KSCE Journal of Civil Engineering最新文献

A detailed exploration about the development of the microscopic behavior of red-bed mudstones and exploration of their anisotropic deformation mechanisms in-depth can help to optimize the improvement of red-bed subgrade. To discuss the effects of single immersion and dynamic wetting-drying cycles, the Aramis system was used to monitor the mudstone deformation, whose results were compared with results of conventional deformation tests; the patterns of moisture migration was analyzed. Variations in mineral compositions, particle orientation and pore characteristics during cycles were investigated. The results show that after encountering water, red-bed mudstones swelled in axial and shrank in radial; the swelling first started around the initial fissures. During wetting-drying cycles, the decrease of equivalent montmorillonite content leads to the weakening of water absorption capacity and deformation capacity of the red-bed mudstone from the sixth wetting-drying cycle; moisture migration causes a directional shift of mudstone particles towards the direction of moisture migration, which triggers anisotropy of the red-bed mudstone deformation; moreover, wetting-drying cycles lead to the increase of pores and fissures inside the red-bed mudstone, with a more complex morphology and the increase of scattered detrital particles, which are the main reasons for the continuous deformation of the red-bed mudstone.

To address the commonly encountered loading and unloading disturbance issues in deep coal resource development, this study analyzes the mechanical properties and deformation characteristics of coal and sandstone. Additionally, a loading and unloading response ratio (LURR) based on crack initiation stress is established to investigate the significance of structural damage and its precursors. Finally, a new rockburst tendency index is defined based on the drop of LURR. The results show that the hysteresis loop of coal and sandstone exhibited three stages of characteristics. The Young’s modulus of both coal and sandstone increased parabolically during loading and unloading process. Sandstone was more prone to larger lateral deformation changes than coal under high confining pressure. LURR of coal could be classified into three stages, while the LURR of sandstone had only two stages. The former could be used as a parameter to evaluate the degradation degree of materials under the collaborative action of coal and sandstone, and the trend of the LURR could be used as a precursor of system failure. it can represent energy dissipation capacity of the mechanical system. The rockburst tendency index based on the drop of LURR effectively reflects the changes in fractal dimension D and surface roughness after material failure, and this index can be classified into three levels: weak, medium, and strong. The research results are expected to improve the understanding of the failure process in underground engineering and system failure.

Recently, digital mines (DM) have plays an increasingly important role in ensuring the safety, effective management and operation of mining activities. One of essential pillars for digital transformation in mining is Building Information Model (BIM), which is also one of the first steps to implement Digital Twin. Additionally, using BIM integrated with Terrestrial Laser Scanning (TLS) and adopting digital technology can provide powerful assistance in life cycle of mining. In this study, integrating BIM and TLS point clouds, which is the basic framework of DM, was applied to build 3D mining information model as well as assessing safety of Nui Beo underground coal mining in Vietnam. Industry Foundation Classes (IFC) standard is used to define the mining information model based on TLS point clouds providing geometric and attributive information of the structures. The 3D model was built for important structures of the mine, including the mine shaft, and tunnels based on TLS point cloud. Additionally, the safety assessment of rail tracks in the mine shaft was performed by comparing the TLS point cloud of rail tracks and their as-designed BIM models. The results showed that the integration of BIM and TLS is a practical solution for the information management and safety assessment of underground coal mines.

To accurately obtain the active earth pressure of a limited-width sandy fill behind a rigid retaining wall under translational failure, finite element limit analysis (FELA) was used to simulate the failure mechanism of the limited-width sandy fill behind the wall under the translational failure mode of the rigid retaining wall. Based on the different development characteristics of the sliding surface, three kinds of failure mode characteristics were identified. Semianalytical expressions of the active earth pressure were obtained by using the limit equilibrium method and the finite difference method, introducing the horizontal differential element and considering the soil arching effect behind the wall. The parameter analysis shows that the width-to-height ratio of the fill and the slope angle play a controlling role in the failure mode and that the position of the resultant force corresponding to the active earth pressure under different failure modes also changes significantly. The active earth pressure exerted on the retaining wall is maximized at a particular threshold of the friction angle at the wall–fill interface, which varies according to the geometric shape of the backfill and its internal friction angle.

In order to ensure construction efficiency and stability during tunnel excavation, it is essential to predict geological risks ahead of tunnel faces. In this study, a geological risk prediction model was developed based on a machine learning (ML) algorithm. The database used to implement the ML model was synthetically acquired from a series of finite-element (FE) numerical analyses, which could simulate electrical resistivity surveys during tunnel excavation. The developed FE model helped obtain resistivity data representing various risky ground conditions (such as typical fault zones, water intrusion, mixed ground, geological transitions, and cavities) encountered during tunnel advancement. Four ML algorithms (support vector machine, k-nearest neighbors, random forest, and extreme gradient boosting) were used to develop the prediction model. The evaluation results showed that the proposed ML prediction models produced highly accurate results. Among the ML algorithms, the prediction model based on the random forest (RF) algorithm exhibited superior performance, with an accuracy of 97.33%. Given the feasibility and efficiency of recognizing hazardous ground conditions, the proposed model is expected to serve as a reliable approach for risk management. Finally, an engineering flowchart was proposed to assist in the application of the study results to actual tunneling sites.

