Abstract:To explore the influence of hydraulic parameters of the drainage layer (UDL) on the anti-seepage performance of the capillary barrier cover (CBC) layer, the VG model was adopted to fit the soil-water characteristic curve and permeability function of soil based on the principle of unsaturated seepage in this paper. A simplified model of “fine-UDL-coarse”-type CBC layer containing a UDL was established using Geo Studio finite element software. By carrying out the numerical simulation of seepage of expansive soil slope treated with the cover layer under heavy rain conditions, the influence rules of different hydraulic parameters of the UDL on the anti-seepage performance of the CBC layer were systematically analyzed, and the reasonable hydraulic parameter values of the UDL were determined. The results show that the optimal values of hydraulic parameter n, saturated permeability coefficient k_s, and air-entry value a of the UDL are 3.5, 5.79 × 10^?4 m/s, and 9 kPa, respectively. For the UDL, increasing n, k_s, and a can all effectively extend the effective drainage length of the UDL under long-term rainfall conditions, reduce the volume of water breaking through from the sand layer to the gravel layer, and significantly reduce the range of the saturated zone of expansive soil. Therefore, when the “UDL CBC”-type cover layer is adopted in practical engineering applications, various hydraulic parameters of the UDL should be comprehensively coordinated to improve the anti-seepage performance of its CBC layer. The research results can provide a reference basis for material selection in the design of expansive soil treatment engineering using the CBC layer.

Abstract:Embankment filling on weak subgrades is prone to sliding and collapse failures. Positive-negative batter pile combinations were proposed to be installed at the embankment slope toe to constrain lateral deformations, but systematic inquiries into the mechanical characteristics of positive-negative batter pile combinations are still lacking. The mechanical responses of positive-negative batter pile combinations under lateral loads with different pile length ratios (1/2, 2/3, 1, 3/2, and 2/1) were systematically investigated by the finite element software Abaqus, and calculation and verification were conducted by the structural mechanics force method, providing a basis for the design of positive-negative batter pile combinations at the slope toe. The results indicate that: ① Compared with vertical double-row piles, positive-negative batter pile combinations with the same pile length ratio reduce horizontal displacement by approximately 25%, and displacement of pile bodies of rear-row positive batter piles decreases with the increase of lengths of front-row negative batter piles; displacement of rear-row positive batter piles exhibit “rotation around the fixed end + outward movement in the upper-middle section”, and peak values of horizontal displacement appear in the upper-middle section of pile bodies; ② Peak values of bending moments of pile bodies appear in the upper-middle section of pile bodies; bending moments of rear-row positive batter piles and front-row negative batter piles increase with the increase of lengths of front-row negative batter piles; bending failures easily occur in the upper-middle section of pile bodies of positive and negative batter piles, and rear-row positive batter piles experience bending failures earlier than front-row negative batter piles. As the pile length ratio of front-row negative batter piles to rear-row positive batter piles increases, the peak bending moment ratio of negative batter piles to positive batter piles gradually decreases to 1; ③ By comprehensively considering mechanical mechanisms and construction feasibility, lengths of front-row negative batter piles in actual engineering should be greater than lengths of rear-row positive batter piles, so as to reduce horizontal displacement and peak bending moment ratios of rear-row positive batter piles and improve the overall stability of the subgrade.

Abstract:To reveal the distribution characteristics of stress and strain, load characteristics, and influence mechanism of super-long and large-diameter steel casings during the construction process in deep-sea areas, the dynamic stress and strain of the casing body were dynamically monitored during the static pressure construction of the steel casing in deep-sea areas in this paper to calculate the stress distribution of the steel casing; meanwhile, finite element simulation was conducted using Abaqus software to analyze the variation characteristics of pile top load, side friction resistance, and end resistance during the static pressure process of the steel casing on the inclined rock surface of the seabed. The research results indicate that: ① In the initial pressing stage, the overall deformation of the steel casing is relatively large, and the average strain rates are 40 × 10^?6/h and 56 × 10^?6/h, respectively, indicating significant overall deformation; in the counterweight pressing stage, affected by the pile end resistance, the average strain rate increases from 2.5 × 10^?6/h to 28 × 10^?6/h. The development of the pile top load and side friction resistance determines the magnitude of the end resistance; ② Affected by the thin-wall effect, the axial force of the above-water and underwater sections of the steel casing is unevenly distributed, with the upper axial force gradually increasing, the middle part remaining unchanged, and the lower part gradually decreasing; ③ The side friction resistance of the steel casing is related to soil parameters and penetration depth. In the initial stage, the side friction resistance is greatly affected by the penetration depth, and with the increase of depth, soil parameters become the main factor. The research conclusions can provide a theoretical basis for the design and construction of super-long and super-large steel casings for deep-sea engineering under similar construction environments.

