3.3.2 Effect of the cu profile and value

Variations of cu with depth have been shown to affect the performance of braced excavations（Wong，1989）.It found the strut force of the lowest strut falls within the applicable range of the reference APD even in a very soft clay with which the ／γH value is still very small.The reference APD actually increasingly overestimates the lowest strut force when the c∗u／γH value enlarges.This situation further enhances when it is compounded by a high Ei／cu ratio.

Conversely，the reference APD appears to be consistently underestimating the strut force at higher strut levels regardless of ／γH value，and the situation of underestimation worsens when both of the ratios of ／γH and Ei／cu are low.Nevertheless，the trend of underestimation appears to level off around a ／γH value of 1.5.It is postulated that in the Ei／cu－／γH space，the area within the borders marked by ／γH of 1.5 and Ei／cu of 500，defines a non⁃applicable zone for the reference APD.Outside the zone，the reference APD is able to provide a reasonable estimation of strut forces together with a factor of safety of 1.5.