CA1112884A - Complex process and machine group for the support of underground cavities and cavity systems - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The invention describes a complex process, and machine group for the support of underground cavities such as mine roads. In the knowledge of a comprehensive number of the characteristics of the cavity of the rock and of the support apparatus to be employed, a correlative equation deter-mines the best machines to be used for the various stages of the support installation such as determining the periodicity of the support, the deter-mination of the concrete lining, the choice of the forepoling and clamping mechanism and the prestressing of the arch supports.

Description

The invention concerns a process and apparatus for the complex support of mainly underground cavities such as mine roads or drifts, tun-nels, liquid reservoirs and industrial halls.
The most important disadvantages of known and generally used cav-ity support systems are as follows:
As a consequence of the manner in which temporary and permanent support de-vices (TH rings, props, shafts etc.) are installed, full contact between the rock and the support devices is formed at a time determined by the rheolog-ical properties of the surrounding rock and generally after a significant rock deformation.
As a consequence, even before the support is loaded, a rock dete-rioration process starts up which results in a considerable narrowing of the sections and requires maintenance activity of significant cost. This cir-cumstance causes a short support life. The load on the support changes with time and is distributed in a random manner so that it cannot be pre-selected.
Consequently, at certain locations of the support, stress peaks may be formed which result in damage to or destruction of not only the rock but also the support.
The hitherto known support mounting and installing technologies and methods cannot predict how the support device will react on the sur-rounding rock. This reaction effect may on the one hand start an irrevers-ible destructive process and on the other provide for balance or equilibrium while providing a favourable rock support. Attempts have been made to clas-sify rock strata into different categories or classes on the basis of great-er or lesser idealisation of their actual behaviour. The strength charac-teristics of the support have been associated with these idealised charac-teristics (e.g. Rabcewicz-Sattler: Die neue Osterreichische Tunnelbauweise, Bauingenieur 1965, ~o. 8). ~aturally this idealisation does not allow the Ir most recent research into the mechanics of rock to be employed in practice and has hindered the spread of recent technology. Consequently, it is no I~

coincidence that, for example, the cited method has only remained in the field of tunnel construction. Generally, conventional solutions cannot modify the value of the rock pressure within wide limits, rather in their case the pressure of the surrounding rock arises as an in situ natural char-acteristic, and thus in most cases load levels arise which virtually neces-sitate destruction of the support and thus make it mandatory periodically to carry out re-supporting work. Generally the conventional solutions only provide specialised constructions relating solely to the support, and do not provide a modular process and apparatus, with regard to the complete system of cavity formation and support, which is utilisable with the most widely varied cavity forming methods regardless of the geometric configuration, i.e. dimension and shape of the cavity and regardless of the associated widely varying transport or rock removal systems, forming an integral part with such systems and methods.
The present invention aims at a process and apparatus wherein the changes that take place in the course of forming the cavity are interpreted according to the latest rheological research as they relate to the combined system of the rock and the support apparatus, relevant parameters are deter-mined within the framework of a complex system involving all the character-istics of the surrounding rock and their change with time, and the processesand apparatus are controlled according to these parameters. The technolog-ical steps determined by the invention are thus time-dependent functions, the relative use of which are interpreted on the basis of the rheological changes of the rock and the support.
From this it follows that the invention aims at a system for the formation and support of underground cavities wherein the emphasis is not on defense against nature by taking up the pressure of the rock with a sup-port apparatus, but rather through sufficient knowledge of the laws of na-ture affecting the apparatus, the effects of natural phenomena are used.
This represents an advance from the concept of defense to the concept of deliberate regulation. Thus the in~ention aims at a system of practical deductions inferrable from new theories concerning the mechanics of rock wherein the planning, dimensioning and technological formation of the sup-port and supporting devices as well as the installations therefore are all incorporated.
The support of cavities made by various technological processes is a complex task. In the course of solving this task one must have regard to a complexly interrelated system of conditions of which the principal e]ement groups are the following:
- the stress conditions around the cavity;
- the physical and mechanical characteristics of the surroundings of the rock;
- the manner, the apparatus and the technology of forming the cavity;
- the geometry (dimensions, shape) of the underground cavity;
- the characteristics of the support.
The a-pparatus elements determined purely by way of example and described below as a technological system may naturally be substituted or replaced by technical elements of similar function but the essence of the invention is their co-ordination into a unitary system.
In accordance with the foregoing the rock formation and the sup-porting apparatus form a collaborating double system wherein a suitably con-structed support apparatus and the excess pressure caused by opening the cavity, the so-called transferred pressure, are divided between the rock and the support in such a way that both can accommodate the excess pressure with-out damage or destruction.
This recognition has led to a re-evaluation of the task of sup-porting devices and to the development of support systems and installation technologies suited to these new circumstances. Accordingly, the most basic requirements of the support system are the following:

a) Activity, by which is meant the property of the support system by means of which immediately on installation it takes part in load balancing, does not allow for the whole of the excess pressure to be exerted on the rock and thus prevents the commencement of damaging or destructive processes which could lead to rock falls and the loss of the controllability of the mechanical phenomena.
b) Yieldability, which is the property employed to realise the auto-matic control of the ~ual rock-support system. The support apparatus in-stalled at the time of the cavity construction is in contact with the rock and takes part in the bearing of excess pressures or stresses. The transfer of load from the rock to the support apparatus takes place with certain at-tendant deformations. Since all rock-mechanics process are rheological, this transfer of stress to the support apparatus takes place continuously at a rate dependent upon certain rock constants and characteristics of the support. The yieldability of the support is destined to fulfill the reg-ulating function of undergoing a permitted small deformation or yield when-ever the load on the supporting apparatus reaches a non-permitted or un-desired value, so as to avoid a destructive load. This process continues until an equilibrium is reached wherein both the support and the rock carry 0 a load supportable without damaging consequences.
c) Load-Bearing Capacity, represents the totality of the mechanical strength characteristics of the supporting apparatus. Without suitable load bearing capacity, the equilibrium state could only be reached after complete closure of the cavity and the destruction of the cavity and its surround-ings.
~ he requirements of the support are fully met by A) a tensioned steel supporting apparatus, and/or B) shaft support with shot or sprayed concrete possessing adequate resil-ience and rigidity characteristics.

