Petroleum exploration and production in recent years have moved into increasingly deeper water off the continental shelf. Some of these facilities are anchored in water depths in excess of 1000 meters. Exploration and production in deep water present new technological challenges where traditional fixed platforms have given way to floating structures. Today suction caissons are the most commonly used anchorage system for permanent offshore oil production facility. The objective of this study is to numerically predict the ultimate capacity of suction caissons in normally consolidated and lightly overconsolidated clays. Representative soil profile from the Gulf of Mexico and the North Sea are taken and analyzed for suction caissons with length over diameter ratios of 2, 4, 6 & 8. Normalized failure load interaction diagrams are generated for each of the cases. The location of optimum attachment point is also reported for each of the cases. General purpose finite element computer program ABAQUS is used for the numerical prediction. The finite element study is carried out with three-dimensional models using hybrid elements. A simplified elastic perfectly plastic model with von-Mises yield criterion is used for the study. The saturated clay is treated as an incompressible material. Results of the study compares well with existing simplified method for estimating load capacity of suction caisson anchors.

Petroleum exploration and production in recent years have moved into increasingly deeper water off the continental shelf. Some of these facilities are anchored in water depths in excess of 1000 meters. Exploration and production in deep water present new technological challenges where traditional fixed platforms have given way to floating structures. Today suction caissons are the most commonly used anchorage system for permanent offshore oil production facility. The objective of this study is to numerically predict the ultimate capacity of suction caissons in normally consolidated and lightly overconsolidated clays. Representative soil profile from the Gulf of Mexico and the North Sea are taken and analyzed for suction caissons with length over diameter ratios of 2, 4, 6 & 8. Normalized failure load interaction diagrams are generated for each of the cases. The location of optimum attachment point is also reported for each of the cases. General purpose finite element computer program ABAQUS is used for the numerical prediction. The finite element study is carried out with three-dimensional models using hybrid elements. A simplified elastic perfectly plastic model with von-Mises yield criterion is used for the study. The saturated clay is treated as an incompressible material. Results of the study compares well with existing simplified method for estimating load capacity of suction caisson anchors.

Liquefaction of sandy soil has been observed to cause significant damage to infrastructure during major earthquakes. Historical cases of liquefaction have typically occurred in sands containing some portion of fines particles, which are defined as 75μm or smaller in diameter. The effects of fines on the undrained behaviour of sand are not however fully understood, and this study therefore attempts to quantify these effects through the undrained testing of sand mixed with non-plastic fines sourced from Christchurch, New Zealand. The experimental program carried out during this study consisted of undrained monotonic and cyclic triaxial tests performed on three different mixtures of sand and fines: the Fitzgerald Bridge mixture (FBM), and two Pinnacles Sand mixtures (PSM1 and PSM2). The fines content of each host sand was systematically varied up to a maximum of 30%, with all test specimens being reconstituted using moist tamping deposition. The undrained test results from the FBM soils were interpreted using a range of different measures of initial state. When using void ratio and relative density, the addition of fines to the FBM sand caused more contractive behaviour for both monotonic and cyclic loadings. This resulted in lower strengths at the steady state of deformation, and lower liquefaction resistances. When the intergranular void ratio was used for the interpretation, the effect of additional fines was to cause less contractive response in the sand. The state parameter and state index were also used to interpret the undrained cyclic test results – these measures suggested that additional fines caused less contractive sand behaviour, the opposite to that observed when using the void ratio. This highlighted the dependency on the parameter chosen as a basis for the response comparison when determining the effects of fines, and pointed out a need to identify a measure that normalizes such effects. Based on the FBM undrained test results and interpretations, the equivalent granular void ratio, e*, was identified from the literature as a measure of initial state that normalizes the effects of fines on the undrained behaviour of sand up to a fines content of 30%. This is done through a parameter within the e* definition termed the fines influence factor, b, which quantifies the effects of fines from a value of zero (no effect) to one (same effect as sand particles). The value of b was also determined to be different when interpreting the steady state lines (bSSL) and cyclic resistance curves (bCR) respectively for a given mixture of sand and fines. The steady state lines and cyclic resistance curves of the FBM soils and a number of other sand-fines mixtures sourced from the literature were subsequently interpreted using the equivalent granular void ratio concept, with bSSL and bCR values being back-calculated from the respective test data sets. Based on these interpretations, it was concluded that e* was conceptually a useful parameter for characterizing and quantifying the effects of fines on the undrained behaviour of sand, assuming the fines influence factor value could be derived. To allow prediction of the fines influence factor values, bSSL and bCR were correlated with material and depositional properties of the presented sand-fines mixtures. It was found that as the size of the fines particles relative to the sand particles became smaller, the values of bSSL and bCR reduced, indicating lower effect of fines. The same trend was also observed as the angularity of the sand particles increased. The depositional method was found to influence the value of bCR, due to the sensitivity of cyclic loading to initial soil fabric. This led to bSSL being used as a reference for the effect of fines, with specimens prepared by moist tamping having bCR > bSSL, and specimens prepared by slurry deposition having bCR < bSSL. Finally the correlations of the fines influence factor values with material and depositional properties were used to define the simplified estimation method – a procedure capable of predicting the approximate steady state lines and cyclic resistance curves of a sand as the non-plastic fines content is increased up to 30%. The method was critically reviewed based on the undrained test results of the PSM1 and PSM2 soils. This review suggested the method could accurately predict undrained response curves as the fines content was raised, based on the PSM1 test results. It also however identified some key issues with the method, such as the inability to accurately predict the responses of highly non-uniform soils, a lack of consideration for the entire particle size distribution of a soil, and the fact the errors in the prediction of bSSL carry through into the prediction of bCR. Lastly some areas of further investigation relating to the method were highlighted, including the need to verify the method through testing of sandy soils sourced from outside the Christchurch area, and the need to correlate the value of bCR with additional soil fabrics / depositional methods.

