In the past few decades, demand for construction in underground spaces has increased dramatically in urban areas with high population densities. However, the impact of the construction of underground structures on surrounding infrastructure raises concerns since movements caused by deep excavations might damage adjacent buildings. Unfortunately, the prediction of geotechnical behaviour is difficult due to uncertainties and lack of information of on the underground environment. Therefore, to ensure safety, engineers tend to choose very conservative designs that result in requiring unnecessary material and longer construction time. The observational method, which was proposed by Peck in 1969, and formalised in Eurocode 7 in 1987, provides a way to avoid such redundancy by modifying the design based on the knowledge gathered during construction. The review process within the observational method is recognised as back analysis. Supervised learning can aid in this process, providing a systematic procedure to assess soil parameters based on monitoring data and prediction of the ground response. A probabilistic model is developed in this research to account for the uncertainties in the problem. Sequential Bayesian inference is used to update the soil parameters at each excavation stage when observations are available. The accuracy of the prediction for future stages improves at each stage. Meanwhile, the uncertainty contained in the prediction decreases, and therefore the confidence on the corresponding design also increases. Moreover, the Bayesian method integrates subjective engineering experience and objective observations in a rational and quantitative way, which enables the model to update soil parameters even when the amount of data is very limited. It also allows the use of the knowledge learnt from comparable ground conditions, which is particularly useful in the absence of site-specific information on ground conditions. Four probabilistic models are developed in this research. The first two incorporate empirical excavation design methods. These simple models are used to examine the practicality of the approach with several cases. The next two are coupled with a program called FREW, which is able to simulate the excavation process, still in a relatively simplistic way. The baseline model with simple assumptions on model error and another one is a more sophisticated model considering measurement error and spatial relationships among the observations. Their efficiency and accuracy are verified using a synthetic case and tested based on a case history from the London Crossrail project. In the end, the models are compared and their flexibility in different cases is discussed.

O problema de identificação de parâmetros consiste em se determinar parâmetros que minimizem a diferença entre valores medidos e calculados de determinadas grandezas. Certamente, essa identificação é realizada para parâmetros que apresentam razoável grau de incerteza nos seus valores. Neste trabalho apresentam-se os principais conceitos e fundamentos matemáticos envolvidos no assunto, desenvolve-se um procedimento de identificação de parâmetros com base matemática sólida e aplica-se esse procedimento em problemas de interesse prático da engenharia. São estudados o Túnel de Hudvudsta e a barragem de Machadinho, nos quais são identificados parâmetros relacionados com as ações ou com as propriedades físicas dos materiais, considerando modelos hierárquicos para representar as estruturas. Utilizam-se os principais critérios de identificação para a definição das funções objetivo e métodos do tipo Newton para a minimização dessas funções. / The parameter identification problem consists of determining the values of the parameters that minimize the difference between measured and calculated values of some variables. Indeed, this identification is performed to parameters that present some uncertainty on their values. In this work the main mathematical concepts and fundaments related to back analysis are presented. A procedure for parameter identification with a consistent mathematical basis is developed and applied in practical engineering problems. The Hudvudsta tunnel and the Machadinho dam are studied to identify parameters related to loads or material physical properties by using hierarchical models to represent the structures. The objetive functions are defined with the main identification criteria and minimized with Newton´s methods.

A fundamental element of the observational method in geotechnical engineering practice is the utilization of a carefully laid out performance monitoring system which provides rapid insight of critical behavioral trends of the work. Especially in tunnels, this is of paramount importance when the contractual arrangements allow an adaptive tunnel support design during construction such as the NATM approach. Utilization of measurements can reveal important aspects of the ground-support interaction, warning of potential problems, and design optimization and forecasting of future behavior of the underground work. The term back-analysis involves all the necessary procedures so that a predicted simulation yields results as close as possible to the observed behavior. This research aims in a better understanding of the back-analysis methodologies by examining both simplified approaches of tunnel response prediction but also more complex numerical methods. Today a wealth of monitoring techniques is available for tunnel monitoring. Progress has also been recorded in the area of back-analysis in geotechnical engineering by various researchers. One of the most frequently encountered questions in this reverse engineering type of work is the uniqueness of the final solution. When possible errors are incorporated during data acquisition, the back analysis problem becomes formidable. Up to the present, various researchers have presented back-analysis schemes, often coupled with numerical methods such as the Finite Element Method, and in some cases the more general approach of neural networks has been applied. The present research focuses on the application of back-analysis techniques that are applicable to various conditions and are directly coupled with a widely available numerical program. Different methods are discussed and examples are given. The strength and importance of global optimization is introduced for geotechnical engineering applications along with the novel implementation of two global optimization algorithms in geotechnical parameter identification. The techniques developed are applied to the back-analysis of a modern NATM highway tunnel in China and the results are discussed. / Ph. D.

