[Objective] An aqueduct is a simply supported bridge-like structure whose main purpose is to transport water over long-distance and difficult terrains. When an aqueduct is constructed in seismically active regions, base-isolation is often needed. However, current research on aqueducts that considers both the pier-soil interaction and topographic effects is lacking. This paper theoretically analysis the influences of pier-soil interaction and topographic effects (mainly V-shaped canyon effect) on the base-isolated Songlin aqueduct of Central Yunnan Water Division Project during an earthquake event. [Methods] The analysis is achieved through modelling using the universal large-scale finite element analysis (FEA) software ABAQUS. The soil-structure interaction (SSI) is simulated through m-method and the equal-stiffness pier method according to relevant standard and research, respectively. The m-method simplifies the SSI as a series of springs. The stiffness of each spring is related to the pier geometries and soil thickness considered. The fluid-structure interaction is simulated through simplified spring-mass model, which is a commonly used analytical model to simulate fluid-structure interaction. In this paper, the spring-mass model is modified for computational efficiency. The results of the modified and traditional spring-mass model are compared to verify the effectiveness of the modified model. The FEA model mainly consists of beam elements and the popular user-defined material database PQ-fiber is adopted in the analysis. Post-tensioning of the aqueduct is achieved through temperature-gradient and material expansion coefficient in ABAQUS. Three-dimensional earthquake actions selected from PEER database are inputted at the pier base of the model as accelerations to simulate the dynamic structural responses of the aqueduct. The V-shaped canyon effect is considered by transforming the time-history and peak ground acceleration (PGA) of the earthquake records. [Results] The structure periods of aqueduct were 2.81, 1.72 and 1.40 s for the first three deformation modes, respectively. The structure periods changed to 2.82, 1.75 and 1.44 s after the introduction of SSI, respectively. The FEA results indicated that the pier deformation, inter-span relative displacement and isolation bearing deformation were amplified after SSI was introduced. Amongst the parameters, the deformation of the isolation bearings was observed to approach its design limits. This posed the threats of isolation bearing failure during a seismic event. The flexure strength demands at the base of the piers are relatively insensitive to the introduction of SSI. It was also found that the higher the pier, the effects of SSI on inter-span relative displacement, isolation bearing deformation and pier-base flexural strength demand became more pronounced. [Conclusions] the introduction of SSI decreased the stiffness of pier-ground connection which resulted in the slight decrease of the structural period of the aqueduct. Parametric analysis of the angles of incidence between the horizontal surface and the horizontally-polarized shear waves produced due to V-shaped canyon effect demonstrated that the overall response of the Songlin aqueduct is greatest with the horizontal incidence, followed by the oblique incidence, uniform incidence and vertical incidence. It is also found that the inter-span relative displacement and isolation bearing deformation along the aqueduct direction can exceed their respective design limits and should be carefully checked in the design process.

[Objective] Digital twin technology can improve the quality of operation management of pumping station groups in water diversion and transfer projects. However, the current application of digital twin technology in the operation management of pumping station groups remains exploratory. Moreover, certain problems persist, such as difficulties ensuring the operational performance of digital twin scenes and combining the integration of data, knowledge, and models with business, all of which hamper the application of digital twin technology. To bridge this gap, this study constructs a six-dimensional theoretical model and basic framework of a digital twin engine and proposes a high-performance digital twin engine construction method in combination with the business requirements of a pumping station group’s operation management. [Methods] In terms of theoretical modeling, this paper divides the critical elements of a digital twin engine into six aspects: Physical scenes, twin scenes, services, twin data, connections, and feedback and decision-making. These elements are interrelated, thus mapping the physical scenes into twin scenes and realizing the digital twin engine’s dynamic operation and virtual-real integration through services, twin data, and connections. On the basis of the theoretical model, the digital twin engine framework combines the business elements of the pumping station group’s operation management. These include data collection, data storage, support, function, and display layers, which provide a data foundation, operation environment, function services, and interaction window for the engine. Furthermore, the digital twin engine construction method includes the following five aspects: Twin scene generation engine, data management engine, dynamic virtual-physical mapping engine, operation simulation and analysis engine, and reality interaction and feedback control engine. In particular, the twin scenes generation engine generates high-performance and smooth twin scenes through lightweight BIM processing and data-knowledge-model fusion. The data management engine builds a multiprecision, full-factor twin data resource pool. The dynamic virtual-physical mapping engine realizes real-time and dynamic iterative updating of physical scenes in twin scenes. Moreover, the operation simulation and analysis engine supports the core business capability of the pumping station group’s operation management by providing program recommendations, operation process preview, performance analysis, and other capabilities for the pumping station group. The reality interaction and feedback control engine also provides the pumping station group with operational decision-making capability and a safe control environment. [Results] In practical applications through engineering cases, the digital twin engine was mainly constructed in the browser/server mode, with the desktop application as a supplement. The results revealed that the digital twin engine effectively supported the pumping station group’s operational management business requirements. It was found that the operation optimization capability saved 4.14% in operation costs and 1.59% in energy consumption while maintaining high operation efficiency. Simultaneously, the operation scheme generated by the engine enabled a simulation preview of the entire operation process, accompanied by high-performance dynamic virtual-physical mapping. The dynamic virtual-physical mapping engine and timing database significantly reduced the response time of data mapping, maintaining the response time for 10 000 data mappings within 300 ms. Furthermore, after undergoing lightweight processing, the twin scene maintained a high running frame rate, whether deployed as a desktop application or a web-based application. In terms of computer resource consumption, when performing a simultaneous simulation preview and utilizing the weather system, a substantial amount of data and particle effects needed to be processed, necessitating a high-performance computer graphics processor. In contrast, digital twin engines typically operated under low-performance stress conditions and did not demand high computer performance. [Conclusions] This work provides theoretical and methodological support, as well as serves as a practical reference, to help construct a digital twin engine that targets the operation management of pumping station groups in water diversion projects. Nonetheless, this paper describes a digital twin engine construction method that marks a preliminary step in integrating data, mechanisms, algorithms, and knowledge specific to pumping station group systems in water diversion projects. Future research should focus on enhancing the engine’s performance, determining comprehensive engine functions that are customized to meet various business needs, and exploring the applications of deep mining multimodel coupling.