Liquefaction is a phenomenon that occurs in loose saturated sand deposits that are subjected to earthquake loading. This phenomenon can cause massive displacements and significant destruction. Many methods for mitigating liquefaction have been proposed and investigated including compaction, drainage, and grouting. One such liquefaction mitigation technique involves the addition of bentonite fines to the pore spaces of a loose, saturated sand via permeation of an engineered clay suspension. This method of soil improvement has provided the basis and motivation for this research. Also, the effect of plastic and non-plastic fines on the static and cyclic response of sands is somewhat contradictory throughout the literature. Thus, the primary objective of this study was to characterize the affect of an engineered bentonite pore fluid on the undrained monotonic response of loose, saturated Ottawa sand in order to determine its feasibility for use as an effective method for liquefaction mitigation. The permeation of engineered bentonite suspensions is proposed as a passive site remediation technique. Thus, the suspensions were delivered to loose Ottawa sand specimens in the laboratory by permeation in a newly designed three-way split mold. This split mold was used to create easily tested specimens that would have an initial soil fabric similar to that expected after permeation in the field. The bentonite suspensions were treated with sodium pyrophosphate to reduce the initial yield stress and viscosity in order to allow for permeation. Three different bentonite suspensions were utilized throughout this study each having different properties and delivering slightly different amounts of bentonite to the loose, saturated sand. The affect of this engineered pore fluid on the undrained shear response of loose, saturated Ottawa sand was compared to the undrained shear response of clean sand and dry-mixed sand and bentonite. The specimen preparation method (dry-mixed or permeated) was shown to have a significant effect on the response of the sand specimens. While the dry-mixed specimens produced larger and more sustained positive pore water pressures than the clean sand (resulting in an increased tendency to flow), the permeated specimens showed a marked decrease in the generation of excess pore water pressures, displayed a more dilative response, and thus resulted in a soil structure that was less likely to flow. Finally, the results of tests on specimens permeated with engineered bentonite suspensions show that there is little to no change in the effective friction angle at critical state. A method for effectively testing permeated soil specimens was developed in this study. This method has laid the framework for further investigations into the use of engineered bentonite suspensions for liquefaction mitigation by permeation grouting. / text

[Abstract]The bearing capacity of foundations is a fundamental problem in geotechnical engineering. For all structures placed on a soil foundation, geotechnical engineers must ensure that the soil has sufficient load carrying capacity so that the foundation does not collapse or become unstable under any conceivable loading. The ultimate bearing capacity is the magnitude of bearing pressure at which the supporting ground is expected to fail in shear, i.e. a collapse will take place.During the last fifty years various researchers have proposed approximate techniques to estimate the short term undrained bearing capacity of foundations. The majority of existing theories are not entirely rigorous and contain many underlying assumptions. As a consequence, current design practices include a great deal of empiricism. Throughout recent decades, there has also been a dramatic expansion in numerical techniques and analyses, however, very few rigorous numerical analyses have been performed todetermine the ultimate bearing capacity of undrained soils.In this study, finite element analysis has been used to analyse a range of bearing capacity problems in undrained soil. The numerical models account for a range of variablesincluding footing size, shape, embedment depth, soil layering and undrained bearing capacity of footings on slopes.By using the powerful ability of computers a comprehensive set of solutions have been obtained therefore reducing the uncertainties apparent in previous solutions.

No description available.

Geotechnicans in Sweden and rest of Scandinavia have a wide experience of stability calculations in cohesive soils. The two main parameters for this type of calculations are the undrained shear strength and the preconsolidation pressure. The most common methods in Sweden to determine the undrained shear strength in field is the vane shear strength test and CPT-test, in laboratories the fall cone test is well used. To determine the preconsolidation pressure CRS-analyses are well used. For more accurate measurements the odeometer tests are more suitable. However this method is both expensive and time-consuming form of analysis from a commercial aspect. Therefore is different correlation equations used as a compliment in these different stability evaluations.  This research will focus on the empirical Hansbo Correlation and its relation to results from commercial surveys. The commercial data come from Atkins Sverige’s project data base. The results after comparing Hansbo correlation with the commercial data showed on a significant divergence, which indicate a great unsureness of the Hansbo correlation. As a result of this contingency it is of importance to take cautiousness in the use of empirical correlations in stability calculations.

