Elastic-plastic Analysis Of Circular Hydraulic Tunnel Under The Influence Of Many Factors

The stress field,displacement field and minimum overburden thickness of circular hydraulic tunnel are very important in the design of hydraulic tunnel.In order to ensure the safety and stability of hydraulic structure during construction and operation,the stress field,displacement field and minimum overburden thickness of hydraulic tunnel under multi-factor influence are analyzed by theoretical derivation and numerical simulation.The relevant work and conclusions are as follows:（1）It is divided into two working conditions:excavation period（construction period）and water filled period（operation period）.Considering the seepage,lining,elastic brittle plastic constitutive model,three shear unified strength criterion,internal water pressure and external water pressure,the plastic constitutive equation of circular hydraulic tunnel under plane strain is established under the condition of water rock coupling The results show that the intermediate principal stress coefficient b,permeability coefficient ratio k_d/k_c,softening characteristic parameters c₁,φ₁and dilatancy coefficientβhave significant effects on the stress field and displacement field of the tunnel.（2）The hydraulic tunnel is divided into lined tunnel and unlined tunnel.The Hoek Brown yield criterion,Mohr-Coulomb yield criterion and Tresca yield criterion are adopted respectively in the operation period.Meanwhile,the location of plastic zone is obtained under different internal water pressure.The analytical expression of minimum overburden thickness of hydraulic tunnel is obtained.The influences of different strength parameters c,φ,geological strength index GSI,construction disturbance parameter D,rock hardness parameter m_i,in-situ stress and internal water pressure on the minimum overburden of hydraulic tunnel are discussed.The results show that:for the case of unlined rock,with the increase of shear strength index c andφ,the calculation result of M-C criterion decreases gradually;for the same rock hardness,the minimum overburden thickness of H-B criterion decreases gradually with the increase of GSI index,and increases gradually with the increase of weakening factor of engineering disturbed rock mass;for the case of lined rock,the minimum overburden thickness of H-B criterion decreases with the increase of GSI index,and increases gradually with the increase of weakening factor of engineering disturbed rock mass In the case of lining or rock mass,the influence trend of cohesion c and friction angleφis opposite.（3）According to the Mohr-Coulomb yield criterion,according to the water pressure in the center of the hydraulic tunnel,using the linear hydraulic gradient change,and considering the self weight of the overlying rock mass,the model is simplified as the surface force,and the numerical simulation solution of the stress field,displacement field and plastic zone distribution in the case of fluid structure coupling is obtained.The results show that the X and Z direction displacement are in their respective corresponding square in the construction period and operation period From the construction period to the operation period,under the action of internal water pressure,the Z-direction stress maximum area of surrounding rock is in the top area of the tunnel and has a certain growth,other areas have little change,the X-direction stress changes obviously,and finally close to the in-situ stress,and the Y-direction stress has a certain discontinuity.