Soils, like several other materials, exhibit strong time-dependent behaviour which can be evidenced in terms of creep or strain-rate effects. The degree of this rheological behaviour varies with the type of soil, its structure, and with the stress history. This effect is exacerbated in pile load testing where the procedure duration tends to be shortened under increasing time pressures. The modelling needed to interpret the results therefore becomes more and more complex, including soil viscosity, wave radiation into the soil and other significant phenomena. The objective of the research reported herein is to refine the rheological parameters characterizing the influence of the loading rate within the framework of a relevant pile/soil interaction model fed with dynamic measurements acquired during pile Dynamic Load Tests (DLTs). The final goal is to predict and simulate the quasi-static pile load settlement curve. The pile/soil interaction system is described by a non-linear mass/spring/dashpot system supposed to represent the pile and the soil, with constitutive relationships existing within and between them. These relationships account for the static and the dynamic or rheologic behaviour. A back-analysis process based on a matching procedure between measured and computed quantities allows one to characterize the pile/soil interaction in terms of constitutive and rheologic parameters based on the dynamic measurements. After optimisation of the matching procedure, the parameters obtained are used to simulate the “static” load-settlement curve. The matching procedure is based on an automatic and stochastic parameter perturbation analysis. Since the parameters influence the system response with a relative weight, they are sorted in order to optimise all the parameters by successively retrieving the most influential ones and working on the remaining ones. The back-analysis performed on real dynamic measurements in this research leads to an improved pile/soil interaction model. The slippage between pile and soil along the pile shaft must be explicitly taken into account. This refinement increases the number of degrees of freedom needed to describe the pile/soil system but brings deeper insight into the behaviour of an interfacing zone of limited thickness surrounding the pile shaft.

The purpose of this study is to determine the most suitable remediation techniques via engineering geological assessment of the landslide that occurred during the construction of Artvin-Savsat Junction - Meydancik Provincial Road at Km: 12+200 in an active landslide area. For this purpose, the geotechnical parameters of the mobilized geological material which is colluvium along the sliding surface were determined by back analyses of the landslide at three geological sections. The landslide were then modeled along the most representative section of the study area by considering the landslide mechanism, the parameters determined from the geotechnical investigations, the size of the landslide and the location of the slip circle. In addition, pseudostatic stability analyses were performed comprising the earthquake potential of the site. The most suitable slope remediation technique was determined to be a combination of surface and subsurface conditions. A static analysis of the landslide shall also be performed through utilizing finite element analyses. The static analyses were compared with the inclinometer readings in the field to verify the direction of the movement. Consequently, shear strength parameters were specified as c = 0 kPa and f = 10&deg / for the landslide material and pre-stressed anchoring and rock buttressing were considered as a remediation method.

In this thesis, studies associated with the stability analyses of the box-shaped dump-site culvert constructed in Tinaz Surface Mine of Turkish Coal Enterprises (TKi) are presented. In addition, stability conditions of other culvert alternatives are evaluated. Existence of creeks in a surface mining area is a significant factor to be considered in selection of dump-site location. Since, the dumped overburden material on the valley acts as a barrier and behaves like a dam causing flood problem behind the dump-site. TKi engineers prevented the flood potential that might have occurred behind the dump-site by constructing a 480-meter long reinforced-concrete culvert on the downstream of Gevenez Creek Valley. However, considerable amount of deformations occurred in the first 100 meters of the culvert, as a result of overburden material being replaced on this structure. In order to determine the failure mechanism associated with the culvert, a series of numerical modeling analyses were carried out utilizing back analysis technique. The validity of the numerical model was justified by convergence measurements and observations carried out inside the culvert as overburden material being replaced on the stable part of this structure. Finally, based on the numerical model developed, the stability of other culvert alternatives that could be used in future projects were evaluated considering different embankment conditions (positive projecting and negative projecting), bedding conditions (impermissible, ordinary, first-class and concrete cradle), culvert shapes (box and circular) and dumping conditions.

