Underground structures perform an important role in transportation systems in many seismically active regions around the world, but empirical data regarding the seismic behavior of these structures is limited. This research works towards filling that empirical gap through the use of scale model shake table testing. Underground seismic soil-structure interaction (USSSI) effects were investigated for a stiff rectangular tunnel cross-section embedded within soft clay. San Francisco Young Bay Mud was used as a prototype soil for developing a scale model soil mixture consisting of kaolinite, bentonite, class C fly ash, and water. A single cell Bay Area Rapid Transit (BART) cut-and-cover subway tunnel was used as the prototype for the 10th scale model subway cross-section. A flexible walled test container originally developed for a pile study at UC Berkeley was modified for use at Cal Poly, San Luis Obispo. The flexible container allows for close approximation of one-dimensional (1D) free-field site response by significantly limiting the rigidity of the boundary conditions and allowing the soil to deform under simple shear. The study was conducted over two shake table testing phases: Phase I consisted of shaking a model soil column to evaluate the ability of the test container to produce adequate 1D free-field site response, and Phase II tests explored the horizontal racking distortion of a shallow rectangular tunnel cross-section subjected to strong transverse ground shaking. Phase I test results and comparison with SHAKE models indicate that the test container can sufficiently mimic 1D free-field conditions, specifically for the primary shear deformation mode. Similarly, the equivalent linear soil-structure interaction code FLUSH was found to adequately model site response for the Phase II soil-structure system. Comparison of recorded horizontal racking distortions of the model structure with those from numerical modeling suggest that current simplified design methods may overestimate distortions to some degree for cases similar to those examined in this research. Overall, the flexible wall testing container shows promise as a viable means for gaining further insight into USSSI topics, as well as various other geotechnical and soil-structure interaction problems.

Abstract not available

This thesis presents the development of a reliable and efficient technique for the numerical simulation of dynamic soil-structure interaction problems in anisotropic and nonhomogeneous unbounded soils of arbitrary geometry. Such a technique is indispensable in the seismic analysis of large-scale engineering constructions and, to my best knowledge, does not exist at present. The theoretical framework of the research is based on the scaled boundary finite-element method. The following advances are achieved: The scaled boundary finite-element method is extended to simulate the dynamic response of non-homogeneous unbounded domains. The scaled boundary finite element equations in the frequency and time domains are derived for power-type non-homogeneity frequently employed in geotechnical engineering. A high-frequency asymptotic expansion of the dynamic-stiffness matrix is developed. The frequency domain analysis is performed by integrating the scaled boundary finite-element equation in dynamic stiffness. In the time domain, the scaled boundary finite-element equation including convolution integrals is solved for the unit-impulse response at discrete time stations. A Pad?? series solution for the scaled boundary finite-element equation in dynamic stiffness is developed. It converges over the whole frequency range as the order of the approximation increases. The computationally expensive task of numerically integrating the scaled boundary finite-element equation is circumvented. Exploiting the sparsity of the coefficientmatrices in the scaled boundary finite-element equation leads to a significant reduction in computer time and memory requirements for solving large-scale problems. Furthermore, lumped coefficient matrices are obtained by adopting the auss-Lobatto-Legendre shape functions with nodal quadrature, which avoids the eigenvalue problem in determining the asymptotic expansion. A high-order local transmitting boundary constructed from a continued-fraction solution of the dynamic-stiffness matrix is developed. An equation of motion as occurring in standard structural dynamics with symmetric and frequency-independent coefficient matrices is obtained. This transmitting boundary condition can be coupled seamlessly with standard finite elements. Transient responses are evaluated by using a standard timeintegration scheme. The expensive task of evaluating convolution integrals is circumvented. The advances developed in this thesis are applicable in other disciplines of engineering and science to the analysis of scalar and vector waves in unbounded media.

Integral abutment bridges are jointless bridges in which the deck is continuous and connected monolithically with the abutment walls supported typically by a single row of piles. This thesis focuses on the effects of two major parameters on the seismic behavior of an integral abutment bridge in Tennessee by considering soil-structure interaction around the piles and in back of the abutments: (1) clay stiffness (medium vs. hard) around the piles, and (2) level of sand compaction (loose vs. dense) of the abutment wall backfilling. Modal and nonlinear time history analyses are performed on a three dimensional detailed bridge model using the commercial software SAP2000, which clearly show that (1) compacting the backfilling of the abutment wall will increase the bridge dominant longitudinal natural frequency considerably more than increasing the clay stiffness around the piles; (2) the maximum deflection and bending moment in the piles under seismic loading will happen at the pile-abutment interface; (3) under seismic loading, densely-compacted backfilling of the abutment wall is generally recommended since it will reduce the pile deflection, the abutment displacement, the moments in the steel girder, and particularly the pile moments; (4) under seismic loading, when the piles are located in firmer clay, although the pile deflection, the abutment displacement, and the maximum girder moment at the pier and the mid-span will decrease, the maximum pile moment and the maximum girder moment at the abutment will increase.

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.

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.

Anti ram perimeter barriers are part of the protection of important facilities such as power plants, air ports and embassies against unrestricted vehicle access. Many different systems can be used to achieve the containment goal. One of these systems makes use of soil embedded posts either single posts if the soil is hard enough or groups of soil embedded posts tied together by beams if the soil is not hard enough for a single post to stop the in-coming truck. The design of these soil embedded posts needs to take account a number of influencing factors which include the soil strength and stiffness, the post strength and stiffness, the mass of the vehicle and its approach velocity. This dissertation describes the work done to develop a set of design recommendations to select the embedment of a single post or group of posts. The post is a steel beam with an H shape cross section: W14X109 for the single post system and W14X90 for the group system with a double beam made of square hollow steel section HSS8X8X1/2. The spacing of the posts for the group includes 2.44 m, 4.88 m, and 7.32 m. The soil strength varies from loose sand and soft clay to very dense sand and very hard clay. The vehicle has a mass of 6800 kg and the velocities include 80 km/h, 65 km/h, and 50 km/h. The design guidelines presented here are based on 10 medium scale pendulum impact tests, 2 medium scale bogie impact tests, 1 full scale impact test on a single post, 1 full scale impact test on a group of 8 side by side posts with a 5.2 m spacing and connected with two beams, approximately 150 4-D numerical simulations of full scale impact tests using LS-DYNA, as well as fundamental theoretical concepts.

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>