Hasil untuk "Engineering geology. Rock mechanics. Soil mechanics. Underground construction"

Esteban Parra, Sonia Haiduc, Preetha Chatterjee et al.

Peer review is the main mechanism by which the software engineering community assesses the quality of scientific results. However, the rapid growth of paper submissions in software engineering venues has outpaced the availability of qualified reviewers, creating a growing imbalance that risks constraining and negatively impacting the long-term growth of the Software Engineering (SE) research community. Our vision of the Future of the SE research landscape involves a more scalable, inclusive, and resilient peer review process that incorporates additional mechanisms for: 1) attracting and training newcomers to serve as high-quality reviewers, 2) incentivizing more community members to serve as peer reviewers, and 3) cautiously integrating AI tools to support a high-quality review process.

Yuhao Jin, Shuo Yang, Hui Guo et al.

Fractured rock masses are extremely common in geological engineering. In order to improve the stability of surrounding rock under dynamic conditions, new grouting materials and their reinforcement characteristics were studied. In this paper, split Hopkinson pressure bar (SHPB) tests were employed to analyze the dynamic mechanical and failure characteristics of grouted fractured rock with nano-grouting material (nano-grouted fractured rock). Simultaneously, high-speed camera tests were utilized to examine the macroscopic dynamic deformation and failure processes. The following was found: (1) Under a relatively low impact air pressure of 0.1 MPa, the mechanical properties of nano-grouted fractured rock are considerably better than those of traditional cement-based grouted rock. However, when the impact air pressure is increased to 0.3 MPa, the superiority of nano-grouting material diminishes, the possible cause of which is explained from the microscopic point of view. This means the nano-grouting material is more suitable for low-engineering-disturbance conditions (e.g., shield construction). (2) Both for the nano- and superfine cement grouting material, the impact fractures initially emerge at the two ends of the original grouted fracture and form a pair of parallel lines. (3) In comparison with 0.1 MPa, the impact pressure of 0.3 MPa leads to more severe damage to the rock specimen. These findings contribute to a deeper understanding of the behavior of nano-grouted fractured rock under dynamic loading and provide valuable insights for relevant engineering applications in the field of rock mechanics and grouting technology.

Haoyu Wang, Jichen Xie, Jinyang Fu et al.

Small-section hydraulic tunnels are characterized by small spaces and various section forms, under complex environments, which makes it difficult to carry out an inspection by the mobile acquisition equipment. To resolve these problems, an arbitrarily adjustable camera module deployment method and the corresponding automatic image acquisition equipment with multi-area array cameras are proposed and developed. Such method enables the acquisition of full-length surface images of the hydraulic tunnels with different cross-section forms and diameters by a one-way travel, and the overlap rate and accuracy of the acquired image sets meet the requirements of three-dimensional reconstruction and panoramic image generation. In addition, to improve the speed and accuracy of traditional algorithms for tunnel surface defects detection, this paper proposes an improved YOLOv5s-DECA model. The algorithm introduces DenseNet to optimize the backbone feature extraction network and incorporates an efficient channel attention ECA module to make a better extraction of features of defects. The experimental results show that mAP, and F1-score of YOLOv5-DECA are 73.4% and 74.6%, respectively, which are better than the common model in terms of accuracy and robustness. The proposed YOLOv5-DECA has great detection performance for targets with variable shapes and can solve the problem of classification imbalance in surface defects. Then, by combining YOLOv5-DECA with the direction search algorithm, a “point-ring-section” method is established to allow rapid identification of common surface defects by detecting them layer by layer with the bottom image of the stitched panorama as the seed. The presented method in this paper effectively solves the problem that a single image fails to show the overall distribution of the defects and their accurate positioning in a whole large tunnel section and the effective features of defects in an excessively large panoramic image size are difficult to be captured by the neural network. Field applications demonstrated that the presented method is adequate for high-precision and intelligent surface defect detection and positioning for different small-section hydraulic tunnels such as circular, arch-wall, and box-shaped hydraulic tunnels.

Yang Zhao, Rui Wang, Jian-Min Zhang

We present an assumed enhanced strain finite element framework for the simulation of tensile fracturing processes in transversely isotropic rocks. Fractures along the weak bedding planes and through the anisotropic rock matrix are treated with distinct enrichment, and a recently proposed dual-mechanism tensile failure criterion for transversely isotropic rocks is adopted to determine crack initiation for the two failure modes. The cohesive crack model is adopted to characterize the response of embedded cracks. As for the numerical implementation of the proposed framework, both algorithms for the update of local history variables at Gauss points and of the global finite element system are derived. Four boundary-value problem simulations are carried out with the proposed framework, including uniaxial tension tests of Argillite, pre-notched square loaded in tension, three-point bending tests on Longmaxi shale, and simulations of tensile cracks induced by a strip load around a tunnel in transversely isotropic rocks. Simulation results reveal that the proposed framework can properly capture the tensile strength anisotropy and the anisotropic evolution of tensile cracks in transversely isotropic rocks.

