TN C3 A3 m LIBRARY UNIVERSITY OF CAUFORJHIA DAVIS CAIvlKORNIA STTATTK IVIININO BURKAU J. J. ORA"WPORt>, State Mineralogist. BUivLKTiN No. S. San Francisco, June, 1894. METHODS MINE TIMBEEING. By W. H. storms, Assistant in the Field. SACRAMENTO: STATE OFFICE, : : : A. J. JOHNSTON, SUPT. STATE PRINTING. 1894. LIBRARY UKIVERSITY OF CALIFORNIA DAVIS PREFACE. There is no attempt in this Bulletin to present a complete treatise on methods of mine timbering, but simply to give consideration to those systems ordinarily used in, or adapted to, the gold mines of California. Both in the lode and deep gravel mines of this State, those systems in use have been selected from the best practice and applied in various ways according to circumstances. In collecting the material herewith presented, many mines have been visited and the details of timbering work noted, so that those who have not an opportunity of comparing methods for themselves may be enabled to learn the practice of others. It has been thought proper also to give some detailed account of sys- tems of mine timbering used in other States where extensive ore-bodies are worked, since these are adapted to use here under corresponding conditions. W. H. STORMS, Assistant in the Field, State Mining Bureau. METHODS OF MINE TIMBERING. By W. H. Storms, Assistant in the Field. The excavation of any considerable amount of earth, or rock, beneath the surface of the groun'd usually necessitates that the roof, and not infrequently the sides, of such excavation be sustained artificially to prevent caving. In these later years the size of underground excava- tions is so great, as compared with those formerly made, that the ingenuity and skill of the miner is taxed to the utmost limit. So suc- cessful, however, have miners become in devising novel methods to meet daily exigencies that the obstacles usually encountered in mining, among which are flakey rock roofs; soft, running ground; floods of water, sometimes scalding hot; and, worst of all, swelling ground with heavy pressure from all sides, including the bottom, have mostly been successfully overcome. Before Deidesheimer's " square set " system came into use, the ingen- ious placing of posts, caps, and ^' stulls " constituted the only method of timbering, the multitude of conditions met in the mines making the combinations almost endless. Where veins occur in firm, solid rock, being perpendicular, or near it, the danger of caving is greatly lessened, and the amount of timber required is reduced to a minimum, but these conditions are exceptional. Veins dip at all angles between perpendicular and horizontal, and vary greatly in width. Moreover, the character of the wall rocks, as well as of the ore itself, is so variable that unexpected problems are encoun- tered daily. The shape of large bodies of ore is a matter of great impor- tance in determining the system of timbering to be employed. Through all this variety and change in form, dip, size, and character of the vein, or deposit, and in the inclosing walls, certain established principles are followed in sustaining the roof and sides, the constant aim being to prevent caving, and to avoid such a catastrophe timbers are placed with a view of holding the rock masses in place, and always in such a manner as to receive the strain directly. Those timbers which reach from wall to wall of an inclined vein (stulls) are not set at a right angle to the pitch of the hanging wall, but at a somewhat higher angle. The reason is obvious, for, if placed at a right angle, should a subsidence of the wall occur, the timber, partaking of this movement, at its upper end, would then have a tendency to fall of its own weight, whereas, if set originally above an angle of 90 degrees with the hanging wall, the subsidence of that wall only serves to wedge and hold the timber support more firmly, when it must bend and break before falling. When properly placed, stull timbers usually give sufiicient warning of their weakness to permit of placing additional timbers and subsequently the removal and replacement of old or weak timbers. To make an understanding of the various practices more comprehen- sive a number of drawings have been introduced in this article. As a matter of course certain exigencies are likely to arise, the character of — 6 — which has not been anticipated, but in all cases the principles applied remain the same, and it is thought that the conditions most likely to occur have been treated fully enough to meet the demands of metallifer- ous mining generally. KINDS OF TIMBER USED. In some instances solid masonry is built to sustain certain portions of mines, and in late years iron has been introduced as a substitute for timber, but in American mines timber is most commonly employed. Ordinarily the location of the mine determines the kind of timber. Pine of various kinds is more extensively used than any other. Sugar pine and spruce are preferred when obtainable, but yellow pine is by far the most common. Oak is gladly taken when good sticks of sufficient size can be found. There are oak timbers in mines in Mariposa County, apparently sound, that have been in place for twenty years. They cer- tainly outlast any other timber. Cottonwood and redwood are some- times used when no other is obtainable, but are not at all desirable. In the desert in this State, in parts of Arizona and Nevada, miners take any timber they can get, even resorting to the yucca, which answers quite well for a time in that dry climate, when the pressure is not too great. At Silver Reef, in San Bernardino County, green yuccas were used in timbering a drift. They still stand in fair condition, having been in place five years. The Superintendent of the Gover Mine, Amador County, California, has commenced some experiments with spruce and sugar pine, placing them side by side in the same set in the lower levels of his mine, to test their durability. Fig. A. TUNNELS AND DRIFTS. The methods employed to sustain the roof and sides of tunnels and •drifts are numerous, the existing conditions determining the method. Often the rock is sufficiently firm to stand without timber, but at times the conditions are annoying and dangerous. Where the pressure is entirely overhead an upright post is set on either side of the tunnel, usually spread somewhat at the bottom, but otherwise always at right angles to the roof. (Drifts are frequently run on an incline, particularly in blanket veins, and also in fissures having a low angle of dip.) (See Figs. 2 and 4.) On these posts are placed a cross-piece called a cap. "When it may occur that the floor of a tunnel, drift, or cross-cut does not afford a firm foundation for the posts, as in soft, wet fissures, when not in ore, or as is often the case at the entrance to a mine, a cross-piece I I I I A - i « I tt I I I — r ENTRANCE TO TUNNCL, CALAVERA* COWSOLIOATTO MINE, CARBON HILL, CALAVERAS CO^ CAL- or sill is first laid and the posts set upon it. A second cross-piece (the cap) is then inserted at the top, the ends resting upon the posts, the cap being employed in all cases whether the sill is necessary or not. In working ground that is fairly firm, particularly in the drift gravel mines of California, a system of posts and "breasting caps" is used. This consists of a piece of timber, hewn or split, 2^ feet long, 1 foot wide, and 3 or 4 inches in thickness (the cap), which is placed against the roof, and a post of the necessary length is set beneath it, being driven into a perpendicular position by blows of a heavy hammer or maul. It is a cheap and secure method of timbering small drifts, and is often employed in large ones, the breast extending entirely across the channel. Lagging placed at right angles to the cap may be driven in above it when necessary. — 8 — K^^i '[\ 11' I?' s P 9 — Very often pressure is exerted from the sides as well as from the top of a drift. In such cases the timbers are framed with a view to binding them more firmly together when in place. (Fig. 8.) Figs. 1, 2, 3, and 4 show several styles of framing timbers for drifts. Of these Fig. 4 is undoubtedly the best. Better than any of these is the beveled notch, which greatly reduces the liability of the timbers splitting. It has come quite extensively into use of late years. When properly framed and set there is little danger of slipping. Still another, and no doubt the best method of all, has lately come into practice. It is that of nailing a 2-inch plank on the under side of the cap. By this device the fullest strength of the timbers is obtained, with no proba- bility of splitting. THE BEVELLED NOTCH Fig. 9 A. • When round timbers are used they should always be stripped of the bark or they will speedily decay. The manner of framing timbers is the same, whether they be round, hewn, or sawed. — 10 — Figures 5 and 6 show a method of placing posts and caps. It is seldom seen now. There is nothing about it to recommend it. Oak is the only timber that may be safely employed in this manner, pine being too soft and quite certain to split. Where one side of a drift only and the roof need support, the post and cap (Fig. 7) is sometimes employed, One end of the cap rests upon the post, the other on a shelf, or niche, cut in the opposite wall. USa ft. LEVCl AMADOR Co, LAGGING. When the roof or side of a tunnel is loose and shows any tendency to cave, sprawl off, or run, lagging must be employed. Lagging is the name given to strips of wood 4 to 6 feet long, 6 to 8 inches wide, and 2 to 2i inches thick. They are usually split from pine logs, but sometimes 2-inch plank 6 inches in width is substituted. In large shafts in heavy ground 3-inch plank is sometimes employed. The methods of driving lagging are shown in Figs. 10 and 12. The pieces of lagging are inserted over the top of the cap, the ends pointed upward a few degrees. They are driven forward as the work of excavation progresses, when there is danger of caving. Not infrequently ground will stand for many hours and sometimes for months before