History - 1977



Development of Mk 3 HVS

The new machines, Mark IIIs, were commissioned during 1976 and 1977 and began full testing programmes in 1978. Fundamentally similar to the Mk II prototype, there were nonetheless significant differences beyond simple cosmetic improvement: the test wheel carriage was now designed to take normal dual truck wheels (the prototype only had single wheels) as well as aircraft wheels; the machines’ own wheel configurations were redesigned to ensure compliance with the statutory maximum axle loadings. The design also allowed for both uni- and bi-directional trafficking. From this time the Mk II prototype was kept on the NIRR’s test site, undertaking special and ad hoc investigations as funding was made available. undertaking special and ad hoc investigations as funding was made available.

The three new production machines were in continuous use on public roads throughout South Africa from the outset. They were funded from grants received from the DoT (for two machines) and from the TPA (for their machine), and all were operated by NIRR staff. Naturally this was done in close collaboration with the road authorities involved, and representative advisory committees were formed from the beginning. This relationship has been a significant factor in the undoubted success of the programme ensuring the earliest possible application of important findings. of important findings.

The three machines each had somewhat different roles, reflecting the differing priorities of the owners, which were complementary to a large extent. Thus the DoT machine was assigned to undertake specific DoT DoT investigations, which might or might not be related, but were of importance on a National level. The NIRR machine was generally more research focussed, implying perhaps a longer-term view of key factors influencing pavement performance. The TPA machine had a similar type of function but was geared to specific conditions in the Province. With hindsight, it is easy to see that this type of balance was probably extremely beneficial, enabling the findings from shorter-term specific investigations to contribute to and influence the longer-term programmes. In addition, it is very easy to see the benefit of having all the machines operated by the same agency, not in terms of economics of scale (which certainly existed), but rather in terms of the immediacy of communication between all those involved. Given the dynamic nature of the work, this ensured that new findings and developments could be rapidly evaluated and quickly disseminated. evaluated and quickly disseminated. From the late 1970s and throughout the 1980s, the expanded HVS programme was able to underpin virtually all the advantages and developments in South African pavement engineering. pavement engineering.

While South Africa’s political status at this time undoubtedly restricted direct exposure of the HVS’ work there were, nevertheless, significant numbers of overseas visitors during this time, notably from the United States, United Kingdom and Australia.

The subsequent development of Australia’s accelerated loading facility (ALF) from 1984 then provided the only other pavement test facility having an ostensibly similar capability to the HVS. Even so, while broadly comparable to the HVS in concept and appearance, the ALF incorporated several significant departures including the adoption of dead weight test wheel loading (rather than hydraulically applied load), and a wholly uni-directional loading mode. Interestingly, although even the prototype HVS had the capability for uni-directional trafficking, thus reflecting “real life” trafficking conditions more realistically, the decision from the outset was that the HVS machines would normally operate in bi-directional trafficking mode. This was based on the rationale that, given all the variables and influencing factors affecting pavement behaviour, the likely benefits to be gained by the greater rate of trafficking would probably far exceed any disbenefits. However, in specific cases such as in testing jointed concrete pavements, the uni-directional trafficking mode was used. -directional trafficking mode was used.

Again with hindsight, and the wealth of APT data amassed by the HVS, the value of this decision can be fully appreciated. It directly contributed to the extent of application of the machine, and therefore to the extent of influence. application of the machine, and therefore to the extent of influence.

Somewhat surprisingly perhaps, there has still been no direct comparison between uni- versus bi-directional loading undertaken by the HVS, even though this was identified among the earliest test objectives in 1972. This, however, continues to reflect the dominating influence of the pavement structures evaluated to this time.