Theme of the master thesis:

“Selection and reasoning of rational parameters of a method resistance strong rocks of floor heaving of mine workings of deep mines”

Content

Introduction

With increase in depth of mining character of a rock pressure manifestation in developments changes not only quantitatively, but also is qualitative. With the floors containing a development, it is necessary to study many complicated questions of the mechanism of interaction of a support in practice in actual practice deep mines. One of the basic problems of underground coal output is maintenance of poorly repair workings developments. Loss of stability of these developments in 70 % of cases is caused by expression of rocks of floor heaving in a development cavity. Expression of rocks of floor heaving is one of features of the rock pressure manifestation which mechanism remains definitively not studied and opened for the further researches. The general vertical displacement of rocks of floor heaving as shows the analysis of domestic and foreign researches [1-4], basically exceed displacement of a roof and reach 2,5 - 3,0 m and more. It speaks structural features of the hills, essential distinction of physicomechanical characteristics of floors and mining conditions of burial of coal seams [2]. Besides, the important factor influencing process of deformation of adjacent strata on a contour of preparatory mine workings, presence in them a steel support which interferes repacking pedigree cleats in a roof and walls that does not occur to rocks of floor heaving which, as a rule, have a free top surface is.

A considerable quantity of ways of prevention of expression of rocks of floor heaving [3] is by this time developed. But any of these ways is not universal because of a variety and complexity of mechanisms of expression of rocks of floor heaving in the conditions of deep mines of Donbass. Traditional way of prevention floor heaving on mines of Donbass is the ripping of rocks of floor heaving which, as a rule, is repeatedly made lengthwise developments.

Practice of application of the rippings which are carried out in basic about use of drilling-and-blastings and manual loading of broken mined rock, shows that after a ripping the intensification of deformation processes in rocks of floor heaving and increase displacement and speed of displacement of floors on a contour of developments is observed further. The researches spent by employees of department "Mineral Deposits Development" DonNTU by results of researches in the conditions of mine "Trudovsky" have allowed to establish that after a ripping the decrease of speed of displacement of floor is observed at simultaneous increase of speed of displacement of a roof [5]. Researches of the mechanism of deformation of rocks of floor heaving workings developments in the conditions of mine "Juzhnodonbassky №3" have shown that after a ripping speed of displacement has increased more than in 7 times concerning average speeds to a ripping [6].

It testifies that extraction of rocks of floor heaving in a ripping leads to failure of the equilibrium condition established in a massif and activization of proceeding geomechanical processes.

Well-known that the highest indicators of stability of development workings are provided with presence of sandstones and chalkstones in adjoining rocks. However indicators of mechanical durability of rocks not always can characterise their stability in mine workings of deep mines. With increase in depth of mining the intensification of expression of strong rocks of floor heaving that was not on small and average depths is observed. Sandy shales, sandstones and chalkstones concern strong rocks of floor heaving with strength one axis compression 50-60 MPa and more. The mechanism of expression of strong rocks of floor heaving in the conditions of deep mines of Donbass is studied insufficiently.

Research purpose

The operation purpose is the choice and a scientific substantiation of rational parametres of the combined way of counteraction to expression of strong rocks of floor heaving.

Research tasks

Research done

Generalising results of research of many authors, it is possible to believe that the major factors defining process of a floor heaving, are: a tension of floors in a massif, caused in the weight of an overlying strata; durability characteristics of rocks; a corner of their falling α; lamination of a massif; orientation of a development concerning a bedding; watering developments; support resistance and development service life.

So in operation [7] the data about distribution of stresses which are received by methods final (or boundary) elements for a development of any form driven in a massif with a non-uniform original field of stresses (fig. 1) is cited. If hypothetical distribution of stresses round a development is known, from bending around peak and residual durabilities it is possible to estimate the sizes of a zone of destruction.

It is known [10] that depending on used physical models all methods of an estimation of a rock heaving of floor can be divided into four groups:

In conditions of production the most suitable are methods of the fourth group display analysis floor heaving in natural conditions and that is very important, in dynamics of an extraction influence; attempt of definition of the reasons which have caused floor heaving; the analytical description of process by the analysis of the dependences received experimentally. The major factors defining parametres of process floor heaving, are: depth of mining, durability of adjacent strata, their power and petrographic structure, and also a cross-sectional area of a working.

Researches on models have shown that distribution of the maximum stresses to a laminated and fissured massif changes depending on a corner between the enclosed stress and a bedding and resistance to a friction on contacts of layers. In the coal measure rocks having zones of shift on bedding planes on contact of sandstone as a strong layer, with floors of direct floor, resistance to a friction can be low. The general distribution of stresses by results of tests for models presented to operation [7] are shown on fig. 2, and on fig. 3 the separate example showing effect of transfer of stresses under strong floor in laminated floors.

