Behavior Of Soft Clay Research Articles

Percolation Behavior of Soft Clay under Vacuum Suction

Percolation Behavior of Soft Clay under Vacuum Suction

Undrained three-dimensional behaviour of soft clay under horizontal one-way and vertical two-way cyclic loading

The undrained cyclic behaviour of clay under three-dimensional (3D) stress states is vital in marine geotechnical applications, especially in relation to deformation and stability issues of pile foundations under oceanic environmental loadings. However, investigations of the 3D cyclic behaviour of clay are rarely undertaken in the laboratory. This paper presents an experimental study on the undrained 3D responses of clay performed with a true triaxial apparatus, where horizontal one-way and vertical two-way cyclic stresses are applied to the specimen simultaneously. Emphasis is placed on the effects of different combinations of horizontal and vertical stresses on the behaviour of strain, pore water pressure, mobilised friction and modulus. Test results indicated that cyclic behaviour strongly depended on the 3D stress conditions or stress paths. By introducing a new cyclic stress ratio (CSRA), it was demonstrated that the cyclic shakedown behaviours of clay could be made independent of stress paths. An allowable CSRA, acting as a cyclic stress boundary ratio, was established at 0·08. Interestingly, an increase in the modulus of clay was observed during cyclic loading. This phenomenon contradicted the typically observed modulus degradation of clay under undrained cyclic loadings, adding a new perspective to our understanding of the material's behaviour.

A study on the behaviour of soft clay under embankment loading

A study on the behaviour of soft clay under embankment loading

Constitutive modeling of anisotropic small-strain stiffness behavior of Shanghai soft clay

Small strain stiffness plays an important role in determining the deformation of geotechnical engineering in soft soils. To model the anisotropic small strain stiffness behavior of soft clay, an enhancement to the bounding surface plasticity model is proposed. This enhancement involves incorporating the anisotropy in soil stiffness at very small strains and its non-linear degradation. Small strains are considered via cross-anisotropy elasticity, while the concept of intergranular strain is used to reflect the non-linear degradation of stiffness with strains and the effect of recent stress history. Using the proposed model, the triaxial test results on K0 consolidated Shanghai clay specimens are simulated to investigate the model’s performance. In the simulation, three typical shear stress paths are adopted. The comparison of the model simulations against experimental evidence is discussed, where the effects of anisotropy in initial soil stiffness and stress-induced anisotropy on the variation of small-strain stiffness, pore pressure, and shear-volume coupling response are highlighted.

Post-cyclic behavior of Haikou marine clay and their predictions using back-propagation neural network model

The evaluation of post-cyclic behavior of soft clay is critical for the lifetime safety and performance assessment of various infrastructures built on/in it. In this study, by employing the marine clays collected from Haikou, China, a series of both conventional shear tests and post-cyclic shear tests under undrained condition were performed using triaxial setup to investigate the post-cyclic behavior of the clay, with the investigation foci placed on the post-cyclic shear stress and secant modulus. Some important factors, namely confining pressure, loading frequency, cyclic shear strain amplitude and post-cyclic shear strain, were taken into consideration. From both the results from the tests and the parameter sensitivity analysis using random forest method, the confining pressure and cyclic shear strain amplitude were found to be evidently influential on the post-cyclic behavior of the clay, while the influence of loading frequency was relatively insignificant. In addition, an intelligent model was established based on the back-propagation neural network method to predict the post-cyclic behavior of Haikou marine clay, which was proven to be more favorable as compared to other two prediction methods developed based on multi-variate regression analysis and random forest algorithm.

Influence of Cross-Correlation on the Modelled Uncertainty in Stress–Strain Behavior of Soft Clays

Reliability-based design is increasingly being applied to geotechnical problems because it allows the robust consideration of various sources of uncertainty, such as the inherent variability of soil properties. Some soil properties, however, are mutually dependent, and ignoring this cross-correlation may lead to biased estimates of the probability of unsatisfactory performance. Hence, in this study, the Gaussian copula was used to evaluate how the applied cross-correlation or independence between the compressibility properties affects the uncertainty in the stress–strain response of two marine soft clays. Two settlement calculation methods were considered: the compression index and Janbu tangential stiffness methods. The correlation coefficients were defined from the site-specific oedometer data at two extensively studied clay sites, and from a database. The simulated oedometer curves were compared to the observed variability in the site-specific data. The settlements in the clay sublayers were then computed, and different cases were compared by means of boxplots. It is concluded that the Janbu method leads to a significant overestimation of uncertainty in settlement if the cross-correlation between the compressibility parameters is ignored. On contrary, the compression index method seems less sensitive to the assumed correlation structure, and as such, the parameters can be treated as independent in most cases.

