bluuebunny/crossref_metadata_2025 huggingface dataset:
Research on the efficient process-oriented structural optimization method of the large-scale vacuum cryostat for fusion reactors
Authors: Yu Qingzhou , Xu Hao , Chen Zhaoxi , Yang Qingxi
Published: May 2024

An efficient optimization design for the large and complex components of fusion reactors is crucial to address the engineering design requirements and further promote technical standardization. Based on research status, current engineering designs for fusion reactors have some deficiencies, such as time and energy wastage, inefficiency, and difficulties in covering the typical ‘multi-variable multi-objective’ design requirements. These are pressing and common problems that urgently need to be overcome. To deal with the aforementioned technical challenges, it is vitally important to design an efficient, precise, and normalized approach that is tailored for the development of future fusion reactors. Therefore, this paper proposes a process-oriented optimization design method, which involves Coupled external parameterized modeling, Experimental points design, Response surface optimization, and Structural integrity validation (CERS), to improve the currently inefficient design methods. And the vacuum cryostat, the largest and complex component of a tokamak, is taken as an example to present the basic procedures of CERS. Firstly, the functions, basic structures, load types, analysis methods, and verification criteria of the cryostat are presented in detail. Then, real-time data interaction between external global parametric variables and ANSYS via coupling is established by CERS, which achieves parametric modeling of the cryostat and efficient experimental point design and optimization analysis with multi-variables and multi-objectives in an automatic way. Subsequently, this study demonstrates the significance and sensitivity of various structural parameters of the cryostat from such objectives as maximum deformation, maximum equivalent stress, and total mass. And the optimal set of its structural parameters is obtained by establishing a mathematical optimization model. Finally, the structural integrity is verified. The results indicate that the optimized cryostat maintains a minimum safety margin of 23% and will not suffer fatigue damage under various load events during its service. Moreover, the nonlinear buckling load multiplier

∅

is 5.4, obtained by analyzing the load-displacement curve of the cryostat according to the zero-curvature criterion. This shows that the designed cryostat is stable enough. The proposed method is simple, efficient, and reliable, and can be applied to both the cryostat and other complex components of fusion reactors in engineering design fields. It has great value of practical technical reference and can further promote the standardization of engineering design technology for future fusion reactors.
Global fluid simulation of plasma turbulence in stellarators with the GBS code
Authors: Coelho A.J. , Loizu J. , Ricci P. , Tecchiolli Z.
Published: May 2024

The implementation of three-dimensional magnetic fields, such as the ones of stellarators, in the GBS code (Ricci et al 2012 Plasma Phys. Control. Fusion
54 124047; Giacomin et al 2022 J. Comput. Phys.
464 111294) is presented, and simulation results are discussed. The geometrical operators appearing in the drif-reduced Braginskii equations evolved by GBS are expanded considering the typical parameter ordering of stellarator configurations. It turns out that most of the operators have a similar structure as the one implemented in the tokamak axisymmetric version of the code. In particular, the perpendicular laplacian only acts on the poloidal plane, which avoids the need of a three-dimensional solver for the electrostatic potential. The simulation of an island divertor stellarator is then presented, showing the derivation of the magnetic equilibrium in detail and extending the results in (Coelho et al 2022 Nucl. Fusion
62 074004). Although the island magnetic field-lines divert the plasma towards the strike points of the walls, the islands do not seem to have a significant impact on the turbulence properties. The dominant mode, identified as interchange-driven, is field-aligned and breaks the stellarator toroidal symmetry. The radial and poloidal extensions of the mode are of the same order, in contrast to typical tokamak simulations. This has consequences on the poloidal dependence of turbulent transport.
Socioeconomic distributional impacts of evaluating flood mitigation activities using equity-weighted benefit-cost analysis
Authors: Lockwood Joseph W , Oppenheimer Michael , Lin Ning , Gourevitch Jesse
Published: May 2024

As the global impact of climate change intensifies, there is an urgent need for equitable and efficient climate adaptation policies. Traditional approaches for allocating public resources for climate adaptation that are based on economic benefit-cost analysis often overlook the resulting distributional inequalities. In this study, we apply equity weightings to mitigate the distributional inequalities in two key building and household level adaptation strategies under changing coastal flood hazards: property buyouts and building retrofit in New York City (NYC). Under a mid-range emissions scenario, we find that unweighted benefit cost ratios applied to residential buildings are higher for richer and non-disadvantaged census tracts in NYC. The integration of income-based equity weights alters this correlation effect, which has the potential to shift investment in mitigation towards poorer and disadvantaged census tracts. This alteration is sensitive to the value of elasticity of marginal utility, the key parameter used to calculate the equity weight. Higher values of elasticity of marginal utility increase benefits for disadvantaged communities but reduce the overall economic benefits from investments, highlighting the trade-offs in incorporating equity into adaptation planning.
Quantum coherence from Kirkwood–Dirac nonclassicality, some bounds, and operational interpretation
Authors: Budiyono Agung , Sumbowo Joel F , Agusta Mohammad K , Nurhandoko Bagus E B
Published: May 2024

