Note Return to text — EXPERIMENTS ON RETAINING WALLS AND PRESSURES ON TUNNELS.

In the discussion of the paper[Footnote 10] by J. C. Meem, M. Am. Soc. C. E., E. G. Haines, M. Am. Soc. C. E., states that where breaks occur in the sides of an unsupported trench, the solid of rupture often approximates to a quarter sphere, surmounted by a half-cylinder of the same height, the radii of the sphere and cylinder being equal. In Fig. 14, let represent the quarter-sphere, the half-cylinder, and the face of the trench. According to the observations of Mr. Haines, when the part, , of the side of the trench is supported by sheeting and bracing, it sometimes happens that a part of the quarter-sphere, , breaks out, so that the semi-cylinder above would descend but for the bracing, the thrust of which, it is supposed, induces arch action in the earth.