Abstract:To study the influence of excavation and rainfall on the stability of high steep road cutting slopes, relying on an actual project, the unsaturated slope seepage and stability were analyzed by a self-programmed calculation program using FLAC^3D software, and the corresponding reinforcement optimization scheme was studied through the analysis of the pile spacing of anti-slip piles and the length of the anchoring section. The results indicate that: ① The surface soil of the slope is greatly affected by excavation. With the decrease of the excavation slope ratio, the horizontal displacement decreases; the vertical displacement remains basically unchanged, and stress concentration exists at the toe of the slope at all step levels; ② The top and toe of the slope are greatly affected after rainfall; the overall displacement increases; the instability increases, and the location of the potential sliding surface moves to the middle and lower parts; ③ By comprehensively considering the slope states under rainfall and no-rainfall conditions, an excavation slope ratio of 1:1.5 is the most appropriate; ④ By comprehensively analyzing the support effects under rainfall and no-rainfall conditions, it is most suitable when the pile spacing of anti-slip piles is 8 m, and the length of the anchoring section is 13 m.

Abstract:To study the dynamic response and deformation characteristics of the carbonaceous mudstone embankment under traffic load, dynamic triaxial tests were conducted to investigate the variation laws of the dynamic backbone curve and dynamic elastic modulus of the carbonaceous mudstone embankment filler under the influence of different factors. Combined with numerical simulation, the dynamic response and deformation characteristics of the carbonaceous mudstone embankment were analyzed. The dynamic triaxial test results show that the dynamic backbone curve of the carbonaceous mudstone embankment filler can be described by the Hardin-Drnevich model. The dynamic elastic modulus of the carbonaceous mudstone filler is positively correlated with the confining pressure, loading frequency, and static deviatoric stress, and the influence of the confining pressure and static deviatoric stress is much greater than that of the frequency. The dynamic elastic modulus of the carbonaceous mudstone filler decreases with the increase of dynamic strain. An attenuation model of dynamic elastic modulus considering the influences of the confining pressure and static deviatoric stress is established, and its rationality is verified by experiments. The numerical simulation results indicate that the dynamic stress of the soil at the wheel load is the largest under the same embankment depth. The dynamic stress gradually decreases with the increase of depth, and the attenuation is the most serious within 0?1 m. The cumulative deformation of the carbonaceous mudstone embankment under traffic load is small, which indicates that the pre-disintegrated carbonaceous mudstone filler has good dynamic characteristics and meets the specification requirements for embankment filling.

Abstract:Resource utilization of construction waste is an important approach for the sustainable development of infrastructure. To improve the diversified recycling system of construction waste in China and resolve the contradiction between the yield of construction waste and lagging treatment technologies, the physical-mechanical properties, modification methods, and pavement performance of construction waste were systematically summarized in this paper. Firstly, by analyzing the sources and treatment processes of construction waste, material variability was clarified as the key factor restricting its high-value application. Secondly, the application characteristics of construction waste mixtures in the subgrade, base, and asphalt surface layer of road engineering were comprehensively analyzed, and their pavement performance characteristics and process parameters were discussed layer by layer. Finally, the economy and feasibility of the pavement technology of recycled construction waste mixtures were clarified through typical engineering cases, and the significant environmental benefits provide technical support for the construction industry to achieve the carbon neutrality goal. The results indicate that the strength of recycled construction waste mixtures can be effectively improved by addressing the weak interface between old mortar and aggregates, while the low-temperature cracking resistance of asphalt mixtures of construction waste for road use needs to be broken through. It is suggested that research on the effect of low-temperature asphalt modifiers on the performance of construction waste mixtures should be carried out. Meanwhile, the pavement performance of construction waste materials is significantly influenced by the construction compaction process, and conducting research combining material design and process is more conducive to guiding engineering practice.

Abstract:To address the problems of low toughness and poor deformation ability of cement soil, short-chopped polyvinyl alcohol (PVA) fibers were added to modify and toughen the cement soil in this paper, and unconfined compressive and flexural tests were conducted on the PVA fiber-reinforced cement soil with different cement contents. The results show that compared with plain cement soil, the fiber-reinforced cement soil has stronger compressive deformation capacity, a flatter descending branch of the compressive stress–strain curve, a higher residual stress level, and better compressive toughness. When the cement content increases from 5% to 10%, the overall growth rates of compressive strength and flexural strength of the fiber-reinforced cement soil are greater than those of plain cement soil. Adding a certain amount of PVA fibers significantly improves the flexural strength, flexural deformation capacity, and flexural toughness, and the failure mode changes from brittle fracture to ductile failure. The mechanical properties of the specimens increase rapidly at an early age and remain basically unchanged after 28 d, and within a curing age of 90 d, the degree of compressive failure of the specimens gradually becomes increasingly severe as the curing age increases.

