Layered rock masses are common geological formations due to which numerous engineering activities typically confront stratified rock masses. The analysis of tunnel stability issues typically assumes a single homogeneous rock mass. However, the majority of rock tunnel projects are excavated in stratified rock formations. This study introduces a two-dimensional (2D) plane strain model for predicting the stability of a rock tunnel subjected to surcharge along the horizontal surface in the presence of rock stratification. The stability of unlined circular tunnel in layered rock mass is examined using lower bound finite element limit analysis (LB-FELA) to obtain the numerical solutions in parametric form while adhering to the Hoek-Brown (HB) failure criterion. The effects of material constant, geological strength index, layer thickness to diameter ratio, relative thickness between upper and lower layer, and relative strength ratio between top and bottom layer are thoroughly studied through extensive parametric research. The results of the study indicate that the arrangement order of the weak and strong rock layers, the size of the tunnel's diameter, and the thickness of the rock layer all play a significant role in determining the stability of the tunnel. It is important to note that the stability of the tunnel is significantly influenced by alterations in the parameters of the lower layer of rock in which the excavation of tunnel is done, as opposed to modifications in the parameters of the upper layer. Moreover, the geological strength index is found to be the most sensitive parameter out of the group of input parameters considered. The results will provide the field practitioners with a rational approach for dealing with practical aspects of tunnel subjected to surcharge at the ground surface when the rock mass stratification is present.

Artificial ground freezing is employed for temporary ground improvement in tunneling. Ground freezing is commonly used to stabilize the ground before the excavation of cross passages in tunneling. During the construction of the cross passages, the frozen ground is excavated, and the tunnel is supported immediately by shotcrete shells. In this contribution, we present a novel computational framework for the modeling of the interaction of frozen ground and shotcrete during cross-passage construction. The computational framework consists of a three-phase (soil, water, ice crystals) thermo-hygro-mechanical finite element model for the modeling of soil freezing based on [1] and a four-phase (soil, water, air, ice crystals) thermo-mechanical finite element model for partially saturated shotcrete that considers freezing. This framework considers the evolution of the stiffness, strength, and creep properties and the hysteresis effects during freezing-thawing of the ground in conjunction with the shotcrete hydration and creep properties dependent on the hydration degree based on [2]. Finally, we present a numerical case study of the construction of cross passages which is modeled in two stages: the first stage involves the modeling of an artificial ground freezing phase and the second stage involves the tunnel excavation, the shotcrete installation with its internal hydration heat generation and the evolution of the hydration dependent primary creep deformations.

[1] Zhou, M. and Meschke, G., A three-phase thermo-hydro-mechanical finite element model

for freezing soils. Int. J. Numer. Anal. Meth. Geomech. (2013) 37: 3173-3193.

[2] Gamnitzer, Peter, Andreas Brugger, Martin Drexel, and Günter Hofstetter. 2019. "Modelling of Coupled Shrinkage and Creep in Multiphase Formulations for Hardening Concrete" Materials 12, no. 11: 1745. https://doi.org/10.3390/ma12111745

Shield tunnels, as a type of prefabricated assembly structures, have shown their susceptibility to excessive deformation over time due to earth pressure, posing a growing challenge to ensuring the safety and reliability of tunnel structures. Therefore, it is crucial to monitor the structural deformation of subway tunnels to assess their reliability and guide their maintenance. Advanced technologies, such as laser scanning for precise point clouds and close-range photogrammetry for high-definition imaging of internal tunnel surfaces, are currently being employed to obtain essential operation and maintenance data. However, the deformation status of a shield tunnel is complex in practice, including the rigid body displacement of joints and the deformation of concrete segments. Therefore, simple convergence deformation cannot fully represent a tunnel’s service condition. While the circumferential joints can be identified from images via computer vision techniques, the identification accuracy of longitudinal joints within a single ring is low, making it difficult to accurately separate the point cloud of each segment. Additionally, there is a lack of methods for calculating the deformation of concrete segments using point clouds. To address this issue, this study proposes a deep learning-based method for detecting segment joints and calculating segment deformation by respectively leveraging imagery and point clouds. Incorporating model matching mechanism, a deep neural network based on the encoder-decoder architecture is constructed, with the hybrid information of images and point clouds as inputs, and the joint dislocation and segment deformation as outputs. Compared to traditional methods, the proposed method improves segmentation accuracy through enhanced feature extraction based on both intensity and depth information. Additionally, through accurate point cloud segmentation and model matching algorithms, the deformation of segment concrete can be obtained, which can be further applied in the maintenance of real-world shield tunnels.

In order to describe the rheological behavior of squeezing rock surrounding tunnels, the CVISC viscoelastic plastic model is adopted. It consists of the Burgers model and the M-C plastic body in series. The radial displacement of the squeezing rock is divided into instantaneous elastic-plastic and viscoelastic displacement, because of the independence of the viscoelastic and elastic-plastic components of the CVISC model. On this basis, the analytical solutions for the plastic and viscoelastic radial displacements are derived, respectively. Then the obtained solutions are superimposed, resulting the complete close-form solutions for the displacements of the surrounding rock. They allow for analyzing the evolution of the radial displacements and stresses of the surrounding rock over time. With the help of numerical simulations based on FLAC3D and the theoretical solutions obtained from open literature, the reliability of the derived solutions is demonstrated. Parametric studies of the derived solutions with emphasize on long-term deformation of surrounding rock in squeezing ground are carried out. The results show that the three most critical parameters are internal friction angle, cohesion, and Young′s modulus of rock. This inspires us to propose a concept of pre-structure which has much higher internal friction angle, cohesion, and Young′s modulus than the rock. This concept means support structure is constructed prior to the excavation of tunnels. Followed numerical solutions provide evidence that such a concept is beneficial in terms of reducing the deformation of surrounding rock in squeezing rock.