THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CXIII. FRIDAY, MARCH 2, 1917. No. 2931. The Cementation of Llay Hall Colliery Shafts. By P. SIDEBOTTOM, M.I.M.E. The shafts Nos. 1 and 2 are 9 ft. and 13 ft. inside- diameter respectively, and so far as can now be ascer- tained, were commenced some few years previous to 1875,. and sunk to a depth of 75 yds., at which depth the original company gave up the enterprise, and left them standing full of water. About September 1875, sinking was re-commenced, and continued without further inter- ruption until the Crown coal was reached, at a depth of 757 ft. The shafts are in the middle coal measures all the way, and pass through several workable seams. Most of the beds below the freestone are impervious to water. Water Troubles. The upper portion, however, from the surface to-a depth of- 50 yds., consists of heavily-watered measures composed of gravel and freestone.—hard grey sandstone, full of joints—and these rocks lying immediately below the surface carry an inexhaustible supply of water, which only rises and falls a few feet with the varying amount of rainfall. As both shafts are sunk from the same surface level and through the same strata, the position of the brick- ing and tubbing is practically identical in each pit, so that the section through No. 1 pit (see fig.) may be taken for our present purpose to represent both shafts. From the surface to a depth of 5 yds. the shafts are lined with ordinary 9 in. bricks, this portion being in “ made ground.” Below that point, which was the original natural surface of the ground, the shafts are coffered with fireclay blocks (about 9 in. by 6 in. by 4 in.) used for the inner lining, and similar bricks for the outer shell, the intermediate space of about 2 in. having been filled in with clay. The cast iron tubbing commences at a depth of 25 yds., and is 34 yds. long, reaching to a depth of 59 yds. from the surface. Below the tubbing the shafts, are lined with ordinary 9 in. brickwork. In No. 1 pit there is a break in the tubbing 7 ft. 6 in. from the base, filled in with an oaken curb which varies from 3 in. at one side of the shaft to about l in. at the opposite side. It is not known why this curb was inserted, but it is probable that the lower portion, con- sisting of five rings of tubbing, had been added to the original tubbing, and the curb served the purpose of a “ making up ” ring. This curb was a source of trouble, as will be seen later. There were many bad places, chiefly in the coffering above the tubbing and in the brickwork below the tubbing, through which water gained admittance to the shafts, where it was collected in garlands; that above the river level being carried off in a culvert from each shaft (see section), and the remainder piped down the pits to a lodgment, from whence it was pumped to the surface by a Scott and Mountain three-throw electric pump, capable of dealing with 250 gals, per minute. This water amounted in the winter months to over 100 gals, per minute, and was a constant source of trouble and expense. It was no uncommon occurrence for the gar- lands to overflow and the water boxes to become choked, thus allowing the water to fall unchecked down the shafts. There was a large crack, about 5 yds. long, running transversely through the coffering in the wind- ing shaft (No. 2), which was filled with wedges, and these frequently blew out, and had to be re-wedged during the winding shift, thus reducing the output. In No. 1 shaft (the upcast) there was ‘a constant i heavy shower, which must have amounted to many gallons per minute, falling down the pit and counteracting the venti- lation. On December 7, 1915, during the working shift, a portion of the oak making-up piece, about 9 in. in length, blew out of the tubbing in No. 1 pit, and allowed such a volume of water to fall down the shaft that in a few minutes the air was completely reversed, although the fan was running on 3 in. water gauge. Men and horses had to be hastily withdrawn, and water had to be wound, in order to prevent the mine being flooded, as the pump was quite' incapable of dealing with the increased flow. It was only with considerable difficulty that this flow was stopped, the volume and pressure being so great that it was a troublesome matter to insert wedges and secure them before they were again blown out. ‘ ■ • At this time we were in communication with Messrs. Simon-Carves and Company Limited, who assured us that, by the cementation process, they could, at a mini- mum expense, and without interfering with the output,- completely seal off the water, and dry the shafts. We entered into a contract with them to treat the portion of the shafts from the surface down to- the top of the tubbing, and work was commenced in May 1916. . Preparation for Injecting. The system adopted was as follows .'—Holes were- drilled through the brickwork by hand, deep enough to tap the water, behind. Short lengths of 1J in. steel piping, with the outer end screwed to receive a three- way valve, were then inserted into the holes, and wedged tight. The surface plant consisted of two tanks—with the necessary water supply—fitted with rotary arms or beaters for mixing the cement liquor, and a hopper over-' head from which the dry cement could be directed to either tank. A third tank, fixed at a lower level, served as a well from which the liquor could be drawn to supply the cement pump. A double-acting pump, 9 in. stroke by 5 in. steam cylinder by 4 in. , ram, fitted with ball valves, was used to force the cement liquor into the holes bored in the brickwork. A steel pipe, l|in. diameter, was taken from the pump down each of the shafts, and terminated close to the hole about to be B I DRtCKWOFlK — Section on Line, A B C.I. TubbFnq Plan and. Section of Llay Hall Shafts. HWShafef- —Plan— --Scale of Feet- too MADE caou.NP tieatcd; a short' length of armoured rubber hose com- pleted the connection to the three-way valve already mentioned. .... . There can be no hard and fast rules governing the number of holes which are required in any particular length of walling; on the contrary, the successful placing of the holes affords great scope for the judgment and skill of the engineer in. charge. Generally, it is advis- able to bore holes close to the spot where a leakage is visible, but it does” not always follow that the cement injected into that hole will stop that particular leak, although cement may be freely injected into a hole close by which fills the joints and cavities all round the pit and for some yards, above and below. . . Injecting the Cement. When commencing to inject, after having connected the flexible pipe to the three-way valve, it is usual first to pump a small quantity of clear water into the hole, with the object of clearing any obstruction. Then the cement liquor may be turned on, varying from 1 to 50 per cent., or even more, at the discretion of the engineer. When a sufficient injection has been given, pure water is again fed to the pump, and, simultaneously, the three- way valve is turned, shutting oft the borehole, and allow- ing the cement and water to escape from the supply pipe. This is a very necessary precaution, the object being to clear the cement completely from the pump and supply pipes before it has time to set and cause an obstruction. The pressure at which the cement may be injected is a matter for careful consideration. Whilst it is essential that there should be sufficient pressure to force it into the joints of the rocks against the water which is already there, precaution must be taken not to exceed the pres- sure which the brickwork can safely withstand. In our case, 200 1b. per sq. in. was never exceeded. We commenced injecting on May 11, 1916, in No.'2 pit, 24 cwt. of cement being forced into one hole in three hours. The effect was at once apparent, as it sealed up the transverse crack in the coffering. From this date jjkefcl? of (dpcFele J3locK 2oo. to the end of the month, work was continued alter-, nately in the two shafts. In some cases as much as three tons were injected into- a single hole, and after each heavy injection the effect wras immediately notice- able, as we found there was less water to pump. By the end of May the brickwork above the tubbing in both shafts was practically dry, but there was still much water escaping from the bottom of the tubbing and the “ making up ring ” in No. 1 shaft. About -this time, on the East bank of the river (see fig.), a spring of water, having a flow of from 10 to 20 gallons per minute, made its appearance, ebbing and flowing in a curious manner. At.times it would cease to flow for an hour or two, and sometimes it would be dry for a few days. The outlet of this spring is 4*8 ft. above the invert of the culvert where it joins the pit, and the level of the spring practically coincides with the highest point to which the injected cement rose behind the shaft walling.