Xiaomin Liu

Previous studies of train-induced tunnel responses have mainly focused on completed tunnels or symmetric loading conditions, while the dynamic behavior of unfinished double-arch tunnels subjected to unilateral train loading through temporary trestles remains insufficiently understood. To address this gap, this study investigates the asymmetric load-transfer mechanism and short-term structural response of an unfinished double-arch tunnel–trestle system and identifies critical locations for construction-stage monitoring and speed control. A three-dimensional ABAQUS model was established for train speeds of 10–70 km/h and validated using a 63-day field-monitoring program comprising 15 train passages at speeds of approximately 9.4–56.2 km/h. Both numerical and monitoring results show that stress and deformation increase with train speed and are concentrated at the loaded-side invert, lower middle partition wall, and trestle wheel-load region. At 70 km/h, the calculated maximum lining compressive stress and trestle stress reached 6.353 and approximately 172 MPa, respectively, while the maximum horizontal deformations of the loaded and unloaded tunnel bores were 1.110 and 0.565 mm. At the maximum monitored speed of 56.2 km/h, the measured peak compressive stress of the middle partition wall was 5.95 MPa. The mean monitoring-to-simulation ratios for the evaluated responses were approximately 0.94–0.97, demonstrating satisfactory agreement and a slightly conservative numerical prediction. The results clarify the asymmetric coupling response of the tunnel–trestle system and support the identification of sensitive monitoring locations. Based on the combined numerical and field evidence, approximately 30 km/h is recommended as a conservative, project-specific construction-stage operational-control value. This study provides a quantitative basis for monitoring and risk control in similar temporary rail-transport projects, although further verification under different geological, structural, and loading conditions is required.

Environmental concerns associated with the construction industry have drawn increasing attention worldwide. This study addresses the dual challenges of carbon emissions from cement production and construction waste disposal by developing and characterizing a fiber-modified geopolymer recycled aggregate porous concrete (GRAPC). An orthogonal experiment first optimized the GRAPC mix proportion (slag content = 40%, alkali modulus = 1.4, alkali content = 8%). Subsequently, the effects of coir, basalt, and steel fibers (0.25% and 0.5%) on its properties were investigated through laboratory experiments combined with scanning electron microscopy (SEM) analysis. The results show that steel fibers at 0.25% dosage enhanced compressive strength by approximately 25% due to their effective stress-bearing capacity. In contrast, 0.5% coir and basalt fibers reduced compressive strength by approximately 20.5% and 22.2%, respectively, due to low intrinsic strength and agglomeration. In addition, 0.25% coir and steel fibers increased effective porosity by 18.4% and 17.4%, respectively, owing to their uniform dispersion. All fibers promoted a more ductile-like failure mode, with coir fibers providing the best toughness improvement. This study elucidates how fiber type and dosage regulate the macro-properties and micro-mechanisms of GRAPC, providing a basis for designing sustainable eco-friendly concrete with great potential for non-primary load-bearing engineering fields.

Current methods for predicting deep excavation deformation suffer from insufficient accuracy and limited generalization capability. Moreover, the applicability of these methods to different types of monitoring data also requires in-depth analysis. To address this, a machine learning-based prediction model, i.e., the VMD-GWO-CNN model, integrating Variational Mode Decomposition (VMD), the Grey Wolf Optimizer (GWO), and the Convolutional Neural Network (CNN), is proposed to predict various types of monitoring data. The GWO algorithm optimizes both the key parameters of VMD and the hyperparameters of the CNN. The optimized CNN model predicts each subsequence decomposed by VMD, and the final prediction is obtained by superimposing these results. Furthermore, the prediction performance of the proposed model is evaluated against the LSTM, CNN, and GWO-CNN models using four metrics (RMSE, MAE, MAPE, R²). The results indicate that all four algorithms possess effective predictive capability for the monitoring data, in which the VMD-GWO-CNN model demonstrates the best performance across all metrics. Specifically, its RMSE for surface settlement prediction is reduced by 59.2%, 34.1%, and 33.0% compared to the LSTM, CNN, and GWO-CNN models, respectively. Moreover, the VMD-GWO-CNN model exhibits strong predictive performance for deformation in slope engineering and subgrade engineering, demonstrating its good applicability across different geotechnical engineering. The findings provide a scientific basis for safe excavation construction and contribute to efficient and rapid execution of foundation pit projects.