caving, but it is cheaper to timber very soon after the excavation has been made, in order to keep the ground in normal condition, giving it no chance. The two systems shown in Figs. 10 and 12, while the same in principle, differ materially in detail. In Fig. 10 the lagging is inserted between two caps which are separated by wedge-shaped blocks, one of which is placed in the center and one at either end. (See between A and C, Fig. 11.) The lagging is driven forward as explained. If the ground is very heavy a '* false set" (Fig. 12) is set up and the ends of the lagging rest upon it. The excavation progressing and the lagging being driven well forward, the next set is put in position and the lagging driven '' home," that is, until the forward ends find a secure resting place on the true set. The false set is then knocked out and the same procedure gone through with the next set. The only difference between Fig. 10 and Fig. 12 is that in the former there are two caps, as explained above, while in Fig. 12 the lagging is — 11 — — 12 — inserted beneath the forward ends of the next set back. In each case the lagging is kept pointed slightly upward by the insertion of a block of wood shown at B, Fig. 12. When the forward ends of the lagging rest on the false set this block may be allowed to drop out. The system shown in Fig. 10 can be employed much more advantageously and work progress more rapidly in very heavy ground, than when that shown in Fig. 12 is used, which does very well in lighter ground. Where the ground is very bad the lagging must be kept driven as far forward as possible. By observing care in this matter serious runs are sometimes prevented. Sills are only employed when the bottom of the tunnel does not afford a firm foundation for the posts. For lagging, spruce, yellow pine, and tamarack are much used, but the sugar pine of California has no superior for toughness and durability. Lagging should not be too strong, for in the event of extreme weight it should bend and give notice of impending danger. The miner may then relieve the pressure by cutting away a portion and reinforcing the timbers, thus saving the more expensive framed timbers and perhaps preventing a serious cave. Caps and posts are all sizes from 4x4 or 4x6 inches up to 24x30 inches, according to the size of the ex- cavation and the character of the ground. Caps should be free from knots and checks as far as possible. Less care is necessary in the selec- tion of posts, though all timbers should be of good, sound wood. Sills extend somewhat beyond the posts which POST AND SILL JOINT ^^^^ ^^^^ ^^^^^^ A shallow notch is usually cut in the sill to admit the post, the bottom of which is cut at right angles to its sides. (See the ac- companying figure.) The greater care taken in framing and setting up mine timbers the less Fig. 13 A. danger there will be of collapse in the future. The tools necessary to secure this exactness are a plumb-bob and a steel square. A spirit-level is also very useful. TRACK-LAYING. To construct a track, cross-ties, made of 3x4 scantling, are often laid on the floor of the tunnel or drift, and to these are spiked "T" rails. When flat iron is preferred a durable track for permanent use is made by setting long 2x4 scantling in slots sawed in the cross-ties, the long strips being secured by driving in wedges at the side. The details of track construction are shown in Figs. A, Al, A2, A8, and A4, which are on the same plate as Figs. 1 to 9. Upon the scantling-stringers may be spiked the flat iron, or if desired, " T '' rail. The scantling should not be spiked to the cross-ties, as nails are quickly corroded by the mineral vapors and waters of mines. — 13 DRAINAGE. I Provision for drainage should always be made at the very commence- ment of opening a mine, for, though the tunnel may be dry at its mouth, when it has been driven a long way into the mountain more or less water is nearly always encountered. A drain or trench should always be cut in the center or at the sides of every tunnel or drift. Illy drained work- ings cause the timbers to rot quickly, and also endanger the health of the miners. Neglect to provide drainage very often results in the neces- sity of retimbering, which expense might otherwise have been avoided for a long time. Prospectors, in their haste to advance work as speedily and as cheaply as possible, frequently fail to timber properly and to provide for drainage, with disastrous results in the future. Many months of laborious toil are too often lost in this way, to say nothing of the loss of life and limb by the unfortunate miner caught in a cave which might have been easily avoided. SWELLING GROUND. One of the greatest difficulties with which miners have to contend is the swelling of the rock masses into which their excavations have pene- trated. Often the force or pressure against timbers caused by the swell- ing of the ground is irresistible. It is a common feature of many of the Mother Lode mines in California, particularly in Tuolumne, Calaveras, and Amador Counties. Swelling bedrock is quite common in the gravel drift mines of California. All Comstock miners know what swelling ground is. It is one of the most serious obstacles with which they have to contend. In a general way it may be said that the only recourse is to timber in the most substantial manner, and then, by frequently, or as often as necessary, cutting out a portion of the heavy ground and relieving the pressure the timbers may be kept in place and the excavation kept open. Fig. 14 represents a cross-section of a tunnel where this trouble in its worst form was encountered. By setting timbers in the manner shown in the cut, placing the sets close together, and relieving the ground by the removal of the encroaching portion from time to time, the trouble is reduced to a minimum. In the Hardenburg Mine, Amador County, swelling ground has caused a great deal of trouble lately. The 900-foot level is run in a zone of crushed foliated black slate, which, on the foot- wall side of the drift, when first broken, appears firm and solid, but in a few days it commences to spawl off and to noticeably encroach upon the drift. It continues to swell, displacing timbers or breaking them, and causing no end of trouble. Now such places are timbered with 18 and 20-inch round timber and somewhat loosely lagged. But few days pass before it is necessary to take out lagging and cut away the swelled ground. In running the main tunnel of the Hidden Treasure Mine at Forest Hill, in Placer County, swelling bedrock was encountered. Mr. Ross E. Browne, E.M., in his article, " The ancient river beds of the Forest Hill Divide" {vide X report, State Mineralogist of California), says of this occurrence: " The pressure of the gravel is not great, but the swelling bedrock has been a source of trouble, driving the legs of the timber-set inward and — 14 — crushing the cap. After many unsuccessful attempts to overcome this difficulty, the legs were given an increasingly greater bottom spread, until finally it was found that they remained stationary. The swelling bedrock is removed from time to time and the track adjusted. The accompanying cut shows the form of tunnel timber-set now used in bad swelling ground. Sets are first put in 4 feet apart, and in the course of a few months center-sets are placed between these. Timber-sets on this plan have now been in place three years (1879), and are still in good condition. In 8,500 feet length of tunnel there are about 4,000 sets of timbers. Two men are kept constantly employed in easing and repairing the sets and adjusting the track." Fig. 14. ^ ^ LOOSE '^ORAVEl.y 3' 6" €::>■ C3- .o/ O 'I J SWetUNG 0£D'/?OC/C^f 1^ //ilfl / . / Some of the drift mines on Sugar Loaf Mountain, near Nevada City, Cal., that were worked twenty-five years ago, were timbered in a very peculiar and unusual manner, owing to the swelling of the bedrock. Massive timbers had been placed time and again, only to be forced out of place, or broken. At last the method here described was introduced and found to answer every requirement most admirably. It was subse- quently tried in some of the other mines of the neighborhood with equally satisfactory results. Once firmly placed, the timbers were never | again renewed, standing until the mine was worked out. The plan adopted was as follows: A drift of the usual form was run and heavily timbered, being well lagged overhead. The sets were placed 5 feet from center to center. As the work of excavating thei drift proceeded, a triangular section was cut out of each side of the drift | between the posts of the two adjoining sets. These two posts formed the base of a triangle, the apex being directly opposite the center of the base. At the apex a post was set, the center of which was 3 feet from the center line of the posts forming the base. Caps were placed reaching from the post at the apex to each of those of the base, and lagging driven in diagonally from the drift. The two sides of the triangular section opposite the base were lagged, a considerable space being left METHOD OF T/MBrRlNa SWFLLIMG GROUND IN THE DRITT MINES Of •SUQAR LOAF MOUiNTAIN, NEAR NEVAQA CITY, CAL Ft?'