Predicting the lateral effective stress and the coefficient of lateral earth pressure at rest values is an important task in geotechnical engineering since it is used in the design and analysis of earth retaining structures, slope stability, piles and pier foundations. It needs sophisticated test procedures. The laboratory and in situ tests are also expensive and time consuming. In this study, an artificial neural network model is developed to predict the σ′_h, lateral effective stress in cohesionless soils. Back propagation neural networks are used for function approximation and model has been trained by Levenberg-Marqurdt (LM) learning algorithm. The data used in the running of network models have been obtained from extensive series of oedometer tests on Kilyos, Ayvalik and Yalikoy sands. Tests were carried out on loose, medium dense and dense state of compactness in normal loading, unloading and reloading conditions. The test results demonstrate that there is a linear relationship between vertical and lateral stresses for normally loaded cohesionless soils under K₀ conditions. K₀ values obtained for the loose state of compactness are higher than for the dense state of compactness. The results of the artificial neural network model indicate that the model serves as simple and reliable tool to predict σ′_h and also K₀ in cohesionless soils. The variation of K₀ values with internal friction angles is obtained and a simple expression is derived from this relationship.

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The time effects on the stress-strain behaviour of geomaterial consist of effects of loading rate and ageing. The positive ageing effects are analysed based on the results from drained triaxial compression (TC) tests on cement-mixed kaolin and well-graded gravelly soil and incorporated into a non-linear three-component model that can simulate the elasto-viscoplastic behaviour of geomaterials. The inviscid yielding is controlled by the inviscid yield stress that develops basically by irreversible straining and time elapsing following, respectively, a basic inviscid strain-hardening function and an ageing function. The inviscid yield stress may develop additionally by positive interaction between ageing and inviscid yielding following an interaction function, which expresses an additional strength gain by longer ageing at higher shear stress levels. Positive interaction effects are damaged by subsequent irreversible straining following a damage function. These functions are formulated based on experimental results. Illustrative model simulations are presented to describe the structure of the proposed model. The model is validated by simulating drained TC tests exhibiting significant effects of loading rate and ageing.

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A constitutive modelling of the elasto-viscoplastic stress-strain behaviour of geomaterials in shear that has been developed within a non-linear three-component model framework is validated by simulating a comprehensive series of drained triaxial compression (TC) and direct shear (DS) tests on a wide variety of granular materials. Illustrative simulations of rate-dependent stress-strain behaviour of geomaterial under typical laboratory test conditions were performed to analyse the structure of the model. The versatility of the proposed model and its applicability to a wide variety of shear loading histories is examined and demonstrated by these simulations. The following results are shown. Commonly with different basic viscosity types, Isotach, TESRA and P&N, the viscous stress component has a positive component that increases with an increase in the irreversible strain rate, which makes feasible stable and realistic simulations of rate-dependent stress-strain behaviour, including creep deformation, based on the proposed model. With different unbound granular material types having similar relative densities, the creep strain in TC tests and creep shear displacement in DS tests that develop by sustained loading at a given shear stress level for a given period tends to decrease with an increase in the particle roundness. This trend of behaviours is explained by a decrease in the viscosity type parameter, θ, associated with an increase in the particle roundness based on the simulations of these tests.

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Three-dimensional creep analyses are carried out to investigate the significance of soil creep effects on the tilting history of the Pisa Tower. Sensitivity analyses of model parameters are also conducted. Results show that three-dimensional creep analysis, although very time-consuming, is necessary in order to obtain more realistic numerical results. Creep effects have been found to account for 1.5 degrees out of the total 5.5 degrees inclination. Creep causes stress states in the clay layers to move away from the critical state line. It was also found that the deformation behaviour of the soil is not sensitive to any specific parameters. This helps to clarify that the total tilting angle of 5.5 degrees cannot be achieved by creeping of the soil. There must be other reasons that also contribute to the tilting of the tower, which cannot be considered by the constitutive model. Nevertheless, the current study could calculate the tilting history of the tower within reasonable accuracy during its construction period and illustrate more or less, the same trend as observed through the last four centuries. The model could also match the observed maximum settlement on top of the upper clay layers extremely well. Therefore, this study provides considerable insight into the deformation history of the soil and the stresses that are likely to exist in the soil.

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This study investigates the significance of the creep characteristic in the deformation behaviour of the Pisa Tower through the simulation of creep tests as well as plane strain analyses conducted under non-creep and creep conditions. Creep effects account for up to 1.7 degrees of tilting and one meter of settlement. In addition, creep increases the mean effective stresses and decreases the deviatoric stresses in the clay layers. An extensive model parameter sensitivity study shows that the deformation behaviour of the Tower is not controlled by any specific model parameter, but each model parameter becomes more sensitive under high stress level. The total tilt of 5.5 degrees could not be achieved by simply changing the values of model parameters. Other factors may have also contributed to the deformation of the tower, which could not be considered by the current model.