~2~

Relating to A:
In using a steel support the essence of the process is the ten-sioning of the arcs or arches installed in the excavated areas by applica-tion of a predetermined force or pressure with the aid of hydraulic fore-poling and tensioning apparatus. By tensioning the support with a pressure P the pressure on the support is decreased to (P - Po).L compared with the original value PprL, wherein Ppr represents the primary main pressure normal to the plane of the cavity under examination and L is the relevant dimension of the cavity in that plane. In what follows, the correlations are set out on the basis of which:
- the pretensioning of the support in the case of a mine road or drift of long life (1);
- the pretensioning of the support in the case of cavities of planned lifetime (2);
- the pretensioning of the support according to the mechanical condition of the surrounding rock in the case of the most favour-able cavity configuration (3);
- the determination of the installation length or distance of the support (4).
(l) The pretensionin~ f the supPort takes place in the case of long life cavities (exceeding 15-20 years) takes place with a pressure P :
support o ~ pr a permitted

2 a An wherein:
~ is a factor dependent on the role of the cavity, Ppr is a primary main stress prevailing at the location of the opening of the cavity, support is the standard load permitted for the support, permitted n is a safety factor, A is a computed mechanical constant dependent on the configura-tion and dimensions of the support apparatus, a is the value of the co-efficient of co-operation of the rock and the support which is expressed by the mLlti-variant function a = f ~Eb, mb, L, Kb, G) wherein ~ is the elastic modulus of the support, mb is the poisson number of the support, L is the main dimension of the support (span length) is the standard cross-sectional factor of the support, G is the elastic modulus of the rock jacket.
(2) Prestressing of the support in the case of a planned life of to:
o ~ pr support ~ permitted (2) 2 An (1 - e o) wherein:
e is 2.71... the base number of exponential logarit~m, to is the planned life of the cavity, is the co-operation factor in time of the rock and the support which can be calculated on the basis of the rheological constants of the rock and the support as well as the dimensions of the con-struc*ion:
~ = f (Eb, mb, L, Kb, G, T~ n) where T iS the relaxation factor of the rock, ~ is the viscosity factor of the rock, i.e. its creep modulus, ~ is a factor dependent on the function of the cavity, Ppr is the primary principal stress prevailing at the location of opening of the cavity, ~ support is the stardard load permitted for the support, pennitted n is a safety factor, A is a mechanical constant which is computed and which depends on ; 30 the shape and dimensions of the support, and a is the co-operation coefficient of the rock and the support, d~'~

(the symbols not listed have the same significance as above).

(3) In the case where the most favourable shape or configuration of the cavity from the point of view of the mechanical condition of the rock cannot be formed, because of the role the cavity is destined to play, and by most favourable is meant from the point of view of the load distribution of the rock and the support, then the prestressing of the support to be installed in the cavity section of given geometry must be such that it approximates the stress condition corresponding to the optimum. The pressure transmitted on a vice which makes an angle 0 with the primary main stress direction in the clockwise direction is given by:

P~ = o lk + (k-2)cos 27 ~ (3) - ~ 2(k-1) where P is the pressure value computed from formula (1) or (2) and k is the quasi-Poisson number valid for the location of the opening of the cavity.

(4) The installation distance or spacing of the support Let 1 be the installation distance of the support in the case of an un-prestressed support apparatus. If the prestressing is of the value P then the installation distance can be increased by a factor ~, i.e. ~0 = 1 where ~ pr I
V ~ Ppr o Where:
~ is a factor dependent on the function of the cavity, Ppr is the magnitude of the primary main stress, PO is the value of the pre-stressing which can be computed from formula (1) or (2).

