Abstract:In seasonally frozen areas, surface soil is subjected to prolonged and drastic fluctuations in temperature and humidity, causing excessive deformation and resulting in engineering issues such as subgrade settlement and building deformation. The deformation characteristics of kaolin in seasonally frozen areas under the combined influence of freeze-thaw and dry-wet cycles were studied. Through a self-designed experimental setup, experiments with interleaved dry-wet and freeze-thaw cycles were conducted on compacted specimens, and wetting-freezing-thawing-drying cycle experiments were performed to explore the swelling-shrinkage deformation characteristics of kaolin under the combined action of different freeze-thaw and dry-wet cycles. The results indicate that intermittent freeze-thaw cycles destroy the stable strain previously achieved by kaolin specimens during dry-wet cycles, and the new stable strain achieved by the specimens during subsequent dry-wet cycles decreases; furthermore, the longitudinal strain of kaolin specimens gradually tends to a stable state after three wetting-freezing-thawing-drying cycles.

Abstract:During the high-speed and long-runout sliding failure process of large landslides, severe friction and heat generation in the sliding zone induce an interface friction effect between the debris flow and the bedrock, influencing the final accumulation morphology of the landslide. In this paper, a two-dimensional landslide model of the Yangbaodi landslide in Shenzhen was established using the material point method. A contact algorithm was introduced through a multi-background grid method to conduct numerical simulations on the initiation, sliding, and accumulation processes of the landslide. The results show that after initiation, the landslide moves over a long distance in a flow-like state along the bedrock. Influenced by the topographic and geomorphic characteristics of the bedrock, local accumulation is formed in some gently inclined areas. The final accumulation morphology is relatively close to the calculation results of methods such as the particle finite element method, which preliminarily verifies the effectiveness of the method in this paper. Calculations changing the friction coefficient between the debris flow and the bedrock reveal that the interface friction effect significantly influences the movement behavior of the debris flow. The maximum sliding velocity and farthest sliding distance decrease as the friction coefficient increases. However, the soil deformation of the debris flow near the bedrock area is more obviously affected by friction, and the equivalent plastic strain conversely increases as the friction coefficient increases. At the same time, a large number of discontinuous plastic deformation protrusions are formed, influencing the final accumulation morphology of the debris flow. The research results can provide an effective technical means for analyzing the failure mechanism of natural landslides under the interface friction effect.

Abstract:To study the effects of technical parameters, such as geocell specifications and laying types, on the bearing capacity and deformation of highway subgrades in oasis flood irrigation areas, the shear properties of plain soil and geocell-reinforced layers with different specifications were studied through large-scale direct shear tests. Based on indoor compression tests and field load tests, numerical simulation parameters, such as the deformation modulus of different foundation soil layers, were calibrated. A numerical model of the geocell-reinforced highway subgrade was established using , and the effects of geocell specifications and laying types on the vertical settlement of the subgrade, the displacement of the slope toe, and the vertical stress under the reinforced layer were systematically analyzed. The results show that geocells with different specifications can effectively reduce foundation settlement. The reinforcement effect of the geocell with a welding spacing of 40 cm is superior to that of the geocell with a welding spacing of 80 cm, and the reinforcement effect is enhanced with the increase in the number of geocell layers. Before and after the geocell treatment, the variation trend of the horizontal displacement of the slope toe along the depth direction is consistent. The maximum values of both appear at a depth of about 2 m, then gradually decay, and tend to be identical at 6 m, with the influence depth of the geocell reaching 4?5 m. After the subgrade is reinforced by geocells with different specifications, due to the influence of boundary conditions, the geocells undergo flexural deformation after being stressed, exhibiting characteristics similar to the settlement of the foundation surface. At the same time, due to the substantial anti-deformation performance of the geocell-reinforced layer, a stress diffusion effect is generated, which reduces the vertical stress inside the foundation. According to the results of the large-scale direct shear tests, the indoor compression tests, and the numerical calculations, replacing the soil with a mixture of geocells and gravelly soil can effectively improve the strength and modulus parameters of the replacement materials and reduce the subgrade deformation. On the one hand, the construction volume of highway construction units is reduced, which greatly reduces the carbon emissions caused by construction; on the other hand, the harm caused by the construction of high-grade highways to the ecological environment along the oasis-desert areas is reduced, and land resources are saved. The research results can provide a certain reference for the application and theoretical research of geocells in highway engineering in oasis areas.

