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The vacuum preloading method is widely applied in dredged sludge reinforcement, however, prefabricated vertical drain (PVD) clogging affects the effectiveness of ground reinforcement and leads to significant uneven settlement. To alleviate these deficiencies, this paper proposed an alternating prefabricated radiant drain vacuum preloading (APRD-VP) method considering the advantages of the alternating vacuum preloading (A-VP) method (delaying clogging) and prefabricated radiant drain vacuum preloading (PRD-VP) method (combining horizontal drainage and alleviating uneven settlement). The laboratory model experiments were conducted to explore the treatment effect of APRD-VP method, and the particle image velocimetry technology was employed to observe clogging range surrounding PVD. The experimental results demonstrate that APRD-VP method displayed a better reinforcement effect than the traditional method by analysis of water discharge, settlement, pore water pressure, water content, and vane shear strength. By investigating the clogging formation development for APRD-VP method, the maximum clogging range on both sides of the drainage board has been reduced by 3.15% and 14.02%. In addition, the empirical relationship between clogging range and settlement was established to can better judge and predict clogging range, which can lay the foundation for establishing the theory of computation of soft soil ground design suitable for APRD-VP method. • An alternating prefabricated radiant drain vacuum preloading method was proposed. • The effectiveness of the alternating prefabricated radiant drain vacuum preloading method was demonstrated. • The movement of soil particles around the drainage board was observed and the clogging range was determined. [ABSTRACT FROM AUTHOR]

Abstract This paper reviews the recent environmental deterioration in Ariake Sea, Japan, including an increased frequency of red tides and hypoxic waters and decreased fishery production. Analysis of the mechanisms of environmental deterioration suggests that it is possibly induced by the decrease in tidal flat area, decreases in the tide and tidal current and changes in the sediment environment. The Isahaya Bay reclamation project resulted in the loss of 1550 ha of tidal flats, and is one of the possible reasons for the decreases in the tide and tidal current. Therefore, some fishermen and researchers believe that opening the reclamation project dike's floodgates is an effective environmental restoration countermeasure for Ariake Sea. However, the central government decided not to open the floodgates at present due to strong opposition from local farmers, and some researchers believe that the influences of the Isahaya Bay reclamation project on the environmental changes outside of Isahaya Bay are minor. Several lawsuits regarding these relationships and the opening of the dike's floodgates are currently under dispute. To revive Ariake Sea as a sustainable ecosystem, other countermeasures for environmental restoration are suggested and discussed in this paper. Highlights • Ariake Sea has displayed signs of environmental deterioration in recent years. • Possible mechanism is decrease in tidal amplitude, tidal current and tidal flats. • The Isahaya Bay reclamation is one of the potential causes for environmental changes. • Dispute has arisen concerning opening the reclamation project dike's floodgates. • Countermeasures for reviving Ariake Sea as a sustainable ecosystem are suggested. [ABSTRACT FROM AUTHOR]

• The thermal conductivity of soils is of great importance in geothermal utilization. • The effect of multiple factors on soil thermal conductivity was investigated. • A simple and effective model for predicting soil thermal conductivity was established. • A mineral correction coefficient was introduced to widen the application range of the model. • The prediction performance of different models was compared and evaluated. As a renewable energy, geothermal is considered as one of the important approaches to mitigate the energy crisis and climate change. The thermal conductivity of soils is a key parameter required in the utilization of geothermal resources, and it plays an important role in engineering, environmental science, earth science, and agriculture. Generally, the existing models that predict the thermal conductivity of soil are limited to specific types of soil and specific conditions. As a result, it is difficult to apply these models to engineering practice. Therefore, a simple, efficient, and generalized model capable of predicting the thermal conductivity of soils is necessary. In this work, a generalized model for calculating the thermal conductivity of fine-grained soils is established. This model considers the initial dry density, initial water content, temperature, and mineral composition. The proposed generalized model is based on a large amount of measured data from different countries and regions. Its validity is verified after being cross-validated with a back-propagation artificial neural network (BP-ANN) model. Compared with two existing models, the proposed model achieves the best thermal conductivity estimation of fine-grained soils. Additionally, it has a wide range of applications, requires only a few parameters, and does not need recalibration. [ABSTRACT FROM AUTHOR]

