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Accurate prediction of displacements associated with deep excavations is essential to ensure safety and stability of the excavation and to prevent any damage and distress to the adjoining infrastructures. This paper presents a numerical approach for prediction of ground displacements related to a zone-divided deep excavation construction executed in Shanghai soft clays based on a new elasto–plastic constitutive model (small-strain Shanghai model) that incorporates small strain stiffness. This model can describe the mechanical properties and structural and over-consolidated characteristics of natural clays. The model is implemented into a finite element analysis software. Numerical analysis on the deep excavation in Shanghai using zone-divided method is conducted. A comparison between monitored and simulated results of horizontal displacements along the diaphragm wall, the settlements in the surroundings, and the effects on the adjoining metro tunnel due to excavation construction is carried out. Special attention is paid to the stiffness degradation of representative elements in the ground. The simulated displacements show a good agreement with the monitored data. Overall, this study provides an integrated solution for predicting displacements related to deep excavation in soft clays.

In this paper, an elastoplastic constitutive model is proposed to uniformly describe the mechanical behavior of cemented/ non-cemented soil under different loading conditions. A state variable characterizing the degree of cementation is introduced into the yield function of the cyclic mobility model, and an evolution rule is proposed to describe the degradation of cementation and structure. Since the cyclic mobility model is developed based on the concepts of subloading surface and superloading surface, the newly proposed model inherits both its advantages and can systematically describe the effects of cementation, structure, overconsolidation, and stress-induced anisotropy on the mechanical behavior of soil. Compared with cyclic mobility model, this proposed model adds only one state variable associated with cementation, which has clear physical meaning and can be determined by uniaxial compression or tension test. The capability of the proposed model has been validated carefully through a series of tests such as isotropic, uniaxial, and triaxial tests under monotonic and cyclic loading conditions.

With rapid development of infrastructures like tunnels and open excavations in Shanghai, investigations on deeper soils have become critically important. Most of the existing laboratory works were focused on the clayey strata up to Layer 6 in Shanghai, i.e. at depth of up to 40 m. In this paper, Layers 7, 9, and 11, which were mostly formed of sandy soils at depth of up to 150 m, were experimentally investigated with respect to physico-mechanical behaviors. The stress–strain behaviors were analyzed by the consolidated drained/undrained (CD/CU) triaxial tests under monotonic loading. One-dimensional (1D) oedometer tests were performed to investigate the consolidation properties of the sandy soils. Specimens were prepared at three different relative densities for each layer. Also, the micro-images and particle size analyzers were used to analyze the shape and size of the sand grains. The influences of grain size, density, and angularity on the stress–strain behaviors and compressibility were also studied. Compared to the other layers, Layer 11 had the smallest mean grain size (D50), highest compressibility, and lowest shear strength. In contrast, Layer 9 had the largest mean grain size, lowest compressibility, and highest shear strength. Layer 7 was of intermediate mean grain size, exhibiting more compressibility and less shear strength than that of Layer 9. Also, the critical state parameters and maximum dilatancy rate of different layers were discussed.

Reliable assessment of the lateral pile-soil interaction is of pronounced importance for the design of mono-pile foundations of offshore wind turbines. As the offshore engineering moves to deeper waters, the diameter of mono-piles is getting larger, usually about 5 m and could be up to 8 m, which may lead to partially drained behaviors of sand in the vicinity of the pile and thus imply limitations of conventional design methods in which fully drained conditions were assumed. To shed light on this issue, a fully-coupled finite element model was established using an in-house developed finite element code DBLEAVES, incorporating a cyclic mobility constitutive model that is capable of describing the instantaneous contractive and dilative response of sands simultaneously. Triaxial and centrifuge model tests were conducted to calibrate the constitutive model and validate the pile-soil interaction model respectively. This is followed by a parametric study primarily focusing on the effects of loading rates. The initial stiffness of the p-y curve was found to increase with the loading rate whilst the bearing capacity showed the inverse, and the mechanism behind this phenomenon is examined in detail. Then an explicit model was developed to evaluate the development of excess pore pressure in the pile front upon lateral loading, and an upper boundary of normalized loading rate was identified to distinguish fully and partially drained conditions.