Abstract:To address the surface distresses such as surface polishing, aggregate exposure, pitting, and unevenness in cement concrete pavement, a polymer composite modified cement mortar material incorporating both polypropylene fibers and redispersible latex powders was designed for the bonded thin overlay repair of existing cement concrete pavement. Based on the orthogonal test method, composite modified mortars with different mix proportions were prepared, and their performance indexes, including fluidity, flexural strength, compressive strength, and drying shrinkage, were tested to optimize and determine the optimal mix proportion. The corresponding workability, mechanical, bonding, and durability properties, as well as the microscopic characteristics, were verified and analyzed. The results show that the composite modified mortar under the optimal mix proportion is a high-strength and low-modulus cement-based composite material; its strength exceeds the technical requirements of C40 concrete for cement concrete pavement, and it has good workability, volume stability, impermeability, and impact resistance, along with strong bonding performance with concrete. Polypropylene fibers enable hydration products to form a dense microstructure, and redispersible latex powders construct a network membrane structure to fill the microscopic pores of the mortar, thereby enhancing the interface bonding strength and matrix impermeability. The various performances of the composite modified mortar meet the performance requirements for bonded thin overlays of cement concrete pavement.

Abstract:Under the background of the “carbon peaking and carbon neutrality” goals, the improvement and resource utilization of industrial solid waste and waste soil have become increasingly important. High carbon emissions are generated during the production of traditional cement and lime-modified solidifiers, which exhibit poor crack resistance and tensile properties. In contrast, a composite organic-inorganic membrane can be formed by waterborne epoxy resin combined with C?S?H gel in cement soil to cement the internal flaky or spherical soil particles, thereby improving the tensile strength and water erosion resistance of the soil. In this paper, slag and desulfurization gypsum were selected as cement admixtures, and waterborne epoxy resin was added to improve the water resistance. Accordingly, a new water-resistant solid waste-based solidifier combining inorganic and organic materials was prepared to improve soft soil. The results indicate that when the mass ratio of cement to slag to desulfurization gypsum is 4∶2∶0.5, the strength of the inorganic solid waste-based solidified soil material reaches its maximum. In addition, the optimal dosage of waterborne epoxy resin is approximately 15% of the dosage of the inorganic solidifier. When this dosage is exceeded, the hydration process is hindered by the excessive polymer membrane, adversely affecting the strength of the solidified soil.

Abstract:In recent years, expressway reconstruction and expansion projects have been increasing, and expansions from four to eight lanes and from six to ten lanes are relatively common. In the design process of reconstruction and expansion, the rationality of the design for overlay, widening, and lap treatment of “white-to-black” pavement has a significant impact on pavement reconstruction quality. The formation of ultra-wide pavement after reconstruction, especially in sections such as acceleration and deceleration lanes, areas with small composite longitudinal slopes, and the bottom of concave curves, makes pavement drainage difficult, which affects driving safety to some extent. Meanwhile, milling waste generated during pavement reconstruction should be fully recycled to save costs and reduce environmental pollution. Stone materials generated from tunnel excavation are often discarded or only used for subgrade filling, causing resource waste; they can be fully utilized in structural layers of pavement. Based on the practical achievements of the Shenshan West Expressway reconstruction and expansion project, key technologies for the overlay, widening, and lap treatment design of “white-to-black” pavement, drainage design for ultra-wide pavement, waste recycling, and utilization of tunnel slag were proposed in this paper. Currently, the Shenshan West Expressway reconstruction and expansion project has been completed and accepted for two years, and the overall pavement performance is excellent, which indicates that the adopted key technologies for pavement design in the reconstruction and expansion project are feasible.

Abstract:Asphalt pavement generates cracking damage under the action of vehicle loads and other factors, which triggers various distresses. Microwave heating technology can rapidly increase the temperature of mixtures, enhance the self-healing capacity of asphalt, and thereby repair the damage. The research progress on the self-healing capacity of asphalt mixtures by microwave heating was reviewed in this paper and summarized from four aspects: the self-healing mechanisms under microwave heating, test methods, evaluation indicators, and influencing factors of the self-healing capacity. The results indicate that microwaves promote the flow and healing of asphalt through multiple mechanisms; the loading states of mixtures were simulated by researchers through fatigue and monotonic loading, and the self-healing capacity was evaluated using multi-dimensional indicators such as mechanics and cracking characteristics; the influences of factors such as the content of microwave-sensitive admixtures and heating conditions on the self-healing capacity by microwave heating exhibit complex patterns. By summarizing the research progress, the following conclusions are drawn: The nonlinear variation characteristics of the self-healing capacity by microwave heating remain to be further explored; the coupling effects of multiple factors on the self-healing capacity still need to be decoupled; the correlations between the existing test methods and the actual service conditions need to be strengthened; the sources of microwave-sensitive admixtures should be expanded, and the costs should be reduced to promote the engineering applications of the self-healing technology by microwave heating.