Abstract:Dewatering prior to foundation pit excavation is a critical measure to prevent engineering hazards such as slope instability at the pit top, seepage around the pit, and bottom heave. As a key parameter in dewatering design, hydraulic conductivity directly influences the risk control in foundation pit engineering. Based on the east anchor foundation pit project of the Shiziyang Passageway, single-well pumping tests and stratified multi-well pumping tests were conducted. The water level variations in the internal dewatering wells and the external observation wells were monitored in stages. Accordingly, a finite difference numerical model for the pumping tests was established. The hydraulic conductivities of the target aquifers obtained through the classical analytical method were used as the initial parameters of the numerical model, and the hydraulic conductivities of each stratum were determined through back-analysis. The results indicate that the water levels in the external observation wells do not decline synchronously with the internal pumping process, which demonstrates that there is no leakage at the joints of the circular diaphragm wall. The significant differences in water level drawdown among the internal dewatering wells suggest that the power and operation time of the pumping equipment should be differentially adjusted based on the characteristics of the strata where the dewatering wells are located, to achieve an overall uniform dewatering effect. The absolute value of the relative error between the field observation values and the calculated values of the reconstructed finite difference model is 11.58% on average, which validates the reliability of the combined classical analytical and finite difference method. This analysis method provides a reference for the back-analysis of hydrogeological parameters in deep foundation pit engineering.

Abstract:To investigate the effect of phase change materials (PCMs) on improving the thermal erosion resistance of airport pavements and to provide recommendations for selecting optimal PCMs to obtain airport pavements with longer service lives, three PCMs, PCM-G-98 (A), LB-2 (B), and TH-HC-120 (C), were purchased based on literature summaries and market research. Based on microscopic test results and the actual preparation conditions of modified asphalt, PCMs A and B were selected. Subsequently, based on a self-made high-content SBS modified asphalt (S), four groups of composite modified asphalts (S-A-5, S-A-10, S-B-5, and S-B-10) with different mass fractions were prepared. A simultaneous thermal analyzer (TG-DSC), heat storage-exothermic tests, and infrared spectroscopy (FTIR) were used to analyze the latent heat of phase change and functional group characteristics of the PCMs. A dynamic shear rheometer (DSR) was employed to analyze the rheological properties of the composite modified asphalts, and the modification mechanism was analyzed using FTIR. The results indicate that PCM C exhibits the strongest temperature regulation capacity but is not suitable for high-temperature environments, and S-A-10 presents the best thermal erosion resistance.

Abstract:To investigate the mechanical properties and particle breakage effect of construction solid waste, a series of static and dynamic direct shear tests were carried out using a dynamic interface shear tester. Different coarse particle contents (40%, 50%, and 60%), amplitudes (45 kPa, 60 kPa, and 75 kPa), and frequencies (0.5 Hz, 1 Hz, and 2 Hz) were used as variables, and the variation rules of shear stress?shear displacement curves, shear strength parameters, and particle breakage under three normal stresses (50 kPa, 100 kPa, and 150 kPa) were analyzed. The results indicate that under the same initial normal stress, with the increase of coarse particle content, the shear strength, internal friction angle, and relative breakage rate of construction solid waste increase, while the cohesion decreases. With the increase of amplitude and frequency, the shear strength, cohesion, internal friction angle, and relative breakage rate of construction solid waste all decrease. The shear stress?shear displacement curves all exhibit a strain-softening type; during the shear process, fluctuation phenomena occur in the shear stress?shear displacement curves. The particle size distribution curves after shearing show an overall upward shift trend, and with the increase of normal stress, the upward shift amplitude of the curves increases.

Abstract:To investigate the influence mechanism of fiber incorporation on the compaction characteristics of asphalt mixtures, six types of typical road fibers (polyester fiber, polyacrylonitrile fiber, aramid fiber, basalt fiber, polypropylene fiber, and polyvinyl alcohol fiber) were selected in this paper, and gyratory compaction tests were conducted based on AC-20 graded mixtures. The compaction coefficient (a larger compaction coefficient indicates easier compaction) was used as the core evaluation index. The results indicate that the elastic modulus of the fiber is the key influencing factor. When the fiber modulus is 50% lower than the aggregate modulus (such as polyester fiber and polyacrylonitrile fiber), the compaction coefficient decreases significantly (4.43% for the blank group, 3.94% for the polyester fiber, and 4.04% for the polyacrylonitrile fiber), and the compaction difficulty increases; when the fiber modulus is close to or higher than the aggregate modulus (such as 4.41% for the aramid fiber and 4.45% for the basalt fiber), the compaction performance does not change significantly. The influence of fiber length is regulated by the modulus: Increasing the length of low-modulus fibers helps improve the compaction coefficient (such as polyacrylonitrile fiber), while reducing the length of high-modulus fibers is beneficial to compaction (such as aramid fiber). A threshold effect exists in fiber dosage; the compaction coefficient changes nonlinearly with the dosage and reaches a peak at a specific dosage. The construction compaction process is required to be designed differentially; the order of the number of compaction passes required for the mixture to reach the target void content of 4% is polyvinyl alcohol fiber < basalt fiber < polypropylene fiber < aramid fiber < blank group < polyacrylonitrile fiber < polyester fiber. Except for the polyester fiber and polyacrylonitrile fiber, the other fibers have no significant effect on the conventional compaction process.

