Innovative technology for mining parallel superimposed inclined tabular deposits

Ore deposits are often parallel superimposed inclined tabular ones with waste rock inclusions between ore beds. The present research aims to develop an innovative safe and efficient technology to reduce the cost of waste rock transportation outside the stoping block and provide a rational flowsheet for mining superimposed beds with original structural elements. The paper proposes a new technological flowsheet for mining superimposed deposits with disposal of waste rocks occurring between beds in previously prepared rooms and establishes new dependencies of room dimensions on the volume of rocks to be disposed. The research results enable expansion of the scope of employment of room mining systems and significant reduction in costs in the working area. The efficiency of ore mining is achieved by creating room crowns from unmined interbedded rocks, disposing broken waste rocks in worked-out spaces and rationally mining the deposits. Implementation of the proposed technology enables reduction of the cost of mining ore from parallel superimposed inclined tabular deposits.


Introduction
A number of underground ore mine fields are represented by parallel superimposed inclined tabular ore deposits.Efficient mining of such deposits is hindered by active occurence of strain processes directly in the deposits and surrounding rocks, especially when the thickness of the interbedded rocks is insignificant.The underground mines of Kryvyi Rih Basin employ bulk caving systems to mining such complex deposits.This leads to dilution with interbedded rocks, which reduces the iron content in the mined ore and increases ore mass losses.
A considerable number of researches are devoted to the search for and improvement of mining systems with open stopes [1][2][3][4][5].As a rule, they aim to develop new options of systems, improve existing ones, determine effective parameters of stoping and optimal dimensions of underground structures, and methods of forming preparatory-development workings.The idea of using self-propelled equipment in production processes when mining by room systems with bypassing caved rocks into the room cavity and step-by-step destruction of the crown, taking into account the time for block reserves mining, is proposed in [6].However, this technology requires significant improvements in terms of extracting room and pillar reserves and correlation of their parameters with the service life of structural elements of the mining system.
Employment of a more efficient room mining system with selective mining of deposits for similar IOP Publishing doi:10.1088/1755-1315/1348/1/012047 2 conditions is dealt with in [7].In this case, a stoping block is worked out starting from the hanging wall of the deposit with an ore-free inclusion left as a pillar, and then the remaining ore is extracted from the footwall of the deposit, depending on the order and sequence of mining operations.At the same time, when employing a room mining system, it is necessary to ensure stability of pillars and ore and rock exposures for the entire life of stoping blocks to provide high extraction indicators and safety of mining operations.It is also found out that an ore-free inclusion in the mining block undergoes different loads depending on the mining procedure and the deposit development sequence.Thus, a field of tensile or compressive stresses is formed in the massif.At the same time, when a pillar is subjected to compressive and tensile stresses for a long time, normal stresses in the ore-free inclusion first increase and then decrease.The repeated load results in numerous linear strains in the pillar and consequent significant decrease in the compressive strength of the pillar rocks.
The mentioned paper studies and provides recommendations on determining stable parameters of exposures in rooms.However, it does not provide a constructive solution concerning the mining system for superimposed deposits itself.It neither develops an element-by-element procedure for mining levels, nor considers the issue of removing waste rocks from technological workings, or using interbedded rocks as crowns for rooms of the lower bed.Apart from that, the proposed procedure for deposit mining deteriorates indicators of mineral extraction from the subsoil and requires significant costs to ensure stability of structural elements of the mining system and rationality of their mining.
A technological flowsheet for mining tabular deposits by an open stope-based system proposed in [8] provides for division of a stoping block into rooms, inter-room pillars and the crown, and stope reserves; the waste rock inclusion is broken off in layers parallel to the bed formation from the hanging to the footwall using set parameters and sequence.The paper proposes to build an artificial structure with broken rocks on the block sill intended for further broken ore mass drawing.At the same time, it is necessary to ensure passage of crown ore pieces broken at bulk caving through the caved rocks with a determined filtration coefficient.
Disadvantages of this method include the following: significant difficulties and costs for drilling and blasting when stockpiling rocks on the stope sill; no certainty about the ratio of parameters of rock layers in the block and broken rock volumes necessary to form a spatial uncontrolled artificial structure; possible transportation costs for removing waste rocks outside the stoping block boundaries; instability of the resulting workings of the receiving level; deterioration of ore mass extraction indicators, especially in case of bulk caving of the crown or inter-room pillars as rock layers in them are worked out in bulk; troublesome provision of broken mass filtration through previously created waste rock piles on the receiving level.
Thus, employment of mining systems with the caving of ore and surrounding rocks deteriorates mineral extraction indicators in these conditions.The most widely used method -selective mininginvolves high costs for removal and transportation of waste rocks outside stoping blocks.At the same time, it is difficult to ensure safety of mining under-and overworked beds.In addition, most researches mainly touch upon steeply dipping deposits.
Therefore, the present paper aims to develop a new technological flowsheet and conduct additional research on the design features of the new mining system and reduction of indirect additional costs for waste rock disposal when mining superimposed deposits employing more efficient room mining systems.
To this end, the paper considers the following research objectives: -analysis of existing technologies for mining parallel superimposed inclined tabular deposits and justification of the need and possibility of employing room mining systems at deep levels of underground mines; -development of an effective technological flowsheet for mining this type of deposits; -justification of the technological arrangement of interbedded rocks in the structure of the room mining system.