Abstract:To reveal the effects of the number of dry-wet cycles and the material density gradient on the deterioration laws of macroscopic mechanical properties, microscopic damage mechanisms, and failure modes of foam concrete, foam concrete test blocks with densities of 800 kg/m³, 1 000 kg/m³, and 1 200 kg/m³ were investigated in this paper. Macro-micro joint tests and three-dimensional discrete element simulation methods were combined. Specifically, 25 dry-wet cycle tests, nuclear magnetic resonance pore analyses, and uniaxial compression tests were conducted, and a discrete element model considering particle expansion and contraction, as well as crystalline salt deterioration effects was constructed. The results indicate that the interface is deteriorated by dry-wet cycles through periodic particle expansion and contraction and crystalline salt precipitation, and the pore connectivity rate is significantly increased; after 25 cycles, the strength loss rates of the FC-800, FC-1 000, and FC-1 200 test blocks are 23.37%, 17.59%, and 13.97%, respectively. The damage mode is regulated by the density gradient; diffused cracks are induced by the low-density zone to weaken the overall bearing capacity, while localized concentrated expansion of cracks is promoted by the high-density zone. The material instability is caused by force chain fractures and displacement field mutations. Based on the differences in damage modes caused by the density effect, a subgrade layered optimization strategy is proposed in this paper: High-density materials are adopted in the surface layer to resist deterioration, and low-density materials are selected in the deep layer to reduce load. A microscopic theoretical basis and operable engineering recommendations are provided by this paper for the long-term service performance of road and bridge transition sections under the dry-wet cycle environment.

Abstract:To reasonably evaluate the increase in deflection of PC beams after local corrosion, a calculation method for deflection of corroded PC beams based on the stress and strain model of corroded reinforcement was proposed by considering the beam-arch effect formed by reinforcement corrosion and the degradation of bond strength between reinforcement and concrete. Bending tests on a batch of locally corroded PC beams were carried out to verify the calculation method, and a parameter analysis on the corrosion rate and corrosion position was conducted. The results show that the load?deflection curves obtained by the calculation method are in good agreement with the experimental results. When the corrosion rate is less than 5%, the bending stiffness of the PC beams basically does not change; when the corrosion rate exceeds 5%, the weakening degree of the corrosion rate on the bending stiffness of the PC beams gradually increases, and the deflection of the corroded beams increases significantly with the increase of the corrosion rate. The influence of the corrosion position on the deflection is related to the corrosion rate; when the corrosion rate is relatively low, the change of the corrosion position has little influence on the deflection; when the corrosion rate exceeds 10%, the influence increases, and the mid-span is the most unfavorable.

Abstract:To reasonably characterize the stress state of corrugated steel web girders and determine the failure load, the stress state evolution pattern of corrugated steel web girders was investigated in this paper based on the structural stress state theory, relying on the model test of a continuous corrugated steel web composite box girder bridge with a span arrangement of (2.65 + 4.10 + 2.65) m. First, the generalized strain energy density was constructed as a characteristic parameter using the longitudinal strain of the test girder, and then the strain energy density?load curve was obtained. The Mann-Kendall criterion was applied to analyze the stress state curve and identify the characteristic points where abrupt changes occur in the stress state characteristics. The failure load of the corrugated steel web composite girder bridge was defined according to the law of quantitative to qualitative change. Furthermore, the working behavior of the structure was discussed by combining the strain-based stress state mode, the stress state sub-mode, and the energy ratio sub-mode. Finally, the application of calculating the characteristic load using this method in the design of corrugated steel web girder bridges was discussed. The results indicate that the Mann-Kendall criterion can identify three characteristic points of failure during the loading process of the corrugated steel web girder, and the entire stress process is divided into four stages: elastic, elastoplastic, failure, and continuous failure; the strain-based stress state mode, the stress state sub-mode, and the energy ratio sub-mode can all capture the stress characteristics of the corrugated steel web at different stress stages to varying degrees. For structural design, the failure load identified by the Mann-Kendall criterion can be adopted as the design load.