Abstract:The morphological characteristics of coarse aggregates significantly affect the mechanical properties of asphalt mixtures and thus directly influence their road performance and durability. This paper aims to innovatively propose an evaluation method for the angularity of coarse aggregates. A three-dimensional (3D) scanner was used to acquire the surface profile information of coarse aggregates, and local angularity features were extracted through point cloud data analysis. Subsequently, a comprehensive 3D angularity evaluation index for coarse aggregates (A_3D) was proposed by combining local normal vectors and curvature characteristics. The results indicate that A_3D can be more accurately and independently used for angularity evaluation. The relevant evaluation parameters are as follows: When the value of the basic search radius coefficient μ is 0.05, the intersecting areas of arbitrary fracture surfaces can be effectively extracted; when the dynamic dual-threshold coefficients are 40% < η_k < 50% and 70% < η_σ < 80%, the algorithm has good sensitivity to the variations of curvature and normal vectors and can effectively eliminate redundant data while ensuring the accuracy of feature extraction. Parallel control experiments indicate that when measuring the angularity parameters of the same batch, it is optimal to take the uniform amplification parameter λ as 10 000?15 000. When the content of flaky and elongated particles in coarse aggregates is high, increasing λ to 15 000?20 000 can enhance the ability to distinguish local sharp features. Computational analysis reveals that A_3D is more accurate than the traditional two-dimensional evaluation method, has a good correlation with the three-dimensional voxel angularity index, and shows higher sensitivity to the evaluation indices of flaky and elongated or sharp-edged crushed stone particles. Calculation results at different scaling ratios demonstrate that the algorithm has good adaptability to the particle sizes of gravel and crushed stone coarse aggregates and has better adaptability to the differences in gravel particle sizes.

Abstract:Due to the frequent occurrence of building fires, the mechanical properties of concrete, as the most widely used construction material, are severely challenged under high temperatures. To explore the effect of granite manufactured sand content on the performance of ultra-high performance concrete (UHPC) after heating and cooling treatment, three types of UHPC specimens with different manufactured sand contents (0, 50%, and 100%) were prepared in this study. Then, the effects of manufactured sand content, heating temperature, and cooling regime on the P-wave velocity and uniaxial compressive strength of UHPC were obtained through experiments. The results indicate that the P-wave velocity and compressive strength of UHPC both increase slightly with the increase in manufactured sand content. When the specimen is heated from a room temperature of 25 ℃ to 300 ℃, the corresponding P-wave velocity and compressive strength decline gently. When the target temperature is raised to 600 ℃ and 900 ℃, the corresponding P-wave velocity and compressive strength decrease sharply. In addition, it is revealed by the investigation of cooling regimes that the decrease in P-wave velocity and compressive strength of the specimens under water cooling is greater than that under natural cooling, indicating that secondary damage to the specimens is caused by the thermal shock induced by water cooling.

Abstract:As a novel non-destructive testing method for roads, ground penetrating radar (GPR) can effectively prevent road water damage by regularly detecting the internal moisture condition of roads. However, when the moisture data of GPR are analyzed, the moisture conditions obtained by relying solely on the analysis of a single profile characteristic may be misjudged. To improve the accuracy and reliability of GPR in detecting the internal moisture content of pavements, focus was placed on the time-frequency domain analysis of GPR moisture content detection profiles in this paper. Simulation tests were conducted, and the influencing factors and results of moisture detection in the pavement surface layer were deeply investigated. Furthermore, the performance patterns of radar detection profiles under different levels of volumetric moisture content of the surface layer were emphatically analyzed. The results indicate that the change in antenna height has a significant impact on the ground reflected wave, while the change in surface layer thickness mainly affects the arrival time and energy intensity of the echo signal at the surface layer-base interface. In addition, as the moisture content of the surface layer increases, the amplitude of the ground reflected wave increases significantly; the arrival time of the reflected wave at the lower interface of the moisture layer is prolonged, and the frequency of the reflected wave within the layer shows a decreasing trend. The research results provide a theoretical basis for detecting the internal moisture content of roads using GPR.

Abstract:This paper aims to explore whether fly ash, lithium slag, and slag powder (ternary industrial solid wastes) can effectively replace cement as cementitious materials for interlocking large-particle crushed stone bases. A uniform design table U₉(9⁴) was used to design the test scheme for the mixing ratios of ternary industrial solid waste mixtures; the correlation between the mortar strength and the ternary industrial solid waste mixtures was analyzed by Pearson correlation; with the help of the mathematical statistical software SPSS 26.0, mathematical models for the flexural strength and compressive strength of the ternary industrial solid waste mixture mortar specimens were established. The research results show that there is a strong linear negative correlation between fly ash and strength; lithium slag has a weak correlation with strength within a 14-day curing period, and there is a strong linear positive correlation between slag powder and strength. Through the optimization of the mathematical models, the optimal mixing ratio of the three industrial solid waste mixtures is determined as fly ash : lithium slag : slag powder = 40% : 20% : 40%. The tests confirm that the flexural and compressive strengths of the ternary industrial solid waste mixture mortar are significantly improved, which provides strong support for the application of ternary industrial solid waste mixtures in interlocking structures.