For performing certain parts of components of the process earlier attempts are known, such as for instance patent specification No. 1,143,468 of the German Federal Republic relating to the clamping in of the support where the significance of the prestressing of the support has already been recognised. However, the known processes are not sufficiently efficient 3,4 because they do not take into account those mechanical processes taking place with time wherein the knowingly controlled and dimensioned functions of the rock environment and the support are determined. This means that in a primary field characterisable with a quasi-Poisson number of e.g. k = 2 or a figure close thereto, the lateral support clamping in the case of a driven road can cause the start of a process of rock destrllction which only ceases when the cavity is closed.
The present invention bases itself on the modern theory of the mechanics of rocks and on the basis of provably successful experiments and in the knowledge of the characteristics of the primary stress field and the rock provides the possibility with the aid of computers of employing the best technology for maintaining control of mechanical processes which change with time.
Regarding B
Continuous shaft support (shell support) of adequate resilience and strength properties. The defect of traditional shaft support is the lack of co-operation between the shaft and the rock or its insufficient nature and in the case of the usual shaft thicknesses of vd > 8~ the main fault is rigidity or stiffnessO These defects can be reduced in a known manner partially by filling up the back space, that is the gap between the rock mantle and the support, and partly by the use of yielding inserts.
The conventional material, such as slag, is filled into the back cavity manually but this is an imperfect method. Although in given cases the injection of sand or foam can provide superior filling and a better effect, the overall effect is still not satisfactory. The fundamental defect of filling the back space behind the shaft or wall is that this can only be effected after the event and the effect of co-operation arises only belat-edly, in other words only after a partial or complete destruction of the rock has taken place because of its absence. One can accordingly appreciate 3Q the importance of increasing the density of the support points of the mantle of the cavity.
The above described defects are completely eliminated by the shaft support process based on the principles of the new rock mechanics and in-volving continuously shot or sprayed and dimensioned shaft or wall support.
The thickn~ss of the shot or sprayed concrete layer is a predetermined frac-tion of the cavity dimensions but is of significantly smaller magnitude and therefore can be regarded as a shell construction. The small layer thick-ness and the perfect fit to the rock result in such a support being of pre-determined deformability (resilience) which perfectly co-operates with the rock from the commencement of installation.
The new principles of the rock mechanics clarify and unambiguously fix the behaviour of the environment of the cavity and on that basis deter-mine the change with time of the load on the applied concrete shell, i.e.
its increase; the hardening or setting process of the shot concrete can be controlled in a programmed manner accordingly with the deliberate deter-mination of the concrete properties.
The dimensional correlations described below ensure the optimum co-ordination of the two processes and the formation of the most favourable construction as well as the maintenance at a predetermined value of the proportioned of load bearing as between the rock and the support apparatus.
The function of the cavity support construction realised by means of a shot concrete technology can be characterised in that it is a shell construction, it matches or fits the rock perfectly, it has suitable static or rigidity properties, satisfies all demands made on the supporting ap-paratus such as activity, yieldability and load-bearing capacity. A further advantage of it is that it can be employed with any cavity forming technol-ogy and is readily mechanisable, which will be referred to again below.
The wall thickness of the shot concrete wall or shaft in the case of long life, greater than 20 years, can be determined as follows:
- tNo factors can determine the wall thickness of the shot con-_ g _ crete wall or shaft:
a) the load on the rock should not set off a destructive process at the surface of the cavity, i.e. the reduced standard stress arising in the rock mantle should at no time exceed the permitted:

rock < ~ rock reduced permitted the value vl can be determined from the relation:

n where = (........ ,vl..... ) b) the main or standard load of the suppo^rt should remain below that which is permitted:

support < ~ support reduced = permitted i.e. the thickness v2 of the support can be calculated from the equation:

2(~ P - P ) ALo ~ (R v2)~ = a permitted The wall thickness of the support should be taken as being equal to the greater of vl and v2, i.e.:
v = Max ~vl; v ~

The symbols have the following meanings:
~ is a factor dependent upon the role of the cavity, P is the primary stress prevailing at the location of opening of the cavity, PO is the prestressing pressure of the support, A is a computed constant dependent on the shape and size of the opening of the cavity, Lo is a factor dependent upon the installation distance of the sup-port, a is a function or co-operation coefficient of the rock and the support which is a function of the material constants of the rock r and the support, the geometrical dimensions of the cavity and the :

wall thickness of the support, 0 is a function of the dimensions and geometry of the support, and nl.n2 are safety factors.
In the case of a s~pport of shot concrete of circular section with radius R and thickness v:

Eb (2Rv-v ) d= 2 ~ 2-Ebm2b ~2Rv-v ) + 2G(mb+l) r(mb-l)R -2mbRv + mbv 7 e~ =
2Rv - v where Eb is the elastic modulus of the support G is the elastic sliding modulus of the rock mb i5 the Poisson number of the support The wall-thickness of the shot concrete planned for a life of t Vl is determined from the equation:

2(~ P - P ) AL ~1 - (1 - e )~ _a permitted V2 is determined from the equation:
a support 2(~ Ppr - Po) ALo ~(1 e ~ ermitted ~ is a co-operation factor in time of the rock and the support which in the case of a circular road of radius R and thickness v is:
~ mb (2Rv-v2) + 2G(mb+l) l(mb-l)R - 2mbRv + mbv ~
~ = _ TEbm b (2Rv-v ) + 2n(mb+1) ~(mb-l)R - 2mbRv+mbv where is the relaxation constant of the rock n is the creep factor of the rock.
In order to form the shot concrete wall or shaft, one requires a machine line which can produce the supporting apparatus which can optimally adjust itself to the terrain in question and can solve the transport to the site of the additives, the correct dimensioning of the concrete, the func-~ ., -- 11 --tion of a perfectly homogenised and mixture activating mixer and which can apply the homogenised concrete composition of which is in accordance with the prescription to the surface in a suitable manner.
The support construction can be realised with clamped in steel supports which are independent or with such supports stabilised with rein-forced concrete and with reinforced concrete construction. Where a concrete or reinforced concrete is combined with the clamped steel supports account must be taken of the hardening process of the concrete.
As is well known the development of rock pressure is also a time dependent process. The above described dimensioning process makes it pos-sible optimally to co-ordinate the two processes and thus to form the mech-anism in the most advantageous way. This decides the material of the con-struction, the time and manner of the installation.
The installation of the concrete of the construction takes place by way of example with a shot concrete technology and fulfils two functions:
a) the ground work or contact function is a concrete which ccntinuously con-tacts the surface of the rock where it causes an excess stress to prevent loosening of the rock while at the same time forming a transitional layer;
b) a load bearing concrete shell which is expediently of monolithic rein-forced concrete and which takes up the role of load-bearer in the course of the above described mechanical co-operation.
The new interpretation of the per se known contact layer is that account is deliberately taken of the characteristics of the material (the rheological characteristics of the rock, its breaking strength, changes with time, moisture content) and thus serves as a transitional layer formed on the rock surface after breakage which penetrates into the fissures and aligns itself with the load-bearing walls or shafts. Thus in comparison with the known principles, the effecting of the clamping process is given a new con-~; ~ tent.