Small‐radius curved tunnels are increasingly adopted in urban areas to navigate around existing infrastructure. However, their excavation induces more complex and asymmetric soil displacements compared to straight tunnels, especially in S‐shaped alignments where two consecutive reverse curves interact. This study uses 3D numerical modelling (Plaxis 3D) to compare soil settlement patterns from straight, single‐curve and S‐shaped tunnels in soft clay. Results show that the S‐shaped tunnel causes the greatest settlement and the broadest influence zone, with a clear coupling effect between two consecutive reverse‐curvature curves leading to a wavy settlement profile. The settlement field is notably asymmetric, influenced by the intersection angle between the tunnel axis and adjacent infrastructures. The risk assessments of nearby infrastructures are highly dependent on their spatial relationship with the S‐shaped tunnel. These findings highlight the heightened geotechnical risks associated with S‐shaped curved tunnels and underscore the need for tailored design and monitoring strategies in urban tunnelling projects.

This paper studied the feasibility of saturated coal gasification slag (SCGS) as the fine aggregate of cement‐based materials, and discussed the influence of SCGS on the fluidity and compressive strength of cement mortar as fine aggregate based on the study of physical and chemical properties of the particles. The analysis of the mechanism of SCGS on cement hydration was carried out through analysis of the mineral phase composition, pore size distribution and microstructure, as well as thermal analysis of the cement–coal gasification slag (CGS) mixture hydration product. The results indicate that SCGS as fine aggregate does not introduce significant expansion risk. When added to the mortar, SCGS exhibits better flowability and mechanical properties than dry CGS (DCGS). Furthermore, analysis of hydration products shows that SCGS could increase hydration degree of cement and facilitate the formation of calcium–silicate–hydrate (C–S–H gels, contributing to the improvement of the strength. SCGS effectively reduced both the proportion of harmful pores and the pore connectivity within the mortar. Additionally, C–S–H gel fills the microvoids present on the surface of the SCGS mortar, thereby enhancing the compactness of the mortar.

With the increasing utilization of urban underground space in densely populated cities, it is crucial to understand the interactive impact of the excavation sequence on the excavation group of foundation pits. The foundation pit of Tianta Station of Tianjin Metro Line 7 was adjacent to a deep foundation pit of an apartment, which provided a good case for the study of simultaneous excavation of foundation pits. In this paper, based on two deep foundation pit excavation projects, a finite element model was established to better understand the mutual influence of simultaneous foundation pit excavation. The responses of the two deep foundation pits under five different excavation sequences were investigated, including the horizontal displacement of the ground‐connected wall and the displacement of the top of the wall, the settlement of the ground surface, and the supporting axial force of the basement floor slab. The position of the maximum horizontal displacement in different modes is the same, and the shape of the deformation curve was fish‐bellied. When both pits B and C were excavated simultaneously, the surface settlement between adjacent pits was smaller than in other working conditions. Mode 5 is optimal among these five modes, in which not only the construction progress is the fastest but also the underground wall deformation and the ground settlement are relatively small. The findings and lessons learned from these two adjacent pits, both of which were constructed using the cap‐and‐reverse method, can help professionals optimize excavation design and construction, as well as performance prediction and control.

A semi-analytical method is developed to study the visco-elastic interface effect on the dynamic stress of a non-circular symmetrical tunnel in a half-plane subjected to P waves, and the interaction between the visco-elastic interface around the tunnel and the traction free boundary at the half-plane is analyzed. The complex variable function method combined with the wave function expansion method is introduced to obtain the theoretical expressions of waves around the non-circular tunnel. To satisfy the traction-free boundary condition at the half-plane, the large circle assumption is applied. The expanded coefficients are determined by using appropriate boundary conditions with stiffness parameters and viscosity coefficients of the interface. Selected numerical results are presented, and the interface effect on the dynamic stress under different embedded depths is discussed. It is found that the interacting effect of the visco-elastic interface and the traction-free boundary is quite related with the wave frequency. Comparison with existing results is also given to validate the semi-analytical method.

Prestressed high-strength concrete (PHC) pipe pile has the advantages of high single pile bearing capacity, a wide range of applications, good driving resistance, fast construction speed, etc. It has been widely used in high-rise buildings, bridges, ports, and other industries. The application of extra-long PHC pipe piles with a length of more than 50 m is increasing. However, there are few studies on the drivability and hammering criteria of extra-long PHC piles. To analyze the drivability of extra-long piles and predict their bearing capacity, in this paper, high-strain dynamic tests were carried out on 14 test sections with the pile foundation of Temburong Bridge in Brunei as the research background. The hammer stop control criteria calculated according to the Hiley formula would lead to excessive hammering. Three types of damage occurred during construction: pile shaft breakage, weld tearing, and pile head breakage. The weight and drop height of the piling hammer selected for this project were appropriate, and the extra-long test piles can be hammered to the design depth. The values of C_p (Compression of the pile) and n (the efficiency of the blow) were fitted based on the dynamic test data, which provided a more accurate reference for the selection of subsequent piling parameters of the project. It provides a more accurate calculation method for predicting the bearing capacity of extra-long PHC piles and provides control criteria for pile stopping and a scientific basis for their design and construction.