The drilling and blasting method exerts a considerable impact on the surrounding rock, causing significant disturbance and vibration, which poses severe stability challenges in weak rock tunnels. To quantitatively evaluate the stability evolution under non-explosive construction compared to traditional methods, this study takes the New Shangjiagou Tunnel of the Xi'an-Yan'an High-speed Railway as a case study. Numerical simulations using LS-DYNA (for blasting dynamics) and FLAC3D (for excavation response) were combined with on-site acoustic wave measurements and deformation monitoring. The results indicate that the non-explosive construction method using a Boom-type tunnel roadheader offers superior stability. Specifically, it reduces the maximum deformation by 5.7 mm (27%) and the plastic zone area by 30% compared to the drilling and blasting method. Furthermore, the roadheader excavation induces a more uniform plastic zone distribution, whereas blasting increases the damage depth to the surrounding rock by approximately 0.5 to 0.7 m. The vertical deformation during roadheader excavation is primarily concentrated in the initial stage, followed by rapid stabilisation. These findings confirm that the Boom-type roadheader is a viable and superior alternative for tunnel construction in weak rock masses, providing a theoretical basis for optimising excavation methods in complex environments.
Thermal integrity profiling (TIP) has emerged as a powerful non-destructive method for evaluating cast-in-place concrete piles by monitoring heat of hydration (HoH) temperature profiles using temperature probes embedded in the piles. However, conventional TIP interpretation relies either on manual inspection of a series of temperature-depth profiles over time, which is inherently prone to subjective bias, or on back-analysis using simplified modelling approaches. This study presents, for the first time, a fully three-dimensional TIP framework combining finite element (FE) simulations with two deep neural networks (NN). A multi-label classifier detects up to three defects per pile, while a regressor quantifies defect volume, location, reinforcement-cage displacement and hydration parameters. A database with hydration temperature profiles from 19,445 simulations encompassing randomised pile lengths, soil stratigraphies, cage misalignments and multi-defect configurations is used to train the two NNs. The classifier achieves a per-defect accuracy of 93.6% (96.8% per sample). The regression model achieves near-perfect accuracy for cage displacement (R2 = 0.992) and defect volume (mean absolute error of 0.03 m3), and an adjusted R2 of 0.92 for defect location. This novel automated approach significantly enhances the objectivity, test speed and reliability of TIP-based defect detection across a wide range of deep pile foundations.
This paper investigates the dynamic response of saturated sand using a 1-g shake table to explore its dynamic properties under very low confining stresses (<5 kPa), which are useful for shallow soil sites. To overcome the limitations of the classic earth-pressure equations near flexible boundaries, a numerical framework is introduced to precisely calculate the depth-dependent confinement (K) within the test container. Based on this in-situ stress state, the study proposes a new relationship that links stiffness degradation of saturated sand to shear-strain amplitude and loading cycles. It also proposes a correction factor to predict strain-dependent excess pore water pressure at various confinement levels and loading cycles. These findings address the limitation of ignoring pore-pressure-induced loss of stiffness in saturated sand, offering a better approach to assessing strain-based liquefaction potential.
This study investigates the coupled effects of heat treatment, cryogenic thermal shock, chemical dissolution and thawing methods on the mechanical and physical properties of granite and marble in the context of enhanced geothermal reservoir stimulation. Samples were heat treated at 150 degrees C and 300 degrees C, cooled using liquid nitrogen (LN2), exposed to 3% hydrochloric (HCl), hydrofluoric (HF), oxalic and acetic acids and subsequently thawed using either room-temperature or microwave methods. Brazilian tensile tests were conducted, along with P-wave velocity, density and absorbed energy measurements to evaluate damage evolution. Results show that combined thermo-cryo-chemical treatment significantly weakens the rocks. Peak fracture load decreased by up to 43% for granite and 57.6% for marble, with maximum weakening observed at 300 degrees C under HCl treatment with microwave thawing. Damage factors reached 0.43 for granite and 0.58 for marble. Among the acids, HCl produced the strongest weakening effect, followed by HF, oxalic and acetic acids. Marble exhibited higher sensitivity due to its carbonate-rich composition. Numerical simulations using COMSOL Multiphysics showed strong posterior agreement with experimental results (deviations <2.3%) and successfully captured stiffness degradation, peak load reduction and thermal-stress evolution. The model provides insight into microcrack initiation and propagation under coupled thermo-cryo-chemical processes.