Just a few years after the inception of quantum mechanics, there has been a research program using the nonclassical values of some quasiprobability distributions to delineate the nonclassical aspects of quantum phenomena. In particular, in Kirkwood–Dirac (KD) quasiprobability distribution, the distinctive quantum mechanical feature of noncommutativity which underlies many nonclassical phenomena, manifests in the nonreal values and/or the negative values of the real part. Here, we develop a faithful quantifier of quantum coherence based on the KD nonclassicality which captures simultaneously the nonreality and the negativity of the KD quasiprobability. The KD-nonclassicality coherence thus defined, is upper bounded by the uncertainty of the outcomes of measurement described by a rank-1 orthogonal projection-valued measure (PVM) corresponding to the incoherent orthonormal basis which is quantified by the Tsallis

1
2

-entropy. Moreover, they are identical for pure states so that the KD-nonclassicality coherence for pure state admits a simple closed expression in terms of measurement probabilities. We then use the Maassen–Uffink uncertainty relation for min-entropy and max-entropy to obtain a lower bound for the KD-nonclassicality coherence of a pure state in terms of optimal guessing probability in measurement described by a PVM noncommuting with the incoherent orthonormal basis. We also derive a trade-off relation for the KD-nonclassicality coherences of a pure state relative to a pair of noncommuting orthonormal bases with a state-independent lower bound. Finally, we sketch a variational scheme for a direct estimation of the KD-nonclassicality coherence based on weak value measurement and thereby discuss its relation with quantum contextuality.
CPT calibration chamber testing on tailings
Authors: Qi L , Liu W , Zhao H , Talesnick M , Ghafghazi Mason
Published: May 2024

The cone penetration test (CPT) is a widely used technique for on-site investigations. In the field, interpretation correlations of CPT can be established using laboratory calibration chamber tests. Empirical and theoretical correlations were developed for clay and sand under undrained and drained conditions, respectively. However, interpreting these results can be more challenging for intermediate soils that exhibit partial drainage during penetration and lie between fully undrained and drained conditions. Tailings, which are the by-products of mining and are often rich in fine particles, are a typical example of such intermediate soils. To gain a deeper understanding of the behavior of the tailings during CPT, a calibration chamber test was performed at a standard rate of 2 cm/s and subsequently at a slow rate of 0.02 cm/s, and the obtained results were analyzed.
Study on the anisotropic small strain stiffness of marine clay in China using bender elements
Authors: Huang Yuhua , Gu Xiaoqiang , Zuo Kangle , Hu Jing
Published: May 2024

Small strain stiffness anisotropy of marine soils plays an important role in determining the natural frequency of offshore wind turbine structures. The small strain stiffness anisotropy is contingent on stress anisotropy and fabric anisotropy, with the latter being assessable via stiffness anisotropy under isotropic stress conditions. In this study, the small strain stiffness of marine clay obtained from the site of an offshore wind farm on the southeast coast of China was measured using a bender element. The effects of void ratio, effective mean pressure, and overconsolidation ratio on small strain stiffness were investigated and the related empirical equations were proposed for predicting the small strain stiffness of the marine clay. Furthermore, the small strain stiffness anisotropy of the marine clay under isotropic consolidation was also investigated. The findings revealed remarkable anisotropy in the small strain stiffness of the tested marine clay.
Unit cell consolidation of a PVD incorporated soft soil: Comparative of 2D axisymmetric and plane strain analysis considering ideal and actual drain
Authors: Ghose Samrat , Dey Arindam
Published: May 2024

The paper presents two-dimensional (2D) finite element-based study of a surcharge-induced consolidating unit cell model comprising fully saturated soft soil. Radial drainage in the unit cell is ensured through a single prefabricated vertical drain (PVD) along with vertical drainage through the top surface. Finite element based 2D axisymmetric and plane strain modelling has been conducted by considering the smearing of cohesive medium. The PVD is represented by both 1D drain element (ideal drain) and through geometric modelling considering well resistance. The parameters for the ‘Soft Soil’ model for the cohesive medium are adopted from the subsurface data at Krishnapatnam Ultra Mega Power Project (KUMPP), India. Comparative assessment of unit-cell consolidation is carried out between the 2D axisymmetric and equivalent plane strain condition based on Hird’s permeability compatibility approach. The two approaches yielded noticeable disparity in the time rates of consolidation for time factor ≤ 0.4, beyond which the disparity decreases, and the two methods lead to identical results beyond time factor = 4. Further, the influence of permeability of a geometrically modelled PVD and the height of unit cell on the time-rate of consolidation is elucidated, thereby manifesting the importance of well resistance and drainage length in such analyses.
Correlations between physical properties and compression index of fine-grained soils based on a large dataset
Authors: Huang Fei , Fu Bin , Qin Hongyu , Du Yu , Zhu Liuwen , Zhuo Lichun
Published: May 2024

