The general principles of continuum mechanics such as conservation of mass, conservation of momenta, first and second law of thermodynamics are applicable to all materials irrespective of their internal constitutions. These principles alone do not provide sufficient equations to obtain solutions for any boundary value problems. The additional equations are provided by the constitutive laws. There are many groups of constitutive theories. Of them, the theory of plasticity describes rate independent nonlinear and inelastic behavior of materials. A plasticity-based constitutive law is proposed herein for geological materials. The model, however, may also be used for other frictional materials. A generalized approach is followed in formulating the proposed constitutive model. The technique can be used to construct plasticity-based constitutive models for any other materials. A series of laboratory tests are performed on cubical soil specimens using a truly triaxial testing device. The testing device is such that the samples can be subjected to a general three-dimensional state of stress. The test data is used to determine the material constants associated with the proposed constitutive model. The model is then verified by back-predicting the stress-strain curves obtained from the laboratory. As a final step, the proposed constitutive model is implemented into a three-dimensional finite element procedure. A number of boundary value problems are analyzed using the proposed model. The results are compared with the observation. It is found that the proposed model can effectively characterize the nonlinear and inelastic response of frictional materials. Although the proposed model is investigated with respect to soils, it can also be applied for concrete, rocks, etc.

A study of soil variability was performed on an 87 hectare area within a uniform mapping unit--Pima Clay loam-- at The University of Arizona Branch Experiment Station at Marana. The primary interest was with respect to soilwater parameters. From 36 sites selected by an unbalanced three-stage nested design, 180 core samples were collected at 30 cm depth intervals to 150 cm. In addition, 500 bulk samples were taken at the 60 cm depth on an equally spaced grid over a secondary sampling area of 96 by 76 meters. The measured parameters showed different patterns of spatial variation. For example, to estimate means within 10% for the 30 cm depth 5, 51, and 1,011 samples would be needed for bulk density, the porosity index, and the saturated hydraulic conductivity, respectively (using the 0.05 level of significance). Most of the other estimates for number of samples required were in a range of 50 to 100. Most coefficients of variation were between 10 and 50% with bulk density lower and saturated hydraulic conductivity higher. Variance components for the three stages obtained from the analysis of variance revealed that the variation among fields was smaller than within fields and sections for the majority of the measured parameters, their average relative contribution to the total variance being 25, 44, and 31%, respectively. Values of 15-bar moisture retention corresponding to the 500 bulk samples showed a frequency distribution close to the normal with a slight tendency toward skewness. Values of bulk density were normally distributed at each depth and on the combined 180 samples. The highly skewed distributed values of the saturated hydraulic conductivity proved to be normally distributed after a logarithmic transformation. The porosity index showed a nonconsistent distribution pattern at the different depths and a moderately skewed frequency distribution for the composite 180 samples. Close relationships were found between bulk density and per cent sand and silt. A highly significant correlation (significant at th 0.01 level) between 15-bar water retention and clay content existed. Values of the logarithm of the hydraulic conductivity showed a high degree of correlation with values of per cent pores drained at 50 millibars (correlation coefficients of high absolute values and significant at the 0.01 level). Particle size distribution exhibited a decrease of silt and clay and a corresponding increase of sand with depth. The average percentages of sand, silt, and clay at 30 cm depth were 23.3, 41.2, and 35.3, and at the 150 cm depth were 39.7, 35.6, and 24.7, respectively. A similar trend was revealed for bulk density which ranged from 1.42 at 30 cm depth to 1.57 g/cm³ at the 150 cm depth. Soil moisture release curves for each depth showed similar general shapes. The "porosity index" describing the moisture release curve in the low pressure range varied from 3.58 at 30 cm depth to 5.79 at the 150 cm depth. Mean values of the saturated hydraulic conductivity also tended to increase with depth--1.71 and 7.03 cm/hr at 30 and 150 cm depth, respectively. Comparison between the sampling scheme used and three-stage balanced designs revealed that at least two alternatives would be more effective in decreasing the variance of the mean, but they do not provide any degrees of freedom for the third stage. An apparent compromise was found to exist between the scheme used and the optimum unbalanced designs selected for efficient estimation of variance components for the majority of the measured parameters.

