Research on topology optimization and case application of power tunnel structure based on variable density method

Optimizing the structural cross-sections of power tunnels based on variations in geological strata and burial depths of the power tunnels is essential for their long-term operational safety and maintenance. In this study, the topology optimization theory and finite element methods were applied to derive volume constraints for power tunnels using a straight-wall arch tunnel as an example. Consequently, a topology optimization model for power tunnel structures was established, and the structural characteristics of power tunnels were optimized and analyzed under varying burial depths and elastic moduli using the variable density method. The results indicate that the overall profile of the optimized power tunnel transforms from a straight-wall arch to a multi-centered circle. With the increase in the elastic modulus of the surrounding strata, the internal net height and height-to-span ratio of the tunnel generally show an increasing trend, while the external wall span, vault thickness, invert arch thickness, side wall thickness, and upper arch curvature generally show a decreasing trend. Compared to the elastic modulus of the strata, the burial depth has a relatively smaller impact on the structural profile of the power tunnel. Therefore, when conducting related designs for power tunnels, more emphasis should be placed on understanding the geological conditions of the strata. Subsequently, using the design principles of topology optimization, the power tunnel structure was optimized and a two-dimensional model was developed, incorporating stratigraphic characteristics of the power tunnels. Changes in the bending moment, axial force, safety factor, and other indicators were compared before and after optimization. The results demonstrated that the overall safety performance of the power tunnel lining structure improved notably after optimization, verifying the feasibility of applying topology optimization to power tunnels. These research findings provide valuable reference data for the optimization of power tunnel engineering designs.