Towed Graders and Tractor-Based Maintenance of Low-Volume Roads
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116 TRANSPORTATION RESEARCH RECORD 1291 Towed Graders and Tractor-Based Maintenance of Low-Volume Roads R. C. PETTS AND T. E. JONES Th~ hi~t?rical development of equipment for constructing and out to the private sector. Contract agricultural work is already mamtammg the surface of earth and gravel roads is reviewed. well established in many developing countries and road main The use of tractor-drawn graders and drags is emphasized. The tenance and improvement activities could provide an exten case for tractor-based road maintenance operations for these roads sion to the type of work carried out by tractor-owning con in developing countries, instead of the normal motor grader and truck-based operations, is also developed. For many secondary tractors. and tertiary road networks, routine and some periodic mainte The historical development of equipment for constructing nance could be carried out using wheeled agricultural tractors as and maintaining the surface of earth and gravel roads is the_ sole power units towing mechanical graders, gravel haulage reviewed. The use of tractor-drawn towed graders is empha trailers, water bowsers, and rollers, as required. The operations sized and towed drags are briefly described. The case for could be supported by local labor for such activities as gravel tractor-based road maintenance operations for these roads in excavation, loading and unloading, spreading, and drainage main tenance. The road maintenance could be carried out by direct <leveloping countries, instead of the normal motor grader and labor (force account) organizations or contracted out to the pri truck-based operations, is also described. ~ate sector. Contract agricultural work is already well established m many d_e~~loping countries and road maintenance and improve ment act1v1t1es could extend the type of work carried out by HISTORICAL DEVELOPMENT tractor-owning contractors. Tractor-based road maintenance oper~tions would be significantly cheaper in terms of capital and ru_nnmg costs. The logistic and support problems of such oper Tractor or vehicle-drawn graders have been used for grading at10ns would also be less than for current motor grader-based the surfaces of unpaved roads at least since 1909 (see Figure operations. Tractor-based road maintenance operations would 1). Initially, they had solid metal wheels and were normally make more effective use of the limited financial and other resources drawn by tractors (see Figure 2) although some models were available to road maintenance organizations in developing self-propelled, as shown in Figure 1. Very early graders often countries. incorporated complicated mechanical devices for carrying out activities in addition to surface grading. These included the In many developing countries, the motorized grader is the construction of miter drains (turn outs), side drains, and side principal equipment item for maintaining unpaved roads. slopes, as shown in Figures 3 and 4. Early road construction However, the availability of this equipment is low because of techniques also included graders towed in tandem and the use inadequate funding resources, mainly for spare parts and of tractor-drawn trailers with side-tipping facilities for the maintenance facilities, and the shortage of the trained man transportation of gravel wearing course or fill material, as power required to maintain the equipment. (The terms avail shown in Figures 5 and 6. This type of road construction ability and utilization frequently used in the text refer to equipment was used quite extensively in most countries until equipment that is available for maintenance works and is the mid-1930s when the motorized grader was developed from utilized in maintenance activities. Utilization is expressed as a hybrid tractor fitted with a full-width moldboard (Figure 7). a percentage of the time that the equipment is available for In developing countries, particularly in the early 1950s, the work.) This low level of availability has led, particularly in introduction of the motorized grader, often funded by devel African countries, to inadequate maintenance operations on oped countries or donor agencies, led to a decline in the use the majority of the unpaved road networks (J). of tractor-towed grading equipment. However, subsequently Recent research (2) suggests that for many secondary and a range of factors meant that the operation of motorized tertiary road networks routine and some periodic mainte graders in developing countries became problematic, resulting nance could be carried out using wheeled agricultural tractors in extremely low availability of equipment. In many cases, as the sole power units, towing mechanical graders, gravel the end