Search Results (11)

Marine soft clay is widely distributed in coastal areas. Aiming at the characteristics of low strength and stress level of marine soft clay, the effects of normal stress, water content, and resting time on the pile–soil interface shear characteristics of marine soft clay–jacked piles were investigated using improved direct shear test equipment. On this basis, a practical interface shear strength prediction model considering the above factors is proposed. The test results show that the relationship between shear stress and shear displacement at the pile–soil interface can be divided into three stages—initial, transitional, and stable—and the relationship is in accordance with the hyperbolic model. Under the same water content and resting time, the interface peak shear stress increases linearly with the increase in normal stress. The interface peak shear displacement decreased with the increase in normal stress. Under different water content conditions, the peak shear stress decreases with increasing water content, while the corresponding peak shear displacement increases. The internal friction angle and adhesion at the pile–soil interface decreased rapidly and exponentially with increasing water content of the soil around the pile. The interfacial adhesion varies in the range of 1.07–13.76 kPa and the internal friction angle in the range of 1.8–6.1°. The change in water content when the water content of marine soft clay is less than the liquid limit has a great influence on the interface shear strength. The peak shear stress increases with increasing resting time, while the corresponding peak shear displacement decreases for different resting times. The Internal friction angle and adhesion at the pile–soil interface increases exponentially with the resting time. Interfacial adhesion changes in the range of 1.8–4.9 kP, and the internal friction angle is 2.8–4.7°. The strength of the pile–soil interface grows with the advancement of the resting time, and the bearing performance of the jacked pile is improved, with the most significant effect in 14 days. Based on multiple linear regression analyses, the effects of normal stress and water content on interfacial shear strength are comparable and the effect of normal stress on the shear strength is more significant compared with the resting time. The test results provide valuable reference for the design and construction of jacked piles in marine soft ground. Full article

The main purpose of this research is to develop a solid waste-based cementitious material (SWC) instead of cement for solidifying a large amount of marine soft soil with high water content and low bearing capacity in coastal areas. This aims to solve the problems encountered in the practical application of cement soil, such as slow strength growth and poor durability. The SWC includes ground granulated blast furnace slag (GGBS), dust ash (DA), and activated cinder powder (ACP), with admixtures of naphthalene sulfonate formaldehyde condensate (NS) and compound salt early strength agent (SA). Both the 7 d and 28 d compressive strength values of the SWC formulations G4 and G7 are about twice as strong as those of cement soil (GC), even when mixed with seawater. Immersion tests revealed that stabilized soil had superior resistance to seawater corrosion compared to cement soil. X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis explained that the main hydration products in cement soil are C-S-H and CH, while in stabilized soil, SWC generates a large amount of C-A-S-H with gelling properties and AFt with filling properties. These hydration products have better effects on strength and seawater erosion resistance. Full article

This study examines the optimization of ground source heat pump (GSHP) systems and energy piles for sustainable urban development, focusing on Southeast Asia. GSHPs, which utilize geothermal energy for indoor HVAC needs, offer a sustainable alternative to traditional systems by utilizing consistent subsurface temperatures for heating and cooling. The study highlights the importance of understanding thermal movement within the soil, especially in soft marine clays prevalent in Southeast Asia, to improve GSHP system efficiency. Using a one-dimensional finite difference model, the study examines the effects of soil thermal conductivity and density on system performance. The results show that GSHP systems, especially when integrated with energy piles, significantly reduce electricity consumption and greenhouse gas emissions, underscoring their potential to mitigate the urban heat island effect in densely populated areas. Despite challenges posed by the region’s hot and humid climate, which could affect long-term effectiveness, the study highlights the need for further study, including field experiments and advanced modeling techniques, to optimize GSHP configurations and fully exploit geothermal energy in urban environments. The study’s insights into soil thermal dynamics and system design optimization contribute to advancing sustainable urban infrastructure development. Full article