Abstract:Structural safety is directly affected by the mechanical properties of concrete at high temperatures. Firstly, based on the existing compression and tension test data of concrete at high temperatures, the Abaqus finite element software was adopted for numerical simulation reproduction, and the reliability of the simulation method was verified. Secondly, by simulating the uniaxial tension-compression and confining pressure tests of normal concrete with different strength grades under high temperatures of 20?800 ℃, the influence rules of temperature on the compressive strength, splitting tensile strength, elastic modulus, and stress?strain relationship of concrete were elucidated. Finally, based on three commonly used machine learning algorithms, i.e., BP neural network (BPNN), support vector regression (SVR), and Gaussian process regression (GPR), a rapid prediction model for the mechanical properties of concrete at different temperatures was established. The results indicate that the prediction accuracies of the GPR and SVR models are relatively high, and the R² of the prediction models for the compressive strength and tensile strength of concrete are 0.997 23 and 0.979 55, respectively.

Abstract:A large number of built small and medium-span bridges in China are facing the problem of increasingly degrading structural performance. Therefore, it is of great significance to carry out lightweight intelligent monitoring and realize damage identification and early warning, so as to ensure the safe operation of these bridges. For typical small and medium-span simply supported beam bridges, a damage analysis method based on measured dynamic deflection data was established by combining the influence line theory and mechanical constitutive equations. Furthermore, based on the high-precision monitoring algorithm and instruments of digital image correlation (DIC), the real-time dynamic deflection data of the bridges were obtained. It is shown that typical defects such as sectional stiffness degradation, hinge joint damage and failure, and support performance degradation are effectively identified. The results were applied to the digital transformation project of an overpass in Shanghai, which verifies the effectiveness of the dynamic deflection DIC optical measurement technology and the damage identification method and indicates that the proposed method has good value in popularization and application.

Abstract:To solve the problem of excessive tensile stress of the cross-section during the cantilever casting process of high piers with inclined legs, a determination method of tensile force based on the linear programming theory and unstressed state control was proposed. Based on the internal force equilibrium method and the principle of influence matrix, the method optimized the tensile force with “stress control as the primary and alignment control as the auxiliary”. The unstressed state control method was adopted for forward iteration, and the effect of tangential displacement between segments was considered to verify the alignment of the inclined legs. Finally, a calculation process for the tensile force of buckling cables and tie rods that can simultaneously meet the stress and alignment requirements of the V-shaped pier was provided. Taking the main pier construction of a large-span continuous rigid frame bridge with V-shaped piers as the engineering application background, the linear programming theory combined with the unstressed state method was adopted to solve the tensile force for the cable-stayed buckling construction of the V-shaped pier. The variation law of the tensile force of buckling cables/tie rods during construction was analyzed, and the stress and displacement of key cross-sections were analyzed. The results show that the calculated tensile force can effectively ensure that the construction stress and alignment of the inclined legs meet the limit requirements, realizing the dual control of stress and alignment.

Abstract:To investigate the influence of cable clamp slippage on alignment and internal force of the main cable, a theoretical analysis method based on node coordinates of the main cable after cable clamp slippage was proposed in this paper. Based on segmented catenary theory, the influence of hanger inclination caused by hanger slippage on the horizontal force of the main cable was considered. The segmental cable element of the main cable was equivalently expressed as expressions of hanger tension and unstressed length. With total unstressed length kept constant as a control condition, the horizontal force of the main cable was iteratively updated to solve convergent alignment, segmental unstressed length, and hanger tension of the main cable. By taking a single-tower self-anchored suspension bridge as an example, a parametric analysis was carried out to study the sensitivity of node coordinate error to control condition, and a quantitative analysis on the location and quantity of main cable slippage was conducted. The variation characteristics of internal force and alignment of cable structure after slippage were identified, and the mechanical performance of the structure under slippage conditions was qualitatively evaluated.

Abstract:The pouring timing of sealing hinge concrete for concrete-filled steel tube arch bridges directly affects the construction duration and the stress state of arch ribs. To clarify the structural response differences at different pouring timings, the Beiliuhe Extra-large Bridge on the Pingxi?Cenxi Expressway in Guangxi Province was taken as the engineering background in this paper. A finite element model was established using Midas Civil, and the following four pouring timings of sealing hinge concrete were comparatively analyzed: immediately after the butt welding of sealing hinge steel pipes; after the closure of arch ribs and before the pouring of concrete inside pipes; after the pouring of concrete inside pipes and before the lifting of lattice girders; after the pouring of wet joints of the bridge deck and before the application of the second-phase dead load. Through the finite element simulation analysis of the whole construction process, the internal forces, stresses, and deformations of key parts under the four timings, as well as the deformations at the completed bridge stage, were compared. The results indicate that all four pouring timings of sealing hinge concrete are feasible; from the perspective of the strength and stability of chord pipes at the arch feet, timing 4 (pouring the sealing hinge concrete after the pouring of wet joints of the bridge deck) is the most favorable. As long as there is no conflict in working surfaces, the pouring of sealing hinge concrete can be carried out at any construction stage after the butt welding of sealing hinge steel pipes. The reason for the above phenomenon is that the arch rib axis of this bridge is a catenary curve, which is mainly subjected to compression with a small bending moment under the dead load state. The research results provide a basis for selecting the pouring timing of sealing hinge concrete for this bridge and can serve as a reference for related construction of similar bridges.

