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Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies

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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "AI-Enabled Process Engineering".

Deadline for manuscript submissions: closed (31 October 2025) | Viewed by 8249

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Special Issue Editors

Dr. Yaoyao Meng

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Guest Editor

State Key Laboratory of Digital and Intelligent Technology for Unmanned Coal Mining, Anhui University of Science and Technology, Huainan 232001, China
Interests: disaster mechanism of deep underground engineering; deep rock mass mechanics based on 3D printing; rock mechanics and underground engineering

Prof. Dr. Tengfei Guo

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Guest Editor

School of Resources Environment and Safety Engineering, University of South China, Hengyang 421001, China
Interests: rock mechanics and engineering in deep, constitutive of rock, soil, and concrete-based materials; rock blasting and rock-burst; numerical simulation for dynamic problems; structural dynamic response

Dr. Jianyou Lu

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Guest Editor

College of Civil Engineering and Architecture, China Three Gorges University, Yichang 443002, China
Interests: rock dynamics; rock–concrete interface

Dr. Junyu Sun

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Guest Editor Assistant

School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China
Interests: nondestructive testing; pavement maintenance and rehabilitation; geophysical detection

Dr. Linli Yu

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Guest Editor Assistant

State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, China
Interests: coal gangue; concrete; composite structure; durability

Special Issue Information

Dear Colleagues,

We are thrilled to unveil our upcoming Special Issue, “Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies". In this era of the rapid advancement of modern engineering, rock and concrete materials are foundational to numerous sectors, including geological engineering, deep resource exploration, infrastructure development, and energy storage. A profound comprehension of their properties and behaviors, coupled with innovative research methodologies, is crucial for driving sustainable development and technological innovation in these industries.

Recently, the fields associated with rock and concrete materials have encountered increasingly challenging environments and complex conditions. The swift progression of digital technologies like big data, cloud computing, and artificial intelligence has made intelligence, informatization, and digitalization the inevitable trajectory for the future. As a pivotal national science and technology strategy, the intelligent enhancement of engineering rock and concrete materials is imperative. This Special Issue aims to compile the latest research achievements, innovative methods, and visionary insights from across the globe, establishing a robust and authoritative platform for academic discourse among researchers, engineers, and scholars.

We invite submissions of original research articles and reviews. Potential research areas include, but are not limited to, the following:

Innovative monitoring equipment and techniques for multidimensional information acquisition of rock and concrete materials.
Efficient and precise machine learning methods for data analysis in rock and concrete engineering.
Novel experimental and monitoring approaches for rock and concrete materials under multi-field coupling conditions.
State-of-the-art artificial intelligence technologies for intelligent inversion of material parameters, rapid prediction of mechanical behavior, and optimal design of complex engineering systems.

We eagerly anticipate your contributions.

Dr. Yaoyao Meng
Prof. Dr. Tengfei Guo
Dr. Jianyou Lu
Guest Editors

Dr. Junyu Sun
Dr. Linli Yu
Guest Editor Assistants

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

complex engineering systems
advanced digital and intelligent technologies
rock and concrete materials
challenging environments
microscopic failure mechanism

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Published Papers (13 papers)

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Research

17 pages, 8700 KB

Open AccessArticle

Experimental Investigation on Fracture Behaviors of Straight-Wall Tunnels with Defects of Insufficient Lining Thickness

by Wei Han, Xuze Du, Yihan Du, Jiapeng Yue, Bo Huang and Hui Liu

Processes 2025, 13(12), 3909; https://doi.org/10.3390/pr13123909 - 3 Dec 2025

Viewed by 207

Abstract

Fractures in straight-wall linings is a common disease that seriously affects the integrity and service life of tunnels. The presence of insufficient lining thickness can be regarded as one of the most important factors causing fractures. In this study, the fracture behaviors of straight-wall tunnels with insufficient lining thickness under progressive compressive loading were investigated. First, the fracture characteristics and failure mode were explored. Subsequently, the deformation behaviors were investigated by digital image correlation (DIC) technology. Finally, the fracture pattern was systematically discussed. The results show that the deformation intensifies in the areas with insufficient lining thickness, which is prone to induce cracks. As the ratio or range of insufficient thickness increases, the severity of fractures intensifies and the failure mode tends to be more complex. In addition, whether the lining comes into contact with the surrounding rock in the area with insufficient thickness has a significant impact on the failure mode. Furthermore, the more serious the defect is, the more obvious the spalling phenomenon will be. Moreover, the failure mode of straight-wall tunnels can basically be attributed to the combined effect of the fractures of defect zones, arch feet and tunnel floor. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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31 pages, 8670 KB