[Objective] Tunnels are integral to transport infrastructure and often face the formidable challenge of traversing active fault zones during construction. The active fault zones indicate potential geological disturbances, leading to structural damage and posing a severe threat to tunnel safety. Therefore, this study aims to propose a method of resisting dislocation of tunnel based on the brittle buffer concept to enhance the structural integrity of tunnels when confronted with displacements induced by fault activities. The method involves strategically filling the space between the primary and secondary linings with brittle and compressible materials, which serve as buffers to absorb and mitigate localized displacements caused by fault activities, thus protecting the tunnel from substantial damage. [Methods] To rigorously study and validate the effectiveness of the proposed brittle buffer structure in resisting fault displacements, a comprehensive indoor model experiment was designed and implemented. Scaling down the size according to a 40:1 geometric similarity ratio and using similar materials for the surrounding rock, lining, and buffer structures, tunnel model was cast in the laboratory, simulating fault movements within the model box. The analysis focused on the deformations and failure characteristics of the models under different fault loads, confirming the effectiveness of the brittle buffer structure. [Results] Observations of tunnel deformation and failure modes after fault movements revealed distinct patterns. In the hanging wall of the fault, the brittle buffer structure at the arch top was crushed, accompanied by void formation at the arch bottom. Meanwhile, in the footwall of the fault, the arch top exhibited voiding, whereas the brittle buffer structure at the arch bottom was crushed. This deformation pattern effectively dispersed local shear deformations at the fault location, markedly mitigating damage to the lining. Impressively, under the protection of a 50-mm buffer structure, the lining model showed minimal damage even with a 100-mm displacement, equivalent to a substantial 4-m displacement in practical design scenarios, underscoring the robust performance of the brittle buffer structure in preserving the structural integrity of the tunnel. Furthermore, this study delved into strain monitoring data analysis and revealed a considerable shift in the peak strain of the lining away from the fault crush zone. This strategic relocation of strain concentrations to areas farther from the fault indicated a substantial reduction in strain intensity within the fault zone and confirmed the efficacy of the brittle buffer structure in dispersing and minimizing localized damage. [Conclusions] The results confirm the practical feasibility and effectiveness of incorporating a brittle buffer structure in tunnel designs for scenarios involving fault-induced displacements. This design exhibits exceptional performance in resisting fault-induced displacements, particularly suitable for tunnels crossing fault locations with significant estimated displacements. The outcomes of this study provide a crucial theoretical foundation and practical guidance for tunnel designs that cross active fault zones. This research contributes to the selection of antidisplacement solutions in tunnel engineering, paving the way for innovative approaches to address seismic challenges in tunnel construction.

[Objective] The Central Yunnan Water Diversion Project is situated in a high-seismic-intensity area, and the seismic safety of the water conveyance structure is prominent. Specifically, the significant mass of water within the exposed steel penstock and the inadequate restraint provided by bearings often result in obvious seismic displacement responses of the steel penstock. As a result, damage predominantly occurs at the bearings. Therefore, the mechanical properties of bearings are essential for the seismic resistance of steel penstocks. With the exposed steel penstock from the Central Yunnan Water Diversion Project as the research object, the seismic isolation effect of friction pendulum bearings is examined. [Methods] Suppose that the friction pendulum bearing adopts an elliptical sliding surface. A simplified mechanical model of the bearing is derived. Based on this model, a simplified finite element model of the friction pendulum bearing is developed by spring elements and applied to the finite element simulation of the exposed steel penstock. Dynamic time history analysis of the steel penstock using friction pendulum bearings and flat sliding bearings is conducted. In the simplified spring finite element model of the friction pendulum bearing, the COMBIN39 and COMBIN40 elements in the ANSYS software are used to simulate the horizontal nonlinear force-displacement curve of the friction pendulum bearing, and the COMBIN14 element is used to simulate the vertical stiffness of the bearing. [Results] The results revealed that the structural acceleration and displacement distribution and values computed by using the simplified model were close to those of the fine model. Thus, it was obvious that the simplified finite element model of a friction pendulum bearing constructed by spring elements could simulate the mechanical properties of a friction pendulum bearing well and enhance the efficiency of the finite element simulation analysis of the exposed steel penstock structure. The seismic dynamic response law of the steel penstock with friction pendulum bearings was close to that with flat sliding bearings. In the horizontal direction, the ratio of the acceleration of the upper bearing plate to that of the lower bearing plate of the friction pendulum bearing was between 0.25 and 0.55, while that of the flat sliding bearing was between 0.45 and 0.80, demonstrating that the damping effect of the friction pendulum bearing was slightly higher. In the vertical direction, the acceleration of the friction pendulum bearing was slightly greater than that of the flat sliding bearing. Although the friction pendulum bearing could lower the acceleration response of the structure, it augmented the displacement response of the structure. The transverse residual displacement of the friction pendulum bearing was less than 1 mm, and the axial residual displacement was less than 2 mm, which were much smaller than those of the flat sliding bearing. The stress of the steel penstock of the friction pendulum bearing scheme was approximately 10% lower than that of the flat sliding bearing scheme, and the maximum lateral and axial shear forces of the friction pendulum bearing scheme could be decreased by 38.3% and 59.7%, respectively, compared with those of the flat sliding bearing scheme. [Conclusions] Generally, compared with the flat sliding bearings, the friction pendulum bearings can lower the acceleration response of the pipe and the horizontal forces of the bearings more effectively, and the residual displacements of the bearings are small. The friction pendulum bearing has a more obvious effect on the seismic isolation of the exposed steel penstock.