A comprehensive statistical analysis of the correlations between the physical properties and compression index Cc
of fine-grained soils, based on a large dataset from the soil testing results of a railway project in the eastern coastal area of Malaysia, is presented in this paper. More than 1000 soil samples covering a wide range of soil types, with physical properties, such as natural water content, initial void ratio, dry density, liquid limit, plasticity index, and mechanical property-compression index, were analyzed using linear and nonlinear regressions. A very high correlation was observed between the natural moisture content, initial void ratio, dry density, and compression index. A strong correlation was found between the plasticity, liquid, and compression indices. Lower and upper boundaries, confining most of the previous correlations, were found between the natural water content and compression index. A comparison of all the correlations showed the natural water content and initial void ratio as the two best properties for predicting the compression index of fine-grained soils.
Experimental study of the dynamic characteristics of deep silty clay in Shanghai
Authors: Zhang D , Zhou Y , Huang Z
Published: May 2024

To investigate the dynamic properties of deep silty clay, a comprehensive set of cyclic triaxial and resonant column tests were performed on undisturbed samples of silty clay containing sand from depths reaching 54.5 m in Shanghai. This study aimed to characterize the influence of confining pressure on the stress–strain behavior, pore water pressure, and dynamic modulus of the soil. The present findings revealed that the confining pressure, which is correlated with the depth of burial, significantly influenced the soil deformation. Moreover, elevated confining pressures resulted in increased stress within the hysteresis loops, a higher initial shear modulus, and a diminished ratio of excess pore water pressure. Based on the empirical data, a refined model was formulated for the shear modulus and damping ratio as functions of the shear strain for deep silty clay in Shanghai. These insights are intended to offer a robust reference point, facilitating calibration and guiding subsequent investigations into structures situated in the deep subterranean environments of Shanghai.
Investigation of creep characteristics and microscopic mechanism of cemented-soil subjected to freeze-thaw
Authors: Zhou Jie , Chen Lujia , Zhao Wenqiang
Published: May 2024

With the development of underground construction, higher safety demands have been placed on construction methods. The improved freezing method, which combines artificial ground freezing and cemented soil stabilization techniques, is more suitable for studying the typical creep characteristics of muddy clay in Shanghai. However, research on the creep behavior of freeze-thaw cemented-soil is limited. In this study, the creep characteristics of freeze-thawed cemented soil were investigated through triaxial creep tests, and the micromechanism was explored using scanning electron microscopy (SEM). The results indicate that the creep deformation of freeze-thawed cemented soil is higher than that of non-freeze-thawed cemented soil. The freezing temperature decreased with an increase in deformation. By analyzing SEM images, the porosities of non-freeze-thawed cemented-soil and soil freeze-thawed at -5°C, -15°C, and -25°C, were extracted, which were 28.5%, 28.7%, 30.1%, and 39.1% respectively. During the freeze-thaw cycle, both the soil and cemented soil particles undergo movement and reordering. Freeze-thaw exacerbates creep degradation because frost heave weakens particle adhesion and affects structural stability. These results provide a scientific reference for the development of underground spaces in soft areas.
Desiccation cracking behavior and its suppression methods in lateritic soil under drying and wetting cycles
Authors: Gao Qian-Feng , Zeng Ling , Yu Guang-Tao , Huang Xiao-Jian
Published: May 2024

In this study, the desiccation cracking behavior of lateritic soil caused by drying and wetting cycles was investigated and effective methods for mitigating crack development were proposed. Direct mixing and spray coating methods based on different additives were used to modify lateritic soil. Cyclic wet–dry tests were performed to analyze the influence of wet–dry cycles on the cracking behavior. Subsequently, uniaxial tensile tests were conducted to examine the strength degradation caused by crack formation and strength enhancement by additives. In addition, the modification mechanisms were revealed using electron microscopy. The results demonstrated that desiccation cracks developed significantly during the drying process, with some cracks closing upon wetting. However, most of the cracks reopened and expanded further during subsequent drying, leading to a steady increase in the crack rate during the wet-dry cycles. When using the direct mixing method, lignocellulose was the most effective additive for enhancing the crack resistance of lateritic soils. The optimal crack resistance was achieved with a lignocellulose content of 0.75%, resulting in an 18.2% increase in tensile strength. Conversely, when employing the spray coating method, PAC was found as the optimal additive, with a desirable concentration of 1.5–6.0%.
Model test and numerical analysis of shield tunnel face instability in sandy soil with strain-softening properties
Authors: Zhao Y C , Qin H L , Xu K F , Lü X L
Published: May 2024