The main weakness of soil is its inability to resist tensile stresses. Civil engineers have been trying to address this problem for decades. To increase the tensile and shear strengths of soil, different methods of reinforcing such as using geosynthetics have been used in different types of earth structures such as retaining walls, earth dams, slopes, etc. Due to the excellent corrosion resistance of polymers, the use of geosynthetics has increased dramatically in recent years. However, there are some significant problems associated with geosynthetics, such as creep and low modulus of elasticity. In this research, a new Geo-Composite which is made of Carbon Fiber Reinforced Polymer (CFRP) is used to overcome some of the short comings of the existing geosynthetics. The new Geo-Composite has all the benefits of the geotextiles plus higher strength, higher modulus and no creep. In first part of the investigation, over eighty experiments were carried out using direct shear test. The interface properties of the Geo-Composite (CFRP) and fine sand were investigated. Tests showed that the interface shear behavior between Geo-Composite and fine sand depended on the normal forces during the curing of epoxy and curing age of epoxy. The two methods used to prepare the specimen are pre-casting and casting in place, and the results of these two methods are compared. In the second part of the investigation, the pull-out test device was designed and assembled using a triaxial loading device and a direct shear device. In the pull-out test, the normal force applied by the triaxial loading and pull out force is applied by a direct shear device. CFRP samples were prepared in the lab, and pre-cast and cast-in-place samples were tested using fine sand. The pull-out force and corresponding displacements of each of the materials were recorded and compared. In the third part of the investigation, the behavior of the interface between coarse sand and modified CFRP has been studied in larger scale using a device known as Cyclic Multi Degree of Freedom (CYMDOF) device. A constitutive Model, Hierachical Single Surface (HISS) model, is used to characterize the behavior of the interfaces. The constitutive model is verified by predicting the laboratory behavior of interface. In the forth part of the investigation, using the laboratory test data results, a finite element procedure with the hardening model is used to simulate field behavior of a CFRP reinforced earth retaining wall, and compare the results with a geotextile reinforced earth retaining wall. This section shows the advantages and disadvantages of using CFRP in MSE walls.

A field test is developed to assess the collapse susceptibility of soils rapidly and inexpensively. The in situ collapse test device measures the vertical deformations which occur in soils when they are subjected to stress and given access to water while under continuous load. Principles of statistics were employed to show that laboratory testing of soil specimens overestimate the magnitude of collapse as measured in the field and that the magnitude of collapse is, in part, a function of the soil moisture content at the time of loading and at the time of collapse. Good correlation was found between the spatial variability of collapsible soils with the location of alluvium terrace deposits and structurally damaged buildings.

Call number: LD2668 .T4 1986 L39 / Master of Science / Agronomy

No description available.

Uma solução computacional geral e expansível de análise da interação estrutura-maciço de solos foi desenvolvida adotando metodologia orientada a objetos. A técnica computacional apresenta um menu de retaguarda que torna a manipulação dos dados de entrada e os processos computacionais mais criteriosos e seguros. Os materiais possuem comportamento perfeitamente elástico-linear, enquanto o mecanismo de transferência de carga estrutura-solo é não linear. O maciço de solos é modelado através de dados de sondagens SPT e mapeamento geotécnico. A fundação é discretizada verticalmente para se obter as matrizes de flexibilidade da estrutura de fundação (MFEF) e do maciço de solos (MFMS). O processo interativo básico consiste em obter o vetor de recalques nos apoios pelo produto do vetor de cargas verticais com as matrizes MFEF e MFMS. Na seqüência, calcula-se o vetor de redistribuição de cargas pelo produto do vetor de recalques com a matriz de rigidez da superestrutura (MRS). Um procedimento iterativo condiciona a convergência de recalques e cargas verticais nos apoios. A solução foi utilizada para analisar o comportamento de edifícios de diferentes geometrias em planta e espacial, variando o perfil geotécnico do maciço suporte e a técnica de execução da estrutura de fundação. / A general and expansible computational code based in the oriented to object programming technique was developed aiming the soil-structure interaction analysis. This computational technique has a special feature that makes the data input operations and the computer processing safer and more criterious. This model considers that all materials behaves as perfectly linear elastic materials, although the soilstructure transfer mechanism is of non-linear nature. The soil mass compressibility and resistance are modelled from soil data obtained from geotechnical mapping techniques and SPT boreholes data. The flexibility matrix (MFEF) of the structural foundation elements and the flexibility matrix (MFMS) of soil mass elements are obtained through a numerical discretization procedure. The basic interative process consists in the calculation of the supports displacement vectors obtained by the multiplication of the vertical load vector by the MFEF and the MFMS matrix. Finally, the load redistribution is obtained by the multiplication of the displacement vector by the structural rigidity matrix (MRS). The uniqueness of the solution is guaranteed by the convergence of the displacements and vertical supports reactions by using an iterative procedure. This computational code was applied to the analysis of the behaviour of spatial framed buildings with varied geometry, taking into account different geotechnical soil conditions and different types of foundations.