• Visualized model tests are adopted to simulate the tunnel joint leakage with different water environments. • The damage evolutional process of sand erosion and erosion void are investigated in the model tests. • The theoretical model is proposed to predict the volumetric flow rate of the sand erosion and the volume of the erosion void. Sand erosion induced by shield-tunnel joint leakage is one of the most frequent catastrophes, causing ground collapses and tunnel failures. In this paper, a self-designed test device that considers differences in water head, burial depth and leaky joint characteristics was used to investigate sand erosion and void development. The experimental results show that the development of sand erosion has obvious temporal and spatial evolution characteristics. In the temporal dimension, sand erosion development can be divided into four stages: vertical erosion, cavity formation, coarse-particle skeleton distribution (CPSR) and steady seepage. In the spatial dimension, it can be divided into three regions: the stable zone, slip surface and eroded zone shape. It is found that the erosion zone can be described by a rotating ellipsoid and the scope of the erosion zone increases with increasing water head, whereas the influence of the burial depth is not significant. The influence of the invert leakage on the volume flow rate is also determined to be larger than that of the vault leakage and the volume flow rate rapidly increases when the size of the leaky joint exceeds the critical outlet size. Finally, a theoretical model based on the test results is proposed to predict the volumetric flow rate of sand erosion. [ABSTRACT FROM AUTHOR]

The vibration caused by moving traffic loading can create additional shear stress in the soil element, thereby resulting in the rotation of the principal stress axis, which can, in turn, accelerate soil softening and increase the cumulative deformation of soft clay. Nevertheless, the designed parameters are often obtained by the cyclic triaxial test (i.e., the rotation of the principal stress axis cannot be considered), or the cumulative axial plastic strain prediction is inaccurate, and these are some of the main reasons for geotechnical engineering problems. In this study, cyclic triaxial and cyclic torsional shear tests were performed to understand the softening and deformation characteristics of soft clay. The influences of the cyclic stress ratio, shear stress ratio, and loading frequency on the softening index and cumulative axial plastic strain of soft clay were analyzed. When the rotation of the principal stress axis was considered, the softening index decreased by 19.57%–51.09%, or the cumulative axial strain increased by 35.49%–74.39%, and failure occurred under higher cyclic stress ratios and shear stress ratios. Additionally, increasing the cyclic stress ratio and shear stress ratio and reducing the loading frequency will cause a surge in the softening index and cumulative axial plastic strain of soft clay. A cumulative axial plastic strain prediction equation considering the influences of cyclic stress ratio, shear stress ratio, and loading frequency was established and verified on the basis of literature. The availability of the prediction equation was verified by comparison with monitoring data. The relevant results can provide a theoretical reference for the prevention of urban engineering geological disasters. • The cyclic triaxial and cyclic torsional shear tests were run to understand softening and deformation properties of clay. • A cumulative axial plastic strain prediction equation considering was established and verified based on the literature. [ABSTRACT FROM AUTHOR]

A large number of soft soil subgrade projects have been built in the tidal-flat zone of southeast China. Where, in addition to bearing the traffic loading, the soft soil subgrade may be swallowed up by tidal water. Therefore, the soft soil subgrade will bear long-term coupling action of tidal loading and traffic loading in the tidal-flat zone. Excessive settlement accidents of the subgrade occur frequently in the tidal-flat zone. In this study, a new dynamic constitutive relation considering seepage characteristics was used and the UMAT subroutine was embedded in ABAQUS. FE parametric analysis was analyzed considering three influencing factors of tidal amplitudes, traffic loading amplitude and tidal period. A multi-factor coupling settlement prediction expression considering tidal loading and traffic loading of soft soil subgrade suitable for soft soil subgrade in the tidal-flat zone was proposed. In addition, a settlement prediction program of soft clay subgrade under the combined tidal loading and traffic loading was designed and developed to facilitate engineering use. The research results can be applied to the subgrade projects in the tidal-flat zone, and provide a reference for engineering decision-making and disaster prevention and mitigation. [ABSTRACT FROM AUTHOR]