[Objective] Discontinuities are vital components of rock mass, significantly affecting its strength, deformation, and seepage characteristics. They provide essential parameters for rock mass classification and engineering design. Borehole television technology is a widely used method for capturing these discontinuities within the rock mass, offering high-resolution in situ images. However, in complex strata, the discontinuities appear in various morphologies with significant width differences. Coupled with the rapid texture changes on rock wall faces, these discontinuities create a highly uneven contrast, making it challenging for traditional algorithms to recognize them accurately. To address this challenge, this study introduces an improved deep learning network model specifically designed for borehole images of complex strata. [Methods] The proposed model, based on the U-Net architecture, incorporates a deeper encoding-decoding network structure. This structure effectively handles semantic information related to discontinuity breaks caused by uneven contrast. The model integrates channel attention mechanisms and residual modules, enhancing feature extraction capabilities at different levels in the encoding stage. In addition, the channel attention mechanism fuses multichannel discontinuity information from both encoding and decoding layers. A multiscale spatial attention module introduced in the lower-level skip connection improves the ability to process complex morphological discontinuities and enriches the semantic features of discontinuities in the coding layer. In this study, the borehole image data are augmented in various ways, such as using perspective deformation similar to the stratum deformation under geological action. This study also employs joint training with focal loss and Dice loss to handle imbalanced image data. The generalization ability of the network model is thoroughly validated through ablation studies and comparative experiments using the same borehole image as the training set and neighboring borehole images as the test set. For comprehensive quantitative evaluation, this study uses several metrics, including precision, recall, F_1-Score, and F_2-Score. [Results] Our experimental evaluation, conducted on a self-made borehole image dataset, indicated that compared to several common image segmentation network models, our proposed model significantly improved the recognition capability of rock discontinuities in borehole images from complex strata while ensuring faster computational efficiency. The precision and recall on the test set for the proposed model reached 78.23% and 77.85%, respectively. This marked an improvement in segmentation performance by 7.96% and 14.99%, respectively, compared with the basic U-Net model. Both the F_1-Score and F_2-Score were close to 78%. Although the model size was 18.13 MB and had approximately twice the parameters of the base U-Net, the deeper network hierarchy reduced the number of channels of shallow high-resolution feature maps, resulting in a reduction in computational load. The model achieved an FPS of 85, which was slightly higher than that of the basic U-Net model. [Conclusions] This study meticulously improves upon the basic U-Net model by strategically incorporating the attention mechanism, residual connections, and multiscale convolutions. The improved model exhibits high accuracy and robustness. It effectively confronts the challenges associated with balancing detailed features and high-level semantics owing to significant width differences in discontinuities within complex strata. Furthermore, it addresses issues related to incomplete extraction of discontinuities caused by uneven contrast between discontinuities and rock wall surfaces. As such, this improved model provides strong technical support for the automatic identification of rock discontinuities in on-site borehole investigations.

[Objective] Under transverse earthquake excitation, a water body in a large-scale aqueduct experiences evident vibration, which amplifies the seismic response of the aqueduct. This study proposes a water-passing barrier specifically designed for large-scale aqueducts to mitigate water vibration in the transverse direction. The water-passing barrier is strategically installed in the central line in the aqueduct along the longitudinal direction to divide the water body. The holes are reserved on the water-passing barrier that facilitates the passage of water during water vibration, thereby altering the vibration characteristics of the water body. By inducing water spin, it is possible to dissipate the vibration energy of the water body, ultimately leading to changes in the overall dynamic features of the aqueduct and a reduction in the overall seismic response of the aqueduct. [Methods] To investigate the effectiveness of water-passing barriers for vibration control in aqueducts, shaking table tests were conducted on typical large-scale aqueducts with rectangular and U-shaped sections. Various parameters, including the water height in the aqueduct, the permeability of the water-passing barrier, and the amplitude and frequency of the table motion, were considered during the shaking table tests. Through a comprehensive series of shaking table tests, the dynamic responses of the aqueduct were evaluated under white noise, simple harmonic load, and earthquake excitation. These responses encompass water vibration patterns, natural vibration frequency of the aqueduct, peak acceleration of the cap beam, and other structural responses. [Results] The test results indicated that water-passing barriers could enhance the table acceleration threshold for aqueduct overflow and reduce the vibration of the water body in the structure. The seismic reduction coefficient was quantified as the ratio of the peak acceleration of the cap beam in the aqueduct with a water-passing barrier to that without a water-passing barrier. The seismic reduction coefficient was influenced by various issues, such as the cross-section of the aqueduct, water level, excitation frequency, and permeability of the water-passing barrier. [Conclusions] Notably, the water-passing barrier exhibits effective response reduction performance when the excitation frequency is consistent with the fundamental frequency of the aqueduct. Nevertheless, when the excitation frequency significantly deviates from the fundamental frequency of the aqueduct, the water-passing barrier inadvertently amplifies the seismic response of the structure. When subjected to the El centro earthquake excitation, the water-passing barrier consistently exhibits satisfactory response reduction performance across most cases. However, the mean value and standard deviation of the seismic reduction coefficient are mainly influenced by the water level in the aqueduct and the permeability of the water-passing barrier. As the acceleration of the table motion increased, the water body exhibits more vigorous vibrations, leading to improved vibration reduction performance because of the water-passing barrier. Nonetheless, further investigation through more sophisticated tests and detailed analyses is necessary to establish a comprehensive understanding of the quantitative vibration control mechanism.

