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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]

Koefisien tekanan tanah kesamping “at rest” (Ko) untuk setiap jenis tanah tidak sama; tanah inorganic mempunyai harga Ko lebih besar dari pada tanah organik. Harga Ko tersebut juga masih dipengaruhi oleh overconsolidation ratio (OCR). Untuk tanah anorganik, harga Ko dapat ditentukan dengan formula yang telah tersedia; tetapi untuk tanah gambut harga Ko masih harus ditentukan dengan melakukan test di laboratorium.Dalam tulisan ini disajikan hasil penelitian yang menunjukkan hubungan antara Ko, OCR, dan Oc (kadar organik) tanah gambut berserat halus. Sampel yang diteliti dibuat dengan kandungan organik bervariasi (55%, 65%, 71%, 85%, dan 99%); tipe seratnya hanya serta halus saja. Ukuran sampel yang di test adalah : tinggi 15cm dan diameter 7 cm. Besar beban yang diberikan adalah 50, 100, 200, dan 400 kPa; harga OCR yang dipilih adalah 1, 2, 4, dan 8. Harga Ko ternyata makin membesar dengan meningkatnya harga OCR dan kandungan organik. Hubungan antara Ko dan OCR merupakan dua garis lurus patah yang mempunyai kemiringan berbeda. Pada OCR ≤ 2 peningkatan harga Ko terhadap harga OCR adalah sedikit lebih besar jika dibandingkan pada OCR > 2.

This paper reports K0 of dry sand in response to different loading conditions and under secondary compression. The experiments were carried out using an oedometer and tactile pressure sensors were used to measure the horizontal stress for K0 calculations. During loading, K0 remains a constant as the vertical stress δ′v increases. The corresponding discrete element method (DEM) simulations reproduced this experimental finding and suggest that the force transmission pattern is similar and the contact forces among particles are proportionally increased in both the horizontal and vertical directions to give a constant K0 as δ′v increases. K0 increases as the overconsolidation ratio (OCR) increases during unloading because of the locked-in horizontal stress. Reloading makes the sample less sensitive to OCR and thus the sample behaves as if it were in a normally consolidated state where K0 is a constant. Experimental results and DEM simulations demonstrate that the horizontal stress δ′h and K0 continue to increase during secondary compression on the loading path. Secondary compression is initiated by creep at particle contacts and exhibits similar responses like primary creep. The subsequent loading after secondary compression can gradually bring K0 back to its initial value. During secondary compression on the unloading path, however, K0 continues to decrease according to the DEM simulation results. The creep process tends to relax the locked-in horizontal stress and the sample expands in the vertical direction. Therefore, δ′h and K0 gradually decreases. [ABSTRACT FROM AUTHOR]

Abstrak. Koefisien tekanan tanah kesamping “at rest” (Ko) untuk setiap jenis tanah tidak sama; tanah inorganic mempunyai harga Ko lebih besar dari pada tanah organik. Harga Ko tersebut juga masih dipengaruhi oleh overconsolidation ratio (OCR). Untuk tanah anorganik, harga Ko dapat ditentukan dengan formula yang telah tersedia; tetapi untuk tanah gambut harga Ko masih harus ditentukan dengan melakukan test di laboratorium.Dalam tulisan ini disajikan hasil penelitian yang menunjukkan hubungan antara Ko, OCR, dan Oc (kadar organik) tanah gambut berserat halus. Sampel yang diteliti dibuat dengan kandungan organik bervariasi (55%, 65%, 71%, 85%, dan 99%); tipe seratnya hanya serta halus saja. Ukuran sampel yang di test adalah : tinggi 15cm dan diameter 7 cm. Besar beban yang diberikan adalah 50, 100, 200, dan 400 kPa; harga OCR yang dipilih adalah 1, 2, 4, dan 8. Harga Ko ternyata makin membesar dengan meningkatnya harga OCR dan kandungan organik. Hubungan antara Ko dan OCR merupakan dua garis lurus patah yang mempunyai kemiringan berbeda. Pada OCR ≤ 2 peningkatan harga Ko terhadap harga OCR adalah sedikit lebih besar jika dibandingkan pada OCR > 2. Abstract. Coefficient of lateral earth pressure at rest (Ko) is different for each soil type; anorganic soil has higher value of Ko than organic soil. The ko value is also affected by the overconsolidation ratio (OCR) of the soil. For anorganic soil, the Ko value can be determined using the available formula; for peat soil, however, a laboratory testing has to be carried out in order to get the Ko value of the peat. In this paper is presented the research result that show correlation between Ko, OCR, and Oc (organic content) of fine fibrous peat. The soil sample was prepared with different organic content (55%, 65%, 71%, 85%, and 99%); the fibers chosen were only the fine ones. The sample size was 15 cm height and 7 cm in diameter. The loads applied were 50, 100, 200, and 400 kPa; the OCR values chosen were 1, 2, 4, and 8. The study results show that the Ko value is getting higher with the increase of the OCR value and the organic content. The correlation between Ko and OCR shows as two broken straight lines with different slope. At OCR ≤ 2 the increase of Ko is slightly higher compared to the one at OCR > 2.

The paper presents a discussion of some applications of Artificial Neural Networks (ANNs) in geo-engineering using the analysis of the following six geotechnical problems, related mainly to prediction and classification purposes: 1) prediction of Overconsolidation Ratio (OCR), 2) determination of potential soil liquefaction, 3) prediction of foundation settlement, 4) evaluation of piles bearing capacity, 5) prediction of compaction parameters for cohesive soils, 6) compaction control of embankments built of cohesionless soils. The problems presented are based on the applications of the Multi-Layered Perceptron (MLP) neural networks. [ABSTRACT FROM AUTHOR]

As indicated by the profile of overconsolidation ratio (OCR), the stress history of a soil deposit is one of the dominant factors that influence the engineering behavior of soils. A commonly used method to obtain the parameter is the laboratory oedometer test, which is of low accuracy and time consuming because of inevitable sample disturbance. These difficulties can be overcome by in situ pizeocone penetration test, which provides continuous measurement of cone resistance, sleeve friction, and pore water pressure induced during the penetration. Though many methods have been proposed to estimate the preconsolidation pressure and overconsolidation ratio of clay deposits, their validity still needs to be proved. In this study, existing empirical methods for interpreting stress history of clays through piezocone tests are briefly reviewed. It is shown that regional correlations are valid. Piezocone tests utilizing a Vertek-Hogentogler CPTU truck that have been completed at different sites in the Jiangsu province of China. Existing correlations are compared with these field test data. It is shown that the correlation based on normalized net tip resistance is pretty accurate for determining the overconsolidation ratio of Quaternary clay deposits. [ABSTRACT FROM AUTHOR]

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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]