~; 30 For example, the apparatus according to German Federal Republic ~., ~, .
~ - 12 -~:

patent specification No. 1,193,904 iS not suitable for the stressing or clamping of controllable loads in the vertical and horizontal directions or to mount supports of balanced moment and co-operation with the forepoling is not achieved.
The situation is the same with German Federal Republic patent specification No. 1,408,727. The favourable co-operation of the ring and of the rock requires a tensioning apparatus which can transfer not only circum-ferential but also radial loads in a regulable manner and at a controllable location (favourable contact), because of its construction.
For this reason, the disclosures of German Federal Republic patent specifications No. 2326606 and 1283778 are less effective because they are suitable only to exert tangential loads.
The task is only partially solved by clamping or mounting devices of the polygonal type (as is known from German Federal Republic patent spec-ification No. 1,193,457 and ~ungarian patent specification No. 162,676) andthe latter demonstrates that active support can be effective if it is ex-erted on shield surfaces thus foreshadowing the construction of an active shield for drifting with mechanised winning.
~his last solution is fully equivalent as regards the mechanics of 20 the rock, with the present invention but its field of application and its embodiments are different.
The construction according to German Federal Republic Utility Model No. GB 1461 partially solves the above-mentioned disadvantages but its use is limited to specially constructed roof arch supports and is not suit-able for exerting large clamping forces.
The $orepoling mentioned in our process constituting one phase of the technology may in principle be carried out with any of a number of known forepoling devices but the effectiveness of the work is the greater the bet-ter the forepoline the arch mounting and the clamping phases are co-ordinat-30 ed. The possibility of this co-operation of the phases is considerably ., limited with the solutions of e~g. German Federal Republic patent specifica-tion Nos. 2,360,726 and 2,252,450. Other solutions, such as that in German ~ederal Republic patent specification No. 1,080,948 involving crabs cannot exert adequate forepoling forces and thus does not enable the joint mounting of the lining or lagging and the arch. This same disadvantage prevails also with the constructions of German Federal Republic patent specifications Nos.
2,253,670 and 1,180,70~. Other known solutions are limited to solving a given partial task only e.g. supporting the face, or e.g. the so-called Moll arches (see German Federal Republic patent specification No. 1,193,911).
The aim of_the force-introducing mechanism is to change the stress condition of the rock jacket defining the section of the cavity through the supporting element by means of forces of chosen direction and magnitude.
In the sense of the invention the essence of the solution is as follows:
1) The mechanism performs its operations expediently by combination with the working phases of the forepoling device or apparatus, being effected by a displacement of the wire ropeway formed on the forepoling apparatus and is connected in this way to pretensioned (i.e. forepoled) upper prop, so that the position and stress condition of the latter no longer changes.
2) The advantageous exploitation of the available space: it consists of a clamping mechanism involving internal hydraùlics to which temporary supports are connected by way of articulated suspending mechanism wherein the tempo-rary supports are constituted by elements which are effective in the direc-tion of the sides and floor and in dependence on the shape of the cavity section are exchangeable, the upper transition being constituted by suitably formed projections of the forepoling device itself.
3) A divided force introducing support system which is divided by the spac-ing elements into an external and an internal support art; both supports can be clamped by themselves but not necessarily with the same direction and ~ 30 magnitude of force transmission.

!~ _ 14 -a~

4) The mechanism described in 3) may also be constructed so that the outer support system is concreted in and during the hardening and setting time tension of the internal support arch provides the supplementary portion of the conserving reaction system and is dismantled from the set or hardened concrete.

5) A force introducing mechanism wherein the internal hydraulic clamping mechanism and/or the temporary supports connected thereto contain a fixing or securing projection on to which the drilling nachine for drilling the rock and anchoring the rock and the feed lafette can be suitably adjusted for rock bolting.

6) The performance of the fourth introducing process is carried out by par-tially simultaneous rock bolting and the anchoring takes place in the course of the conservation of the mounting.
The mechanism of the clamping: it is a connection which allies itself in the prescribed manner to the cavity and is capable of introducing the forces.
1) The arch elements are mounted by radial devices using such forces as will ensure that the support element, e.g. a ring, should to some extent be de-formed into a cavity, and the points of attack of the forces are so deter-mined that the bending stresses in the arch elements should be equalised or balanced to a suitably chosen value.
2) The mounting and clamping described in 1) is combined with tangential stressinE of the arches and this then becomes simultaneously one of the lo-cations of the conservation.
3) The conser~ation of the introduced stress condition takes place with ~- such a force distribution that the load-bearing of the support element is , ~.
optimal, the force distribution having a radial and tangential component and regarding the combined rock and support mechanism together is of an ~` optimal value.
:"
~ 30 4) The mounting of the support apparatus (e.g. ring) is such that a suitably ,:

~ J4 dimensioned grid is mounted on the ad~acent surfaces which grid is inter-sected by the supporting arches and has transverse elements (for roads, ele-ments directed along the axis of the road) whereby to transmit clamping forces so that the intermediate space is protected from fall and is pre-tensioned by pressure.
5) The mounting can also take place so that the force conservation remains partly in the concrete but partly takes place by way of an external element which can be recovered after the concrete has set.
Forepoling follows the steps of making the cavity and loaaing or is parallel with loading in the operational sequence of cavity formation (road building, tunnel building etc.). ~he task of forepoling is to prevent the covering rock from falling by producing such a stressed condition which is suitable for the disturbance free performance of the transition to the clamping in of the final and permanent support element without loosening the rock.
1) In the forepoling process the roof support elements and the spatial sup-ports (grid) are clamped in at the same time - must be done in such a way that when the final or permanent forces are introduced this situation does not have to change.
2) Forepoling can also take place with paired support beams which are mov-able by way of a hydraulic mechanism via a lever so that during forepoling the beam is not only rocked from its lower position but also performs a for-wardly advancing motion.
3) Another preferred embodiment of the forepoling apparatus is that which, in order to ensure the horizontal and vertical bend of the cavity contains:
- an upper or transitional support wherein the forepoling main support is fitted with the aid of displaceable guides, - the upper part of the main support is divided into two parts by the over pivot or half-pivot, the rear portion can be adJusted in accordance with the radius of curvature in the vertical sense of the ca~ity, - in the so-called "loosening" part of the movement cycle of the working cylinder which performs the forepoling an element is actuated, e.g. a chain, which indexingly advances the forepoling apparatus.
The generation of the stresses and deformed condition as well as their conservation produced by clamping with radial and tangential forces may also be combined with the per se known rock bolting. Rock bolting is suitable for achieving force conservation by radial means. The bedding of the rock bolting can be performed not only along tangential but also along axial elements such as the axial supports of the grid and this means that the stress condition created thereby may be optimally chosen and maintained both in the plane of the ring and in the intermediate fields.
By having due regard to the main directions of the stresses and the magnitudes of the primary stresses, the disposition of the rock bolt can be such that optimal stress condition arises for the given cavity configura-tion.
It is a condition of advantageously using the machine group re-quired for carrying out the process according to the invention that:
- it should fit in well in the complex technological process of cavity formation, - it should enable all further processes to be carried out un-disturbed, - it should provide the output required by the speed or velocity of the face, - it should ensure the multistage wall or shaft formation so that ` in given cases the installation of the required steel support (e.g. installation of ring) is carried out as an accompanying process with the provision of the contacting concrete and the load-bearing final wall or shaft with essentially the same main machines, - it should be suitable for walling a cavity driven in any desired direction such as road or inclined shaft.
The preparation of monolithic shafts or bricklinings can be grouped into two technological main groups:
1) The preparation and homogenisation of the material of the lining, 2) The installation of the lining.
The preparation of the material of the shaft or lining consists in the high efficiency mixing together of solid particulate materials, liquia materials and pulverulent materials and their binders in given unit packs or in doses which are determined by weighing before or after the process.
Because of the given characteristics of the site the preparation of the composition requires optimally variable serving elements that can be put together in a modular manner. Among the conditions for optimisation the available space requirement and the transport paths provide absolute condi-tions while relative conditions are constitutea by the technical processes of the road driving and cavity opening. .-The ~ of the lining or wall is effected by a shooting machine operating on known principles, e.g. German Federal Republic patent specification No. 2000278 by means of a shooting or spraying head formed at the end of its hose. The lining of larger sections cannot be carried out by the operator in a standing position. The variously constructed and known ` moving platforms have been proved in external use and apparatus, but in -` underground working sites can only be used on very large sections. In most practical cases the constructional dimensions of the platform are such that they cannot be kept in operation juxtaposed with the machines carrying out the various technological processes and cannot therefore be fitted into the complex process of cavity formation, such as road driving.
An effective solution to this problem is signified by a manipulat-ing apparatus with automatic position control which enables the operator to carry out in one position the concreting of one section while solving or fulfilling the conditions as regards quality and building technology. The application of shot or sprayed concrete technology requires that the operator should sense or feel the forces exerted on the head to see its movement and the formation of the wall or lining. It is better if the operator is disposed from the spraying head at a distance of a few metres, in a quiet situation and while being in complete possession of the capacity for intervening directly and for sensing the physical parameters nevertheless should be able to form a perfect lining or wall in one fixed position while eliminating the need for downtime due to transforming or advancing the platform.
Thus, in light of the foregoing, the present invention provides the method of bracing an underground cavity in rock with a support structure capable of being tensioned, comprising the steps of a) measuring the primary stress in the rock at a position of the cavity where support is desired;
b) determinlng the permissible load for the support structure;
c) tensioning the support structure at the support position in accord-ance with the measure of the primary stress prevailing at said position, as modified by the determined load permitted for the support;
d) determining the pre-stressing forces required at the support position; and e) forming a concrete shell within said cavity from shot concrete in one or more layers having a wall thickness which is the greater of a computed required wall thickness based on the load bearing capacity of the cavity and a computed required wall thickness based on the load bearing capacity of the support, taking into account in each case the difference between the primary stress at the support position and the desired pre-stressin~ forces at the support position.
The method may also include the step of providing support members at a spacing governed by the ratio of the measured primary stress to the difference between the measured primary stress and the pre-stressing force.

