July 31, 1914. TEEii COLLIERY GUARDIAN. 255 Hydraulic Mine Filling: By CHARLES (Concluded front page 212). Filling Different Classes of Workings. If the area to be filled be taken as the basis of classifi- cation, all systems of hydraulic mine filling may be divided into three groups, as follows : Individual, panel and collective. In the individual system of filling, the filler is discharged directly into each chamber or breast to be filled. This system is generally adopted in flat workings for either total or partial filling. In the panel system the filler is discharged into groups of chambers or breasts, one or more chambers or breasts being left unfilled. This system is generally adopted for partial filling in flat, chute, or pitch workings. In the collec- tive system the filler is discharged at the highest accessible elevation in a given section of the mine, and is allowed to flow unrestrictedly into all the chambers or breasts to be filled in that section. This system is adopted for total filling in chute, or pitch workings. The determination of the most desirable system of filling is dependent on the proposed future operation, the time to elapse between filling and pillar mining, and the ultimate pillar extraction and possible refilling. If the interval between filling and reopening is to be comparatively short, a relatively short-lived, material may be used in constructing the bulkheads. The method of reopening filled areas should be determined by the inclination of the workings. If the bed is flat, the gangway and airway are generally maintained; therefore the filling should be conducted so as to require the least quantity of material to be rehandled, especially where only a partial recovery of pillars can be under- taken. If the workings are inclined over 25 degs., the collective system is the most practical and economical, because, although bulkheads of heavy construction and consequent high cost will be required, comparatively few bulkheads will be necessary. Also, as the reopening of such workings consists in driving a road along the high rib of the old gangway, the least amount of pillar coal is isolated, and the maximum recovery is possible at the least expense in rehandling filler. In fact, with this system the immediate availability of a large quantity of coal somewhat compensates for the high expense incurred. In flat workings, if the greater part or all of the pillar coal is ultimately to be extracted, the collective system possesses a great advantage over the individual or panel system, as the only bulkheads necessary are those pro- vided for ventilation and for entrance and exit for haulage. However, in mines generating inflammable gas the panel system is the only one to be recommended, as this system allows free circulation of the ventilating current around the filled district at all times, and thereby guards again dangerous accumulations of such gas. Collective filling is the least expensive system, panel filling ranks next, and individual filling is the most expensive system. In any form of filling, whether individual, panel, or collective, it is important to guard against the dangers of overflows or “ rushes.” These are frequently caused by piles of gob and dirt or by falls of roof. The water and the filler accumulate behind such obstructions until an overflow or break occurs. Then the onrushing mass often breaks bulkheads or blocks airways, haulage ways, and man ways. If the character of the workings be taken as a basis for classification, hydraulic mine filling systems may be divided into four groups, namely, surface openings, flat workings, chute workings, and pitch workings. Hydraulic mine filling in flat workings, or workings of less than 10 degs. inclination, is the most difficult to perform, and is the most expensive. Filling in such workings must be done almost entirely by the use of pipes; therefore, great care must be exercised to provide a supply of water at all times sufficient to transport the material through the pipe lines. The proper size of the transport pipes should receive special study. For example, if the amount of material to be hydraulicked is less than 200 cu. yds. per day of nine hours, and if the cost of handling water is comparatively high, it may be possible to economise on the quantity of water, and to conduct satisfactory filling with 4 in. pipe, especially if the pipe line is required to conform to an irregular profile, and if the mean effective hydraulic head is high enough to keep the pipe line clear. For lower mean effective hydraulic head, for a larger quantity of material, and for varying grades obviously a pipe of larger diameter, say 6 or 8 in., must be used. To avoid blockages, it is essential to maintain the pipe line so that the filler will flow through at the greatest possible velocity. A good practice is to allow the water to flow through the pipe line for at least 10 minutes before the filler is introduced, and for a sufficient time at the close of a day’s operations to ensure all filler being out of the line. It is obvious that the quantity of water required is dependent on the mean effective hydraulic head; the proportion of water varies from 50 to 90 per cent., depending on the grade of the line and nature of the filling material. In general practice the proportion of water approximates 90 per cent, of the fotal volume passing through the line. One of the most essential conditions in hydraulic mine filling, especially in filling flat workings, is absolute con- trol of the flow until the filler reaches the desired point of deposit. Good practice requires that the pipe line be * From Bulletin 60, issued by the U.S. Bureau of Mines. ITS USE IN THE PENNSYLVANIA ANTHRACITE FIELDS.