[Objective] Deep tunnels exhibit characteristics such as high ground stress and strong excavation disturbance. Especially in an intact hard rock environment, the original elastic strain energy stored in surrounding rocks is suddenly released due to the unloading effect during excavation, which can easily trigger rockburst disasters. Severe rockbursts pose a great threat to construction personnel and equipment such as tunnel boring machine (TBM), delaying the construction period and causing huge economic losses. Rockburst hazard is one of the key factors that affect the safety and efficiency of TBM excavation in deep tunnels. Active prevention is the most important technical method for controlling rockburst risk and ensuring personnel and equipment safety during construction. [Methods] With the deeply buried TBM section of the Xianglushan Tunnel in the Dianzhong Water Diversion Project as the engineering background, numerical simulations were performed to analyze the mechanisms and effects of two active rockburst control methods: destress blasting and pilot tunnel. A creep damage model with internal variables was employed to simulate the TBM continuous excavation process. Factors influencing the effectiveness of active rockburst control, such as the external insertion angle, number of advance blasting holes, and diameter and length of the pilot tunnel, were considered. The mechanisms of two active rockburst control methods were elucidated, and the release effects and spatiotemporal evolution processes of stress and energy of surrounding rocks under different construction parameters were studied. [Results] The results demonstrated that active control had achieved the stress “peak-shaving” effect during TBM excavation by preconcentrating rock stress, thereby preventing sudden energy accumulation and reducing rockburst risk. Briefly, it had transferred rockburst risk during the secondary excavation to the construction process of destress blasting and pilot tunnel. The active control method and specific excavation parameters could be determined based on the actual rockburst risk level and on-site conditions. Destress blasting was suitable for local targeted stress release, ensuring that high stresses within the length of advanced boreholes are effectively released in a controlled manner. Increasing the number of advance blasting holes was more important for reducing rockburst risk than increasing the external insertion angle. Compared with destress blasting, pilot tunnel could better transfer and reduce the high stress of surrounding rocks and fully release energy from high-energy-storing rock masses. Furthermore, the overall stress and energy release effects demonstrated by pilot tunnel were better, and the technique’s impact range was wider than those of destress blasting. Increasing the diameter and length of pilot tunnel could further reduce the risk of rockbursts. In conclusion, the construction of a pilot tunnel was more complex than that of destress blasting, but its stress release effect was generally better. In cases where a tunnel may have faced strong rockburst risk or other ineffective measures, pilot tunnels could be considered for realizing proactive prevention and rockburst control. [Conclusions] These research results can increase our understanding of the mechanism of rockburst prevention and offer a theoretical basis and a reference for rockburst active control and parameter optimization in practical engineering.

[Objective] Dolomite sandification is a distinctive adverse geological phenomenon in the Yuxi section of the water diversion project in central Yunnan Province. It directly or indirectly leads to water inrush, sand gush, strength reduction, collapse, and fractures. microbial-induced carbonate precipitation (MICP) is a novel and efficient soil reinforcement method, yet limited research exists on its application in sandy dolomite reinforcement. Staphylococcus epidermidis X-NM1, known for its robust calcium carbonate production ability, holds significant research value. This paper focuses on the severely sandy dolomite in the Yuxi section of the water diversion project in central Yunnan Province. It explores the application of Staphylococcus epidermidis X-NM1 in grouting reinforcement for severely sandy dolomite, studying the influence of cementing liquid concentration, grouting rounds, and initial relative density on the unconfined compressive strength of the reinforced sandy dolomite. [Methods] Staphylococcus epidermidis X-NM1 is cultured to approximately OD₆₀₀=1.5, and a peristaltic pump is used for the grouting reinforcement experiment. The experiment comprised two stages: firstly, infusing two times the pore volume of bacteria solution at a grouting speed of 1.5 mL/min, and secondly, infusing two times the pore volume of cement solution at the same speed after a 12 h standing period. Three grouting rounds (1, 2, 3) and seven concentrations of cementation solution (0, 0.25, 0.50, 0.75, 1.00, 1.50, 2.00, 2.50 mol/L) are set according to the experimental scheme. Three different initial relative densities (D_r=0.3, 0.5, 0.7) are considered. The dry density of the samples is determined using the weighing method, and the unconfined compressive strength is tested under various conditions. Finally, the calcium carbonate content of damaged samples is assessed through pickling, and the microstructure is analyzed using scanning electron microscope (SEM) to comprehensively evaluate the experimental outcomes. [Results] The calcium carbonate content, dry density, and unconfined compressive strength of the samples exhibited an initial increase followed by a decrease with the concentration of the cement solution. The optimal concentration of the cementation solution was determined to be 2.00 mol/L. Increased grouting rounds and initial relative density positively impacted the physical and mechanical properties of the sandy dolomite cylinder. With three grouting rounds, the calcium carbonate content reached 29.62%, the dry density was 2.253 g/cm³ and unconfined compressive strength reached 7.69 MPa. There was a nonlinear correlation between the unconfined compressive strength and the content of calcium carbonate. When the content of calcium carbonate was low in the early stage, the unconfined compressive strength would increase slowly. With the increasing content of calcium carbonate, the distribution was more uniform, and the cementing effect was stronger, the unconfined compressive strength value increased at a high speed. SEM results indicated effective filling of surface pores and cementation of dolomite particles by calcium carbonate crystals, crucial for enhancing overall strength. [Conclusions] Through a series of unconfined compressive strength tests, calcium carbonate content tests, dry density tests and other experiments, it is concluded that under certain conditions, Staphylococcus epidermidis X-NM1 can effectively induce calcium carbonate production, demonstrating a significant reinforcing effect on severely sandy dolomite.

