US2291669A - Method of strip mining - Google Patents

Description

R. S. wElMER ETAL 2,291,669

METHOD OF STRIP MINING riled March 14, 1941 Aug. 4, 1942.

2 Sheets-Sheet 1 Aug. 4,1942.

R. S. WEIMER ETAL METHOD. OF STRIP MINING Filed Maron 14, 1941 2 Sheets-Sheet 2 Patented Aug. 4, 1942 t 2,291,669 ME'rnop oF s'rmr MINING Raymond S. Weimer, Morris, and Thomas C. Mullins, Chicago, lll.

Application March 14, 1941, Serial No. 383,252

` 13 Claims. This invention relates to improvements' in the method of removing earth `or overburden from valuable deposits of coal or other mineral.

One object of the invention is to provide an improved method of excavating which increases the effective capacities of earth moving machines and effects economies in mining operations.

The improvements have been developed in connection with the art of so-called strip mining of coal and the invention will be described in that connection for illustrative purposes.

In the art of strip mining the overburden or earth overlying a strip of coal is removed and usually is piled along one side of the cut so made. Power shovels or'drag line equipment generally are the means principally employed in removing the overburden and depositing the same in spoil piles. When one cut has been made and the coal removed therefrom'a second cut generally is made alongside the first cut on the side opposite the spoil pile and the earth or overburden removed in making the second cut is deposited in the rst cut.

In removing and depositing the overburden upon the spoil pile the material is loosened from its original compact condition and increases in volume. For example, the swell of the material frequently is from twenty to twenty-rive per cent of the original volume. Hence, if the second cut is of the same width and depth as the lrst cut, the material of the second cut will more than fill the rst cut and the spoil pile formed by the removal of the material will extend substantially above the surface of the terrain. When the cut is about forty feet in depth, for example, the spoil pile formed of material from that cut may extend substantially above the level of the terrain, due in part to the swell of the loosened material and in part to the fact that the spoil pile of such cut is narrower from face to face (measured in a direction normal t o a face) than the base of the spoil pile, due to the inclination of the latter, such inclination being necessary to prevent slides of material back into the cut being made. The slope of the exposed face of the spoil pile, that is, the surface adjacent the cut being formed, cannot be greater than the angle of repose of material that is being removed. 'lhe bank of the cut onthe side opposite the spoil pile may be nearly, if not, vertical,

' depending on the nature of the overburden, but

the angle of repose of the loosened material in the spoil pile is much less, that is, it frequently is approximately 35 to the horizontal. Hence,

as the spoil pile increases in height the crest thereof moves farther and farther from the base of ,the cut from which the material isbeing removed. Where the earth moving apparatus (such as power shovel or drag line equipment) is stationed at the bottom of the cut, the distance from the machine to the crest of the spoil pile l laterally of the cut by reason of the angle of repose of the material of the spoil pile.

A machine with a boom of a given length may make a cut of a given depth and of a certain Width at the base`(such width corresponding to the width -of the strip of coal that may be removed) and deposit the waste directly upon a spoil pile, but the deeper the cut that must be made by that machine to uncover the coal (other conditions remaining lthe same), the narrower the cut must be at the bottom if the machine is to cast the w-aste directly upon the -spoil pile. The width of the cut at the base determines the quantity of coal that will be made accessible for removal from the uncovered portion of the seam.

It will be appreciated that it may be possible to increase the length of a boom of a given ma.- chine to give it the reach required in depositing the bucket loads directly on the remote side of the crest of the spoil pile, but such alteration generally necessitates the use of a smaller bucket and introduces other engineering and mechanical problems that may slow up the process of removing the overburden to the point where operations become uneconomical. Such factors and others, v

such as the depth of the coal vein, limit the `depth at which it is commercially feasible to carry on strip mining operations. An excavating machine of a particular power rating may have a boom of a certain maximum length and a bucket or scoop of a certain maximum capacity but if the length of the boom can be decreased not only can a bucket of greater capacity be used herein.