* ENZIAN, laid to this point, no allowance being made for flow in the chambers. This method will guard against the dangers of “ rushes,” with a consequent possible loss of output or life if the filling is being conducted in work- ings on a “ live ” lift or level. Further, the most suc^ cessful filling is obtained by systematically changing the discharge into different districts. To allow for re-filling or supplementary filling, a period of two weeks should elapse before the filler pipe line is withdrawn from any section considered filled by the first filling. The filler will shrink from 1 to 10 per cent, during the seeping period. In all horizontal places or places of low dip overflow or “ telltale ” pipes should be so placed as to indicate by discharge when the filler deposited has reached the roof at the highest point in those places. The proper ventilation of mine workings while being filled requires more attention than is usually accorded that feature. The drainage of the seepage water from the filling material deposited requires careful attention, so that the least possible amount of filler shall be carried away in suspension. The very fine material, called sludge, that escapes from the deposited mass generally consists of the particles essential to perfect cementation. Great care should be exercised to retain the sludge in the body of the mass, instead of allowing it to seep out and cause troublesome accumulations in the main sumps. Proper seepage will not take place if the filler is deposited con- tinuously or at frequent intervals, but it is obtained to a satisfactory degree if filler is deposited only during periods not exceeding four hours. As previously stated, the practice of filling flat work- ings by continuous flow should be discouraged for several reasons. The most important of these are :—(1) The filling is incomplete both horizontally and vertically; B B Ch{ DETAIL SECTION ON X-X DETAIL SECTION ON Y-Y -Graded auction well chamber^ rOutleta of diochargo I pipes p (5 Old chambers to be f illed with sump cleanings reserved for that purpose Dam with I pipe and valve cofitroli Dam with pipe and valve control v1 or __________— Concrete lining Figure 12.—Mine drainage System. (2) the workings can not be properly ventilated while filling is in progress; and (3) .improper seepage takes place. These objections are eliminated to a great extent by using either the individual or the panel system. There is opportunity for general improvement of the present system of preparing mine workings for filling. The change most essential is in the manner of opening chambers and of driving crosscuts. New chambers should be opened as narrow as possible, allowing only sufficient room for ventilation and necessary car clear- ance. The opening width of the room neck might be reduced, for a distance equal to the width of the open- ing, to about two-thirds that of the regulation width of chamber, thereby decreasing the cost of bulkhead con- struction by at least one-third, and providing better conditions for re-opening. In the distribution of filler in chute workings the usual practice is to construct a pipe line along the air- way of the gangway or lift next higher than the section to be filled (fig. 12, lines A, B, C, D, and E), or if there is an impregnable chain pillar between the chamber faces and the next higher lift or level, the pipe line is led through the headings or crosscuts at the face of the chamber of the filling lift. If the section to be filled consists of more than five chambers, T connections with valves are placed at intervals of five chambers, for instance, at the third, eighth, thirteenth, etc. (fig. 12, line A), the pipe line being made long enough to supply at least three groups of five chambers each. When fill- ing is started and the number of chambers ready to receive the filler is greater than 15, the filler may be conducted from the various connections for half-shift periods. If the collective system is employed and another sec- tions is not available for filling, the pipe line should be so constructed as to permit the discharge of filler at intervals of 10 chambers, the first point of discharge being at the fifth chamber in, the second point of dis- charge at the 15th