Methods
The object of the present research is superimposed deposits of useful minerals mined by open stopebased systems with disposal of rocks from workings of the receiving level.Existing technologies for mining superimposed tabular deposits are analyzed and generalized as well.
Stable parameters of the main structural elements of the room mining system are determined on the basis of the methods given in [9][10][11].For the conditions under study, we consider the version of the guidelines developed in [9] the most acceptable to justify stable optimal dimensions of underground structures.Dimensions of stopes are taken in accordance with boundary spans of rock and ore exposures in the conditions under consideration.In the proposed technological flowsheet, parameters of various types of pillars are set according to calculated functional characteristics, taking into account mining and geological factors.The procedure for mining reserves of superimposed deposits is determined by the logical mining technology including formation of preparatorydevelopment workings, ore extraction in blocks and partial disposal of waste rocks in rooms of the lower deposit.Structural modeling of elements of the room mining system and the procedure for their mining is implemented in accordance with the recommendations given in [12].The analytical research on the process of disposing waste rocks from workings that advance on the receiving level depending on the dimensions of disposal rooms is conducted as well.Mathematical statistics methods are used to process the data and determine the values of mining and geometric parameters that are typical for underground iron ore mining conditions [13].Based on the values obtained, a mathematical model is created and analytical studies are conducted to determine the impact of mining and geological factors on parameters of rock disposal rooms.