Yu Zhang, Jian Chu, Shifan Wu et al.

Accurate determination of rockhead is crucial for underground construction. Traditionally, borehole data are mainly used for this purpose. However, borehole drilling is costly, time-consuming, and sparsely distributed. Non-invasive geophysical methods, particularly those using passive seismic surface waves, have emerged as viable alternatives for geological profiling and rockhead detection. This study proposes three interpretation methods for rockhead determination using passive seismic surface wave data from Microtremor Array Measurement (MAM) and Horizontal-to-Vertical Spectral Ratio (HVSR) tests. These are: (1) the Wavelength-Normalized phase velocity (WN) method in which a nonlinear relationship between rockhead depth and wavelength is established; (2) the Statistically Determined-shear wave velocity (SD-Vs) method in which the representative Vs value for rockhead is automatically determined using a statistical method; and (3) the empirical HVSR method in which the rockhead is determined by interpreting resonant frequencies using a reliably calibrated empirical equation. These methods were implemented to determine rockhead depths at 28 locations across two distinct geological formations in Singapore, and the results were evaluated using borehole data. The WN method can determine rockhead depths accurately and reliably with minimal absolute errors (average RMSE = 3.11 m), demonstrating robust performance across both geological formations. Its advantage lies in interpreting dispersion curves alone, without the need for the inversion process. The SD-Vs method is practical in engineering practice owing to its simplicity. The empirical HVSR method reasonably determines rockhead depths with moderate accuracy, benefiting from a reliably calibrated empirical equation.

Jikai Chen, Zhi Zeng, Hao Ma et al.

Four ultra-low background germanium spectrometers, called GeTHU, have been installed at the first phase of China Jinping Underground Laboratory (CJPL-I), and served for material screening of dark matter and neutrino experiments. Recently, a new multi-detector spectrometer with five germanium detectors has been developed and installed at the second phase of CJPL (CJPL-II) with a minimum detectable activity (MDA) of about 10 μBq/kg. In addition, another fifteen GeTHU-like spectrometers have been installed at CJPL-II with an MDA of about 1 mBq/kg. This paper will introduce the ultra-low background germanium spectrometers including shielding design, background characteristics and application to material screening.

LI Jiong 1, 2, 3, LI Mingguang 1, 2, ZHAN Hongbing 4, CHEN Jinjian 1, 2, XIA Xiaohe 1, 2

To address the issue that the traditional models of well hydraulics for constant-head tests (CHTs) fail to reflect the effects of the clogging in well vicinity on groundwater flow dynamics, a semi-analytical model of the groundwater hydraulics in well vicinity is developed for CHTs using partially penetrating wells. A combination of variable substitution, Laplace transform and finite Fourier cosine transform is used to develop the solutions for the proposed model in the Laplace domain. Then, the solutions in the real-time domain are obtained using the Stehfest numerical Laplace inversion method. A parametric study of the developed solution indicates that a smaller asymptotic hydraulic conductivity Kr, ∞ leads to the smaller hydraulic head increment s and the less injection flux Q and reduces the quasi-steady flow dynamics of the recharged aquifer, while a larger permeability reduction exponent λ decreases s and Q only in the middle stage of the injection tests but has few effects on the quasi-steady flow dynamics. The hydraulic head difference due to various values of Kr, ∞ and λ first increases and then decreases with the radial distance and reaches its maximum value at the interface of the clogging region and the formation. The clogging in well vicinity results in an obvious inflection point at the outside boundary of the clogging region on the distribution curve of s and leads to an apparent decreasing stage of the history curve of s, which can offer theoretical reference for the evolution and prediction of the clogging development.

MA Zhicong, MEI Bo, SU Li et al.