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. Full article

Cement-stabilization of weak and soft soils is an efficient way for ground improvement. Traditional Portland cement remains the most popular cementitious material in practice, and thus, a proper dosage design of cement-stabilized soil is of practical interest to meet the sustainable engineering requirements and to remedy environmental concerns. Based on the unconfined compression test of cement-stabilized Qiantang River silty clay, the effects of cement content, mixing moisture content, mixing-water-to-cement ratio, and curing time on the unconfined compressive strength were investigated. The results show that the mixing-water-to-cement ratio can comprehensively characterize the effects of cement content and water content on the unconfined compressive strength of the cement-stabilized clay. A prediction method for the unconfined compressive strength of cement-stabilized Qiantang River silty clay has been proposed with considerations for mixing-water-to-cement ratio and curing time. By comparing the experimental data of the present study with the existing literature data, it is found that there is a unified relationship between the unconfined compressive strength and the mixing-water-to-cement ratio of cement-stabilized Qiantang River silty clay, kaolin, Singapore marine clay, and Bangkok clay under the same curing time. The prediction method recommended by the standard may overestimate the unconfined compressive strength of cement-stabilized Qiantang River silty clay cured for 90 days. Full article

Large quantities of abandoned marine soft soil are generated from coastal engineering which cannot be directly utilized for construction without modification. The utilization of traditional binders to modify abandoned marine soft soil yields materials with favorable mechanical properties and cost efficiency. However, the production of traditional binders like cement leads to environmental pollution. This study uses a CGF all-solid-waste binder (abbreviated as CGF) composed of industrial solid waste materials such as calcium carbide residue (CCR), ground granulated blast furnace slag (GGBS), and fly ash (FA), developed by our research team, for the modification of abandoned marine soft soil (referred to as modified soil). It is noteworthy that the marine soft soil utilized in this study was obtained from the coastal area of Jiaozhou Bay, Qingdao, China. Physical property tests, compaction tests, and unconfined compressive strength (UCS) tests were conducted on the modified soil. The investigation analyzed the effects of binder content, compaction delay time, and curing time on the physical, compaction, and mechanical properties of CGF-modified soil and cement-modified soil. Additionally, microscopic experimental results were integrated to elucidate the mechanical improvement mechanisms of CGF on abandoned marine soft soil. The results show that after modification with binders, the water content of abandoned marine soft soil significantly decreases due to both physical mixing and chemical reactions. With an increase in compaction delay time, the impact of chemical reactions on reducing water content gradually surpasses that of physical mixing, and the plasticity of the modified soil notably modifies. The addition of binders results in an increase in the optimum moisture content and a decrease in the maximum dry density of CGF-modified soil, while the optimum moisture content decreases and the maximum dry density increases for cement-modified soil. Moreover, with an increase in binder content, the compaction curve of CGF-modified soil gradually shifts downward and to the right, while for cement-modified soil, it shifts upward and to the left. Additionally, the maximum dry density of both CGF-modified and cement-modified soils shows a declining trend with the increase in compaction delay time, while the optimum moisture content of CGF-modified soil increases and that of cement-modified soil exhibits a slight decrease. The strength of compacted modified soil is determined by the initial moisture ratio, binder content, compaction delay time, and curing time. The process of CGF modification of marine soft soil in Jiaozhou Bay can be delineated into stages of modified soil formation, formation of compacted modified soil, and curing of compacted modified soil. The modification mechanisms primarily involve the alkali excitation reaction of CGF itself, pozzolanic reaction, ion-exchange reaction, and carbonization reaction. Through quantitative calculations, the carbon footprint and unit strength cost of CGF are both significantly lower than those of cement. Full article

In the southeastern coastal regions of China, thick layers of marine soft soil are widely distributed, exhibiting characteristics such as high compressibility, high porosity, low strength, high sensitivity, and easy thixotropy, and these viscoelastic behaviors of foundation soil have significant implications for elastic compression bending bar, as evidenced by issues such as post-construction settlement of roadbeds and long-term operation deviation of bridge pile foundations. In this study, a mechanical model of an elastic bar embedded in an elastic and viscoelastic medium, fixed at the base and free at the top, is established based on the Winkler foundation assumption. The deflection function of a bar subjected to both axial force and locally distributed horizontal load is derived using the Rayleigh-Ritz method. Utilizing the elastic-viscoelastic correspondence principle, the viscoelastic medium surrounding the bar is modeled as an elastic medium in which the ground reaction coefficient varies within phase space formulation. This study provides a robust theoretical foundation for soft soil foundation engineering projects and fills a significant gap in the literature by offering a comprehensive framework for understanding displacement in elastic bars within viscoelastic media. Drawing upon the derivation of the deformation function for elastic rods within a viscoelastic medium, the findings of this research hold significant applicability across a range of domains. These include, but are not limited to, the expansion of roadways in regions characterized by coastal soft soil, as well as the monitoring of deformation and lifespan in bridge pile foundations. Full article

