The Plastic Zone of Tunnel Surrounding Rock under Unequal Stress in Two Directions Based on the Unified Strength Theory

Figure 1

The mechanical model of the circular tunnel under unequal stress in two directions. r₀ is the tunnel radius, p_s is the support stress evenly acting on the tunnel inner wall, p₀ (= γh, where γ is the rock gravitational density and h is the depth from the ground surface to the tunnel center) is the vertical ground self-gravity stress, λ is the lateral pressure coefficient, and θ is the polar angle. According to the superposition principle of the linear elasticity theory, the elasticity solution of the model, shown in (a), can be seen as the sum of that of the model in uniform stress condition, shown in (b), and that of the model in one-single direction stress condition, shown in (c).