the effective reach of a substantially longer boom. A

In utilizing the present improvements to the greatest extent advantage is taken of the tendency of the loosened or dislodged cover of the overburden of a face of an excavation to gravitate toward the base thereof. At nearly every loading stroke of an excavator-dipper or bucket earth is loosened which rolls or slides down the face into which the bucket is cutting. During the course of an average days strip mining operation actually many tons of such material are loosened and move downwardly to a greater or lesser distance from the original positions thereof. If such downward movement is toward the spoil pile such gravitational shifting of the material represents valuable work done and is of substantial advantage economically, whereas, if the movement of the loosened material is away from the machine or away from the spoil pile or even parallel to the spoil pile its recovery by the bucket entails additional work and hence increases the cost of operation. In order that the tendency of the dislodged material to move gravitationally can be taken advantage of to the maximum degree it is desirable that the loading strokes of the machine bucket generally be'in a directiontoward the spoil pile which thus augments the tendency of dislodged material to move by gravity or to be pushed by the bucket toward the position of final deposit. While the advantages the waste or overburden removed therefrom having been deposited to form a spoil pile I3 at one side thereof and the coal removed from the bot- Y tom of the cut. The formation of this ilrst cut mentioned, of course, are not. available duringv the complete process of removing overburden and casting it directly upon the spoil pile they are available generally during a substantial portion of such operations and they and other advantages are of such importance that in order t'o benefit more fully from them it is, paradoxically, as will appear hereinafter, advantageous to deposit some of the overburden within the confines of the cut being made although it is necessary later to remove the same.` In'order words, to gain the advantage resulting from locating the machine in certain advantageous positions otherwise impossible, a fill is made of excavated material which later must be partially or wholly rem'oved, as will be more specifically described Other advantages of the present improvements will be apparent from a consideration of the following specifica-tion and accompanying drawings, wherein Figure 1 is a diagrammatic cross section of a strip mine showing a cut from the base of which the coal has been removed;

Figure 2 is a similar sectional view illustrating the partial formation of a second cut with the removed overburden deposited within the first cut; t

Figure 3 is a broken, perspective view of a strip mine illustrating progressive steps in the formation of the second cut above referred to;

Figure 4 is a transverse section of a mine illustrating excavating machines in different advantageous positions; and

Figure 5 is a diagrammatic view'illustratin rain is indicated by the line I0 and the vein or s eam of coal lII may be assumed to be at any usual distance beneath the surface which is with- `in the range at which strip mining operations I2 may have been effected by conventional methods, such not being important to the understanding of the present improvements, which generally are applicable primarily to the formation of cuts following the first one. Making the initial cut in opening up a strip mine may be, of course, more difficult than making subsequent ones generally, since the waste or overburden must be disposed of generally by piling the same upon the surface of the terrain as indicated at I3 in the drawings. In making subsequent cuts each previously made cut is available for receiving the spoil and hence such cuts, as compared with the rst cut, are more economically formed, other conditions remaining the same. It will .be noted that the angle of the face I4 of the cut I2 is approximately 35 degrees to the horizontal, such angle being the angle of repose of the loosened material. of which the spoil pile may be assumed to be formed. I'he angle of repose varies with different materials as is well understood. The surface I5 of the opposite bank of the cut is shown as being somewhat steeper than the face I4, which generally is feasible since the material of the surface I5 has been undisturbed and remains in compact condition. When the second cut is to be made, that is, after the coalhas been removed from the bottom of the first cut, advantage can be more fully taken of the present improvements. Instead of locating an excavating machine-in the bottom of the first formed section of the second cut, as has heretofore been common practice, for the purpose of cutting away the overburden and swinging successive bucket loads laterally to deposit the same in the cut I2, a bench is formed in the overburden which is to be removed in forming the second cut and upon which bench the excavating machine opcrates.

