mining haul roads by abhishek mishra
Post on 05-Sep-2015
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DESCRIPTIONMining Haul Roads
INVESTIGATION OF SOME HAUL ROAD DESIGN PARAMETERS AFFECTING DUMPER PRODUCTIVITYINDEX1. INTRODUCTION1.1 General1.2 Objectives of the project2. LITERATURE REVIEW 2.1 Haul Road Design Categories 2.2 Geometrical Considerations 2.2.1 Stopping Distance 2.2.2 Sight Distance 2.2.3 Road Width 2.2.4 Curves and Switchbacks 2.2.5 Super-elevation 2.2.6 Super-elevation Run-out 2.2.7 Road grade 2.2.8 Cross-slope 2.2.9 Safety Berms and Ditches 2.3 Haul Road Cross-section 2.3.1 Sub-grade 2.3.2 Sub-base 2.3.3 Base 2.3.4 Wearing Surface 2.4 Haul Road Surface Characteristics 2.4.1 Roughness 2.4.2 Traction 2.4.3 Rolling ResistanceCHAPTER 1: INTRODUCTION1.1GENERALThe haul road design forms a principal component of a transport operation on both surface and underground mines. Most mine operators will agree that a strong relationship exists between well-constructed and maintained roads and safe, productive mining operations. The expansion of surface mining has led to the development of very large off-highway trucks currently capable of hauling payloads in excess of 290t. Mine haul roads have historically been designed empirically, relying heavily on local experience. The trend in increasing truck size has thus rendered the current pavement systems inadequate. Improper road design not only would increase the maintenance costs of roads but would also increase, vehicle operating and maintenance costs prohibitively. There is thus a need for improved design technologies encompassing the construction and management techniques of mine haul roads, appropriate for the wheel loads of vehicles now in use. The design and management of mine roads has developed over the past decade, both in response to the requirements of mine operators for more safe and productive haulage systems, and the truck manufacturers requirements for a more predictable and controlled operating environment. Whilst it is possible to construct a mine haul road that requires no maintenance over its service life, this would be prohibitively expensive. On the other hand, a cheaply-built haul road would be expensive to operate, in terms of truck operating and road maintenance costs. So a need of optimizing the design parameters has arose in order to keep the haul road construction and management cost within the economics of the mining project. This project thus aims to critically investigate into the various design parameters that affect dumper productivity. By dumper productivity we are referring to the production potential of a dumper in a unit time interval. Although dumper productivity depends to a great extent on how well the driver reads and anticipates road conditions, but its dependency on the geometrical and structural design of the road is also an established fact.
1.2 OBJECTIVES OF THE PROJECT Investigation of the haul road design parameters Study of the haul road surface characteristics Designing a cross-section of a haul road for a surface mine Developing a predictive model for estimating dumper productivity Investigation of haul road maintenance and management techniques to improve its productivity
CHAPTER 2: LITERATURE REVIEW
2.1 HAUL ROAD DESIGN CATEGORIESDesigning a safe and efficient haul road can only be achieved through an integrated design approach. If one design component is deficient, the other components will not work to their maximum potential and road performance and safety is often compromised. The operating performance of a haul road is viewed under three distinct design categories:a) Structural Designb) Functional Designc) Maintenance Design
FIGURE: Three components of a haul road design strategy a) The structural design which will provide haul road strength to carry the imposed loads over the design life of the road without the need for excessive maintenance, caused by deformation of one or more layers in the road , most often soft or wet in-situ materials below the road surface.b) The functional design, centered on the selection of wearing course (or surfacing) materials where the most suitable choice, application and maintenance strategy is required which minimizes rolling resistance and the formation of defects in the road surface and generation of dust.c) The maintenance design The maintenance aspect of haulage-road design cannot be considered separately from the structural and functional design aspects since the two are mutually inclusive. An optimal functional design will include a certain amount and frequency of maintenance (watering, grading, etc.), and thus maintenance can be planned and scheduled within the limits of the expected road performance. The major problem encountered in the analysis of maintenance requirements for haulage roads is the subjective nature of the problem; the levels of acceptability or serviceability for the road are user specific.