With the purpose of studying the mechanical properties of uncompacted rockfill and the creep deformation behaviour of rockfill under a load as well as finding a suitable method for estimation of creep deformation behaviour, a full scale embankment loading experiment was performed. The results of this experiment were then evaluated. During the course of this study it became evident to the author that the deformations which were seen in the collected data from the experiment could be classified as creep deformations due to the linear decrease of the deformation against the logarithm of time and the study therefore came to focus on creep. One constitutive equation and one model for estimation of creep deformations were studied, and parameters were obtained through back analysis of experiment data as well as calculation of soil stresses. The creep model was based on a logarithmic approximation of the creep deformations and the creep equation was based on a power function. The creep model could also be simplified and evaluated as an equation and when a comparison was made between the equations and the measured results this showed that the logarithmic equation resulted in estimates closer to the measured deformations than what the power function did, therefore a logarithmic function is a better approximation to the deformations of the rockfill at Norvik than the power function. When the creep model was evaluated as intended, based on the soil stresses, the resulting creep estimates were less accurate, they was however still within the limits of what can be considered as admissible. The conclusion is that a logarithmic function describes the creep deformation of the rockfill at Norvik better than a power function and that the creep model by Kristensen is suitable for estimating the creep deformations. This since the creep model also provides a way of estimating deformations occurring under stress conditions other than the ones for which the creep test was performed.

Subsurface volume loss takes place in many geotechnical situations, and it is inherently accompanied by complex stress and displacement fields that may influence the performance of engineered geosystems. This research is a deformation-centered analysis, it depends on soil compressibility and it is implemented using finite elements. Soil stiffness plays a central role in predicting ground deformation. First, an enhanced Terzaghi’s soil compressibility model is proposed to satisfy asymptotic conditions at low and high stress levels with a small number of physically meaningful parameters. Then, the difference between small and large strain stiffness is explored using published small and large-strain stress-strain data. Typically, emphasis is placed on the laboratory-measured stiffness or compressibility; however, there are pronounced differences between laboratory measurements and field values, in part due to seating effects that prevail in small-thickness oedometer specimens. Many geosystems are subjected to repetitive loads; volumetric strains induced by drained repetitive ko-loads are experimentally investigated to identify shakedown and associated terminal density. The finite element numerical simulation environment is used to explore the effect of localized subsurface mass loss on free-surface deformation and shallow foundations settlement and bearing capacity. A stress relaxation module is developed to reproduce the change in stress associated to dissolution features and soft zone formation. The comprehensive parametric study is summarized in terms of dimensionless ratios that can be readily used for engineering applications. Field settlement data gathered at the Savannah River Site SRS are back-analyzed to compare measured values with predictions based on in situ shear wave velocity and strain-dependent stiffness reduction. The calibrated model is used to estimate additional settlements due to the pre-existing cavities, new cavities, and potential seismic events during the design life of the facility.