Bio-stabilisation with plant roots offers a sustainable solution in geotechnical engineering, yet accurately modelling the mechanical behaviour of these composites remains a challenge. This study evaluates the performance of four gradient boosting algorithms - CatBoost, XGBoost, LightGBM and GradientBoosting - for predicting the stress-strain response of unsaturated clayey silt reinforced with Nandina domestica roots. A comprehensive dataset was generated from direct shear tests conducted under varying moisture content (W), root weight density (RWD), depth and normal stress (NS). Using a 70/30 training-testing split, all four models showed robust generalisation in 5-fold cross-validation (mean R2 = 0.90-0.92). On the held-out test data, the models yielded exceptional accuracy. GradientBoosting was the top-performing model with a coefficient of determination (R2) of 0.998, a root mean square error (RMSE) of 0.64 kPa and a mean absolute error (MAE) of 0.43 kPa. The remaining models also performed strongly, with R2values from 0.996 to 0.997. These results validate the capacity of boosting algorithms to capture the complex, non-linear behaviour of root-soil systems, positioning them as powerful and efficient tools for geotechnical analysis and design.
The presence of flaws in naturally occurring rock masses is one of the major factors contributing to its strength and failure behaviour. The present study focuses on analysing the failure mechanisms associated with different types of flaws (open and closed) and their orientations. In this paper, the behaviour of open and closed flaws in artificial rock specimens (gypsum) of different strengths under uniaxial loading is investigated. Experimentally, the critical flaw angle corresponding to the minimum peak strength is identified, and the final failure crack patterns emerging from the pre-existing flaws are examined. Numerically, the Particle Flow Code (PFC) is employed to study microcrack development using a calibrated flat-jointed bonded-particle model. The calibrated models for the various gypsum strengths successfully reproduce the maximum and minimum peak strengths, as well as the final failure patterns, for most cases. Experimental stress analysis indicates that a 45 degrees closed flaw for high-strength gypsum is more critical than a 45 degrees open flaw. This behaviour is further investigated numerically by analysing the sliding behaviour along the closed flaw through tracking the displacement of rigid particles surrounding the flaw.
Active fault oblique dislocation, involving coupled strike-slip and dip-slip motions, generates complex deformation patterns that threaten tunnel - track systems. Polyurethane-stabilised ballast beds (PSB), combining the stability of ballastless tracks with the deformation adaptability of ballasted tracks, are a promising solution for fault-crossing tunnels. A three-dimensional model is developed in ABAQUS and calibrated using a segmental articulated tunnel to evaluate the effects of dislocation magnitudes, fault zone width and fault dip angle on track irregularities and stress distribution. Comparisons between monolithic and segmental tunnel responses are conducted. The results indicate that: 1) Track irregularities are mainly concentrated near the fracture plane. Profile irregularity increases nearly linearly with vertical dislocation, while alignment and cross-level irregularities grow linearly with lateral dislocation; gauge variation remains negligible. 2) Wider fault zones significantly attenuate profile and alignment irregularities, and steeper fault dip angles further reduce profile irregularity. 3) Although segmental tunnels effectively mitigate structural plastic damage, they amplify local rail profile and alignment irregularities and increase sleeper stress. Thus, while segmental designs protect the tunnel structure, the track system requires reinforcement or specialised design to control local geometric distortions. These findings provide guidance for the seismic design and maintenance of railway tunnels in active fault regions.
