Thesis (M.S. in civil engineering)--Washington State University, August 2009. / Title from PDF title page (viewed on Aug. 10, 2009). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 45-46).

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The calculation of a consolidation settlement is an important problem encountered in the foundation of buildings. Due to need for simplicity engineers are mainly using the one dimensional theory of Terzaghi for calculations of consolidation settlements with time. Consolidation tests are still performed in most laboratories with the traditional oedometer cell. Although the results of the oedometer can provide relatively reliable results, they are not equally effective for the calculation of the rate of consolidation. This primarily because of the inability of the oedometer cell to obtain full saturation of the sample. To ensure full saturation, back pressure must be applied which is not possible for conventional oedometer cell. The alternative use of the triaxial cell to examine the consolidation behavior of soils is discussed here.

This research provides an insight into the quality of a soil sample during the penetration of a soil sampler. The investigation of the mechanical disturbances in a clay soil is conducted by using an updated Lagrangian finite element formulation with the 2nd Piola-Kirchhoff stress rate (the Truesdell stress increment) to account for the large deformation behavior near the sampling tube. The penetration of the sampler is simulated by spliting a group of nodes ahead of the penetration route up to a sufficient depth and applying incremental deformation to match the geometric configuration of the sampling tube. Consolidation effect is included to account for the rate of penetration. Thin-layer elements are added into the inside wall of the sampling tube to model the soil-sampler interface. The modified Cam-clay model is used to simulate the behavior of the soils. An experimental study was conducted to study the variations of stresses and pore water pressures at the soil-sampler interface. The numerical results show that (1) soil samples are subjected to three distinct stages of vertical strain history, compression-extension-recompression. The first stage of compression, in particular, causes irrecoverable changes in the virgin soil properties of the soil; (2) the undrained shear strength of a disturbed sample reconsolidated to the in situ stress condition is larger than the virgin soil for normally consolidated soils but it is smaller for over consolidated soils; (3) the sampling disturbances due to friction at the soil-sampler interface increase as the sampler penetrates the soil. As a result, long samples will be seriously degraded; (4) the increase of the rate of penetration can reduce the degree of disturbances; (5) the piston sampler induces much larger disturbances than the open-drive sampler.

The research presented in this thesis focuses on the spatial variability of the Keswick and Hindmarsh Clays within the Adelaide city area. Keswick Clay is locally significant since many of Adelaide's multi-storey buildings are founded directly on it, and internationally significant, since it has been shown by Cox (1970), that this clay exhibits remarkably similar properties to those of the well-documented London Clay. The assessment of the small-scale variability of the undrained shear strength of these clays is based on measurements obtained using the electrical cone penetration test (CPT), and a micro-computer based data acquisition system, designed specifically for this study. A significant feature of the data acquisition system is that it enables measurements to be obtained at intervals of 5 mm, both reliably and efficiently. The development of the data acquisition system is discussed, and the accuracy of its measurements is examined. The small-scale variability of the undrained shear strength of the Keswick Clay is based on more than 200 vertical CPTs, performed within an area of 50 X 50 metres at a site located in the Adelaide city area. The CPTs were spaced at lateral intervals varying between 0.5 and 5 metres, with each vertical CPT extending to a typical depth of 5 metres. In addition, the small-scale horizontal spatial variability of the Keswick Clay is examined using an electrical cone penetrometer driven horizontally into the face of an embankment, again located within the Adelaide city area. The accuracy of the CPT measurements is examined, and discussion is given of the shortcomings associated with a commonly used technique, by Baecher (1982), for estimating the random measurement error associated with various test procedures. The assessment of the large-scale spatial variability of the undrained shear strength of the Keswick and Hindmarsh Clays is founded on a data base of geotechnical engineering properties, compiled from a number of consulting engineering practices and government instrumentalities. The data base, known as KESWICK, contains approximately 160 site investigations, 380 boreholes, and 10,140 measurements obtained from a number of different laboratory and in situ tests. In addition, KESWICK is used to establish generalised trends and bounds, associated with the various geotechnical engineering design properties contained within the data base. The techniques of random field theory and geostatistics are used to quantify, model and predict the spatial variability of the Keswick and Hindmarsh Clays. These techniques are compared with one another in order to assess the suitability and shortcomings of each, when applied to the study of the spatial variability of geotechnical engineering materials. Furthermore, a number of specifically-written computer programs, which were developed to enable the various spatial variability analyses to be performed, are discussed. It is demonstrated that the lateral undrained shear strength of the Keswick Clay, within the Adelaide city area, exhibits a nested structure; that is, one which is the compound effect of several genetic sources of spatial variation. In addition, it is shown that this nested structure can be adequately modelled by means of a spherical semivariogram model. The nested structure is used, together with the kriging estimation process, to provide preliminary estimates of the undrained shear strength of the Keswick Clay, within the Adelaide city area. The analyses demonstrate that the nested model and the kriging process provide a useful facility for generating preliminary estimates of the strength of the clay. Finally, the significance of the spatial variability of the undrained shear strength of clay soils is examined, with reference to the design of embankments and pile foundations. It is demonstrated that the correlation distance can greatly influence the design of each of these geotechnical systems. / Thesis (Ph.D.)--Dept. of Civil and Environmental Engineering, 1995.

Graduation date: 1998

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Spatial variability is all that stands between hydrology and science, forcing us to deal in probabilities and averages. Because of scale, we can not consider forces on individual soil particles, water molecules and solute ions when addressing human size problems. We must therefore look at aggregate properties and mean values for parameters and inputs in computer modeling of hydrologic phenomena. This research explores the impact of spatially variable inputs on the Water Erosion Prediction Project soil erosion computer program. Distributions of input variables are generated and assigned randomly to a grid of homogeneous rangeland hillslope elements. Values for runoff volume and sediment loss from each flow path are recorded and averaged to provide a distribution of outputs in the form of a sensitivity analysis. Variabilities of slope, slope length, soil textures, soil characteristics, terrain, convex and concave slopes, soil saturation, rainfall amount and vegetation were examined. Results show that use of mean inputs values in the WEPP representative hillslope model yields very similar outputs to the spatially variable research model using a distribution of inputs in all simulations in the case of totally random bare rangeland soils. When a decreasing trend in soil clay content is introduced in the variable model, the hillslope model using average values as inputs no longer provides a good estimate of the sediment loss. When random vegetation is generated and added to the simulation, runoff volume continues to be similar between the two models, but the sediment loss is much higher in the spatially variable model. In addition, the results of the standard hillslope model are much less responsive to changes in slope than those of the spatially variable model. It is concluded that spatial variability of soils must be considered when there is a linear change in input values with slope position. Likewise spatial variability of vegetation needs to be addressed in order to accurately estimate erosion on the rangeland watersheds considered in this dissertation. It is also found that this type of simulation provides a model for sensitivity analysis of a complex computer programs. Physically related inputs can be generated in such a way as to preserve the desired interrationships and distributions of inputs can be directly compared to generated distributions of outputs.

published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy

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