Effect of Wall-Soil Interface Parameters on Seismic Response of Retaining Walls

Reinforced soil retaining walls are important public structures. Typically there are two kinds of reinforced soil retaining walls: cantilever retaining walls and Geosynthetic reinforced soil retaining walls. While seismic performance of retaining walls is very important for public safety in the event of an earthquake, there are very limited studies on that. The main objectives of the present thesis are to (i) examine the behavior of the interface between structure and soil under various loading and boundary conditions for RC cantilever retaining walls; (ii) conduct sensitivity study on the seismic response of such walls considering the key parameters such as the cohesion (C), friction angle (φ), shear stiffness (Ks), normal stiffness (Kn) and dilation (ψ); and (iii) study the size (height) effect of the relating walls on the seismic performance of such walls. In order to achieve the above objectives, a baseline model of an RC cantilever retaining wall has been constructed for static and dynamic analysis using the Finite Difference Method (FDM). The data for the baseline model are obtained from a published work on seismic response such a wall subjected to an earthquake in India (1991 Uttarkashi earthquake, 20th October), which used the Finite Element Method (FEM) for analysis. The validated baseline model is then used for an extensive parametric study on the static and dynamic behavior of the system which is not available in the literature. Based on the results of numerical modeling, in the static condition, wall deformation was decreased by increasing the cohesion (C), friction angle (φ), shear stiffness (Ks), normal stiffness (Kn) and dilation (ψ) values. The dynamic behavior of the wall was quite different from the static behavior. With increasing the values of shear strength parameters (Cohesion and friction angle) and also shear stiffness (Ks), the wall displacements increased whereas with increasing normal stiffness (Kn) value, the wall deformation decreased. A sensitivity analysis of wall-soil interface parameters on seismic response of the retaining wall was carried out using the ground motion records from Canada earthquake motion database (6th March, Quebec, 2005) and the results were compared to the Uttarkashi earthquake in India. The results of this comparison showed that the response parameters in terms of the retaining wall deformation are similar for both earthquakes. Moreover, parametric studies on the behavior of the soil retaining walls under Montreal earthquake with three different heights (3 m, 6 m and 9 m), and two different types of soil (clay and sand) and eight input earthquakes motions were performed. Results show that the behavior of wall facing in terms of displacement in both horizontal and vertical direction is different, and the type of soil has a main role in the wall deformation. Finally, a statistical estimation of parameters between soil and retaining wall structure was done. According to this statistical study, cumulative percentage distribution of cohesion (C) and stiffness parameters (shear and normal) against wall deformation were calculated. Then, lower and upper boundary ranges of wall-soil parameters were established for both static and dynamic condition

Hypoplastische Modelle für Boden-Bauwerkskontakte: Modellierung und Implementierung

