A Novel Method of Building Concrete Sewers and Subways.
A new method of constructing concrete sewers and subways by means of a movable and adjustable mould is shown in the annexed illustration. This mould is constructed of sheet metal, preferably steel, rolled to the required size and shape, with the edges overlapping, but not welded or riveted. The forward portion, as will be seen by reference to Figs. 1 and 3, slopes gradually from the top to a point on the lower circumference, and is covered by a metal cap riveted at one side only, to allow of contraction and expansion.
Figs. 1 and 2 show the mould with the means for moving, and Fig. 4 is a plan view showing a series of toggle joints attached to the sides of the mould and connected with a rod furnished with a screw, by means of which all of the toggles may be moved simultaneously, so as to either expand or contract the mould as may be required.
In the construction of all concrete work there are two essentials. There must be continuous construction to insure unity, and every portion of the work must be accessible for tamping. In the construction of a hollow cylinder—especially in a narrow excavation—the convexity of the mould interferes to prevent access to a portion of the tube upon the lower side if the line of construction be vertical.
The effective feature of this invention is the inclining of the line of construction to the plane of the tube at such a small angle as to bring every portion of the cylinder within reach while the constant movement of the mould makes the construction continuous, and insures a perfect bond.
In operating, the mould is placed in position and expanded to the full size required. The concrete is then filled in before and around it, and tamped in place, the tapering front of the mould, as it moves forward, determining the line of construction, and permitting every portion of the tube to be reached and tamped as laid.
The mould may be moved at the rate of say one foot per minute, carrying the construction forward at that speed, and leaving behind a perfectly constructed tube formed about it. By means of the interior mechanism, after any interval of suspension of the work, the diameter of the mould may be slightly diminished, when it is easily moved forward into place, and again expanded to full size and the work resumed.
In loose or sandy soil there is used in connection with the mould a frame termed the “shaper,” consisting of a hollow cylinder, the complement of the mould in form, which is placed within the excavation in advance of the mould, but in a reverse position, to hold the earth in place. Thus the pointed end of the mould enters between the side arms of the shaper, and the concrete is laid in the intervening space. The shaper is not shown in the drawing, but will be readily understood.
The perspective views, Figs. 1 and 3, and transverse section. Fig. 2, of a cable road in process of construction, by means of this patent mould, give a clear idea of the mode of procedure with an open mould for subways.
The mould is formed of jointed sections, which give it flexibility for curves. It is of such length as, with the taper of the forward portion, will permit the employment of a number of laborers and bring the entire construction within reach of the tamping tool.
After digging the trench for the subway, temporary timbers are fastened by iron clamps to the posts which have been firmly set in the ground on either side of the track. From these temporary supports the rails and channel irons are suspended exactly in their proper positions, and there firmly held, while the concrete subway is built up around the mould beneath.
As the mould is moved slowly but steadily forward, it is held rigidly in true position by means of iron rods which pass between the channel irons, as seen in Fig. 1, where one side is cut away for the purpose. A traveling shoe and grooved rollers move along these irons, and prevent the mould from rising or falling.
Ernest L. Ransome of San Francisco is the inventor of this novelty in subway construction, the description of which we obtain from The Scientific American. For it is claimed that it insures great economy in construction owing to the rapidity with which operations can be carried on.