July 24, 1914. THE COLLIERY GUARDIAN. 211 Hydraulic Mine Filling: By CHARLES ENZIAN, From Bulletin 60, issued by the U.S. Bureau of Mines. (Continued from page 137). Comparative Efficiency of Various Kinds of Pipes. In stating the efficiency of various kinds of pipes employed for hydraulic mine filling, it must be borne in mind that accurate experimental data are not avail- able. Proper regard must, of course, be had for the geological conditions under which any of the methods is operating. For example, where the grades are undulating it is absolutely necessary to have a stout metal pipe unless the back pressure is comparatively light. Roughly, such pipe should be used’when there is a difference of 100 ft. between the highest and lowest points in the line. At no point throughout the system should the velocity be less than 6 ft. to 8 ft. per second. This will insure against deposition of the filler in the line. Wood pipe possesses a number of distinctive advan- tages. (1) It is immune from chemical attack; (2) it has a tough wearing surface; (3) it is easily turned; (4) it is easily cleaned; (5) its cost of installation is low; (6) it can be used under difficult physical conditions. The disadvantages attendant on the use of wood pipe are : (1) It dries out and collapses when not regularly in use; (2) it wears unevenly; (3) it easily springs out of Line; and (4) its life is comparatively short. One of the greatest disadvantages of steel and wrought iron pipe is its tendency to corrode. Each morning considerable care must be observed when the mixture of water and filler is turned into the line, as otherwise blockage from friction, caused by the corrosion over- night, may be the first thing to occur in a day’s operation. Although there is a serious objection to the weight of cast iron pipe of standard length (12 ft.) this pipe has become rather popular for use in hydraulic mine filling. Tlie bell-and spigot connection allows great flexibility in vertical and horizontal alignment, and because the pipe keeps a smooth surface during use the proportion of water and velocity of the current can be reduced to a minimum. On account of the short lengths in which cast iron pipe is made it can be installed in caved and tortuous openings. Cast iron pipe is subject to the corrosive effect of acid water, and although it deterior- ates less rapidly than pipe made of wrought iron or steel, nevertheless such water has a very destructive effect and shortens the life of the pipe decidedly. It is claimed that under a pressure of 100 lb. to the square inch cast iron pipe will wear three times as long as wrought iron and about five times as long as steel pipe. Use and Character of Bulkheads. The construction of the bulkheads to be placed to retain the filler in mine workings should be given careful consideration. The construction must permit proper drainage, possible future use in ventilation, and the reopening of the filled section in such manner as to make second mining possible at minimum expense. The type of bulkhead used throughout the anthracite field is prac- tically the same and is generally that first adopted, with the improvement of a few minor details. However, several details can be still further improved. Mine workings (chambers) should be so opened as to entail the least possible expense in bulkhead construction. Instead of full-width chambers, the openings should be as narrow as haulage and ventilation will permit. In general, bulkhead construction is considered a part of timbering. The haunch distance (fig. 8, A; fig. 9, and fig. 10, A)—that is, the distance along the rib from the entrance opening to the bulkhead hitches—should be equal to one-half the width of the opening for flat and chute workings, and two-thirds the width of the opening for pitch workings. As to the props used, their diameter in inches should be equal to their length in feet for flat workings, or to a multiple of corresponding lengths for chute and pitch workings, plus the depth of the top and bottom hitches in feet. The empirical formulas for the diameter of props are as follows :— Flat workings D — L Chute „ D ~ Pitch „ D = ^ ' 4 L = length of props, in feet. D = diameter • f props, in inches. Formulas for the spacing of props are as follows :— Flat workings S = Chute ,, S = Pitch „ S = W = width of opening, in feet. H = height of opening, in feet. S = spacing of props, centre to centre, in feet. The materials of construction to be employed depend upon the form and type of bulkhead to be erected. In general, it may be said that props and plank, gob, dirt, blasted rock, concrete, and stone are usually adopted. In conjunction with these materials, limestone and calcareous shales have been used to neutralise sulphuric acid in the water. Packing, necessary to avoid excessive leakage and to form a filter curtain or “ screener,” may consist of burlap or brattice cloth, hay, shavings, manure, ashes, straw, forest leaves, etc. Props, planks, H 2W 3H 4W 7H ITS USE IN THE PENNSYLVANIA ANTHRACITE FIELDS. or boards are used for practically all flat workings. Timber, gob, stone, and