Flexible Shaft Structure
Conventional excavation method is a typical example of using the shaft with flexible construction. Using this method, the rock is excavated in the first step and afterwards concrete is sprayed on to hardened surface to support the rock. There are specific technological downtime (ground excavation, shotcrete or arch timbering) with enabling stress rearrangement in the surrounding soil and the consequent value of the earth pressure acting on the shaft will be equal to the active earth pressure. This fact is well described by V.G. Berezantsev's method (1958).
Load on flexible shaft is defined using this formula:
depth of cross-section
magnitude of a surcharge
shear strength of soil
radius of shaft
angle of internal friction of the soil
ξ = 1
λ = 1
Berezantzev, V. G.: Earth pressure on the cylindrical retaining walls, Brussels conference on Earth pressure problems, 1958.