2.2 GEOMETRICAL CONSIDERATIONSGeometric design refers to the layout and alignment of the road, in both the horizontal (curve radius, etc.) and vertical (incline,decline, ramp gradients, cross-fall, super-elevation etc.) plane, stopping distances, sight distances, junction layout, berm walls, provision of shoulders and road width variation, within the limits imposed by structural, functional and maintenance design parameters.
2.2.1 STOPPING DISTANCEFrom a safety standpoint , haulage road grades must be designed to accommodate the braking capabilities of those vehicles having the least braking potential which will most frequently traverse the haul route. In the majority of cases, rear, bottom, and side dump trucks, by virtue of their function within the mining operation, are the most frequent haulage road users. Due to their extreme weight and normally high operating speeds in relation to other equipment , their ability to decelerate by braking is lowest of the constant haulage road users. The design of routes that accommodate the braking systems of haulage trucks should leave a sufficient margin of safety for other equipments less frequently used , such as dozers, loaders, scrapers, graders, etc.To assess stopping distances for different grades and speeds, Kaufman and Ault (1977) developed an empirical formula based on the SAE stopping distance limitations:
Where:SD = stopping distance (m)g = gravitational acceleration (9.81 m/s2)t = elapsed time between drivers perception of the need to stop and the actual occurrence of frictional contact at the wheel brakes (s) = angle of descent (degrees)Umin = coefficient of friction at the tire-road contact areaVo = vehicle speed at time of perception
2.2.2 SIGHT DISTANCEVertical and horizontal alignment in road design requires judicious selection of grades and vertical curves and turning radius that permit adequate stopping and sight distances on all segments of the haul road. The relationship between operator sight distance and vehicle stopping distance is illustrated in the figure below for safe and unsafe conditions. All corners and bends in road shall be made in such a way that the operators and drivers of vehicles have a clear view upto a distance not less than 30 metres along the road as per the coal mine regulations , 1957.
FIGURE: Illustrations of safe curve design2.2.3 ROAD WIDTHThe width of haul roads on both straight and curved sections must be adequate to permit safe vehicle manoeuvrability and maintain road continuity. Since the size of equipment that travels on haul roads varies significantly from mine to mine, vehicle size rather than vehicle type or gross vehicle weight are best used to define road width requirements. For straight road segments, it was recommended that each lane of travel should provide clearance on each side of the vehicle equal to one-half of the width of the widest vehicle in use. For multiple lane roads, the clearance allocation between vehicles in adjacent lanes is generally shared. Roads that are too narrow can drastically reduce tire life by forcing the truck operator to run on the berm when passing another vehicle. This results in sidewall damage, uneven wear, and cuts. This is a particular problem when an operator adds new larger trucks to an existing fleet but does not change the road layout to accommodate the wider trucks.The minimum width of running surface for the straight sections of single and multi-lane roads can thus be determined from the following expression:
Where:W = width of running surface (m)L = number of lanesX = vehicle width (m)
Additional road width in excess of the minimum determined might be required locally along the road alignment, for example: to accommodate equipment larger than the primary road users, such as shovels or draglines, to allow sufficient room for vehicles to pass on single lane roads, and if, on single lane roads, the sight distance is less than the stopping distance, sufficient space must be provided for moving vehicles to avoid collision with stalled or slow-moving vehicles.
A wider road is required on curves to account for the overhang occurring at the vehicle front and rear. The procedure for determining road width on curves to account for vehicle overhang, lateral clearance between passing haul trucks and extra width allowance to accommodate difficult driving conditions on curves is shown in Figure below. 2.2.4 CURVES AND SWITCHBACKSEquation below is a generally accepted formula for curve design. This formula considers the speed of the truck, friction on the road surface, super-elevation and curve radius. The formula tries to balance the outward centrifugal forces with siding resistance plus the inward component of force from the ve