Results and discussion
The paper aims to develop a new technology for mining parallel superimposed inclined tabular deposits employing the proposed flowsheet of ore reserves extraction in the working area.The technology involves: management of surrounding rocks stability by temporary pillars; formation of workings of the receiving level in waste rocks in proportion to the amount of extracted rock disposal in the previously mined-out spaces of the lower deposit and their subsequent monolithization; and use of the created structure to support surrounding rocks and reduce dilution of the ore mass during extraction of the lower level reserves.This is achieved in the following way.The technology of mining parallel superimposed inclined tabular deposits includes advance mining of the upper deposit as compared with the lower one within the boundaries of working fields, panels and stopes, inter-panel and inter-room pillars.The receiving level for the ore mass from the upper deposit is created in the rocks between the deposits.Waste rocks removed from the mentioned level are disposed and then monolithized with solutions in previously mined-out spaces (rooms) of the lower deposit.These rooms are filled in the course of broken and shrinked ore mass drawing.The proportionality of rock volumes extracted from the workings of the receiving level with parameters of rooms for disposal is calculated.Temporary inter-room and interpanel pillars are left to support the thickness of the overlying rocks.The technological flowsheet of the sequence of reserves extraction from parallel superimposed deposits involves managing stability of mined-out spaces by temporary pillars and their subsequent mining.Inter-room pillars are removed as the room reserves are mined out, and inter-panel pillars are removed in parts as the panels are mined out.Ore reserves of the adjacent wing of the panel are mined in the similar way.The ore mass is transported through workings created in the rocks between the deposits and along orepass raises to the haulage level.The similar procedure is used to mining reserves of the lower deposit.Later on, the next two-winged panel and the inter-panel pillar are mined.
The developed mining technology is illustrated in figure 1 (section I-I) which is the cross-strike projection of the parallel superimposed deposits ABCD and EFGH with the receiving level FADG created in the interbedded rocks, the mined-out room, the drilling pattern for the next panel down dip, the inter-panel pillar (IPP) and technological workings.Prior to the structural modeling of the mining system with open stopes (stopes with a height equal to the deposit thickness), we conduct some research according to the methodology [9] to determine stable parameters of the structural elements of this mining system.Technologically, taking into account stoping processes, the dimensions of the two-winged panel are 100-120 m along the strike and 35-40 m down dip for each deposit.
Pillar dimensions are determined taking into account the depth of mining, physical and mechanical properties of the surrounding rocks and ores, the order of mining the deposits, and the service life of the underground structure.It is determined that the optimal stable dimensions of inter-panel pillars are: width -12-15 m, heightequal to the thickness of the deposit but not exceeding 30 m, lengthequal to the size of the panel along the strike.The design dimensions of temporary inter-room pillars can be maximum 10-12 m along the strike of the deposit and 25-30 m down dip.Depending on stability of ores (rocks) in the unmined massif, thickness of the crown of the working rooms is 10 to 15 m.The room reserves can be mined onto one or two funnels that are 10 to 20 m long along the strike and 20-25 m long down dip.We adopt a rational sequence of mining deposits from top to bottom and within the deposit: behind the wings of the panel and panels down dip with timely depletion of stopes with mass pillar depletion (mining).
According to the accepted technology, reserves in a mine field of parallel superimposed deposits are mined with division into working fields and advance mining of the upper deposit within the working field as compared with the lower one.The working field in each deposit is divided into two-winged panels GCC′G′ (upper deposit) and IGG′K (lower deposit) (figure 2) and LMNO (figure 3), which are mined by rooms ,,, with temporary inter-room pillars (IRP) left behind.The dimensions of the structural elements of the mining system (parameters of rooms and various types of pillars) are taken in accordance with the guidelines [8].Inter-panel pillars (IPP) LMM′L′ are left between the panels and subsequently mined in the element-by-element way , after working out two adjacent panels down dip of the corresponding bed.After working out the elements of the other wing of the panel in the similar way, the remaining reserves of the trouser-leg-shaped inter-panel pillars are extracted employing bulk caving (figure 2).The receiving level is formed in the interbedded rocks FADG when mining the upper bed (figure 1).The reserves of the lower deposit are worked out similarly employing a room mining system with a crown of waste rocks of the upper deposit receiving level.Preparation of the working fields and paneling are carried out by means of creating main transportation incline 1, main raises for various purposes (not shown on the projections); orepass raise 2 and ventilation and service raise 3 are built in the inter-panel pillar of the lower deposit.The ventilation and service raise will be used as an orepass raise when mining the second wing of the panel along the strike.Sub-level (sub-tier) ventilation and service incline 4 is built in the rock band (figures 1-3).At the bottom of the lower deposit, delivery drift 5 is made, from which drawpoints 6 and funnels 7 are formed, and part of room RR is worked out with ore shrinkage, leaving a stable crown (ridge) behind.Inclined working 8 through the screening facilities ensures transportation of extracted rocks from workings 5, 6, 7 of the receiving level of the upper deposit as the shrinked ore is drawn.At that, dimensions of the RR are regulated by the required volume of these rocks, which are monolithized with solidifying solutions to form an artificial preventive and supporting pillar.A pillar in the other wing of the panel is formed in the similar way (figure 2).This enables an increase in stability of the ore and rock massif, ensures protection of raises 2, 3 of the delivery level workings and contributes to an increase in indicators of ore extraction from inter-panel pillars IPP.After completing these works, the panels are mined by rooms ,, etc. with pillars IRP left behind (figures 1, 2, 3).In each stope, slot raises 9 (in the mined-out rooms, the raises are depleted) and drift 10 are built from drawpoint 6 and a cutoff slot is formed.After that, drill inclinе 11 is created and longholes 12 drilled from it are used to blast the room reserves onto one or two funnels, depending on stability of the ore massif and surrounding rocks.The broken ore mass is transported through funnels 7 and drawpoints 6 to delivery drifts 5 and further along the scraper level through screens to orepass raise 2, the loading hatch or reloading unit, depending on the dip of the deposits and transportation equipment on level 1 (figures 1, 2, 3).After extracting reserves of rooms  and  of the adjacent panel wing, part of the inter-panel pillar  is mined by bulk caving with subsequent drawing according to the specified ore mass delivery scheme (figure 3).The reserves of rooms , are worked out similarly; inter-room pillars IRP and the next part of pillars IPP  are mined by bulk caving.After that, reserves of the panel wings on the other side are also worked out in the same way.And finally, the inter-panel trouser-legshaped pillar is worked out employing bulk caving (figure 2).This operation is performed after the required strength of the artificial pillar made of the rocks on the lower bed is reached.The reserves of this bed are worked out similarly to the upper one, except for the technology of mining the inter-panel pillar reserves.
Our research conducted to determine the technological parameters of rooms for disposing waste rocks from the interbedded space and their conversion into artificial pillars consists in providing disposal of rocks resulted from formation of delivery workings, depending on the size of mined-out room spaces, rock properties, thickness of the lower deposit, etc.The methods described in [13] are used for analyzing the procedure for creating preparatory-development workings of the ore delivery level, their dimensions and properties, and the volume of waste rocks to be removed and disposed.For analytical research, average statistical data are collected and accepted.
The developed technology involves placement of extracted rocks resulted from creation of the receiving level of the upper deposit in spaces of the lower deposit stopes.This reduces transportation and other costs for their disposal on the daylight surface.The environmental conditions are also improving.In addition, creation of artificial structures from these rocks adds to improvement of ore extraction from inter-panel pillars.
At this stage of the research, it is necessary to determine dependencies of optimal dimensions of disposal rooms on several factors that affect the number and size of ore mass draw funnels, delivery level niches, parameters of scraper workings (in case of scraper delivery), etc.
Thus, the total volume of rocks V (m 3 ) from one panel wing per rock disposal room is as follows V is the volume of the draw funnel, found as the space of a truncated cone, m 3 ; n V is the niche volume, m 3 ; c V is the volume of the scraper working of one panel wing, m 3 .The volume of the draw funnel B V (m 3 ) is determined as follows: ( ) where (3) The volume of the scraper working (length c l , m and cross-sectional area cc V D S =   45-50 m 3 .For n rooms of the upper level, the number of draw funnels and niches, as well as the length of the scraper workings, increases proportionally.Taking into account the loosening factor (for the given conditions, Kp = 1.3) and formulas (2-4), formula (1) for determining the total volume of rocks from one panel wing to be placed in the disposal room on the lower deposit is transformed into the following expression: ( ) The volume of the disposal room k V (m 3 ) can be determined from the formula where H = 28-32 m is the room height; H  = 8-10 m is the height of the disposal room crown; D is the width of the room, m; L is the length of the room along the strike, m.
Then, the minimum length of the disposal room is L (m): The present research shows that the length of the receiving room for rock disposal is directly proportional to the number of rooms in the upper deposit.With the average values of the input parameters, a proportionality factor of 1.11 is received.For various other possible values, the factor is K(0.88÷1.35).Thus, the conclusion can be drawn that, in iron ore mining conditions of Kryvyi Rih Basin, the length of the disposal room is correlated by the proportionality factor which is equal to: Figure 4 shows that for each stope (its receiving workings), the length of the rock disposal space should be increased by 0.88÷1.35m (1.11 m on average).The other parameters of the disposal room remain unchanged.This conclusion will be true if the height of the disposal room is 28-32 m.It is regulated by the thickness of the lower deposit.
Study the change in the length of the receiving room when increasing or decreasing its height.
For the above values, the following is taken Then the formula for the length of the receiving room looks like For the above values of mining and geometric parameters (at n=1), the increase in the length of the room ∆L (m) is found as follows:

Conclusions
1.An innovative technology is developed for mining parallel superimposed inclined tabular deposits.In the proposed flowsheet, ore reserves in the working field are mined with stability of the surrounding rocks managed by temporary ore and artificial rock pillars.Waste rocks from the workings that are advanced to create the receiving level are disposed and monolithized in proportion to dimensions of the lower deposit rooms.
2. New dependencies of disposal room dimensions on the volume of rocks extracted during formation of the receiving level are established.
3. Implementation of the proposed technology eliminates the costs for moving waste rocks outside

Figure 2 (
Figure2(section II-II) shows along-strike projection with the parallel superimposed deposits, the mined-out and working rooms, and pillars on the upper deposit, with the space waste rock disposal room (RR) and technological workings backfilled with waste rocks from delivery workings.Figure3(section III-III) shows an inclined level (common for the upper deposit panels) with delivery workings, interpanel IPP and inter-room pillars (IRP), the order of mining panel elements (rooms, pillars) ----- and technological workings.Prior to the structural modeling of the mining system with open stopes (stopes with a height equal to the deposit thickness), we conduct some research according to the methodology[9] to determine stable parameters of the structural elements of this mining system.Technologically, taking into account stoping processes, the dimensions of the two-winged panel are 100-120 m along the strike and 35-40 m down dip for each deposit.Pillar dimensions are determined taking into account the depth of mining, physical and mechanical properties of the surrounding rocks and ores, the order of mining the deposits, and the service life of the underground structure.It is determined that the optimal stable dimensions of inter-panel pillars are: width -12-15 m, heightequal to the thickness of the deposit but not exceeding 30 m, lengthequal
h is the funnel height, m; D and d are the diameters of the upper and lower surfaces of the cone respectively, m (h = 4-5 m; D = 5 m; d = 2 m; VB = 30-40 m 3 ).The volume of the niche (

Figure 4 .
Figure 4. Dependency of the length (at H = const) of the room for rock disposal along the strike on the number of stopes at different proportionality factors: 1, 2, 3 -for the factors of 1.35; 1.1; 0.88 respectively.

Figure 5
Figure 5 clearly shows the nature of the change in the increase in the room length at the increase (decrease) in the thickness of the lower deposit (room height).At H = 35 m, for each upper level room, the length of the receiving room should be increased by an average of 0.95 m (0.86÷1.04), and at a height of 10 m -by 3.33 m (3.0÷3.63).

Figure 5 .
Figure 5. Dependency of the increase in the length of the waste rock disposal room on its 1, 2, 3 -for the maximum, average and minimum values of the numerator of (11) respectively.