Abstract:To address the problems of severe damage to the pier concrete caused by wall attachments of components such as guide rails and low climbing efficiency in traditional hydraulic climbing formwork construction, a new type of hydraulic climbing formwork structure suitable for the construction of variable cross-section hollow thin-walled high piers was designed based on the Miaolu River Bridge project of the Zhengzhou?Luoyang Expressway in this paper. To ensure the safety of the structure during construction, a finite element model of the climbing formwork structure was established using Midas Civil; the stress and deformation of components such as formwork, climbing formwork frame, operation platform, and support bracket were analyzed, and the stability of the structure was checked. The results show that the maximum combined stress of the formwork panel is 16.85 MPa; the maximum combined stresses of the transverse and vertical ribs are 89.18 MPa and 153.52 MPa, respectively; the maximum deformations of the formwork structure are 4.60 mm and 3.68 mm; both the stress and deformation meet the requirements. The maximum stresses of the climbing formwork frame and the operation platform are 162.16 MPa and 122.97 MPa, respectively, which are both less than the yield strength of Q235B steel; the maximum deformations are 7.63 mm and 7.98 mm, meeting the requirements. The support brackets are anchored to the pier body through bolts. The stability and safety factor are checked according to the maximum reaction force values at the connection points between the brackets and the pier body when the climbing of the climbing formwork structure is completed, and the results all meet the specification requirements. In the actual construction process, the climbing of the new hydraulic climbing formwork structure is completed by four vertical hydraulic jacks set on the support brackets, which is simpler and easier to operate and improves the construction efficiency.

Abstract:To achieve the girder-end displacement control of long-span cable-stayed bridges under static and dynamic loads such as temperature, vehicle load, wind load, and earthquake, a new type of nonlinear spring and damping restraint device was developed in this paper, and a dynamic analysis finite element model of the structure was established. The influence laws of the limit parameter variations of the device on the girder-end displacement, the relative displacement between tower and girder, and the internal force at the tower bottom were analyzed, and reasonable parameter values were determined. On this basis, the dynamic responses of the long-span cable-stayed bridge before and after the installation of the device were compared and studied. The results show that the girder-end displacement decreases with the increase of the equivalent stiffness of the device and increases with the increase of the gap. The reasonable setting of the nonlinear spring and damping restraint device can greatly reduce the girder-end displacement of the long-span cable-stayed bridge under static and dynamic actions and will not cause adverse effects on the internal force distribution of the structure.

Abstract:To construct urban three-dimensional transportation systems and reduce space occupation under bridges, the large cantilever-Y-shaped pier system was applied as a substructure of urban viaducts, with its application demand increasing year by year. However, related research on its reinforcement ratio under vehicle eccentric load has been rarely conducted. Based on an engineering case of an expressway construction project in Jiaxing City, Zhejiang Province, a 1∶5 scaled finite element model was established using Abaqus. The reinforcement ratios of Y-shaped piers in four models were set to 0.42%, 1.17%, 1.69%, and 2.29%, respectively. Among them, the reinforcement ratio of 0.42% was lower than the minimum reinforcement ratio (0.5%) stipulated in the Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts (JTG 3362—2018). To study the failure mode of the Y-shaped pier, numerical simulations were conducted on the above four models under vehicle eccentric load. The results indicate that: ① Under vehicle eccentric load, when the reinforcement ratio increases from 0.42% to 2.29%, the crack resistance of the pier column is not significantly improved, and the concrete cracking load at the Y-shaped turning area of each model is 64.8 kN; ② with the increase in reinforcement ratio, the concrete crushing location moves from the turning area at the waist on the compression side to the bifurcation on the compression side; ③ when the reinforcement ratio increases from 1.69% to 2.29%, the bearing capacity of the pier column is significantly improved, with an increase of approximately 29.85%.

Abstract:To analyze the applicability of the ultra-high performance concrete (UHPC) reinforcement method for box arch bridges, a reinforcement project of a reinforced concrete box arch bridge with a span of 125 m was taken as the background in this paper. By analyzing the limitations of the steel plate bonding method in reinforcing large-span box arch bridges, a UHPC reinforcement scheme was proposed, and the corresponding simplified calculation formulas were established. The research results indicate that: ① Before reinforcement, the box arch of the bridge exhibits a large eccentric compression failure. After pasting steel plates on the bottom slab of the box arch, the failure mode transforms into a small eccentric compression failure, and the failure location shifts from the tension bottom slab to the compression top slab. However, the bearing capacity requirements still cannot be met, indicating that the section thickness of the compression top slab of the box arch is insufficient; ② When a 6 cm thick UHPC is added to the top and bottom slabs of the box arch, the self-weight of the reinforcement layer is reduced by 60%. The bearing capacities of the sections at the arch foot, 3L/8, and L/2 increase by 68%, 61%, and 48% compared to those before reinforcement, respectively, and the minimum safety factor is 1.05, indicating that the UHPC reinforcement method has a significant reinforcement effect on eccentric compression members such as box arch bridges; ③ The bearing capacity values obtained by the simplified calculation method are in high agreement with the actual bearing capacity values. The maximum error is less than 5%, and the calculated values are slightly smaller than the actual bearing capacity values, indicating that the simplified method has good calculation accuracy and tends to be safe, which can effectively improve the design efficiency.

