This thesis presents a study of the effects of deep excavations on adjacent metro or utility tunnel in soft to medium soil. The main objective of the thesis is to develop a method of estimating these effects quantitatively. Extensive review of relevant literature published in the past four decades was conducted in order to understand the trends and the key developments in this area. It was revealed from the literature review that the concurrent use of the Observational Method and the finite element method for monitoring and controlling of ground deformations around the excavation has become a norm for deep excavation projects. Several design charts and guidelines for estimation of effects of deep excavations on adjacent raft foundations or pile foundations were found in the literature; however, no such charts or guidelines were found for estimation of effects of deep excavations on existing circular tunnels. Consequently, the development of these guidelines was established as one of the objectives of this study. <p>The initial phase of the research was focused on detailed study and analysis of two well-documented case studies the Chicago Subway Renovation Project, USA and the Tan Tock Seng Hospital Deep Excavation, Singapore. The back analyses of these two case studies were carried out using the finite element software PLAXIS. Exact site conditions and input parameters for the soil and the structural components were incorporated as much as possible. Appropriate adjustments in some of the input parameters were necessary to achieve good match between the computed and the observed results. <p> The back analyses were followed by parametric studies to identify important variables controlling the mechanisms of soil-structure interaction. The variables identified from the parametric studies of the two case studies were: soil stiffness, tunnel lining thickness, the depth of the excavation, and the location of tunnel. These variables were used to conduct a series of finite element analyses using simplified geometry and ground conditions for the purpose of formulating preliminary design charts. Results from these analyses were recorded in terms of in-plane and out-of-plane distortion of tunnel lining as well as additional shear forces and bending moments induced in the tunnel lining due to an adjacent deep excavation. The results were made non-dimensional before presenting them as contour plots. These contour plots constitute preliminary design charts, which can be used for the estimation of tunnel lining deformation caused by adjacent deep excavation.<p> Based on the results of this study, it can be concluded that a finite element program (such as PLAXIS) that is able to model construction processes associated with tunnelling and deep excavation in urban environment can be an invaluable tool in exploring the mechanism of ground deformation around the deep excavation and in quantifying the effects of ground deformation on existing adjacent structures. The modeller must, however, be aware of the fact that ways of modelling a particular construction process could be different for various finite element programs. It is important to interpret the instructions given in the manual of the program correctly. <p>Detailed back analyses of well-documented deep excavation case histories are vital from the point-of-view of building confidence in the selected finite element program. Such analyses also have the potential to identify key variables influencing the soil-structure interaction. <p> Preliminary design charts proposed in this thesis are very convenient for obtaining approximate values of tunnel lining deformation caused by adjacent deep excavation. Non-dimensional nature of these design charts makes it possible to be used for any depth of the deep excavation and for tunnels of any size, depth of cover, and distance from the vertical face of the excavation. These design charts can be used by engineers and contractors for initial estimation, selection and preliminary design of excavation support system, and are particularly useful during the planning phase. Town planners and project managers, who need to decide on the feasibility, damage control and risk management aspects of a deep excavation project, may also find these design charts equally useful. It should, however, be kept in mind that the estimates obtained from these design charts are highly approximate and as such, should be taken as guidelines for decision making processes. These estimates do not replace site specific detailed analysis and monitoring.

AN INVESTIGATION OF ACCURACY OF INERTIAL INTERACTION ANALYSES WITH FREQUENCY-INDEPENDENT IMPEDANCE COEFFICIENTS Yilmazok, &Ouml / zg&uuml / n M.S., Department of Civil Engineering Supervisor: Assoc. Prof. Dr. B. Sadik Bakir November 2007, 79 pages The inertial interaction between the soil and structure alters dynamic response characteristics of a structure due to foundation deformability, such that the flexibility and energy dissipation capability of surrounding soil may lead to a significant increase in period and damping of structural oscillations. The inertial interaction analyses can be accomplished through utilisation of frequency dependent foundation impedance coefficients that are reported in literature for various soil conditions and foundation types. However, such analyses should be performed in frequency domain, and applicable to only cases that linear structural response is considered. Alternatively, equivalent frequencyindependent foundation impedance coefficients can be employed, such that a constant excitation frequency is assumed in calculation of these coefficients. In this study, it is assumed that the fundamental frequency of a fixed-base structure, which can be obtained through employing available empirical relationships or a modal analysis, can be substituted for excitation terms in impedance expressions. The error induced in calculation of peak structural distortions is investigated through comparisons of structural response due to frequency-dependent and frequency-independent foundation impedance coefficients. For analyses, a linear single-degree of freedom oscillator is considered for modeling the structure. The frequency-dependent impedance of a rigid disk foundation resting on elastic halfspace is simulated by a limited number of discrete elements. The response calculations are performed in frequency domain, through employing 72 acceleration records. It is concluded that, the natural frequency of fixed-base building can be considered as effective excitation frequency for calculation of foundation impedance coefficients, when the effect of inertial interaction on structural response is moderate. Through employing equivalent-linear approximation for the structural response, it is shown that the conclusion is also valid in cases that nonlinear structural response is considered. However, when the inertial interaction has more profound effects on the structural response, the use of natural frequency of flexible-base structure, which is calculated iteratively due to its dependence on foundation-impedance factors is recommended.