Subgrade soils are subjected to coupled dynamic-static and changeable-frequency traffic loading. Considering different cyclic modes of single-frequency, coupled dynamic-static and intermittent combined-frequency loading, deformational characteristics of the Tianjin soft clay in each vibration period were analyzed by triaxial testing. Results show that the accumulative plastic strain and pore pressure have quite different development patterns under coupled dynamic-static and intermittent combined-frequency loading than single-frequency cyclic loading. The combined-frequency loading caused a considerable increase of pore pressure increment, but intermittency resulted in a decrease. During the loading of either coupled dynamic-static or intermittency, the static loading caused the soft clays to be more resistant to later undrained cyclic loading. The intermittency and combined-frequency loading have an integrated effect on the accumulative plastic strain development pattern and increment during each vibration period. The degradation index under the coupled dynamic-static loading decreased much less than that under single-frequency loading, especially with increasing cyclic stress ratio. • An experimental method to simulate the subway loading considering effect of intermittency and combined-frequency is proposed. • Deformation development pattern and increment of soft clays in each vibration period are investigated rather than the overall pattern under conventional cyclic loading. • The influence of intermittency and combined-frequency on soft clay pore pressure and deformation are compared with those under single-frequency cyclic loading. [ABSTRACT FROM AUTHOR]

The dynamic constitutive relationship of soil is essential for seismic dynamic calculations in geotechnical seismic engineering. Numerous experiments have demonstrated that cohesive soil exhibits cyclic strain softening characteristics under dynamic loading (equal-amplitude loading and unequal-amplitude loading) conditions. However, the Masing criteria (Masing's 2-fold method) cannot describe the cyclic strain softening behaviour of soil for equal-amplitude loading and often fail to estimate the damping ratio accurately (underestimation of the damping ratio at low strain; overestimation of the damping ratio at high strain). Furthermore, the Masing criteria are not applicable for nonequal-amplitude loading. To solve these problems, the research in this paper is based on the Davidenkov skeleton curve, and Masing's 2-fold method is utilized to establish a hysteretic curve. The cyclic strain softening coefficient and damping ratio adjusting coefficient were proposed for equal-amplitude loading to accurately capture the cyclic strain softening properties of cohesive soil. For nonequal-amplitude loading, Masing's n-fold method is employed to establish stress‒strain hysteresis curves, and using the customized constitutive interface reserved by FLAC3D, the development of this constitutive model is achieved on the Visual Studio (VS)2015 platform. The calculation accuracy of the model is verified by comparison with the theoretical values and experimental data, and the rationality of the constitutive model is verified by cyclic direct simple shear tests and cyclic torsional shear tests of soil subjected to equal-amplitude loading and centrifuge model tests of ground bearing unequal-amplitude loading, which provides effective help for the study of earthquake disasters in cohesive soil sites. • A nonlinear dynamic constitutive model of cohesive soil captured cyclic strain softening characteristics was established. • The program of this constitutive model was achieved on the visual studio (VS) 2015 platform, and model rationality was verified. • The simulation performance of this constitutive mode is superior to FLAC 3D's built-in constitutive model. [ABSTRACT FROM AUTHOR]

Shaking table test is an effective method to study the soil-structure dynamic interaction under earthquake conditions. However, during the design process of the soil container, it is usually impossible to simulate the soil-structure dynamic interaction for three-dimensional (3D) seismic input. In this study, a cylindrical 3D laminar shear soil container was designed for use in the shaking table test. This soil container is composed of 1 base plate, 18 H-shaped laminar frames, 144 3D limit connectors, and 8 guardrails, with the characteristics including large stiffness, light weight, and 3D shear movement. The soil container simulates the free site boundary conditions and minimizes the boundary effect, which meets the requirements of the shaking table test to implement the soil-structure dynamic interaction during 3D seismic input. Moreover, a series of shaking table tests was performed to verify the performance test requirements of the container and to measure the seismic response of the soil. The results of this study indicate that the container does not impose significant boundary effects and is able to maintain 3D soil column behavior. • A cylindrical 3D laminar shear soil container for use in the shaking tables is designed. • The designs and features of existing soil container are classified and summarized. • The function of the components and assembly process of the container are introduced. • A series of shaking table tests are performed to verify the performance of the container. [ABSTRACT FROM AUTHOR]

