of the groove to the edge of the lip extending 1 in. beyond the inner face of the wall was constructed to catch any seepage or water from the surface of the lining. This groove and lip has a fall of 3 in. from its highest to its lowest point, where a 2-in. wrought-iron pipe passes through the lining wall on an angle of 45° leading all water caught in the groove to the water ring. Thus, all the water both behind the lining wall and all water on the inner surface is collected in the water rings and thence led to the pumps and expelled from the shaft. In the shaft, the approaches leading to the shaft bottom from both the loaded and empty sides are of concrete. These are of 18-ft. span having a minimum thickness of 24 in. for side walls and crowns. Each arch extends 13 ft. from the face of the shaft lining. Arches of 9-ft. span having a minimum thickness of 18 in. extend a distance of 11 ft. 6 in. from both ends of the face of the shaft lining. These arches connect with the cross-entries, and manway around the shaft bottom. An archway of 4-ft. span was placed in the side walls for entrance to the run-around. At the intersection of all arches with the shaft-lining wall, steel bars were placed for reinforcement. The method of this reinforcement is shown in Fig. 13. All centering was built of 2-in. oak plank, spaced 2 ft. center to center, covered with 2-in. tongued-and-grooved oak lagging. Concreting for the four arches was brought up at one time and also at the same time as the shaft-lining wall was placed. MASONRY MATERIALS OF CONSTRUCTION STONE The materials employed in the construction of masonry are stone, brick, terra cotta, and the cementing materials used in the manufacture of mortars; namely, lime, cement, and sand. Strength of Stone. In ordinary buildings and engineering structures, stones are generally under compression. Occasionally, they are subjected to cross-stresses, as in lintels over wide openings. They are never subjected to direct tension. As a general rule, a stone should not be subjected to a greater compressive stress than one-tenth of the ultimate crushing strength, as found by experiment. The resistance to crushing varies within wide limits, owing to the great variety in the structure of the stones; the method of preparing and finishing the test pieces also affects the results; hence, the great variations found in the values given by different experiments. The accompanying table shows the average resistance of the principal building stones to crushing and to rupture when used as beams. Absorptive Power of Stone.-The absorptive power of a stone is a very important property, a low absorption generally indicating a good quality. The accompanying table gives the average percentage of water absorbed by stones. Size and Weight.-The dimensions of bricks vary considerably. The standard adopted by the National Brickmakers' Association is, for common clay brick, 8 in. X4 in. X2 in., and for face or pressed brick (clay) 8 in. X4 in. X2 in. The weight of a common clay brick is about 43 lb.; that of a pressedclay, enameled brick, about 7 lb. Enameled and glazed bricks are made in two sizes: English size, 9 in. X3 in. X4 in.; American size, 8 in. X2 in. X4 in. The usual dimensions for firebricks are 9 in. X4 in. X2 in.; various sizes and forms are made to suit the required work. The dimensions of the lime-sand bricks are 8 in. X4 in. X2 in. The weight varies between 5 and 6 lb. The accompanying table gives the approximate weight and resistance to crushing of brick. WEIGHT AND STRENGTH OF BRICK Requisites for Good Brick.-Bricks of good quality should be of regular shape, with parallel surfaces, plane faces, and sharp square edges. They should be of uniform texture; burnt hard; and thoroughly sound, free from cracks and flaws. They should emit a clear ringing sound when struck a sharp blow. A hard well-burned brick should not absorb more than one-tenth of its weight of water; it should have a specific gravity of 2 or more. The crushing strength of a brick laid flat should be at least 6,000 lb. per sq. in. The modulus of rupture should be at least 1,000 lb. per sq. in. WIRE ROPES* GENERAL DESCRIPTION WIRE-ROPE MATERIALS Wire ropes are used about mines chiefly for hoisting from shafts, for haulage and the transmission of power, for the cables of aerial tramways, for the guy ropes of derricks and smokestacks, etc., and, rarely, for the cables of small, short-span, suspension bridges, as where the town or settlement is situated on the opposite side of a narrow stream from the mine. While wire ropes are now almost universally made of steel, manufacturers still make and list iron ropes, which have a limited field of usefulness. Swedish, Swedes, or charcoal-iron ropes are made of a very pure wrought or puddled iron having a tensile strength of from 50,000 to 100,000 lb. per sq. in. These ropes are soft, tough, and pliable, and are adapted especially for passenger elevators, small hoists, steering gear of vessels, etc., where the loads are intermittently applied and are not too great, or where the speed is high and the bending stresses great. It will be noted from tables given later that the ultimate breaking strength of a 6X19 Swedish iron hoisting rope 1 in. in diameter, is but 14.5 T., whereas, the breaking strength of a steel rope of the same kind and size is from 30 to 45 T. For general mine use, iron ropes have been almost entirely superseded by steel ropes because of their greater strength and elasticity. The Steel ropes are generally made of open-hearth steel having a tensile strength of from 150,000 to 275,000 lb. per sq. in. and in some cases even more, the tensile strength depending on the composition of the metal and the method of its treatment. Steel ropes are in almost every way superior to iron ropes. principal advantage is that they have more than double the strength of iron ropes of the same size; consequently, for equal strains, they can be made of much less diameter than iron ropes and can, therefore, be used in connection with much smaller and lighter drums, sheaves, or pulleys. Iron-wire ropes are not so elastic as ropes made of steel wire, hence a larger sheave is required for iron than for steel ropes of the same diameter. Iron ropes, however, are usually more flexible than steel ropes, are less brittle though not so strong, and better resist the acid in mine water. A 1-in. Swedish iron rope has about the same strength as a §-in. ordinary cast-steel rope; weighs 1.58 lb. per ft. as opposed to .62 lb.; costs (list price) 26c. per ft. as opposed to 16.5c.; and requires a sheave or drum 6 ft. in diameter as against one 2.5 ft. for a cast-steel rope. Cast-steel, crucible-steel, and crucible cast-steel ropes are the trade names given to the ordinary grades of ropes made from wire having an ultimate tensile strength of 160,000 to 210,000 lb. per sq. in. The breaking strength of a 6X 19 standard hoisting rope of this grade and 1 in. in diameter is given, in the manufacturers' tables, as 30 T., more than twice the strength of a similar iron rope. Ropes of this material are those commonly used in and around mines for haulage and hoisting purposes. Extra strong cast-steel, extra strong crucible-steel, special steel, and patent steel ropes are the trade names for the next stronger grades of ropes, intermediate in strength between cast-steel and plow-steel ropes in strength. The wire from which they are made has an ultimate tensile strength of from 190,000 to 230,000 lb. per sq. in. The breaking strength of a 6X 19 hoisting rope of this grade and I in. in diameter is given as 34 T, 11.33% more than that of an ordinary cast-steel rope of the same dimensions. These ropes are also standard and are in general use where it is desirable to increase the factor of safety while retaining the same diameter of rope. * Acknowledgement for the use of data and tables in this section is made to the Broderick & Bascom Rope Co., Hazard Manufacturing Co., A. Leschen & Sons Rope Co., John A. Roebling's Sons Co., The Trenton Iron Co., The Waterbury Co., and the Link Belt Co. As in most instances, the manufacturers have identically the same tables, etc., credit is given generally in this manner, rather than specifically for each item. |