The consideration of interfaces is an important issue when modelling the holistic global structural behaviour of geotechnical engineering structures. The most prominent example is the shaft friction of axial loaded piles and anchors. In this thesis, a stochastic assessment scheme was proposed and applied. This scheme was modified to take into account the special considerations for the assessment of interface models. Based on the assessment and a state-of-the-art review, theoretical considerations were used and a novel scheme was developed. This scheme uses reformulated mathematical operators as well as reduced stress and strain rate tensors, based on existing constitutive equations, to model interfaces. Shear stress mobilization and the volumetric behaviour are predicted more accurately, and the bearing behaviour of frictional contacts can be modelled in a better way. By using the novel scheme, an older hypoplastic interface model for granular interfaces was enhanced, and three different hypoplastic clay interface models were proposed. In addition to the theoretical constitutive model formulation, an implementation method was developed. This allowed a user-friendly implementation of advanced constitutive models as interface models using the capabilities of a commercial finite element software package. This concept was exemplary applied to various 3D boundary value problems and the benefits of such advanced hypoplastic interface model are discussed.Das Kontaktverhalten von geotechnischen Strukturen ist wichtig zur Berechnung des ganzheitlichen Strukturverhaltens bei der Berücksichtigung von Boden-Bauwerks-Interaktion. Bekannte Beispiele dafüur sind axial belastete Pfähle und Anker. In dieser Arbeit wurden verschiedene existierende Modelle zur Modellierung von Boden-Bauwerks-Kontakten mit Hilfe eines stochastischen Ansatzes untersucht und bewertet. Anhand dieser Bewertung und dem Stand der Forschung wurde basierend auf theoretischen Überlegungen ein Methode entwickelt. Diese erlaubt es, die Kontaktflächen mittels modifizierter mathematischen Operatoren und reduzierten Spannungs und Dehnungstensoren, basierend auf existierenden Kontinuums-Modelle zu berechnen. Dies führt zu verbesserten Modellierung der Scherspannungs-Mobilisierung und des volumentrischen Verhaltens der Kontaktzone. Basierend auf dem neuen Konzept wurde ein existierendes, hypoplastisches Modell für granulare Kontaktreibung verbessert und drei unterschiedliche hypoplastische Modelle für das Kontaktverhalten von feinkörnigen Böden entwickelt. Alle Modelle wurden verifiziert und mit experimentellen Daten validiert. Zusätzlich zur Formulierung der theoretischen Modelle wurde ein Konzept erarbeitet, mit dem die entwickelten Modelle in eine Finite-Elemente Software implementiert werden konnten. Hierzu werden existierende Boden-Kontinuumsmodelle benutzt. Die Implementierung dieser Modelle wurde mittels unterschiedlicher Randwertprobleme erfolgreich validiert und die Vorteile der Modelle sowie des Implementierungskonzeptes diskutiert. Die theoretischen Überlegungen und das benutzerfreundliche Implementierungsschema wird die Zugänglichkeit dieser zukunftsweisenden Modelle für Ingenieure verbessern. Hierdurch können die Ergebnisse der Modellierungen und die experimentelle Beobachtungen angeglichen werden, was die Aussagefähigkeit von Finite-Elemente Analysen weiter verbessern wird

Estudo experimental de interfaces solo-concreto no contexto de solos não saturados