Abstract:Concrete cracking and bond degradation caused by corrosion lead to retraction slip of prestressed steel strands and changes in transfer length. Simulating the retraction effect of corroded prestressed steel strands is a difficulty in current research. A numerical model for corroded prestressed concrete (PC) components based on Cohesive contact was established. The effects of different corrosion locations and corrosion rates on the retraction slip and transfer length of prestressed steel strands were analyzed. The rationality of the model was verified based on existing experimental data. Results indicate that Cohesive contact can effectively simulate the retraction effect of prestressed steel strands under local corrosion. The retraction slip at the cut end of the steel strand increases with the increase of corrosion rate. Compared with uncorroded components, the retraction slip increases by 16.10% when the corrosion rate at the end is 35%. When the local corrosion rate reaches 35%, the transfer length increases by 30.6%. As the corrosion location moves from the end to the mid-span, the effect of local corrosion of the steel strand on the transfer length gradually weakens.

Abstract:To study the temperature field and temperature effects of a continuous rigid-frame bridge with horizontal bottom cables, a large-span prestressed concrete continuous rigid-frame bridge with a horizontally arranged bottom cable system was selected as the research object. A Python program was developed to calculate the solar radiation boundary conditions, and the Abaqus software was used to establish a two-dimensional transient heat conduction model of the bridge. The time-dependent temperature field of the bridge during summer and winter was analyzed. Based on this, the temperature effects caused by the vertical temperature gradient, transverse temperature gradient, effective temperature, and various temperature modes on the bridge structure were further investigated. The research results show that the temperature distribution characteristics of the bridge cross-section calculated by the finite element method are in good agreement with the current specifications. The horizontal arrangement of bottom cables can effectively improve the mechanical performance of the continuous rigid-frame bridge and reduce the temperature effects during the operational period.

Abstract:For self-anchored suspension bridges, reasonable auxiliary span setting, cable force optimization, and structural system selection can not only effectively eliminate the negative reaction effect at the anchorage end, but also improve and optimize the mechanical performance of the stiffened girder. However, current theoretical research is mostly focused on large-span bridges crossing rivers, lakes, and seas, with fewer applications and a lack of corresponding attention in the field of small- and medium-span bridges. In particular, theoretical research on single-tower structures is relatively scarce. In this paper, combined with a practical engineering project, the bridge was studied using a simulation analysis method based on the mechanical performance of the main bridge. Recommended values for the setting length of the auxiliary span, the bearing proportion of cable force, and the selection of the structural system were provided, which can serve as a reference for the design of other similar projects.

Abstract:In view of the temperature field problem of Asia’s first four-season cross-country skiing tunnel reconstructed from an existing tunnel, based on the study of the thermal conductivity of tunnel materials by the HOTDISK method, steady-state heat transfer models under different protection conditions were established by using the finite element method and the multi-layer cylinder heat transfer theory, respectively. The temperature field distribution characteristics of the negative temperature tunnel were analyzed, and the influence laws and sensitivities of various factors were investigated. The results show that the freezing of the tunnel affects the material properties of the tunnel structure; the thermal conductivities of the saturated rock sample and concrete in the frozen state are 8%?20% higher than those in the thawed state; the thermal resistance under the protected condition increases by nearly 9 times compared with that under the unprotected condition, and the heat flow decreases to 1/10; the thermal resistance component of each material layer is inversely proportional to its thermal conductivity and increases approximately logarithmically with the thickness of the insulation layer; the tunnel temperature field has an approximate logarithmic relationship with the thermal conductivity of the surrounding rock and the thickness of the air layer and has a low correlation with the thermal conductivity of the lining; as the thermal conductivity of the insulation material increases, the insulation effect decreases rapidly. The main factors affecting the distribution of the tunnel temperature field are the thickness of the insulation layer, the thermal conductivity of the insulation layer, and the thermal conductivity of the surrounding rock. Intervals can be set in the air layer to reduce the impact of convective heat transfer, and active heating technology can be applied in the lining to prevent the freezing of the tunnel structure.