[Objective] To elucidate the action mechanisms of external water pressure on the composite system of surrounding rock, grouting ring, and tunnel lining under complex geological conditions, a large-scale high external water pressure physical model experimental system suitable for deep-buried tunnels was developed. [Methods] The typical tunnel sections of the Songlin Tunnel T_SLT-005 and T_SLT-006 cross faults in the Kunming section of the Central Yunnan Water Diversion Project were selected as the research objects. The research encompassed physical model experiments on the external water pressure impacting the tunnel lining in deep-buried environments crossed by faults. The study aimed to determine the pressure variation laws across different tunnel depths, groundwater levels, and drainage conditions, proposing a range of recommended values for external water pressure reduction coefficients applicable under various operational scenarios. [Results] The findings indicated that tunnel depth and groundwater level substantially impact the external water pressure exerted on tunnel linings. An increase in tunnel depth enhanced the geostress effects, which, in turn, decreased both the porosity and permeability of the surrounding rock and grouting circle. This reduction effectively diminished the potential energy of groundwater seepage, thereby lowering the overall external water pressure on the lining. Conversely, rising groundwater levels increased the full-ring external water pressure on the lining, with high water pressure dispersing finer particles within the rock mass and fostering the development of more extensive seepage channels. This reduction also resulted in a higher rate of infiltration pressure increase correlated with rising groundwater levels. Furthermore, incorporating drainage holes into the lining substantially lowered the external water pressure affecting the upper shoulder areas of the tunnel. However, the presence of cross faults within the surrounding rock of the tunnel can mitigate the effectiveness of this pressure reduction, especially at the lining sections influenced by faults. The presence of cross faults had a significant impact on the water pressure outside the lining. Under high water table conditions, the influence range on the surrounding rock lining structure must be considered. Regarding specific recommendations, for tunnels at 600 m depth, the external water pressure reduction coefficient was approximately 92% of that at 200 m depth when undrained and approximately 85% when drained. In scenarios with cross faults, the external water pressure reduction coefficient at the most disadvantageous point of the lining without drainage should be no less than 0.95. With drainage, this coefficient can be more leniently adjusted to 0.82. Finally, the finite element numerical simulation method was used to verify the physical model test results of water pressure outside the lining, and the error was approximately 9.3% under the undrained lining condition and 7.8% under the drained lining condition, which indicated that the physical model experimental results were reasonable and feasible. [Conclusions] This research results provide crucial scientific guidance for designing, constructing, and safely managing deep-buried tunnel projects in regions with abundant water resources.

[Objective] Recently, several large-scale water conservancy projects have opened in China to alleviate the regional water shortage problem. Inverted siphon structure, an essential part of long-distance water transfer projects is widely used in interbasin water transfer projects. Arch-inverted siphon has characteristics of a water pipeline and an arch bridge, and the mass of the upper water body is vast, which is “top heavy” compared with the supporting structure. Structural seismic problems are prominent; however, studies on the seismic performance of this type of structure are fewer. Therefore, this study conducted shaking table tests to study the effects of changes in the state of water conveyance and ground vibration excitation categories on the seismic response of the structure. [Methods] Based on similarity theory, this study designs a similar relationship of Longchuan River inverted siphon, assembles a corresponding similar model using Plexiglas and steel processing, arranges a certain number of acceleration sensors and displacement sensors in the critical parts of the model, and then, performs 13 shaking table test conditions, which consider the state of water conveyance, the category of ground vibration, and the direction of ground vibration excitation. Dynamic acceleration response of similar models in the tests is collected by the sensors, and the acceleration response in the white noise sweep test can identify the intrinsic frequency of the structure, whereas that in the ground vibration excitation test can be converted into the displacement response by integrating the response to compare and analyze the changes in structural self-oscillation characteristics, peak acceleration, and peak displacement under different working conditions. [Results] The shaking table test results revealed the following points: (1) The acceleration response of the Longchuan River inverted siphon had a pronounced amplification effect under the increase in elevation, and this effect was nonlinear growth, X-direction excitation—the maximum response of the structural acceleration occurs at the top of the pier, and Y-direction excitation—the maximum response of the structural acceleration occurred at the steel pipe. (2) Under different water transfer conditions, the structural period would be extended after the mass of the upper water body was increased, which was far away from the seismic excellence period and reduced the seismic action on the structure. This effect was greater than that of the increased inertia force caused by the increase in mass, which reduced the dynamic response of the structure to a certain extent, and the seismic performance was improved. (3) Under different ground shaking excitations, the same intensity would affect the structure differently. The structural response was strongly correlated with the frequency component of the excitation waveform at the fundamental frequency of the structure, and the larger the frequency component in the fundamental frequency band, the larger the response. [Conclusions] These results reveal the effects of water conveyance state and ground vibration type on the seismic performance of arch-inverted siphon structures, which can provide theoretical guidance for the seismic design of such structures.

[Objective] This study aims to address the significant challenge of predicting rockburst risks during the excavation of deep tunnels using tunnel boring machine (TBM) tunnel boring machine and develop a rapid prediction model to provide the basis for rockburst prevention and control, enhancing the safety and efficiency of deep tunnel construction. The proposed model leverages numerical samples and random forest (RF) algorithms to overcome the limitations of existing methods, which often do not achieve real-time and rapid prediction or consider the underlying mechanisms and factors influencing rockbursts. [Methods] Considering the Xianglushan Tunnel within the Dianzhong Water Diversion Project, we introduced a model that utilizes geostress and rock constitutive parameters as inputs and the elastic strain energy density of the surrounding rock as output. Numerical simulations of tunneling using the TBM under various working conditions arewere conducted, and 611 numerical samples were crafted through an orthogonal experimental design. We employed RF as the underlying classifier, with hyperparameters optimized through 10-fold cross-validation to create an efficient prediction model. The accuracy and applicability of the model were confirmed by comparing several machine learning algorithms. [Results] We conducted a series of numerical simulations of excavation using the TBM, employing an elastoviscoplastic constitutive model with internal variables. These simulations disclosed the energy evolution within the rock mass throughout the excavation process. Energy concentration occurred during transient unloading and the time-dependent deformation of the surrounding rock, leading to two distinct peaks in strain energy density. The second peak indicative the final energy storage during the creep phase of the surrounding rock postexcavation and unloading. Notably, a higher value at the tunnel wall—under identical conditions—correlated with an elevated risk of strainburst. We verified the rationality of the input and output parameters by analyzing energy evolution and correlation. The predictive accuracy and computational efficiency of the model were enhanced following the optimization of the hyperparameters using a 10-fold cross-validation. The input parameters partially mirrored the factors influencing rockburst, while the output parameters measured the energy storage status of the surrounding rock before potential rockburst failure. The RF-based rockburst risk prediction proxy model exhibited commendable performance on the training and testing sets, achieving accuracies of 99.75% and 82.02%, respectively. The performance of the RF-based rockburst risk prediction proxy model was superior to that of four other machine learning models—decision tree, K-nearest neighbors, support vector machine, and logistic regression—achieving prediction accuracies of 82.02%, 76.40%, 79.77%, 75.28%, and 76.40% for all samples, respectively. This result indicateds the robust predictive capability and generalization performance of the RF-based rockburst risk prediction proxy model in assessing rockburst risk levels. [Conclusions] We offer a novel approach and framework for the rapid prediction of rockburst risks during the excavation phase of deep tunnels. The RF-based rockburst risk prediction proxy model is reportedly an effective tool for rockburst risk prediction, marking a significant advancement in rockburst risk management. We provide a research path and framework for the rapid prediction of rockburst risk during the excavation period of deep tunnels.