In Figure 1 line I6 indicatesv the plane which will be occupied by the right-hand face of the second cut when th'e latter has been completed. In making the second cut an upper section of the overburden thereof is removed to form an approximately horizontal machine supporting surface. This surface preferably is in a plane lo-` l cated about of the vertical distance measured from the coal I I tothe surface of the terrain IIJ. The surface of the bench so formed is 1ngenerally the sequence of removal of sections of .overburden from a cut and the disposal thereof. Referring to Figure 1, the surface of the ter- -dicated at I1 in Figure 3, which figure indicates that the upper portion of the overburden of the second cut h'as been removed down to the plane of line I1 and has been deposited in cut I2, thus starting a second spoil pile I8 the base of which corresponds to' the base of the cut I2. The nal angle of repose of the spoil pile I8 is indicated by the line I9 and if prior methods were employed the spoil pile would be built up along the plane indicated by the line I9 until all the overburden from the second cut had been removed. .It will be seen, however, that where this method is followed a V-shaped channel would remain between the planes indicated by the lines I5 and I9 and that were an excavating machine to be located on the surface of the bench indicated by line II the excavator necessarily would have to be kept at a distance to the right from the edge of the I bench to avoid the possibility of causing th'e latter to slide and possibly wreck the machine. Hence, in accordance with the present improvements, instead of leaving a channel between I I I the places indicated by lines I and I9 the upper portion of the overburden is deposited not only in a position to initiate the formation of the spoil pile I8 but some of it is deposited also in the V-shaped channel 20 between the planes of surfaces indicated by the lines I5 and I8 and thus is formed a lateral extension of the' surface of the bench' I1, the surface of which extension is indicated by the line .2|, Hence it will be seen that not only is the face I5 laterally supported by the filled in material 28, but the latter receives lateral support also bythe initial portion I8a of the spoil pile I8. Hence a machine operating on the bench may move laterally beyond the plane of the face I5 and onto the surface 2| which constitute a lateral extension of the bench and may for convenience be designated a shelf upon which the machine is free to move into the space of the first cut and thus take a position adjacent the plane of the face I8 of the spoil pile.

By operating from the supporting plane of the line I1 the machine has the advantage of such elevated position and hence the vertical reach of its boom is effectively increased an extent not less than the vertical distance between the surface of the coal and the top surface of the bench. If a single machine is located on the surface'of the bench I1 and on the extension or shelf 2|, it can, as indicated at Figure 3, by removing overburden above the plane of the bench, extend the latter longitudinally of the cut to be formed and, by operating from the opposite end of the bench, remove the material of which' the bench is composed down to the surface of the coal and thus uncover the same. In thus removing the bench material the machine can also remove the material 'of the extension or shelf 2|, depositing such material on the spoil pile. This method of operation is pictorially illustrated in Figure 3 of the drawings.

Referring to Figure 3 of the drawings, I2 is the cut from which the coal has been removed, the material of the out having been deposited in a spoil pile I3 at one side of the cut, the face of the cut opposite the spoil pile being indicated by numeral I4, as above described. The second cut to be made by utilizing the present improvements will extend parallel to cut I2, and this second cut is shown as being partially formed in Figure 3. Inthis figure it will be observed that the bench I1 has been formed by removing an upper portion of the overburden as above described and depositing the same in the cut I2 to form the initial portion I8a of th'e spoil pile I8. A shelf 2I has been formed also of the material removed in forming the bench which enables an excavating machine 22 to` move laterally to the left in Figure 3 beyond the plane of the face I8. In fact the machine 22 can move to positions adjacent the face I4 of spoil pile I3 by traveling upon the surface I8b of the initial portion I8 of the spoil pile I8 where such portion h'as been formed in advance of rearward and more elevated portions thereof as will be explained later. In the foreground of Figure 3 the second cut is shown as completed at one end, that is, the material of the bench I1 and shelf 2| has been removed by the machine 22, and the material deposited upon the initial portion I8a of the spoil pile I8, thus forming the upper portion I8c of the pile and exposing the coal 23.

The machine 22 is shown as being of the dragline type and is provided with a boom 24 of such length that when the machine is located on the bench or shelf adjacent the s poil pile I8, as

shown, the bucket 25 can be moved outwardlyof th'e boom to the point where its load can be discharged at or beyond the crest I8d of the completed portion of the pile. As the machine progresses along the plane of the bench longitudinally of the strip of coal the material of the bench and shelf are removed to uncover the coal and the portion I8c of the spoil pile of maximum height is, of course, extended by the deposition of the material upon the previously formed sections of the pile I8. The machine 22 by operating at the opposite end of the bench by cutting into the bank or face 26, can advance the bench longitudinally, the material so removed being deposited in the cut I2 and thus advancing th'e initial section I8a of the spoil pile and likewise extending the shelf 2 I. Hence, by alternately extending the bench and shelf as described and later removing the bench and shelf material at the first mentioned end thereofthe coal will be uncovered, the machine operating always from the plane defined by the surface of the bench, shelf and initial portion of the spoil pile.

