Top-down crack is a typical disease of composite pavement, its occurrence and expansion adversely affect the life of continuous reinforced composite pavement (CRCP). In order to explore the formation mechanism and propagation rule of top-down cracks in CRCP, based on the theory of linear elastic fracture mechanics, a 3D finite element model of pre-nstalled cracks on the top of AC layer is established. According to the main stress parameters that affect the formation of top-down cracks, the most unfavorable load position and the most unfavorable point corresponding to the stress parameters are determined. On this basis, the stress intensity factor of the crack tip under multi-factor coupling is calculated by contour integration. The variance analysis of the multifactor crack tip stress intensity factor is carried out through the orthogonal test method, and the main factors affecting the formation and development of top-down cracks are determined. At the same time, the single-factor sensitivity analysis on these influencing factors is carried out, thus the:formation and expansion rule of top-down cracks in continuous reinforced composite pavement is revealed. The result shows that (1) for the top-down cracks in continuous reinforced composite pavement, the most unfavorable load position is the loading position on the lateral crack side of the CRC layer, the unfavorable point of the longitudinal top-down crack is the loading position on the lateral crack side of the CRC layer at the inner edge of the proximal double wheels, while the unfavorable point on the transverse top-down crack is the loading line on the lateral crack side of the CRC layer; (2) the transverse top-down cracks is a comprehensive cracking mode with K2 type (sliding type) as the dominant type and K1 type (opening type) as the supplement, and AC layer thickness and crack load transfer capacity are the main influencing factors; (3) the cracking mode of longitudinal top- down cracks is dominated by K1 type, AC layer thickness, crack load transfer capacity, crack spacing and instantaneous temperature difference are the main influencing factors for its formation and propagation.

The mechanical response of asphalt layer of asphalt pavement is an essential parameter for pavement design. An accurate characterization of the mechanical response of the in-situ asphalt layer is of great significance to improve the reliability of pavement design. The strain data of the service flexible asphalt pavement were collected by field vehicular loading tests. The characteristics of strain waveforms and the strain values under various loading conditions including different axle loads, vehicular speeds and temperatures were investigated by the statistical approach. The results show that the strain waveforms at the bottom of the asphalt layer are significantly influenced by the loading position of the tire. The axle load, temperature and vehicular speed all have significant effects on the strains at the bottom of asphalt layer, but do not significantly change the strain waveform shapes. The increase in the axle load/temperature or the decrease in the vehicular speed all leads to an overall increase in the peak-to-peak strains values of transverse and longitudinal strain pulses. Compared with the waveforms at the bottom of the asphalt layer, the strain response waveforms at the bottom of the ATB layer show significantly viscous behaviors. The interaction of two factors, axle load and temperature, on the mechanical response of the pavement is obvious. The effect of axle load on the extreme values of horizontal-vertical strains at different temperatures was shown to be significantly different. The interaction between vehicle speed, axle load and temperature was not significant. In addition, the model for describing the relationships among strains, vehicular speed, axle load and temperature are established, to predict the strain values under various loading conditions. The research findings are helpful to evaluate the real stress state of flexible pavement asphalt layer, and provide reference data for the design of flexible pavement in China.

In order to study the influence of air void on the performance of paved rubber asphalt stress absorption layer, two typical air voids, 2.5% and 4.0% are selected. High temperature rutting test, water immersion Marshall test and freeze-thaw splitting were used, to evaluate high temperature performance and water stability of asphalt mixture respectively. Trabecular bending test and SCB crack propagation test were used to evaluate the stress absorption performance. After reducing the air air void from 4.0% to 2.5%, tests show that:the dynamic stability of mixtures decreases, but the decrease range is less than 10%; The residual stability and freeze-thaw splitting strength ratio were improved; the increase range of flexural tensile strain and strain energy density at -10℃ is 19.0%-46.6%, and the increase range is 2.1%-6.7% at 15℃; The growth range of fracture energy of three gradation mixtures is 11.0%-17.8%, and the growth range of flexibility index is 4.4%-40.0%. The results show that, the evaluation results of different test methods are not consistent. The flexural tensile strain and strain energy density of trabecular bending test, fracture energy and flexibility index of SCB crack propagation test should be used to evaluate the stress absorption performance of asphalt mixture comprehensively. The small air air void may reduce the high-temperature stability, but improve the water stability, low-temperature tensile performance and stress absorption performance. Therefore, the design of paved stress absorption layer with rubber asphalt has good application potential. when the designed air air void controlled at 2.0%-3.0%, it has better performance for the stress absorption layer.

