lb. per sq. ft., water pressure, giving a total of 3 417 and 1 746 lb. per sq. ft., respectively, for the vertical and horizontal unit pressures at the top of the tunnel lining.
In connection with this subject of underground pressures, it may not be inappropriate to make some concluding remarks on the maximum vertical pressures to which culverts may be subjected.
Let [Fig. 16] now represent a longitudinal vertical section along the axis of a road embankment, built over an arch culvert or box-drain,
, the line,
, passing through the summit of the arch or the top of the covering stone of the box-drain, and the lines,
and
