Projection of the recultivation (restoration) of the quarries and open pit mining, methodologies of calculation of the main parameters

Category Mine
Group GSI.IR
Location 20th WORLD MINING CONGRESS 2005
Author José Enrique Pérez Gonzلlez*
Holding Date 14 January 2006
ABSTRACT
 
The projection of the Recultivation (Restoration) works is one of the main processes to obtain good results in the process of return the mining fields to the environment with the best technical and economical results
The two main processes of the recultivation works are:
  • Technical-mining recultivation
  • Biological recultivation
In the paper the projection of the technical-mining recultivation is describe by the main processes, include the calculation of the main parameters for each process, in base of the experience accumulated during years of projection of the recultivation works by the author.
In the paper we also offers the proposal of classification of the types of works of recultivation (restoration) of the quarries and open pit mining, with examples of these works made in Cuba and in other countries.
 
 

INTRODUCTION
 
One of the most important decisions is the selection of the recultivation type that will be made, being based on the conditions obtained by the execution of the mining works, in the paper they offer examples of these so much solutions of the Cuban experience as well as of the experience accumulated by different countries in the visits made by the author.
 
The decrease of the angle of the banks, for each type of recultivation, is one of the crucial processes during the works of technical-mining recultivation, in the paper we offers the calculation proposals for the different variants of execution of these works.
 
In the work intend the classification of the recultivation types that can be carried out according to the accumulated experience, to facilitate the economic - technical evaluation and to make the works of mining technical recultivation.  
The areas occupied by the quarries of construction materials oscillate among 30 - 250 ha, the Open Pit Mines of manganese and coal among 1000 - 2000 ha, the Open Pit Mines of iron among 150 - 500 ha. As you can notice the areas they are significant, of here the importance that represents the selection of the recultivation type to carry out and their agreement with the environment.
 
Classification of the Recultivation Works
 
The recultivation works are divided in (Pérez Gonzلlez, José
Enrique, 2001):
Technical Mining Recultivation: It is the cycle of the mining works that pursue the purpose of the preparation of the altered lands for their use for the different branches of the economy. In the works of Technical Mining Recultivation are included the works of levelling of the dump,  the stretched out of the banks and to give him a convenient form for the placement of the vegetable layer, or works of aquatic improvements  and/or the construction of access roads, etc. 
Biological Recultivation: He is carried out after when finished the Technical Mining Recultivation. Their purpose is the restoration of the vegetable layer and the biological productivity of the altered lands, the formation of agricultural and forest cultivations, the reproduction of fish in the reservoirs, of the animals in the planted forests, etc.; that is to say, the formation of the favourable landscapes for the life and the man's work.
In dependence of the purpose of the works, the terminologies of the recultivation acquire their denomination, for example (Pérez Gonzلlez, José Enrique 2004):
Agricultural Recultivation: when their purpose is sowed for grasses, agricultural products, etc. 
Figure 1: Agricultural Recultivation old quarry of useful mineral for ceramic, location Wajay, province of Havana City, Cuba
Forest Recultivation: formation of forests and green areas.
 
Figure 2: Reforestation in areas in that the geologic resources have been extracted in the nickel mines, Cuba
Aquatic Recultivation: formation of reservoirs for the breeding of fish, sport competitions, development of aquifer birds, with industrial ends.
Figure 3: Gravel quarry where all their geologic resources
were exploited in Orange County, California, USA
 
Constructive Recultivation: formation of lands for the construction of civil and industrial buildings. 
 
Figure 4: Construction of houses on a gravel quarry where their geologic resources ended in Dallas, USA
Recreational Recultivation: formation of areas for the amusement and the rest.
 
Natural Recultivation: recultivation carried out by the own nature, in a short period of years
Proposal of the content of a Project of Technical Mining Recultivation
 
The Methodology for the making of the Project of the Technical Mining Recultivation offers next, constituting the parts to carry out the following ones (Pérez Gonzلlez, José Enrique 2004 ARINSEMA):
1. Introduction
In the introduction the basic conditions will be given for the realization of the recultivation, as well as the main decisions that determine the election of the recultivation type (agricultural, forest, constructive recultivation, miner-technique for the conservation of the nature, the related with the waters and other).
 