Open AccessArticle

Shear Mechanical Properties and Acoustic Emission Characteristics of the Interface of a Surrounding-Rock–Backfill Composite

by Pengyu Wang, Huixian Huang, Hao Liu, Shuhong Wang and Tianjiao Yang

Processes 2025, 13(11), 3631; https://doi.org/10.3390/pr13113631 - 10 Nov 2025

Viewed by 343

Abstract

Understanding the shear behavior of the interface between surrounding rock and backfill is of significant engineering importance for enhancing stope stability in cemented tailings backfill mining. However, the evolutionary mechanisms of shear properties and damage under varying mechanical conditions remain insufficiently studied. This investigation employed tailings and surrounding rock from a Guangdong tailings pond, with basic mechanical parameters determined through laboratory tests. Numerical models of the rock-backfill composite were developed using PFC2D, considering different shear rates (0.3, 0.6, and 0.9 mm/min), lateral confinement levels (0.5, 1.0, and 1.5 MPa), and roughness coefficients. The analysis compared the interface’s peak and residual shear strengths, revealed crack evolution patterns, and explored damage mechanisms using acoustic emission monitoring and energy dissipation theory. Key findings include the following: (1) Shear stress–displacement curves under all conditions exhibited three stages, ascending, shearing-off, and sliding, with distinct peak and residual strengths. (2) Increasing lateral confinement, shear rate, and roughness transformed failure from localized to global sliding, with cracks occurring at the interface and propagating into the backfill. (3) Cumulative acoustic emission events increased with all three factors, with lateral confinement showing the most substantial effect on interface energy accumulation (83% increase). These results provide theoretical support for assessing interface stability in deep backfilled stopes. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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15 pages, 17825 KB

Open AccessArticle

Study on Tensile Mechanical Behavior and Crack Propagation Mechanism of Yellow Sandstone Containing Randomly Distributed Fissures

by Zhimin Sun and Yaoyao Meng

Processes 2025, 13(11), 3462; https://doi.org/10.3390/pr13113462 - 28 Oct 2025

Viewed by 362

Abstract

To address the complexity of tensile mechanical behavior in fissured rock masses, this study conducted Brazilian splitting tests and numerical simulations on yellow sandstone containing randomly distributed fissures. Based on secondary development of the ABAQUS platform, a numerical model considering the spatial distribution of mineral components was established. A random fissure network was generated using the Weibull distribution, and crack propagation was characterized by employing cohesive elements. The influence mechanisms of the fissure inclination angle (θ = 0°~90°) and fissure ratio (R = 3~15%) on Brazilian tensile strength, failure mode, and crack propagation were systematically analyzed. The research demonstrates the following: (1) Brazilian tensile strength exhibits an overall decreasing trend with an increasing fissure ratio, while the effect of the fissure inclination angle is non-monotonic: at a low fissure ratio (R = 3%), Brazilian tensile strength shows a “decrease–increase–decrease” characteristic; at a medium to high fissure ratio (R ≥ 9%), Brazilian tensile strength continuously increases with an increasing fissure inclination angle. (2) The fissure ratio dominates the deviation of the failure path (deviation intensifies when θ ≤ 67.5° and is minimal at θ = 90°). At the mesoscale, the proportion of tensile cracks increases with an increasing R, while the contribution of shear cracks significantly enhances with an increasing θ (sharply increasing after θ > 45°). (3) Crack propagation is controlled by the spatial interaction of initial cracks. Under the combined action of a high inclination angle (θ = 90°) and high fissure ratio (R = 15%), a tensile–shear composite failure pattern forms, characterized by dual-source crack initiation and central coalescence. This study provides a mesoscale mechanical basis for the stability assessment of engineering structures in fissured rock masses. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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22 pages, 6803 KB

