Expansion of raw-material resources in the iron-ore industry will be accomplished mainly by opening new mines and reconstructing old ones. The greatest relative contribution to the output of ore will be made by open pits working the deeper parts of steeply dipping deposits. These will constitute 67-78~ of the total amount of rock excavated by the open system, and 85-93~/c of this will be ledge rocks. Whereas at present the depths of ironore mines do not exceed 150-190 m, many mines are planned which will exceed 500-700 m. Thus, in the coming 7-10 years, the expansion of ore recovery will involve an increase in the relative contribution made by open pits, a great increase in the depths of these mines, and a marked increase in the proportion of ledge rock in the total rock excavated. In these circumstances, special attention will clearly be paid to the development of more efficient techniques for extraction operations, and this will only be possible if we can acquire data on the physical conditions of mining.
In the technical literature on the exploitation of high-capacity motor transport in open pits and quarries, there are no articles with precise mathematical treatments of the real process of transportation by motor dump trucks.Research performed by the Institute of Mining of the Ministry of Ferrous Metallurgy of the USSRon th'emodeling, of quarry [open pit] motor transport and experimental work on the exploitative parameters and operational conditions of contemporary models of motor transport media in open-cut ore mines have served as a basis for a mathematical representation and computer modeling of the real process of rock transportation by high-capacity motor tracks.Solution of an optimization problem by means of mathematical models involves the choice of assessment criteria, which must satisfy the following principal requirements, 1) They must have a quantitative value (possibility of measurement for any combination of independent variables). 2) They must satisfy the uniqueness condition (a given choice of values of the independent variables must correspond to a single value of the optimization criterion). 3) They must actually give an estimate of the effectiveness of transportation media in particular conditions of exploitation (on the basis of economic analysis). 4) They must be universal (must possess the capacity for characterizing all aspects of the operation of the motor transport medium as a whole). 5) They must have physical meaning for facilitation and simplicity of the subsequent interpretation of the results.In our formulation of the problem, as a criterion for assessing the optimum solution we used the maximum output (throughput) of the motor transport medium, giving minimum cost of rock transportation.This optimality criterion gives the greatest satisfaction of the above requirements.If the calculated indices characterizing the process of rock transport are to give the best approximation to reality, the following factors must be taken into account: the parameters and complexity of the motor road layout; the speed of the dump trucks at the beginning and end of each transportation section; the influence of grades on the acceleration and inertia; the power reserve for climbing; the speed limits on the curves, downgrades, face and dump roads; and the constructional features of the motor trucks. The initial data for the model are: the constructional parameters of the dump trucks; the actual parameters of motion of the motor trucks in the quarry, found experimentally and by means of analytical formulas, characterizing the standard components of the conditions of motion. The suggested theoretical-experimental method of reproducing the transportation process on a computer involves multivariant computations, which would require much labor and time without a computer.The operational conditions of the dump trucks in the transportation cycle are modeled with the following conditions.1. The roiling resistance of a motor truck on the characteristic sections of the quarry motor roads (main, face, and dump sectio...
THEWhen ledge rocks are worked by blasting, the grain-size composition of the spoil depends largely on the jointing. Information on the state of the rock, obtained by detailed surveying, helps to predict the natural block size of ledge rocks. In this connection, the principal difficulty is that core descriptions give only qualitative features, and the core yield remains the only source of information on the block size of these rocks.To enable data on the core yield to be used for assessing the natural block size of ledge rock, in a number of open-cut ore mines we performed comprehensive investigations, 'including the following: a) the degree of jointing in the direction of borehole drivage to the surfaces of the slopes of the benching banks; b) the fragment size of the core in boreholes intersecting the exposure in which the jointing was surveyed; c) the dependence of the core yield on the drilling procedure and condition and on the strength and jointing of the rocks in these boreholes. These conditions revealed the following:Under identical drilling conditions (hard-alloy bits 93-112 mm in diameter, length of operating cycle 1.0-2.0 m), the ratio of the distances between the natural uncemented joints separating the rocks along the bbrehole axis to the actual size of the core fragments is 7-30;When the boreholes are drilled in identical rocks the ratio of the mean sizes of the core fragments is directly proportional to the ratio of the inner diameters of the drill bits;When the boreholes are drilled with hard-alloy bits in rocks with Protod'yakonov hardness more than 6, the core yield is virtually independent of the hsrvluess of the rock; Additional crushing of the core during drilling by fracture and torsion has no effect on the core yield if the size of the natural blocks is 2-3 times greater than the inner diameter of the drill bit;The influence of abrasion of the core as it is twisted can be disregarded if the ratio of the operating cycle to the core diameter is not more than 10-15;The following relation exists between the core yield (k, %) and the mean size of the blocks along the borehole axis (l, m):which holds true with a correlation coefficient of 0.76 for the following conditions: drilling with hard-alloy bits of diameter 93 mm or more with mud circulation for an operating cycle of length not more than 2 m and a core yield of not less than 60%. Equation (1) enables us to use the data of detailed surveying for predicting the block size.A rational procedure for processing the data is described below.On the composite plan of the mine workings and on the geological cross sections we draw all the faults and folds and the stratigraphic and lithologie contacts, and establish the boundaries of the structural-tectonlc blocks within which the block size of the rocks can be regarded as constant.On this graph we plot all the data on the block size of the rocks, obtained from large-scale measurements of the jointing or by processing photographs and stereopairs, and the information on the yield of oversized material ...
Transportation of rock in open pits in automotive dump tracks is performed in cycles which, during rhythmical operation of the loading and transport equipment, follow one another in a fixed sequence. The duration of the transport cycle is governed by the speeds, tractive dynamics, and braking characteristics of the high-capacity automotive dump trucks, by the mining parameters, and by the conditions in the pit.The conditions in the pit directly influence the speeds of the automotive dump trucks; their relative weightings, in relation to the height of raising of the rock, the length and combination of the elements of the longitudinal profile of the route, the gradients, and the type and state of the road surface, vary over appreciable ranges. Research on the quantitative indices of the transport cycle -journey times on various elements of the longitudinal profile of the motor roads, the frequencies of starting from rest, the times required for gear changing, and the acceleration, deceleration, and braMng distances -enables us to estimate the influence of the dynamics of the trucks on the duration of the transport cycle. The principal index of the dynamics of a truck is the acceleration, which characterizes its ability to start rapidly from rest and to increase its speed [1]. It has been found that when automotive dumptmeks operate in open pits, the time of motion at constant speed is very small. Most of the time (50-80~ is spent in acceleration or deceleration. The dynamics of automotive dump trucks are especially important in automotive transport over short distances wi thin the pit. The use of a computer to make an analytical representation and mathematical model of the motion of a truck enables us to determine the minimum time and acceleration distance of a dump truck on roads with a variety of different surfaces, taking account of the operating conditions of the motor, the time taken to change gear, the loss of speed during gear changing, and the useful load and type of loading equipment. The calculations are based on an analytical method involving direct integration of the differential equation of motion of the truck (2) obtained by substituting expanded values of the forces in the equation of tractive balance (1) [2, 3]:
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