concrete bulkheads are generally constructed where the dip of the coal bed is steep and the workings are comparatively new. The bulkheads can then be utilised to assist ventilation before actual filling is undertaken. Packing is used only on inclined workings, and the quantity is almost proportional to the degree of inclination. Its purpose is to filter out of the seepage water any filler held in suspension. Care must be exercised not to make bulkheads too water- tight, as allowance must be made for partial relief of hydraulic head. Timber can be used for all kinds of bulkhead construc- tion, but is especially suited for use in flat and chute workings. Roof or bottom (floor) hitches in hard sand- stone are cut one-half the depth of those in shale or “slate.” The bottom hitch is generally of the trough type (fig. 8, D), whereas the top is more frequently of the sliding type (fig. 8, C), especially where the roof is hard. If the roof and the floor are of shale or “slate,” Bottom _ Btringer- 1 double board.or /Patching with ' short pieces of boards ----------- ----------- W „ haunch W 2 distance Figure 8.—Bulkhead and hitches for flat workings. A, plan view and front elevation; B, side elevation ; C, prop held by a sliding and a trough hitch; D, prop held by trough hitches. Drainage trough FRONT ELEVATION AT c-d PLAN VIEW SIDE ELEVATION AT a-b ■ Gob or dry wall Ailed with dirt x Drainage box ‘Drainage ditch ! 7/ (WI \ t1 J Hf-*- *■ ^,.4. , 2 plank 1= Gore props Wringer the hitches would be cut as trenches 12 in. wide and 8 in. deep. Where the roof and the floor are sandstone the hitches would be cut separately 10 in. or 12 in. square, but only one-half as deep as in the shale or “ slate.” The props are securely wedged at the top, and manure or dirt is firmly packed around the bottom after the bottom plank has been attached, so as to avoid leakage. One and one-half inch plank or double 1 in. boards are then nailed to the inside face of the props for the entire height. The bottom, sides, and top are carefully joined or “ patched ” with short pieces of board nailed to the main boarding and the solid coal or pillar. If the dip of the bed is between 5 degs. and 15 degs., a straw, hay, burlap, or brattice-cloth packing is used; or, in order to avoid heavy hydraulic head, a drainage trough to draw off excess water may be constructed as illustrated in fig. 8, A and B. In chute workings the heavier hydraulic pressure on bulkheads naturally demands a more massive and substantial construction than is required for flat work- ings. The character of the overlying and the under- lying rock influences the construction to a certain degree as regards obviating water squeezes. The method of construction is illustrated in fig. 9. Drainage for this type of bulkhead is best accomplished by means of a trough, as illustrated in fig. 9. This method axoids heavy hydrostatic pressure on the bulkheads and makes the water used available in the shortest time for re-use for hydraulicking, a feature that is of vital importance in nearly all mines where filling is done. Where the inclination of the bed is 18 degs. or more, manure, straw, or hay is placed between the two courses of boards as a “ screener,” and in many places a wall of dry gob is constructed to act as a partial filter. Pitch workings include workings in which the inclina- tion of the bed exceeds 25 degs., and in which the coal will run in chutes or troughs not lined with sheet iron. The construction and the materials must be heavier and more substantial. If the bulkheads are intended to withstand great pressure in beds of steep dip, the form of an inverted V is most preferred (fig. 10). In this form of construction it is at times highly desirable to provide the “ screener ” and the gob-wall filter men- tioned above. Masonry, rather than timber, can be used for this form of construction. If masonry (fig. 11) is employed instead of timber, the form of the bulkhead is that of a full-struck arch, a semi-circle with a radius equal to the width of the opening; the thickness of the bulkhead at the haunches is equal to one-third of the height, and at the crown to one-sixth of the height. Drainage troughs (fig. 11) must be provided. Under special conditions dry walls are in places used in conjunction with the timber construction. It is impractical to formulate any general rules for using such walls. However, it is safe to state that wherever the inclination of the coal bed is over 18 degs., dry walls are invariably constructed if rock is available. Great faith is placed in this type of bulkhead. The specific purpose of the dry wall is to act as a breakwater or cushion and a partial filter, thus relieving the bulkhead of a portion of the direct hydrostatic pressure. Concrete bulkheads have been tried in several mines, and although their first cost is high they prove fairly w ( £ S’ - ' 2W _ haunch ST distance \ I ^z/zzlzZzzZz. -EQin WT A B wurb 10—Bulkhead for pitch workings. A. plan view and front elevation ;’B. plan view of modification of bulkhead shown in A; C, side elevation at