Abstract:To explore the mechanism of pavement arching disease in phyllite soft rock tunnels and propose targeted disease treatment measures, based on the Yunling Tunnel in the Shiyan?Manchuanguan section of the Fuzhou?Yinchuan Expressway, typical tunnel diseases were investigated, and triaxial compression tests of phyllite in natural and saturated states were conducted to study the failure laws of the tunnel under the combined action of fault fracture zones and groundwater. The research results indicate that the compressive strength and elastic modulus of the rock in the saturated state are lower than those in the natural state, which demonstrates that the structure of phyllite undergoes damage and deterioration after being exposed to water. The fault penetrates the tunnel in an inclined manner, resulting in the phenomenon of unsymmetrical loading in the tunnel. A larger permeability coefficient of the fault means a larger volume of the plastic zone. Under the seepage?stress coupling effect of the tunnel, groundwater and faults reduce the bearing capacity and shear resistance of the surrounding rock at the tunnel bottom, leading to pavement arching in the tunnel. Starting from improving the integrity and bearing capacity of the surrounding rock and lining structure, three categories and six types of disease treatment schemes were proposed for different disease causes and degrees. A new technology of embedded arch reinforcement structure was proposed for sections with severe pavement arching. The on-site construction effects show that the treatment and reinforcement achieve the expected effects, with good economic and social benefits.

Abstract:To explore the influence of wind speed on the smoke temperature and distribution characteristics of the bifurcated diverging tunnel fire, Hangzhou West Station Tunnel on National Highway G235 was taken as the engineering background in this paper. The numerical simulation method was used to investigate the influences of different upstream wind speeds and fire source positions on the fire smoke propagation in the diverging expansion section. The results indicate that: ① A higher wind speed at the tunnel entrance results in a shorter smoke backflow length in the tunnel, and the rate of smoke backflow in the tunnel decreases accordingly; ② The temperature near the side wall close to the fire source in the expansion section is higher. As the fire source moves laterally towards the ramp, the vault temperature in the main tunnel decreases while that in the ramp increases. A higher tunnel wind speed leads to a lower maximum vault temperature in the tunnel;③ When the longitudinal ventilation in the tunnel encounters fire smoke, convection forms, causing the smoke flow velocity in the tunnel to decrease, while the smoke flow velocity at the fire source increases sharply.

Abstract:To address the transition problem between the W-beam guardrail and the combined bridge guardrail during the upgrading and reconstruction of in-service highway guardrails, an SB-level wing-wall-free transition section with simple construction and high efficiency was proposed. Computer simulation technology was adopted to study the stiffness transition, height transition, and cross-section transition of the wing-wall-free transition section. The guardrail stiffness transition was achieved by optimizing the column spacing and column cross-sectional dimensions. By comparing the contact area between the vehicle and the guardrail and the vehicle redirection situation under different height differences, it was preliminarily determined that the vehicle can be safely redirected when the height difference of the guardrail is less than 15 cm. On this basis, a collision simulation analysis was conducted on the specific scheme of the wing-wall-free transition section, and its protection performance was further verified through a real vehicle collision test. The test results indicate that the structure can achieve the SB-level protection capacity stipulated by the standard.

Abstract:It is a general way to construct expressway interchanges by stages. The engineering construction cost, road network operational efficiency, and operational security are directly affected by the rationality of the scheme design. Considering the features of short-term and long-term integrated design of interchange, the necessity of research on design ideas was analyzed. Two short-term and long-term integrated design principles were defined, and their applicable conditions, advantages and disadvantages were analyzed. The main control factors of design principles were thus determined. With the main control factors as the criterion and design principle as the goal, the analytic hierarchy process (AHP) was employed to construct the short-term and long-term integrated design idea of interchange. This idea was applied to the scheme research and decision-making of the Yisong interchange on the Ninglang?Shangri-La expressway, which verifies the effectiveness and rationality of the design idea and can provide a reference for similar interchange scheme design.

Abstract:To achieve real-time monitoring data collection, intelligent evaluation and warning of safety risks, and rapid disposal of emergency plans for steel cofferdam structures during the construction process of deep water foundations of bridges. Research on intelligent safety control of steel cofferdams of deep water foundations of bridges was conducted based on digital twins. Firstly, BIM software was used to construct a virtual model of the entire construction process of the steel cofferdam, and IoT devices were used to collect real-time data on the stress, displacement, and construction water level of the steel cofferdam structure. Secondly, by using the Web-GL engine to couple physical data with virtual models, a real-time interconnected digital twin scene was built. Finally, based on finite element simulation analysis and construction technology, a structural safety assessment index system was established, as well as a safety warning and response system, achieving intelligent safety control throughout the entire process of steel cofferdam construction. The reliability and scientificity of this technology have been verified through practical engineering applications, and the research results will effectively improve the efficiency and accuracy of steel cofferdam monitoring, ensuring controllable construction safety risks.