For the determination of if it is feasible or not the execution of the Recultivation works, we propose the following formula:
 
 
 
 

Where: 
  
SR - index of the volume of the real land in the given period, m3/ha 
SP - index of the volume of the land that is the maximum thing possible to occupy according to the land, m3/ha
 
With a coefficient kt> 1 the use is uneconomical in comparison with that projected. The deviations of the project are eliminated with a coefficient kt = 1. they can have cases when kt <1, what attests the existence of reservations of the company in the lands obtained before in more dimensions by different causes (insufficient study of the location, variation of the solutions planners of the opening of the location and of the dump  formation, of the plans of development of the mining works).
 
The recultivation coefficient changes significantly in the different stages of the mining works. In the period of construction of the quarry and in the initial years of the exploitation of the location the same one is similar to zero, since like rule in this period is not carried out recultivation works. In the fundamental period of mining works the coefficient of recultivation can under certain conditions (for example, during the mining works of horizontal locations) to reach the unit. During the mining works of locations with a great inclination in the period of termination during the finalization of the mining works the alteration of the lands in the fundamental thing is eliminated. Under these conditions, and in the case of the production of the recultivation works in the dump areas, the coefficient of recultivation overcomes the unit.
 
2. Mining chapter. 
The mining chapter consists of the following aspects: 
- General organization of the recultivation works. 
- Work regimen. 
- Types and models of the equipment used for the recultivation. 
2.1 Extraction and conservation of the vegetable and sterile layers. 
- Extraction method and conservation. 
- Order of realization of the works. 
- Data of the continuity of the operations and calculation of the volumes of the vegetable layer. 
- Calculation of the equipment’s parameters.
2.2. Transportation and placement of the vegetable layer. 
- Selection of the type of transport. 
- Calculation of the productivity. 
- Calculation of the number of the equipment. 
- Method of placement of the vegetable layer. 
- Graphic annexes. 
2.3 Plan calendar of the extraction works and transport. 
- Calculation of the fundamental volumes of the extraction works and transport of the vegetable layer and their distribution for years of the period that embraces the project. 
- Calculation of the preliminary works of exploitation. 
- Graphic annexes.
2.4 Roads. 
- Construction of roads and necessary engineering works for the execution of the recultivation. 
- Calculation of the volume of the works to carry out. 
- Graphic annexes.
2.5 Preservation of the borders of the quarry
- Measures techniques for the preservation of the borders of the quarry, the interior and external banks of the erosion. 
- Calculation of the volume of the works to carry out. 
- Selection of the equipment to use. 
- Calculation of the number of equipment. 
- Realization method of the stretched out of the banks 
- Graphic annexes.
 
For the making of the mining chapter we recommend the following calculation methodologies (Pérez Gonzلlez, José Enrique 2004 HABISAL):
For the extraction of the vegetable layer with bulldozer two fundamental outlines can be defined: 
1 - Address of extraction of the traverse, longitudinal vegetable layer and combined with the formation of a store of layer vegetable in the area in which the same one is extracted; 
 2 - Address of extraction of the parallel and radial vegetable layer, with a movement of the stores formed to the inferior step. 
The width of work of the bulldozer settles down leaving of the calculation of the heap formed with the parameters that assure a total it loads to the extraction means and it loads of a single passing. The distance of transport of the vegetable layer with the bulldozer the 30-50 m should not overcome. 
The productivity of the bulldozer depends on the physical-mechanical properties of the rocks, of the depth of the cut layer, of the distance and speed of transportation of the floor, of the slope of the work sector and of the construction of the dump or store. 
The work experience in different quarries has demonstrated us that the most rational power in the bulldozer to use for the extraction of the vegetable layer is of 180-300 HP (under certain conditions of lands with many roots> 300 HP). 
The productivity for shift of the bulldozer (in situ), with a mining work of the vegetable layer with transfer, you can calculate for the following formula:
 