Open AccessArticle

An Investigation of Water–Heat–Force Coupling During the Early Stage of Shaft Wall Pouring in Thick Topsoil Utilizing the Freezing Method

by Yue Yuan, Jianyong Pang, Jiuqun Zou and Chi Zhang

Processes 2025, 13(10), 3319; https://doi.org/10.3390/pr13103319 - 16 Oct 2025

Viewed by 438

Abstract

The freezing method is widely employed in the construction of a vertical shaft in soft soil and water-rich strata. As the construction depth increases, investigating the water–heat–force coupling effects induced by the hydration heat (internal heat source) of concrete is crucial for the safety of the lining structure and its resistance to cracking and seepage. A three-dimensional coupled thermal–hydraulic–mechanical analysis model was developed, incorporating temperature and soil relative saturation as unknown variables based on heat transfer in porous media, unsaturated soil seepage, and frost heave theory. The coefficient type PDE module in COMSOL was used for secondary development to solve the coupling equation, and the on-site temperature and pressure monitoring data of the frozen construction process were compared. This study obtained the model-related parameters and elucidated the evolution mechanism of freeze–thaw and freeze–swelling pressures of a frozen wall under the influence of hydration heat. The resulting model shows that the maximum thaw depth of the frozen wall reaches 0.3576 m after 160 h of pouring, with an error rate of 4.64% compared to actual measurements. The peak temperature of the shaft wall is 73.62 °C, with an error rate of 3.76%. The maximum influence range of hydration heat on the frozen temperature field is 1.763 m. The peak freezing pressure is 4.72 MPa, which exhibits a 5.03% deviation from the actual measurements, thereby confirming the reliability of the resulting model. According to the strength growth pattern of concrete and the freezing pressure bearing requirements, it can provide a theoretical basis for quality control of the lining structure and a safety assessment of the freezing wall. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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21 pages, 3448 KB

Open AccessArticle

Prospective Evaluation of Gaseous and Mineralized Dual CO₂ Sequestration in Mined-Out Area—A Case Study in Yu-Shen Coal Area

by Jiangtao Zhai, Liqiang Ma, Yujun Xu, Yangyang Wang, Kunpeng Yu, Zhiyang Zhao, Chengkun Peng and Zhishang Zhang

Processes 2025, 13(10), 3225; https://doi.org/10.3390/pr13103225 - 10 Oct 2025

Viewed by 464

Abstract

This research introduces a novel dual CO₂ storage (DCS) approach by simultaneously storing CO₂ gas in abandoned mines and securing it within mineralized backfill. For this method, CO₂ mineralized backfill materials (CMBM) are pumped into CO₂ mineralized storage segments (CMSSs) to support the roof while gaseous CO₂ is injected into gaseous CO₂ storage segments (GCSSs) to maximize storage amounts. This study focuses on the Yu-Shen coal area in Yulin City, Shaanxi Province, China. A three-level evaluation model was constructed to predict DCS feasibility based on the analytic hierarchy process (AHP) and fuzzy comprehensive assessment method. The model was generalized and applied to the whole coal area. Each indicator affecting adaptability is plotted on a thematic map to determine the corresponding membership degree. The aptness for 400 boreholes distributed in the entire area was derived and a zoning map which divides the whole area into different suitability was drawn. This paper puts forward a mathematical model for predicting DCS suitability. The findings establish an engineering paradigm that simultaneously addresses CO₂ sequestration, industrial waste recycling, and ecological water table preservation. The research results can provide references for determining the site of DCS, contributing to the generalization of DCS in a larger range. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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23 pages, 8003 KB