In today&rsquo / s world, buried structures are used for a variety of purposes in many areas such as transportation, underground depot areas, metro stations and water transportation. The serviceability of these structures is crucial in many cases following an earthquake / that is, the earthquake should not impose such damage leading to the loss of serviceability of the structure. The seismic design methodology utilized for these structures differs in many ways from the above ground structures. The most commonly utilized approach in dynamic analysis of underground structures is to neglect the inertial forces of the substructures since these forces are relatively insignificant contrary to the case of surface structures. In seismic design of these underground structures, different approaches are utilized like free-field deformation approach and soil-structure interaction approach. Within the confines of this thesis, seismic response of highway tunnels is considered through a case study on Bolu Tunnels, which are well documented and subjected to D&uuml / zce earthquake. In the analyses, the seismic response of a section of the Bolu tunnels is examined with 2-D finite element models and results are compared with the recorded data to evaluate the capability of the available analysis methods. In general, the results of analyses did not show any distinct difference from the recorded data regarding the seismic performance of the analyzed section and that the liner capacities were sufficient, which is consistent with the post earthquake condition of the Bolu Tunnels.

<p>The focus of this study is on potential problems resulting from construction on expansive soils in Kibaha region, Tanzania. For the fact that most of the affected structures are founded on expansive soils, a clear understanding of the soil behaviour and their interaction with structures, specifically as they relate to shallow foundations, has been of more interest to the study in order to evaluate properly the source of the problem.</p><p>The geotechnical behaviour of expansive clay soils is investigated by looking into the geomorphologic, geological and climatic conditions and mineralogical composition of the soils in the study area. The geotechnical results are linked with the performance of the foundation as well as structures.</p><p>Two sites, representative of known problem-areas in Kibaha were selected for geotechnical tests. Geotechnical site investigation consisted of open trial pits, profile description and the collection of both disturbed and undisturbed samples.</p><p>The collected samples were submitted to soil laboratories at KTH and DIT for mineralogical composition tests, natural water content, density, Atterberg limits and swell tests (free swell and swelling pressure). The results of this investigation indicate that soil in Kibaha contains clay (31%), have high liquid limit (59%) and plastic limit (37%) which indicate high potential swell.</p><p>Since swell potential and swell pressure are key properties of expansive soils, the swell parameters were measured by free swell tests and one-dimensional oedometer swell tests respectively. The free swell ranged from 100% to 150% and the swell pressure was in the region of 45 kPa.</p><p>The properties of expansive soils were confirmed by the x-ray diffraction test which showed the presence of montmorillonite in the soil. It is from this fact that the source of the problem is in the expansive soils coupled with poor building materials.</p><p>Physical conditions of the surveyed properties in the area confirmed the hypothesis of building damages due to poor building materials triggered by expansive soils. In support of the obtained data, the actual behaviour of the foundations is supplemented with prototypes of strip foundations whose performances are to be monitored over a long period. Finally, suggested are the ways forward to solve the problem of foundation on expansive soil.</p>

A technique that allows for nonparallel interfaces and lateral inhomogeneities in an irregular layered medium is described. The formulation combines a semidiscrete finite-element technique with a perturbation method, providing an approximate treatment of wave propagation in irregular layered media. The procedure treats the irregularities as perturbations with respect to a reference, horizontally-layered, laterally-homogeneous medium and produces approximations of the perturbed wave motion with little additional computation effort. Within the framework of the method, consistent transmitting boundaries and other semidiscrete hyperelements as well as Green’s functions, already available for regular layered media, can be reformulated. The method is relevant in problems of foundation dynamics, ground response to seismic waves and site characterization. Example problems are presented toward evaluation of the effectiveness of the method. / text

The research described in this dissertation undertakes a computational study of wave motion due to ground excitation in layered soil media. Adjustments of soil properties consistent with the level of deformation is applied using an equivalent linear approach. The finite element method provides the basis of the numerical procedure for soil-structure system response calculation in conjunction with a first-order perturbation scheme. Available experimental data are employed for shear-modulus and damping adjustments. The findings of the research are expected to lead to efficient calculation of structural response to earthquake ground motion. / text

published_or_final_version / Civil Engineering / Master / Master of Philosophy

No description available.