 
Where: 
Tt - duration of the shift, hours 
V - Volume of the floor in fluffy state, transferred by the knife of the bulldozer, m3
 
Where: 
l - Longitude of the knife of the bulldozer, m 
h - Height of the knife of the bulldozer, m 
a - wide of the prism of having poured, m
Where:    
- Angle of the bank of natural rest of the rock 
KE - coefficient that keeps in mind the difficulty of excavation of the rock 
KD - Coefficient of change of the productivity of the bulldozer, in dependence of the magnitude of the slope in the sector of work of the bulldozer and of the distance of transportation of the rock. 
KO - Coefficient that keeps in mind the increase of the productivity during the work of the bulldozer with special additions. 
Kp - Coefficient that keeps in mind the losses of the rocks in the process of their transfer.
 
 
Where: 
l2 - transportation distance, m 
ک - Coefficient of loss in dependence of the rock type 
KW - Coefficient of use of the bulldozer in the time. 
KR - Coefficient of swelling of the rock in the prism of having poured. 
Tts - Duration of a cycle, s
 
   Where: 
l1 - longitude of the one on the way to court of the soil, m 
V1 - speed of transfer of the bulldozer during the cut of the soil, m/s 
l2 - distance of transportation of the soil, m 
V2 - speed of movement of the bulldozer with the soil, m/s 
V3 - speed of the bulldozer empty, m/s 
tp - time of change of the speeds, s 
tr - time of turn of the bulldozer, s
 
The productivity for shift of the ripper you can be calculates using the following formula: 
- During the execution of the passes in parallel:
- During the work of the passes in parallel in crossings:
 Where: 
Tt - Duration of the shift, hours 
c - Distances among the parallel passes, m
c1 - Distances among the crossed passes, m 
kE - effective Depth of the ripper, m 
ke - Depth of introduction of the tooth of the ripper, m 
KW - Coefficient of use of the ripper in the time 
V - Middle Speed of work of movement of the tractor during the ripper's works, m/s 
T - Total Time that gets lost in the transfer from the harrow to the other furrow, s
 
 
Where: 
t1 - time of the profundity of the tooth of the ripper, s  
t2 - time of manoeuvre of the bulldozer during the furrow change, s 
t3 - time of ascent of the tooth of the furrow, s 
L - Longitude of the parallel passes, m 
M - Longitude of the crossed pass, m 
n - Quantity of teeth, units.
 
For the mining works of the vegetable layer, apart from the bulldozers, they are used with success the scrapers. They are capable by themselves, of executing several serial operations. As disadvantages of the scrapers they can be related: strong decrease in the effectiveness of the work, with an increase of the humidity in the rocks above 10-15% or during the existence of inclusions of calcareous in the loose rocks. The scrapers can be effective with a transportation distance of up to 2, 0-2, 5 km. 
 
Different technological outlines of use of the scrapers exist for the extraction of the vegetable layer.
 
Scheme 1: The vegetable layer is extracted, it transports and it stores to the surface of the sector that you recultivated in a single cycle. The work front in the step is divided in blocks with a width similar to the longitude of load of the scraper. The longitude of each block corresponds to the annual advance of the step of advanced. The placement of the floor in the dump is carried out with horizontal layers in the area where, in the fundamental thing, you has concluded the intensive establishment of the dump.
 
This scheme is distinguished for the simplicity of organization of the works; it is not required of a complementary area as temporary store of the floor. A disadvantage is the relative great transportation distance.
 
The middle distance of transportation of the floor with the scraper to an interior dump is possible to calculate using the following formula:
 
lt = 0,5 (B + Bo + L) +BTRA + B . Ti + 3C1, m     (10)
Where:  
B - it advances yearly of the front of the mining works, m 
Bo - wide of the sector in the dump, covered with the floor during the year, m 
L - Longitude of the front of work of the step of advanced, m 
 
Btra - wide of the area of work of the quarry, m 
Ti - time of intensive establishment of the quarry, m 
C1 - distance of security from the work front or of the layout of the movement of the scraper until the superior border of the bank of advanced, m
 
Scheme 2: In this scheme we propose the formation of a temporary deposit of the soil in the surface in the angular area of the border of the quarry and the transportation of the soil with the scrapers for the shortest road. This deposit of soil constantly you increase from the area of work of the quarry and ends in the area of the dump.
 