Shear Strength Behavior of Soft Clay Reinforced with Ordinary and Geotextile-Encased Granular Columns

Shear Strength Behavior of Soft Clay Reinforced with Ordinary and Geotextile-Encased Granular Columns

One-Dimensional Consolidation Properties of Soft Clay under Multi-Stage Loading

The consolidation characteristics of soft clay under multi-stage loading and single-stage loading exhibit significant differences. In order to investigate the consolidation behavior of soft clay under multi-stage loading, one-dimensional oedometer tests were conducted on marine sedimentary soft clay from northern China. The results indicate that the overall time-deformation pattern of multi-stage loading is a cyclic nonlinear extension of that of single-stage loading. The final deformation between multi-stage loading and single-stage loading is approximately equal; however, the consolidation rate of single-stage loading is four times that of multi-stage loading. Furthermore, the coefficient of consolidation (Cv) decreases with increasing stress. Subsequently, the traditional Terzaghi one-dimensional consolidation equation was modified and a consolidation equation suitable for multi-stage loading is proposed in this study. The analysis of engineering applications demonstrates that the traditional theory provides more accurate predictions of consolidation rate and settlement when the load is small. However, when the load is large, the settlement predicted using the Terzaghi one-dimensional consolidation equation may have an error of 0–25% compared to that using the modified equation. The modified Terzaghi one-dimensional consolidation equation provides a more accurate representation of the actual consolidation of soft soil.

Improving Soft Clay Behavior with Alkali-Activated Waste Eggshell for Sustainable Ground Engineering

Improving Soft Clay Behavior with Alkali-Activated Waste Eggshell for Sustainable Ground Engineering

Horizontally Layered and Vertically Encased Geosynthetic Reinforced Stone Column: An Experimental Analysis

Because of the smaller confinement of the neighbouring soil in very weak soils, the carrying capacity of stone columns may not substantially increase. Geosynthetics can be used to reinforce columns by employing vertical encasement or horizontal layers. In the present study, large-scale laboratory investigations were carried out to evaluate the efficacy of vertical encasement and horizontal layering geosynthetics on the performance behaviour of soft clay. A series of tests were carried out for a horizontal layering of a geotextile with an equal distance throughout the height of the column (the total height of the column is ‘L’); horizontal layering over only the top half (i.e., 0.5 L from the head of the considered column); and horizontal layering over only the bottom half of the column (0.5 L from the centre to the foot of the column). Tests were also carried out for vertical encasement in the form of vertically encased stone columns (VESCs) that were employed for various lengths of encasement (i.e., L, 0.75 L, 0.5 L, 0.25 L). The tests were conducted for three different diameters of stone columns, i.e., 50 mm, 75 mm, and 100 mm. As per the findings, the utilisation of horizontal and vertical reinforcing layers enhances the carrying capability of stone columns. Moreover, because of their interlocking and frictional actions with the aggregates of stone columns, the layering decreases the lateral bulging of the considered stone columns. A comparison was performed to find the effectiveness of the horizontal and vertical types of reinforcement, and it was observed that VESCs with full-length encasement and a geotextile with a higher tensile strength for a 100 mm diameter of the stone column were the most desirable arrangements among all.

Thermo-mechanical Behaviour of Soft Clay between Operation and Shutdown of Submarine Hot Oil Pipeline

The interaction between the pipeline and the surrounding soil is a critical factor in the buckling analysis of the pipeline operating at high temperatures and pressures. The heating pipeline alters the temperature and induces excess pore pressure in the surrounding soil, which in turn affects the mechanical properties of the soil. Therefore, a comprehensive understanding of the thermo-mechanical response of the soil surrounding the pipeline during operation and shutdown is essential. To address this issue, this study developed a temperature-controlled pipe model test device that simulates the heating and cooling cycle of the pipe and the temperature field and pore pressure response of the surrounding kaolin clay. The test results showed that the soil temperature at the closest location to the pipe (0.1 D) reached a peak value of approximately 48.7°C when the pipe was heated from 12.5°C to 55°C. The peak temperature decreased with increasing distance, reaching 22.5°C at 0.875D. Heat transfer analysis using ABAQUS software revealed that the influence range of the pipeline on the soil temperature field during the heating cycle was about 2D. Additionally, a parametric study focused on the thermal conductivity (λsoil) of kaolin, and the best-fit value was determined to be 0.6 W/(m·°C. The excess pore pressures were generated in the kaolin surrounding the pipes during the heating cycle, and negative pore pressures were observed after cooling cycle. Furthermore, a theoretical solution for calculating the thermally induced pore pressure was derived, and preliminary verification showed good agreement between the theoretically computed and experimentally measured results. These findings provide valuable insights into the thermo-mechanical response of the soil surrounding pipelines during operation and shutdown, which can improve the design and safety of oil and gas pipelines.