Open AccessArticle

Study on Meso-Mechanical Evolution Characteristics and Numerical Simulation of Deep Soft Rock

by Anying Yuan, Hao Huang and Tang Li

Processes 2025, 13(8), 2358; https://doi.org/10.3390/pr13082358 - 24 Jul 2025

Viewed by 592

Abstract

To reveal the meso-mechanical essence of deep rock mass failure and capture precursor information, this study focuses on soft rock failure mechanisms. Based on the discontinuous medium discrete element method (DEM), we employed digital image correlation (DIC) technology, acoustic emission (AE) monitoring, and particle flow code (PFC) numerical simulation to investigate the failure evolution characteristics and AE quantitative representation of soft rocks. Key findings include the following: Localized high-strain zones emerge on specimen surfaces before macroscopic crack visualization, with crack tip positions guiding both high-strain zones and crack propagation directions. Strong force chain evolution exhibits high consistency with the macroscopic stress response—as stress increases and damage progresses, force chains concentrate near macroscopic fracture surfaces, aligning with crack propagation directions, while numerous short force chains coalesce into longer chains. The spatial and temporal distribution characteristics of acoustic emissions were explored, and the damage types were quantitatively characterized, with ring-down counts demonstrating four distinct stages: sporadic, gradual increase, stepwise growth, and surge. Shear failures predominantly occurred along macroscopic fracture surfaces. At the same time, there is a phenomenon of acoustic emission silence in front of the stress peak in the surrounding rock of deep soft rock roadway, as a potential precursor indicator for engineering disaster early warning. These findings provide critical theoretical support for deep engineering disaster prediction. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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21 pages, 6724 KB

Open AccessArticle

Experimental Study on Damage Characteristics and Microcrack Development of Coal Samples with Different Water Erosion Under Uniaxial Compression

by Maoru Sun, Qiang Xu, Heng He, Jiqiang Shen, Xun Zhang, Yuanfeng Fan, Yukuan Fan and Jinrong Ma

Processes 2025, 13(7), 2196; https://doi.org/10.3390/pr13072196 - 9 Jul 2025

Viewed by 657

Abstract

It is vital to stabilize pillar dams in underground reservoirs in coal mine goafs to protect groundwater resources and quarry safety, practice green mining, and protect the ecological environment. Considering the actual occurrence of coal pillar dams in underground reservoirs, acoustic emission (AE) mechanical tests were performed on dry, naturally absorbed, and soaked coal samples. According to the mechanical analysis, Quantitative analysis revealed that dry samples exhibited the highest mechanical parameters (peak strength: 12.3 ± 0.8 MPa; elastic modulus: 1.45 ± 0.12 GPa), followed by natural absorption (peak strength: 9.7 ± 0.6 MPa; elastic modulus: 1.02 ± 0.09 GPa), and soaked absorption showed the lowest values (peak strength: 7.2 ± 0.5 MPa; elastic modulus: 0.78 ± 0.07 GPa). The rate of mechanical deterioration increased by ~25% per 1% increase in moisture content. It was identified that the internal crack development presented a macrofracture surface initiating at the sample center and expanding radially outward, and gradually expanding to the edges by adopting AE seismic source localization and the K-means clustering algorithm. Soaked absorption was easier to produce shear cracks than natural absorption, and a higher water content increased the likelihood. The b-value of the AE damage evaluation index based on crack development was negatively correlated with the rock damage state, and the S-value was positively correlated, and both effectively characterized it. The research results can offer reference and guidance for the support design, monitoring, and warning of coal pillar dams in underground reservoirs. (The samples were tested under two moisture conditions: (1) ‘Soaked absorption’—samples fully saturated by immersion in water for 24 h, and (2) ‘Natural absorption’—samples equilibrated at 50% relative humidity and 25 °C for 7 days). Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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18 pages, 4203 KB

