According to Concrib , retaining walls are too often viewed as an ‘afterthought’ in the residential and commercial building process.
The necessary characteristics of retaining walls are a combination of:
- Structural ability (requiring engineering definition)
- Durability (for longevity of application)
- Aesthetic acceptability
- Cost efficiency
Considering these necessary characteristics for retaining walls, cost appears to be the overriding decider in most cases.
This observation is easily validated by an inspection of almost any new subdivision or active ‘new housing’ area. Dry stacked rocks and boulders, untreated or minimally treated timber walls, one metre high walls (to escape building application procedure) with steep batterslopes on top. Somehow, many inadequate retaining walls seem to escape the ‘net’ of engineering and local government requirements.
The Australian Standard, AS 4678-2002, Earth Retaining Structures, is a recent ally to enforce adherence to ‘engineering correctness’ of retaining wall design and construction.
The code addresses the crucial, yet neglected aspect of ‘design life’ as well as structural design. Table 3.1 in the code nominates design life (years) for various types of works e.g.: 30 years for industrial structures and 60 years for residential dwellings.
This practically rules out the use of hardwood timber retaining walls, since the best that can be achieved with Class 1 durability timber and H5 CCA treatment is in the order of 25 years. This is bearing in mind that virtually no current timber sleeper walls meet this standard.
It would seem an appropriate time for builders, designers and authorities to reassess their views towards proprietary concrete retaining walls, where the products and systems are engineer designed and tested, then manufactured to their respective standards to ensure that compliance to AS 4678 is assured.
Given society’s current preoccupation with the question of ‘liability’, how will current and future clients, owners and insurers (and their lawyers) view the liability of the consequences of poor retaining wall construction if it is shown not to have paid any heed to Australian Engineering Standards.