The deterioration of soft rocks caused by freeze-thaw (F-T) climatic cycles results in huge structural and financial loss for foundation systems placed on soft rocks prone to F-T actions. In this study, cementtreated sand (CTS) and natural soft shale were subjected to unconfined compression and splitting tensile strength tests for evaluation of unconfined compressive strength (UCS, qu), initial small-strain Young's modulus (Eo) using linear displacement transducers (LDT) up to a small strain of 0.001%, and secant elastic modulus (E50) using linear variable differential transducers (LVDTs) up to a large strain of 6% before and after reproduced laboratory weathering (RLW) cycles (-20 degrees C-110 degrees C). The results showed that eight F-T cycles caused a reduction in qu, E50 and Eo, which was 8.6, 15.1, and 14.5 times for the CTS, and 2.2, 3.5, and 5.3 times for the natural shale, respectively. The tensile strength of the CTS and natural rock samples exhibited a degradation of 5.4 times (after the 8th RLW cycle) and 2.7 times (after the 15th RLW cycle), respectively. Novel correlations have been developed to predict Eo (response) from the parameters quand E50 (predictors) using MATLAB software's curve fitter. The findings of this study will assist in the design of foundations in soft rocks subjected to freezing and thawing. The analysis of variance (ANOVA) indicated 95% confidence in data health for the design of retaining walls, building foundations, excavation in soft rock, large-diameter borehole stability, and transportation tunnels in rocks for an operational strain range of 0.1%-0.01% (using LVDT) and a reference strain of less than 0.001% (using LDT). (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

Polyurethane foam, when used as a compressible layer in deep soft rock tunnels, offers a feasible solution to reduce the support pressure on the secondary lining. The foam spraying method using sprayed polyurethane material is convenient for engineering applications; however, the compressive behaviour and feasibility of sprayed polyurethane material as a compressible layer remain unclear. To address this gap, this study conducts uniaxial compression tests and scanning electron microscope (SEM) tests to investigate the compressive behaviour of the rigid foams fabricated from a self-developed polyurethane spray material. A peridynamics model for the composite lining with a polyurethane compressible layer is then established. After validating the proposed method by comparison with two tests, a parametric study is carried out to investigate the damage evolution of the composite lining with a polyurethane compressible layer under various combinations of large deformations and compressible layer parameters. The results indicate that the polyurethane compressible layer effectively reduces the radial deformation and damage index of the secondary lining while increasing the damage susceptibility of the primary lining. The thickness of the polyurethane compressible layer significantly influences the prevention effect of large deformation-induced damage to the secondary lining within the density range of 50-100 kg/m3. In accordance with the experimental and simulation results, a simple, yet reasonable and convenient approach for determining the key parameters of the polyurethane compressible layer is proposed, along with a classification scheme for the parameters of the polyurethane compressible layer. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

A novel discrete element method (DEM) model is proposed to better reproduce the behaviour of porous soft rocks. With the final goal of simulating pile penetration problems efficiency and scalability are two underlining features. The contact model is based on the macro-element theory and employs damage laws to govern the plastic deformations developing at the microscale. To attain (i) high porosity states, (ii) represent irregular shaped grains and (iii) incorporate the physical presence of bond fragments, the model is cast within a far-field interaction framework allowing for non-overlapping particles to transmit forces. After presenting a calibration procedure, the model is used to replicate the behaviour of Maastricht calcarenite. In particular, the mechanical response of this calcarenite is explored within the critical state theory framework. Finally, the efficiency, performance and scalability of the model is tested by simulating physical model experiments of cone-ended penetration tests in Maastricht calcarenite from the literature. To boost efficiency of the 3D numerical simulations, a coupled DEM-FDM (Finite Differential Method) framework is used. The good fit between the experimental and numerical results suggest that the new model can be used to unveil microscopic mechanism controlling the macroscopic response of soft-rock/structure interaction problems.