One-Dimensional Nonlinear Consolidation for Soft Clays with Continuous Drainage Boundary Considering Non-Darcy Flow

Adopting the non-Darcy flow presented by Hansbo and considering the nonlinear compression and permeability characteristics of soils, the one-dimensional nonlinear consolidation problem of soft clays is investigated by means of a continuous drainage boundary. The numerical solutions of average consolidation degrees defined by settlement and excess pore water pressure are derived by using the finite difference method, and the correctness of these solutions is verified by comparing them with existing analytical and numerical solutions. Based on the proposed solutions, a parametric study is conducted to study the influence of interface parameter, non-Darcy flow parameter and soil nonlinearity on the consolidation behavior of soft clays. The results show that the solutions based on the continuous drainage boundary can be degenerated into the solutions based on the Terzaghi drainage boundary if the interface parameter is taken as a reasonable value. The soil consolidation behavior considering both non-Darcy seepage and nonlinear characteristics of soil is very complex.

Application of Hardening State Parameter Constitutive Model for Prediction of Overconsolidated Soft Clay Behavior Due to Embankment Loading

This paper investigates the possibility of the application of the HArdening State Parameter (HASP) constitutive model for numerical modelling of overconsolidated soft clay under embankment loading. The HASP constitutive model is a critical state soil model with a combined hardening rule that uses a state parameter to determine the dilatancy of overconsolidated clay. The model overcomes some shortcomings of the Modified Cam Clay (MCC) model in the prediction of overconsolidated clay’s behavior, while preserving the simplicity and the same set of five parameters. The HASP model was implemented in finite element software. In order to verify the applicability of the model in predicting the behavior of soft overconsolidated clay due to embankment loading, two examples reported in the literature are analyzed. The numerical predictions of the HASP model are compared with the field measurements of ground settlements and pore water pressures, and with the MCC model’s predictions. The results indicate that the HASP model predicts the development of the settlements of the overconsolidated soft clay deposits with a high accuracy from an engineering point of view. There are certain deviations from the field measurements in predicting the pore pressure development, which is often observed for other models as well. For the embankment settlement assessment, as important serviceability issue, the HASP model has an advantage over more complex models that require a large number of parameters. Since the parameters of the HASP model are obtained from standard laboratory tests, it can be easily applied for routine geotechnical analyses.

Numerical analysis of dynamic behavior of piled embankment under train loading

Piled embankments, which have many advantages, have been widely employed in the construction of railways over soft soil. However, the load transfer mechanism and deformation characteristic induced by train loading, which has great importance for piled embankment design, are not well known and deserve more research attention. In this paper, a three-dimensional numerical model of a piled embankment subjected to train loading is proposed and calibrated by test results, which considers the dynamic behavior of soft clays by a simplified dynamic constitutive model based on bounding surface theory that has been successfully encoded into the ABAQUS. Based on the proposed numerical model, the development of soil arching and accumulative deformation in a piled embankment subjected to train loading is investigated. The load transfer mechanism and deformation characteristics of a piled embankment in terms of the embankment height, velocity of the train, pile spacing and wheel static load are analyzed. The research results can provide some reference for the design of piled embankments under train loading.

Multi-fidelity data-driven modelling of rate-dependent behaviour of soft clays

ABSTRACT Conventional phenomenological elasto-viscoplastic models include numerous parameters that need to be calibrated by case-specific experiments. Data-driven modelling has recently emerged and provided an alternative to constitutive modelling. This study proposes a modelling framework based on multi-fidelity data to model the rate-dependent behaviour of soft clays. In this framework, low-fidelity (LF) data generated by an elasto-viscoplastic model and high-fidelity (HF) data from experimental tests are necessary. Stress–strain-strain rate correlations behind LF and HF data can be captured by long short-term memory and feedforward neural networks, respectively, such that final predictions can be given by a multi-fidelity residual neural network (MR-NN). Such a framework with the same LF data is applied in Hong Kong marine deposits and Merville clay to investigate its feasibility and generalisation ability. In addition, the effect of LF data on the performance of MR-NN is discussed to verify the robustness of the framework. All results demonstrate that rate-dependent undrained shear strength and pore-water pressure can be accurately modelled through the framework, showing adaptive non-linear modelling capability, less demand for experimental data, and superior robustness. These characteristics indicate a considerable potential in modelling the rate-dependent behaviour of clays.