- '4-. A between the lagging to atibrd an opportunity for the soft swelling ground to force its way through the open spaces, when it is removed. These triangular spaces were continuous; that is, were cut opposite each set of the main drift. The method involved considerable extra expense in mining and timbering, but it was so infinitely superior to any plan pre- viously tried that it was looked upon as a success mechanically and financially. The accompanying sketch will make plain the details of this peculiar method which since its use in the mines on Sugar Loaf Mountain, seems to have been lost sight of. Drifts sometimes require but a few posts to support particular rock masses that threaten to fall. Where a post alone affords insufficient support, a heavy piece of plank (plate) is inserted between the top of the post and the roof. RUNNING GROUND. Tunnels and shafts at times must pass through soft, running ground. Zones of rock of this description are often found lying between walls of firmer rock. The occurrence is not infrequent on the Mother Lode of California when the fissure is barren of quartz and filled with a mass of soft crushed foliated black slate. It is prominent in the Quaker City, Gwin, Hardenburg, Kennedy, and many other mines on the lode. Such ground is nearly always wet, and the process of sinking or drift- ing in it is attended with expense and danger. In sinking through such ground the miners usually make an effort to push the work and pass through it as quickly as possible. When the ground is very wet and runs easily it is not always the best plan to " crowd " it. In some cases the difficulties are more easily overcome, the expense reduced, and the completion of the task sooner accomplished by going slowly, allowing the ground to assume a more normal condition by cutting out and removing the material falling into or forced into the excavation. When water is troublesome in ground of this character, the better plan is to permit it to drain off. By so doing the ground sometimes becomes firmer, and, as a consequence, is more easily handled, timbers more readily placed in position, and the work carried on more satisfactorily. Another kind of ground difficult to timber is found in some much altered rocks where talc, steatite (soapstone), and serpentine, containing i much water, have to be passed through. The ground often breaks well and sometimes stands well for a time, but it is treacherous and should be promptly and substantially timbered. Rocks of this description are abundant in the great auriferous belt of California, and as miners there well know, are usually fissured in every direction and upon exposure to the atmosphere exhibit a tendency to break up (called blocky ground). I Great angular blocks and " heads " (round bowlders) drop from the roof and sides without warning. The former are often wedge-shaped and slip out from the fissured rocks when the ground had appeared firm and solid. The heads are usually hard in the center, while the outer portion is quite soft, feeling greasy to the touch. In size these masses range from an inch or two in diameter to those which weigh tons. Timber must be placed in ground like this immediately as the work progresses. The sets should not be more than 2^ feet from center to center, instead of the usual distance, 4 to 5 feet, whether it be in shaft or tunnel. Lag- ging, when used, must also be short. When passing through slips or fissures, whether single or in zones, in — 16 — any kind of rock, extraordinary precautions should be taken, as accident is much more likely to occur at such points than in solid, unfissured ground. Rock in the vicinity of veins is nearly always more dangerous than that at a distance from the vein. SHAFTS. Working shafts, as well as tunnels and drifts, should be arranged with a view to securing their permanency. Indeed, in consideration of future possibilities, even greater care should be exercised in the selection of their location and in deciding upon their size, while the manner of timbering is most important. Worldng shafts should be so equipped as to remain open and be in use as long as ore remains in the mine which it will pay to extract. As in all other mine work, the amount of timber required depends largely on the size of the shaft and more particularly on the character of the rock through which it passes. Prospecting shafts are sometimes sunk in good-standing ground to the depth of several hundred feet without other timber than a few stulls, to which ladders are secured. The few timbers thus placed often become insecure through neglect, particularly in regions where there are climatic alternations of wet and dry. When wet, the timbers and the wedges securing them, swell. With the change to dryness they shrink and are likely to drop out. An additional danger results when the rock walls crumble, and men working below are in constant danger from falling rocks and tim- bers. The wedges demand frequent attention, for they must be kept driven well in at all times. On the desert and in mines above timber line, where timber is expensive, miners endeavor to get along with as little as possible and are not very particular as to the kind and quality of that which is used. It would perhaps be a better plan to dispense with timber altogether than to place too much dependence on sticks that are likely to drop out of position unexpectedly. As a matter of fact, the writer has seen shafts in the Mojave Desert mines more than 200 feet in depth without a single stick of timber. The necessities of the case in sparsely timbered regions and on the desert have obliged the miner to resort to many novel plans to protect himself against danger at the least possible expense. He puts in as substantial a frame of timbers as he can obtain, or as he may think he can afford, using a few frail saplings, thin, split lagging, or even brush, to support the sides of his shaft. Fortunately for him, in the desert regions, where scarcity of timber forces upon him this economical '' system " of timbering, the rock, being nearly always dry, stands fairly well, as a rule, and expensive timbering is not necessary. The extremities to which prospectors are often reduced to procure timber in these timberless regions has resulted in the adoption of a method peculiar to such districts. While the result is not particularly pleasing from a workmanlike standpoint, it nevertheless exemplifies most faithfully those principles which are the foundation of the most elabo- rate system of timbering. In these shafts all timbers are stulls, each one being placed to support some particular rock or mass which seemingly threatens to fall. Each stick is independent of the others; there are no superfluous timbers, and no attempt at system or regularity. As a result — 17 — these sticks cross the shaft at many angles. Some are horizontal, but most of them inclined somewhat from that position. It sometimes gives the shaft timbers a spiral appearance as viewed from above. Despite the fact that these timbers are placed so much at variance with recog- nized methods, if placed at the time of making the excavation, or shortly thereafter, and are properly and firmly wedged, they usually render the shaft fairly safe. In that region old redwood railroad ties are very fre- quently used for mine timbers, and answer admirably, even though unsuited for such use from having lain for months in a railroad bed, being split and often cut by the rails. The miners are glad to get them, poor as the timber is, for when once properly placed they have been found to do very well, where the pressure js not too great. Shafts having a single compartment, such as are frequently seen in small mines, are timbered in a simple manner. The timbers consist of two wall and two end plates and four posts to each set. The method shown in Fig. 14 C is quite common and suited to shafts of moderate size (5x7 in the clear), having a single compartment. The four frame timbers are placed in position and tightly wedged, the posts being driven in at the corners. Care must be taken to keep the sets in line. Sets are ordinarily 5 feet apart from center to center. When the ground is heavy, sets may be placed closer than 5 feet. They are often only half that distance from center to center. Lagging, either split or sawed (2-inch plank), is driven in behind the timbers. It is driven one half to three quarters of the way down, when the lower ends of the next set below are inserted between the timber and the wall. Later the lagging of the set above is driven down to its proper place. CRIBBED SHAFT. When the pressure of the ground is very heavy a crib of timbers is built, the timbers being placed one on another with only a notch at the ends to hold them in place. In soft ground it may be necessary to use lagging, even in a cribbed shaft. All open spaces between the walls and the crib or lagging should be filled with broken rock to secure firmness, and to counteract any tendency of the timbers to shift. The manner of framing crib timbers is shown in the cut on page 18. 2c — 18 — Fig. 14 B. REACHERS IN SHAFTS. When sinking can be carried on somewhat in advance of timbering, it is sometimes the custom, in firm ground, to place long timbers, called " reachers," across the shaft, the ends resting in niches cut in the walls. These having been firmly placed, the four timbers of the set are laid upon them and firmly wedged, and from this foundation the sets are built upward to the next set of reachers above, a distance of 25 to 30 feet. Where the shaft is sunk in country rock, or in a large pillar of ore (the latter to be avoided when possible), the reachers are placed alternately in sets at right angles. The manner of framing the ends of shaft timbers where they join at the corners is shown in the cuts of the Requa, Forman, and Alma shafts and the Argonaut incline. Men working in shafts placing timbers usually work suspended on slings secured to timbers above. — 19 — fl — :-]! - ^ JLa^ft^...^^.=..^«^^^fe^ht>/WJ.^^tJ^ ■^Mmmr--^irn^iU"\\ ^^M\mMl -.