During excavation of a shield tunnel in a sandy stratum, variations in the state of the sand affect the stratum stability of the shield tunnel face. When dense sand is loaded, its strength decreases gradually owing to dilatancy and it exhibits strain-softening behavior. Model tests and finite element numerical simulations were performed to clarify the failure characteristics of the tunnel face induced by strain-softening. In the model tests, a dense sand stratum was constructed; the movement of the supporting plate of the excavation face was controlled to simulate the progressive failure of the shield tunnel face. Based on a material state-dependent plasticity model, a numerical analysis model of the tunnel face was established to capture the strain-softening behavior of dense sand by including a nonlocal regularization technique. Comparing the model test and numerical simulation results, the evolution of the material state of the sand with progressive failure of the tunnel face was analyzed, and the failure characteristics caused by the strain-softening of sand were revealed.
Influence of repeated surface surcharge loading on tunnel displacement considering the structural characteristics of soft clay
Authors: Xie W B , Zhang Q , Ye G L
Published: May 2024

Shanghai soft clay is a typical marine clay with specific structural characteristics. However, the effects of surface surcharge loading on structured soft clay and existing tunnels remain unclear. In this study, the effect of repeated surface surcharge loading on tunnel displacement was numerically investigated, considering the structural characteristics of Shanghai Layer 4 soft clay. An elastoplastic constitutive model (Shanghai model) that describes the mechanical properties and structural characteristics of natural clay was used to simulate the soil response. The results indicate that the first cycle of repeated surface surcharge loading had the greatest effect on the displacement of the tunnel and overlying clay; subsequent loading cycles further increased the displacement. With repeated surface surcharge loading, the displacement of the overlying clay exhibited a significant decreasing trend with increasing depth. The maximum excess pore pressure of the clay exhibited a decreasing trend with increasing loading time. The displacements of the tunnel and overlying clay were greater when the effects of the soil structure were considered. However, the initial degree of the structure had no significant effect on the accumulation of excess pore pressure when the surface surcharge loading did not reach the ultimate bearing capacity of the clay.
Undrained cyclic behavior of underconsolidated marine clay in multidirectional simple shear tests
Authors: Tan J , Ren F F , Gao Y
Published: May 2024

In the field of marine reclamation engineering, underconsolidated marine clay often presents challenges owing to its susceptibility to multidirectional cyclic stresses and potential for excessive deformation. This research examined the undrained cyclic behavior of underconsolidated marine clay through multidirectional cyclic simple shear tests. It explored shear strain evolution, the cyclic shear stress–strain relationship, and stiffness degradation by analyzing the impacts of clay consolidation levels and phase differences in the cyclic stress. The findings indicated that as the degree of consolidation increased, the rate of cyclic shear strain development in marine clay gradually diminished. Conversely, an enhanced phase difference led to a quicker evolution of shear strain. Additionally, as loading continued, the tested clay exhibited notable softening behavior, leading to stiffness degradation. A larger phase difference resulted in more pronounced stiffness degradation, although a higher degree of consolidation effectively delayed this degradation. These findings provide new insights on the cyclic behavior of underconsolidated marine clay under multidirectional loading, offering crucial information for marine reclamation engineering.
Influence of spatial variability of soil shear-wave velocity considering intralayer correlation on seismic response of engineering site
Authors: Zhong Zilan , Ni Bo , Shi Yuebo , Li Jingqiang , Shen Jiaxu , Du Xiuli
Published: May 2024

Shear-wave velocity uncertainty significantly impacts seismic response analysis at engineering sites. Previous studies focused on the correlations of shear-wave velocities within soil layers. However, the influence of the vertical spatial variability of shear-wave velocity within individual soil layers was not considered. This study selected a typical Site Class II engineering site to investigate this influence based on the equivalent linear seismic response analysis method of layered soil deposits. Existing field test data on shear-wave velocity were used to discretize the shear-wave velocity within soil layers into a one-dimensional (1D) random field through covariance matrix decomposition and local average process theory. Monte Carlo simulations generated random shear-wave velocity profiles with different vertical correlation distances. Three artificial records with different earthquake return periods were used as input motions at the engineering bedrock for the 1D free-field model. Considering soil shear-wave velocity uncertainty, the peak shear strain increased by 19–27% with the input ground motion amplitude. Moreover, the site peak shear strain variability increased by 25–34% with the vertical correlation distance. The proposed 1D random field model effectively simulated the interlayer correlation and spatial variability of shear-wave velocity within soil layers, demonstrating its significance in seismic response analysis.
Research on the method of damage theory applied in underground lining structure’s durability
Authors: Pan H
Published: May 2024

