This study integrates macroscopic dynamic triaxial tests with microscopic discrete element simulations to comprehensively examine the dynamic deformation characteristics of marine soft soils under cyclic loading. Unlike previous research that typically focuses solely on experimental or numerical methods, this approach combines both techniques to enable a holistic analysis of soil behavior. The dynamic triaxial tests assessed macroscopic responses, including strain evolution and energy dissipation, under varying dynamic stress ratios, confining pressures, and water contents. Concurrently, discrete element simulations uncovered the microscopic mechanisms driving these behaviors, such as particle rearrangement, porosity variations, and shear zone development. The results show that (1) The strain range of marine soft soils increases significantly with higher dynamic stress ratios, confining pressures, and water contents; (2) Cumulative dynamic strain and particle displacement intensify at water contents of 50% and 55%. However, at a water content of 60%, the samples exhibit significant damage characterized by the formation of shear bands throughout the entire specimen; (3) As water content increases, energy dissipation in marine soft soils accelerates under lower confining pressures but increases more gradually under higher confining pressures. This behavior is attributed to enhanced particle packing and reduced pore space at elevated confining pressures. This integrated methodology not only enhances analytical capabilities but also provides valuable engineering insights into the dynamic response of marine soft soils. The findings offer essential guidance for the design and stabilization of marine soft soil infrastructure in coastal urban areas.

Soft marine soil exhibits unique mechanical properties that can lead to significant deformation and instability in the surrounding rock of urban subway tunnels. This presents a critical challenge for tunnel engineering researchers and designers. This thesis investigates the stability characteristics of surrounding rock in marine soft soil tunnels under cyclic loading conditions. Focusing on the shield tunnel segment between Left Fortress Station and Taiziwan Station of Shenzhen Urban Rail Transit Line 12, a discrete–continuous coupled numerical analysis method is employed to examine the deformation characteristics of the surrounding rock. This analysis takes into account the effects of dynamic loads resulting from train operations on the arch bottom’s surrounding rock. The findings indicate that damage to the surrounding rock occurs gradually, with the marine soft soil layer, particularly at higher water content, being prone to substantial plastic deformation. Additionally, under the influence of train vibration loads, the degree of vertical fluctuation in the internal marine soft soil diminishes with increasing depth from the bottom of the tunnel arch. This coupled numerical analysis approach offers valuable insights and methodologies for assessing the structural safety of tunnel projects throughout their operational periods.

The concrete used in the main structures of subway stations has a high degree of constraint. Consequently, temperature changes and shrinkage during construction frequently lead to significant constraint stress, which can result in structural cracking. Therefore, cement with low hydration heat is commonly used in engineering to reduce the temperature of concrete during its age. Aiming at the problem of hydration and heat release caused by concrete construction, based on the principles of concrete hydration heat release and a numerical analysis method, an optimized semi-adiabatic temperature rise test method has been introduced to investigate concrete temperature rise characteristics with different mineral admixtures. The following conclusions were obtained: The effect of reducing the heat of hydration is related to the content and material properties of different mineral admixtures, but not the type of mineral admixture to be incorporated. The temperature rise performance of four common mineral admixtures is as follows: ① total cooling capacity: limestone powder > slag, fly ash > metakaolin; ② early heat generation rate: metakaolin > slag > fly ash > limestone powder; ③ heat reduction rate in the middle and late periods: metakaolin > limestone powder > fly ash > slag.

The study of energy evolution laws has been widely applied in the geotechnical analysis of soft rocks and coal seams. However, research on marine soft soil has primarily focused on consolidation behavior, shear properties, and microstructural evolution, with limited exploration of systematic methods based on energy evolution laws. This paper addresses this gap by analyzing dynamic triaxial test data to explore the relationship between energy loss rate and the number of cyclic loadings in marine soft soil. Through energy loss calculations and derivations, a mathematical expression for the energy loss rate is established using curve fitting. Additionally, an envelope diagram depicting the energy dissipation rate of marine soft soil under varying perimeter pressures and water contents is presented. This diagram serves as a criterion for assessing the stability of marine soft soil, which is further validated through engineering applications. The findings offer novel approaches and insights for developing theoretical models and rapid strength assessment techniques for marine soft soil in engineering practices.