An imperative task for successful underground mining is to ensure the stability of underground structures, since it influences the safety, and in turn, the production capacity and economic performance of the mine. This is more so for deep excavations in soft rock which may be under significantly high stresses. In this thesis, stability studies on two tunnels, a horseshoe-shaped and an inverted arch-shaped tunnel, have been presented. The tunnels, running at a depth of 1325 m, are part of the Xiezhuang Coal Mine, in the Xinwen mining area, in China. Using the available information on stratigraphy, geological structures, in-situ stress measurements and geo-mechanical properties of intact rock and discontinuity interfaces, a three-dimensional numerical model has been built using the 3DEC 3-Dimensional Distinct Element Code to simulate the stress conditions around the tunnels. Based on available discontinuity geometry constraints, the rock mass has been modelled as a mixture of a discontinuum medium close to the tunnels and as an equivalent-continuum in the far field. Due to the unavailability of field measurements for rock mass mechanical parameters, the parameters have been estimated by incorporating the available intact rock mechanical properties and field deformation monitoring data into a strength reduction model calibration procedure. This back-analysis (calibration) has been carried out through a pseudo-time dependent support installation routine which incorporates the effect of time through a stress-relaxation mechanism. The results from the back-analysis indicate that the rock mass cohesion, tensile strength, uniaxial compressive strength, and elastic modulus values are about 35-45 % of the corresponding intact rock property values. Additionally, the importance of incorporating stress relaxation before support installation in numerical modeling has been illustrated, for the first time in literature, through the increased support factors of safety and reduced grout failures. The calibrated models have been analyzed for different supported and unsupported cases in an attempt to quantify the effect of supports in stabilizing the tunnels and to estimate the adequacy of the existing supports being used in the mine. A direct outcome is that the findings indicate that longer supports may be better suited for the existing geo-mining conditions around the tunnels since they have fractured zones that are larger than the supports currently in use at the mine. The effects of supports have been demonstrated using changes in deformations and yield zones around the tunnels, and changes in the average factors of safety and grout failures of the supports. The use of longer supports and floor bolting has provided greater stability for the rock masses around the tunnels. A comparison between the closure strains in the two differently shaped tunnels indicates that the inverted arch tunnel may be more efficient in reducing roof sag and floor heave for the existing geo-mining conditions. Additional analyses focusing on parametric sensitivity studies on the rock and joint mechanical properties show that the tunnel stability is highly sensitive to changes in cohesion and internal friction angle of the intact rock, and changes in joint basic friction angle. Tunnel stability is seen to not be very sensitive to changes in intact rock tensile strength and joint shear stiffness for the tunnels being studied. Finally, support optimization studies conducted by studying the effect of changing cable diameters and grout uniaxial compressive strengths on support factors of safety and grout failures show the trade-off that is necessary in selecting cable strength vis-à-vis grout strength. The results indicate that simply increasing either one of cable or grout strength parameters without considering their interactions and compatibilities could be detrimental to the stability of the support system.

O projeto de engenharia é desenvolvido baseado em um modelo de comportamento da estrutura a ser construída. Por sua vez, este modelo incorpora uma série de hipóteses de trabalho que, durante a fase de construção ou de utilização da obra, podem não ser observadas na sua totalidade. Dentro deste cenário, a retroanálise probabilista mostra-se uma ferramenta poderosa para avaliação contínua das hipóteses de trabalho durante a construção e toda a vida útil da estrutura, uma vez que permite incorporar novas informações ao modelo inicial através de métodos formalizados. Este trabalho apresenta uma revisão da retroanálise probabilista e sua aplicação prática na atualização do campo de permeabilidades de uma barragem de terra existente, com base em leituras piezométricas. Os resultados do estudo permitiram rever os valores dos parâmetros do modelo adotado, isto é, as permeabilidades dos diversos materiais, sugerindo ao mesmo tempo a aceitação do próprio modelo. Um estudo paramétrico destaca a importância relativa, para a retroanálise probabilista, das diversas variáveis envolvidas, indicando assim áreas em que a investigação complementar é mais necessária. / The engineering project is based upon a model that can predict the behavior of the facility to be constructed. Such model incorporates a series of working hypotheses which may or may not be fully realized during construction or operation. Under such circumstances, probabilistic back-analysis is a powerful tool for continuous evaluation of the working hypotheses, during construction and throughout the lifespan of the structure, given that it provides for the formal updating of the initial model and its parameters on the basis of incoming information. This study presents a review of probabilistic back-analysis and a practical application to the updating of the permeability field of an earth embankment, on the basis of piezometer readings. Results of the study led to updating of the parameters of the adopted model, that is, permeabilities of the several materials, while suggesting acceptance of the model itself. A parametric study reveals the relative importance of the several variables involved in the probabilistic back-analysis, thus indicating areas in which complementary research is mostly needed.