Damage or deterioration may occur in underground lining structures under the effects of external loads, groundwater seepage, and corrosive ions. Consequently, the durability and reliability of the structure can be severely affected. This study first analyzed and summarized the current situation of damage theory used in the durability research of concrete structures and underground. Consequently, the concept of a “deterioration degree function,” which can reflect the degree of damage to a structure, was proposed. Subsequently, the Gurson meso-damage model was analyzed for its application in the durability research of underground structures concerning the theory, formulae, and steps. A type of specimen was designed as an example, wherein the track model of steel corrosion expansion as assumed and deduced, and the numerical calculation of the damage stress was calculated to predict the durable life of the structure. The analysis concept developed in this study can be extended and applied to other research fields with similar durability problems.
Method for macro-microscopic damage observation of rock hydraulic fracturing based on dic and thin section techniques
Authors: Xing J , Zhao C , Niu J , Huang L , Qian Y , Fu J , Ding H L , Tian Y Z
Published: May 2024

This study conducted systematic studies and in-depth analyses of micromechanics of hydraulically induced crack propagation. This study introduced a method for observing macromicroscopic damage in rock hydraulic fracturing based on DIC and thin-section techniques. We developed an advanced sealed visualization system equipped with high-speed cameras and macrolenses to facilitate precise observation of the hydraulic fracturing process. Additionally, Digital Image Correlation was used to accurately track and analyze the evolution of fractures. Our methodology clearly distinguished between intergranular and transgranular cracks using polarized light microscopy, thereby offering novel insights into grain-scale damage and strain localization within crystalline rocks. This research contributes to the understanding of the mechanisms underlying hydraulic fracturing at both the macroscopic and microscopic scales.
Preliminary study on the mechanical behavior of clay in one-dimensional compression with DEM simulations
Authors: Shen Z F , Li X X , Yi X J , Wang Z H , Gao H M
Published: May 2024

The mechanical behavior and physical properties of clay are closely associated with its microstructure. Current research on the macroscopic mechanics and physical properties of clay is comprehensive and systematic. However, the microstructural variations underlying these characteristics have been predominantly examined under mercury intrusion porosimetry and scanning electron microscopy, while quantitative and systematic studies are notably limited. This research employs the discrete element method (DEM) simulation to investigate the microscopic responses of clay, simulating one-dimensional compression tests on two clay types: card-house and book-house structures. The analysis of pore size and morphology was conducted using virtual mercury intrusion porosimetry and the pore segmentation method. The clay microstructure was quantitatively characterized by parameters such as pore aspect ratio, orientation distribution, and cumulative pore volume curve. The findings demonstrate that DEM effectively replicates the fundamental mechanical behavior of clay, revealing and explaining the evolution pattern of clay pore structure during one-dimensional compression in terms of platelet alignment adjustment. This macroscopic compression is characterized by variations in pore size distribution, orientation, and aspect ratio.
Microscale Mechanical Behaviour Evaluation of Unsaturated Granular Soils via 4D in situ Triaxial Test on μ-CT
Authors: Luan Ji-yuan , Wang Ji-peng , Dadda Abdelali
Published: May 2024

Owing to the complex structure and stress history of unsaturated soils, the micro-mechanism of effective stress theory in unsaturated soil mechanics remains unelucidated. In this study, we developed a miniature triaxial test apparatus for a micro-focus computed tomography (μ-CT) scanning system for the microscopic study of the mechanical behaviour of unsaturated soil. By comparing the results from the developed mini-triaxial test device system with those from a conventional triaxial device, its experimental accuracy was verified. Micron-level high-resolution CT images of sheared specimens at different strain stages were obtained using the device for in situ suction-control triaxial compression 4D (3-Dimensional+Dynamic) tests with a μ-CT scanning system. The multiscale evolution behaviours of the physical parameters (porosity and degree of saturation) of the specimens corresponded to the stress–strain relationship revealed by the in situ test. Triaxial shearing drains out the pore water, and the decomposition of the largest water clusters causes the quantity of small-volume liquid clusters to increase, shifting the distribution of the interfacial areas. The degree of saturation scale indicates the presence of liquid bridges within the shear band that provide interparticle cementation effect and thus enhance the global strength of unsaturated granular soil specimens.
Investigation of particle size effect on particle breakage of carbonate sand under one-dimensional compression
Authors: Wu Y , Dai B , Liu P , Xu K
Published: May 2024

Previous studies on the particle-size effect have indicated that larger particles tend to exhibit lower strength under equivalent loading conditions; however, the underlying mechanism remains unclear. This study investigated the influence of particle size on the macrocompression behavior of carbonate sand by performing one-dimensional compression tests on various uniformly graded samples. The variations in particle size and shape resulting from particle breakage during compression were quantitatively analyzed. In addition, X-ray micro-tomography (μCT) is employed to obtain microstructural insights into the intra-particle porosity of carbonate sand particles, and its role in the particle size effect was further discussed.
A prediction model of maximum dry density of over coarse-grained soil
Authors: Jia Mincai , Zheng Yiming
Published: May 2024