This study presents a fully coupled thermo-hydro-mechanical (THM) constitutive model for clay rocks. The model is formulated within the elastic-viscoplasticity framework, which considers nonlinearity and softening after peak strength, anisotropy of stiffness and strength, as well as permeability variation due to damage. In addition, the mechanical properties are coupled with thermal phenomena and accumulated plastic strains. The adopted nonlocal and viscoplastic approaches enhance numerical efficiency and provide the possibility to simulate localization phenomena. The model is validated against experimental data from laboratory tests conducted on Callovo-Oxfordian (COx) claystone samples that are initially unsaturated and under suction. The tests include a thermal phase where the COx specimens are subjected to different temperature increases. A good agreement with experimental data is obtained. In addition, parametric analyses are carried out to investigate the influence of the hydraulic boundary conditions (B.C.) and post-failure behavior models on the THM behavior evolution. It is shown that different drainage conditions affect the thermally induced pore pressures that, in turn, influence the onset of softening. The constitutive model presented constitutes a promising approach for simulating the most important features of the THM behavior of clay rocks. It is a tool with a high potential for application to several relevant case studies, such as thermal fracturing analysis of nuclear waste disposal systems. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Due to their distinct geotechnical and structural features, soft rock tunnels pose serious issues because of their seismic sensitivity. These tunnels, often constructed in formations with lower shear strength and higher deformability, are particularly susceptible to damage during earthquakes. Fragility curves, which graphically represent the probability that a structure may sustain damage up to or beyond a particular threshold as a function of seismic intensity, are essential tools for evaluating the seismic resilience of these infrastructures. This research looks closely at the use of fragility curves to assess the seismic vulnerability of soft rock tunnels. Exploring the fundamental concepts and methodologies involved in constructing fragility curves, including seismic hazard analysis, structural modeling, damage state definition, data collection and statistical analysis is looked at first. The review highlighted the integration of soft rock characteristics such as strength and deformation properties into the fragility assessment process. Key developments in the topic are covered such as how machine learning and Bayesian inference might improve the precision and usefulness of fragility curves. The paper identified key findings such as the high sensitivity of fragility curves to geotechnical properties and seismic intensity levels and emphasized the importance of accurate data collection and model calibration. Important gaps in seismic risk evaluations are filled by integrating cutting-edge methodologies, such as Bayesian inference and real-time machine learning models that clarify the seismic behaviour of soft rock tunnels in the real world. For the purpose of strengthening earthquake-resistant infrastructure in earthquake-prone areas, engineers, scholars and policymakers are given practical insights.

Surrounding rock deterioration and large deformation have always been a significant difficulty in designing and constructing tunnels in soft rock. The key lies in real-time perception and quantitative assessment of the damaged area around the tunnel. An in situ microseismic (MS) monitoring system is established in the plateau soft tock tunnel. This technique facilitates spatiotemporal monitoring of the rock mass's fracturing expansion and squeezing deformation, which agree well with field convergence deformation results. The formation mechanisms of progressive failure evolution of soft rock tunnels were discussed and analyzed with MS data and numerical results. The results demonstrate that: (1) Localized stress concentration and layered rock result in significant asymmetry in micro-fractures propagation in the tunnel radial section. As excavation continues, the fracture extension area extends into the deep surrounding rockmass on the east side affected by the weak bedding; (2) Tunnel excavation and longterm deformation can induce tensile shear action on the rock mass, vertical tension fractures (account for 45%) exist in deep rockmass, which play a crucial role in controlling the macroscopic failure of surrounding rock; and (3) Based on the radiated MS energy, a three-dimensional model was created to visualize the damage zone of the tunnel surrounding rock. The model depicted varying degrees of damage, and three high damage zones were identified. Generally, the depth of high damage zone ranged from 4 m to 12 m. This study may be a valuable reference for the warning and controlling of large deformations in similar projects. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

This study undertakes a comprehensive examination of the characteristics of the argillaceous, hard soil/soft rock (HSSR) lithology of the Unterangerberg formation in Tyrol, Austria, focusing on its swelling properties and anisotropic material behavior. The objective is to achieve an extensive material characterization to be able to calibrate material models accurately. This is to be achieved by means of an in-situ test campaign within the Angath adit tunnel construction site and accompanying laboratory tests. The geotechnical monitoring concept in a designated test gallery includes a chain inclinometer, extensometers, geodetic targets, shotcrete strain meters, photogrammetric observations, and a long-term irrigation test field, with a of the invert left exposed intentionally. The in-situ tests yield valuable insights into the intricate behavior of the HSSR lithology, offering a comprehensive description of material variability, and recommendations for characterization. Results indicate that despite the high swellable clay mineral content, significant swelling occurred only to a small extent during the observation period to date. The study concludes that the in-situ behavior of such formations significantly contributes to a better understanding of their characteristics, leading to a substantial reduction in critical load cases for future planning phases.