Aiming at the corrosion problem of steel bars in concrete in subtropical marine environment, the full immersion corrosion experiments of reinforced concrete specimens with different strength grades and rust inhibitor contents were carried out by simulating the subtropical marine environment.The macroscopic indexes such as chloride ion content were tested by electrochemical non-destructive testing, and the experimental results were verified by microscopic detection methods.The corrosion degradation patterns of reinforced concrete was analyzed.The results show that the improvement of concrete strength grade and the increase of rust inhibitor content can significantly improve the corrosion resistance of reinforced concrete.Among them, the corrosion resistance of C30 concrete is the worst.At 120 d, the corrosion current density is 0.118 μA/cm2, the polarization resistance is 220 kΩ cm2, the concrete resistance is 87.3 kΩ cm2, and the transfer resistance of the steel-concrete interface area is 77.3 kΩ cm2, reaching the passivation state.When the concrete strength grade is increased to C50, the corrosion current density is reduced by 58.47%, the polarization resistance is increased by 3.82 times, and the concrete resistance is increased by 44.56%;when the amount of rust inhibitors is 6 kg/m3, the corrosion current density is reduced by 47.45%, the polarization resistance is increased by 2.81 times, and the transfer resistance at the reinforcement-concrete interface is increased by 72.43%.

A. Yassine Karoui, Remco I. Leine

The aim of this paper is to explore the relationship between invariant cones and nonlinear normal modes in piecewise linear mechanical systems. As a key result, we extend the invariant cone concept, originally established for homogeneous piecewise linear systems, to a class of inhomogeneous continuous piecewise linear systems. The inhomogeneous terms can be constant and/or time-dependent, modeling nonsmooth mechanical systems with a clearance gap and external harmonic forcing, respectively. Using an augmented state vector, a modified invariant cone problem is formulated and solved to compute the nonlinear normal modes, understood as periodic solutions of the underlying conservative dynamics. An important contribution is that invariant cones of the underlying homogeneous system can be regarded as a singularity in the theory of nonlinear normal modes of continuous piecewise linear systems. In addition, we use a similar methodology to take external harmonic forcing into account. We illustrate our approach using numerical examples of mechanical oscillators with a unilateral elastic contact. The resulting backbone curves and frequency response diagrams are compared to the results obtained using the shooting method and brute force time integration.

Jacinto Ulloa, Laurent Stainier, Michael Ortiz et al.

This paper explores the role of generalized continuum mechanics, and the feasibility of model-free data-driven computing approaches thereof, in solids undergoing failure by strain localization. Specifically, we set forth a methodology for capturing material instabilities using data-driven mechanics without prior information regarding the failure mode. We show numerically that, in problems involving strain localization, the standard data-driven framework for Cauchy/Boltzmann continua fails to capture the length scale of the material, as expected. We address this shortcoming by formulating a generalized data-driven framework for micromorphic continua that effectively captures both stiffness and length-scale information, as encoded in the material data, in a model-free manner. These properties are exhibited systematically in a one-dimensional softening bar problem and further verified through selected plane-strain problems.

Kaimin Duan, Guofeng Zhang, Hui Sun

The construction practice of water conveyance tunnels often encounters various complex geotechnical engineering conditions, which bring huge challenges to the design and construction of water conveyance tunnels. Based on the theory of rock elastic–plastic mechanics and finite element analysis technology, this article carried out investigations of engineering geological features, geological formations and hydrological conditions establishes a calculation model for the 3# water conveyance tunnel of the Fenhe River Diversion Project, and analyzes the variation law of surrounding rock stress and displacement during TBM excavation of the tunnel. The results indicate that the dominant direction of the rock mass principal stress measured by the hydraulic fracturing method is NE84°, and the maximum horizontal principal stress, minimum horizontal principal stress, and vertical stress decrease sequentially, analyzing the characteristics of shield TBM construction technology, it is applied to the construction of water transfer tunnels. The numerical simulation of TBM construction using FLAC3D software shows that as the excavation surface advances, the subsidence value of the tunnel roof first slowly increases, then rapidly increases, and then tends to stabilize. The horizontal displacement of the surrounding rock is increasing. The maximum principal stress of the surrounding rock gradually increases. The final surrounding rock stress is 35 MPa. The TBM shield machine with mud water balance driven by indirectly controlled frequency conversion motor is selected for TBM construction of the tunnel. The study offers statistical information to support tunneling technology for water conveyance in the geotechnical engineering practice.

Xingyu Zhang, Jinsong Du, Chao Chen et al.