Due to the peculiarity of the spring domain strata in Jinan, the phenomenon of serious water seepage appears in the process of excavation. The macro permeability of soil is closely correlated with its microstructure. In this study, by using the X-ray micro-tomography (micro-CT) system and a self-designed soil seepage device, the internal pore structure of Jinan red clay and the water flow inside the sample under different seepage stages were observed. The microstructure of water phase and air phase in the sample was segmented by the watershed algorithm. Calculation and comparison of pore and throat size distributions at different seepage stages were conducted by establishing Pore Network Model (PNM). Meanwhile, the seepage experiment simulations were conducted based on the 3D pore structure of red clay. The results show that the preferentially flow of Jinan red clay is obvious due to the existence of the vertically developed macropore channel. The fine particles (mainly silt particles) are washed away during seepage, thereby expanding the pore channels. The maximum pore radius and pore connectivity have important influence on seepage characteristics of Jinan red clay, but the correlation between porosity is small.

This experimental study investigates the consequences of one-dimensional consolidation pressure on the macro and micro soil structure during the reconstitution process of marine clay as well as to determine the effect of pressure on the soil structure generated due to material self-weight at the lower portion of fillings. For this research, soft marine clay is selected, and specimens are reconstituted with low percentages of cement. The clay-cement slurries are consolidated under 98 kPa and 50 kPa vertical pressure with the drained condition. The consequences of consolidation pressure on macro and micro structure are determined by performing the oedometer tests, scanning electron microscope analyses, and mercury intrusion porosimetry tests. It is noted that consolidation pressure has a significant effect on the structure of marine clay concerning void ratio, compression index, yield stress, and pore size distribution. The total pore volume decreases with increasing the consolidation pressure as well as the medium pores larger than 1 μm also decreases and converts into fine and micro pores having the size among 1μm–0.01 μm.

Flow liquefaction is a catastrophic failure phenomenon of loose sand when subjected to wave or seismic load, and an instability state can be regarded as the onset of flow liquefaction. Most of the ...

The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray microtomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of 8 mm × 16 mm (diameter × height). In situ triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils.

The objective of the present study is to preliminarily clarify the mechanism of carbohydrates metabolism in cobia (Rachycentron canadum) (85 ± 3 g) receiving injection of glucose solution. We examined plasma glucose (GLU), total protein (TP), triglyceride (TG), cholesterol (CHOL), insulin, liver glycogen and muscle glycogen, activities of hepatic hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK), as well as relative expressions of glucose transporter 1 (GLUT1), GLUT2, GLUT3, GLUT4, GLUT5 and GLUT9 in hemocyte, liver and muscle of R. canadum when fish were injected with 200 μl of glucose solution (255 mg/ml) after 0, 1, 2, 4, 8, 12, 24 and 48 hr. Fish received injection of 0.68% saline served as control. Results indicated that the plasma GLU, TG and CHOL increased and reached peak at 1, 8 and 48 hr postinjection (hpi) respectively. The hepatic glycogen increased from 1 hpi, and reached peak at 8 hpi, plasma insulin increased at 1 hpi, and reached peak at 2 hpi, and activity of hepatic PK peaked at 8 hpi. Furthermore, the relative expressions of GLUT1, GLUT2, GLUT3, GLUT4 and GLUT5 in hemocytes reached peak at 1,4, 8, 4 and 8 hpi, respectively, relative expressions of GLUT2, GLUT3, GLUT5 and GLUT9 in liver reached peak at 24, 24, 12 and 24 hpi, respectively, and relative expressions of GLUT1 and GLUT3 in muscle were significantly higher at 2 and 2–4 hpi, respectively compared with those in controls. In conclusion, low ability of utilizing glucose in R. canadum may be attributed to insufficient insulin secretion, low activities of key glycolytic enzymes (HK, PFK and PK) regulated by glucose injection and slow increase of GLUTs.