Prefabricated vertical drains (PVDs) with staged riprap preloading have been widely used in soft soil ground improvement and embankment construction. However, ground treatment effectiveness evaluation is still a difficult problem due to multiple factors. Considering this, in situ monitoring and numerical simulation were conducted to study the deformation and strength characteristics of marine soft soil ground treated by PVD-assisted staged riprap under the Lingni Seawall construction in China. Monitoring and analysis of results showed that use of PVD-assisted staged riprap resulted in a good improvement effect. In particular, in the PVD-treated zone within 10 m in depth, corresponding to a half-length of the PVD, the average radial degree of consolidation reached up to 75–100%, and the soil strength increased significantly by 200–700%. Moreover, numerical simulation showed that the linear 1-dimensional drain element of PVD closely met the engineering accuracy requirements with good consistency with the monitoring data. Compared with a totally solid element model, the numbers of elements and nodes were reduced and the calculating efficiency and model accuracy were increased by using a PVD linear element, which provides a basis for building large complex finite element models. Full article

Foundations supporting infrastructure built on soft and compressible marine soil are unlikely to sustain due to possibility of undrained shear failure or excessive settlement of the supporting soil. This necessitates the importance of implementing an adequate ground improvement strategy. Among different techniques, soft soil reinforcing by the installation of stone columns is one of the most successful methods in terms of long-term stability of foundations. To investigate the load-settlement characteristics of such reinforced soil, a group of closely spaced stone columns was constructed at a location along the eastern coast of Australia. The site geology revealed thick layers of soft, compressible marine clay deposit. These stone columns were loaded by constructing earthen embankment and the resulting load-settlement characteristics were measured by an array of sensors. A two-dimensional plane strain analysis was performed using finite element modeling simulations. Comparison of numerical results with the field data demonstrated accuracy of the numerical model. Additional studies were carried out to investigate the efficiency of the model. This paper integrates the new findings from the full-scale field study and advanced numerical simulations while drawing pertinent conclusions. Full article

Lightweight sand–EPS soil (LSES) is regarded as a kind of sustainable geomaterial for providing a way to reutilize fast-growing waste expanded polystyrene (EPS) packages. It is usually applied in marine geotechnical engineering to solve the excessive settling of soft ground or bumps at bridge heads due to its merits such as low density, high strength, and adjustability. Aiming to investigate the dynamic shear strength of LSES made from marine sand, a series of laboratory dynamic triaxial experiments was conducted on LSES with different proportions and control sand (CS). The influences of cement content, EPS bead content, and confining pressure on dynamic shear strength were analyzed, as were comparisons with the material sand. It was found that the dynamic strength of LSES increased with the increase in cement content and confining pressure. The bonding function of cement hydration products contributed to the dynamic strength of LSES; however, the work required a certain content of cement. The dynamic strength of LSES decreased with the increase in EPS bead content due to the low particle strength and smooth surface of EPS beads. The cyclic number of failure (N_f) of both LSES and CS decreased linearly with the increase in dynamic shear stress in semilogarithmic coordinates. Both the slopes and the intercepts increased with the increase in cement content and confining pressure. However, they decreased with the increase in EPS bead content. Full article

The use of artificial freezing can change the mechanical properties of marine clay. In the construction of cross passages in metro tunnels in which the artificial ground freezing (AGF) method is applied, freeze–thaw circulation and cyclic loading could weaken the engineering properties of the clay, thus resulting in differential settlement. In this paper, the authors studied the dynamic properties of frozen–thawed soils under cyclic loading, with the help of dynamic triaxial testing. According to the dynamic triaxial test results and the images from scanning electron microscopy (SEM), the authors explained the weakening effect of both the freeze–thaw cycle and dynamic loading on soft soil. After freezing, the number of large pores increased. In addition, after cyclic loading, the pore structure of the soil showed a tendency towards compaction, which led to the large pores breaking into small ones. Subsequently, the potential reasons for the change of macroscopic dynamic characteristics were explained from a micro-scale point of view. Full article