-market stairway, you can use the special Terraforce 4 x 4 step block to build very comfortable steps. Many stairways of both kinds are depicted on our website. To download a basic how to tutorial click here.

22. Is there a recommended procedure to follow when installing a wall? Top of page

On our website and on our brochures you can find illustrated installation details or a step by step illustration of a Terraforce installation. We also have a design manual that deals with the issue in detail. Please always start building at the lowest point of a wall and follow our instructions carefully to ensure structural integrity and lasting performance.

23. Are Terraforce walls cost-effective? Top of page

They are, but not cheap. A product meant to have a good service life of 70 years plus, at a reasonable price. As a rule of thumb it can be assumed that they can be built at a cost of about 70% of  what a conventional retaining wall will cost.

24. Are Terraforce blocks environmentally friendly? Top of page

They definitely are, our track record in this regard can leave no doubt. In addition, many of our licensees make use of recycled aggregates. The blocks are light to handle and transport, are free of toxic preservatives, and once completed with suitable planting, can provide food and shelter for many birds and insects.

25. How important is the drainage layer? Top of page

 The wall itself and the foundation are important, and the drainage layer is at least as important. A layer of coarse, well draining material of not less 300mm ( 1ft ) behind the blocks as shown in our typical cross sections, and well compacted. The engineer may also specify a permeable drainage pipe above foundation level. Channel surface water away from the top of the wall in an open swale.

26. How important is backfill compaction? Top of page

Inadequate compaction of the backfill and of the drainage layer are the cause of some spectacular failures that we have seen in segmental block walls. Backfill for relatively high walls must be approved by the engineer and compacted to his specification, and care must be taken to prevent surface water ingress from above the wall.

27. Can I build terraces, what about converging terraces? Top of page

Terraces can be built with much success as our case studies clearly show. The overall stability of the whole slope will have to be determined by a suitable professioanal. Each terrace wall will have to be properly founded in accordance with accepted engineering principles. Walls can merge and separate again with ease.

28. Can I change the inclination within a wall, if so, how? Top of page

Terraforce walls can merge seamlessly from near vertical to a low 55 degree inclination by simply shifting the blocks back or forward before filling. You must ensure that stability  parameters are still intact when doing this. Check with your engineer or other competent person.

29. Can I match up to existing buildings or structures? Top of page

Matching up to existing masonry walls with the stack bond method ( Refer question 14 ) is easy but not always possible. Blocks then need to be cut to match existing structures and the cut blocks should then be filled with concrete or mortar.

30. Can damage to bocks due to handling and transport of blocks be repaired on site?

Minor cracks that are the result of the manufacturing process or minor chipping of blocks (up to 25 mm) during transport and handling are not to be rejected. Split or rock-face blocks are excluded from this requirement as their appearance is meant to look uneven.

Blocks with deeps cracks should be rejected, but blocks with chips of up to 50 mm in diameter have on many occasions been repaired succesfully on site. provided that this is done in a professional manner and in a matching colour - some experimentation may be required.

31. How can intermediate drainage outlets be installed in a long wall? Top of page

The best method is to cut slots to suit the pipe diameter into the blocks and feed the outlets through these. These individual blocks should be filled with concrete
or mortar.

32. Do I need an engineer to design my wall? Top of page

For low walls of up to 1m ( 3ft ) you generally do not need an engineer. Terraforce has basic design tables for mass gravity walls ( walls that rely on self-weight to achieve stability ) and for composite retaining walls ( walls that rely mostly on a body of reinforced earth behind the blocks to achieve stability ), available in our brochures, our website and in two of our design manuals. We also have a design software available free of charge from www.maxiwall.com Design are prepared in terms of accepted engineering principles and judgement.

33. Are submitted plans required by local authorities? Top of page

Most building departments worldwide do require plans for approval, for walls that are over 1m ( 3ft ) high. Check with your local building inspector.

34. What about maintenance? Top of page

Like with any project that has been designed to be aesthetically pleasing and environmentally sound, maintenance is not avoidable. On some walls, planting has to be kept weed free, has to be rejuvenated occasionally and the irrigation system has to be maintained. On other walls, care has to be taken that larger invader species are removed or sometimes any form of vegetation is not welcome.

35. Is Terraforce a proven system – how long has it been on the market?

We have been planning and building earth retaining and erosion control measures for the past 30 years. ( since September 1979 ) Our products are now available on 5 continents, a record that we think, speaks for itself.

36. What options exist to reinforce the backfill of high and/or steep walls?

You could use a number of options and materials. Cement stabilised backfill has often been used as a cost effective method of increasing stability, sometimes in conjunction with a double row of Terraforce blocks. Low strain ( extruded ) geogrids may be used in some instances and for critical installations one would specify high tensile ( woven ) geogrids for extra strength. Ground anchors of steel and wire mesh sheets may in rare occasions be specified.

37. What about multiple rows of blocks? Top of page

This method is becoming popular in areas where geogrids  are increasingly expensive due to the high oil price. Where bocks are made in pairs, for splitting to create the popular rock-face look, it is feasible to supply un-split pairs of blocks to the site for this application. The method is usually applied when available space is limited and reinforcing geogrids can not be used. It is thus possible to fill the inner layer of blocks with reinforced concrete and the outer layer with garden soil.