In this paper, we conducted the axial compression test on one improved welded concrete filled L-shaped steel tube (IWCFLST) stub column and two stirrup-enhanced IWCFLST stub columns. The experimental results indicate that the stirrup-enhanced IWCFLST stub columns exhibit better compressive mechanical properties. The stirrups can increase the axial compressive load-bearing capacity by up to 35% and the ductility coefficients by 77%. The impact of the equivalent stirrup ratio on the axial compression mechanical behavior was investigated. Three-dimensional (3D) solid finite element (FE) model of the specimens was constructed by ABAQUS. Parametric analysis was performed and the restriction action of IWCFLST stub column under axial compression was studied. The numerical study revealed the working mechanism of stirrups, steel tubes on concrete, while direct confinement of concrete elevates its axial stress level. Considering the shape and the stirrups, the axial compression ultimate load-bearing capacity design method of the IWCFLST stub column was proposed, providing data support for the promotion and application of special-shaped CFST columns.

This article reports a study on the performance of the alkali activated slag (AAS) mortars upon exposing to the elevated temperatures. Two cooling methods (i.e., cooling in air and water-spring) were adopted following the heating treatment. The mechanical properties, durability, microstructure and phase evolution of AAS and OPC after heating-cooling process were researched. For AAS specimens, the compressive strength loss was smaller, but the flexural strength loss was greater compared to that of OPC specimens after undergoing the heating-cooling process. AAS specimens exhibited higher carbonation depth, and lower penetrated chloride ion. AAS-W specimens shows a higher resistance to cracks formation than OPC-W. With the heating temperature increased, the capillary pore proportion of AAS specimens gradually increased above 80% at 800°0;C. However, high content of transition pores and capillary pores were found at 800°0;C in OPC specimens. The new substances were generated when the temperature was 800°0;C for AAS specimens.

To reasonably evaluate the damage degree of a single-layer spherical mesh shell structure during an earthquake, we develop an improved two-parameter nonlinear combined damage model based on the existing Park-Ang damage model for mesh-shell structures by subtracting the displacement of the elastic phase from the displacement term and adopting the form of a nonlinear combination of the displacement term and the energy dissipation term. Based on material damage accumulation, 144 sets of numerical models covering different spans, rise/span ratios, roof masses, and member sizes were developed and fitted to obtain the values of the parameters to be determined in the damage model, and then, an improved Park-Ang two-parameter damage model for mesh-shell structures was proposed. The critical values of damage indices of the structure at the four performance points were 0, 0.3, 0.7, and 1. The validity of the two-parameter damage model was verified using a single-layer spherically mesh shell structure with three different structural parameters. The results revealed that the improved Park-Ang two-parameter damage model has a damage value of zero in the elastic phase, which satisfies the lower bound convergence and has a good computational accuracy and small dispersion. In addition, the index values of the four performance points reflect the performance status of the mesh-shell structure, indicating that the improved Park-Ang damage model is suitable for evaluating the damage evolution process of the structure under seismic action. This proposed damage model lays a foundation for vulnerability analysis and seismic risk assessment of mesh shell structures, a basis for post-earthquake repair, the development of an optimal design for mesh shell structures, and the analysis of casualty and economic loss statistics.

As the operational velocity of high-speed railways significantly increases, the dynamic interplay among trains, route alignment, and track-bridge systems notably intensifies. To investigate the intricate relationships among track alignment, vehicles, and their underlying structures, as well as to identify suitable alignment parameters, this paper introduces a dynamic simulation model rooted in the principles of vehicle-track-bridge dynamic interactions. A variety of methods and metrics for assessing the comfort of train rides are compiled, and corresponding software is developed for verification. Three case studies illuminate the pragmatic application of dynamic analysis techniques in the determination of track alignment parameters, the adjustment of track geometry, and the compatibility of track-bridge structures. Furthermore, the design of high-speed railway lines is evaluated and refined. The findings of this research not only furnish theoretical and technical support for the crafting of high-speed railway tracks but also present practical instruments for enhancing the operational performance of trains and ensuring structural safety.

This paper investigated the effect of different loading methods on the collapse mechanism of reinforced concrete (RC) structures by conducting tests on two RC beam-column sub-assemblages. Tests employed two loading methods, i.e., concentrated loading (CL) method and uniformly distributed loading (UDL) method. Failure modes and load-displacement curves of the sub-assemblages were obtained by the tests. The results revealed that the specimens subjected to different loading methods exhibited different failure modes. The CL method would over-estimate the deformation capacity of the sub-assemblages. The ultimate displacement of the specimen subjected to CL was 3.5% higher than that subjected to UDL. The ANSYS/LS-DYNA based finite element (FE) analyses were performed to discuss the effects of different initial uniform loads on UDL specimen beams. The FE results indicated that the deformation capacity decreased with the increase of initial uniform loads. A 200% increase in initial uniform load decreased the ultimate displacement by 10.3%. Moreover, comparison of results under single- and multi-point loading demonstrated that the failure modes of specimens were influenced by the number of loading points.