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Abstract An attempt is initiated to obtain the dynamic and static explicit solutions for the unloading effect in underground engineering based on rock dynamics and elastoplastic theory. So，the mechanical model of dynamical excavation in circular tunnel with nonuniform geostress was explored；and the distribution law of initial stress and the processing method for unloading are studied firstly. Based on the Laplace transform and residue theorem，a dynamically analytical method to calculate the behavior of surrounding rock in the condition of excavation is put forward；and the stress and deformation analytical formula of surrounding rock is obtained under the condition of linear unloading. Then，taking the nonlinear strain hardening and softening properties into account，using elastoplastic analytical method，some analytical expressions for the stress and deformation of surrounding rock are deduced. Comparison between dynamically and statically analytical results is drawn to get the difference. The results show：(1) The existence of inertia force is beneficial to reducing the damage of surrounding rock generated from excavation unloading and maintaining its integrity. Thus，the disturbance scope，deformation and stress concentration factor is relatively smaller while the stress gradient is higher in surrounding rock according to the dynamic results. (2) According to the dynamic results，the radial stress is in compression status all the time，while the tangential stress becomes from tensile stress at first time to high compressive stress，which contributes to the formation of tensile crack in radial direction and sandwich structure. (3) A critical value is found in the unloading rate. It is meant that the vibrating amplitude and frequency of particle reach the maximum when the unloading rate is equal to the critical value.
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Received: 25 July 2012
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2013, Vol. 32 
