THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CVIII. FRIDAY. JULY 17, 1914. No. 2794. Hydraulic Mine Filling: ITS USE IN THE PENNSYLVANIA ANTHRACITE FIELDS. By CHARLES ENZIAN, From Bulletin 60, issued by the U.S. Bureau of Mines. This report is intended purely as a preliminary state- ment of the present development of hydraulic mine filling as conducted in the anthracite region of Pennsylvania. A discussion of different methods, their variations and modifications, as well as their probable extension as a result of amplified tests of the various roof-supporting materials, will be presented in a future bulletin. The first instance of the application of hydraulic mine tilling is reported to have been at a mine in the Schuylkill region in 1884 for the purpose of extinguish- ing a mine fire at an intermediate level on the main haulage slope. About 1886 and 1887 hydraulic mine filling was introduced in the Lehigh and Schuylkill regions for the purpose of sealing off mine fires, arrest- ing squeezes, and supporting the surface. During the latter part of 1890 and the early part of 1891 hydraulic mine filling on a more systematic and economical basis was introduced in the northern field. This installation was practically the first in which the filling material was conveyed to the mine workings through a pipe line laid from the breaker down the shaft and into the worked-out chambers. Shortly after this time a party of foreign engineers visited Pennsylvania. The mem- bers studied hydraulic mine filling as then practised, and after returning to Europe proceeded to adopt it. The method has now become highly developed in several European coal fields and has been described repeatedly in foreign publications. In the mines throughout the northern anthracite field of Pennsylvania hydraulic mine filling has become a part of the regular scheme of mining operations, being used particularly in areas in which inaccessible mine fires exist, or where squeezes are active, or where there is danger from surface subsidence, or where it is desired to reclaim coal pilars. The development of hydraulic mine filling in the anthracite mines was due in a marked degree to a serious problem confronting operators—the proper disposition of the principal by-product resulting from the mining and the preparation of anthracite coal for the market. This by-product, generally called “ culm,” consists of that part of the breaker product that passes through the screens over which the smallest size of commercial pro- duct passes. The filling of mine working may be said in general to be the outcome of a desire to get more merchantable coal from a given area of ground. The use of hydraulic filling for arresting mine squeezes was adopted many years ago, shortly after its introduc- tion for the purpose of extinguishing mine fires. Hydraulic mine filling has also played an important part and been highly effective in the prevention of surface subsidence. The first recorded application dates back to 1886, and the published account substantiates the assertion that hydraulic filling effectively avoided the settling of a large part of a mining town. In the Pennsylvania anthracite fields work of this kind is under- taken by either the surface owners or the operators, according to the provisions in the deed or lease convey- ing the surface. Usually the operators perform the work, the expense being borne by them or by the surface owner, as stipulated. A use of hydraulic filling that is practical and at the same time directly profitable was devised for the double purpose of disposing of refuse and of reclaiming pillars. By means of systematic filling the pillars were made available for extraction by the splitting, blocking, or slabbing methods, as the con- ditions required; later by refilling the rooms (chambers) the maximum yield of coal was obtained. Although hydraulic mine filling originated as a matter of necessity, it was developed to serve many different purposes in the anthracite industry. The huge unsightly spoil banks, the silent evidences of the waste caused by an exacting market, began to disappear and now are the exception rather than the rule. These methods of waste disposal appeal to landowners because they make the valuable space occupied by useless spoil banks available for colliery buildings and for habitation, and assist in solving the problem of how to provide space for needed buildings in mining districts. Several thriving mining villages are at present located on ground previously occupied by spoil banks. Along with the developments mentioned came the realisation that river flats, after periodic floods, had been subjected to the deposit of enormous quantities of culm mixed with fine clay, loam, and silt. State and local regulations were directed against such conditions, and a number of civil and criminal suits at law hastened the installation of filling systems whose operation has pro- duced valuable results. The action of the streams involves a great waste of natural resources as proven by the fact that during each of the years 1910 and 1911 over 90,000 tons of coal was dredged from the North Branch of Susquehanna River several miles below Wilkes-Barre, Pa. Proper credit has been accorded the middle field in which hydraulic