The control of maximum dry density is an important issue for over coarse-grained soil. A theoretical formula of the maximum dry density for over coarse-grained soil was derived, which is related to the maximum dry density of the original soil, particle density, and mass fraction of giant particles in the mixed soil. Maximum dry densities of seven groups of mixed soil were calculated by the discrete element method (DEM) and theoretical formula, and the results showed that the maximum dry densities obtained from the DEM were always lower than the results calculated by theoretical formula, and the difference increased with the increase in giant particle proportion. The volume growth coefficient was proposed to describe the increase in pore volume of the mixed soil caused by the embedding of giant particles, and the maximum dry density model for over coarse-grained soil was proposed. The results showed that the model fitted well to the DEM results, validating the high rationality and reliability.
Constitutive and experimental study of unsaturated fine-grained soils over a wide suction range
Authors: Zhou G Y , Shi Z H , Qian J G
Published: May 2024

The instabilities exhibited by unsaturated fine-grained soil, stemming from coupled hydro-mechanical phenomena, represent crucial engineering characteristics essential for geotechnical designs. This study introduces a constitutive model for unsaturated fine-grained soils, incorporating the framework of sub-loading surface plasticity. The model integrates Bishop’s effective stress and capillary degree of saturation as basic variables, while also addressing the distinct influences of soil volume change on capillarity and adsorption mechanisms. Validation of the proposed model is conducted using a diverse set of experimental data derived from suction-controlled triaxial compression tests conducted under low and high suction conditions. The results demonstrate that the new constitutive model can achieve a reasonable agreement with the observed data.
A review on thermal conductivity of unsaturated bentonite
Authors: Ye W M , Shao C Y , Lu P H , Liu Z R , Chen L
Published: May 2024

As unsaturated bentonite is used a buffer/backfill material in the construction of engineered barriers for high-level nuclear waste disposal, understanding its thermal properties is crucial for maintaining the operational stability of the repository. This review paper synthesizes research on the thermal conductivity of unsaturated bentonite, encompassing aspects of heat transfer mechanisms, measurement techniques, influencing factors, and prediction models. The results highlight that the transient and steady-state methods have emerged as the predominant techniques for measuring the thermal conductivity of unsaturated bentonite owing to their efficiency and the prevention of water redistribution within the sample throughout the testing phase. Factors such as dry density, degree of saturation, additive content, and temperature were observed to positively influence the thermal conductivity of unsaturated bentonite, whereas an increase in the ion concentration of the pore fluid decreased the thermal conductivity. The prediction models for the thermal conductivity of unsaturated bentonite are categorized into empirical, normalized, and theoretical models. Although empirical and normalized models provide some insight, they suffer from a lack of theoretical foundation, and the parameters they incorporate often lack clear physical significance, complicating their practical application despite their capacity to represent the multifield coupling characteristics of thermal conductivity. The advancements in microscopic testing methods and computational technology herald the potential of mesoscale models and machine learning as formidable tools for predicting the thermal conductivity of unsaturated bentonite, suggesting a promising direction for future research.
Effect of volumetric deformation on saturation of unsaturated soils under constant suction
Authors: Chen Ke , Liang Fayun
Published: May 2024

The soil–water retention curve (SWRC) represents a fundamental relationship in the study of unsaturated soils, where volumetric deformation plays a crucial role in shaping the water retention characteristics by impacting the pore size distribution. This study conducted a thermodynamic analysis to derive a relationship between the effective stress parameter and the water retention properties of unsaturated soils. Consequently, a streamlined formula was introduced to forecast the impact of volumetric deformation on saturation at constant suction. This formula, incorporating a singular parameter from the effective stress parameters equations, can be seamlessly integrated with any prevailing SWRC model to characterize the influence of volume deformation on the SWRC. The effectiveness of the proposed model was corroborated through seven sets of experimental data spanning various soils, affirming its capability to precisely describe the water retention behavior of deformable soils under deformation.
Hydro-mechanical model for small-strain stiffness of unsaturated soil
Authors: Wang Fangtong , Shen Kanmin , Shan Zhigang , Wang Yong
Published: May 2024

This study aims to investigate a novel method for predicting the small-strain stiffness of unsaturated soil. A hydro-mechanical model is proposed to estimate the small-strain stiffness of unsaturated soil with various matric suction and stress states. A series of saturated and unsaturated bender element tests are conducted, and the test results indicate that the small-strain stiffnesses of saturated and unsaturated soil have similar changing trends with the variation of the stress state. The small-strain stiffness of unsaturated soil is calculated by the proposed model based on the test results of saturated soil. The model has two parameters that have a physical meaning and can be measured by tests. Thus, combined with the mature prediction model and measurement method of saturated soil and the proposed hydro-mechanical model, the complex unsaturated bender element tests are unnecessary. The proposed model is anticipated to be of practical value for solving engineering problems during the determination of small-strain parameters in the design of pits and foundations.
Numerical analysis of the indentation of a poro-elastoplastic half space by a rigid cylinder
Authors: Zhang Tiansheng , Liu Ming , Huang Haiying
Published: May 2024

