3.3.1 Effect of soil modulus

The strut force exceedance ratio between the strut force is derived from the finite element analysis；the corresponding value computed from the reference APD，and the initial tangent modulus，Ei quantified in terms of the cu values.The secant modulus，Eu，is approximately 60%of Ei.

It is observed that，when the Ei／cu ratio falls between 200 and 500，except the lowest strut，the reference APD underestimates the strut forces by as much as 100%.As the Ei／cu ratio increases to 1000，the reference APD becomes more applicable.