Abstract:To study the effect of polyurethane grouting on the crack repair performance of cement stabilized crushed stone, a microscopic model of cement stabilized crushed stone was established by the discrete element method (DEM) in this paper. SCB fracture simulation tests were conducted on specimens with different initial notch-to-depth ratios to obtain load?displacement curves, and sensitivity analysis of microscopic parameters was performed. Then, by comparing microscopic characteristics such as crack propagation paths, crack types, and particle displacements before and after grouting, the repair effect of polyurethane grouting materials was evaluated. The results indicate that the grouting filler significantly enhances the overall stress uniformity of the specimens, expands the tension zone, and disperses internal particle displacements; after grouting, the crack propagation paths of the specimens are similar to those before grouting, but the polyurethane grouting material effectively suppresses crack initiation from the pre-cut notch; cracks mainly propagate along the aggregate?mortar interface at the bottom central axis and the mortar interface at the bottom of the loading plate; crack propagation undergoes three stages: slow accumulation, rapid propagation, and stabilization; the grouting filler significantly improves the crack resistance of the specimens, delays the time of crack generation, and suppresses the rapid propagation of cracks, among which the crack resistance is optimal when the notch-to-depth ratio is 0.4R (R is the specimen radius); tensile stress is the driving force for crack propagation, and the aggregate-mortar interface and the interior of the mortar are the main weak failure interfaces; polyurethane grouting can significantly improve the crack resistance of cement stabilized crushed stone, enhance the structural integrity of the specimens, and improve stress distribution.

Abstract:To reveal the main factors influencing vehicle exhaust emissions at signal-controlled intersections and their action mechanisms, a professional software system for analyzing intersection vehicle fuel consumption and emissions, SIDRA INTERSECTION, was used as the research tool in this paper. The influencing factors and their variation laws of the exhaust emissions of carbon dioxide (CO₂), nitrogen oxides (NO_x), carbon monoxide (CO), and hydrocarbons (HC) in the intersection area were explored from the aspects of traffic flow characteristics, signal cycles, and signal timing schemes. The research results indicate that: ① The average vehicle exhaust emissions at road intersections increase with the rise in traffic volume, and a greater total traffic volume at the intersection means a larger increment in average vehicle exhaust emissions; ② As the signal cycle increases, all types of exhaust emissions first decrease sharply, reach a minimum value, and then they show a slow upward trend. Meanwhile, a larger total traffic volume means a longer signal cycle when the exhaust emissions reach the lowest value; ③ Among the four types of exhaust gases, the sensitivity of NO_x emissions to cycle changes is lower than that of the other three types of exhaust gases; ④ When the traffic volume on the approach exceeds 800 veh/h, the vehicle pollutant emissions under the split phasing strategy at the intersection show a significant upward trend, and their emission levels are significantly higher than those of the two release methods of the left-turn protection strategy under the same conditions; ⑤ The magnitude of the traffic volume at the intersection significantly affects the correlation between the proportion of left-turn vehicles and vehicle pollutant emissions, and with the increase in the total traffic volume at the intersection, the effect of the left-turn proportion on exhaust emissions becomes more prominent.

Abstract:With the goal of “achieving carbon peak by 2030 and carbon neutrality by 2060” proposed by China in 2020, energy conservation and carbon reduction in the transportation industry have become particularly important. As an established industrialized country, Britain started its research on carbon emission reduction in the transportation sector relatively early. This paper compared and analyzed the similarities and differences between the highway carbon emission accounting systems of China and Britain, so as to explore their respective policy backgrounds, accounting methods, and application effects and provide relevant suggestions for highway carbon emission reduction in China. Through literature analysis and case studies, the policy frameworks and implementation mechanisms of carbon emission accounting in the two countries were systematically reviewed. The results indicate that China focuses on government-led regulation and monitoring and ensures data accuracy through laws, regulations, and monitoring systems; meanwhile, Britain adopts a market-oriented flexible mechanism to encourage multi-party participation and voluntary emission reduction. This difference leads to China being rigorous in setting and implementing emission reduction targets but lacking flexibility, whereas Britain demonstrates greater adaptability in practice. Based on this, the following suggestions are proposed: China should comprehensively evaluate its accounting modules, clarify medium-term emission reduction targets, and refine them into annual operable targets; renewable energy policies should be promoted in the energy sector to reduce dependence on high-emission energy; in the transportation sector, the promotion of electric vehicles should be continuously increased, and public transportation networks should be improved. The research results can provide a useful reference for China to optimize the highway carbon emission accounting system, emphasize the importance of international cooperation and knowledge sharing in promoting low-carbon technology innovation, and provide a new perspective for the improvement of future carbon emission reduction policies and practices.