result is that road maintenance is simply not carried haulage trailers, water bowsers, and rollers as required. The out, particularly on important and highly trafficked routes. operations could be supported by local labor for such activities The low availability of maintenance equipment is one of as gravel excavation, loading and unloading, spreading, and the principal reasons for the poor condition of a substantial drainage maintenance. The maintenance could be carried out amount of the unpaved road networks in Africa (J). More by direct labor (force account) organizations or contracted recently, this situation has led to countries looking at cheaper and more reliable alternatives. In the last 20 years, a number R. C. Petts, Intech Associates, United Kingdom. T. E. Jones, Trans of countries, particularly in Africa, have started to utilize port and Road Research Laboratory, Crowthorne, Berkshire, United tractor-towed graders for surface treatment of gravel roads Kmgdom. (Figure 8) and, more recently, tractor-towed compactors, water "' c FIGURE 1 Self-propelled grader, 1919. FIGURE 2 Road leveler, 1919. Steering shaft Hand wheels Wheel Blade drawbar Blade FIGURE 3 Basic towed grader, 1920. Ditching an earth road Note lean of wheels Blade This type of Grader has a blade that can be set to any angle on either side to form road surfaces, ditches or banks. This one is tractor-hauled, but some are self-propelling FIGURE 4 Ditching and side slope techniques. 11 8 TRANSPORTATION RESEARCH RECORD 1291 FIGURE 8 Grader in use in Africa in 1960s. FIGURES Tandem towed grader, 1920. bowsers, and trailers. Some countries are now exploring the feasibility of operating maintenance units based entirely on tractor-towed systems. One example is Thailand, where the Office of Accelerated Rural Development (ARD), which is responsible for the construction and maintenance of 19 000 km of unpaved road, has already started to implement such a system (Figures 9 and 10). The development of mechanical drags for leveling unpaved roads has changed only slightly from the 1920s when the prime mover was a horse as shown in Figure 11. Early models of the drags shown in Figures 12-14 are basically the same as those used today in developing countries. They are effective in reducing surface irregularities on gravel roads and on low trafficked routes and are often the most appropriate solu tion. Current usage and models are discussed in detail else where (2). CURRENT PROBLEMS OF MOTOR GRADER BASED ROAD MAINTENANCE IN DEVELOPING COUNTRIES FIGURE 6 Early side-tipping trailers. In many developing countries, the principal item of routine maintenance equipment for earth and gravel roads is the motor grader. It is also sometimes used to reshape the unsealed shoulders of paved roads. FIGURE 7 Prototype motorized grader, 1926. FIGURE 9 Towed grader currently utilized in Thailand. Petts and Jones 119 FIGURE 13 Road hone. bowsers are used for the provision of gravel surfacing, which is required for routine patching and periodic regraveling. FIGURE 10 Tractor-towed compactor. Haulage is normally carried out using tipping trucks. These equipment-based operations were set up before the The motor grader is used for reshaping the running surface, global oil crises of the 1970s. Before these events, equipment removing corrugations, and cleaning the side and miter drains was relatively cheap and road authorities in developing coun (turn-outs). The machines typically work alone, operating tries did not face the serious problems of procurement and from a road camp base. Grader operations are usually sup equipment support that many of them face today. plemented by labor gangs also working from road camps. The operating environment of road authorities has changed Although the support operations are manual, a truck is considerably over the last 20 years. Motor graders, front-end usually required to transport the gang from the road camp to loaders, and bulldozers are now expensive and specialist items the worksite each day. Other specialist equipment such as of equipment, ideally suited for use by medium or large con bulldozers, front-end loaders, and self-propelled rollers and tractors in developed countries. These organizations are able to closely support their equipment on construction sites with good site workshops and mobile workshop facilities. Highly skilled mechanics and operators, readily available spares, and technical support enable the full potential of the machines to be realized in these circumstances. These conditions rarely exist in developing countries. Typ ical problems currently encountered by the road authorities include the following: •Equipment working individually at long distances from workshop facilities. •Poor workshop facilities-mobile workshops rarely exist. • Lack of necessary trained workshop