In removing the upper portion of the material of thev cut to form the bench and shelf and the .initial portion I8a of the spoil pile, surplus material not requiredin forming th'e shelf and initial portion I8a is deposited upon the portion I8a and may form an intermediate portion I8e of the spoil pile. However the surface I8b of the initial portion of the pile preferably is advanced beyond the section I8e whereby a machine such as the machine 22 can travel from the bench I1 across the shelf 2| and take a position adjacent the face I4 of the first formed spoil pile I3.- From this advantageousposition afforded by the elevation of the surface I8b the machine may deposit material upon or beyond the crest of the first spoil pile I3, in many instances if desired, and can also deposit waste in the V-shaped channel lying between the contiguous faces of adjacent piles thus leveling off the terrain as indicated by line I8f in Figure 4. Generally the spoil piles of territory that has been strip-mined by conventional method consists of a series of ridges which render the surface practically useless thereafter. The V-shaped valleys between the ridges represent valuable spoil-receiving space which' if filled during the excavating operation would leave the terrain in a more desirable condition for future use and result in the formation of spoil piles of lower elevation.

In Figure 3 of the drawings a machine 21 is shown in the position above mentioned, that is onethe surface I8 of portion I8a of the second pile I8 and adjacent the face I4 of the pile I3 from which position the machine may deposit spoil upon the pile I3 or in the V-shaped channels between the upper portions of piles I3 and I8.

The second machine 21 may be employed merely for the purpose of advancing the bench, shelf and initial portion I8HL of the spoil pile. By cutting away at the face I5 and depositing the material in the cut I2 the first section I8*l of the spoil pile I8 and likewise the bench I1 and the shelf 2| can be extended longitudinally ofthe cut. With two machines operating, the latter machine 21 may, of course, `be provided with a boom 28 substantially shorter than the boom of the rst machine, since such machine is required only to deposit material upon or beyond the crest |88 of the intermediate portion I8l of the, spoil pile I8 and to advance the formation of the portion I 8*. Since the crest I8! of the section I8 of the spoil pile is closer tov the face I6 than is the crest VII!d of the highest section I8c of the spoil pile, the boom 28 of machine 21 may be substantially shorter than the boom of machine 22 and preferably is of such length only as to enable it to drop the bucket into the upper portion of the face I6 and to deposit the load upon or beyond the crest |88.

The machine 21 like machine 22 when the latter only is used, can be moved to different positions on the surface formed by the bench I1, shelf 2|, and the initial portion III*i of the spoil pile and when either is in a position of machine 21 as is shown in Figure 3 and in dotted lines in Figure 4, the bucket can -be dropped into the overburden in advance of the bench and can be hauled substantially transverselyof the cut, thereby moving the load in the shortest route to the place of deposit. Material loosened by the bucket can gravitate down the slope vof the face I toward the place of deposit when the bucket is cutting into the face and in many instances will slide into the space of the cut I2. The movement of such material by gravity reduces the cost of operations. When the bucket is cutting into the bench material such quantities of the loosened material as are moved or pushed by the bucket during the loading operation but which do not actually enter the bucket are moved toward the place of deposit and hence the energy so consumed is not entirely wasted.

Referring to Figure 4, which is a vertical section through a mine of the character under consideration, line III indicates the surface. of the terrain, while indicates a vein of coal which may be assumed to be 80 feet beneath the surface. This gure indicates that a first cut 12 was made and the waste material thereof deposited in a spoil pile I3 upon the surface of the earth at one side of the cut. The cross sectional area of the second cut to be made, indicated by the numeral 29, extends from the faceA I5 to the plane I6. If it be assumed that the width of the first cut was 100 feet at the base and that of the second `cut 29 is also to be 100 feet at the base, the cross-sectional area of the second cut 29 will be about 8,000 square feet. However, since the material when loosened by the excavator will swell or increase in volume by approx-1 imately 25 per cent, such loosened material, when moved to a spoil pile Il will have a cross-sectional area of about 10,000 square feet. While the base of the spoil pile |81 will be 100 feet wide, the distance between the faces 3|- and 32 of the spoil pile, measured in a direction normal to the faces, will be substantially less than 100 feet, for example, about 60 feet, due to the inclination of such faces which constitute the angle of re-` pose of such loosened material. 'I'he spoil pile I 8 therefore, under the conditions assumed, will have a face approximately 200 feet in height measuring from the surface of the coal II tothe crest |84 of the spoil pile. Should an excavating machine22 be located adjacent the base of the spoil pile II upon the coal, as has been common practice heretofore, its boom would have to be suiliciently long (not less than 200 feet). to enable it to deposit the material upon or beyond the crest Ild of the spoil' pile unless recasting or `other methods were employed in disposing of the waste. A boom of such length would be much in excess of that required in removing the material lying between the faces I5 and I6. Since the direct deposit of the removed material by the excavating machine generally is more economical than such recasting or rehandling methods. it is desirable to avoid such more expensive methods where possible and by utilizing the present improvements a machine having a boom of 150 feet in length can be employed under the conditions presented in Figure 4 for directly casting the last portions of removed material upon or beyond the crest of the spoil pile Il. Such boom is of sufllcient length that by pivoting or turning the machine upon its base in the customary manner, but without moving the machine from the location shown, the 4bucket can be dropped into the upper portion of the face I6 opposite the machine. Where the second inachine 21 is employed the boom thereof need be no more than 135 feet in length under'the conditions assumed in Figure 4 to enable it to advance the formation of the bench I1, the shelf 2| and the initial portion I8a of the spoil pile. Since such machine can shift its position laterally. of the cut over a substantial range and a shorter boom thereby employed, a larger capacity bucket can be'used.

