, ordinarily, the theoretical earth pressures computed by
Rankine and Coulomb are not realized by one-half, and sometimes not even
by one-third or one-quarter in trenches well under-drained, rapidly
excavated, and thoroughly braced.

J.C. MEEM, M. AM. SOC. C. E. (by letter).--The writer has been
much interested in this discussion, and believes that it will be of
general value to the profession. It is unfortunate, however, that
several of the points raised have been due to a careless reading of, or
failure to understand, the paper.

Taking up the discussion in detail, the writer will first answer the
criticisms of Mr. Goodrich. He says:

"The writer believes that, in the design of permanent structures,
consideration of arch action should not be included, at least, not
until more information has been obtained. He also believes that the
design of temporary structures with this inclusion is actually
dangerous in some instances."

If the arching action of earth exists, why should it not be recognized
and considered? The design of timbering for a structure to rest, for
instance, at a depth of from 200 to 300 ft. in normal dry earth, without
considering this action, would be virtually prohibitive.

Mr. Goodrich proceeds to show one of the dangers of considering such
action by quoting the writer, as follows:

"About an hour after the superimposed load had been removed, the
writer jostled the box with his foot sufficiently to dislodge some
of the exposed sand, when the arch at once collapsed and the bottom
fell to the ground."

He fails, as do so many other critics of this theory, to distinguish the
difference between that portion of the sand which acts as so-called
"centering" and that which goes to make up the sustaining arch. The
dislodgment of any large portion of this "centering" naturally causes
collapse, unless it is caught, in which case the void in the "centering"
is filled from the material in the sustaining arch, and this, in turn,
is filled from that above, and so on, until the stability of each arch
is in turn finally established. This, however, does not mean that,
during the process of establishing this equilibrium of the arch
stresses, there is no arching action of any of the material above, but
only that some of the so-called arches are temporarily sustained by
those below. That is, in effect, each area of the material above
becomes, in turn, a dependent, an