Mu He

Traditional pipe roof support design methods generally assume horizontal ground conditions and treat the pipe roof as a monolithic beam, thereby neglecting the differential stress distribution among individual steel pipes under unsymmetrical loading. To address this gap, this paper presents two main contributions: a low-carbon cement-based grouting material suitable for pipe roof reinforcement, and a new mechanical model that simultaneously accounts for biased pressure conditions and the inter-pipe micro-arch effect. First, the working performance of limestone calcined clay cement (LC³) grout was systematically tested at a water–cement ratio of 1:1, and the optimal mix ratio was determined. Grout–soil reinforcement tests on weathered granite show that, for grout-to-soil volume ratios between 0.2 and 0.8, the compressive strength of the reinforced material exceeds 10 MPa and the elastic modulus exceeds 600 MPa. Second, a mechanical model for the pipe roof was established based on the Pasternak two-parameter foundation theory, incorporating both biased pressure conditions and the inter-pipe micro-arch effect. The model predictions were compared with existing field monitoring data in the literature, showing consistent trends and good agreement in peak deflection values. Parametric analysis reveals that under horizontal ground conditions, the pipe roof response is symmetric, with the vault as the most critical area. As the bias angle increases, the maximum response shifts toward the higher side of the terrain, and the stress difference between pipes on both sides increases significantly. Theoretical analysis of the low-carbon grouting material shows that pipe roof deflection is moderately reduced compared to traditional grouting materials, but at the cost of increasing bending moment and shear force within the steel pipes. The proposed low-carbon grouting material and the validated mechanical model provide theoretical support for the design optimization of pipe roof support in shallow unsymmetrical loading tunnels.

Environmental conditions at shallow-buried tunnel portals often cause stratum moisture content variations, where pipe roof support is commonly used for pre-reinforcement. While studies show water content significantly affects soil strength, its impact on pipe roof behavior remains largely unexplored. This study develops a theoretical model for pipe roof longitudinal internal forces and deformations using Pasternak two-parameter foundation theory, incorporating subgrade reaction and shear moduli expressions that vary with saturation. Validation against field measurements shows good agreement with peak values, confirming model reliability. Parametric analysis reveals that increasing water content markedly amplifies pipe roof deformation: in unsaturated ground, deflection and rotation increase significantly with water content, while peak bending moment and shear force near the tunnel face slightly decrease. Under saturated conditions, the increases in deflection and rotation become substantially greater. The model quantitatively evaluates water content’s influence on pipe roof mechanical behavior, providing a theoretical basis for optimizing support systems in water-rich strata.

Given the dominant failure mode of steel bridge deck pavement layers, which is flexural–tensile damage, the dynamic modulus parameters conventionally determined through uniaxial compression testing are found to be inadequate for the design or performance analysis of these layers. In order to simulate the actual stress of a pavement structure under wheel load, the four-point bending fatigue test method and uniaxial compression test method are used to measure the dynamic modulus of an epoxy asphalt mixture, and the differences between the two test methods are analyzed. Furthermore, the four-point bending fatigue test is employed to investigate the dynamic modulus and phase angle properties across varying temperatures and frequencies, facilitating the creation of master curves for these properties and utilizing Sigmoidal models to correlate dynamic modulus data at diverse temperature conditions. This study delves into the influence of epoxy resin content, mixture composition, and aging on the dynamic modulus. The experimental results show that the dynamic modulus measured by uniaxial compression exceeds that obtained from bending fatigue tests, with the difference initially increasing and then decreasing as temperature rises. This discrepancy significantly impacts the mechanical calculations of pavement layers, underscoring the importance of selecting the appropriate testing method. Temperature, frequency, and epoxy resin content have pronounced effects on the viscoelastic properties of the mixtures. Specifically, as temperature increases, the dynamic modulus undergoes a decrease, whereas the phase angle exhibits an increase. Additionally, the dynamic modulus augments with an increase in loading frequency, while the phase angle exhibits varied trends with frequency shifts across different temperatures. Both the WLF and Sigmoidal models are effective in constructing master curve representations for the dynamic flexural modulus and phase angle. The incorporation of epoxy resin transforms asphalt from a primarily viscous to a more elastic material, significantly enhancing the viscoelastic properties of the mixture. Notably, mixtures with 50% and 60% epoxy resin content exhibit comparable dynamic moduli and phase angles, while displaying notably superior performance compared to those with 40% epoxy resin content. For large-scale steel bridge deck pavement, 50% epoxy resin content is recommended. Moreover, epoxy asphalt mixtures demonstrate robust aging resistance, with minimal variations in the dynamic modulus and phase angle before and after aging. The research results can enable the acquisition of dynamic modulus and phase angle data in the whole temperature domain and the whole frequency domain, and provide reliable mixed performance parameters for the study of different application environmental performance of steel bridge deck pavement.

To realize the application of epoxy asphalt concrete on roads and solve the problem of the high cost of epoxy asphalt concrete and the causes of bulging in the construction process, a low-content epoxy asphalt mixture was experimentally studied. Rheological and microscopic tests were carried out to study its performance. At the same time, 17 kinds of low-content asphalt mixture Marshall test pieces and rut plate test pieces with different oil stone ratios were made. Their road performances were tested, and a watertight breathable epoxy asphalt mixture was studied to solve the bulging problem. The research shows that, for ordinary roads, a content of epoxy resin of 10–15% can meet both the high-temperature and the low-temperature requirements. For sections with special rutting resistance requirements, a controlled epoxy resin content between 15 and 30% is recommended. When the content of epoxy resin is greater than 30%, epoxy asphalt initially forms a crosslinked spatial network. An epoxy asphalt with a complex structure from asphaltene to epoxy, with ultra-high performance, can be used for small steel bridge pavements. A BBR test showed that, with an increase in epoxy resin content, the low-temperature performance of asphalt gradually weakens. When the content was 20%, epoxy asphalt’s low-temperature performance was weaker than that of SBS-modified asphalt. Under extremely low-temperature conditions, the performance of epoxy asphalt could not meet the specifications. When the voids of low equivalent epoxy asphalt mixture are controlled at 4.1–4.5%, it is watertight and breathable; this can solve the problem of bulging and greatly reduce the cost of projects.