^^ I :,tK>^a.;.4fc ^^P^#-%J( 3^ W'^^^ir^ Fig. 14 C. IRON DOGS AND BOLTS. In places where the above described methods of building sets of shaft timbers on reachers is not possible, owing to the soft nature of the rock in which the shaft is sunk, or where it is desirable to run cages to the bottom of the mine, it was formerly the custom to suspend the shaft timbers by ropes in a position as near to that desired as possible, and to then maintain them in that position by driving iron dogs into the timbers, the weight being supported by the set next above, which had previously been secured by wedges. In some cases these dogs were never removed. Many of them may be seen in the older California mines. The dogs were made of round or square iron bars 1x1 inch or 1x1^ inches, and having the ends turned at right angles. The points were 3 or 4 inches in length and sharp. The length of the dog was deter- mined by the distance from center to center of the sets. When the rock was sufficiently firm to admit of the timbers being firmly wedged the dogs were knocked out. Iron dogs or bolts are useless as a means of support when the surrounding rock masses have once firmly settled on the timbers. A safer and more convenient device has been introduced in later years, in the form of iron bars having a thread at one end and a ring or hook at the other. These go in pairs, their combined length exceeding by 6 inches the distance from the top of one set to the bottom of the next set beneath. The manner of using these hangers is as follows: A set having been securely wedged in its proper position, the threaded end of the bolt provided with a hook is passed upward through a hole in the plate (bored in all timbers for the purpose), a washer passed over the end of the bolt, and a threaded nut screwed down onto it. A second '' lock- nut " may be used, but is not necessary. A second similar bolt with — 20 — hook is passed through a hole near the opposite end of the same timber, and also secured with washer and nut. The timber to be placed directly below is suspended by ropes in a position approximating that desired and a bolt having a ring at one end is passed downward through this timber, immediately below that in the timber above, and a similar bolt is passed through the opposite end. Washers and nuts are placed on the* ends of these bolts and the rings are caught in the hooks of the bolts above. The nuts may now be turned and the timber drawn to exactly the position required, when the ropes may be removed. All four of the timbers of this set having been placed in position, and being suspended on the hangers, the posts are slipped in, the nuts tightened still further, and the whole firmly wedged, when the next set below may be put in in like manner. The hangers are left a few days or weeks, and in some instances permanently, but, as previously stated, they are useless as a means of support when the weight of the surrounding rock has settled on the timbers. Where, owing to the soft nature of the ground, it is thought desirable to have the hangers remain in place indefinitely, a bar having a thread at one end and simply turned at a right angle at the other, or having a solid hammered head with a washer, may be used, being passed upward through the bottom timber and then through that above, where the adjustment is made by means of a washer and nut; but as these bars are longer than the distance between sets, their removal is impossible, a set below once having been put in place. There is no question as to the superiority of the bolts having rings and hooks for either temporary or permanent use. RETIMBERING SHAFTS. It very frequently occurs that shaft timbers have to be removed and new ones inserted, and also often necessary to reinforce timbers already in place. This work frequently necessitates the suspension of hoisting through the shaft. The Superintendent of the Wildman Mine, at Sutter Creek, Amador County, California, having occasion to retimber the shaft between the 500 and 600 levels of the mine, constructed a chute 1 foot square of 2-inch plank in one corner of a compartment of the shaft reaching between these levels. It was built in short sections, each the length of a set of timbers. The work of retimbering was commenced above and carried downward, all of the refuse rock, timber, etc., being dumped into the chute. This material was taken up on the 600 level, dumped into a skip from time to time, and sent to the surface; by this means the work was quickly and safely carried on, sections of the chute being removed to keep pace with the work. By means of this device there was very little delay in operating the skips, and hoisting of ore was continued almost without interruption during the retimbering of that portion of the shaft. SHAFTS HAVING TWO OR MORE COMPARTMENTS. Lafge shafts are separated into two or more compartments by placing timbers called " dividers " at intermediate points between the end plates. They reach from the wall plate on one side to that on the opposite side of the shaft. These dividers are framed with a short beveled tenon, broader at the top than at the bottom. (See cuts of Forman, Requa, — 21 — lER or rRAMIN & DIVIDER and Alma shafts.) These tenons fit exactly into mortices or notches in the wall plates. At each of the four corners of the shaft and between the wall plates, opposite each divider, is placed a post, which is set in a shallow notch or seat cut in the plates. In size the posts may equal that of the plates, or if desired they may be of smaller dimensions. The dividers are made the same depth as the wall plates, but are usually narrower across the upper face. The dividers separating shafts into two or more compartments may be made most secure by permitting the upper portion of the beveled tenon to extend into the wall plate 2 or 3 inches, the bottom portion being let in but 1 inch. The post setting directly on the divider holds it much more firmly, and the danger of having the dividers knocked out by shots fired directly blow is greatly decreased, if not obviated entirely. It not infrequently occurs when dividers are framed so as to set but 1 inch into the wall plates a heavy blast will tear them out altogether, incurring expense of timber and time, which may be avoided in the manner stated above. Drawings of two Comstock shafts illustrate the manner of framing and placing timbers in them. One of these is called an " L" shaft, and was sunk by the Overman and Caledonia companies jointly. It is known as the Forman shaft. The other is the Requa shaft, sunk by the Chollar, Norcross, and Savage companies. It is a large rectangular shaft having four compartments, and is a splendid example of its kind. An illustration of the new Alma shaft at Jackson, Amador County, California, shows a different style of framing. In fact, the manner of framing and joining the timbers of these three shafts is totally different. In size, shaft timbers range from 8x8 to 20x24, and even larger dimen- sions are sometimes employed in very heavy ground, particularly in inclined shafts. The wall plates are usually broader on one side than on the other, and are placed in position with broad side up. End plates are usually the square of the smaller dimension of the wall plate. Pumping and manway compartments do not require lining, but hoist- ing compartments, particularly where cages are run, should be lined throughout to prevent accident to men who sometimes overcrowd a cage. EDGE OF WALL PLATE W. FACING INSIDE OF SHAFT 'ORMAN SHAFT OF THE OVERMAN ANO CALEDONIA 3r SILVER MIMNG COMPANIES COMSTOCK LODE VIRGINIA CITY NEVADA SCALE A INCH TO 1 FOOT. Fig. 10. EDGE OF END PLATE INStOEOF SHAFT Fig. 15 A. — 24 — There appears to be less danger of this where buckets or skips are used. Every shaft in a mine should be provided with ladder ways as a means of exit in case of accident to shaft or hoisting machinery. Sinking large shafts in swelling ground, in loose, watery, running ground, or in quicksand greatly multiplies the difficulties and dangers of the miner. There are instances where shafts have been abandoned owing to insurmountable obstacles which a combination of engineering skill, capital, and labor were unable to overcome, but such instances are of rare occurrence. Few shafts present greater difficulties than were encountered at Leadville, Colorado; in the Lake Superior region; in some coal mines; on the Comstock, and in Calaveras and Amador Counties, California (the latter are mostly inclines), and some of the shafts in the regions mentioned are to-day splendid and substantial monuments to American engineering and to the enterprise of the companies owning them. The shaft of El Capitan Mine, Nevada County, now the property of the Providence Mining Company, was sunk through decomposed slate and altered dyke rock under the most trying and dangerous conditions. After several failures, the shaft was carried down to solid ground under the direction of Francis Burns, who worked slowly and carefully, giving the soft running ground time to drain. The water being pumped from the sump, after standing for a time, appeared to drain the ground, and it was found that by this means progress was much more rapid than when the work was hurried. " Breast-boards " were carried down until the dangerous places had been safely passed. It is sometimes necessary in sinking large shafts to carry them down in sections by driving lagging or planks down in advance of the exca- vation. This is known as '' fore-poling.'^ The section is started at one end of the main opening and advanced several feet, the lagging being well braced. Considerable water will drain into this depression, making the removal of the ground from the remainder of the shaft much easier. By carrying one side of the shaft somewhat in advance of the remainder, in this manner, loose, wet ground can be worked more quickly and at less expense than when it is attempted to carry down the entire shaft at once. SPLICED WALL PLATES. In cases where sinking cannot be carried on in shafts much in advance of timbering the wall plates may be spliced. The better plan is to extend the plate from one side entirely across the two hoisting compartments, that portion in the pumping compartment being in a single piece, and joining the longer piece directly opposite the divider next to the pumping compartment. These joining ends of the two sections of wall plate should be framed so as to permit the divider to lap over their entire width, the upper half of the plate sections being removed so as to admit the upper half of the divider, as shown in the illustration. The post standing immediately upon the divider, and covering the entire splice and overlap, prevents the divider from being blown out by heavy shots below. This plan also greatly facilitates the placing of shaft timbers, as there is not that great loss of time in getting the wall plates in position, which results when long timbers are handled. There is always difficulty and loss of time where the shaft cannot be carried 25 — ' -jj^^^^^ATp^-*2 ^=-\ ' T;r q^., ., "~n — . _-^ i WAtJF-; PjyrrrL- :-.