Failure Performance of 3DP Physical Twin-Tunnel Model and Corresponding Safety Factor Evaluation

Quantitative stability evaluation of multi-tunnel structure is an important issue related to the safety assessment and stable construction of geotechnical underground tunnels. In this work, the overall failure process of twin tunnels were exhibited by a physical simulation based on the 3D printing (3DP) sandstone analogues model, and a safety factor method was also presented for evaluating the general safety of multi-tunnel structure. For checking the 3DP material performance of physical model, uniaxial and triaxial compressions for the 3DP cylinder specimens were first tested and showed that their mechanical properties and failure characteristics were similar to natural rock in general. Then, the overloading tests for twin-tunnel model were carried out and have exposed the critical position of overall failure of twin-tunnel structure through visual observation and automatic measurement. Testing results and corresponding numerical back analysis indicated that the connectivity of plastic strain between tunnels can be deemed as the conservative instability criterion (i.e. yielding of material) and the inflection point of tunnels’ displacement can be deemed as overall failure criterion (i.e. structure failure) for twin-tunnel structure. The safety analysis for underground hydraulic caverns indicated that this method can provide a reference for quantitative and reasonable evaluation of the general safety of multi-tunnels or caverns and the local instability zone of surrounding rock.