back of the walls nearer than 9 ft., while on 33d Street the extreme
position of the back was fixed at the north line, as there were no
buildings, except those belonging to the Railroad Company, on the house
line at the low points in the rock.

The assumptions made in designing the wall were as follows:

_First._--Weight of concrete, 140 lb. per cu. ft.

_Second._--Weight of material from the surface of the ground to a
depth of 12 ft. (which was shown by tests made in bore-holes to be
the elevation of the ground-water surface), 100 lb. per cu. ft.;
and angle of repose, 30 degrees. The distance of 12 ft. below
the surface was the depth of the inverts of the sewers, which
undoubtedly drained the ground above them, thus accounting for the
standing of the ground-water in planes practically parallel with
the surface.

_Third._--Weight of buildings back of wall neglected, as that of the
present type will about equal the cellars filled with material at
100 lb. per cu. ft., and if large buildings are erected in the
future they will undoubtedly be carried to rock.

_Fourth._--Reaction from superstructure, live and dead load, 20,000
lb. per lin. ft. of wall.

_Fifth._--Weight of materials below the 12-ft. line, 124 lb. per
cu. ft., ascertained as follows: The material was considered as
weighing 165 lb. per cu. ft. in the solid, and having 40% of voids
filled with water at 62.5 lb. per cu. ft., the resulting weight