Cement-stabilised soils are widely employed in sustainable geotechnical systems; however, their long-term durability under realistic cyclic environmental actions remains insufficiently quantified. Coupled wetting - drying and loading - unloading cycles activate concurrent fatigue-driven bond degradation and moisture-induced healing, generating nonlinear durability trajectories that classical deterioration formulations fail to capture. This study investigates these competing mechanisms and introduces a mechanistically informed fatigue - healing evolution framework that explicitly accounts for cumulative damage and progressively decaying healing. A controlled experimental program was conducted on silty sand mixtures with and without supplementary cementitious materials (SCMs), subjected to 30 coupled hydro-mechanical cycles. Results reveal rapid early-stage degradation of stiffness and strength, followed by a transition towards a fatigue - healing equilibrium regime. SCM-amended specimens exhibit measurable recovery pulses of approximately 6-12% during environmental cycling, indicating enhanced healing capacity. The proposed evolution framework integrates fatigue kinetics with diminishing healing potential using four physically interpretable parameters and achieves high predictive accuracy up to N = 100 cycles (R-2 > 0.97). Requiring only engineering-scale inputs, the framework enables durability forecasting and binder optimisation. By treating cemented soils as cyclically reactive geomaterials rather than monotonically degrading materials, this study provides a solid basis for resilience-oriented performance assessment under environmental cyclic loading.
The study provides a generalised approach for the estimation of earth pressure forces on the excavation support system using a diaphragm wall, taking into consideration the presence of a cavity in the retained ground as well as load transferred to the supporting wall due to the self-weight of the buried pipe or utility tunnel, as well as the overburden load of the soil. The theoretical perspective of the proposed solution is based on Rankine's earth pressure theory and Spangler's solution, based on Modified Boussinesq's approach. A parametric study is then performed, taking into account different buried pipe or utility tunnel diameters located very near the 15 m deep excavation support system in the upper, middle, or lower zone. Numerical analysis using STAADPro is involved to estimate the deformation as well as the shear and bending moment in the diaphragm wall by assuming its cantilever action, and the results are presented to analyse and discuss the influence of the presence of a buried pipe or utility tunnel very near the deep excavation support system using a diaphragm wall.
This study develops a bidirectional dynamic seepage-stress-damage coupling model using FLAC3D to elucidate the hydro-mechanical coupling mechanisms of permeable linings in water diversion tunnels under high internal water pressure. Utilizing continuum damage mechanics and equivalent tensile and plastic strains, it governs damage evolution, integrating a dynamic feedback mechanism where permeability and mechanical parameters degrade alongside damage.Results show that post-construction, the lining remains undamaged under compression. During the pressurisation stage, exceeding a critical internal water pressure initiates micro-cracks. Increased pressure propagates these into macroscopic fractures, raising local reinforcement stress and permeability, ultimately causing lining-rock interfacial debonding. Post-failure, rapid seepage transfers the water load to the surrounding rock mass, which becomes the primary load-bearing component and undergoes further damage.The model effectively captures the 'seepage-damage' positive feedback mechanism and water pressure transfer characteristics. Because damage and radial displacement peak at the tunnel invert, targeted grouting and reinforcement there during construction are recommended for overall structural safety.
Rock bursts pose a significant challenge in deep hard rock tunnel engineering. This study investigates the energy evolution during rock failure through uniaxial upper-limit loading and unloading tests, establishing a connection between rock energy storage characteristics and rock burst tendency. True triaxial loading tests on tunnel models are employed to analyse the relationship between stress paths, rock stress magnitude, and rock bursts. By integrating the rock's energy storage properties and the stress conditions within the rock mass, a new evaluation index, Stress and Energy Storage Density (SESD), is proposed to assess the rock burst tendency. A case study on rock burst during double-shield TBM excavation reveals that the disaster incubation process progresses in six stages: elastic state, crack initiation, crack propagation, fragment ejection, slab fracture buckling, and unstable failure. The SESD index incorporates both rock strength and energy dynamics, capturing the stress state during excavation and the associated energy accumulation-release process in surrounding rock. Numerical results show that SESD variations closely match actual rock burst occurrences, validating their effectiveness in simulation-based analysis. This study introduces a novel energy-stress coupled method for rock burst prediction, offering clear modelling principles, practical applicability, and robust adaptability for complex engineering scenarios.
