=Strutting.=--When the excavation is begun by bottom side drifts these drifts are strutted by erecting vertical posts close against the sides of the drift and placing a cap-piece transversely across the roof of the drift. The side posts are usually supported by sills placed across the bottom of the drift. These frameworks of posts, cap, and sill are erected at short intervals, and the roof, and, if necessary, the sides of the drift between them, are sustained by means of longitudinal poling-boards extending from one frame to the next. The cap-pieces of the strutting for the bottom drifts serve as sills for the exactly similar strutting of the heading next above. To support the additional weight, and to allow the construction of the side walls, the strutting of the bottom drifts is strengthened by inserting an intermediate post between the original side posts of each frame. These intermediate posts are not inserted at the center of the frames or bents, but close to the wall masonry line as shown by Fig. 78. This eccentric position of the post avoids any interference with the hauling, and also allows the removal of the adjacent side post when the masonry is constructed. [Illustration: FIG. 78.--Sketch Showing Work of Excavating and Timbering Drifts and Headings.] [Illustration: FIG. 79.--Sketch Showing Method of Roof Strutting.] Two methods of strutting the soffit of the excavation are employed, one being a modification of the longitudinal system employed in the English method of tunneling described in a succeeding chapter, and the other a modification of the Belgian system previously described. Fig. 79 shows the method of employing the radial strutting of the Belgian system. At the beginning the center top heading is strutted with rectangular bents such as are employed for strutting the drifts. As this heading is enlarged by taking out the haunch sections, radial posts are inserted, as shown by Fig. 79, which also indicates the method of strutting the side trenches when the excavation is carried downward from the center top heading instead of upward from bottom side drifts. =Masonry.=--Whatever plan of excavation or strutting is employed, the construction of the masonry lining in the German method of tunneling begins at the foundations of the side walls and is carried upward to the roof arch. The invert, if one is required, is built after the center core of earth is removed.