The minimum width of the deposit in its superior part is determined, above all, for the lineal dimensions of the scraper using the following formula:
lB = lRAZ + R + 0,5 bx + C   ,   m     (11)
where: 
lraz - longitude of the one on the way to discharge of the scraper, m 
R - Minimum radius of turn of the scraper, m 
Bx - wide of advance of the scraper, m 
C - Distance of security from the tire of the scraper until the superior border of the deposit, m
The width of the deposit in their inferior part you can calculate using the following formula:
 Where: 
HSKL - height of the deposit, m 
- Angle of the natural bank of the soil, grades 
- Angle of ascent access of the scraper to the deposit, grades.
We recommend determining the main parameters of the deposit in the following sequence
1 - The minimum width of the deposit is determined in its superior part; 
2 - The height of the deposit is calculated by means of the following formula:
where: 
                Lf - longitude of the step of advanced, m 
                Mp - height of the vegetable layer, m 
                Krp - swelling coefficient of the soil.
 
If hs> 10 m, then it is necessary to increase the width of the deposit, in a magnitude that is multiple of the radius of discharge of the scraper and, again to determine their height.
 
The distance of middle transportation of the vegetable layer from the work front, until the deposit, we recommended use following formula:
lTR1 = 0,5 (B + B0 + L + ln) + 3 C   ,   m     (14)
 
The distance of transportation of the vegetable layer from the deposit until the area that you recultivated, is calculated by the formula (Pérez Gonzلlez, José Enrique 2004 ARINSEMA):
 
lTR2 = 0,5 L - 0,5 ln   ,   m     (15)
 
Scheme 3: This scheme anticipates the formation of a temporary deposit of the vegetable layer, located in the dump of sterile rocks or in a special area. After the termination of the intensive establishment of the dump and all the necessary conditions are constituted for the recultivation, from the deposit of the vegetable layer they are transported with the scrapers until the recultivation area. This scheme is used in external dumps. 
 
The productivity for shift of the scrapers (in situ) it is determined by the formula:
Where: 
Tt - duration of the shift, h 
Ek - geometric volume of the box of the scraper, m3
Kn - coefficient of having filled with the box 
KB - coefficient of use of the scraper in the time 
Ke - coefficient of swelling of the soil 
Tc - duration of a work cycle, s
 
 Where: 
l1 - longitude of the one on the way to having filled with the box of the scraper, m
 
Where: 
Kp - coefficient that keeps in mind the losses of the vegetable layer during the formation of the one poured 
0,7 - coefficient that keeps in mind the irregularity of the thickness of the cut 
a - wide of the cut, m 
h - Depth of the cut, m
V1 - speed of the scraper during the one filled, m/s 
l2 - distance of transportation of the vegetable layer, m 
V2 - middle speed of the movement of the scraper with the vegetable layer, m/s 
l3 - longitude of the one on the way to discharge the vegetable layer, m
 
 
Where: 
b - Average thickness of the discharge layer, m
V3 - speed of the movement during the discharge of the vegetable layer, m/s 
l4 - distances of the movement of the empty scraper, m 
V4 - speed of the movement of the empty scraper, m/s 
tp - time of change of the speeds, s 
tr - time of a turn of the scraper, s
 
When dragline is used, the extraction of the vegetable layer can be carried out with front of wide work, pouring to temporary deposits. The width of the work front is determined leaving of the conditions of location of the layer extracted in the deposit and in dependence of the parameters of the digger, you can determine for the following formula:
Aexc £ Rexc 1 + RR 1 + hskl . ctg کp   ,   m     (20)
 
Where: 
Rexc1 - excavation radio of the dragline in the level in that is located, m 
RR1 - radio of discharge of the cube of the dragline, m 
Hskl - height of the deposit of the vegetable layer, m 
کp - angle of the bank of the deposit, grades.
 
