A 30-ft deep braced excavation in stiff clay (su = 1800 psf, gamma = 125 pcf) is supported by steel sheet piles with one level of struts at 12 ft depth. Using apparent earth pressure diagrams per Terzaghi & Peck, what strut load in kips per foot of wall results?

Why is this the answer?

For stiff clay, the apparent pressure diagram is rectangular with intensity p = 0.3 * gamma * H = 0.3 * 125 * 30 = 1125 psf. The strut at 12 ft depth supports a tributary area extending from 0 to 20 ft (midway between surface and bottom). Load = 1125 psf * 20 ft = 22,500 lb/ft = 22.5 k/ft. The provided options and original explanation are inconsistent with standard Terzaghi & Peck calculations for this geometry.

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