A presente pesquisa apresenta resultados de uma série de ensaios de palheta de laboratório, com a finalidade de determinar a resistência não drenada de um solo residual compactado. Durante o ensaio foram realizadas medições continuas de sucção com uso de um tensiômetro de alta capacidade, disposto na base dos corpos de prova, sendo este procedimento inédito. O objetivo secundário do estudo é a avaliação de aspectos relacionados com a variação da resistência e sucção quando a distância do tensiômetro de alta capacidade é modificada com relação à superfície inferior do plano de ruptura pré-estabelecido. Para a realização destes experimentos foram modificados e adaptados equipamentos de laboratório. O estudo foi realizado com um solo residual de gnaisse compactado obtido do antigo campo experimental da Escola Politécnica da Universidade de São Paulo. O estudo constata que o valor medido da resistência não drenada é afetado pela proximidade do tensiômetro a palheta. / This research presents results of a series of mini-vane tests in order to determine the undrained shear strength of a residual compacted soil. During the tests and for the first time, continuous measurement of suction has been made using a high capacity tensiometer placed at the base of the specimen. The secondary aim of this study is to evaluate aspects related to resistance and suction variation when the distance of the high capacity tensiometer is modified in relation to the lower pre-set failure surface. For this reason laboratory equipments were modified and adapted in order to perform the study. The tests were performed with a compacted residual soil of gneiss obtained from the experimental site of the Polytechnical School of the University of São Paulo. The study showed that the undrained shear strength is affected when the vane are closer to the tensiometer.

A presente pesquisa apresenta resultados de uma série de ensaios de palheta de laboratório, com a finalidade de determinar a resistência não drenada de um solo residual compactado. Durante o ensaio foram realizadas medições continuas de sucção com uso de um tensiômetro de alta capacidade, disposto na base dos corpos de prova, sendo este procedimento inédito. O objetivo secundário do estudo é a avaliação de aspectos relacionados com a variação da resistência e sucção quando a distância do tensiômetro de alta capacidade é modificada com relação à superfície inferior do plano de ruptura pré-estabelecido. Para a realização destes experimentos foram modificados e adaptados equipamentos de laboratório. O estudo foi realizado com um solo residual de gnaisse compactado obtido do antigo campo experimental da Escola Politécnica da Universidade de São Paulo. O estudo constata que o valor medido da resistência não drenada é afetado pela proximidade do tensiômetro a palheta. / This research presents results of a series of mini-vane tests in order to determine the undrained shear strength of a residual compacted soil. During the tests and for the first time, continuous measurement of suction has been made using a high capacity tensiometer placed at the base of the specimen. The secondary aim of this study is to evaluate aspects related to resistance and suction variation when the distance of the high capacity tensiometer is modified in relation to the lower pre-set failure surface. For this reason laboratory equipments were modified and adapted in order to perform the study. The tests were performed with a compacted residual soil of gneiss obtained from the experimental site of the Polytechnical School of the University of São Paulo. The study showed that the undrained shear strength is affected when the vane are closer to the tensiometer.

The objective of the present study was to develop a fluid flow-coupled distinct element model capable of capturing the undrained behaviour of granular soils by considering fundamental physical mechanisms that involve fluid flow and particle interaction. The method considers granular media as assemblies of ellipsoidal particles arranged on a plane and interacting by means of contact forces. Saturation effects are incorporated by assuming that particles are immersed in fluid, the flow of which is simulated as occurring through a network of conduits. The flow through conduits is according to a Hagen-Poiseuille relation; a transient solution is obtained by solving a system of differential equations. The developed fluid-flow coupled distinct element was used to conduct various numerical simulations and the mechanisms of undrained deformations were examined from a micromechanical point of view. The dissertation begins with a literature review on the undrained behaviour of granular materials as observed in laboratory experiments. A review of previous attempts to simulate undrained tests micromechanically is also presented, and the advantages and disadvantages of various methods are examined. The capability of the developed model to simulate two-dimensional fluid-flow and pressure dissipation problems is demonstrated by means of comparisons with analytical solutions. Fluid pressure dissipation problems are qualitatively compared with Terzaghi's one-dimension theory of consolidation. It is shown that transient flow problems are accurately modelled by the fluid flow network approach. Simulated compression tests were carried out to examine the effects of different confining pressures and initial densities on the macroscopic response. The results compare favorably with those commonly observed in undrained laboratory experiments. Simulated tests are analyzed from a micromechanical point of view. It is shown that macroscopic behaviour can be traced to changes in micromechanical fabric descriptors. The effects of the interparticle friction angle on the undrained behaviour of the assemblies are investigated. The undrained strength is considerably increased by increasing interparticle friction. The main mechanism found to be responsible for the development of higher strength is the tendency of the specimens to dilate during shear distortion. The effects of the principal stress direction on the macroscopic response are examined. The behaviour of initially anisotropic samples is significantly altered by the direction of the principal stresses relative to the anisotropy direction. It is demonstrated that macroscopic permeability of the media has a considerable effect on the strength. This behaviour is attributed to the inhomogeneity of pore pressure distributions which increases with decreased permeability. The results presented are generally in agreement with observations previously reported from laboratory experiments. The possible applications of the model for future research are also discussed.