[Objective] The monitoring value of surrounding rock displacement has the characteristics of complexity and nonlinear dynamic change, and the static one-time learning of previous optimization algorithms combined with a single regression model cannot be practically applied in real scenarios. The regression fitting model uses several displacement monitoring point data to construct a general model of the surrounding rock displacement change, which cannot be applied to predict the future changes in monitoring points. The autocorrelation of the surrounding rock displacement data makes it more practical as a time series prediction problem. However, the generalization performance of a single model is easily disrupted by historical monitoring data, resulting in inaccurate prediction of test applications. In this study, a dynamic prediction method for surrounding rock displacement time series combined with time series monitoring data preprocessing is proposed. [Methods] First, the displacement monitoring data of the tunnel-surrounding rock are preprocessed. The intercepted stability monitoring data are isometrized by cubic spline interpolation, and the monitoring data are decomposed into trend and random term displacement components by variational mode decomposition signal processing. Adaboost integrates 10 long short-term memory networks to construct an integrated optimization model for time series prediction. Then, the weights of the training samples are initialized, the weight coefficients of the base model in the integration are calculated by training the first base model, and the weights of the training samples of the next base model are updated. Finally, the weight coefficients of all base models are obtained. After Adaboost integration optimization, the prediction results are calculated using all base models and their weight coefficients. After training and learning, single-step dynamic prediction is performed, and monitoring changes are updated in real time to model learning. The cumulative displacement prediction results can be obtained by superimposing the trend and random term displacement sequences using the time series decomposition principle. [Results] The displacement components of the rock surrounding the Central Yunnan Water Diversion Project were predicted and superimposed, and three displacement data were obtained. Compared with the traditional time series prediction model, each displacement index exhibited good performance. The complete data of the surrounding rock displacement time series were obtained by the FLAC 3D numerical simulation engineering section, and the application performance of the integrated optimization model was verified. Results showed that the integrated optimization model exhibited good performance in each component and cumulative displacement and was less affected by deformation rate fluctuation than the traditional model. [Conclusions] After preprocessing the time series data, the influencing factors of surrounding rock displacement and deformation are decomposed, and multiple time series prediction models are integrated for single-step dynamic prediction, which improves the shortcomings of previous studies. The correction determination coefficient and symmetrical average absolute percentage error are used as performance indicators to verify that the prediction accuracy achieves the expected goal and is superior to the traditional classical model in solving the time series problem, which promotes the predictability of surrounding rock displacement in practical applications.

[Objective] The issue of external water pressure is a key problem in the construction of deep-buried tunnels. It is a great challenge to determine the external water pressure of deep tunnel due to the large depth of deep tunnel, high groundwater level and complex hydraulic relationship between strata. Clarifying the hydraulic connection law of groundwater in the whole life cycle of tunnels is the key to accurately evaluate the external water pressure of deep tunnels and the impact of tunnel construction on groundwater environment. [Methods] In this paper, two different initial groundwater distribution conditions are applied to two geological models of different stratum types respectively, and a total of three stratum models are generalized for seepage calculation by numerical simulation. By monitoring the groundwater pressure of the corresponding strata and the amount of water inflow in the tunnel during the tunnel excavation process, the influence of different stratum types on groundwater evolution and distribution after tunnel excavation is studied. Then, on this basis, a groundwater stratified hydraulic connection monitoring technique for deep tunnel is proposed. This monitoring technique uses deep holes on the surface to monitor the undisturbed groundwater pressure in different strata above the tunnel in advance in front of the tunnel face. The strata with poor water permeability are regarded as water-proof strata, and the strata with better water permeability are regarded as water-permeable strata. The monitoring section is arranged in the water-permeable stratum, and the blocking section is arranged in the water-proof stratum. And the core key issues of this monitoring technique are verified by indoor experiments in the laboratory. Finally, this monitoring technique is successfully applied to Caijiacun tunnel of the Central Yunnan Water Diversion Project. A deep hole named ZKSY301 is divided from bottom to top into “monitoring section-blocking section-monitoring section-blocking section-monitoring section”. The blocking section is used to restore the water-proof characteristics of the water-proof stratum. The monitoring section is used to monitor the groundwater pressure of the water-permeable stratum. Several monitoring instruments are used to monitor groundwater pressure in different water-permeable strata during tunnel excavation. [Results] The numerical simulation showed that whether there was water-proof formation above the tunnel had different influence on the groundwater hydraulic connection after excavation. When there was a water-proof stratum, tunnel excavation only affected the groundwater in the stratum that the tunnel traversed but had no effect on the groundwater above the water-proof stratum. Groundwater stratification occurred between different strata, and led to that the amount of water inflow into the tunnel was significantly reduced. The feasibility of stratified monitoring technology and the existence of stratified groundwater hydraulic connection in deep tunnels were verified by engineering application. And it founded that as the Caijiacun tunnel continued to advance, the groundwater pressure in the stratum where the tunnel traversed dropped rapidly, while the groundwater pressure in the stratum above the water-proof stratum dropped slowly or was basically unchanged. In-site monitoring results confirmed the existence of stratification in the hydraulic connection of groundwater in deep tunnels. Finally, based on engineering applications, several suggestions were put forward for the in-site application of layered monitoring technique for technical personnel’s reference. [Conclusions] The stratified monitoring technique pioneered in this paper provides the real initial external water pressure in deep tunnels. And the evolution law of groundwater distribution throughout the life cycle, before construction-construction-operation, can be obtained. The stratified monitoring technique provides an effective mean for the study of high external water pressure in deep tunnels and improves the deficiencies in the existing tunnel external water pressure design specifications.