Abstract:For negative bending moment prestressed tendons in simply supported-to-structurally-continuous bridges, the flat anchorage method of flange plate is more reasonable, but its widespread application is limited due to the anchoring capacity restrictions of flat anchor plates. To improve the anchoring capacity of a single anchorage zone, reduce the number of prestressed ducts, save concrete, and improve construction efficiency, a novel 6-hole flat anchor plate was developed, designed, and manufactured in this paper. By combining finite element analysis and experimental methods, a finite element analysis model of the concrete load transfer specimen beneath the novel 6-hole flat anchor plate was established, and its performances, including crack development, ultimate bearing capacity, stress distribution, and failure modes, were calculated and analyzed. Additionally, a cyclic loading test of the anchor plate was designed, and the load transfer performance of the novel 6-hole flat anchor plate was tested. The results indicate that under the design tension control stress, neither the anchor plate nor the steel reinforcement reaches the yield strength, and the 6-hole flat anchor plate can work stably under the design tension stress; after 10 loading cycles, the development of strain and crack width of the specimen tends to be stable, and the ultimate bearing capacity is higher than the nominal ultimate tensile force of the six prestressed tendons, indicating that the 6-hole flat anchor plate can adapt to more severe working conditions and has a higher safety margin; the cracking load and ultimate bearing capacity calculated by the finite element analysis are basically consistent with the experimental results, which demonstrates that the finite element model is reliable. The novel 6-hole flat anchor plate has excellent load transfer performance and safe stress reserves, possessing engineering application value.

Abstract:To investigate the bearing mechanism of modified clothoid (MCL)-shaped composite dowel shear connectors and the influence laws of various factors on their shear bearing capacity, the stress states and failure modes of the steel dowel, concrete dowel, and transverse through-reinforcement that constitute the MCL-shaped shear connector were deeply analyzed in this paper based on an experimentally validated finite element model. Furthermore, the influence laws of transverse through-reinforcement, steel dowel thickness, and concrete strength on the shear bearing capacity of the MCL-shaped composite dowel were explored. The research results indicate that the bearing process of the MCL-shaped composite dowel exhibits elastic, elastoplastic, and failure stages. When the MCL-shaped composite dowel reaches its ultimate bearing capacity, the concrete dowel is severely damaged, dominated by shear failure; the steel dowel is in a compressive-shear state and locally enters a plastic state. Compared to the lower transverse through-reinforcement far from the shear action end, the upper transverse through-reinforcement is significantly deformed and serves as the primary source of ductility for the concrete dowel. Increasing the concrete strength can enhance the shear bearing capacity of the MCL-shaped composite dowel and delay the development of splitting cracks and prying failure. A larger diameter of the transverse through-reinforcement leads to a stronger shear resistance capacity. The thickness of the steel dowel significantly affects the shear performance of the MCL-shaped composite dowel, determining whether the shear bearing capacity of the MCL-shaped composite dowel is controlled by steel dowel failure or concrete shear failure.

Abstract:To solve the problems of lacking comparative research on the improvement effects of different reinforcement methods when formulating reinforcement schemes for prestressed concrete small box girders and that existing bearing capacity improvement tests mostly focus on scale models with insufficient reliability of results, full-scale model tests and numerical simulation analysis of five 30 m span prestressed concrete small box girders with different joint reinforcement measures were conducted in this paper. Finite element models for two single reinforcement measures were established, and the improvement effects of different reinforcement methods on the bearing capacity of prestressed concrete small box girders were studied. The results indicate that compared with the unreinforced test girders, the damage ranges of all strengthened girders decrease, and their ultimate bearing capacities are improved to a certain extent. In terms of joint reinforcement measures, the joint reinforcement measure of pasting steel plates on webs, thickening bottom plates, and adding prestress has good effects in all aspects. The mid-span deflection decreases by about 42.7%; the structural stiffness increases by about 23%; the concrete stress decreases by about 28.6%; the cracking load increases by about 64.71%, and the ultimate bearing capacity increases by about 40%. Among the effects of single reinforcement measures, the measure of thickening the bottom plate (adding prestress) has good effects in reducing mid-span deflection, improving structural stiffness, reducing mid-span concrete stress, improving cracking load, inhibiting crack development, and improving ultimate bearing capacity. The test and simulation analysis results in this paper can provide a certain reference for the subsequent reinforcement reconstruction and bearing capacity improvement of similar bridges.