^_____=^ rn/NMiNC POR SPLICED WALL Plate: and ovcrlapp.inc divider. FOR SHArrs. down in advance of the timbers far enough to give room to turn the long wall plates. This system also permits of the renewal of wall plates and other shaft timbers by the ease with which they may all be removed. BREAST BOARDS. When the ground has a tendency to thrust itself up in the bottom of the shaft, the plan of planking and bracing the ground is sometimes resorted to. (The same principle is applied in drifting, when the method is referred to as "carrying breast boards.") In this method lagging is driven down in advance of the sinking, being supported in position above by a frame of timbers, either permanent or temporary. Planks are laid on the bottom of the shaft, being secured by upright posts, which abut against strong stulls or cross-pieces firmly wedged above. When the pressure from below begins to exert itself, a board near the center is removed and the soft, pulpy mass allowed to force itself upward. The material is removed until the ground is eased somewhat, when a second board is removed, the first being replaced somewhat lower than before, and again secured; the material coming up through this new space is removed as in the first instance, and in this manner work proceeds entirely across the excavation. The process is slow and requires consid- erable timber, but it is a plan which may prove successful when all others fail. The method of driving lagging in shafts is similar to that explained under the head of drifts. (See Fig. 12.) — 26 — In some instances iron caissons have been sunk outside or inside the timbers to enable miners to pass through very loose, watery ground and quicksand. Where this is not absolutely necessary, wet places have been passed through by making a clay lining between two layers of close planking. It may be from 2 inches to 1 foot in thickness, according to the requirements. It has been successfully employed in passing through quicksand and watery, loose ground. In very bad wet ground the idea is to form a caisson-like structure with lagging, the interior being sustained, as explained above, by massive timbers, so placed as to resist the pressure of the surrounding rock mass. The exigencies of each particular case must determine the course to be pursued. The expedient of freezing soft, wet, running ground, quicksand, etc., is now much resorted to with great success. It is a patented process, but finds general use where applicable. Circular shafts are seldom sunk in America now, though very common in the early days in California. There are circular shafts all through the old river-bed region, which pass down through the tufa capping with- out a single stick of timber from top to bottom. Many of them are over 250 feet in depth, and, notwithstanding they were made more than forty years ago, are still in good condition and likely to remain so for a cent- ury. The rectangular shaft is the most common form in this country. " L" shafts do not find much favor and have nothing to recommend them. The size and number of compartments of a shaft must be determined by the amount of hoisting expected to be done through it. STATIONS. The accompanying sketch shows the manner of placing timbers at a station in an inclined shaft. The method in perpendicular shafts is essentially the same. The chain blocks are for the purpose of landing timbers sent down in the skip. JOINING OF GUIDES IN SHAFTS. Guides in shafts where cages are used or where skips run on guides should be so joined that there is no likelihood of their warping and pro- jecting beyond their plane, and jam the cage, or skip, which is a most dan- gerous thing and a great strain on the cable. The overlapping of the ends has been for years a common practice; the two ends being secured at the overlap by a single lag bolt. An improvement has been made on this plan, with a view to greater safety, by joining the adjacent ends of sec- tions with a simple tongue and groove, like ordinary flooring or wains- coting. , The ends each have a lag bolt, which makes them doubly secure. The drawings show both styles for framing guides. Spikes or nails should never be used, as it requires much more time to remove a section when repairs are necessary. Guides are most easily repaired by laying a secure platform in the compartment at the point requiring repairs, the men working upward from set to set. Should the whole shaft, or any large portion of it, require new guides at any time, the platform should be put in as described. The hood is removed from the cage and a bottom of loose boards laid on the floor. The workmen at the platform unscrew the lag bolts and take out the old, worn guides. The cage being lowered I 1 CrUlOE 'M li I 'ii(,'///'/ ^ r,X,X I I I Jl i 1 ' . ■ I •-qrq^:yA\;^^.' -^'>^ v/ is. QU»DE MANNER OF FRAMlfx/G AND SECURING GU/DETS. p FJQ fS.D. — 27 — 1 to the proper point, the old guides are passejd up through a hole made in the bottom of the cage, and the new guides passed down in the same manner and put in place. In this way the guides may be removed for a thousand feet in a single day by a gang of good workmen. Other repairs in the shaft may be made in a somewhat similar manner. INCLINES. Inclined shafts are somewhat different from those that are vertical, and are probably quite as numerous. In California the number of inclined shafts far exceeds those that are vertical, being, as a rule, sunk on the vein, which, in a majority of cases, dips at some angle from the horizontal. In a general way what has been said of vertical shafts applies to those that are inclined. There is considerable dilference, how- ever, in the manner of framing timbers for an incline, and while timbers framed for an incline will do, perhaps, equally well in a vertical shaft, those framed as already shown in the illustration are not preferred in an incline. An illustration of the method of framing timbers for the new Argonaut shaft at Jackson, Amador County, California, which is expected to reach a depth of 2,000 feet on the incline (63°), is given. It resembles somewhat the new Alma shaft, also at Jackson, though the first 400 or 600 feet of the Alma will be vertical. STOPES AND CHAMBERS. The cuttings in mines which require the most care and greatest skill in placing timbers to support overhanging ground are " stopes " and large " chambers." The method adopted must always depend upon the size of the excavation, character of the ore and of the walls, the pitch of the vein or ore shoot, and also on the expense of the timber. TAKING ANGLES AND DISTANCE BETWEEN WALLS. A very convenient instrument for measuring the distance between the hanging and foot walls of the vein, and to determine their respective angles of inclination, for the purpose of cutting stulls with proper length and bevels, is shown in the accompanying illustration. It consists of two flat planed boards having slots, as shown in the drawing, and fitted with thumb screws, s s s. At either end is a movable arm, A A. These are placed against the walls and the screws tightened, the distance between walls being ascertained by lengthening or shortening the instru- ment by means of the sliding arrangement. Having carefully taken the required measurements, there can be no mistake as to the kind of stull required. TIMBERING A SOFT HANGING WALL. In some portions of the New Almaden Quicksilver Mine, where the width of ore stoped is about 10 feet, an unusual method of timbering has been adopted. The foot wall is usually hard and solid, while the " alta," as the hanging wall is called, is almost always soft and shelly, and is considered dangerous ground. Heavy stulls are placed at regu- lar distances (about 8 feet), and are set in line one above another. Im- — 28 »^>^^;;''" / ^ METH 00 or TIM^eRING SMALL STORES IN THC NEW ALMADEN QUICKSILVER MINC. ¥-MMu^^- '^n$'Mij:n^r. y. mediately above the stull a second shorter timber is laid, which rests upon the foot wall and reaches within about a foot of the hanging wall. A plate or cap is inserted over the upper end of this auxiliary stull, which reaches horizontally across to the next stulls, which are similarly placed. Heavy lagging is driven upward along the hanging wall, the lower ends of which rest upon the cap and the upper ends upon the lower ends of the lagging of the next set above. The two stulls are bolted together near the top and bottom for additional strength and security. Redwood has been used quite extensively in timbering this mine, and it is claimed it has given satisfaction. The accompanying sketch will show this method of timbering. The large stopes of the New Almaden are timbered in square sets. FLAT OR BLANKET VEINS. In veins which lie quite flat, the thickness of the vein and the system of mining must determine the character of timbering to a great extent, as well as the character of the walls. Where the vein is thin (a foot or — 29 — two) very little timber is required, the waste rock filling the entire spac8 behind the miner. Where the mineral deposit is thicker and timber is necessary various methods are pursued. Some ground stands well by simply leaving pillars of mineral. In other cases a series of upright posts and breasting caps will sustain the roof, the posts being placed in rows directly back of the workmen and as close to the face as the neces- sity demands. The foot of the post rests either directly on the rock floor or upon a block of wood or piece of heavy plank. The posts are forced into position by driving them up with heavy hammers. Care must be taken that these posts are so placed as to receive the weight of the roof directly and not at an angle. These timbers are set in lines