The interlayer bonding performance between the base and surface of pavement has a great influence on the integrity and durability of the whole pavement structure. In order to enhance the interlayer bonding effect of this heterogeneous structure, a reinforced interlayer bonding material with a combination of permeable layer and sealing layer was designed. Self-made shearing device and pull-out device were used to carry out the interlayer shear strength and tensile strength test of the composite specimen under different interlayer oil consumption and different temperature conditions, and the influences of various factors on the interlayer strength were analyzed. Finally, the optimum combination of the reinforced interlayer bonding materials between base and surface of asphalt pavement based on the regional ambient temperature characteristics was explored. The results show that:(1) at low and normal temperatures, the interlayer strength between the base and the surface layer increases with the increase in the tack coat rate, while the interlayer strength at high temperatures first increases and then decreases with the increase in the tack coat rate. When the prime coat rate is 0.6 L/m², there is a characteristic cut-off point for the interlayer strength; (2) compared with a single permeable layer material, the use of combination material of "permeable layer + sealing layer" is beneficial to the improvement of the bonding performance between the base layer and the surface layer; (3) the combination materials of prime coat and tack coat should be selected reasonably according to the ambient temperature characteristics of the project area. For example, in areas without high temperature in summer, choosing the PC-2 emulsified asphalt tack coat with an application rate of 0.6 L/m² + 1.8 kg/m² of asphalt mixed with fiber rubber modified asphalt gravel seals to enhance interlayer bonding performance; In areas with hot and high temperature in summer, it is recommended to adjust the amount of rubber-modified asphalt in the aforementioned reinforced interlayer bonding measure to 0.9 kg/m². The research results provide experimental support for the optimal design of reinforced interlayer bonding materials between base and surface of asphalt pavement based on regional ambient temperature.

In the analysis of slope engineering stability, due to the limitation of the original sample information of the obtained parameters and the limitation of the conventional reliability calculation method based on probabilistic reliability, the non-probabilistic comprehensive indicator of the slope convex set model is introduced, and a solution method by non-probabilistic reliability of slope under the condition of fuzzy characterstics of sample information is formed. First, based on the limited sample information, a rough interval is delineated for the parameters, and the slope hyper-ellipsoid convex set model is constructed in this interval. Then, Latin hypercube sampling is used for sampling within the interval. Since the limit state equation of slope engineering is generally highly nonlinear and implicit, the Kriging proxy model is used to fit its function. Finally, according to the compatibility of non-probabilistic reliability and probabilistic reliability, non-probabilistic index η is introduced to comprehensively evaluate the stability of the slope. When η>1, the evaluation criterion is the shortest distance from the origin of the coordinates to the limit state surface in the standard vector space; When 0<η<1, probability reliability is used as the evaluation index. At this time, the slope reliability indicator can be obtained by using the MonteCarlo method relying on the MATLAB programming language. The calculation examples show that the method is feasible, efficient in calculation and accurate in results. It has made beneficial extensions and supplements for the probabilistic reliability method, and also provided new possibilities for solving slope reliability. Finally, using this method when the sample information of an actual slope project is incomplete, the results show that the failure risk of the slope is very low, which is consistent with the analysis conclusion of the simplified Bishop method, and conforms to the target reliability index standard of highway subgrade in "Unified Standard for Reliability Design of Highway Engineering Structures" (JTG 2120-2020).

To investigate the bearing capacity and force mechanism of steel and concrete joint section in hybrid tower,on the basis of analyzing the stress of front bearing plate, rear bearing plate and plug-in joint section, finite element models concerning with back bearing plate based on a specified pylon joint section of Yuejiang bridge in Zhaoqing City were conducted to study mechanical behaviors of the joint section.According to the calculation results of the model, the shear force of shear studs in the back bearing plate joint section increases gradually from top to bottom. The farther away from the bearing plate, the greater the shear force borne by the shear studs, and the peak value was reached at the bottom of the joint section. The axial force transmitted by the bearing plate accounts for 68% of the total axial force, and the other axial forces are transmitted through shear nails, which has a good force transmission effect. An experimental specimen with back bearing plate, with a reduced scale at 1:4 of the single limb of a tower was conducted, and structural deformation and stress distribution were measured here. The results show that the existence of a bearing plate and its position in connection will lead to a totally different shear force distribution of the shear connectors. The joint section with back bearing plate has an excellent bearing capacity and can transfer force fluently from steel tower to concrete tower. The tested specimen basically kept a linear behavior in the whole loading process. The steel plates in the connection hold a gradually decreasing stress distribution downward, while the distribution of concrete is opposite. The maximum relative deformation between steel and concrete was about 0.1mm in this test. The hybrid connection with back bearing plate has a good application in engineering hopefully. In view of the test results that the stress level of the concrete under the bearing plate was slightly higher, the C60 concrete with steel fiber in the steel-concrete joint section was used to improve the compressive capacity of the structure. At the same time, in order to improve the stress concentration phenomenon of concrete at the corner of bearing plate and wall plate in steel-concrete joint section, trial mixing test and grouting were used to ensure the compactness between steel and concrete, and good use effect was achieved.

