,
and
have been taken here the same as those used by Mr. Meem, in framing his table of pressures,[Footnote 13] ] which may be supposed to embody, in part, practical experience. The results found from [Figs. 17] and 18 by the writer, for a depth of covering of several hundred feet, are uniformly much larger than those given by Mr. Meem. Are they too large for safety? In answering this question, it must be remembered that, of the weight of earth directly over the tunnel, all has been transferred to the sides that it was possible to transfer, for the coefficients of friction and cohesion given. We know scarcely anything of the cohesion coefficients, so that the value assumed,
lb. per sq. ft., may not be near the truth. Certainly it must appear plain from this discussion that the values of
and