However common fault of any empirical methods is that application of the established laws is limited only concrete mining’s geologic by conditions in which limits selection of the statistical information was made. Now selection of corresponding mathematical model for mining of the mechanism of the description of process floor heaving is carried out, and also search of effective ways of maintenance of stability of the development workings which are in a zone of an extraction influence proceeds.

The mathematical difficulties arising in connection with complication of physical models, describing geomechanical processes, can be to a certain extent eliminated by application, for example, numerical methods. The most convenient and widely applied to solutions of problems of geomechanics is the method of final elements which now is actively used in a modern science.

Measures of struggle against displays floor heaving can be subdivided into measures on prevention floor heaving or to a decrease to an admissible minimum of its harmful displays and a measure on liquidation of consequences floor heaving. From among the last on mines usually apply:

At the heart of the majority of applied ways of struggle with floor heaving rocks modern representations about physicomechanical essence of process floor heaving, reduced to that an original cause floor heaving is change of a tension of floors lie. After carrying out of a development under the influence of stresses surrounding floors lose durability. Besides, durability of floors decreases under the influence of water and air moisture.

The analysis floor heaving and factors accompanying it shows that prevention floor heaving or a decrease of its intensity can be spent in two basic directions:

The first direction concern: a location of developments in zones of the minimum stresses, a choice of ways of protection of a development, rational in the set conditions, and an artificial decrease of stresses in massifs of the floors surrounding a development.

To the second direction concern: a support setting for the purpose of prevention of destruction of floors and their expression, hardening of massifs of floors by artificial ways and a protection of floors for the purpose of preservation of their properties. Measures on a location of developments in zones of the minimum stresses include pillars of the big sizes, a drivage behind stope, a goaf to a goaf, carrying out of rock drifts in strong floors, etc.

Perspective way is the drivage to a goaf. In this case the development is spent in in advance weakened massif, in the conditions of a roof fall of consoles of rocks is more direct also than a main roof. The principal causes constraining now application of this way, are necessity of change of an order of preparation of mine sections and difficulty of preservation at difficult a seam. An important direction of prevention of a floor heaving is the artificial decrease of stresses in massifs of floors surrounding a development. This direction includes an overworking and an underworking of seams, and also application of means of an induced caving of floors.

Ways of the second direction can be applied as independently, and together with a decrease of a tension of floors. Rock consolidation by anchors, cementation, use of force of explosion and chemical methods has not received wide application and is in a perfection stage. The widest application is found by supports, especially in the developments not subject to an extraction influence.

For struggle with еxpression of rocks in workings developments, supports with a floor arch (fig. 4) which work in a yielding mode in the conditions of an unsteady rock pressure with considerable displacement of rocks of floor heaving [2,8] are applied.

For prevention of expression of rocks of floor heaving in workings developments along with application of the closed supports and other preventive actions the roof bolting possessing high bearing capacity (fig. 5) can be used.

On the standard representations [2], roof bolting operation in floor of developments at display floor heaving is characterised by following signs:

However roof bolting tests for mines in various geological conditions have yielded various results. Experience of their application [2] shows that they are effective only in the conditions of presence in floor of developments concerning small power (1,5-2) weak laminated floors behind which strong floors lie down. In this case the roof bolting carries out a role of elements "filing" soft rocks to stronger. At presence in floor of developments of soft rocks more powers (4-6 and more metres) occurs the destroyed pedigree roof bolting. This results from the fact that floor floors are exposed to intensive mechanical and chemical influence, the external layer of earth quickly loses and durability. As a result the tension of anchors reduces to zero, then floor floors free direct in a development. Repair work on a bottom ripping in which there were anchors, is rather long and labour-consuming.

Often use fastening of floor by floor bars, the bottom braces and the central legs. Efficiency of this action is estimated on separate mines very much differently. Just as it was mentioned by consideration of a way of a roof bolting, to make essential impact on deformation of pedigree layers and development convergence timely fastening can only. Lacks at installation of braces and the central legs sometimes observe considerable deformations of an arch support. The top lateral segments of an arch are bent and braided because braces interfere with expression of lateral walls.

For elimination of these lacks the author [6] offers, being based on a mechanical way of prevention expression of rocks of floor heaving after a ripping to use two variants of repulse to floor floors: application of flexible cross-section communication of legs of an arch support by the coupled ropes (fig. 6,а) or packing between frames of an arch support of cross-section floor bars with two holding props on its ends (fig. 6,б).