If it be assumed that the surface of the bench I1 is 30 feet above the surface of the coal II and the machine 22 has been moved over upon the shelf 2| to the approximate position shown in coal, an advantage would be gained insofar as the effective reach of the boom is concerned with stantially more material would be required to form the shelf and since the material of the shelf generally must be later removed it has been found advantageous to locate the plane of the shelf at about of -the vertical distance measured from the coal to the surface of the terrain. However, in the ilnal removal of the material constituting the bench and the shelf, such material must be elevated wholly by the machine and little or no advantage is attained from the free gravitational movement of the material which occurs when the upper portion of the cut is made, that is, in removing the overburden that lies above the plane of the bench. In the in-v stance under consideration the first 50 feet of the overburden can be removed by the machine or machines under conditions wherein the movement of the drag-line bucket or buckets is -level or downwardly toward the machine and hence the material which is loosened by the bucket will gravitate tdward the machine, or toward the cut into which the material is to be deposited.

In the making of the' upper portion of the cut adjacent'a previously made cut, it is not necessary that the material be moved wholly by the excavating machine or machines shown in the causing` the material to gravitate down the face burden o f any cut without actually lifting and shifting the material by mechanical means represents substantial economies in the earth moving operations.

In taking advantage 'ofl the tendency of loosened material to slide and roll down the face of a cut, it is desirable thatv the loading strokes .of the excavating machine be such as to cause such loosened material to move toward the machine or, where possible, to gravitate directly toward the position of nal deposit. Where such loosened material slides down the face of the cut, for example, toward the machine, the succeeding stroke of the machine in picking up such loosened material will be shorter and hence less time will be required in taking on the-load and depositing it in the spoil pilenthan would be the case had such loosened material moved away from the machine or had remained in its original position. i

As contrasted with prior strip mining methods wherein an excavating machine initially digs down to the surface of the coal and from that level continues the' removal of the. overburden along the strip of coal to be uncovered, the present method effects substantial economies. Of major importance is the fact that by means of the new method ,the length of the boom of the excavator need not be of such length as to enable it to reach from the bottom of the cut to and beyond the crest of the spoil pile since, in carrying out the novel method, the machine is maintained at an advantageous level which is above the plane of the coal. Since the use of a shorter boom on a machine enables the use of a bucket or scoop of greater capacity and permits of greater acceleration and deceleration of swinging movements of the boom, larger and more frequent loads can be handled by the machine. The utilization of the machine-supporting shelf or bench-extension and the initial portion of the spoil pile to enable the machine to be moved laterally to a position close to the face of the spoil pile being formed or close to the face of the previously formed spoil pile as above described, thus lgiving the boom a greater effec- .tive length, has been found to be of substantial advantage, notwithstanding that the material of which the shelf is formed generally must be later removed.l Frequently not all the shelf material must be nally removed, depending on the characteristics thereof, since the movement of the machine upon the shelf packs some materials so rmly that a portion of it may be left in position at the base ofthe spoil pile, as indicated by the dotted line 33 in Figure 4, without likelihood of its sliding down upon the coal.