chamber in, and so on. In fig. 12 the figures along the pipe lines A, B, etc., refer to the mining periods, the figs. 1, 1, 1, etc., referring to the first mining, 2, 2, 2, to second, etc. The arrows indicate the direction of the mining. The general remarks under the section relating to flat workings apply equally to the filling of chute workings, except that in chute workings filling by unrestricted flow is decidedly more efficient than in flat workings, but the practicability of its adoption under any given conditions should .be established by careful study. The hydraulic filling of workings in which the inclina- tion exceeds 25 degs. is less difficult that that of flat or chute workings, and the method of depositing the material is much less expensive. Fewer bulkheads need be constructed, and less attention to chamber flow is required. The most satisfactory system of mine filling is that which allows inspection from the point of intro- duction to the point of discharge. This is possible where shafts or slopes form the connection between the mine workings and the surface. A special caution should be observed, however, in the adoption of unrestricted filler flow. This is particularly dangerous when the filler has been deposited in a chamber from the bulkhead in the first crosscut to the adjoining vacant chamber. In the crosscuts, as a rule, temporary wooden stoppings are constructed for the control of the ventilation current; frequently the crosscuts are partly blocked with “ chip- ping ” coal or with small falls of roof. The stoppings or blockages may cause the filler to accumulate, and the hydrostatic pressure, as soon as it becomes great enough, may cause the mass to break through, rush down the vacant chamber, and strike the bulkhead with great force, disastrously affecting the operation of the mine and even causing loss of life among workmen in the lower levels. Sedimentation of the filler in pitch work- ings is practically perfect. The filler is usually depo- sited so compactly as to make refilling or supplementary filling practically unnecessary until pillar mining is undertaken. Effect of Hydraulic Mine Filling on Ventilation and Drainage. The ventilation and the drainage of a mine are directly influenced by the filling. The entire ventilation is improved by the general filling of old workings. In unfilled workings, air stoppings, if made of wood, rot and become leaky, the constant partial combustion of car- bonaceous matter evolves considerable carbon dioxide gas, and the coal itself takes up oxygen. Furthermore, through the filling of chambers and entries the frictional resistance to the air current may be greatly diminished, thus allowing, with the same water gauge, a much larger quantity of air to be circulated through the mine; pro- vided, of course, that the main upcast or downcast is of larger cross-sectional area than the main mine air course. The ventilating pressure necessary is consider- ably decreased by the filling of the “ dip ” workings. The drainage of a mine is often seriously affected by the introduction of mine filling. Water courses must be changed so as to obtain steeper grades, or the water must be piped, because the increased proportion of solids carried in suspension causes frequent accumula- tions that threaten the flooding of haulage roads or pump- ing stations. Special provision must be made to inter- cept and to remove as much sediment from the water as is possible before it enters the sump. In most instances the introduction of hydraulic mine filling requires addi- tional pumping facilities. If the water contains acids, special wood or cement lined pipes and pump parts are required. On the other hand, when an inadequate pumping plant is replaced by one of the requisite capa- city, the total cost of handling the mine water is often materially reduced. Mine filling serves to reduce to a minimum the dust collecting surfaces in old workings. In the process of hydraulic filling a perceptible rise in the temperature of the surrounding atmosphere has been noted, particularly where iron pyrites was present in the filler. Although such generation of heat at first caused alarm as possibly indicating a fire, experience has demonstrated that it has a beneficial result. Owing to the rise in temperature from the heat developed by the iron pyrites or other oxidisable material, the humidity of the air is increased. The moisture taken up by the air is condensed in cooler parts of the mine, and helps to keep the dust there from becoming dry. Cost of Hydraulic Mine Filling. The conditions under which hydraulic mine filling is conducted are extremely variable, and statements of cost must necessarily be prefaced with the remark that the geological and physical characteristics of a mine greatly influence and may determine the ultimate cost of filling its workings. The cost of surface transportation depends largely on local conditions. The total cost in cents, C, may be expressed by the formula :— 1 G>>)