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The main causes of soil setup effects on pile response are generation of excess pore water pressure (EPWP) due to installation of prefabricated piles in saturated soils and subsequent dissipation of EPWP and, hence, stress state variations around the pile shaft. The main objective of this paper is evaluating the effects of pile diameter and over-consolidation ratio (OCR) on variations of stress state in soil adjacent to the pile and variations of the pile ultimate load over time using a nonlinear finite-element method numerical scheme and comparisons with field test data. The numerical model involves simulation of the pile penetration throughout the installation process and, hence, simulation of EPWP inducement and its dissipation over time during consolidation. The field data include pile driving and load test data in normally consolidated (soft) and overconsolidated (stiff to very stiff) fine-grained strata. The results have shown that the ratio of EPWP dissipation to overconsolidation stress reduces with an increase of OCR. The coefficient of lateral soil pressure has also increased with OCR and pile diameter. A "setup ratio" is defined as the ratio of shaft resistance at the end-of-consolidation to end-of-drive and is shown to have a proportional relationship with the pile diameter and a nonlinear and reducing trend with an increase in OCR. Correlations are proposed to modify existing relations for an increase in shaft resistance with time, incorporating OCR and pile diameter as well. Finally, the field data interpretations of a site having sufficient pile-load testing data in normally and overconsolidated fine-grained stratifications have validated the findings of the numerical model. [ABSTRACT FROM AUTHOR]

Despite ample research reported on the shaft resistance of closed-end displacement piles, the mechanism of the shaft resistance in cohesionless soils is not fully understood. In the literature, the available theories produce a wide range of discrepancies in predicting the shaft resistance of these piles. This is due to the complexity of incorporating the stress history and recognizing the critical depth. The role of the overconsolidation and the critical depth concept has been the subject of debate for some time. Arguments were made for both sides, nevertheless, no definite conclusion has yet been drawn. This paper presents experimental investigations on the capacity of closed-end displacement piles in overconsolidated cohesionless soils. The set-up was capable of measuring the overconsolidation ratio of the sand, and the shaft resistance of the pile shaft. It is of interest to know that the critical depth was observed only when mean shaft resistance was analyzed. [ABSTRACT FROM AUTHOR]

One of the main concerns in cyclic behavior of soft clay is gradual degradation with the progression of loading cycle. A series of cyclic constant-volume direct simple shear (CDSS) loading tests was performed on Malaysia offshore clay to study its undrained degradation. The testing program consists of stress-controlled tests with cyclic shear ratio ranging from 0.34 to 0.83 at different overconsolidation ratios (OCRs). For a given cyclic stress ratio in stress-controlled tests, the accumulated cyclic strain and pore water pressure increase with elevated number of cycles. In heavily overconsolidated clay specimens, the negative cyclic pore water pressure is generated followed by positive cyclic pore water pressure as cyclic tests progress. The post-cyclic strength of offshore clay specimens is reduced by undrained cyclic stress-controlled loading.

This study investigated the pore pressure responses of overconsolidated (OC) soils during a piezocone penetration test (PCPT). The influences of overconsolidation ratio (OCR) and hydraulic conductivity were accounted in investigating the generated pore pressures during the PCPT. The modified Cam-clay model and Darcy's law were incorporated in the quasi-static Biot theory to study the fluid-mechanical interaction during PCPT. The study found that a substantial negative pore pressure could be developed at the u2 position (cone shoulder) for heavily OC soils with low hydraulic conductivity. Moreover, an increase in u2 pore pressure was observed for a hydraulic conductivity range from 10−10 to 10−8 m/s. This was attributed to the instantaneous dissipation of shear generated negative pore pressure due to the diffusion of positive pore pressure from the u1 position (cone face), where the diffusion process is faster in high hydraulic conductivity condition. The findings of this study could explain a complicated multiphysics problem, and therefore may enhance the general understanding of PCPT results and the accuracy of specialized techniques such as on-the-fly estimation of the hydraulic conductivity of soils. [ABSTRACT FROM AUTHOR]

In this study, a relationship between small-strain shear modulus (Gmax) and overconsolidation ratio (OCR) based on shear wave velocity (Fs) measurement was established to identify the stress history of centrifuge model ground. A centrifuge test was conducted in various centrifugal acceleration levels including loading and unloading sequences to cause various stress histories on centrifuge model ground. The Vs and vertical effective stress were measured at each level of acceleration. Then, a sensitivity analysis was conducted using testing data to ensure the suitability of OCR function for the tested cohesionless soils and found that OCR can be estimated based on Vs measurements irrespective of normally-consolidated or overconsolidated loading conditions. Finally, the developed Gmax-OCR relationship was applied to centrifuge models constructed and tested under various induced stress-history conditions. Through a series of tests, it was concluded that the induced stress history on centrifuge model by compaction, g-level variation, and past overburden load can be analysed quantitatively, and it is convinced that the OCR evaluation technique will contribute to better interpret the centrifuge test results. [ABSTRACT FROM AUTHOR]

The overconsolidation ratio is an important parameter that determines the value of stress history exerted in the past on the subsoil in the geotechnical engineering. Overconsolidation ratio (OCR) is one of the main criteria conditioning soil behavior and characteristics. To know the relation between geological background, history and mechanical behavior of the soil, aims a knowledge that can help engineers who often have to predict soil behavior based upon the soil geological history and a geotechnical data. In order to evaluate the overconsolidation ratio of eemian gyttja, it is necessary to restore this soft soil as much as possible to the in situ conditions. The eemian gyttja is an organic soft soil from the "Zoliborz channel" located in Warsaw. These soils are used as a base construction in the foundation engineering. In practical geotechnical engineering, evaluation of stress history is based on the overconsolidation ratio. The overconsolidation ratio is one of the basic parameters for the geotechnical design of the structure. Determination of this parameter using for example dilatometer tests, is usually based on empirical formulas which were established in different countries. Therefore, regional geotechnical conditions could have substantially affected on the empirical relationships. The laboratory tests are used to determinate the preconsolidation pressure and then the overconsolidation ratio. The laboratory tests were made in the automatic oedometer and the in situ tests were carried out on the dilatometer test (DMT). The paper presents results of determination the overconsolidation ratio of eemian gyttja from the laboratory and in situ tests. The studies have shown that the values of the overconsolidation ratio determination from the laboratory tests are a little higher than determination from the in situ tests. [ABSTRACT FROM AUTHOR]

The disturbed state concept (DSC)-based model for overconsolidated clay was proposed mainly in a previous paper that aims to analyze the influences of the model parameters on model predictions, calibrations of the model parameters, and the model validation through different overconsolidated clays. It is found that the disturbance parameter in the model predictions can greatly influence the evolution of stress, volumetric strain, undrained shear strength, and excess pore pressure with axial strain. Detailed calibrations of the model parameters, such as the disturbance parameter, potential-failure and dilatancy parameters, and plastic modulus parameters, are introduced. The comparison results demonstrate that the DSC-based model predictions are in good agreement with the test data of different overconsolidated clays on strain softening and volumetric expansion under the drained condition, as well as the evolution of undrained shear strength and excess pore pressure during the undrained shearing process. [ABSTRACT FROM AUTHOR]