Finite Element Analysis of Mechanical Behavior of Cohesive Soil Tunnel Excavation Based on D-P Condition Equivalent

Abstract:

Based on the stress-strain results of triaxial test， the strength parameters of cohesive soil were obtained. A Drucker-Prager （D-P） criterion-based simulation method for Mohr-Coulomb （M-C） cohesive soil is then established according to the Drucker-Prager condition equivalence. The ‘Gap Constraint Method’ is applied to simulate the influence of the supporting time on the soil mechanical behavior. The influence of stratum parameters and construction characteristics on stratum mechanical behavior and support reaction force of shield tunnel in cohesive soil is finally discussed by using the proposed numerical calculation methods. It can be found that he radius of plastic zone and support reaction force of surrounding rock have a linear relationship with the cohesion， the internal friction angle and the tunnel diameter. The radius of the plastic zone and the supporting reaction decreased significantly with the increase of cohesion and internal friction angle， and the influence of the internal friction angle is more distinct. When the tunnel diameter increases from 6 m to 14 m， the radius of plastic zone increases by about 210 %， and the support reaction increases by about 230 %. The lateral pressure coefficient will significantly affect the shape， the range， and the distribution of the plastic zone after excavation. The plastic zone gradually increases and the support reaction force gradually decreases with the extension of support time. When the released displacement exceeds by 40 % of the total displacement， both the increase and the decrease tend to mitigate. Taking the engineering practice in this paper as an example， when the stratum moisture content is controlled between 8 % and 15 %， the stratum convergence is about 20 % of the total displacement， the stratum self-supporting ability can be fully exerted to reduce the support reaction.

Key words:tunnel;cohesive soil;plastic zone;supporting reaction force;Drucker-Prager condition equivalence