of any kind; but, as soon as the hole or heading was 10 ft. out, 6 by
12-in. laggings or polings were put up in the roof, with the rear ends
resting on the iron lining and the leading ends resting on vertical
breast boards. The heading was then widened out rapidly and the lagging
was placed, down to about 45° from the crown. The forward ends of the
laggings were then supported by a timber rib and sill. Protected by this
roof, the full section was excavated, and three rings of the iron lining
were built and grouted, and then the whole process was repeated.

[Illustration: PLATE LXIV, FIG. 1.--TUNNELING IN COMPRESSED AIR WITHOUT
SHIELD.]

[Illustration: PLATE LXIV, FIG. 2.--T-HEAD AIR-LOCK.]

[Illustration: PLATE LXIV, FIG. 3.--CUTTING EDGE OF CAISSON ASSEMBLED.]

[Illustration: PLATE LXIV, FIG. 4.--CAISSON SUPPORTED ON JACKS AND
BLOCKS.]


CONCRETE CRADLES, HAND-PACKED STONE AND GROUTING.

Had the East Avenue Tunnel been built by shields, as was contemplated at
the time of its design, the space between the limits of excavation
and the iron lining would have been somewhat less than by the method
actually used, especially in the earth portions. This space would have
been filled with grout ejected through the iron lining. The change in
the method of doing the work permitted the use of cheaper material, in
place of part of the grout, and, at the same time, facilitated the work.