standing in two, three, or four rows back from the face, the waste being piled behind as the work advances. In this manner, by exercising care, many sticks can be recovered before the weight settles so heavily on the refuse rock as to render it impossible to remove the timbers. Some fiat veins make little or no waste. It is then necessary to follow the " pillar and stall " system of extraction, considerable blocks being left to sustain the roof. Posts and caps are used in this system also. Frequently the caps reach in a continuous line from post to post, joining the next set, the ends of two caps resting on a single post, the combined sets being a hundred feet or more in width. Large timbers thus placed will support great weight, but if small rocks fall from the roof lagging must also be employed. This system is much in use in California gravel drift mines. When a vein lying nearly, or quite horizontal, and making no waste, is to be mined, a drift should be run along the lowest portion of the deposit, this point having been reached by incline or shaft. The work advances toward the surface, good sized pillars being left to sustain the roof. If timber is necessary, it is put in place in the manner required. The work having advanced sufficiently far toward the surface, the pillars may now be cut out at the back end, while the work progresses as before. As the pillars are removed more timber must be put in, or waste from the surface must be piled in cribs of timber built in the workings already made. Usually some timber can be recovered in this way and the caving of the roof after the complete removal of the ore, or mineral, does no harm. The main gangways should be substantially timbered, if necessary, as it is desirable to keep it open to the lowest working level at all times. The ''long wall" system of extracting ore is usually carried from the surface inward, a main gangway having been first driven ahead to a con- nection with a ventilating shaft, when possible. All the ore is removed at once, the waste being thrown back of the miners, who carry the breast forward with the center considerably in advance of the sides, the excava- tion being in form somewhat like the letter "A," with the apex forward. The waste is thrown into the center to support the roof, while the side passages permit of a free circulation of air all along the face. STEEPLY INCLINED VEINS. In vertical or steeply inclined veins, the principles governing the methods of timbering are essentially the same as those above explained, though the application is different. In such workings the post of the flat vein becomes a " stull." — 30 — OVERHAND STOPING. When a working drift is driven along a vein in ore and it is the intention to "stope" out the ore, the character of the walls and the width of the vein or deposit must determine the method of timbering. If the walls be hard and firm, and the vein not more than 10 or 12 feet wide, posts are not absolutely necessary. Stulls of the proper length are placed with the lower end resting on the foot wall, or in a niche cut for the purpose, the upper end being placed against the hanging wall and driven downward until it stands at a few degrees above a right angle with that wall. (See Figs. 16 and 18.) When the foot wall has a greater inclination than the hanging wall, a support resting on the floor of the drift must be placed under the lower end of the stull. Should the foot wall have a less inclination than the hanging wall, the foot of the stull may be secured by driving in stout wedges from the upper side. Where the foot wall is sufhciently hard and firm, a niche in either case; will answer as a secure rest for the: lower end of the stull. Where the vein is more than 10 feet in width and additional support appears nec- essary, resort may be had to the plans shown in Figs. 19 to 29. In case either wall, or both of them, is too soft to safely sustain stulls under the pressure of ore or waste to be piled upon them, a plate (usually a 2 or 3-inch plank) is inserted behind the stull on either wall or both, as may be necessary. (Figs. 17 and 25.) When the walls are very soft, and even with the use of plates, render timbering insecure, the stulls may be placed at right angles to the walls, the ends resting upon posts. Mining upward, the posts of each floor rest upon the stulls under foot and immediately above the posts on the floor below. In this manner a stope in soft walls may be carried to any desired height. (Fig. 24 A.) In such instances it is necessary to place longitudinal braces or "ties" reaching from cap to cap at — 31 — — 32 — right angles to the stull. These ties may be of smaller dimensions than| the stull and post timbers. The method shown in Fig. 19 may be employed where the vein exceeds 8 or 10 feet and when sticks sufficiently large to support the weight of ore or waste cannot be obtained. Fig. 20 may be employed in the same manner with a greater width of vein. Both of these instances presume considerable waste to result from mining, which will, to a great extent, fill the excavation. Fig. 23 afibrds a firm support to a stull in a wide place in the vein, and Fig. 22 the same in a still broader vertical vein. Fig. 25 shows how, in a vein of low dip and considerable width, a stull may be firmly supported to retain waste or ore coming down from the stope above.] In soft vein and wall rock a substan- tial method of placing sill, stull, and post is shown in Fig. 26. Stulls are placed at distances rang- ing from 2 1 to 6 feet, as may be required. On them are laid split lagging, forming a floor. As the miner stands on the floor thus im- provised, he breaks down the ore, separating it from the waste, if there be any, and sending the ore into the ''level" or main passageway below, allowing the waste to accumulate on the floor. The waste often occurs; to such an extent that a portion of; it also has to be sent to the surface. When this is the case, very little timber is required in the stopes. When, however, the quantity of waste is small, it is often necessary to build a temporary staging upon which to stand until a sufficient space is cut out above to admit of laying a second tier of stulls to sustain the floor. Floors are 6 to 8 feet apart and sometimes even more. A passageway, called a "mill hole," "chute," or "slide," is left every 30 to 50 feet for the purpose of sending ore to the level below, as the work progresses upward. The distance between these slides is deter- mined by the dip of the vein. They may be a greater distance apart in a steeply inclined vein than in one having a low angle of inclination. Rock will not run freely on a slope having a slope of less than 40 degrees, and more is preferable. In cases where the slope angle is low, it is a good idea to line the slide with plank to facilitate the delivery of the ore to the level beneath. In opening a stope between levels, the best method is to make a raise from level to level, building a loading chute at the bottom. Then at a short distance to one side (15 or 20 feet) a second raise is carried up about 1 5 feet and connected with the winze. From this point the stope is opened, the excavation being carried upward and the ore being passed down through the winze to the loading chute. As the floors are carried up a crib is built around the winze, keeping it constantly — 33 — open. This plan secures economy of labor and affords the best obtain- able ventilation. The stoping of ore continues to within a few feet of the level above, and is then discontinued for the time being, this mass of ore and that remaining within a few feet of the floor beneath being left to be taken out the last thing before abandoning this portion of the mine. When ore is very rich it is the custom to blast or pick it down upon canvas or boards, keeping it separate as far as possible from the waste, the ore being sacked in the mine. The methods above described apply to overhand stoping, that is, excavating from a level upward. 3c — 34 — UNDERHAND STOPING Is the term used to indicate an operation the reverse of that just described, being the method by which the miner takes out the floor of his level and continues the excavation downward in a series of steps 7 or 8 feet in height. In this method it is best for the economical handling of the ore, for ventilation, and for drainage, to have established a con- nection by winze with the level next below, or it will be necessary to hoist all the ore and water from the stope to the level above. The waste, if there be any, is thrown on platforms or floors between the face of each floor and the winze, slide,* or chute. This method is not advisable except in narrow, rich veins. Underhand stoping is not commonly followed, but may be recom- mended in working small veins of very rich ore. It requires usually more timber than overhand stoping and the timber cannot be recov- ered as in the latter method. CONNECTING LEVELS. When stoping by the overhand system, on approaching the floor of the level above it is necessary, where posts and caps have been used, whether sills were used or not, to take some precaution to prevent the falling out of these timbers and the consequent caving of the filled stope above, should there be any. The plan adopted in the Bi-metallic Mine, near Phillipsburgh, Montana, is the most expeditious and the safest. When ready to break through the floor under any particular sill or set of timbers, a stout piece of timber (sprag) is placed between the posts a few inches above the floor (at A) and wedged in hard with shingle wedges. A heavy stick of timber (B B) long enough to reach across three sets (kept on each level of the mine for this purpose) is lifted to the roof of the gangway, midway between the posts, one end being under the cap which forms a portion of the set of which the sill to be removed is also a part. This timber acts like a lever having a fulcrum at C, in the form of a post which supports it, the foot resting in the center of the drift on the sill D. Wedges are driven in at E, making it firm and rigid. Wedges are then driven in at F and at C, and the rock beneath may then safely be extracted, the timber-set G G being held in position, the superincumbent weight being transferred to the points D and E. As a matter of course, the sill of the set G G will drop out when the rock upon which it has rested has been removed. The remainder of the set may then be connected with the timbers of the sets beneath in any manner the case requires. STRENGTH OF TIMBERS. In placing stulls to sustain the weight of waste, or to store ore already broken, the size and number of timbers to be employed must be deter- mined by the width of the vein and the height to which the waste or ore is likely to accumulate. It is considered better to increase the number rather than the size of stulls. With good walls, stulls 7 feet in lengtli, having a thickness of 1 2 inches, placed 30 inches apart, are calculated ♦The term "ore slide " appears preferable to the word "cliute,"as conflict is thereby ayoided with the word "ore shoot^' as applied to a body of ore. \ RT^ — Rf. ^M OEVICC USED I N CONNECTIN Q LCVCLff. ^<\-^ ./,' STO P E ^ .' . ' ■' .'