One of the most important parameters of calculation is the stretched out of the banks, for their calculation we recommend the following methodology
 
The volume of the levelling works during the stretched out of the banks, it depends on the angle of natural rest of the bank, of the height, of the perimeter and of the number of bench. 
 
The volume of the works for the stretched out of the banks of the bench and dump it is calculated by the following formulas:
When the stretched out of the banks execute in one floor
When the stretched out of the banks execute in various floor:
Where: 
K - Coefficient of stretched out of the bank 
h - Height of the bench, m 
- Angle of the natural bank, in grades. 
- Angle of the bank after the stretched out of the banks, in grades. 
P - Perimeter of the works for stretched out of the banks, m 
n - Number of floors
The stretched out of the banks for the perimeter of the works is possible to carry out for two methods: "of up down" and "of below up"
The stretched out of the banks of "up down" it is executed by means of the transportation of the rocks from the superior border from the floor to the inferior border. During this method of the stretched out of the bank it is necessary the increase of the area for the placement of the volumes of rocks that will move. The decrease of this area it's possible to calculate for the following formula:
where: 
lRP - Increase of the horizontal projection of the line of the bank of the first floor, during the stretched out of the bank of "up down"
The banks can "stretched out" with dragline or front-shovel excavators with a lengthened arm. It is rational to carry out the stretched out of the banks with bulldozer, with an angle = 30o -12o, with a capstan placed in the axis of taking of the power and anchored.
If the stretched out of the banks "of up down" it is impossible (because free areas don't exist), then the method is used of stretched out of the bank "of below up". With this method the rocks move from the inferior border of the bank up of the surface.
The volume of the works you increases in 4 times in comparison with the method "of up down"
During the storage of the rocks in the bench or dump of multiple floors, it is necessary the formation of terraces. To avoid the erosion during the levelling of the terraces, to these they are given a traverse inclination of 1,5-2, toward the side of the superior terrace.
The volume of the levelling works, for the condition of:
h1 = h2 = h3 = ... = hn
It's possible to calculate for  the following formula:
VTR = bTR. hTR [ P2 + 2 P3 + ... + (n - 1)Pn ]   ,   m3     (23)
Where: 
BTR - Wide of the horizontal platform of the terrace, m. 
HTR - height of the terrace, m 
n - Quantity of floors
With the condition of:
(24)
The volume it's possible to calculate for the following formula:
 
 
3. Miner-mechanics Chapter. 
3.1 - repair works and supply of the spare parts to the equipments used for the recultivation. 
3.2 - graphic annexes
4. Economic Chapter
4.1 - the personnel's insole used for the recultivation. 
4.2 - calculation of the costs of the recultivation works 
5. Budgetary Chapter 
5.1 - presupposed by work object
5.2 - presupposed total, which will serve as base for the financing of the recultivation works
 
 CONCLUSIONS
 
The experience planner has taken us to carry out two different projections and interrelated for the realization of the Recultivation (Restoration) of the mined areas, that is to say: 
1.        Projection of the works of Technical Mining Recultivation
2.        Projection of the works of Biological Recultivation
The application of the calculation methodologies and their recommendations presented paper presently can cooperate to an improvement in the making of the projects, in specific the projection of the Technical Mining Recultivation
 
REFERENCES
 
1.        Pérez Gonzلlez, José E., 2001, Recultivaciَn de las Minas a Cielo Abierto y Canteras de Materiales de Construcciَn: CCSTP-GEICON-MICONS.
 
2.        Pérez Gonzلlez, José E., 2004, Proyecto Tیpico de Recultivaciَn: ARINSEMA.
 
3.        Pérez Gonzلlez, José E., 2004, Recultivaciَn. Perspectivas y Soluciones: UNAICC Ciudad Habana.
 
4.        Pérez Gonzلlez, José E., 2004, Recultivaciَn de las Canteras de Materiales de Construcciَn: HABISAL.

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