Poro-elasto-plastic cylindrical indentation as a means for material characterization is explored numerically in this work. When a rigid cylinder is being pressed into a semi-infinite, fully saturated poroelastic medium via step displacement loading, undrained and drained elastic constants are reflected in the responses at the early and late times, while hydraulic diffusivity is manifested in the transient behavior. Such an indentation test can therefore be used in principle to identify material parameters. For geomaterials, plastic deformation may occur due to the indentation action. How the hydromechanically coupled indentation response is affected by plastic deformation is investigated here using finite element analysis. We consider the problem to be plane strain with frictionless contact. Drucker-Prager failure criteria with and without a cap are considered. We show that if there is only limited plastic deformation, the concept of using the transient response for determining hydraulic diffusivity may be extended from poroelasticity to poro-elasto-plasticity.
Experimental study on quantitative drilling of composite rock mass
Authors: Liu Zhenghao , Wang Jing , Shi Shaoshuai , Sun Fahe , Li Quanjiang , Fu Shinong , Chen Yuning
Published: May 2024

Effective identification of the interface position and characteristics of rock formations is important for identifying dangerous sources of structural deterioration in rock formations. To explore the sensitivity of the drilling parameters to changes in the formation characteristics and the influence of the interface on the drilling response of a composite rock mass, 28 test models with varying interface inclinations are designed. Laboratory quantitative drilling test research is conducted using the laboratory digital drilling test system at Shandong University. The influence law of the rock interface dip angle on the drilling parameters is established. Empirical equations for estimating the peak drilling pressure and peak drilling torque at the rock interface and the steady-state drilling pressure, drilling torque, and their differential values are established using multiple regression analysis. This study is expected to serve as a reference for improving digital drilling measurement accuracy.
A fast and automatic establishment method of the calculation formula for the tunnel face safety factor based on analytical solution
Authors: Man Jianhong , Huang Hongwei , Chen Jiayao
Published: May 2024

Assessing rock tunnel face stability when constructing mountain tunnels is of utmost importance because it is influenced by various factors, including the tunnel diameter, depth, excavation dimension, geological strength index, uniaxial compressive strength, and Hoek-Brown constant. This study established a tunnel face stability database based on analytical solutions that considered the correlation between the influencing parameters. Finally, a safety factor prediction equation was constructed by combining response surface methodology and the multivariate adaptive regression spline algorithm. The results of this study find applications at construction sites and provide a reference for the rapid evaluation of rock tunnel faces during construction.
Damage characteristics of rock induced by unloading in hole under true triaxial boundary stresses: Experimental study
Authors: Xiao Y , Wang S F
Published: May 2024

In order to study the effect of unloading of underground rock excavation on the stability of surrounding rock, the true triaxial compression (TTC) and coupled true triaxial compression and in-hole loading-unloading tests (TTC-HU) were conducted on hollow cubic rock (100mm × 100mm × 100mm). The experimental results indicate that the compressive strengths of the specimens increase as confining pressure increases in the equal biaxial stressand increase with increasing intermediate principal stresses in the unequal biaxial stress. At low confining pressure (σ < 30 MPa), the internal stress at unloading damage in the hole of hollow cubic specimen increases with the increase of the three-directional boundary stresses. At high confining pressure (σ ⩾ 30 MPa), the specimen will not be damaged during the entire unloading process in the hole. The damage mode of the specimen is dominated by tensile damage. The shape of the holes in the specimens did not significant change, and hole wall of specimen have layered destruction along the circumference in low confining pressure. In high confining pressure, the hole area of the specimen undergoes significant deformation damage, forming a V-groove along the direction of the minimum principal stress, and the wall of the hole is completely peeled off. This study can reasonably predict the actual engineering damage patterns and guide the optimization of surrounding rock support.
Key principles of stress control method
Authors: Xiao Y M , He M C , Qiao Y F , Peng M L
Published: May 2024