Soft marine clay is susceptible to deformation under cyclic loading, controlled by microstructure variations. To investigate the microscopic characteristics of soft clay with the progression of deformation under cyclic loading, a detailed study has been conducted using consolidated undrained cyclic triaxial tests, as well as mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The relationships between the micro parameters and accumulated plastic strain of soft marine clay are discussed. Cyclic triaxial test results show that low cyclic stress ratio (CSR) induces stable deformation, while for greater CSR the deformation of soft marine clay presents a closely linear or exponential increase, which leads to the destructuration of the soil structure. The microanalysis shows that with vibration cycles under 0.15 CSR, the content of pore obtained by SEM decreases from 37% to 25%, and large aggregates are visibly crushed into smaller ones, leading to a 24% increase in the pore numbers, which shows the slow increase of the deformation. When the CSR is greater than 0.25, large diameter pores generate resulting in divergent development of accumulated plastic strain. An empirical model of accumulated plastic strain involving micro parameter is proposed for assessing the deformation of soft marine clay. [ABSTRACT FROM AUTHOR]

Cone Penetration Tests (CPTs) are usually performed on the lunar regolith simulant on the Earth to study the geotechnical characteristics of lunar soil, which will be then used for the possible human activities on the Moon in the future. However, the gravity effect should be fully investigated before applying these experimental results to the Moon exploration, because the gravity level on the Moon is much lower than that on the Earth. For this aim, a series of CPTs was carried out in a centrifuge with a carefully designed testbed made of Tongji-1 lunar regolith simulant (TJ-1 simulant). The measured results were employed to examine the applicability of two traditional solutions and linear equation in describing the gravity effect along with some other existing experimental data. In addition, the linear equation fitted by the experimental data was used to predict the values of normalized tip resistances of lunar soil on the Moon. The results show that the two traditional solutions cannot describe the gravity effect well while the linear relationship between the peak (stable) normalized cone tip resistance and the reciprocal of gravity level can quantitatively describe the gravity effect on the penetration resistance. The predicted normalized peak (stable) tip resistances are larger than those of lunar soil on the Moon, which may be probably due to the unique in-situ conditions on the Moon. [ABSTRACT FROM AUTHOR]

• Field monitoring in combination with elaborate numerical modelling. • Clear insight into settlements of pile-tip and its surrounding soil. • Two load transfer mechanisms of pile foundation due to adjacent shield tunnelling. This study investigates the response of piled buildings to shield tunnelling in soft ground based on both a case history and numerical modelling. The findings indicate that building settlement can be significantly affected by the position of the tunnel relative to the pile foundation. Basically, two different settlement patterns of the pile toe are observed when the tunnel is excavated below and to the side of the pile foundation, implying the presence of different load transfer mechanisms: when the tunnel is excavated on the side of the pile foundation, the loads carried by the raft and pile shaft are transferred to the pile toe. The foundation may settle by compressing the pile-tip soil. In contrast, when the tunnel is excavated below the pile foundation, the loads carried by the pile toe are transferred to the pile shaft and raft. Unloading in the soil above the tunnel crown gives rise to foundation settlement. Notably, the settlement of the foundation in the latter mechanism is shown to be more significant. [ABSTRACT FROM AUTHOR]