The polyurethane foam (PU) compressible layer is a viable solution to the problem of damage to the secondary lining in squeezing tunnels. Nevertheless, the mechanical behaviour of the multi-layer yielding supports has not been thoroughly investigated. To fill this gap, large-scale model tests were conducted in this study. The synergistic load-bearing mechanics were analyzed using the convergenceconfinement method. Two types of multi-layer yielding supports with different thicknesses (2.5 cm, 3.75 cm and 5 cm) of PU compressible layers were investigated respectively. Digital image correlation (DIC) analysis and acoustic emission (AE) techniques were used for detecting the deformation fields and damage evolution of the multi-layer yielding supports in real-time. Results indicated that the loaddisplacement relationship of the multi-layer yielding supports could be divided into the crack initiation, crack propagation, strain-hardening, and failure stages. Compared with those of the stiff support, the toughness, deformability and ultimate load of the yielding supports were increased by an average of 225%, 61% and 32%, respectively. Additionally, the PU compressible layer is positioned between two primary linings to allow the yielding support to have greater mechanical properties. The analysis of the synergistic bearing effect suggested that the thickness of PU compressible layer and its location significantly affect the mechanical properties of the yielding supports. The use of yielding supports with a compressible layer positioned between the primary and secondary linings is recommended to mitigate the effects of high geo-stress in squeezing tunnels. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The plastic flow behavior of soft rock exhibits non-coaxial features under complex stress paths, while traditional plasticity theories are ill-equipped to adequately represent this, which leads to the mechanism of soft rock failure still unclear. To investigate the evolution law of strain increments and non-coaxial characteristics of weakly cemented soft rock, the directional shear tests are conducted using the hollow cylinder apparatus (HCA). The results show that non-coaxiality does not occur when alpha is distinct from 0 degrees or 90 degrees. The oscillation of the non-coaxial angle is significantly more variable in soft rock experiencing combined tension-torsion (45 degrees < alpha < 90 degrees), as opposed to those under the influence of combined compression-torsion (0 degrees < alpha < 45 degrees). The non-coaxiality swiftly dissipates when the sample is approaching the failure state. The stress rate is decomposed into stress magnitude and direction to describe non-coaxial features of plastic strain. And a new method for non-coaxial stress rate is proposed which can express the plastic strain increment directions. The spherical interpolation coefficient method is utilized to describe the continuous change in non-coaxial plastic flow direction between tangential and normal directions of the yield surface. The non-coaxial parameter (Delta) is introduced to quantify the non-coaxial characteristics of soft rock and its validity is confirmed through test results. This method effectively captures the principal stress direction influence on non-coaxial behavior of soft rock and have significance for rock mechanics.

Micron-scale crack propagation in red-bed soft rocks under hydraulic action is a common cause of engineering disasters due to damage to the hard rock-soft rock-water interface. Previous studies have not provided a theoretical analysis of the length, inclination angle, and propagation angle of micron-scale cracks, nor have they established appropriate criteria to describe the crack propagation process. The propagation mechanism of micron-scale cracks in red-bed soft rocks under hydraulic action is not yet fully understood, which makes it challenging to prevent engineering disasters in these types of rocks. To address this issue, we have used the existing generalized maximum tangential stress (GMTS) and generalized maximum energy release rate (GMERR) criteria as the basis and introduced parameters related to micron-scale crack propagation and water action. The GMTS and GMERR criteria for micron-scale crack propagation in red-bed soft rocks under hydraulic action (abbreviated as the Wmic-GMTS and Wmic-GMERR criteria, respectively) were established to evaluate micron-scale crack propagation in red-bed soft rocks under hydraulic action. The influence of the parameters was also described. The process of micron-scale crack propagation under hydraulic action was monitored using uniaxial compression tests (UCTs) based on digital image correlation (DIC) technology. The study analyzed the length, propagation and inclination angles, and mechanical parameters of micron-scale crack propagation to confirm the reliability of the established criteria. The findings suggest that the Wmic-GMTS and Wmic-GMERR criteria are effective in describing the micron-scale crack propagation in red-bed soft rocks under hydraulic action. This study discusses the mechanism of micron-scale crack propagation and its effect on engineering disasters under hydraulic action. It covers topics such as the internal-external weakening of nano-scale particles, lateral propagation of micron-scale cracks, weakening of the mechanical properties of millimeter-scale soft rocks, and resulting interface damage at the engineering scale. The study provides a theoretical basis for the mechanism of disasters in red-bed soft-rock engineering under hydraulic action. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V.