Marine soft soils, characterized by high water content and low strength, present significant challenges to foundation stability. These soils often lead to settlement and uneven deformation, posing risks to infrastructure safety. This study tackles these challenges and promotes industrial waste utilization by developing a novel curing material for marine soft soils. The material consists of ground granulated blast furnace slag (GGBS), phosphogypsum (PG), and calcium carbide slag (CCS), and is compared to ordinary Portland cement (OPC). A D-optimal design was employed to establish regression equations for unconfined compressive strength (UCS) at 7 and 28 days. The interactions between factors were analyzed to optimize the mix ratio. The effects of different curing ages on the unconfined compressive strength, modulus of elasticity, moisture content, and pH of GPCOR solidified soft soil and cement solidified soil were investigated. The microstructure of the solidified soils was analyzed using SEM, XRD, FTIR, and BET techniques. The results indicated that the optimal GPC ratio was GGBS: PG: CCS = 64.81: 20.00: 15.19. After 28 days, GPCOR solidified soil exhibited superior UCS (4.48 MPa), 1.47 times greater than that of OPC solidified soil, and a deformation modulus 2.04 times higher. Furthermore, GPCOR exhibited a denser microstructure with smaller average pore sizes, improved durability, and better water retention than OPC. These findings underscore the potential of GPC as a sustainable alternative to conventional cement for reinforcing marine soft soils, promoting both soil stabilization and industrial waste resource utilization.

Many engineering activities are conducted on marine soft soil foundations, with various types of soft soil influencing these projects differently. Studying the engineering characteristics and deformation mechanism of marine soft soil is crucial for the design and construction of marine structures. To reveal the dynamic mechanical characteristics of marine soft soil under wave loading, a set of soil samples under different confining pressure conditions were tested via a dynamic triaxial apparatus. Furthermore, a constitutive model was developed to predict the dynamic strength of marine soft soil subjected to wave loading. The experimental results demonstrate that the dynamic stress-strain behaviour of marine soft soil progresses through three stages: compaction, deformation, and failure. The dynamic strain-time history curve of the soil exhibited a cyclic trend characterized by a superposition of monotonic changes, which was attributed to the simultaneous occurrence of plastic deformation and cyclic deformation. The strain rebound gradually disappears with increasing number of loading cycles; the strain accumulation mainly occurs as compressive strain during the postvibration period. Within each stage, the dynamic shear modulus decreases with increasing shear strain, showing consistent curve characteristics across different dynamic stress amplitudes. During long-term cyclic loading, the damping ratio initially decreases and then stabilizes, with a negligible influence from the confining pressure. The Martin-Davidenkov constitutive model effectively characterizes the correlation between the dynamic shear modulus and shear strain, with fitting curves closely matching the measured data.

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.

Prefabricated vertical drains combined with heating is a new approach to improving the mechanical properties of soft clay foundations. Rising temperatures cause the formation of concentric and radially aligned soil regions with distinct heterogeneous characteristics. This results in incomplete contact between adjacent soil layers, with the water in the interstices impeding heat transfer and manifesting as a thermal resistance effect. Based on the theory of thermo-hydro-mechanical coupling, a two-dimensional dual-zone axisymmetric marine soft soil model improved by a prefabricated vertical thermo-drain has been established. A generalized incomplete thermal contact model has been proposed to describe the thermal resistance effect at the interface of concentric soil regions. The effectiveness of the numerical solution presented in this paper is verified by comparison with semi-analytical solutions and model experiments. The thermal consolidation characteristics of concentric regions of soil at various depths under different thermal contact models were discussed by comprehensively analyzing the effects of different parameters under various thermal contact models. The outcomes indicate that the generalized incomplete thermal contact model provides a more accurate description of the radial thermal consolidation characteristics of concentric regions of soil. The influence of the thermal conductivity coefficient on the consolidation characteristics of the concentric regions soil is related to the thermal resistance effect.