The acoompanying purely schematic drawings illustrate a purely exemplary embodlment of the full technological machine line according to the invention, wherein:
Figure 1 is a "flow diagram" of the oomplete machine line, with the bottom portion continuing on from the top portion, Figure 2 is a side view of the foroe applying me-hanism, Figure 3 is an enlarged detail of Figure 2 ~ut showing a variant, Figure 4 is a view taken along the line m~m in Figure 2, Figure 5 is a variant of the apparatus shc~n in Figure 2, adapted for a circular sectian, Figure 6 is a partial view of the conserved state after application of foroe, Figure 7 is a side view of the forepoling mechanism in its clamped positian, Figure 8 is a detentio.ned or collapsed position of the mechanism shcwn in Figure 7, Figure 9 is a section along the line n-n of the apparatus ~; sho~n in Figure 8, Figure 10 is a detail in side view of the nixing machine line, Figure 11 is a cantinuatian of Figure 10, Figure 12 is a sectional view of the container for the : concrete - l9a -additive, Figure 13 is a longitudinal section of the mixer unit forming part of the mixing ~achine line shown in Figure 10, Figure 14 is a plan view taken along the arrow F of the apparatus shown in Figure 13, Figure 15 is a side view of the manipulating device for the ap-plication of the shaPt or lining, and Figure 16 is the sensing unit forming part of the manipulator of Figure 15.
Machines for achieving the process according to the invention are shown in schematic assembly in Figure 1. The support of the e.g. road is commenced by installing the main props la of steel arches 1 which is applied by the forepoling apparatus 200 after the surface of the driven cavity has been coated with the so-called contact concrete layer 2. This latter elemi-nates unevenness and provides a good surface against which the steel arch 1 and a grid 3 placed therebetween can bear. In the next working phase, the clamping in of the steel arches is finished by means of the force applying construction 100.
In parallel with the advance of the forepoling device, a temporary wire ropeway ~ is installedj it is on this that the force applying mechanism 100 and the manipulator 600 can be displaced.
The formation of the lining by means of shot concrete is illus-trated as being in two stages: the application of the contact concrete 2 for the forepoling device is effected by a manipulator 600 connected to the forepoling device by a connecting element 600a; the application of shot con-crete for the load bearing lining is effected by a manipulator 600_ dis-placeable along the wire ropeway 4, with the construction of the manipulator 600b being, if desired, the same as that of the manipulator 600. Conveying hoses 6 effect the conveying of the concrete mixture to the spraying or shooting heads 7 and the material issuing from the shooting or spraying machine 300 can be directed to one of the manipulators 600 via a distributor 8. The mixer unit 500 receives its supply from containers 10 advanced along a conveying trac~ 9 either by way of direct emptying of the containers or via balance members 450. Belts 401 are provided after the mixer and between the mixer and the spraying or shooting head there is a transfer belt 402.
The general constructional form of the force applying mechanism 100 is shown in Figure 2 for the case of a generally non-circular section road. On the left hand side of the Figure the construction is shown partly in section in order better to illustrate it. In this case, the arch sup-port l comprises a roof arch la, side arches l_ and a floor or sole arch ld pivotally connected by hinges lc to the side arches. The hydraulic working cylinder lOl is connected by an upper hinge or pivot to a transmitting sup-port 102. The forepoling apparatus 200 and the wire ropeway 4 are carried by this support 102. The lower pivot of the working cylinder is connected to a transverse beam 103 which is connected via hinges 104 to bellcrank levers 105. The fixed pivot of the bellcrank lever is the pivot 106, which can be positionally adjusted relative to the pivot 104. The horizontal forces are transmitted from the bellcrank levers 105 to the transfer or transmitting supports 108 by a push rod 107. The transmitting or transfer supports 105 transmit the vertically downwardly acting forces. The base body llO serves to hold the whole mechanism together. The configuration of the floor or sole arch ld may be constructed in various ways and thus the constructional form of the transmitting support lO9 may change also. In the drawing the supports 109 only transmit vertical loads. The variant according to Figure 3 shows a transmitting support lO9a which can be clamp-ed by means of a wedge 112 and can form a load of any direction by way of the support 111.
Figure 4, which is a partial section of Figure 2 along the line m illustrates that the three pivot supports 113, 114, 115 serves for the adjustable support of the carrier 108 and with its aid can be driven next to the base body llO and thus a favourable position changing condition can be formed.
Figure 5 illustrates the case where the force application takes place with the intermediation of a double arch supporting system. The as-sembled actuating mechanism lO0 of the force application construction res-sembles that according to Figure 2 but here the constructional form of the supports is matched to the arch carrying system which in this example is of circular section. The arches ~m of the double arched supporting system are fixed to each other by way of fixed elements ln and clampable elements lk which exert their effect in a tangential direction. This system subse-quently remains in the concrete wall and is connected to the internal arch supporting system by way of intermediate rods 1~, the internal system con-sisting of a roof arch support 131, side arch supports 132 and a floor sup-port 133. The application of force takes place in the previously described manner by means of the actuating mechanism lO0, the intermediate supports 108a and lO9a and the working cylinder lOl. A wedge 135 fixes the clamped state in the internal arch support system. The wedge 135 is inserted into a guide which is formed either fixedly or adjustably along a stirrup 13~.
A clamping element lk is fixed on the part which remains in the concrete wall. In the Figure, this is a suitably dimensioned flat steel strap bent onto the perpendicularly bent ends of the arches 1~ ~aturally, the con-servation may also be carried out with other suitably formed arch fixing elements, what is essential however is that the clamped-in condition should not release in the event of loosening or de-actuating the force application mechanism 100.
The Figure illustrates a mode or variant of roof bolting wherein specially purpose built drilling element 151 is used to form the holes for the anchor bolts. Expediently, the drilling member 151 is mounted on a drilling support 152 which can provide for the required adjustments and the drilling support is connected to the base body 110 by way of a fixable pivot connection 153.
The left hand side of Figure 6 illustrates the condition wherein after clamping-in of the double arch support according to Figure 5, the force application mechanism 100 is to be removed and where the application of shot or sprayed concrete to produce the lining 5 has been achieved. It can be seen that the length of the transmitting rods lp should expediently be dimensioned so that tpey are somewhat shorter than the thickness of the lining. The right hand side of the Figure as seen snows the finished road section; here the cutting off of the rods 1~ has been accomplished although of course it is possible to utilise the projecting ends of the rods e.g. for suspending some desired element from them.
The mechanism accomplishing forepoling is designated by 200 in Figure 1. Its actual construction is shown in Figures 7, 8 and 9. Figure

