Design and performance evaluation of vertical shafts: rational shaft design method and verification of design method

Abstract

Ground deformations around axisymmetric shafts cannot be determined with the design approaches currently available, which are mostly based on plasticity methods. The convergence–confinement method (usually applied to tunnels), with consideration of gravitational effects and the three-dimensional conditions near a shaft, is proposed as a tool to predict formation pressure on a shaft and radial ground displacements. It is shown that the behaviour of a shaft is governed by (1) the mode of yield initiation dominated by the in situ stress state and the soil strength parameters and (2) the extent of the yield zone that develops if wall displacements are allowed to occur during construction.Closed-form solutions are presented to approximate the pressure–displacement relationship for cohesionless and cohesive soils. Results from this approach compare well with those obtained by finite element analyses. The conventional design methods that provide the minimum support pressures required to maintain stability are not conservative. These pressures are generally less than those actually encountered if ground movements during construction are restricted with good ground control. Key words: shaft, design method, support, interaction, yielding, stress, displacement, earth pressure, arching.