For marine soft soil under the periodic wave loading, the pore water content in soil suffering dry-wet cycle for a long time, which affects its microstructure and macroscopic mechanical strength, resulting in insufficient bearing capacity and excessive deformation of soft soil. To reveal the microstructural characteristics and strength attenuation law of marine soft soil under dry-wet cycle condition, electron microscopy scanning and direct shear tests under different times of dry-wet cycles were carried out, and the mathematical equations of pore structure and strength parameters were established based on fractal theory. The research results showed that: (1) The pore structure changed considerably after the first dry-wet cycle, and then changed gently with the increase of dry-wet cycle times, which was reflected by the fractal dimension D value decreases to a constant value gradually. (2) The shear strength of the soil diminishes with an increase in the number of dry-wet cycle times, and the maximum attenuation occurs after the first dry-wet cycle. (3) The relationship between cohesion (c), internal friction angle (phi), and fractal dimension (D) is exponential, with the curve shapes being concave and convex, respectively.

In order to identify the upper and lower boundary cement content for modified marine soft soil (i. e., semi-solidified soils), physical, compaction, and unconfined compressive strength tests of cement-treated soils with a wide range of cement content were carried out to study their variation law of physical-compaction-mechanical properties. The test results show that cement-treated soil can be divided into uselessly treated soil, semi-solidified soil, and solidified soil with the increase of cement content. For uselessly treated soil, the treated soil cannot be compacted even after compaction delay. Cement hydration in semi-solidified soil significantly improved its physical and compaction properties. However, compaction destroyed the skeleton structure of solidified soil, resulting in lower strength than compacted semi-solidified soil. Based on the cement-soil particles-water relationship, soil particles-water transfer mechanism, cement hydration mechanism and the state of soil particles-water before and after treated, the bound method of semi-solidified soils based on cement content and moisture content ratio of untreated soil was established. The test parameters of bound method are simple, easily obtained and have small dispersion, which provides design basis and theoretical support for resource utilization of marine soft soil.

By comparing different settlement forecast methods, eight methods were selected considering the creep of marine soft soils in this case study, including the Hyperbolic Method (HM), Exponential Curve Method (ECM), Pearl Growth Curve Modeling (PGCM), Gompertz Growth Curve Modeling (GGCM), Grey (1, 1) Model (GM), Grey Verhulst Model (GVM), Back Propagation of Artificial Neural Network (BPANN) with Levenberg-Marquardt Algorithm (BPLM), and BPANN with Gradient Descent of Momentum and Adaptive Learning Rate (BPGD). Taking Lingni Seawall soil ground improved with prefabricated vertical drain-assisted staged riprap filling as an example, forecasts of the short-term, medium-term, long-term, and final settlements at different locations of the soft ground were performed with the eight selected methods. The forecasting values were compared with each other and with the monitored data. When relative errors were between 0 and -1%, both the forecasting accuracy and engineering safety were appropriate and reliable. It was concluded that the appropriate forecast methods were different not only due to the time periods during the settlement process, but also the locations of soft ground. Among these methods, only BPGD was appropriate for all the time periods and locations, such as at the edge of the berm, and at the center of the berm and embankment.

Understanding the mechanical changes of marine soft soil under temperature is crucial for the construction and long-term operation of submarine pipelines. A series of basic physical and mechanical properties tests was carried out on the marine soft soil in Shanwei, Guangdong province. X-ray diffraction, X-ray fluorescence spectrometry, and scanning electron microscopy were employed to achieve the marine soft soil's mineral composition, element composition and microstructure. The consolidated undrained laboratory tests under isotropic consolidation and biaxial consolidation conditions were carried out using a temperature-controlled triaxial apparatus. The test results revealed significant findings. Firstly, when the axial strain is small, the undrained shear characteristics of saturated marine soft soil are influenced by the ambient temperature and the consolidation stress ratio. Specifically, a higher ambient temperature or a smaller consolidation stress ratio results in a greater secant modulus. The secant modulus exhibits an inverse relationship with the consolidation stress ratio and demonstrates a power function relationship with the ambient temperature. As the axial strain increases, the peak strength of the soil is affected by both ambient temperature and consolidation stress ratio, while the peak pore pressure is less affected by ambient temperature. Furthermore, the initial dry density of the sample was found to impact the undrained shear characteristics of the isotropic consolidated soil (K-c=1.00). A greater initial dry density resulted in a smaller peak pore pressure, a greater peak strength, and a more significant decrease in peak strength with rising temperature. Additionally, the consolidation stress ratio was observed to affect the peak strength and effective stress path of saturated marine soft soil under different ambient temperatures. Specifically, when K-c=1.00 or 0.67, an increase in the ambient temperature softened the saturated marine soft soil; whereas when K-c=0.50 or 0.40, the rise in ambient temperature hardened the soil.