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Civil e Ambiental, 2020.O contato entre solo e concreto é muito comum nas obras de engenharia geotécnica. Apesar deste fato, são poucos os estudos sobre a interface entre solos tropicais e concreto, sobretudo quando estes materiais são submetidos ao contato com o concreto ainda em estado fresco e os solos estão em condição não saturada. Em pesquisas recentes, constatou-se que as sucções do concreto de uma estrutura de fundação e do solo circundante são inicialmente distintas e somente se equilibrarão no médio ou longo prazo. Entretanto, na maioria dos casos, a prática geotécnica não considera tal fato, tanto que os ensaios que atestam as previsões feitas durante a fase de projeto – as provas de carga – podem, por norma, ser realizados após 10 dias da concretagem da estaca, sem que, no entanto, se defina o período apropriado. Cita-se, também, que a sucção do concreto é, geralmente, estudada em termos de sucção total (umidade relativa) e relacionada às propriedades de transporte de massa. Também não tem sido avaliada a migração de compostos químicos do concreto para o solo e seus impactos na interação solo- estrutura de fundação. Assim, esta dissertação buscou estudar, experimentalmente, a variação da sucção na interface solo-concreto ao longo do tempo e sua implicação na resistência ao cisalhamento da interface. Além disto, estudou-se como as propriedades físicas e químicas dos materiais constituintes da interface variam durante o período de interação. Para o desenvolvimento do estudo laboratorial, escolheu-se dois tipos de solo – um profundamente intemperizado (solo laterítico) e outro menos alterado (solo saprolítico) – e um concreto utilizado na fundação de uma obra rodoviária no Distrito Federal, cuja especificidade é comumente adotada em estacas hélice contínua da região. Nos ensaios de campo, um terceiro solo, também laterítico, foi usado para avaliar a interação solo-concreto em um segmento representativo do topo de uma estaca. A partir dos resultados obtidos, concluiu-se que a variação da sucção dos materiais da interface depende do tipo de solo de fundação e das condições de saturação do mesmo quando da concretagem e que esta variação tem influência sobre a resistência ao cisalhamento da interface. Além disto, verificou-se que a migração de compostos químicos do concreto para o solo também é função da sucção atuante e que é possível obter curvas características de concretos a partir de métodos simples como o do papel filtro. Complementarmente, atestou-se que há certa correlação da sucção com a resistência do concreto e que a estimativa do módulo de elasticidade à compressão do concreto pode ser feita a partir de resultados de ensaios de tração indireta com corpos de prova com relação comprimento/diâmetro de no mínimo 0,5, desde que considerada a margem de erro obtida.The contact between soil and concrete is very common in the geotechnical field. Despite this fact, there are few studies about the interface between these tropical soils and concrete, and even fewer when the materials are submitted to contact with the concrete still in fresh state and soils are in an unsaturated condition. In recent studies, it was found that the suctions of the concrete from the structural foundation element and of the surrounding foundation soil are initially distinct and will only equilibrate in mid or long-term. However, in most cases, the geotechnical practice does not take this fact into account, so much that the tests that attest the predictions made during the project phase – load tests – can be done only 10 days after the concreting of the pile according to the ruling standard, but an appropriate period of time is not specified. It is also cited that the suction in concrete is mainly studied in terms of total suction (relative humidity) and related to mass transportation properties. Also, the migration of chemical compounds from the concrete to the soil and its impacts on the soil-foundation structure has not been evaluated. Therefore, this dissertation aims studying, experimentally, the suction variation in the soil-concrete interface over a period of time and the implication of this very variation upon the interface’s shear resistance. Beside this, it was studied how the physical and chemical properties of the interface’s materials varied during the interaction period. For the development of the laboratorial study, two types of soil were chosen – a very altered one (lateritic soil) and a less altered (saprolitic soil) – and a concrete that was used in a foundation of a highway infrastructure construction in the Federal District, whose specificity is commonly used in continuous helical displacement piles across the region. On the field tests, a third soil, also lateritic, was used to evaluate the soil-concrete interaction in a segment that represents the top of a pile. From the results, it is concluded that the suction variation of the interface’s materials depends on the type and the initial saturation conditions of the foundation soil when the pile is being executed and that this variation influences the interface’s shear resistance. Moreover, it was verified that the migration of chemical compounds from the concrete to the soil is also function of the acting suction and that is possible to determine the concrete’s characteristic water retention curve with the simple filter paper method. In addition, it was attested that the concrete’s suction has some correlation with its resistance and that the estimation of the concrete’s elasticity modulus can be made from results of indirect traction tests made with specimens that have a length/diameter relation of at least 0,5, as long as the obtained margin of error is considered

Elastoplastical Analysis of the Interface between Clay and Concrete Incorporating the Effect of the Normal Stress History

The behaviour of the soil-structure interface is crucial to the design of a pile foundation. Radial unloading occurs during the process of hole boring and concrete curing, which will affect the load transfer rule of the pile-soil interface. Through large shear tests on the interface between clay and concrete, it can be concluded that the normal stress history significantly influences the shear behaviour of the interface. The numerical simulation of the bored shaft-soil interaction problem requires proper modelling of the interface. By taking the energy accumulated on the interface as a hardening parameter and viewing the shearing process of the interface as the process of the energy dissipated to do work, considering the influence of the normal stress history on the shearing rigidity, a mechanical model of the interface between clay and concrete is proposed. The methods to define the model parameters are also introduced. The model is based on a legible mathematical theory, and all its parameters have definite physical meaning. The model was validated using data from a direct shear test; the validation results indicated that the model can reproduce and predict the mechanical behaviour of the interface between clay and concrete under an arbitrary stress history