y carried through safely by going farther into the hill.

As to the angle of repose, Mr. Thomson seems to feel that its
determination is so often impracticable that it is not to be relied on;
and yet all calculations pertaining to earth pressure must be based on
this factor. The writer believes that the angle of repose is not
difficult to determine, and that observations of, and experiments on,
exposed banks in similar material, and general experience in relation
thereto, will enable one to determine it in nearly all cases within such
reasonably accurate limits that only a small margin of safety need be
added.

Engineers are sent to Europe to study sewage disposal, water
purification, transit problems, etc., but are rarely sent to an
adjoining county or State to look at an exposed bank, which would
perhaps solve a vexed problem in bracing and result in great economy in
the design of permanent structures.

Mr. Thomson's general views seem to indicate that much of the subject
matter noted in the paper relates to unsolvable problems, for it appears
that in many cases he believes the Engineer to be dependent on his
educated guess, backed perhaps by the experienced guess of the foreman
or practical man. The writer, on the contrary, believes that every
problem relating to work of this class is capable of being solved,
within reasonably accurate limits, and that the time is not far distant
when the engineer, with his study of conditions, and samples of material
before him, will be able to solve his earth pressure and earth
resistance problems as accurately as the bridge engineer, with his
knowledge of structural materials, solves bridge problems.

The writer, in the course of his experience, has met with or been
interested in the solution of many problems similar to the following:

What difference in timbering should be made for a tunnel in ordinary,
normally dry ground at a depth of 20 ft. to the roof, as compared with
one at a depth of 90 ft.?

What difference in timbering or in permanent design should be made for a
horizontally-sheeted shaft, 5 ft. square, going to a depth of 45 ft. and
one 25 by 70 ft., for instance, going to the same depth, assuming each
to be braced and sheeted horizontally with independent bracing?

What allowance should be made for the strength of interlock, assuming
that a circular bulkhead of sand, 30 ft. in diameter, is to be carried
by steel sheet-piling exposed around the outside for a dept