Trial check of a way of power counteraction to expression of rocks of floor heaving has been spent in the conditions of belt entry of 7th east longwall of a seam l'₈ mines "Lidievka" and has shown efficiency of means of mechanical repulse to rocks of floor heaving after a ripping.

However the author recommends to apply these actions only to prevention repeated floor heaving after a ripping to compensate absence pressure upon the undermined floor of weight of the cleaned floors of a ripping rather small efforts of repulse of a floor bar.

For deep mines of Donbass in operation [9] the technique, definitions of stability of floor for main workings has been offered. Developments of flat seams in Donetsko-Makeevskom, Torezsky and Krasnoarmeysk areas with appreciable deformations of floor in the form of expression and with steady floor of 600-1200 m spent on depth, in floors durability MPa have been surveyed from 30-90. By results of natural gaugings the experimental curve has been constructed (fig. 7) on which as a first approximation it is possible to do the forecast about display of a floor heaving of a development, and depending on development appointment to solve a question on expediency of application of the closed or not closed construction of a support.

For an estimation of a floor heaving of developments not subject to an extraction influence, Ph.D Zaslavsky criterion - dimensionless parametre К_Засл = γН/σ_сж,the connecting weight of a strata of floors and strength of rocks of floor heaving on one axis compression with which help it is possible to estimate influence of depth of location of a development taking into account durability of floors has been accepted. For steady developments of value К_Засл<0,25, middle stable - К_Засл=0,25-0,4, unstable - К_Засл=0,4-0,65 [9].

According to [10] boundary or "a threshold floor heaving", was in dependence from other dimensionless parametre - a/l_o:

where а - width of a development, and l_o=0,2 м — floor quelling size at which process floor heaving starts to affect a development condition considerably.

Thus, intensive displacement of floor is observed in developments located on the sufficient depth which floor is combined by rather weak laminated floors, and with increase in width of a development the size of a raising of rocks of floor heaving in a development cavity increases.

Hence, stronger floors (chalkstones, sandstones, sandy shales) at more to depth of minings keep stability, hold out the big stresses at influence of an abutment pressure owing to an extraction influence. Less strong floors (aleurolites, argillites) lose stability on smaller depths, at smaller stresses, and their deformations can be shown as in the form of expression of floors from a loose sole, and in the form of support deformations if it has insufficient bearing capacity.

The given technique allows to consider both depth of location of a development, and its durability and gives the chance to judge influence of depth of mining. Hence, durability in itself without other factors cannot define propensity of floor to deformations in a development. Criterion К_Засл shows convention of concept "deep mine" and necessity of its consideration together with durability of floor. However this criterion does not give the answer to a question, what development is deep and what its signs. For developments in an extraction influence zone to define a stability indicator it is represented difficult since on the natural field of stresses connected with depth, it is necessary to consider and abutment the pressure which factor of concentration can reach 3-5 depending on ways of a location and protection workings developments.

The big variety mining-and-geological in mining conditions of carrying out and a roadway maintenance of deep mines of Donbass often leads to necessity to study complicated questions of the mechanism of a rock pressure manifestation in practice in actual practice.

General characteristics

For the further perfection of a way of counteraction to expression of strong rocks of floor heaving workings developments of deep mines, it is necessary to apply in a complex natural, laboratory and theoretical researches [10].

Natural researches allow to establish quantitative dependences горногеомеханических processes and the phenomena from ways experimented on them and control facilities a rock pressure and to develop engineering methods of calculation and a choice of a demanded way of counteraction to expression of strong rocks of floor heaving of developments in concrete conditions.

The general problems mining-and-geomechanical researches can be divided into following groups:

Hence, for a scientific substantiation of rational parametres of a way of counteraction workings developments of deep mines analysis of all stages mining-and-geomechanical processes with definition of type and a place of destruction of a massif of floors in floor, the sizes of layers formed at its destruction and blocks and the mechanism of the further deformation, destruction and a roof fall of is discrete-block environment is necessary for expression of strong rocks of floor heaving.

Laboratory methods of research mining-and-geomechanical processes, with reference to workings to developments in which character and intensity of rock pressure manifestations is defined by intensive influence of the coal faces, the most comprehensible are models from equivalent materials. Carrying out of industrial experiments with new ways and protection and fastening means workings developments regarding their preliminary approbation, and also an establishment of possible conditions of carrying out of experiments and admissible limits of change of experimented ways and means should be the primary goal of laboratory researches on models from equivalent materials further. For solution of this problem performance of similarity of models not only on structural properties and a tension of various typical massifs, but also on power and deformation properties, design features of supports both other experimented ways and means, and also on features of carrying out and a roadway maintenance is necessary at different technological schemes non-pillar workings of seams.