In -Figure 4 the combined width of the bench and shelf is approximately 150 feet and during the removal of the bench material with the machine 22 located near the face 3 I of the spoil pile, as ,shown in full' lines, the bucket can be dropped onto the remote side of the bench and in being drawn toward the machine on the loading stroke e will push`loose material toward the spoil pile. Hence, when the strokes of the machine are in a transverse orpartially transverse direction of the cut, the movement by the bucket of the material which does not enter the bucket does not represent wholly wasted energy since the movement .of such material is toward the spoil pile.

Where a machine lis located on the surface of the coal and its loading strokes to a large extent are additional time and results in increased costs.

Hence filling in the V-shaped space to form the shelf, in addition to enabling the use of a shorter boom on a machine and al larger bucket, enables the machine to be located generally at the side of the cut adjacent the spoil pile and sufficiently removed from the opposite side of the cut that a substantial portion of the operating strokes of the bucket can be made `in a direction transverse the cut, rather than lengthwise, thereby rendering advantageous the loosening and displacement of the waste by the bucket during loading operations. The machine 22 may also be moved laterally beyond the bench 2| if desired,- to. or adjacent the face I4 of the pile I3, that is, to the position of the machine indicated by dotted lines in Figure 4. The'machine in such positionfwill be located uponthe initial portion I8a of the pile I8 in advance of the more elevated or completed portions of the pile andwhen in such position can, in loading, haul its bucket transversely of the cut and deposit the loads upon the pile I3 or the pile I8 or directly within the V-shaped spaces between the crests of those piles, thus leveling oif `the terrain. Where the machine 22 having a boom feet in length is in approximately the position of the machine shown in dotted lines in Figure 4, the bucket can be swung to discharging positionv which will be more than 250 feet from the left hand ed e of the coal seam II. Hence the improved me hod increases to avery substantial extent the effective length of a machine boom, enabling it to deposit material a distance so remote from the cut being formed that it becomes practicable to strip-mine to greater depths or to make substantially Wider cuts and without re-casting the removed material and without increasing the likelihood that loose spoil pile material will slidedown upon the coal. Utilizing the vV-shaped. spaces between spoil piles, as mentioned, results in the formation of spoil piles of lesser elevation (other things being equal) and hence permits the use of shorter booms and of larger capacity shovels than would otherwise be required under like conditions if prior methods were employed.

Figure 5 illustrates diagrammatically the direction of movement of successive portions of the overburden of a strip into an adjacent cut to form a spoil pile. Upper vcase letters A to E, inclusive, indicate arbitrary divisions ofthe upper portions of the overburden, while letters F to J, inclusive, indicate similar arbitrary sections ofl the overburden which constitute the bench and shelf. As indicated, the section A is moved to the position a, while sections B, C, D, and E are moved to the positions b, c, d.; and e, respectively, thus forming the shelf 2| and forming the first or initial portion' I8a of the spoil pile..` The Vmovement of sections A toE can be' elected without any -substantial elevation of the materials as will be seen and, if desired, `by means other than drag-line apparatus as mentioned above. Section 1 gravitate toward thespoil pile and will tend to.

llongitudinally of the strip.the gravitational be moved in that direction by the bucket of dragline apparatus located upon the shelf 2| or upon an advanced portion I8 of a spoil pile and making its loading strokes from right to left transversely or substantially transversely of the cut or at some transverse component of such direction.'

duction in time required in completing the bucket loading and dumping cycles resulting from the employment of the shorter boom than would be required in following conventional practices.

It will be noted that by lthe described method the material of the upper portion of a section of overburden becomes generally the lower portion of the section of the spoil pile directly, or substantially directly, opposite the place of origin of the material and that the lower portion of that section of overburden becomes the upper portion of said section of the spoil pile.` The movement of the successive portions of overburden into positions of deposit "opposite or substantially opposite the positions of origin, that is, by the shortest routes, rather than into positions substantially in advance of the respective positions of origin, enables loading operations to be accelerated and reduces the costs thereof. y

By means of the present improvements the effective reach of the boom or booms of excavating apparatus is substantially increased in that suchapparatus operates not only froman advantageous elevation above the mineral but from advantageous lateral positions as well. Advantage is taken of the tendency of substantial quantities of the material, when loosened by the buckets to gravitate toward the place of deposit and of the known fact that during loading strokes the buckets push substantial quantities of material along in front of them but which do not enter the buckets. Where the loading strokes are transverse or partially transverse with respect to the cut being formed such movement of the material entails less loss of. power or energy than shouldthe movement of such material be away from the positions of final deposit. Furthermore, by increasing the effective length of the boom, larger buckets can be employed on machines of given power ratings without increasing the loads on the machines and hence the overburden can be removed at a lower cost per ton by utilizing the present improvements.