7 shows the construction in its side view in its clamped basic position.
Figure 8 shows it in its released condition in side view, while Figure 9 is a diagrammatic and enlarged view of the section n-n.
An intermediate support 102 bears against the roof arch la and has a lower connection portion of inverted T profile, which at the bottom forms a horizontal plane. At the foot of the T profile there is a displace-able shoe 201 the lower projection of which serves as a guide of the fore-poling body 202. A pair of forepoling beams 203 lie against the foot of the T profile and are pivotally engagea at the rear by a guide 204, so that angular displacement in a vertical space or plane is permitted while hori-zontal displacement can take place along a guide formed on the lower edge of the forepoling body 202. A workine cylinder 205 is adapted to rotate the bellcrank lever 206 about a pivot 207 which has arcuate parts 208 to support the forepoling beams 203.
Sliding on the shoes 201 along the foot of the intermediate sup-port 102 enables a horizontal change of direction to take place while a change of direction in the vertical plane ls produced with the aid of aworking cylinder 212 by way of the sliding shoe 210 and the pivot 211 form-ing part of the upper guide of the forepoling body.
A wedge 214 fitting into the guide of a hook 213 mechanically fixes the forepoling beams 203. The forepoling device is advanced by moving the working cylinder 205 internally so that a rod 215 pivotally connected to the bellcrank lever 206 pushes a slide 209 "backwards", the chain 216 being fittable to the slide 209 and at its other end to a supporting ear of the shoe 210, whereby a horizontal advancing force is generated on the pivot 20~.
According to Figure 10 the shot or sprayed concrete lining can be produced with the aid of the spraying machine unit 300 so that a feeding head 304 rigidly connected with an air boiler mounted on a subframe 303 is connectable to a aistributor 8 by way of a flexible duct 6a.
The subframe 303 is so constructed that the concrete application machine units may be mounted serially or in parallel next to each other in the above described manner ana can be connected together in the manner of a console. The operation of the concrete application units is co-ordinated by a control system 305 so as to be synchronised with the distributor 8 but given individual units may be suitable for working in the material of the lining by themselves.
The feed funnels 301 of the sprayer units are connected together by a hopper mechanism 306 which can ensure the distribution as desired of the material arriving from the conveyor 402. A mix unit 500 makes up the starting mixture of the material of the lining. Feed vessel(s) 550 and feed horns 551 located on the mixer serve to feed the mixing unit at the appropriately rapid manner, the horns being simultaneously charged in an appropriately programmed manner by supply belts 401 and dosing outlets 403.
The dosing outlet 403 may operate in the known manner, it may be a screw mechanism or a fluidised mechanism or the like and is preferably angularly displaceable about the vertical axis of the rotary plate 404.
Figure 11 contains the three basic cases of providing solid feed for the mixing unit.
The material may be directly charged into the feeding vessels 550 from the containers 10. This is expedient principally in the case where the containers contain a single previously charged-in and pre~lixed dose.
Essentially, this same is true for the direct emptying of the container on-to the transport belt 401. One should remark however that in the latter case, the principle of unitary package is interpreted more broadly.
The container 10 with a discharge mechanism at the bottom can be mounted on an emptying hopper 451. An amount of material appropriate to the process is emptied from the container 10 by means of the balance members 450. The balance members 450 can be serially connected under automatic control and are suitable for the assembly of the material in situ and in certain conditions can also form the layers of shot concrete which can be varied on application.
For example, the container 10 is a known type with elastic walls, provided with a charging and bottom-discharge opening and is foldable to-gether. In Figure 12 there is shown a variant with a double chamber or space wherein the material filled into the bottom space via the charging orifice lOb is covered by a partition plate lOd and a second material phase, e.g. a dry powder phase can be fed in on top of it. When the discharge opening 10c is opened, both materials are emptied simultaneously. The con-tainer 10 may be suspended by way of support ears 10a. All phases of the filling can be carried out with the containers 10 being suspended or mount-ed on the ground but emptying or discharging can only be carried out in the vertical position.
Figure 13 shows the mixer unit in longitudinal section while Figure 14 is a view of the mixing unit along the arrow F.
The mixing vessel has two parts: a bottom part 501 and an upper part 502 connected together by a pivot 501l. In the closed position, the vessel is expediently at an inclined position, optimally 15-25 , so as to ensure that the emptying or discharging spout 503 should be at a higher level than the bottom. On tilting the bottom part 501, of the mixing ves-sel, it turns about the pivot 511 while the upper part 502 mo~es relative thereto about the pivot 50~, as well as about the two pivot points 505a and 505_ of the spacer rod 505, whereby the discharge spout 503 empties the material to the transfer belt ~02.
~he lower part 501 and the upper part 502 of the mixing vessel form an internally cylindrical space the axi~ of which is shown in the drawing with the reference letters xx. The mixer is driven from a motor 506 by way of transmission 507 and mixing drive 508, the mixing being ef-fected by the mixing blades of a planetary-movement blade system 509 and the rotary blade system 510. The working cylinder 512 is provided to ef-fect the tilting. Even with very steep tipping angles, it can occur that a material containing adhesive or agglomerative additives does not flow out through the discharge spout. The pivot 505b is provided on a bellcrank lever 513 which in the tipped position of the mixed vessel can be rotated by way of the working cylinder 51~ about a pivot 515 and in this tipped position, the two parts of the mixing vessel are close together. Then, the mixing blades of the blade systems 509 and 510 separate the adhered mate-rial from the wall of the vessel and by extending the working cylinder 51 again and rotating the mixer 508 perfect discharge or emptying can be achieved.
The filling of the mixer vessel can expediently take place through three apertures at any desired time distribution. The side hopper 501a may receive from the feeding vessel 550 expediently solid particulate additives, from the feed horn 551 it can receive dry pulverulent additives or a hydraulic binding material while along the pipe 551a it can receive liquid phase additives.