Abstract:In view of the shortcomings of traditional incremental launching calculation methods and the assembly construction control of incremental launching beams, an incremental launching calculation method based on nonlinear analysis was proposed in this paper. This method could truly simulate the running state where the incremental launching pier remains stationary, and the beam moves forward. The assembly alignment of all segments of the beam and the real alignment of the beam under specified working conditions could be directly output. The prefabricated alignment of the main beam (i.e., unstressed alignment) did not need to be consistent with the slide alignment. When the two were inconsistent, the main beam could automatically adapt to the slide alignment without manual intervention. The whole-process finite element modeling and calculation were carried out for the background project. The calculation results indicate that the method can directly output the accurate theoretical assembly alignment of the beam. The reaction force state of the incremental launching pier is associated with the stress state of the main beam, and the elevation adjustment of the top surface of each pier only affects the reaction forces of the current pier and adjacent piers. The slide alignment can be preliminarily formulated as the bridge design alignment, and optimizing the slide alignment according to the reaction forces of piers and the stress variation curves of the beam can meet the requirements of incremental launching control.

Abstract:Given the problems of narrow construction sites, difficult construction organization, and high safety and quality risks faced in the construction of bridges in steep canyon regions of mountainous areas, this paper carried out research on key technologies for bridge construction in mountainous areas based on the Yellow River Three Gorges Bridge of the Jiyuan?Xin’an Expressway. For the excavation of deep and large anchorage foundation pits in mountainous areas, a technical scheme of “loosening controlled blasting combined mainly with mechanical excavation and supplemented by manual excavation” was adopted. As this project is a single-tower single-span ground-anchored rotating-cable suspension bridge, the technologies of cable strand folding and coiling and cable strand pre-bending forming were studied and applied. To address the common problems of erecting super-heavy steel girders in mountainous areas, construction technologies such as single-side site overall assembly and bridge deck section-divided girder storage and transportation were adopted; moreover, a construction process simulation analysis was conducted on the steel girder erection to seek the optimal scheme for main girder erection. The research shows that the technologies investigated in this paper have been implemented and applied, which demonstrates that they are not only advanced and efficient but also significantly reduce construction costs, providing a useful reference for the future construction of bridges in mountainous areas with complex terrains.

Abstract:Tunnel construction produces a large amount of waste slag, which cannot be effectively utilized due to various factors. By using tunnel slag to prepare manufactured sand to replace natural sand, resources can be saved; costs can be reduced, and the environment can be protected. Based on the Xi’an?Shiyan high-speed railway project, the physical and mechanical properties of diorite along the tunnel were tested; the physical properties and concrete performance of manufactured sand and natural sand were comparatively studied, and the effects of water-binder ratio and sand ratio on the performance of shotcrete were analyzed by designing multiple sets of mix proportion tests. The results indicate that diorite has few impurities, good stability, and a low radioactivity index, which is suitable for preparing manufactured sand; compared with natural sand, manufactured sand particles are characterized by rough surfaces, a high fineness modulus, and a high water demand, and meanwhile, the manufactured sand concrete has slightly poorer fluidity but higher strength; when the water-binder ratio is 0.41?0.43, and the sand ratio is 51%?52%, the overall performance of the manufactured sand shotcrete is optimal, and the designed mix proportion shows a good application effect in field trial spraying. It is practicable to apply diorite manufactured sand in shotcrete, which can meet the engineering requirements of tunnel shotcrete, and its application in concrete materials can be further promoted in the future.

Abstract:The tertiary semi-diagenetic sandstone of the Wangjiazhai Tunnel on the Yunnan Linqing Expressway is characterized by loose structure, low diagenetic strength, and poor cementation. The geological disasters such as collapse, water gushing, and mud bursting are very easy to happen when the tunnel passes through the water-rich section. With the surface deep well dewatering of the tertiary water-rich semi-diagenetic section of Wangjiazhai Tunnel as an example, the surface deep well dewatering methods and key parameters for tunnel crossing the tertiary water-rich semi-diagenetic section were discussed. Based on the single well surface dewatering test, the groundwater level and strata permeability of the tunnel site were studied. According to the test, the permeability coefficient is 8.5 × 10^?4 cm/s, and the influence radius of single well dewatering is 60 m, which indicates that this area is a low-permeability formation. Based on the generalization of the aquifer in this area, design and calculation were carried out. The optimum spacing of dewatering wells is determined to be 15 m. The well sites in the test area were set up with the spacing of 15 m. The surface deep well dewatering effect was verified by observing the excavation of the tunnel and monitoring the pore water pressure of the surrounding rocks. The on-site verification shows that the water pressure around the tunnel face is reduced by about 70% after surface dewatering, which meets the safe excavation conditions. The construction progress is significantly improved, and the average monthly footage reaches 30 m.

