720 ANNUAL REPORT SMITHSONIAN" INSTITUTION, 1913, 



ing conveyor. The machine is mounted on a turntable so that it may 

 be turned about in any direction. 



Some of the work on the city pressure tunnel has been hurried so 

 far that certain sections are now being lined with concrete. The 

 forms used for this purpose are very interesting. Our illustra- 

 tion, plate 11, shows their construction. They cover 120 feet alto- 

 gether and are arranged in two sections, 60 feet of the lower half 

 of the tunnel being concreted in advance of 60 feet of the upper 

 part. The first step is to lay the " invert ;" that is, a narrow seg- 

 ment of the lining running along the bottom of the tunnel. This, 

 when completed, forms the track upon which the forms for the rest 

 of the lining travel. The forms are mounted on trucks with wheels 

 tapered to fit the curve of the invert. The forms for the lower half 

 cylinder are practically the same as those for the upper half cylin- 

 der. After the lining has set, the sides of the upper form may be 

 drawn in to free them from the concrete by operating the turn- 

 buckles A, and those of the lower forms by operating the turn- 

 buckles B. Then jacks may be unscrewed to lower the upper section 

 slightly, freeing it completely from the concrete, and jacks E may 

 be screwed up to raise the bottom section slightly upon the truck. 

 In this collapsed condition the forms may be drawn forward to 

 complete the next section of tunnel. The detail view in the drawing 

 (pi. 10, fig. 2) -shows how the lower forms are supported on the 

 trucks. To the longitudinal beams C, vertical guides D are bolted, 

 which fit against the framework of the truck. The jacks E mounted 

 on the truck bear against cross pieces running from C to C. The 

 filling of the lower half of the forms is comparatively simple. It is 

 quite a different task, however, to lay the concrete into the upper 

 form. Sections of the plating of the upper forms are removed and 

 the concrete is shoveled in, adding the plates step by step as neces- 

 sary, until finally the topmost plate is added, when the concrete can 

 be introduced only from the end of the form. It will be observed 

 that small pieces of board are temporarily nailed against the edge 

 of the forms and fitted up as neatly as possible against the rock 

 above, so as to retain the concrete until it sets. As each section is 

 completed, grouting holes are left in the top through which, when 

 the lining is completed otherwise, grout will be forced under high 

 pressure to fill up all cracks and crevices and make the lining per- 

 fectly sound. 



At each shaft access will be had to the tunnel through risers or 

 vertical pipes, 48 or 72 inches in diameter. At most of the shafts two 

 such pipes will be provided, each fitted with valves at the bottom, 

 which may be operated from the surface to close either of them when 

 it is desired to gain access to them or to effect any necessary repairs. 

 The valves at the bottom of the risers will be of such a design as to 