The understanding of the spatial distribution of lead (Pb) in soil is important in the assessment of potential risks and development of remediation strategies for Pb contaminated land. In situ heterogeneity of Pb was measured at two heavily contaminated sites in the United Kingdom using the Portable X-ray Fluorescence Spectrometer (P-XRF) over a range of spatial scales (0.02 to 50 m). The pattern of the distribution of Pb was very variable, and when expressed as heterogeneity factor (HF), it ranged from 1.2 to 3.2 (highly heterogeneous). The effect of such Pb heterogeneity on plant uptake was investigated in greenhouse pot trials. Two earlier pot trials, which assessed the effect of Pb in a fixed concentration (1000 mg/kg) and in a range of concentration (100 to 10000 mg/kg) found a significant effect of the Pb added treatments, when compared to a control treatment (0 mg/kg Pb added). Biomass and uptake varied by 20 to 100% within and between 16 species/varieties. Results enhanced the selection of two species (Brassica napus and Brassica juncea) for further pot trials. A third pot experiment with Brassica napus and Brassica juncea in simplistic binary model of heterogeneity found 20 to 60% lower uptake in the binary treatment, than homogeneous the treatment. Biomass was higher by 10 to 50% in Brassica juncea and 20 to 40% lower for B. napus in the bianary treatment, when compared to the homogeneous and control treatments. The effect of a more realistic in situ heterogeneity on plant uptake was investigated in a further pot trial, which simulated low (LH), medium) (MH) and high (HH) heterogeneity treatments, compared to a homogeneous (HO) treatment. It detected a significant (P < 0.05) impact of heterogeneity on biomass and uptake between treatments and species. Four to five fold lower biomass were recorded in HH treatment, when compared to the HO treatment. Shoot and root uptake in (mg/kg) concentration increased with increasing heterogeneity with peak uptake (twice as high as HO treatment) in LH for B. napus and in HH and MH treatments for B. juncea respectively. Shoot and root Pb masses in (μg) were maximum in HO and MH treatments respectively with 50 to 70% lower Pb mass in the HH treatment. Results showed that response to heterogeneity is species specific. A sub-experiment explored the behaviour of plant roots in HH treatment and found 20 to 80% variation in root biomass between concentric patches with same nominal soil Pb concentrations. This provided insights into varied responses of these species to realistic Pb heterogeneity. The research demonstrated that the presence and extent of in situ heterogeneity of Pb in soil plays an important role in Pb uptake by plants. It also showed that the homogeneous and simplistic binary model of heterogeneity do not give reliable estimates of plant growth and Pb uptake in realistic field conditions. This work has implications for improving the efficiency of phytoremediation of Pb contaminated land, phytomining, reliability of risk assessment and models of human exposure to Pb.

Heterogeneity of contaminants in soils can vary spatially over a range of scales, causing uncertainty in environmental measurements of contaminant concentrations. Sampling designs may aim to reduce the impact of on-site heterogeneity, by using composite sampling, increased sample mass and off-site homogenisation, yet they could overlook the small scale heterogeneity that can have significant implications for plant uptake of contaminants. Moreover, composite sampling and homogenisation may not be relevant to target receptor behaviour, e.g. plants, and studies, using simplistic models of heterogeneity have shown that it can significantly impact plant uptake of contaminants. The alternative approach, to accept and quantify heterogeneity, requires further exploration as contaminant heterogeneity is inevitable within soils and its quantification should enable improved reliability in risk assessment and understanding variability in plant contaminant uptake. This thesis reports the development of a new sampling design, to characterise and quantify contaminant heterogeneity at scales, from 0.02m to 20m, using in situ measurement techniques, and 0.005m to 0.0005m, using ex situ techniques. The design was implemented at two contaminated land sites, with contrasting heterogeneity based upon historic anthropogenic activity and showed heterogeneity varying between contaminants and at different spatial scales, for Pb, Cu and Zn. Secondly, this research demonstrates how contaminant heterogeneity measured in situ can be recreated in a pot experiment, at a scale specific to the plant under study. Results, from 4 different plant species, demonstrated that existing simplistic models of heterogeneity are an inadequate proxy for plant performance and contaminant uptake under field conditions, and significant differences were found in plant contaminant concentrations between simplistic models and those based upon actual site measurements of heterogeneity. Implications of heterogeneity on plant roots were explored in the final experiment showing significant differences in root biomass between patches of differing contaminant concentrations.

No description available.