The stabilisation of problematic soils using sustainable binders has attracted increasing attention due to environmental concerns associated with conventional cement-based methods. This study investigates the mechanical performance, microstructural characteristics, and durability of a novel Fe-Si geopolymer system developed using iron-rich tailings and recycled glass powder for soil stabilisation. A series of mixtures with varying tailings content, glass powder dosage, and hydrogen peroxide (H2O2) levels were prepared and evaluated. Unconfined compressive strength (UCS) tests were conducted at curing periods of 28 and 90 days to assess strength development. The results indicate that the optimised mixture (FT40-G10-H3) exhibited the highest strength and structural integrity,demonstrating the governing role of Fe-Si interactions in strength development. Microstructural analyses confirmed the development of a dense Fe-Si-Al geopolymeric network with a refined mesoporous structure, leading to enhanced load-bearing capacity. Wet-dry cycling demonstrated superior durability, with higher strength retention and markedly lower mass loss than ordinary Portland cement (OPC) stabilisation. Taguchi and ANOVA analyses identified tailings content and glass powder dosage as the primary parameters governing strength performance. The strong correlation between electrical resistivity and compressive strength provides a reliable basis for non-destructive strength estimation.
Slope failures are a significant concern in geotechnical engineering, often resulting in catastrophic consequences for infrastructure and human safety. Real-time monitoring and early warning systems are critical to mitigating these risks. This research focuses on the development of a Smart Wired Module (SWM) designed for real-time slope failure tracking. The proposed system integrates soil moisture, vibration, accelerometer, force-sensitive resistor and temperature sensors, wired communication technologies, and data analytics to provide accurate and timely information on slope stability. Design and develop a SWM will help to monitor the present condition of the soil slope, which will ultimately help to take the preventive measures to avoid slope failure. It will help to improve the efficiency of real-time data analysis for slope failure monitoring systems. The study reveals an inverse relationship between water flow rate and the time to detect variations: at 0.023 L/s, changes appeared in 280 s; at 0.05 L/s, in 148 s; at 0.027 L/s, in 210 s; and at 0.067 L/s, in just 84 s. This demonstrates that higher discharge rates result in shorter detection times.
Cement sheath fracture is a critical integrity concern in CO2 injection wells under cyclic thermal and pressure loading. This study presents a coupled transient thermal-static structural finite element model of a CO2 injection well with a pre-existing semi-elliptical fracture in the cement sheath, applied to the Waseca Formation in Lloydminster, Saskatchewan. Fractures aligned with the minimum horizontal stress produced the highest Mode I stress intensity factor (approximate to 0.096 MPa center dot root m), about 90% below the cement fracture toughness (1 MPa center dot root m), indicating unstable fracture propagation is unlikely under the investigated conditions. Sensitivity analyses show that increasing Young's modulus from 5 to 25 GPa raises K-I by similar to 1289%, while increasing Poisson's ratio from 0.20 to 0.40 raises it by similar to 45%, suggesting that moderately stiff cement may be optimal for minimising crack-tip driving forces under the investigated conditions. Injection temperature has the strongest influence, with KI decreasing from 0.17 MPa root m at-20 degrees C to near zero at +20 degrees C, consistent with crack-face closure as the thermal differential decreases. In contrast, injection pressure (4.0-5.5 MPa) changes K-I by less than 0.3%. No plastic strain accumulated after five 30-day injection-shut-in cycles. A normalised risk classification is proposed for the Waseca formation to guide cement design and fracture monitoring.
The compressional behaviour of backfill soils is critical for assessing the stability of reclaimed ground. This study investigates the influence of fine particle content on the compressibility of mixed granular fill materials. A series of tests were conducted using a self-developed lateral confinement device, systematically evaluating the compression characteristics of mixed fills with fine contents. The results indicate that the compressibility of the mixed fill increases with higher fine particle content. During compression, the compressive modulus of mixtures with varying fine contents exhibits a three-stage evolution - hardening, softening and re-hardening - directly mirroring the micro-scale process of force chain restructuring, collapse and reformation within the fill. Fines act as a 'lubricant', reducing the stability of the coarse skeleton, with the most pronounced impact occurring during the softening stage. At 35% fine content, the compressive modulus dropped by more than 70 MPa in this stage. Furthermore, the lateral pressure coefficient exhibits a nonlinear decay with increasing vertical stress. The lateral pressure coefficient increases with fines content, leading to differences of up to 0.1 under identical stress conditions across mixtures with different fines contents. These findings provide direct guidance for the design and stability evaluation of backfill structures.
