Open pit automobile transport
OPEN PIT AUTOMOBILE TRANSPORT (EN: open-pit truck haulage, opencast automobile transport; DE: Kraftverkehr im Tagebau; FR: transport par camions aux mines à ciel ouvert; ES: transporte por camiones en minas à cielo abierto; RU: автомобильный карьерный транспорт) is the technological process of moving, with the help of the dump trucks, of the rock mass from the open pit to the waste dump, to the reloading place, to the receiving device of the benefication factory. In the broad sense, it is the complex, which integrates the transport vehicles and the auxiliary equipment, open pit roads, the technical instruments for the control of the performance of the activities, as well as the resources for the technical maintenance, and for the repair of the equipment and the roads.
The usage of the open pit automobile transport at the earthworks during the development of the sand and gravel deposits in the USSR has started in 1932. The dump trucks up to 3 tonnes of the load carrying capacity, as well as the side loading trucks with the manual unloading, served as the rolling stock for the transportation of the rock mass. Since the late 40's, they use the open pit automobile transport at the copper ore open pits of the Urals.
The large volumes of the transportation by the open pit automobile transport have been carried out for the first time in 1954 during the construction of the Sokolov-Sarbai mining-benefication combine. The further development of the open pit automobile transport has become possible because of the creation of the new family of the BelAZ dump trucks with the load carrying capacity of 27-180 tonnes (see the "Open pit dump truck" article).
The open pit automobile transport is widely used at the foreign open pits (for example, in the U.S.A. and Canada). The areas of the effective usage of the open pit automobile transport are: the construction of the open pits; the development of the deposits with the irregular outlines, or of the deposits, which are located in the mountainous rugged terrain; the development of the horizontal or slightly inclined strata during the rapid advancement of the front of the works; the excavation of the minerals according to their grades, or the excavation of the individual layers and blocks; the development of the deposits, which are embedded at the great depth (using the automobile transport in the combination with the other transport means on the short arm of the haulage).
The open pits, where the open pit automobile transport is used, have the limited sizes (the usual length in the plan projection not more than 2-3 kilometres, the depth of 150-200 metres) in the most of the cases. The optimization of the open pit automobile transport is usually associated with the fullest usage of the loading equipment in the stopes. Because of this optimization, the layout of the approaches for the loading is designed while taking into account the least time for the maneuvers, the delivery and replacement of the dump trucks (Figure). The productivity of the excavator (loader), and the volume of the bulk body of the dump truck, which must be the multiple (from 3:1 to 8:1) of the volume of the bucket of the excavator, influence the duration of the loading. The mode of the movement of the rolling stock is determined, first of all, by the type of the open pit.
The transportation of the load uphill is characteristic for the open pits of the deep type, and downhill for the open pits of the upland type. During the usage of the open pit automobile transport in the combination with the other transport means, their work is possible in the both modes during the movement to the reloading place: downhill from the one part of the open pit banks, and uphill from the other part.
They implement the organization of the movement of the automobile transport in the open pit according to the closed or open loop methods. In the first case, the group of the dump trucks is dedicated to the specific excavator. Such organization is simple, but often causes the delays. During the organization of the movement according to the open loop, the dump trucks are distributed among the excavators, in order to decrease as much as possible their downtime while waiting for the transport, and the demurrage (delay) of the dump trucks at the loading places.
The work of the automobile transport according to the closed loop method is ensured by the system of the control, which represents the information about the performance of the loading and unloading works to the dispatcher. At the start of the shift, the dump trucks are dedicated to the excavators according to the schedule of the work of the open pit for the shift, and during the work, in the case of the sharp changes of the productive situation, the correction is performed, as the indication of which serves the maintenance of the required quality (sic) of the ore, which is delivered to the benefication factory.
During the organization of the movement according to the open loop method, the number of the excavator, to which the next dump truck must arrive, is determined with the help of the computer according to the given algorithm; they perform the recognition of the dump trucks and their automatic weighting. Such system of the control allows to optimize the flows of the load, to ensure the uniform blending of the ore, to decrease as much as possible the demurrage (delay) of the dump trucks, on the condition that every excavator would carry out the required job during the shift.
The performance indicators of the open pit automobile transport are determined by the conditions of the exploitation (including the distance of the transportation), the status of the rolling stock and of the system of the technical exploitation, which are characterized by the coefficients of the technical readiness (st) of the fleet of the automobiles, and by the coefficient of the usage (s) of the fleet of the automobiles. These coefficients are determined according to the formulae
st = N / Ncp, s = np / nx, where
N - the quantity of the technically operational dump trucks;
Ncp - the total quantity of the dump trucks in the register at the open pit;
nx - the quantity of the machine-days (machine-hours) of the dump trucks in the fleet of the enterprise;
np - the quantity of the working machine-days (machine-hours) during the same period.
Usually st = 0.7-0.9 and depends on the organization of the repair, the status and the working order of the rolling stock; s = 0.4-0.6 and depends on the technical condition of the dump trucks, the roads, the climatic conditions, the quality of the organization of the work, the manning of the trucks by the drivers, etc.
The productivity of the open pit automobile transport is determined by the distance of the transportation, the technical velocity of the movement, the types of the excavators, the quality of the usage of the working time. For the widely available open pit conditions the productivity of the typical dump truck in the register is 7-8 thousand tonnes per 1 tonne of the load carrying capacity per year. The cost of the transportation of 1 tonne of the load for the distance of 1 kilometre with the usage of the automobile transport is 0.08-0.1 rubles; the main lines of the expense are: the amortization (25-30%), the wages of the drivers (20-25%), the repair of the tires (20-25%), the technical maintenance and repair (12-17%), the expenditures on the fuel (8-11%).
The effectiveness of the work of the open pit automobile transport increases with the creation of the perfect system of the technical exploitation, which takes into account the quality of the rolling stock, the conditions of the exploitation, the status of the productive resources, the system and organization of the technical maintenance and repair, the system of the logistics of the supplies, the training of the maintenance personnel and the improvement of their professional qualification. The planned preventative system of the technical maintenance of the machines and the aggregate method of the repair are promising the good results. The main advantages of the open pit automobile transport are determined by the good manoeuvrability of the rolling stock, the decrease of the length of the transport communications because of the implementation of the relatively steep inclinations of the roads, the simplification of the process of the waste disposal because of the lesser labour requirement and the possibility to decrease the area of the waste dumps, the high operativeness of the control.
To the disadvantages of the open pit automobile transport there belong the limit up to 3-4 kilometres on the distance of the transportation of the loads, the dependence of the exploitation of the roads and the rolling stock on the climatic conditions, the high tailpipe pollution of the environment during the work of the automobile transport machinery.
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