Active Thrust on Braced Cut in Clay

Active thrust in a braced cut is considerable different then that calculated by Coulomb.s or Rankine.s theory, due to the restriction imposed on the yielding of lateral support. Due to the lateral deformation conditions in braced cuts, the surface of the failure wedge is generally assumed to intersect the ground surface at a right angle. For a C − Φ soil, the curve of sliding approximates an arc of a logarithmic spiral. For undrained shear of saturated clays (Φ = 0 condition), the curve of sliding transforms into an arc of a circle with the center of the circle located at the ground level. For temporary deep braced cuts in soft and medium clays, engineers sometimes resort to the tedious trial-and-error process to determine the maximum active thrust for comparison with semi-empirical design values. In the present study, using Terzaghi.s general wedge theory, simple generalized equations are presented for active thrust calculations in saturated soft and medium clays under varying conditions of construction.