Nonuniform seismic excitation cannot be neglected in the seismic design of long-span tunnels in soft soil areas, as it might induce tunnel damage. This paper proposes a method that combines an integrated nonuniform seismic random excitation method with the finite element method to solve the problem of nonuniform seismic input for geotechnical tunnel seismic design in soft soil areas. The integrated nonuniform seismic random excitation method of producing multipoint random seismic waves is investigated considering the effects of passage, incoherence, and energy attenuation. Design codes are developed to achieve random seismic ground waves, baseline adjustment and filtering, and inversion of bedrock. The correctness of an integrated nonuniform seismic random excitation is verified by analysis of the differences (5%–10%) between the simulated and theoretical power spectrum functions. Based on this modelling, the dynamic responses of tunnels subjected to longitudinal and lateral seismic excitations are investigated. Nonuniform seismic excitation will cause greater tunnel deformation and internal forces than uniform seismic excitation due to the tunnel consuming more seismic energy under nonuniform seismic excitation. Longitudinal nonuniform seismic excitation induces compressive and tensile states in the tunnel, and the maximum tension is close to the tensile strength of the concrete. Lateral nonuniform seismic excitation can enlarge the bending moment and shear force, and bending moment and shear force distribution ranges are recommended for this case study. [ABSTRACT FROM AUTHOR]

• A novel sequential excavation method (S-CRD) was implemented in practice. • Field monitoring was carried out. The monitoring data were provided in detail. • A theoretical model was proposed for analysing the performance of the S-CRD method. Sequential excavation (SE) methods involve the division of a tunnel passage into drifts to limit ground settlement. However, an increase in the number of tunnel drifts may prolong the construction duration. In this case study, a 4-drift centre cross diaphragm (CRD) method with a suspension system at the ground surface, termed the suspension-type CRD (S-CRD) method, was proposed and applied to the construction of a large-cross-section tunnel in soft ground. A theoretical settlement prediction model based on Mindlin's elastic equations was established to predict the ground settlement induced by the excavation of an S-CRD tunnel. The proposed theoretical model was validated to have satisfactory performance, as the predicted ground settlement agrees well with the field monitoring results. The effects of three crucial design parameters (the prestress F a , spacing S a , and diameter D a of the prestressed anchors) were analysed and compared using this theoretical model. It was found that the spacing of the prestressed anchors is more effective than the prestress and diameter in limiting the ground settlement. [ABSTRACT FROM AUTHOR]

Air booster vacuum preloading is a newly improved method applied in land reclamation projects. Highly pressurized air can provide an additional pressure difference between the prefabricated vertical drain (PVD) and injection point, thereby increasing the hydraulic gradient and generating small fractures that can improve the soil permeability and the transmission efficiency of the vacuum pressure. However, with a premature activation time, the pressurized air can create air channels connected to the PVD, which may drastically decrease the vacuum pressure. With a delayed activation time, the strength of the dredged clay may be too high to permit fractures, thus limiting the permeability improvement. In this study, soils with degrees of consolidation (DOCs) of 0%, 40%, 60%, and 80% were selected for testing the efficacy of initial booster activation times in four tests. The results show that the pressurizing groups were more effective in improving the consolidation of soils, and the best effect of the use of air booster is obtained when soil has been consolidated to a DOC of 60%. The lower soils of the pressurized groups showed greater increase rates than those demonstrated by conventional vacuum preloading. [ABSTRACT FROM AUTHOR]

Highlights • The apparatus and testbed are carefully designed to obtain reasonable forces. • Effects of cutting depth, rake angle, blade width and cutting speed were studied. • The applicability of the six typical analytical models was validated. Abstract In this paper, a series of excavation tests were conducted with a carefully designed apparatus and testbed based on soil mechanics theories to obtain reliable excavation forces in Tongji-1 lunar soil simulant at first. Then the measured data were compared with the forces predicted by six typical analytical models to verify their capability of accurately capturing the effects of cutting depth, rake angle, blade width and cutting speed. The results show that for the horizontal excavation forces, the Zeng model, the Kobayashi model, the Mckyes model and the Swick and Perumpral model can capture the effects of cutting depth, and the Lockheed-Martin/Viking model could capture the effects of the cutting depth, blade width and rake angle. For the vertical excavation forces, the Swick and Perumpral model and the Mckyes model can capture the effects of the cutting depth, blade width and rake angle. The overall assessment of excavation force predictions shows that the Lockheed-Martin/Viking model, the Zeng model, the Swick and Perumpral model and the Mckyes model are recommended for predicting the horizontal excavation force, and the Swick and Perumpral model and the Mckyes model are recommended for predicting the vertical excavation force. [ABSTRACT FROM AUTHOR]