In recent years, many tunnel excavation projects are planned despite swelling ground conditions and/or great depths subjected to high ground pressure around the world. In such cases, there is a risk that the high ground pressure will exceed the loading capacity of the conventional rigid supports, leading to brittle failure. Accordingly, the authors have been developing new deformation-controlled supports that can reduce stress acting on steel supports, shotcrete, and rock bolts by gradually resisting high ground pressure while controlling tunnel deformation. Here, we report on a study of support specifications suitable for actual tunnel excavation, performed by developing the constitutive model of deformation-controlled supports and analyzing 3D tunnel excavation.
Deep excavation in squeezing ground presents many challenges in tunnel engineering and construction. Adverse geological conditions, such as high overburden pressure, extremely shallow tunnel cover, unsymmetrical earth pressure / anisotropic stress condition and large cross-section certainly add complexity to this matter. As such, the role of the deformation-controlled (DC) tunnelling supports, which absorb certain displacement while effectively supporting the tunnel, has become more crucial and beneficial to ensure the tunnel stability as the conventional rigid tunnelling support systems may not work effectively with such tunnelling difficulties. Prior to this work, relevant studies were undertaken mainly for individual tunnelling support component. However, a holistic and comprehensive study of the complete support mechanism is required for a deep understanding and better application of the DC supports. In this paper, three-dimensional numerical analyses were performed using the FLAC3D 6.01) to study the effect of the DC supports to the overall tunnelling support system under the static load condition. Code scripts implemented in fish and python languages were developed and used in conjunction with the FLAC3D 6.0 to parametrically evaluate the mechanical state of each component (i.e., rock bolts, steel support, shotcrete) of the tunnelling support system. The effective utilization of the DC supports has also been discussed with the aim of optimizing the support system performance.
