=Excavation.=--The plan of excavation in the Italian method is shown by the diagram Fig. 99. Work is begun by driving the center bottom heading No. 1, and this is widened by taking out parts No. 2. Finally part No. 3 is removed, and the lower half of the section is open. As soon as the invert and side wall masonry has been built in this excavation, parts No. 2 are filled in again with earth. The excavation of the center top heading No. 4 is then begun, and is enlarged by removing the earth of part No. 5. The faces of this last part are inclined so as to reduce their tendency to slide, and to permit of a greater number of radial struts to be placed. Next, parts No. 6 are excavated, and when this is done the entire section, except for the thin strip No. 7, has been opened. At the ends of part No. 7 narrow trenches are sunk to reach the tops of the side walls already constructed in the lower half of the section. The masonry is then completed for the upper half of the section, and part No. 7 and the filling in parts No. 2 are removed. The various drifts and headings and the parts excavated to enlarge them are seldom excavated more than from 6 ft. to 10 ft. ahead of the lining. [Illustration: FIG. 99.--Diagram Showing Sequence of Excavation in Italian Method of Tunneling.] [Illustration: FIG. 100.--Sketch Showing Strutting for Lower Part of Section.] =Strutting.=--The bottom center drift, which is first driven, is strutted by means of frames consisting of side posts resting on floor blocks and carrying a cap-piece. Poling-boards are placed around the walls, stretching from one frame to the next. As soon as the invert is sufficiently completed to permit it, the side posts of the strutting frames are replaced by short struts resting on the invert masonry as shown by Fig. 100. To permit the old side posts to be removed and the new shorter ones to be inserted, the cap-piece of the frame is temporarily supported by inclined props arranged as shown by Fig. 103. When parts No. 2 are excavated the roof is strutted by inserting the transverse caps _a_, Fig. 100, the outer ends of which are carried by the system of struts _b_, _c_, _d_, and _e_. The longitudinal poling-boards supporting the ceiling and walls are held in place by the cap _a_ and the side timber _e_. To stiffen the frames longitudinally of the tunnel, horizontal longitudinal struts are inserted between them.