We claim:

1. The method of removing overburden from a strip of mineral contiguous one side of a previously formed cut which comprises removing an upper portion of the overburden to a level intermediate the surface of the Yterrain and the mineral to provide a machine-supporting bench and depositing said removed overburden in said cut to form a spoil pile and also depositing a portion of the material alongside the bench intermediate the same and said spoil pile to provide a shelf co-planar with and extending laterally from the bench to the spoil pile for receiving lateral support from the latter and providing lateral support for the bench, placing an excavat- 1Ds machine on the bench and manipulating the same thereon and on the shelf for removing the bench and shelf material to uncover the strip at one side of the machine by excavating strokes thereof moving generally in a direction transverse with respect to the bench and shelf and .toward the spoil pile, and by similar operating strokes advancing the bench and shelf formation on the other side of the machine to enable the machine to advance at said level toward the other end of the strip as the material of the strip is uncovered on the first mentioned side of the machine. v

2. The method of removing overburden from a strip of mineral contiguous one side'of a previously made cut which comprises removing an upper portion of the overburden down to a selected level between the surface and the mineral to provide a bench and Adepositing the overburden in said cut to forni a spoil pile and depositing also a portion of such overburden between the spoil pile and the adjacent face of the bench to provide a co-planar shelf, and thereafter progressively removing successive portions of the bench and shelf material and depositing the same on the spoil pile by means of an excavating ma-l chine operating on the bench and shelf in advance of the portions being removed.

3. The method of removing overburden from a strip of mineral contiguous one side of a previously made cut which comprises removing an upper portion of the overburden down to a selected level below the mid-plane of the overburden to provide a bench and depositing the overburden in said cut to form a spoil pile and depositing also a portion of such overburden between the spoil pile and the adjacent face of the bench to provide a co-planar shelf, and thereafter progressively removing successive portions of the bench and shelf material and depositing the same on the spoil pile by means of an excavating machine operating on the bench and shelf in advance of the portions being removed.

4. The method of removing overburden from a strip of mineral contiguous one side of a previously made cut which comprises removing an upper portion of the overburden down to a level spaced above the mineral a distance corresponding approximately to three-eighths the vertical distance between the mineral and the original surface of the overburden to form a spoil pile and depositing also a portion of such overburden between the spoil pile and the adjacent face ofthe bench to provide a co-planar shelf, and thereafter progressively removing successive portions of the bench and shelf material and depositing the same on the spoil pile by means of an excavating machine operating on the bench and shelf in yadvance of the portions being removed.

5. 'I'he method of increasing the eiective capacity of a boom-provided excavating machine in removing overburden from a strip of mineral contiguous a previously opened cut and in casting the overburden directly in said cut to form a spoil pile which comprises forming a machine supporting bench above the strip by removing an upper portion of the overburden down to a predetermined level and depositing the spoil so removed in the cut to initiate the formation of a spoil pile and form a shelf for laterally supporting the bench and for receiving lateral support by the spoil pile, and locating an excavating machine on said bench and shelf and operating the same to progressively remove the portions of the `bench and shelf at one side of the machine and casting upon the spoil pile the material so removed'by the machine while operating at the eleand shelf. l

6. The method of removing overburden from a strip of mineral contiguous a previously formed cut which comprises forming a supporting bench for a boom-type excavating machine at an elevation intermediate the surface of the terrain and the strip of mineral by moving that portion of the overburden above said level into the cut to initiate the formation of a spoil pile and providing from some of such removed material a shelf intermediate the bench and spoil pile and co-planar with the bench for extending the machine supporting surface of the bench laterally to the spoil pile and upon which extension the machine can move for increasing the effective reach of the boom thereof in casting spoil upon or beyond the crest of the pile, and operating the machine while on said bench and shelf for removing the bench and shelf material at one side of the machine to uncover the mineral strip and advancing vthe machine longitudinally of the bench and shelf intermittently as the uncovering of the mineral progresses.