. ■ . ' FFR CAP 5PRAG SI LL CAR SECTION AT «•& S J L L SECTION AT H — 35 — — 36 — to sustain 60 feet of waste or broken ore in a vein standing at a high angle. After waste has remained in place for some time it settles, and in some instances becomes so firm as to retain its solidity after the stulls have fallen out or have been removed. This need not be expected in wide veins. When it becomes necessary to quickly catch up settling stull timbers or caps, a stout post, which will just slip under the sinking timber, is placed in position and four stout wooden wedges, having the inclined planes sloping alternately in different directions, are driven in between the post and stull. This plan will recover the subsidence, if not too great, and permit of reinforcing the timbers without losing ground. THE SAODLC WEDGES, IN USE AX THC BUCHANAN MINC, roOLUMNE COUHTY, CAL. SADDLE BACKS. A peculiar method of timbering, known as the " saddle, back," is in vogue in some portions of Colorado. It appears to do well in the lead- silver mines having good limestone roofs and walls. It may be considered a modification of the " square-set." It requires less timber and is far less substantial. It will not do in heavy ground. The details differ with the various conditions encountered, but the. principles are those obtain- ing in all other timber systems — the application of resistance to pressure. The drawings illustrate one method of setting up the saddle back. LOADING CHUTES. The accompanying sketch shows a design for a loading chute or slide, though they are not always made as elaborate as represented in the drawing. The inclination of the bottom should exceed 30 degrees, ores that are soft and wet requiring the slide to have a greater pitch than those that are dry. Between the two upright posts which reach from the floor of the drift to the roof or to stout stulls overhead, two short — 37 — A LOADING CHUTE Fig. 31. uprights are placed, and on top of them, reaching from one to the other, is laid a 4x6 scantling. The gate, furnished with ratchet and wheel and pinion, may be dispensed with, loose boards being substituted, which may be pried up, when desired, with a bar. It is well always to build loading chutes in a substantial manner, so that rebuilding may not be — 38 — necessary. It is a wise plan to provide false sides and bottoms, which may be quickly renewed. The posts supporting loading chutes are not alwaj's placed perpen- dicular. In steeply inclined veins it is sometimes desirable to set them inclining forward. In vertical veins they are built across the vein. In square sets, ore bins are constructed within the sets and the chutes are attached to the caps or ties, being arranged at convenient distances from each other. In some mines, as in the Golden Gate, at Sonora, in Tuolumne County, large storage bins are constructed below the floors of the levels at the hoisting shaft, provided with a loading chute. The skip is stopped at the proper point and loaded. In this manner the necessity of waiting for cars, or loaded cars and men waiting for the skip, is obviated. In this mine loading chutes are provided on the several levels from the stopes over- head, as a matter of course being constructed in the ordinary manner. GREAT CHAMBERS AND SQUARE SETS. The systems of timbering hereinbefore described refer particularly to veins having a width not exceeding 12 feet, though mines have been worked under great difficulties, and where the operations were attended with extreme danger, where the distance between walls was 20 and even 25 feet. An instance may be mentioned in California in the Mount Jefierson Mine, at Groveland, in Tuolumne County, where the vein was 25 feet from wall to wall. A very ingenious system of timbering was introduced in 1854, or thereabouts, consisting of long stulls supported by wall and inside props 7 feet apart. Longitudinal braces, or ties, were also introduced to support the timbers longitudinally, but the support was insufficient, and a most disastrous case resulted. It is a matter of absolute impossibility, however, to recover, by the methods thus far given, all the ore from such great masses of mineral as were found in the Com- stock Lode, where one ore body, the Great Bonanza, measured 340 feet in width at one point, 600 feet in height, and 1,250 feet in length. Stopes in the various mines of the Homestake group, in the Black Hills, South Dakota, range from 40 to 150 feet in width and several hundred feet in length and height. The Caledonia Mine, of this group, measured on the 300-foot level 195 feet horizontally. The Homestake vein at the sur- face, in the open cut, is 360 feet wide, by actual measurement. In California there are many mines of great value that cannot be worked by any system of stulls. The Stonewall Mine, in San Diego County, has 20 feet or more of vein in places. The Alvord Gold Mine, in San Bernardino County, is a very wide vein. The Odessa, Occidental, Oriental, Silver Monument, and Waterloo Mines, of the Calico District, measure 30 to over 100 feet in width. Some of the mines of Bodie have very broad veins. The Josephine Mine, in Mariposa County, has an immense ore shoot 50 feet wide. The Utica-Stickles Mine, at Angels, Calaveras County, is 40 to over 100 feet wide, and the Gover Mine, of Amador, has an ore body 30 to 50 feet wide. The Zeila, at Jackson, is working an immense mass of ore. The Boston Mine, near Mokelumne Hill, is 40 to 60 feet wide, and some of the ore bodies in the larger quick- silver mines are of prodigious size. In addition to these there are many other mines on the gold belt of California where the great width of vein — 39 — ]n'ecliides the extraction of the ore by the use of any system of stulls or oo f— C/O <^ f/o C OD 1331 n n X) 00 — 51 — placing of wall plates and angle braces is the same in each system. The accompanying drawings, showing a horizontal and vertical section of a corner in both the top and side pressure systems, show plainly the details of both methods. BULKHEADS AND CRIBS. It frequently occurs that bulkheads of solid timber, or cribs filled with rock, have to be built to sustain sinking roofs which have already been substantially timbered. Bulkheads are formed by laying massive squared timbers side by side, filling the space between sets. Upon these are laid a second layer at right angles to the first, and so on from floor to roof of the stope. Cribs are constructed by building up timbers in the form of a hollow square or rectangle, the interior space being filled with large broken rock, and also extends from floor to roof. Either of these devices forms a very substantial support to settling ground, though sometimes inefficient. Bulkheads of solid masonry are sometimes built in mine workings to stop a heavy influx of water. They should be constructed with the greatest care and in the most substantial manner possible to prevent future collapse. When it becomes necessary to build a bulkhead of this kind a section should be cut in the floor, sides, and roof of the drift, and the masonry extended into these spaces. Water bulkheads are sometimes built of dry timbers, which, swelling, effectually shut off the influx of water. An instance recently came to the knowledge of the writer in which a large flow of water followed the cutting of a subterranean reservoir by a power drill. As usual in such cases, wooden plugs were inserted and driven in, but to no purpose, the force of the water driving them out. The protection of a bulkhead seemed necessary to prevent the flooding of the mine. An experiment was first tried, which, proving successful, rendered the bulkhead unnecessary. A section of pipe provided with a globe valve was inserted in the hole, the valve remaining open until the pipe was firmly secured by wooden braces and tightly wedged in the rock. The valve was then closed and the flow shut off. Provision then being made to handle the water, the valve was opened partly and the reservoir drained. It seems that this plan might be adopted with ad- vantage where the influx of water interferes with the construction and completion of a water-tight bulkhead, for at times the flow of water is so great that it is almost impossible to construct a bulkhead, owing to the pressure of the water back of it. TIMBERING AT THE UTICA MINE. The largest known. body of ore in California to-day is in the Utica- Stickles Mine, at Angles Camp, Calaveras County. Its extent is, as yet, unknown. The workings have thus far exposed a mass of gold-bearing rock ranging from 40 to more than 100 feet broad, over 400 feet high, and exceeding 1,000 feet in length. Stopes of this size require a very sub- stantial system of timbering, and the square set system, which has been described at length, is exactly suited to its requirements. It is not in use, however, but in its stead another