Open AccessArticle

Long-Term Anisotropic Mechanical Characterization of Layered Shale—An Experimental Study for the BaoKang Tunnel of the Zhengwan Railway, China

by Jun Zhao, Changming Li and Wei Huang

Processes 2025, 13(6), 1900; https://doi.org/10.3390/pr13061900 - 16 Jun 2025

Cited by 1 | Viewed by 651

Abstract

With the further implementation and development of the Western Development Strategy, studying the mechanical behavior and deformation characteristics of deep-buried tunnels in layered hard rock under high ground stress conditions holds considerable engineering significance. To study the mechanical properties and long-term deformation and failure characteristics of different bedding stratified rocks, this research employed an MTS815 electro-hydraulic servo rock testing system and a French TOP rheometer. Triaxial compression tests, rheological property tests, and long-term cyclic and unloading tests were conducted on shale samples under varying confining pressures and bedding angles. The results indicate that (1) under triaxial compression, shale demonstrates pronounced anisotropic behavior. When the confining pressure is constant, the peak strength of the rock sample exhibits a “U”-shaped variation with the bedding angle (its minimum value at 60°). For a fixed bedding angle, the peak strength of the rock sample progressively increases as the confining pressure rises. (2) The mode of shale failure varies with the angle: at 0°, shale exhibits conjugate shear failure; at 30°, shear slip failure along the bedding is controlled by the bedding weak plane; at 60° and 90°, failure occurs through the bedding. (3) During the creep process of layered shale, brittle failure characteristics are evident, with microcracks within the sample gradually failing at stress concentration points. The decelerated and stable creep stages are prominent; while the accelerated creep stage is less noticeable, the creep rate increases with increasing stress level. (4) Under low confining pressure, the peak strength during cyclic loading and unloading creep processes is lower than that of conventional triaxial tests when the bedding plane dip angles are 0° and 30°, which is the opposite at 60° and 90°. (5) In the cyclic loading and unloading process, Poisson’s ratio gradually increases, whereas the elastic modulus, shear modulus, and bulk modulus gradually decrease. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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15 pages, 2853 KB

Open AccessArticle

Thermodynamic Method for Evaluating the Gas Adsorption-Induced Swelling of Confined Coal: Implication for CO₂ Geological Sequestration

by Zhigang Du, Tianxiang Chen, Shuigen Hu, Yanqiang Du, Fuqiang Gao, Pengli He, Qiang Huang, Shaoyang Yan and Ning Li

Processes 2025, 13(5), 1504; https://doi.org/10.3390/pr13051504 - 14 May 2025

Viewed by 687

Abstract

Geological storage of CO₂ in coal seam is an effective way for carbon emission reduction. Evaluating the adsorption-induced swelling behavior of confined coal is essential for this carbon emission reduction strategy. Based on the thermodynamic theory and the Gibbs adsorption model, a thermodynamic method for evaluating the gas adsorption-induced swelling behavior of confined coal was established. The influences of factors such as stress, gas pressure, and the state of gas on the adsorption-induced swelling behavior of confined coal were discussed. The predicted swelling deformation from the thermodynamic method based on the ideal gas hypothesis was consistent with the experimental result only under the condition of low-pressure CO₂ (<2 MPa). The predicted swelling deformation from that method was larger than the experimental result under the condition of high-pressure CO₂ (>2 MPa). However, the method based on the real gas hypothesis always had better prediction results under both the low- and high-pressure CO₂ conditions. From the perspective of phase equilibrium and transfer, in the process of CO₂ adsorption by the confined coal, gas molecules transfer from the adsorption site of high chemical potential to the low chemical potential. Taking the real gas as ideal gas will result in the surface energy increase in the established model. Consequently, the prediction result will be larger. Therefore, for geological storage of CO₂ in coal seam, it is necessary to take the real gas state to predict the adsorption-induced swelling behavior of the coal. In the process of CO₂ adsorption by the confined coal, when its pressure is being closed to the critical pressure, capillary condensation phenomenon will occur on the pore surface of the confined coal. This can make an excessive adsorption of CO₂ by the coal. With the increase in the applied stress, the adsorption capacity and adsorption-induced swelling deformation of the confined coal decrease. Compared to N₂ with CO₂, the coal by CO₂ adsorption always shows swelling deformation under the simulated condition of ultra-high-pressure injection. However, the coal by N₂ adsorption will shows shrinking deformation due to the pore pressure effect after the equilibrium pressure. Taking the difference in the adsorption-induced swelling behavior and pore compression effect, N₂ can be mixed to improve the injectivity of CO₂. This suggests that CO₂ storage in the deep burial coal seam can be carried out by its intermittent injection under high-pressure condition along with mixed N₂. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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21 pages, 31440 KB