Quantitative laboratory studies on the structural behavior of natural intact marine clays require a large number of identical natural samples leading to an expensive and challenging task. This study proposes a simple method to reconstruct an artificial structured marine clay as the state of its natural intact clay at both macro and micro levels. For this purpose, the Shanghai marine clay is selected and mixed with low cement contents (1–6%). The clay-cement slurry is mixed in a container with the ice-covered sides at a low temperature about 0 ± 2 °C to postpone the hydration reactions until consolidation began. The purpose of adding cement is to generate the inter-particle bonding and structure in reconstituted samples. Initially, the reconstituted samples are consolidated under the in situ stress of 98 kPa and then under the pre-consolidation pressure of 50 kPa. Mechanical characteristics such as compression index, yield stress, unconfined compression strength, shear strength ratio, and the stress paths from triaxial tests are compared with natural intact clay accordingly. Scanning electron microscope and mercury intrusion porosimetry analyses are also performed to analyze the microstructure of clays for comparison. Furthermore, the proposed method is also examined by using natural intact marine clays of different locations and characteristics.

Flow liquefaction will cause the sudden failure of loose sand specimens when they are subjected to stress-controlled cyclic loading in undrained triaxial tests, and thus few data points can be obtained during this process. To overcome this problem and conduct a detailed investigation of the flow liquefaction behaviours, a two-staged loading method was proposed, in which stress-controlled cyclic loading was switched to strain-controlled monotonic loading after reaching the initial point of the last cycle (IPLC) in undrained cyclic triaxial tests on flow liquefaction. The characteristics of the IPLC were first investigated through a series of undrained triaxial tests, and then a linear relationship between the excess pore water pressure (EPWP) ratio at the IPLC and the cyclic stress ratio (CSR) was obtained for predicting the location of the IPLC. The verification testing results proved that the relationship can predict the IPLC accurately, which makes it possible to switch the loading mode at the right point and make a detailed investigation of the flow liquefaction behaviours of loose sand.

Based on a new elasto-plastic constitutive model, this paper presents a soil–water coupled numerical prediction of the bearing capacity for shallow foundation constructed on Ballina soft clay for u...

Solid propellants are typical viscoelastic materials that are subject to chemical ageing and mechanical damage under whole life cycle conditions. Through high and low temperature cycling tests on PBT propellant specimens under constant strain conditions, the effects of mechanical damage and temperature ageing on the mechanical properties of PBT propellant are simulated and analysed during the motor delivery, storage and operational duty cycles of PBT propellants subjected to environmental loads. The tests show that: during the ageing process of PBT propellant in the simulated natural environment, the tensile strength will gradually increase due to the influence of temperature load and manoeuvring load, and the initial modulus will increase due to the influence of internal stresses generated by curing and cooling, which will reduce the tensile strength, both of which will jointly affect the mechanical properties of the propellant. The force-thermal coupling accelerated ageing experiment can simulate the ageing process of solid motor pillars under natural conditions and predict their mechanical properties at various time stages.

The sustainable utilization of dredged soft clays for land reclamation requires a lower strength with lesser cement content as compared to traditional cement-treated clays. The mechanical behavior of soft clays at low cement content can differ from clays treated with higher content. For land reclamation, the required cement content is generally used up to 10%. Hence, this study is focused on analyzing the sustainable utilization of soft clays treated with cement content lower than 7%. Additionally, a comparison is drawn between a low-cement-treated soft clay with the highly cemented clays to determine the difference in mechanical behavior. Shanghai soft clay is reconstituted with cement content from 0 to 6%. The experimental investigation indicates that the low cement content has a significant effect on the microstructure, compression characteristics, compressive strength, undrained stress paths, and stress-strain behavior. However, the effect of curing time on such characteristics is limited. The mechanical behavior of low-cement-treated soft clay is similar to the highly cemented clays with respect to the relationships of compressive strength with strain at failure, yield stress and clay-water/cement ratio but is different with respect to deformation modulus versus compressive strength. The outcomes of this study can help to choose the minimum required cement content for the fill materials of land reclamation projects.