The steel-UHPC composite deck is an advanced measure to improve the fatigue resistance of orthotropic steel decks. However, there are penetrating cracks on the steel panel in some bridges. In this case, the penetrating cracks would cause reflective cracks in the UHPC if the UHPC was in direct contact with the penetrating cracks. To ensure the good mechanical performance of the UHPC layer and avoid reflective cracks, this study proposes a reinforcement scheme of steel-UHPC composite deck with steel strips. The good performance of the reinforcement scheme was verified by finite element analysis and field tests. Firstly, the basic information of a long-span cable-stayed bridge and the reinforcement scheme was introduced. Secondly, the global and local mechanical performance of the bridge after reinforcement are analyzed by finite element analysis. Finally, the performance of the steel-UHPC composite deck in improving the fatigue resistance of the orthotropic steel decks was verified by field test. The results show that:(1) Overall stress state of the bridge is basically unchanged and has a large safety reserve after the downstream deck of the bridge was reinforced. (2) Tensile stress of the UHPC layer is greatly influenced by penetrating cracks. After adding steel strips, the crack risk of the UHPC layer is greatly reduced. (3) After reinforcement, the effective stress ranges of fatigue-prone details are reduced, and the stress ranges of fatigue-prone details are lower than the constant-amplitude fatigue limit. The reinforcement scheme effectively improves the fatigue resistance and reduces the crack risk of fatigue-prone details. In a word, the reinforcement scheme of the steel-UHPC composite deck with steel strips is an advanced measure to reduce the crack risk of the UHPC layer and improve the fatigue resistance of orthotropic steel decks.

Root anchorage formed by the rigid cap connecting the cluster root foundation,is a new type of anchor foundation of suspension bridge, which bears the load together through the interaction of cap, cluster root foundation and soil. As for the practical engineering of Qiupu River Bridge Root Anchorage Foundation, the numerical simulation method is used to analyze the overall displacement of Root Anchorage in two practical engineering conditions, the end of integral construction of anchorage (Case 1) and the operation stage of suspension bridge (Case 2).Besides, the stress characteristics of the group of Pile and Root Foundation are analyzed while the displacement characteristics of root anchorage are compared with the monitoring data. The results show that the horizontal and vertical displacement of anchorage under the load of main cable meets the requirements of similar suspension bridge anchorage displacement and the relevant regulations in domestic and abroad. In Case 1, under the eccentric load of the anchor body, the anchorage presents an overall backward state, and the vertical load is mainly borne by the pile caps and the cluster root foundation. In Case 2, under the action of the main cable force, the anchorage presents an overall forward state, and the overall horizontal displacement of the anchorage increases due to cable force. The vertical load is mainly borne by the pile platform (accounting for 33.37%) and the cluster root foundation (accounting for 66.63%), while the horizontal load is mainly borne by the cluster root foundation (accounting for 91.92%).

To study the bearing capacity of the silt soil bridge pile foundation in the river estuary, the pile foundation of the Nangang River Bridge in Hainan Province was choosen as the research object in this paper. Through ABAQUS finite element software established the bridge pile-soil contact model, and analyzed the influence of foundation axial force, side friction resistance and ultimate bearing capacity under the different pile lengths and pile diameters. At the same time, the influence in the silt soil layer on the bearing capacity of bridge in the silt soil layer was analyzed. The calculation results showed that when the pile diameter was fixed and the pile length increased from 30 m to 60 m, the bearing capacity of the pile foundation increased by 10 200 kN, while when the pile length increased to 60 m, the bearing capacity only increased by 3 400 kN. When the pile diameter increased from 0.6 m to 1.5 m, the bearing capacity of the pile foundation increased by 10 200 kN, but when the pile diameter exceeds 1.5 m, the bearing capacity only increased by 3 400 kN. When the ratio of pile diameter to pile length was 1/40, the pile diameter and pile length can give full play to the maximum bearing capacity. With the depth of the silt soil increasing, the bearing capacity of the pile foundation gradually decreased. The reason was that the side friction of silt is very small compared with other soils, which leads to the smaller bearing capacity. The bearing capacity of pile foundation can be improved by enlarging the pile diameter, increasing the pile length, increasing the cohesive force of the soil around the pile and changing the position of the load box. This study provides a reference for the design and construction of bridge pile foundations in silt-filled soil in the river estuary.

In the context of carbon peaking and carbon neutrality policy, the promotion of highway transportation clean energy facility construction is in urgent need. This paper suggests that a new business model can be applied to solve the financing problem in this field which is referred to as "DTBB". The paper first gives the definition of the DTBB business. In DTBB business, commercial banks provide favorable financing for highway transportation clean energy facility construction projects. In exchange, future cash flow generated by the projects will be deposited into commercial banks. Using mathematical model, this paper then gives the theoretical value of DTBB in providing funds for the construction of clean energy facilities in highway transportation. Theoretical model suggests that the ability of providing funds is proportional to the cash flow generated by highway transportation clean energy facility construction projects for DTBB. And the risk of DTBB will gradually decrease with the growing number of similar businesses carried out by commercial banks. This dissertation follows a case-study design, with in-depth research of wireless charging highway project and hydrogen refueling station in the future. The results show that (1) the theoretical value of DTBB is about 15.7% of the total initial investment of the hydrogen refueling station project when discounting rate of the project is 0.1 and the lifetime of the project is 15 years; (2) the theoretical value of DTBB is about 1.4% of the total initial investment of the wireless charging highway project when discounting rate of the project is 0.1 and the lifetime of the project is 15 years.