system, which is quite similar, and based on exactly the same principles, still having very important differ- — 52 — ences. A study of the accompanying timber sketch of the Utica Miiu" will suffice to make an understanding of the method plain. The timber used in this mine is exclusively round, peeled pine logs, which are delivered by contract at the surface works. The cost of these logs, I am informed, is 10 cents for each inch of diameter, making ;i 16-foot 18-inch log cost $1 80, and a 24-inch log, $2 40. These timbers are all cut into two lengths of 8 feet each. They are mostly over 18 inches in diameter, and occasionally are found as large as 28 and 80 inches in diameter. The posts are framed to 14 inches, top and bottom. the tenon being 4 inches high. Caps are framed to 14 inches at either end, the tenon being 6 inches long. Thus it will be seen when two adja- cent caps are placed on a post the tenons will not meet, but will have a 2-inch space between them. This space is filled by driving in a section of 2-inch plank 14 inches square. At the junction of caps and posts, it will be noticed, are two ties in place of one, as in the square set system. These ties range from a foot to 1 6 inches in diameter, and are about 4 feet in length. The lower one has a horn 4 inches in length on its upper half. These projections rest upon the shoulders of the posts. The upper tie is tightly wedged between the posts, as shown in the drawing. This system has replaced that formerly in use at the Utica Mine, in which the posts were 16 feet high; caps being let into the sides at 8 feet and others resting on the top. The new system is much preferred and has many advantages over the old (a 30-inch post 16 feet in length weighed over 3,300 pounds). In the present system the posts and caps weigh from 700 to over 1,000 pounds each. Owing to the impossibility of procuring round timbers that are exactly uniform in size, the Utica system involves a vast amount of dressing timbers underground to secure the necessary uniformity in joining. While the system is one affording great strength when properly placed, it would seem to possess no advantages over the square set system, and to be more troublesome, cumbersome, and, in the writer's opinion, more expensive than the latter, though the first cost of round timber is less than that of sawed square timber. No wall plates, excepting short single pieces, are employed, and no sills are laid upon the levels of the floors. It would appear that neglect to provide sills will in time prove a great disadvantage in connecting the stopes from level to level. HANDLING TIMBERS. The manner of handling timbers at mines depends to a great extent on the size and number of timbers used, and on the character of the shaft, whether it be vertical or inclined. In drift mines and mineral deposits which lie nearly horizontal, they are sent in on flat cars (trolleys) built for the purpose. When cages are used in vertical shafts the timbers are set upright on the floor of the cage, lashed together, and lowered into the mine. At inclines it is a common practice to load the timbers into the skip and lower them down the shaft in that way to the desired point. At the Utica Mine the heavy timbers are handled quickly and easily on the surface. They are sent from the framing machine to the shafts on trolleys. Two men are kept busy a great deal of the time in sending timbers underground. A number of stout chains 8 feet in length are — 53 — jtrovided. In the center of each chain is a 4-inch ring, and at each end a (log, having a point projecting at about 70 degrees 4 inches in length. One of these dogs is driven into the side of a post or cap somewhat al)0ve the center. The chain is passed over the end of the timber and the other dog is driven into the opposite side. A spike 6 or 8 inches long, having a 5-foot piece of rope attached, is driven well into the lower end of the timber, and it is ready to lower into the mine. Beneath the skips are stout chains with rings. An extra chain having hooks at the ends is at hand. This forms the connecting link between the chain 1 leneath the skip and that attached to the timber. Having been securely hooked the skip is raised slowly, lifting the timber from the platform. The rope and spike at the bottom are used to bring the timber to a standstill before the skip is lowered. Having reached the level where it is wanted the rope again comes into use in landing the timber at the -lation. CL-CViCC FOR LOWERINC TJMSCR j UNDER TME ' CAGC OR SKIP. The Utica shaft is almost vertical. This process, while a convenient and quick way of handling these heavy timbers, cannot well be used in shafts departing very far from the perpendicular, unless a slide of plank be laid between the guides or runway of the skip, and it would then be advisable to line the slides with strips of flat iron. It would appear that timbers might be handled in this manner in shafts having as low an inclination as 35 degrees, particularly if the slide be lubricated. It is certainly a superior method to that of loading the timbers into skips. — 54 — wh* jh involves much difficulty, particularly in landing them at stations. Most mines have blocks and tackle at the stations, secured to heavy timbers overhead, for unloading timbers from skips. It is always a good plan, where possible, to have complete connection from level to level by means, of winzes in veins requiring very large timbers. The timbers may then be unloaded on the level above where they are to be used and lowered through the winze nearest the stope where they are to be placed, and to the particular floor of the stope where they are required. Winzes for this purpose should have, if possi- ble, an inclination of 65 degrees. Where the slope is too low for them to run, however, the timbers may be dragged down, which is certainly much cheaper and easier than hauling them up. All timbers should be framed on the surface where possible, as it saves much time and trouble. Gang saws are much to be preferred to any other method of framing timbers for square sets. The timbers can, in this way, be framed as exactly if not more so than by hand, and in one tenth of the time. In mines where cages are used, when it is necessary to send long tim- bers down into the mine, as sills for square sets, or long plates, much time is saved by boring an auger hole through the timber near the end and passing an iron bar (|-inch) through it. The ends of the bar are provided with threads and nuts. These ends pass through the ends of a U-shaped frame, forming a large clevis. The clevis is attached by a chain to the bottom of the cage, and in this manner lowered to the point desired. The principle is the same as that employed at the Utica Mine. The drawing on page 53 will convey an idea of the device above described. INDEX A Page. Alma shaft, Jackson, Cal 21-27 Aiuiconda Mine, Montana .- 50 Angle braces, in square sets 50 Angles, taking in shafts 27 Lionaut inchne, Jackson, Cal. 27 B ]'>ark on timbers .-. -. 9 liedrock, swelling _ -- 14 r.eveled notch, the _ - -- 9 I'.i-metallic Mine 34 " r.locky ground " _ 15 r>olts and dogs for hanging shaft timbers _ 19 I'.owlders from roof - 15 IJraces, diagonal 50 r>reast boards, method of using.. .- - 24^25 r.reasting caps 7-9 liuehanan Mine, Tuolumne County 36 JUilkheads and cribs for support 01 roofs 51 lUUkheads, water-tight - 51 C ssons, where used 26 averas Consolidated tunnel, timber in 7 edonia Mine, timbering of -. 43-44-45 ' iiifornia mines, square sets in 38 Caps and posts, in drifts. - 9 In square sets 48 Size of... 12 Careless timbering, in Caledonia _ '. 43,44 In Con. Virginia _ _ - 43 Chambers and stopes _ _ 27 Chambers, great _ - 38 Chutes or ore slides __- -- 32 Chutes, loading, in drifts _ 32-36-37 In shafts .- — 32 Clay linings for shafts... - -- 26 Comstock shafts 21-22-23 Cottonwood for timbers 6 Cribbed shaft ... - 17 Cribs and bulkheads _ 51 D Deidesheimer's square sets 39 Diagonal braces - - --- 50 Dividers in shafts.... - 20-21-24-25 Dogs for hanging timbers - 19 Drainage, importance of - Drains - Drift mines, timbering in Drift of Kennedy Mine, timber in Drifts and tunnels E El Capitan shaft, Nevada County, Cal — F False sets Fissures, precautions with.. "Forepohng" Forman shaft, Comstock Lode --- — 56 — Page. Framing of shaft timbers 19-22-23 Of drift and tunnel timbers 9 Of guides in shafts -_ 26-27 Of square set timbers ...46-47-48-49 Freezing quicksand and watery ground 26 G Golden Gate Mine, Sonora, loading chute in shaft of 38 Gover Mine, timber tests in G Great chambers and square sets 38 Guides in shafts 26 H Hanging bolts and dogs for shafts 19-20 Hanging bolts and dogs, manner of using _. 19-20 Hanging wall, timbering a soft _ 27 Handling timbers, on the surface at Utica Mine 52 Handling timbers, underground _. 52 Honduras Mine, timbering in , 6 I Inclines 27 Timbering 27 Argonaut, at Jackson, Cal. 27 Iron dogs for hanging timbers 19 K Kinds of timber used in mines 6 L Lagging, how made 10 In drift mines.. 7 Kinds of wood used in making 12 Manner of driving in drifts 10 Manner of driving in shafts 10,24-25 • Size of shafts - 10 Levels, connecting 34 Loading chutes, manner of constructing... 32 In drifts... 32 In shafts 36,37 Square sets 38 Long wall system 29 Lost ground, recovering _ 50 Lowering timbers 53 M Manner of stoping large ore bodies '^ Measuring distance between walls -'7 N New Almaden Quicksilver Mine, timbering in i'7 O Oak for timbers 6 Ophir Mine 43 Ore bins 38 Orp Rhont, 34 •r chutes 36,37 toping ''^ P jtall system 29 re to support roof -- 29 trcaps --- 5) II joint 12 are set ...: 47 48 t 7 9 •ifting cap 9 )f timbering mines 5 JRia Tl THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO 50 CENTS ON THE FOURTH DAY AND TO $1.00 ON THE SEVENTH DAY OVERDUE. StP6 ISe5 JAN 3 1S6 FEB 26 19S6 IV ED HEFILEPPSL— m APR SCI '. 'BRA im Book Slip-20m-5,'59(A2537s4)458 I (1cn\vA or Vx. dK, PHYSICAL SCIENCE? UBRAfry C3 A3 UBKAKY UVIVSRSITY OF CAUFQiJad pAVia 181585 1175 00998 7051