Timely Constructed and Enhanced Lining for Managing Extensive Deformations of Tunnel in Coal Stratum: A Case Study

The Sanlian Tunnel case study exemplifies that even after implementing the initial support within the coal stratum, the surrounding rocks exhibited ongoing deformation devoid of stabilization indications. Addressing this issue calls for innovative control technologies that mitigate extensive deformations and redefine safe and sustainable coal stratum tunnel construction.

The field experiment was adopted to select the appropriate technical measures to control extensive deformations. Three experiment schemes were developed and applied to the construction. Scheme One was the enhanced initial support structure, and Scheme Two was the combined use of enhanced initial support structure, lengthened sidewall anchor rods and added steel pipe piles. Scheme Three was the “timely constructed and enhanced lining structure” proposed on the basis of Scheme Two, and the secondary lining was applied if the horizontal displacement exceeded 450mm. Then, field observations of displacements and stresses were implemented to evaluate the effectiveness of different experimental schemes in controlling extensive deformations.

Scheme One and Two cannot control extensive deformations effectively, as the displacement of the initial support continued to increase with no sign of stabilization. Regarding Scheme Three, structural deformation progressively attained a state of stability around 80 days subsequent to the secondary lining construction. Additionally, the stress within the support structure remains stable below the permissible threshold, affirming the secure condition.

Emanating from the field monitoring results, it is evident that the suggested “timely constructed and enhanced lining structure” scheme control technology holds substantial promise for practical implementation in engineering scenarios.