8~4 The feed vessel 550 is actuated by a tilting mechanism 552 so that a spout 550_ turns about the pin 550a and sits on the side hopper 501a. The closing plate 515 inhibits the formation of dust and during feed the spout 550_ tips it out of the way so as to open a free cross-section for the discharge.
The operation of the manipulator 600 shown in Figure 1 is shown in detail in Figure 15.
A holding tube 601 serves to fix the manipulator 600 and its po-sition is generally parallel with the axis of the road. Pivots 602 and 603 disposed on the holding tube 601 as well as pivots 60~, and 605 disposed on the manipulator 607 form a rod parallelogram as a consequence of which when the working cylinder 606 moves, the manipulator body 607 is displaced in a direction parallel with the axis of the holding tube 601. This represents the advance of the manipulator in the direction of the axis of the road.
The working cylinder is controlled or guided by a manual arm 608. The aoy-stick or directing arm 609 is held in the hand of the operator, its posi-tion is always parallel with the spray head 7 and its displacements are of the same direction so that the displacements are in a predetermined direc-tion.
In the cylindrical shaft bore of the manipulator body 607, there is an element 601 which can rotate with the aid of the working cylinder 611 about the bore axis of shaft parallel with the axis of the road. Its move-ment is controlled by the appropriate displacement of the manual arm 608.
Pivots 612 and 613 are on the element 610. The operating arm 614 and the indicating arm 615 are connected to the pivots. A collecting rod 618 lo-cated between pivot 616 and 617 is so-chosen that the angular displacement of the two arms should be mirror images of each other. The operating arm 61~ is mo~ed by a working cylinder 619 and is controlled by a control valve 620 on the connecting rod 618, the valve being responsi~e to the apppropri-ately directed force ef~ect of the directing arm 609. A bellcrank lever 630 is displaceably mounted about a pivot 612 on the body 610 Qnd a lifting lever 629 at the pivot 613 is so disposed that the pivots 612, 613, 624 and 625 should form a rod parallelogram. This system ensuring parallel move-ment also includes on the operative side the rod parallelogram 612, 621, 622 and 623 while on the guide side the rod parallelogram 613, 626, 625, and 627, consequently the displacements of the shooting or spraying head 631 and the base body of the aiming device 632 are in conformity with each other. The displacement is carried out by the working cylinder 633 by way of the control valve 628 in response to the force effect of the arm 609.
A bore of the base body 631 of the head rotatively mounts the head casing 634. Working cylinders 635 causes the angular displacement. A
flexible shaft 636 connects it to a similar flexible shaft of the base body 632. A control valve 639 connected to the tubular shaft 637 the member 638 and the coupling 634 ensures that the movement is in conformity.

Figure 16 shows the construction in principle of the sensing and connecting rods 618 and 628.
Coaxial and telescoped rods 640 and 641 are arranged between pi-vots kl-k2 and are connected together by way of the linkage of a valve 642.
The normal centre position of the valve is ensured by a spring against which 20 the rod may be displaced externally or outwardly or inwardly to produce the appropriate piston position of the valve.
It is an adYantage of the invention that every operational step of supporting or ensuring roads designed for long life are fully mechanised to enable them to be carried out purely by machines. In this way, it achieves a significant reduction in the physical labour carried out in very difficult conditions as well as a shortening of the time required.
The invention also enables the optimisation of utilisation as well as the quantity of the installed supporting materials because after deter-mining the parameters of the rock, it utilises the latest rock mechanics 30 principles and can compute all road supporting parameters by computation so as to select the most appropriate support construction and machines.

Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of bracing an underground cavity in rock, with a support structure capable of being tensioned, comprising the steps of a) measuring the primary stress in the rock at a position of the cavity where support is desired;
b) determining the permissible load for the support structure;
c) tensioning the support structure at the support position in accord-ance with the measure of the primary stress prevailing at said position, as modified by the determined load permitted for the support;
d) determining the pre-stressing forces required at the support position; and e) forming a concrete shell within said cavity from shot concrete in one or more layers having a wall thickness which is the greater of a computed required wall thickness based on the load bearing capacity of the cavity and a computed required wall thickness based on the load bearing capacity of the support, taking into account in each case the difference between the primary stress at the support position and the desired pre-stressing forces at the support position.

2. The method according to claim 1, including the step of providing support members at a spacing governed by the ratio of the measured primary stress to the difference between the measured primary stress and the pre-stressing force.