mine filling originated. However, the process, like many others, was studied, and the methods were improved by mining men in other sections of the anthracite region. The general application of the svstem in the northern field is considerably more ad- vanced than in the sister fields. This is mainly due to the exceptionally favourable geological conditions. The beds are much less folded than in the other anthra- cite fields and large areas of the coal-mine workings are flat. Materials Used. The material first used for mine filling was that part of the mined product that passed through the smallest sized screen used in the preparation of anthracite for market. This fine material is known as culm. Thus far culm alone has been the chief material used for hydraulic filling, because of uncertainties as to the source and available supply of other material, such as sand, gravel, loam, and clay, and because of the difficulties of transportation. As a result of the scien- tific investigations now in progress relating to the utilisation of the finer sizes for briquetting and firing under boilers by compressed-air blowers the culm mav become of commercial value, so that its use for mine filling mav ultimately be discontinued. Although it is considered a part of the efficient operation of an anthracite steam plant to dispose of ashes by mixing them with culm from the breakers and washeries, the idea of hydraulicking this refuse into the mines is of comparatively recent date. Many industrial plants over mines, particularly over old workings, can make arrangements to hydraulic the ashes from the boilers into the mines by means of boreholes and pipes leading to predetermined points. The ashes from out- lying industrial plants and from railroad engine houses might also be made available by being transported in returning empty cars. An appreciable supply of filling material may be made available by crushing breaker rock, “ slate,” and bone: also clinkers from spoil bank fires. An effective method of disposing of the rock separated from the coal dumped into the travelling tables, or picking chutes, is to convey it to gyratory or swinging hammer crushers, which break it down to chestnut size and smaller, and make possible its transportation into the mines through either troughs or pipes. The availability of sand, gravel, clay, loam, and river silt is limited practically to the northern field. Granulated slag has not been used in Pennsylvania tc any great extent, at least not in such quantity as t< show how it compares in cheapness and efficiency with other materials. Crushed rock and sandstone other than mine refuse has not been used to any appreciable extent, and the practicability of its use is somewhat conjectural. Transportation of Filler. The breaker or washery by-product that is hydrau- licked into the mines is that which passes through the finest screen used in preparing the commercial sizes of anthracite. The openings in these screens vary from in. to in. in diameter. To the washery product the waste from the “ chippings ” elevator or scraper pits is added; by means of a trough the mixture is conveyed to a | in. screen, and what passes through enters the borehole or the receiving pit. Throughout the Wyoming and Lackawanna Valleys, where the surface slopes are gentle, many of the colliery yards are drained to this .No.8 sheet- steel lining: 2*x 12 "plank B 12 or 18'pipe loused for press molds C Bell- —10 between centers of uprights- Joints packed with oakum fund grouted D Figure 1.—Types of troughs used for surface transportation of mine filler A, plank trough; B, plank trough with sheet-iron lining: C, concrete trough: D, cross-acction on line c-tZ. and longitudinal section of terra-cotta or cast-iron trough same pit, which thus receives the excess storm water. Where hydraulic mine filling has not yet been introduced the refuse mentioned is collected in a hopper and, by means of gravity lines, pumps, or elevator and scraper lines, is conveyed into troughs or cars to be delivered to the spoil or waste bank. The sheet iron lining is generally bent so as to form a semicircle (fig. 1, D) or a half hexagon (fig. 1, B), and is placed in the plank trough in lapping or flowing joints. Such sheet iron lining is used only where the inclination of the troughs is Xi Mine opening See E for detail 'Bunton or wall plate Bunton or/ wall plate i i OtR Figure 2.—Methods of pipe arrangement in Intermediate transportation, a. sectional view of pipe line in shaft: B, detail of clamping at a: C, detail of clamping between couplings at b, front and side elevations; D. detail of clamping at couplings at b front and side elevations: E, detail of foot elbow for fillingpipe standard at c. less than -J-in. to the foot. Concrete troughs (fig. 1, C) are constructed in various forms and sizes. The con- crete is made of one part cement, three parts sand, and five parts crushed stone. Broken “ slate ” and rock from the breaker make a satisfactory substitute for the crushed stone, as their resistance to wear is very nearly that of the matrix. The concrete is moulded by the use of either a V-shaped wooden trough or a round pipe embedded in it and removed before the final set begins. Whenever large troughs requiring large quantities of