Modeling consolidation of soft clay by developing a fractional differential constitutive model in conjunction with an intelligent displacement inversion method.

Studying the constitutive relation of soft clays is of critical importance for fundamentally understanding their complex consolidation behavior. This study proposes a fractional differential constitutive model in conjunction with an intelligent displacement inversion method based on the classic particle swarm optimization for modeling the deformation behavior of soft clay. The model considered the rheological properties of soft clay at different consolidation stages. In addition, statistical adaptive dynamic particle swarm optimization-least squares support vector machines were implemented to identify the model parameters efficiently. The accuracy and effectiveness of the model were validated using available experimental results. Finally, the application results showed that the proposed model could efficiently simulate coupling properties of soft clay’s primary and secondary consolidations.

Large-strain rheological consolidation analysis of multi-layered marine soft clays exhibiting natural structural characteristics

The destruction of marine soft clays’ macropore structure results in large-strain deformation during consolidation, as well as the potential to alter rheological deformation characteristics. A sectionalised regimes rheological model was adopted to describe the structural characteristics under the isotache framework, which led to a nonlinear variation of geometrical boundaries and material properties during consolidation. A semi-analytical theory combining numerical and analytical methods was developed, and the solutions for excess pore water pressure, degree of consolidation, and settlement were derived and computationally programmed. Using parametric analysis, the effects of rheological and structural characteristics on the consolidation behaviour of soft clay were discussed compared to the solutions of other theories. The coefficient of secondary consolidation in the transitional regime has an impact beginning in the middle of primary consolidation. The proposed solutions for degree of consolidation are smaller than the small-strain solutions during the early period of primary consolidation but change larger as consolidation progresses.

Geomechanical Behaviour of Clay Stabilised with Fly-Ash-Based Geopolymer for Deep Mixing

Geopolymer has recently become an attractive alternative to traditional binders (e.g., cement and lime) used for chemical soil improvement, with several environmental benefits including lower toxic emissions and energy consumption. This paper presents an evaluation of the geomechanical behaviour of soft clay treated with fly-ash-based geopolymer incorporating slag for deep soil mixing (DSM) applications. The geomechanical properties of stabilised clay were evaluated using unconfined compressive strength (UCS) tests and durability against wetting–drying. Thermal conductivity and pH tests along with microstructural analysis using scanning electron microscopy (SEM) were also performed to provide insights into the effect of geopolymer on treated clay. The results indicate that the inclusion of geopolymer with the increase in curing time and activator content considerably improves the geomechanical performance of geopolymer-treated soft clay in terms of stress–strain response and attainable peak compressive strength. Although it was found that a small percentage of geopolymer can enhance the initial compressive response, a larger dosage of geopolymer up to 30% was necessary to maintain stable durability performance over successive wetting–drying cycles. Such improved durability performance is related to the enhanced soil structure due to the cementation development and overall reduction in thermal conductivity. The reduction in thermal conductivity of treated clay was found to be activator-dependent and was suppressed steadily with the increase in activator concentration. Overall, geopolymer-treated clay showed promising potential for DSM applications due to its enhanced strength and durability responses.

Effect of vertical drains and preloading on the creep behavior of soft clay

Effect of vertical drains and preloading on the creep behavior of soft clay

Long-term cyclic behavior of soft clay under different variable confining pressures and partially drained conditions

Traffic loading is one of the essential causes of the excess settlement of soft subgrade. The stress path induced by traffic loading is more complex than a single dimensional path and coupling of both vertical and horizontal stresses. Also, under long-term cyclic loading, the pore water pressure (PWP) generated in soft clay eventually dissipates. Therefore, to study the cyclic behavior of soft clay under a long-term traffic loading, a series of long-term (50,000 cycles) cyclic triaxial tests involving variable confining pressure (VCP) on saturated remolded clay were conducted under partially drained conditions in this study. The result shows both the cyclic vertical stress and VCP have detrimental effects on the soft clay. Thus, a new index (CSRη) is proposed to synthesize these two factors. The peak PWP and final volumetric strain are all linearly related to CSRη. An empirical model involving CSRη is proposed to predict the final permanent axial strain. Compare to the empirical models in previous studies in which both the constant confining pressure (CCP) and VCP tests are necessary, only three CCP tests are needed to obtain the parameters in this model.