At present

theoretical analyses on double-arch tunnel construction effects have rarely considered the construction impacts induced by the middle guide tunnel

despite its prevalence in practical designs. During construction

the middle guide tunnel is excavated first

sharing its lining boundary with adjacent left (tunnel 1) and right (tunnel 2) caverns

while requiring backfilling and reconstruction of the central diaphragm wall. Based on complex variable function theory and the Schwarz alternating method

this study proposes a calculation approach for stress and deformation in lining-surrounding rock systems of double-arch tunnels incorporating middle guide tunnel effects. For the shared lining boundary between the middle guide tunnel and lateral caverns

the Cauchy integral method transforms boundary integral conditions into the difference between complete single-cavity integrals and shared boundary integrals. This aligns with the Schwarz alternating method’s concept of “additional surface forces” generated during three-cavity interaction analysis. Validation against monitoring data and numerical simulations from the Suzhou Qizi Mountain double-arch tunnel project confirms the feasibility of this complex function approach. Parametric sensitivity analyses were conducted for Poisson’s ratio

surrounding rock elastic modulus

middle guide tunnel aspect ratio

and double-arch symmetry. Key findings include: elastic modulus variations exhibit consistent impacts on Tunnel 1 and 2 lining displacements-higher modulus correlates with reduced total displacement at equivalent angles

showing “W”-shaped profiles with inflection points at arch springings. Increased middle guide tunnel aspect ratio (toward “tall-narrow” geometry) elevates maximum principal stresses in both surrounding rock and lining. Symmetrical enlargement/reduction of adjacent cavern sizes while maintaining middle guide tunnel dimensions amplifies/reduces original cavern lining displacements

particularly in shared lining regions.