7. The method of removing overburden from a strip of mineral contiguous apreviously formed cut which comprises moving an upper portion of i the overburden laterally into the cut to form a spoilpile and to provide a horizontal bench above the strip at a level intermediate the surface of the terrain and said mineral and depositing a portion of such overburden contiguous the bench to provide lateral support for the bench and to provide also a lateral extension of the surface thereof extending into the original space of the cut and upon which surface extension a boomtype excavating machine can be placed at a distance sufiiciently remote from the opposite side of the bench to enable the machine-to be so operated that the loading strokes thereof vare substantially in a transverse direction with respect to the bench and toward the cut and to increase the distance from the bench at which the machine can discharge the loads, and placing such a machine on the bench and extension for operation as stated in removing the remaining overburden constituting the bench and bench extension. f

8. The method of removing overburden from a strip of `mineral alongside a previously formed cut which comprises removing a portion of the overburden down to a plane intermediate the surface of the terrain and the strip to form a supporting bench for an excavating machine, depositing the material so removed infsaid cut to initiate the formation of a spoil pile and forming also a machine-supporting shelf co-planar with the bench and extending laterally to the adjacent face of said spoil pile, and operating drag line equipment on the surface of said bench and shelf at the side thereof adjacent the spoil pile for extending the formation of the supporting surface at one side of the equipment and removing the bench and shelf material. at the other side thereof whereby the machine is able to deposit its loads directly upon or beyond the crest of the pile and is suiilclently remote from the opposite side of the supporting surface to enable the loading strokes of the machine to be in a direction substantially transverse the cut being made.

9. The method of removing overburden from a strip of mineral adjacent'a previously formed cut which comprises removing an upper portion of the overburden from a longitudinal section of the cut to form a machine-supporting bench above the strip and depositingthe lremoved mai terial in said cut to ,form a lateraltmachine-'sup- 'porting extension of the -bench extending from the bench across the cut to the opposite side thereof, and operating excavating apparatus on ythe bench and bench extension to extend the formation of the bench and extension in advance of the apparatus-and to remove successive portions of the bench at the other side of the machine to uncover the mineral.

10.v The method of removing overburden from a strip of mineral adjacent a ipreviously formed cut which comprises removing an upper portion A of 'a section of the overburden to form a machine-supporting bench, depositing the material so removed in said cut to form a supporting extension forexcavating apparatus co-planar with respect to the bench and extending across the cut, and operating excavating apparatus on the bench and bench extension to remove the upper vportions of successive sections oi .the overburden for extending the bench and bench extension llongitudinally of the strip and cut respectively in advance of the apparatus and for removing the bench at the otherside of the machine and depositing the removed bench material upon the extension substantially opposite the place of removal.

11. The method of removing overburden from f `line apparatus on the ben-ch extensionand operating the bucket or buckets thereof in direc-l tions substantially transverse the bench during the loading strokes to remove the bench material and depositing the material so removed upon said extension.

12. .The method of removing Aoverburden from a stri-p of mineral adjacent a previously formed cut which comprises removing an upper portion of a section of the overburden to form a supporting bench at a level not above the horizontal median plane Aof the overburden, depositing material so removed in the cut to form a co-planar extension of the bench extending from the -bench to the remote side of the cut, and removing the material of the .bench by boom-type excavating apparatus 1ocated on the extension at positions laterally re- Imote4 from the bench whereby such removed bench material can be deposited in positions in a spoil pile laterally beyond the range of the boom of said apparatus when located on the bench.

13. The method of removing overburden from 1 a strip of mineral adjacent a previously formed cut the spoil of which is located alongside the cut on the side remote from the bench, which comprises removing an upper portion of a section of the overburden to form a bench at a level'not above the longitudinal median plane of the overburden, depositing the material so removed in said cut to form an extension ofthe bench coplanar with the latter, operating boom-type excavating apparatus on the extension to remove additional upper portions of contiguous sections of the overburden and depositing the removed material in the cut to extend the bench and bench-extension longitudinally of the strip and cut respectively, removing by said apparatus porformed portion o! the bench extension to form a spoil pile, and movixm the apparatus to positions on said bench extension in advance of the upper portion of the spoil pile and operating the same for removing additional portions of the -ierst formedsecntion of the ybeneh and -depositing the removed material on the rst overburden and depositing the same between said upper portion of the last mentioned spoil pile and the adjacent face of said first mentioned Spoil pile.

RAYMOND S. WEIMER. THOMAS C. MULLINS.

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