Numerical simulations are employed to predict deep excavations’ performance and the magnitude of the associated wall and ground displacements. Accurate prediction of these displacements is essential to prevent any distress or damage to the adjoining structures. A novel numerical approach is proposed in this paper to predict the wall and ground displacements related to deep excavations in Shanghai soft clays by using a new elastoplastic small strain constitutive model. The small strain Shanghai model incorporates the effects of small shear strain, elucidates both the clays' structure and mechanical properties, and describes the dilatancy characteristics and strain-softening in a three-dimensional state. A deep excavation case study in Shanghai soft clay is simulated on Plaxis 2D. The material parameters and the monitored values of displacements are obtained from the site. A user defined soil model of small strain Shanghai model is made in the form of Dynamic Link Library (.dll) file to be used in this analysis. A comparison of the monitored values of displacements is made with ground and wall displacements' simulated values. The effects of the excavation activity on the adjoining historical buildings are evaluated. The simulated results agree well with the monitored results. The comparison lays out a novel numerical approach for predicting the performance of deep excavation in Shanghai soft clays and the associated displacements by using a new constitutive model.

The objective of the present study was to assess the effects of substituting fishmeal (FM) with peanut meal (PNM) on growth performance, immunity, and intestinal microbiota in juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). Hybrid grouper (initial weight 16.85 ± 0.02 g) were fed diets (isonitrogenous and isolipidic) with PNM replacement rates of 0% (FM), 10 % (PNM10), 20 % (PNM20), 30 % (PNM30), 40 % (PNM40) and 50 % (PNM50) FM protein, respectively. The growth trial lasted for a 10-week period. The results showed that FM replaced by PNM had no significant effect on the growth performance, feed utilisation, somatic indices, and whole-body composition of hybrid grouper (P > 0.05). Acid phosphatase first became more active and then less active with the increased replacement level (P > 0.05), while the activities of lysozyme and the contents of immunoglobulin M in the intestine were significantly enhanced (P 0.05). The mRNA expression of epinecidin and hepcidin in the PNM40 and PNM50 groups was significantly lower than in the FM group (P

This study presents a sophisticated elastoplastic constitutive model for unsaturated soil using Bishop-type skeleton stress and degree of saturation as state variables in the framework of critical state soil mechanism. The model is proposed in order to describe the coupled hydromechanical behavior of unsaturated soil irrespective of what kind of the loadings or the drainage conditions may be. At the same time, a water retention characteristic curve considering the influence of deformation on degree of saturation is also proposed. In the model, the superloading and subloading concepts are introduced to consider the influences of overconsolidation and structure on deformation and strength of soils. The proposed model only employs nine parameters, among which five parameters are the same as those used in Cam-Clay model. The other four parameters have the clear physical meanings and can be easily determined by conventional soil tests. The capability and accuracy of the proposed model have been validated carefully through a series of laboratory tests such as isotropic loading tests and triaxial monotonic and cyclic compression tests under different mechanical and hydraulic conditions.

In this study, a critical state-based thermo-elastoplastic model for soft rock is proposed. The model is able to describe the basic mechanical behavior of soft rock such as strain-hardening, strain-softening and the influence of intermediate principal stress, but also temperature dependency with a unified set of parameters. In the model, concepts of subloading and superloading are introduced to describe the influence of overconsolidation and structure on the deformation and strength of soft rock. The influence of intermediate principal stress is also properly taken into consideration by adopting a transformed stress tensor tij. In order to consider the temperature effect, a thermo-induced equivalent stress is proposed to consider the influence of temperature on yield surface, evolution of overconsolidation and structure during shearing. By comparing the calculated results with test results under different loading and temperature conditions, the availability and the accuracy of the proposed model are carefully investigated. Finally, the performance of the proposed model is discussed with a series of parametric studies in detail.