[Objective] In the expansive field of geology, where anisotropic fractures intricately pattern rocks, this study focuses on unraveling the nuanced evolution mechanisms of microscopic cracks within rocks featuring a solitary joint. Rooted in the jointed rock mass of the Xianglushan Tunnel in the Dianzhong Diversion Project, China, the research aims to discern the profound impact of single joints on a broad spectrum of macroscopic mechanical parameters and failure characteristics. This exploration seeks to deepen our understanding of the intricate interplay between micro-mechanical phenomena and the broader geological context, contributing valuable insights to the field of rock mechanics. [Methods] In this pioneering study, the methodology hinges on leveraging the advanced two-dimensional particle flow code (PFC2D) to meticulously orchestrate uniaxial compression simulation tests. The experimental scope spans both pristine rock specimens and those featuring a distinct single joint. The crux of the analysis entails a detailed exploration into the repercussions of joint length and inclination on a diverse array of macroscopic mechanical parameters and failure characteristics.To dissect the intricate relationships between joint attributes and the mechanical response of the rock mass, the study employs numerical experiments. These simulations, akin to a virtual laboratory, diligently replicate the dynamic response of the rock mass under varying joint conditions. The computational prowess of PFC2D ensures a high-fidelity representation, unraveling the nuanced interplay between joint characteristics and macroscopic mechanical behaviors.The numerical experiments extend beyond the confines of traditional physical testing, enabling a systematic investigation across a spectrum of joint conditions. This not only enhances the efficiency of the study but also broadens the horizons of exploration, providing insights into diverse joint scenarios that might pose challenges in a laboratory setting. [Results] The results indicated that for rocks with a single joint: (1) smaller joint inclinations and larger lengths corresponded to decreased uniaxial compressive strength, peak strain, and elastic modulus. (2) Longer joints exhibited increased sensitivity of joint inclination to peak stress, peak strain, and elastic modulus. (3) Specimens predominantly underwent tensile failure, with a sequence of crack initiation: wing cracks, shear cracks, secondary shear cracks, and far-field cracks. (4) As the joint inclination increased, the crack initiation location shifted from the middle to the tip of the joint, and the crack initiation direction changed from perpendicular to the joint strike to parallel. (5) Longer joints resulted in fewer primary tensile cracks, simpler crack types, earlier initiation of wing cracks, and delayed initiation of shear cracks. [Conclusions] This groundbreaking research represents a significant leap forward in unraveling the micro-mechanical intricacies inherent in single-joint rocks and their profound implications on macroscopic mechanical parameters and failure characteristics. The acquired insights not only substantively contribute to the academic discourse in the field of geomechanics but also hold practical implications for the assessment and prediction of the mechanical behavior of jointed rock masses in engineering applications. The findings serve as a cornerstone, providing a robust foundation for future research endeavors in the dynamic realm of rock mechanics. The practical implications extend beyond theoretical boundaries, offering valuable guidance for engineers and practitioners engaged in the design and evaluation of structures within jointed rock formations, thereby bridging the gap between theoretical understanding and real-world applications.

[Objective] The settlement of roadbeds caused by the construction of shallow large-span tunnels passing under highways in soft strata has always been one of the outstanding technical difficulties encountered in underground engineering. The key to controlling the settlement of highway roadbeds is to restrain the deformation and stress release of tunnel surrounding rock as much as possible. This study thoroughly analyzes the scheme and process of controlling the settlement of roadbeds and the deformation of surrounding rock in the construction of tunnels under highways. Furthermore, it analyzes the settlement pattern and influencing factors of the top arch and roadbed in the tunnel excavation process. [Methods] Based on the Xianglushan Tunnel Project, this study adopts on-site monitoring and numerical simulation and conducts comparative experiments through four design and construction schemes to analyze the influences of systematic support, over-advance support, and construction process on the settlement and deformation of the tunnel vault and roadbed. [Results] The preconvergence deformation of the surrounding rock in front of the palm face of the shallow-buried large-span tunnel accounted for a relatively high percentage of the total displacement of the top arch. It accounted for about 79% of the total displacement of the top arch in the construction of the Xianglushan Tunnel under the highway. After applying overrun support, the extrusion deformation of the tunnel face and the preconvergence deformation of the surrounding rock in front of the tunnel were substantially reduced, the stability of the surrounding rock of the tunnel was improved, and the highway foundation settlement was reduced. The highway foundation settlement was reduced by about 26.4%, while the tunnel vault settlement was reduced by about 31.3%. Compared with strengthening the initial support parameters, the adjusted construction approach was more effective in controlling the settlement of highway roadbeds. The adjusted construction approach, which included measures such as reserving core soil, temporary arches with vertical supports, and staggered excavation on the same step, effectively restrained the release of surrounding rock stress and deformation, maximized the bearing capacity of the support structure. Compared with the four-step method, the improved construction method resulted in a 9.2% decrease in the roadbed settlement of the Shanghe Highway, a 30% increase in the average axial stress of the anchors of the tunnel system, and a 52.91% increase in the average axial stress of the steel arch. [Conclusions] In summary, the optimized design and construction program achieves better application results, effectively controlling the settlement of the tunnel vault and roadbed of the Shanghe Highway during the construction process of the Xianglushan Tunnel Project. Research findings provide valuable insights into the construction of tunnels beneath highways in similar complex environments.