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In this research, several different kinds of specimen's preparation methods which include the hydraulic transportation method (HY), multiple sieving pluviation method (MSP)and wet-tamped method (WT)were used to compare their initial fabric. Moreover, the anisotropic permeability test was performed to those three kinds of specimens. Then, a series of cyclic simple shear tests was conducted on the specimens of HY and WT to investigate the dynamic deformation properties of the sand. The influence of fabric orientation for each kind of specimens to both permeability and dynamic deformation properties were discussed based on the testing results. It is observed that the difference in fabric orientation of the testing soil given by various sample preparation methods results in the difference of permeability and liquefaction resistance. On the other hand, the strength as well as deformation properties obtained by different shearing apparatus appear to have different results. Nevertheless, from the viewpoint of fabric orientation with respect to flowing direction and shearing force direction, an identical conclusion can be obtained. These phenomena demonstrate that the anisotropic characteristics of the soil have significant effect on the permeability, shearing strength and deformation behavior.

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This paper describes an elasto-plasticity damage model, termed the EPDI model, of the interface between a structure and gravelly soil. The formulations are derived on the basis of a new model framework, with test-basis concepts and assumptions, for a unified description of monotonic and cyclic behavior of such an interface. The model parameters, with physical meaning, are easily determined from a group of cyclic shear tests and a confining compression test. The comparisons of model predictions with the results for a series of tests under varying loading conditions demonstrate that the EPDI model is effective in accurate description of monotonic and cyclic stress-strain relationship of the interface between a structure and gravelly soil with capturing new features, including: 1) shear stress-strain relationship and comprehensive volumetric strain response (e.g., partly dependent on shear strain); 2) volumetric strain response that is dependent on the shear direction; and 3) evolution of behavior of the interface associated with the evolution of physical state.

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Shallowly embedded skirted foundations are an attractive alternative to piles for jacket structures and buoyant facilities as they can resist uplift but are cheaper to install than deep foundations. Bearing capacity of shallow skirted foundations in compression is moderately well understood while there is still considerable uncertainty over uplift capacity, particularly for loading sustained over a period of time. This paper reports results from beam centrifuge tests on a shallow skirted foundation in clay, subjected to uplift and compression. Rapid and sustained loading is considered and the effects of consolidation stress level and stress history on undrained capacity and sustained load response are reported.

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In-situ tests have been increasingly used to estimate the shear strength of soils. In this paper, we propose methods to evaluate in-situ strength and dilatancy of sandy soils based on cone penetration test (CPT) results. It takes into account the silt content, relative density and stress state of the sand. A series of laboratory test results from fundamental property tests and triaxial tests are analyzed to develop methods for in-situ evaluation of strength and dilatancy for sands. Based on test results, modified and simplified dilatancy equations, in terms of the cone penetration resistance q_c and intrinsic soil variables, are proposed. Results from proposed and original dilatancy indexes show close agreements for various soil conditions. Values of intrinsic variables for the proposed dilatancy relationships were proposed as a function of silt content. Based on TX test results, a direct CPT-based correlation, applicable to both clean and silty sands, is proposed as well. In order to verify the proposed methods, calibration chamber CPT results obtained in this study and collected from the literature are adopted. It is observed that the results from the proposed methods show good agreement with the measured results.

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This paper presents a case history on the failure of Suranivet 9, a student dormitory in the campus of Suranaree University of Technology (SUT), Thailand. The dormitory encountered excessive differential settlement due to the variation in soil profile. Part of the building was underlain by very stiff to hard SUT silty clay and part by loose clayey sand. Underpinning to extend the foundations down to stable stratum was employed to strengthen bearing capacity and minimize settlement. The underpinning design and procedure were summarized. In practice, the static formula was used for the preliminary micro-pile design (selection of pile section and length for different loads and soil profiles). The undrained shear strength (S_u) of SUT silty clay was approximated using the Stress History and Normalized Soil Engineering Properties (SHANSEP) technique and standard penetration number (N). The finite element method was employed to predict the load-settlement curve of the micro-pile. Modified cam clay model was proved as a suitable model for this prediction. The measured settlements of the underpinned foundations after one year service were less than 0.5 mm. This small settlement guarantees the stability of the underpinned structure. It is also found that the settlement ratio (ratio of the measured settlement of underpinned foundations to the predicted settlement of single micro-pile) varied from 0.7 to 3.0.

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An experimental technique for reconstructing the received wave of bender element tests based on linear system theory is shown in this paper. In order to identify the frequency response of testing apparatus, bender element tests using frequency-swept signals are performed. Received waves for one-period sine pulse transmitting with various frequencies are calculated and compared with observed waves in several kinds of soil samples and testing apparatuses. The linearity of the testing system is also confirmed by coherence function. It is shown that calculated data are less affected by random noise and show good agreement with observed data in regards to not only waveform itself but also resulting shear wave velocity. It is mentioned that this technique can provide simulations for arbitrary transmitted waveform with high signal/noise ratio after laboratory tests are performed. It is also mentioned that this technique is advantageous when sufficient amplitude of received wave cannot be ensured or shear wave velocity must be verified, for example, due to uncertainty of arrival time by near-field effect.

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