Pile foundations that support offshore structures are required to resist not only static loading, but also dynamic loading from waves, wind and earthquakes. The purpose of this study is to gain a better understanding of the behavior of offshore piles under cyclic or dynamic loading using the finite element approach. To achieve this goal, an appropriate constitutive model is required to simulate the behavior of soils and interfaces. The DSC constitutive model is developed for saturated interfaces to study the behavior under severe shear deformation at the soil-pile interface. Monotonic and cyclic simple shear experiments are conducted on Ottawa sand-steel interfaces under drained and undrained conditions using the Cyclic-Multi-Degree-of-Freedom shear device with porewater pressure measurement (CYMDOF-P). The effect of various parameters such as normal stress, surface roughness of steel, type of loading, and the amplitude and frequency of the applied displacement in two-way cyclic loading are investigated. The data from the simple shear tests on saturated interfaces are used to calculate the parameters in the DSC model. The resulting parameters are then used to verify the DSC model by back predicting tests from which parameters are determined and independent tests that are not used in parameters determination. The model predictions, in general, were found to provide a highly satisfactory correlation with the observations. In the context of DSC, the concept of critical disturbance is developed to identify initiation of liquefaction in saturated Ottawa sand-steel interfaces. This method is based on using microstructural changes in material as an indication of liquefaction identification. The finite element method, along with DSC constitutive model, is used to investigate the response of offshore piles to dynamic loading. These include cyclic loading of axially loaded instrumented pile in clay and full-scale laterally loaded pile in sand. The DSC model is used to model the nonlinear behavior of saturated soils and interfaces. A nonlinear dynamic finite element program DSC-DYN2D based on the DSC modeling approach and the theory of nonlinear porous media is used for this purpose. Results from numerical solutions are compared with field measurements. Strong agreement between numerical predictions and field measurements are an indication of the ability to solve challenging soil-structure interaction problems.Based on the results of this research, it can be stated that the finite element-DSC model simulation allows realistic prediction of complex dynamic offshore pile-soil interaction problems, and is capable of characterizing behavior of saturated soils and interfaces involving liquefaction.

Soil structure influences many chemical, biological and physical processes and it is well established that organic carbon acts as a soil binding agent. However, the precise location of organic matter and carbon in relation to structural features within intact samples is unknown. The sensitivity of organic carbon to decomposition is dependent not only upon its intrinsic chemical recalcitrance, but also its location within the soil structure. Soil structure provides organic carbon with chemical and physical protection, the extent of which varies between structural units. Furthermore soil structure is transient, and is sensitive to both environmental changes and physical disturbance, therefore it is difficult to determine and quantify the impact of this dynamic entity upon the storage of organic carbon. To date the majority of research that has advanced our understanding of the role soil structure plays in the storage of organic carbon, has relied upon some form of fractionation technique to separate aggregates from the bulk soil. However this approach has its disadvantages as much of the soil structure is destroyed; clearly when studying the impact of soil structure upon organic carbon-storage it is advantageous to implement any method that minimises disturbance to the soil structure. This study entails removing intact soil samples (through the use of kubiena tins) from long-term agricultural experimental fields at Rothamsted Research, (Hertfordshire, UK) with the aim of comparing and evaluating the location of organic matter and it’s associated organic carbon, in soils with contrasting organic carbon contents and a well documented land-use history. Thin sections will be analysed by integrating conventional micromorphology, image analysis and sub-microscopy combined with microscale chemical analysis scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). In doing so a new alternative method for analysing the distribution of organic matter and organic carbon is proposed. It was found that agricultural soils, which are the same in all aspects except total-OC content, differ in total organic matter, water release characteristics, aggregate stability and pore size distribution; therefore these differences could be attributed to the relationship between OC and soil structure. The water release curve, aggregate stability and pore size distribution also differed between soils with similar OC-contents but from different land-uses. The analysis of organic matter within intact soil samples provided evidence for the redistribution of organic matter as it is decomposed within the soil structure, for instance, less decomposed organ and tissue forms were located in or near to soil pores while more decomposed amorphous forms were located within the soil matrix. Since the same pattern of redistribution was observed in both agricultural and grassland soil this is likely to be directed by soil macro and micro fauna. It is concluded that since the location of different forms of organic matter is consistent across all soil, organic matter location is not responsible for creating differences in aggregate stability between treatments. Instead the results indicate that the amount and strength of organic carbon bonds and its hydrophobic properties are responsible. Micromorphology results demonstrated an absence of defined aggregation between treatments. Despite the difficulties in the interpretation of aggregation, the results contradict theories of aggregation, which state that aggregates are formed around “fresh” organic matter and it is argued that OM will undergo substantial decomposition before it acts as core for aggregation. Initial SEM-EDS analysis, has shown that in the soil matrix adjacent to organic matter (plant/organ) fragments there is a heightened concentration of C, indicating that these fragments are acting as a source of organic carbon. Interestingly BC, which represent one of the most recalcitrant C forms is also acting as a source of C, although these initial results suggest to a lesser extent than more labile C-sources. This source of organic carbon could stimulate microbial activity thereby enhancing soil structural stability. Alternatively, the release of liable carbon into soil pores may represent one route by which labile carbon enters sub-soil horizons.