Underground excavation would cause two main excavation effects: (1) stress redistribution, including radial stress decrease and tangential stress concentration; and (2) surrounding rock degradation. Comprehensive consideration of excavation effects is crucial to prevent underground engineering disasters. However, the two excavation effects are not considered in the predominantly used Platts pressure arch theory, whereas the New Austrian tunneling method is focused on the full utilization of the strength of the surrounding rock. Construction designing using these methods could lead to disaster deep underground. Thus, in this study, the stress control method (SCM) was proposed to comprehensively consider the two excavation effects. The following two key SCM principles were introduced in this study: (1) adopt the largest possible prestressing force to increase the low radial stress caused by excavation; (2) timing of support should be as early as possible to minimize surrounding rock deterioration. The application principles of SCM in hard rock tunnels and soft rock tunnels are explained
Quasistatic progressive crack propagation behavior of crystalline rocks based on SCB tests
Authors: Zhao Cheng , Zhao Yinghui , Xing Jinquan , Xiang Fubin , Qian Yuan
Published: May 2024

To explore the influence of mineral grains on the mechanical strength and crack propagation behavior of rocks, this study investigates the quasi-static crack propagation characteristics in four types of granular structured rocks (three varieties of granite and one type of diabase rock) through a semi-circular bend three-point bending test. The implementation of a servo-controlled crack-opening displacement mechanism facilitated the realization of quasistatic crack propagation. The entire experimental procedure was documented on a camera. Subsequently, the quasistatic propagation and development of cracks in crystalline rocks were examined using digital image correlation, whereas the distribution of mineral grains and their relationship with the pattern of crack evolution were investigated under optical microscopy. The paths of the cracks exhibited noticeable deviation, which were further influenced by the mineral grains. Specifically, cracks tended to circumvent harder minerals while gravitating towards softer ones, highlighting the significant role of mineralogical composition in determining the fracture behavior of granite.
Study on the characteristics of granite rock impact crack based on grain-based model
Authors: Cao Ansheng , Wang Jianxiu
Published: May 2024

The type and heterogeneity of minerals control the initiation, aggregation, and expansion of rock blasting cracks and significantly affect the rock failure process. Granite was used to investigate the law of rock cracking under impact loading at the scale of mineral particles, and a two-dimensional grain-based model (GBM) was developed using PFC based on CT) scanning and laboratory mechanical tests. The GBM’s reliability was validated using laboratory uniaxial compression tests and numerical simulations. The specimen failure modes and evolution of microcracks during rock impact were analyzed, as well as the impact cracks’ characteristics under various impact velocities. The findings show that the GBM can simulate the microfracture behavior of several types of mineral fractures during rock impact. The evolution of granite cracks under impact loading can be divided into three stages: rapid growth, decreased growth, and gradual stabilization. The impact failure cracks of the samples were primarily tensile and intragranular. Granite’s tensile and shear fractures and intergranular and intergranular cracks of granite exhibit various trends with varying impact velocities. The GBM is viable for researching the dynamics of crystalline rocks and is a powerful tool for exploring the dynamic characteristics of rocks at the mineral particle level.
Seismic source of rock drill and its application in in-situ vibration monitoring of rock mass
Authors: Liu Z , Wang W , Li Q , Wang J , Chen Y , Zhang R , Zhou D
Published: May 2024

This study suggests the use of a seismic source of a rock drill as a new excitation method for real-time monitoring of the vibration frequency of rock masses in tunnel engineering. In this study, a laboratory rock drill seismic source test system was developed. The rock mass excitation and vibration response under real in situ stress were simulated, and a natural frequency test of different lithologic materials under various in situ stresses was carried out based on the developed system. Empirical equations for estimating natural frequency were established using regression analysis. The test results show that (1) the laboratory rock drill seismic source test system exhibits good performance and can simulate the horizontal excitation process of the tunnel rock drill. Rock drill excitation may be used as the seismic source to continuously measure the in-situ vibration information of the rock mass. (2) The natural frequency of rock is positively correlated with rock elastic modulus and geostress and negatively correlated with rock density. This is not directly related to the seismic source.
Plastic zone and surrounding strain analysis in a lined cavern for compressed air energy storage subjected to cyclic high internal gas pressure and temperature
Authors: Wei Chao , Zhao Cheng , Zhao Chunfeng , Qian Yuan , Zhou Biaohe
Published: May 2024

In the context of compressed air energy storage (CAES) technology, the strategic excavation of hard rock caverns is pivotal for overcoming geological challenges and advancing CAES deployment. This study adopts a circular profile for the cavern and investigates the impact of variables such as cavern diameter and depth. Considering the influence of cyclic internal gas pressure, temperature fluctuations, and potential leakage on the cavern, a thermo-hydro-mechanical coupled numerical model is developed using Comsol software. This model, grounded in classic elastoplastic constitutive relations, aligns with the conditions of a proposed project. It facilitates the computation of the plastic zone and surrounding strain for both the cavern lining and adjacent rock, post-excavation and throughout a typical ‘charging-storage-discharging-storage’ operational cycle. Through detailed analysis, the study delineates the variations and characteristics of the plastic zone and surrounding strain, thereby providing a solid foundation for a comprehensive examination of cavern stability, and the design of linings and sealing mechanisms.