Abstract:To explore the ventilation optimization and energy saving issues in the construction of multiple working faces in extra-long highway tunnels, the air volumes required for a single working face under drilling and blasting construction conditions and TBM tunneling conditions were determined respectively based on theoretical calculations. Combined with the tunnel construction organization scheme, two ventilation schemes were proposed, and they were compared and selected according to the configured power of axial fans. Based on the recommended scheme, the layout scheme of pollutant-discharging jet fans was designed, and its feasibility was finally verified by on-site measurements of pollutant concentrations. The research shows that the air volumes required for the working faces of the drilling and blasting method and the TBM method are 1 980 m³/min and 1 500 m³/min, respectively, which are both controlled by the minimum allowable air velocity in the tunnel. The total fan power of the alternating construction scheme for multiple working faces is only 39% of that of the conventional construction scheme, which significantly reduces energy consumption. On-site measurements indicate that the alternating construction scheme for multiple working faces can meet the requirements of air velocity and oxygen content during the construction period. The average mass concentrations of CO, SO₂, PM_2.5, and PM₁₀ are lower than the allowable values specified in the Technical Specifications for Construction of Highway Tunnel (JTG/T 3660—2020), indicating that the scheme is highly feasible. However, short-term pollutant accumulation occurs in local areas during excavation blasting, requiring an appropriate increase in air supply. The research results effectively guide the construction ventilation of Tianshan Shengli Tunnel and can provide a reference for similar projects.

Abstract:To improve the accuracy of water inrush and mud outburst disaster prediction during tunnel construction through karst caves, a method of first forecasting the unfavorable geological conditions of karst caves and subsequently predicting water inrush and mud outburst geological disasters was proposed in this paper. First, a karst cave advanced prediction model based on the polynomial naive Bayes algorithm was established to predict the scale grade of karst caves. Secondly, taking the scale prediction results of karst caves as the input condition for water inrush and mud outburst, a support vector machine (SVM) grade prediction model for karst cave water inrush and mud outburst based on the genetic algorithm (GA) was established. The random seed was regarded as an optimizable hyperparameter, and the overall training effect of machine learning models could be improved by adjusting the random seed during data partitioning; the prediction imputation methods, namely the K-nearest neighbor algorithm and SMOTE algorithm, were adopted to generate synthetic samples to fill in missing sample values and solve the problem of sample imbalance. By comparing the GA-SVM model with three models (SVM, GS-SVM, and IPOS-SVM), the results indicate that the overall prediction accuracy of the GA-SVM model is the highest. Model testing demonstrates that the accuracy of the comprehensive advanced prediction model for karst caves is 81.25%, and the accuracy of the grade prediction model for water inrush and mud outburst is 91.67%. Applications in multiple tunnels indicate good effects, and the research results provide a new method for the prediction of water inrush and mud outburst in tunnel karst caves.

Abstract:To solve the practical problems in vehicle type classification on toll roads, a deep learning network based on dual-view feature fusion, named ETCLNet, was proposed in this paper. A dual-branch architecture was adopted by the network to extract the features of vehicle head and side body images, respectively, and combined with an innovatively designed multi-scale feature extraction module, namely IPFE and an adaptive weighting-based bilinear feature fusion (AWBF) mechanism, efficient and fine-grained vehicle feature representation was achieved. Through the design of parallel multi-scale convolutions and residual connections, the problem of gradient vanishing was effectively alleviated, and the adaptability to complex scenarios was enhanced by the IPFE module. The high-order interaction of features between angles was further optimized by the AWBF mechanism, and efficient fusion of multi-angle features was achieved, and classification performance was significantly improved through adaptive weighting and element-wise multiplication. Experimental results indicate that ETCLNet outperforms existing mainstream models in multiple evaluation metrics (e.g., accuracy, precision, recall, F₁ value, and S_AUC), which solves the problem of the low vehicle type recognition rate of cameras in existing toll road audit systems. In addition, existing hardware devices are fully utilized by this design, which reduces deployment costs. A scientific and efficient solution for multi-view vehicle recognition and smart transportation is provided by this paper, and new ideas for deep learning network design are offered.