Necessary requirements can be executed at scale of modelling not less 1:40-1:50 with reproduction in models only a massif adjoining to a development with the sizes in a roof 6-8 and in floor of 2-3 seam thickness and replacement of other part of a massif by means of compensating loading. Thus along with flat models it is necessary to conduct also researches on volume models which allow to study dynamics of development of processes at a various location of developments concerning coal-face works.

Concrete private problems of theoretical researches should be narrowly connected with experimental natural and laboratory researches. Correctly put theoretical researches should generalise and explain indicators of natural and laboratory researches and predict results in conditions where experiments were not spent.

Preparation and carrying out of theoretical researches include following stages:

For solution of problems of mining geomechanics it is necessary for researcher to have the information containing:

The settlement scheme considered as a final result of a preparatory stage, at the same time serves as the initial stage of a mathematical part of theoretical research.

At the heart of the settlement scheme the general idea of process or the phenomenon, generated of a know-how, laboratory or natural supervision lies.

At the final stage of theoretical research define area and conditions of application of the received solutions, plan volume and the maintenance of auxiliary means necessary for it and experimental researches if there is a necessity for their carrying out.

Summary

The present master's works is continuation of researches of my supervisor [11,12,13] and the further development of works [14,15] direct on specification developed now mining geomechanics bases of the mechanism of course of processes of change of a tension of strong rocks of floor heaving, deformation, destruction and moving of pedigree cleats to the areas adjoining on coal faces.

For today while one research of expression of rocks of floor heaving are visual and natural of the basic methods. For finding-out of features of the mechanism of expression of strong rocks of floor heaving researches on mine of M.I.Kalinina in the conditions of seam working h₁₀"Livensky" by power of 1,0-1,3 m and a corner of burial 18-21° on depth of 1360 m with use of continuous mining method "horizon-face" were conducted. The Belt entry is spent drilling-explosive by way in advance longwalls on 20 m. In seam floor strong floors of sandy shale (m=0,3-4,0 m lie down; σ_сж=50-60 МPа) and sandstone (m=0,3-4,0 м; σ_сж=60-80 МPа). During carrying out of a development of displacement of floor are insignificant and make about 0,1-0,15 m, and in an extraction influence zone there is an intensive expression in a development cavity so displacement on distance of 50-60 m behind stope make 1,5-1,6 m, and on distance of 60-120 m - 1,8-2,2 m and on distance of 120-180 m - 2,5-2,9 m accordingly. On this site of a development the bottom ripping on depth of 1,0-1,2 m with giving to it of the horizontal form of a location was made. After a bottom ripping the belt entry was used on distance of 250-300 m after longwall, and then repaid in process of carrying out of a new intermediate crosscut from the drift spent in seam floor on distance of 25 m on a normal in a strong layer of sandstone of the basic seam floor.

Feature of the mechanism of deformation of seam floor is the mechanism of formation of a pedigree fold at expression of strong rocks of floor heaving in a belt entry cavity. Thus, expression of a strong layer of sandy shale and sandstone in belt entry occurred to formation of asymmetrically pedigree fold which axis of symmetry has been inclined towards a longwall goaf bevel way 50-55° (fig. 8). The asymmetry fold, in our opinion, is formed at the expense of simultaneous influence on a strong layer of sandstone of direct floor of vertical and horizontal loading from a massif of coal which considerably surpasses horizontal loading in the size from a goaf.

The presented analysis of the mechanism of deformation of strong rocks of floor heaving allows to draw a conclusion on necessity of carrying out of additional researches of deformation process for definition of rational parametres of a way of counteraction to expression of strong rocks of floor heaving workings developments of deep mines.

Conclusion

Master's works analysis of modern representations about the mechanism of expression of strong rocks of floor heaving of development workings is resulted.

The analysis of results of researches of ways of struggle to expression of rocks of floor heaving allows to draw a conclusion that in above listed operations features of the mechanism of expression of strong pedigree cleats of floor in workings developments of deep mines are insufficiently studied. Questions of interaction of the basic and strengthening supports with abutment constructions on longwall interfaces are not studied, possibility of a choice of the combined way of counteraction to expression of strong rocks of floor heaving at the expense of consecutive or parallel application of known ways for stability maintenance workings developments in an extraction influence zone is not established.

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WARNING

During the writing of this abstract master's degree work is not yet complete. Final completion: December of 2011. Complete text of work and materials on the topic can be got for an author or his leader after the named date.