Open AccessArticle

The Effects of Bedding and Holes on the Mechanical and Microfracture Behavior of Layered Limestone Based on the CZM Method

by Xiaofei Wang, Linghong Gao, Xiangxi Xu and Fei Lin

Processes 2025, 13(4), 1223; https://doi.org/10.3390/pr13041223 - 17 Apr 2025

Viewed by 478

Abstract

The mechanical and fracture behaviours of rocks are largely influenced by the rock structure and existing flaws. To study the effects of bedding and holes on the mechanical and microfracture behaviour of layered limestone, numerical specimens based on the cohesive zone model (CZM) method were first established. The cracks’ initiation, propagation and penetration processes during the entire loading process were used to reveal the fracture mechanism of numerical layered limestone under different conditions. The effects of bedding angle, hole location and hole number on the peak stress, failure pattern, length of total cracks and crack ratio of numerical layered limestone were then deeply studied. The numerical results indicate that the existing holes cause damage to the numerical layered limestone at different bedding angles. The hole has stronger and weaker damage influences on the peak stress at bedding angles = 0° and 30°. The hole location has different damage degrees on the peak stress at different bedding angles. The location and number of holes have no obvious influence on the failure pattern of numerical layered limestone at bedding angle = 60° and have a strong influence on the failure pattern of numerical layered limestone at bedding angle = 30°. Under most conditions, the length of total cracks is smaller than that of the intact numerical specimen. The location and number of holes have a strong influence on the ratio of tensile and shear cracks along the matrix for numerical specimens at bedding angles = 0°, 30° and 90°. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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21 pages, 4734 KB

Open AccessArticle

Experimental Study on the Mechanical Properties of Cracked Limestone Reinforced by Modified Cement Grouting

by Dong Zhu, Yijiang Zong, Min Chen, Xiangling Tao and Liang Yue

Processes 2025, 13(4), 1205; https://doi.org/10.3390/pr13041205 - 16 Apr 2025

Viewed by 755

Abstract

Grouting reinforcement is a pivotal approach to enhancing the integrity and load-bearing capacity of fractures in surrounding rock. In this study, standard limestone specimens were fractured through uniaxial compression. Then, the specimens were reinforced with grouting, using ultrafine cement paste containing varying mass fractions of enhancers and a grouting apparatus developed by the authors. After the specimens were cured under standard conditions for 28 days, CT scanning technology was used to investigate the microstructure and grouting effect characteristics of grouted bodies containing different mass fractions of enhancers from a mesoscopic perspective. Then, uniaxial compression tests were conducted on those grouted specimens. The experimental results revealed that the content of the enhancer significantly affected the post-peak characteristics, mechanical parameters, and failure modes of the grouted specimens. When the content of the enhancer increased from 2.50 wt.% to 15.00 wt.%, the uniaxial compressive strength of the grouted specimens exhibited a positive correlation with the enhancer content, with the maximum improvement rate reaching 18.10% compared to the residual strength. However, when the enhancer content ranged from 15.00 wt.% to 20.00 wt.%, the uniaxial compressive strength was negatively correlated with the enhancer content. At an enhancer content of 15.00 wt.%, the overall stability of the grouted specimens was optimal, with all mechanical parameters reaching their maximum values. Utilizing three-dimensional CT scanning and reconstruction technology, it was observed that when the enhancer content was less than 15.00 wt.%, the cracks were concentrated in the limestone matrix rather than in the grouted solid in the edge regions of grouted specimens. However, in the whole specimens, the cracks in the grouted solid exceeded that in the limestone matrix. Conversely, when the enhancer content was greater than 17.50 wt.%, the grouted solid was predominantly distributed within the edge fissures of the specimens, while the internal regions exhibited a lower volume fraction of the grouted solid. In this scenario, the volume fraction of the grouted solid in the specimens was significantly lower than that of the fissures. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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18 pages, 11277 KB