Abstract:To investigate the traffic congestion pattern changes in continuous bottleneck sections of highway construction zones under mixed passenger and freight traffic conditions, the spatio-temporal evolution laws of vehicle speed and lane-changing trajectory distribution in construction sections with successive lane-narrowing bottlenecks were studied. Based on measured highway data, traffic flow simulation parameters were calibrated using a genetic algorithm. By taking traffic volume and the proportion of passenger and freight vehicles as entry points, a traffic simulation experiment for continuous bottleneck construction zones under multi-factor coupling effects was constructed, and the spatio-temporal variation characteristics of speed and lane-changing trajectory distribution in the construction section under different parameters were analyzed. The traffic volume and speed fluctuation characteristics at key congestion nodes were identified using the continuous wavelet transform method. A congestion early warning model for the construction zone was established, and early warning control measures based on diversion and traffic restriction were proposed, with their control effects verified. The results indicate that under low-flow conditions, when the proportion of trucks increases from 0 to 10%, the average running speeds of vehicles in the upstream and downstream continuous bottleneck sections decrease by 5.85% and 9.71%, respectively. When the proportion of trucks increases from 10% to 30%, the average running speeds of vehicles decrease again by 10.34% and 14.54%, respectively. When the congestion warning threshold is reached, adopting control measures such as truck restriction or overall diversion and detour makes the propagation speed of congestion waves in the construction section slower, and the running speeds are increased by 77.46% and 61.56%, respectively.

Abstract:To clarify the influence of high-temperature steam curing of steel-ultra-high performance concrete (UHPC) lightweight composite bridge deck paving on the temperature field of the steel box girder, taking a certain bridge in Hunan Province as an example, finite element numerical simulation and actual bridge testing were conducted on the temperature field of the steel box girder during the high-temperature steam curing process of the bridge deck paving. The numerical calculations were generally consistent with the test results. The analysis results indicate that under the superimposed effect of solar radiation heating and high-temperature steam curing heating, the maximum temperature of the top plate of the steel box girder can reach 85.5 ℃, and the maximum value of temperature gradient is 51.5 ℃, far exceeding the maximum vertical positive temperature difference due to solar radiation specified in the General Specifications for Design of Highway Bridges and Culverts (JTG D60—2015). In steel box girders constructed with high-temperature steam curing of steel-UHPC lightweight composite bridge deck paving, the adverse effects of temperature gradients on the structure under the superimposed conditions of high-temperature steam curing and solar radiation temperature should be considered. In the early stage of high-temperature steam curing of steel-UHPC lightweight composite bridge deck paving, the maximum measured temperature and temperature gradient of the flat steel box girder depend on the high-temperature steam curing; therefore, the occurrence time of the maximum temperature and maximum temperature gradient depends on the duration of high-temperature steam curing, rather than the midday period with the maximum solar radiation. While in the later stage of high-temperature steam curing and after the completion of high-temperature steam curing, the maximum measured temperature and temperature gradient primarily depend on the solar radiation intensity. Different regions, seasons, bridge locations, and construction conditions may cause certain differences in the temperature of the steel box girder; the related issues of the temperature field of the steel box girder during the steam curing construction process of the steel-UHPC composite bridge deck are worthy of further research.

Abstract:To investigate the typical disease characteristics of energy transport channels in winter cold regions and guide the design for extending road service life, the causes of diseases such as pavement reflective cracks, continuous potholes on bridge decks, and failures of bridge drainage systems were analyzed based on the 20-year operation data of a 531 km in-service expressway in the coal energy region of northern Shaanxi. The research results indicate that when the asphalt pavement thickness reaches 22 cm, the reflective crack spacing of the expressway operated for 15 years can be controlled to over 50 m. Basically, no base layer water damage caused by cracks occurs, and the pavement service life can be significantly extended. The relatively thin 8 cm thickness of the cement reinforced concrete leveling layer on the bridge deck is the main cause of the continuous potholes on the bridge deck, and the ineffective removal of the laitance layer on the surface of the reinforced concrete is the main cause of the upheaval and slurry pumping diseases in the asphalt layer on the bridge deck. It is recommended to perform precision milling twice to thoroughly eliminate the laitance layer. Under the influence of coal slag and freeze-thaw cycles, conventional bridge drainage systems are highly susceptible to damage and failure. In this special environment, the bridge drainage systems are innovatively optimized. Prefabricated external hanging drainage gutters combined with vertical drainage systems are adopted to perfect the drainage systems of the bridge and the bank slope under the bridge, adapting to the special operating environment of energy transport channels in winter cold regions.

Abstract:With the continuous advancement of China’s “Belt and Road Initiative”, Chinese enterprises have become increasingly involved in international engineering markets, undertaking numerous transportation infrastructure projects, particularly in Africa and Southeast Asia. However, international engineering projects commonly face the challenge of inconsistent design standard systems across different countries, posing significant difficulties for Chinese enterprises during project implementation. To address this issue, the differences in BRT road design under Chinese and French standards were focused on in this study, and their respective design philosophies and methods were analyzed. Taking a BRT project in a West African country as an example, field investigations, design scheme comparisons, and data analyses were conducted to explore the key points of road design for BRT projects under the French standard system, with an emphasis on key issues encountered in the design process. The results indicate that the French standard system emphasizes a people-oriented approach, places high demands on design details, particularly with strict standards in road geometric layout, accessible pathway design, and traffic management, and possesses strong flexibility and adaptability. The findings provide a reference for Chinese enterprises engaged in BRT road design under the French standard system.