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ACCURATE CALCULATION FOR STRESSES AND DEFORMATIONS OF SURROUNDING ROCK PLAYS AN IMPORTANT ROLE IN TUNNEL STABILITY EVALUATION AND SUPPORT DESIGN. IN THIS STUDY, A MECHANICAL MODEL FOR TUNNELS EXCAVATED IN A NON-UNIFORM STRESS FIELD IS DEVELOPED. A NEW STRAIN-SOFTENING MODEL SIMULTANEOUSLY CONSIDERS THE WEAKENING OF COHESION AND INTERNAL FRICTION ANGLE IS PROPOSED. THEN AN ANALYTICAL SOLUTION FOR POST-PEAK REGION RADII, STRESSES, AND DISPLACEMENTS IS DEDUCED BASED ON THE STRAIN-SOFTENING MODEL AND MOGI-COULOMB CRITERION. THE NEW SOLUTION, WHICH IS VERIFIED BY TRADITIONAL RESULTS, HAS MORE EXTENSIVE APPLICABILITY. TAKING A TUNNEL IN TAOYUAN COAL MINE AS AN ENGINEERING CASE, THE POST-PEAK REGION RADII, SURFACE DISPLACEMENT, AND STRESSES DISTRIBUTION ARE DETERMINED. FURTHERMORE, THE EFFECTS OF SIDE PRESSURE COEFFICIENT, INTERMEDIATE PRINCIPAL STRESS, RESIDUAL COHESION, AND RESIDUAL INTERNAL FRICTION ANGLE ON TUNNEL DEFORMATIONS ARE DISCUSSED. RESULTS SHOW THAT THE POST-PEAK REGION RADII AND STRESSES DISTRIBUTION AROUND THE TUNNEL VARIES WITH DIRECTION DUE TO THE NON-UNIFORM STRESS FIELD. THE DEFORMATION AT TUNNEL SIDE IS LARGEST WHEN THE SIDE PRESSURE COEFFICIENT IS LESS THAN ONE, WHILE THE TUNNEL CROWN SUFFERS FROM THE MOST SEVERE DAMAGE WHEN THE SIDE PRESSURE COEFFICIENT IS GREATER THAN ONE. THE POST-PEAK REGION RADII AND SURFACE DISPLACEMENT ARE LARGER WITH THE CONSIDERATION OF INTERMEDIATE PRINCIPAL STRESS. ADDITIONALLY, TUNNELS SURROUNDED BY ROCK MASSES WITH HIGHER RESIDUAL COHESION AND INTERNAL FRICTION ANGLE EXPERIENCE LOWER POST-PEAK REGION RADII AND SURFACE DISPLACEMENT.
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