The Tibetan Plateau underwent rapid uplift and complex lithospheric modification during the Cenozoic under the continuing collision and subduction of the Indian Plate, but the present-day vertical dynamic motion and crustal deformation of the plateau remain controversial. This paper calculates the flexural isostatic gravity anomalies on the Tibetan Plateau and its neighboring blocks based on the flexural model with variable effective elastic thickness and using topographic data and Earth's gravity field model. The results show that the isostatic gravity anomalies on the Tibetan Plateau range from -120 to 90 mGal, with the central part characterized by distinct positive anomalies and the margins by significant negative anomalies. Minimal values occur in the northwest Tibetan Plateau and its adjacent Pamir Plateau, while maximal values occur in the northwest part of the Himalaya block. In addition, to the north and east of the Tibetan Plateau, the Tarim Basin and Sichuan Basin show large areas of positive isostatic anomalies. These features suggest that the crust of the Tibetan Plateau and its surroundings is now in a nonisostatic state, with the overall uplift of the older block under the effect of plate collision and compression, leading to positive isostatic anomalies. In younger orogenic regions, crustal deformation is primarily characterized by surface uplift and strong thickening of the lower crust, resulting in negative isostatic anomalies. In the central and northern parts of the plateau, the direction of isostatic adjustment is consistent with the trend of crustal vertical motion. However, south and east of the plateau (e.g., the Himalaya block and Sichuan Basin), the direction of isostatic adjustment is opposite to that observed for surface deformation. This suggests that the Indian Plate collision and subduction still control the crustal deformation processes in the southern and eastern parts of the Tibetan Plateau and its neighboring blocks. However, further north, the crust regains an isostatic state through isostatic adjustment.

Xuemei Liu

Engineering geological conditions include the nature of rock and soil, geological structure, landform, hydrogeological conditions, and adverse geological processes. Among them, faults, fissures, folds, karst, and lithology changes seriously affect the safety and construction cost of mountain tunnels, hydraulic tunnels, and other projects. For this reason, a new method based on feature fusion is proposed to detect the geological anomalies in London and Sheffield. It established a 3D raster data model oriented to attribute information modeling and visualization of urban underground space to obtain geological data. Based on this acquired data, authors adopted the feature-level fusion extraction method based on the multi-attribute geological abnormal body to extract, fuse, fill and surface the multi-attribute data of underground space geological data. Smooth processing can realize the detection of abnormal geological bodies in underground space. It has been proved that this method can be used in geological data display, feature extraction, feature fusion, and abnormal physical examination.

Kevin Chew, Gabriele Chiaro, Jayan S. Vinod et al.

In this paper, a newly developed 3-dimentional discrete element model (DEM) for gravel-rubber mixtures (GRMs), namely DEM4GRM, that is capable of accurately describing the macro-scale shear response (from small to large deformation) of GRMs in a direct shear box apparatus is presented. Rigid gravel grains are modelled as simple multi-shape clumps, while soft rubber particles are modeled by using deformable 35-ball body-centered-cubic clusters. Mixtures are prepared with different volumetric rubber content (VRC) at 0, 10, 25, 40 and 100%, statically compressed under 30, 60 and 100 kPa vertical stress and then sheared, by closely simulating a reference laboratory test procedure. The variation of micro-scale factors such as fabric, normal and tangential force anisotropy is carefully examined throughout the shearing process and described by means of novel micro-mechanical relationships valid for GRMs. Moreover, strong-force chains are scrutinized to identify the transition from rigid to soft granular skeleton and gain insights on the load transfer and deformation mechanisms of GRMs. It is shown that the development of the fabric and force anisotropy during shearing is closely related to the macro-scale shear strength of GRMs, and strongly depends on the VRC. Besides, strong-force chains appear to be primarily formed by gravel-gravel contacts (resulting in a rigid-like mechanical behavior) up to VRC = 30%, and by rubber-rubber contacts (causing a soft-like mechanical response) beyond VRC = 60%. Alternatively, at 30% < VRC < 60%, gravel-rubber contacts are predominant in the strong-force network and an intermediate mechanical behavior is observed. This is consistent with the behavioral trends observed in the macro- and micro-mechanical responses.

Longchuan Deng, Xiaozhao Li, Yun Wu et al.

Abstract In deep‐earth engineering, the high earth temperature can significantly affect the rock's mechanical properties, especially when the rock is cooled during the construction process. Accordingly, whether the cooling speed affects the mechanical and physical properties of rocks is worth to be investigated. The present study explored the influence of the cooling rate on the physical and chemical properties of granite heated at 25–800 °C. The mechanical and physical properties involved in this study included uniaxial compression strength, peak strain, modulus, P‐wave velocity, mass and volume, the change of which could reflect the sensitivity of granite to the cooling rate. Acoustic emission (AE) monitoring, microscopic observation, and X‐ray diffraction (XRD) are used to analyze the underlying damage mechanism. It is found that more AE signals and large‐scale cracks are accounted for based on the b‐value method when the specimens are cooled by water. Furthermore, the microscopic observation by polarized light microscopy indicates that the density, opening degree, and connectivity of the cracks under water cooling mode are higher than that under natural cooling mode. In addition, the XRD illustrates that there is no obvious change in mineral content and diffraction angle at different temperatures, which confirms that the change of mechanical properties is not related to the chemical properties. The present conclusion can provide a perspective to assess the damage caused by different cooling methods to hot rocks.