In this paper, we propose an isotropic hardening elastoplastic model for structured marine clay that can describe its strength and deformation behavior under general loading conditions. A series of drained true triaxial tests were performed on structured and remolded marine clay to investigate the effect of intermediate principal stress. The test results show that the intermediate principal stress has a considerable effect, not only on the strength, but also on the deformation behavior of marine clay. A modified stress-dilatancy equation is defined in transformed stress space to capture this feature. Then, the model is extended to consider the influence of structure by incorporating the superloading surface concept. Compared with the modified Cam-Clay model, the proposed model requires only two additional parameters, which can be determined conveniently from triaxial and oedometer tests. The proposed model was validated by performing undrained triaxial tests and drained true triaxial tests at various confining stresses and Lode angles, respectively, on remolded and structured clay.

The engineering properties of marine clays are closely related to its depositional environment. However, the correlation between the chemical properties and depositional environment and their effect on engineering properties of upper Shanghai marine clay are still pending. The sedimentary processes of upper Shanghai marine clays from the Quaternary transgression, the correlation between the chemical properties and its depositional history are investigated in this study based on a series of laboratory experiments. The distribution of chemical indicators (e.g., pH value, oxidation-reduction potential and salt content) with depth showed that the depositional environment directly affected the chemical properties of the soil layer. The correlation of salt content with sensitivity, liquid limit and liquidity index in upper Shanghai layers represents a unique two-stage distribution, with the boundary at the bottom of the Layer-4 clay. The two-stage distribution is caused by the Quaternary transgression and regression, which is confirmed to have different effects on the salt content, sensitivity, liquid limit and liquidity index. The quantitative approaches used to evaluate the correlation between depositional environment, chemical and mechanical properties can provide valuable references for investigating the engineering properties of soft clays.

A large number of breakwaters have been constructed along coasts to protect humans and infrastructures from tsunamis. There is a risk that foundation soils of these structures may liquefy, or partially liquefy during the earthquake preceding a tsunami, which would greatly reduce the structures’ capacity to resist the tsunami. It is necessary to consider not only the soil’s liquefaction behavior due to earthquake motions but also its post-liquefaction behavior because this behavior will affect the breakwater’s capacity to resist an incoming tsunami. In this study, numerical tests based on a sophisticated constitutive model and a soil-water coupled finite element method are used to predict the mechanical behavior of breakwaters and the surrounding soils. Two real breakwaters subjected to two different seismic excitations are examined through numerical simulation. The simulation results show that, earthquakes affect not only the immediate behavior of breakwaters and the surrounding soils but also their long-term settlements due to post-earthquake consolidation. A soil profile with thick clayey layers beneath liquefied soil is more vulnerable to tsunami than a soil profile with only sandy layers. Therefore, quantitatively evaluating the seismic behavior of breakwaters and surrounding soils is important for the design of breakwater structures to resist tsunamis.

Dynamic seabed response under wave loading is one of key factors for the design and construction of offshore structures. Most previous studies were based on poroelastic seabed model. In this paper, based on a unified elasto-plastic constitutive model that can describe the liquefaction of sand and two-phase u-p theory for saturated soils, numerical tests are conducted to analyze the dynamic responses of a sandy seabed subjected to cyclic wave loads. The development of liquefaction zone, the change of excess pore water pressure (EPWP), the effective stress path, and the displacement vector are investigated. Numerical tests show that the proposed method is able to capture the mechanical behaviors of wave induced liquefaction of a sandy seabed. The calculated effective stress path and change of EPWP are similar to those of earthquake-induced liquefaction. In other words, the mechanism of wave-induced and earthquake-induced liquefaction are similar, despite of the loading forms. The liquefaction depth increases with the number of wave cycles. Meanwhile, a phase lag is observed between the liquefied seabed and wave motion. A comparison between the dynamic response of elastic and elasto-plastic seabed is presented to underline the importance of considering the plastic deformation of seabed.