[Objective] To solve the problem of the uneven distribution of water resources, the country has built many water infrastructures, with long engineering pipelines, strong water conveyance capacity, and high safety and reliability. The Dianzhong water diversion project is the largest water infrastructure project under construction in China, which can effectively alleviate the shortage of water resources in the central area of Yunnan Province, and ensure sustainable economic and social development after its completion. The aqueduct is one of the important water diversion structures in the project, which is generally used to cross special terrains such as rivers and valleys. The aqueduct construction of the project faces many challenges, such as high seismic intensity, multiple active faults, and complex geological conditions. Ensuring the structural safety of the aqueduct is the key prerequisite for guaranteeing the continuous water diversion function. [Methods] Extensive theoretical analysis, model tests, and numerical simulation studies have been conducted on the structural safety of the aqueduct in the Dianzhong water diversion project. The researches include various aspects, such as the design and optimization of the aqueduct structure, water-aqueduct interaction, soil-structure interaction, complex geological conditions, and the seismic performance and isolation performance of the aqueduct, etc.. [Results] Specifically, to improve the cracking resistance ability of the aqueduct, the influence of temperature gradient and layout of prestressed steel strands was discussed, and the design recommendation was suggested. In order to better illustrate the water-aqueduct interaction and the soil-structure interaction, some design methods were successively proposed, and the interaction mechanism was further explored. The impact of complex geological conditions was considered when conducting the dynamic analysis to obtain a more realistic earthquake response to the aqueduct. To effectively control the seismic response of aqueducts, many types of energy dissipation devices and isolation bearings were proposed, and the seismic performance and isolation performance of the aqueduct with new devices were investigated. [Conclusions] Based on the actual practice of the Dianzhong water diversion project, this paper summarizes the relevant research results and the future research trends of aqueducts, aiming to provide a reference for the project construction. Research shows that a key to accurately analyzing the seismic response of the aqueduct is to simulate the interaction between water and aqueduct, and soil and structure. The analysis technique considering the water-aqueduct interaction and the soil-structure interaction is formed, which provides support for numerical analysis of the aqueduct. On this basis, the seismic performance and isolation performance of aqueducts under high seismic intensity and complex geological conditions are deeply investigated. The impact mechanism of terrain differences on structural seismic performance, such as V-shaped river valleys, is analyzed. The seismic isolation mechanisms of different seismic isolation measures are clarified. With the continuous development of society, the demand for aqueduct structures in terms of water conveyance capacity and spanning capacity increases. It is significant to further ensure the safety and sustainable water transportation of aqueducts under high seismic intensity and complex geological conditions. Utilizing the shaking of water in the aqueduct to achieve seismic reduction effects, and developing new seismic isolation devices and anti-seepage waterproofs are important development directions in the future.

[Objective] Xianglushan tunnel is a key project of the Yunnan Dianzhong Water Diversion Engineering, and rock bursts are one of its main hazards. The precise positioning of microseismic sensor coordinates is the basis for microseismic monitoring and early warning systems for rock bursts, which is controlled by drilling coordinates and angles. However, the drilling location needs to be measured manually, which has low accuracy and poor timeliness, seriously hindering the development of automatic microseismic monitoring systems for rock bursts. Meanwhile, the precise positioning of multi-dimensional features is the key to realizing the full automation of drilling operations, including the coordinates, diameter, plane direction, and busbar direction of drilling. This study presents a method for the precise positioning of multi-dimensional features of tunnel drilling based on deep-machine vision called YOLO-AT. [Methods] The proposed method includes two modules: drilling contour detection and drilling multi-dimensional feature positioning. The drilling contour detection module adds rotation angle prediction to the YOLO V8 model, thereby constructing a YOLO V8 OBB model that can accurately fit the drilling contour. The drilling multi-dimensional feature positioning module establishes an anchor tracking algorithm, selects anchor points on contour ellipses, and achieves anchor tracking from multiple perspectives based on epipolar line constraints and projective invariance of anchor order. The spatial coordinates of each anchor point and multi-dimensional features were solved using the parallax method and analytical geometry theory, respectively. [Results] To verify the robustness of the proposed method to contour quality, a synthetic drilling contour database with controllable quality was established for Xianglushan tunnel, and the positioning results were compared with those of the ALSR, FED, AAMED, YOLO V8, and DLT methods. Results showed that: (1) concerning contour detection accuracy, the proposed method exhibited the best performance among other methods, with the average intersection over union (IoU) ratio, average F₁ score, precision, and recall at an IoU threshold corresponding to 0.9 of 0.957, 0.948, 0.977, and 0.977, respectively. (2) Concerning contour detection stability, the proposed method was less affected by contour quality and always maintained high accuracy. By contrast, YOLO V8 had less fluctuation and low indicators, whereas other methods had poor stability and high accuracy under good contour quality. (3) Concerning the accuracy of multi-dimensional feature positioning, the median errors of the proposed method for the coordinate, diameter, plane direction, and busbar direction of drilling were 0.835 mm, 0.795 mm, 0.567°, and 1.751°, respectively, which were the best among all methods. (4) Concerning the stability of multi-dimensional feature positioning, the proposed method and YOLO V8-AT had better stability. Conversely, the stability of other methods rapidly decreased as the quality of the drilling contour deteriorated. [Conclusions] The proposed YOLO-AT method can achieve accurate and stable positioning of multi-dimensional features in Xianglushan tunnel drilling, with a performance superior to that of existing methods, thereby having the potential to be extended to various underground engineering drilling positions. Next, the research intends to focus on combining the proposed method and laser ranging technology to measure hole depth and eliminate ambiguity in drilling direction, in addition to analyzing the roles of RANSAC and reprojection methods in improving algorithm accuracy and stability.