W. Pan

Vinamra Agrawal, Brandon Runnels

Many solid mechanics problems on complex geometries are conventionally solved using discrete boundary methods. However, such an approach can be cumbersome for problems involving evolving domain boundaries due to the need to track boundaries and constant remeshing. In this work, we employ a robust smooth boundary method (SBM) that represents complex geometry implicitly, in a larger and simpler computational domain, as the support of a smooth indicator function. We present the resulting equations for mechanical equilibrium, in which inhomogeneous boundary conditions are replaced by source terms. The resulting mechanical equilibrium problem is semidefinite, making it difficult to solve. In this work, we present a computational strategy for efficiently solving near-singular SBM elasticity problems. We use the block-structured adaptive mesh refinement (BSAMR) method for resolving evolving boundaries appropriately, coupled with a geometric multigrid solver for an efficient solution of mechanical equilibrium. We discuss some of the practical numerical strategies for implementing this method, notably including the importance of grid versus node-centered fields. We demonstrate the solver's accuracy and performance for three representative examples: a) plastic strain evolution around a void, b) crack nucleation and propagation in brittle materials, and c) structural topology optimization. In each case, we show that very good convergence of the solver is achieved, even with large near-singular areas, and that any convergence issues arise from other complexities, such as stress concentrations. We present this framework as a versatile tool for studying a wide variety of solid mechanics problems involving variable geometry.

Chen Zhen, Zhang Zengzhi, Wang Lining et al.

To explore slag-based geopolymer porous material under the condition of different porosity, pore diameter distribution of performance and improve the mechanism of water absorption, the experiments on the water absorption, water release properties of the slag-bnsed geopolymer were Conducted, with blast furnace slag, fly ash, and sodium silicate as the main raw material, and hydrogen peroxide as foaming agent, Image analysis softwares and the fractal theory were adopted to analyze its microstructure and pore structure fractal characteristics.The results show that the porosity, maximum pore size and water absorption of the porous material increase with the increase of the foaming agent, while the time needed to release water per unit mass and fractal dimension of the pore surface decrease.When the dosage of foaming agent is 1.6 ml, the water absorption rate of the material reaches 62 %, and the time required to release water per unit mass is only 1.38 h.At this point, both water absorption and water release properties of the material are taken into account.

Amirsalar Moslehy, Khalid Alshibli

Polycrystalline rock salt’s compression is a function of applied stresses, exposure duration to the applied stresses, ambient temperature, and water content. Rock salt’s compressional behavior under different conditions and its effects on the specimens’ mechanical properties have been investigated in the literature. However, the one-dimensional (1D) compression behavior of polycrystalline rock salt at various water contents and how the specimen’s compression at different water contents further affects its physical and mechanical properties are not fully understood yet. In this study, polycrystalline rock salt specimens were prepared under nominally dry and wet conditions and some of the dry and wet specimens were annealed after the preparation. The relationship between the porosity of the specimens and the logarithm of the applied axial stresses during the 1D compression was found to follow a linear relationship after reaching unique critical porosities of 32% and 37% for the dry and wet specimens, respectively. Unloading and reloading the specimens did not result in any major changes in the porosity of the specimens. The specimens compressed under wet condition showed an average final porosity of 2.6% compared to 6.9% for the dry specimens. The dry and wet specimens that were annealed after the compression exhibited a lower porosity in comparison to the dry and wet specimens, respectively. Unconfined compression experiments on the specimens showed dry and wet specimens possess averaged unconfined compressive strengths (σu) of 64.3 and 16.2 MPa, respectively. Annealing decreased σu of the dry specimens to 39.6 MPa and increased σu of the wet specimens to 41 MPa.

S. S. Shishvan, S. Assadpour-asl, E. Martínez-Pañeda

A new gradient-based formulation for predicting fracture in elastic-plastic solids is presented. Damage is captured by means of a phase field model that considers both the elastic and plastic works as driving forces for fracture. Material deformation is characterised by a mechanism-based strain gradient constitutive model. This non-local plastic-damage formulation is numerically implemented and used to simulate fracture in several paradigmatic boundary value problems. The case studies aim at shedding light into the role of the plastic and fracture length scales. It is found that the role of plastic strain gradients is two-fold. When dealing with sharp defects like cracks, plastic strain gradients elevate local stresses and facilitate fracture. However, in the presence of non-sharp defects failure is driven by the localisation of plastic flow, which is delayed due to the additional work hardening introduced by plastic strain gradients.