Open AccessArticle

Mechanical Characteristics and Mechanisms of Destruction of Trapezoidal Sandstone Samples Under Uneven Loading

by Bao Pan, Weijian Yu, Ke Li, Zilu Liu, Tao Huang and Jie Yang

Processes 2025, 13(4), 1169; https://doi.org/10.3390/pr13041169 - 12 Apr 2025

Viewed by 596

Abstract

Predicting rock failure under excavation-induced non-uniform stress remains challenging due to the inability of conventional homogeneous specimens to replicate field-scale stress gradients. A novel trapezoidal sandstone specimen with adjustable top-surface inclinations (S75/S85) is proposed, uniquely simulating asymmetric stress gradients to mimic excavation unloading. Geometric asymmetry combined with multi-scale characterization (CT, SEM, PFC) decouples stress gradient effects from material heterogeneity. The key findings include the following points. (1) Inclination angles > 15° reduce peak strength by 24.2%, transitioning failure from brittle (transgranular cracks > 60) to mixed brittle-ductile modes (2) Stress gradients govern fracture pathways: transgranular cracks dominate high-stress zones, while intergranular cracks propagate along weak cementation interfaces. (3) PFC simulations reveal a 147% stress disparity between specimen sides and validate shear localization angles θ = 52° ± 3°), aligning with field data. This experimental–numerical framework resolves limitations of traditional methods, providing mechanistic insights into non-uniform load-driven failure. The methodology enables targeted support strategies for deep asymmetric roadways, including shear band mitigation and plastic zone reinforcement. By bridging lab-scale tests and engineering stress states, the study advances safety and sustainability in deep roadway excavation. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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19 pages, 10551 KB

Open AccessArticle

Study on the Evolution Law and Theoretical Solution of a Freezing Temperature Field in Transcritical CO₂ Ultra-Low Temperature Formation

by Zihao Zhang, Bin Wang, Xiuling Liang, Chuanxin Rong and Zhongbao Ye

Processes 2025, 13(4), 1154; https://doi.org/10.3390/pr13041154 - 10 Apr 2025

Cited by 2 | Viewed by 668

Abstract

This study explored the feasibility of applying transcritical CO₂ in an artificial ground freezing method. By carrying out indoor modeling tests, the temperature field evolution law and the development characteristics of the freezing front during the freezing process of transcritical CO₂ in a sand layer were analyzed, and the freezing effect of transcritical CO₂ was compared with that of traditional alcohol. The theoretical solution of the freezing temperature field was derived, and the accuracy of the theoretical analytical solution was verified by test results. The results showed that the freezing efficiency of transcritical CO₂ was significantly higher than that of alcohol. After 6 h of freezing, the temperature range of the measuring point (C1–C7/C10–C16) can reach −28 °C–3.5 °C, and the freezing front radius exceeded 60 mm. The temperature range of the alcohol measuring point (J1–J7/J10–J16) was only −12.6 °C–8.8 °C, and it took 24 h to achieve the same radius. The test data were in good agreement with the theoretically predicted values, verifying the rationality of the theoretical formula. Freezing temperature T_d had a significant influence on the calculation results of freezing front radius. After transcritical CO₂ freezing for 24 h, the difference in the freezing front radius R(T_d = −2) reached 8.02 mm when the freezing temperature T_d was −2 °C and 0 °C. The difference in the freezing front radius caused by the freezing temperature T_d was concentrated in the range of 1.5–8.1 mm, and the difference in the effect on different types of refrigerants was small. The research results not only confirm the feasibility of the application of transcritical CO₂ in the freezing method but also provide test data and experience for engineering applications, which promotes the innovation and development of freezing method technology. Full article

(This article belongs to the Special Issue Optimization of Complex Engineering Systems and Application of Advanced Digital and Intelligent Technologies)

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