Modelling Ground-Foundation Interactions

Geotechnical practice deals with designing foundations and earth structures. Structure – Foundation –\ud Grou nd interaction is a unique field or topic that concerns both structural and geotechnical engineers. Most geotechnical problems are very sensitive to foundation geometry (length, diameter, spacing), flexural stiffness etc. Even basic parameters such as bearing capacity of shallow foundations, ultimate axial and lateral load capacities of deep/pile foundations, are influenced by the foundation characteristics. More importantly, the serviceability criterion can be satisfied only by proper and rational estimates of structure – found ation – ground interactions. The paper summarizes modelling approaches for foundation – ground interactions, a leaning instability approach for tall structures, and analysis of geosynthetic-reinforced foundation beds

Development of modified p-y curves for Winkler Analysis to characterize the lateral load behavior of a single pile embedded in improved soft clay

In the past decades, the behavior of pile foundations in liquefiable sands has been studied extensively; however, similar investigations of soft clays or static/seismic response of piles in improved soft clay soils are scarce. Despite the widespread presence of this soil type in high seismic regions and the frequent need to locate bridges and buildings in soft clay, only a few investigations have been carried out to guide engineers in evaluating the effectiveness of ground improvement techniques on increasing the lateral resistance of pile foundation embedded in soft clay, and no numerical models have been validated to evaluate this approach. Thus, the objective of this research was to develop modified p-y curves for Winkler analysis to characterize the lateral load behavior of a single pile embedded in a volume of improved clay surrounded by unimproved soft clays. A detailed literature review was completed in the study, aiming to gain knowledge on the development and fields of applications together with limitations of different ground improvement techniques. The ability of each available analysis method for lateral loaded piles was assessed for determining lateral responses of pile foundation in a volume of improved soil surrounded by unimproved soil. A method of developing p-y curve modification factors to account for the effect of the improved soil on enhancing the lateral load behavior of a single pile embedded in soft clay was developed by integrating the effectiveness of the improved soil into the procedures of constructing p-y curves for stiff clay recommended by Welch and Reese (1972). It was achieved by estimating the effective length for a infinitely long soil layer with soil improvement so that the fraction of the load resisted by the soil improved over a limited horizontal extent could be accounted for by taking the ratio between the soil resistance attenuation at actual length of the soil improvement and the effective length. The accuracy of the method was verified against the centrifuge test data from Liu et al. (2010) and the full scale field test from Fleming et al. (2010). The verifications using experimental data demonstrated that the Winkler analysis with proposed p-y modification factors is able to capture the full range of elastic and inelastic pile responses with slopes that correspond well with the results obtained from both centrifuge and field testing, the effectiveness of the soil improvement can be adequately evaluated. In addition, an analytical study on the effectiveness of the cement-deep-soil-mixing (CDSM) ground improvement technique on controlling the lateral displacement of pile foundations embedded in different clay soil conditions with and without ground improvement was carried out. A set of lateral load analyses was performed to establish permissible displacements for precast, prestressed concrete piles as well as open-ended steel pipe pile prior to reaching the curvature capacity of piles. The analysis results showed an average of 66% reduction on the permissible displacement limit by providing a volume of CDSM soil improvement around the prestressed precast concrete piles embedded in medium clay and soft clay. And an average of 79% reduction was observed on steel pipe pile embedded in CDSM improved medium clay and soft clay

Dynamic and Probabilistic Analysis of Shear Deformable Pipeline Resting on Two Parameter Foundation

The nonlinear dynamic deterministic and probabilistic analysis of pipeline undergoing large deflections and resting on Winkler-Pasternak foundation have been done. Dynamic analogues of Euler Bernoulli and Timoshenko Von-Kármán type beam equations are used. The stochastic finite element approach based on the Vanmarcke method combined to Monte Carlo simulations has been used to solve the governing nonlinear equations of soil-pipe interaction. The influence of different parameters of random soil is has been analyzed and the obtained results are compared with those obtained from the literature. It is concluded from the present work that the spatial variability of the soil properties has a great impact on the seismic response of the pipe and the developed model which is based on the accurate method is efficient to determine the real response of the safe and economic pipeline

Elastoplastic solutions to predict tunnelling-induced load redistribution and deformation of surface structures

In this paper, an elastoplastic two-stage analysis method is proposed to model tunnelling-induced soil-structure interaction and incorporated into a computer program `ASRE'. This solution allows considering both vertical and horizontal greenfield ground movements, gap formation and slippage, continuous or isolated foundations, and a variety of structural configurations and loading conditions. After introducing the proposed formulation, the model predictions are first compared with previously published data for validation. Then, to isolate the effects of various structural characteristics (relative beam-column stiffness, presence of a ground level slab, column height, number of storeys) and foundation types (continuous versus isolated), several example structures are analysed. Results demonstrate the value of the proposed analysis method to study a broad range of building characteristics very quickly, and show how the soil-structure interaction occurring due to underground excavations is altered by both foundation and superstructure configurations. In particular, the difference in behaviour between equivalent simple beams and framed structures on separated footings is clarified.Engineering and Physical Sciences Research Counci

Global Sensitivity Analysis of Mat Foundation Behavior by Using Finite Element Modeling

Mat foundation is used mostly for high-rise buildings and, since the demand for high- rise buildings is growing, having extensive understanding of mat foundation behavior leads us into more efficient structural design. Mat foundation behaviors are affected mostly by soil’s materials properties, foundation size, and thickness and loading conditions. In this study, the sensitivity of mat foundation structural responses to some of the design parameters are evaluated. Sobol decomposition, which is a variance-based technique, is used to perform the global sensitivity analysis. In this study, Patran, a finite element-based software, is used for modeling and simulations. Approximate flexible method is a basic method which is used to calculate the structural response of a mat foundation. In this study, the responses of the mat foundation are verified by regenerating the ACIC 336 figure, which is used in approximate flexible method. After verification of Patran model responses, the global sensitivity analyses are performed. “Modulus of elasticity of soil”, “Modulus of elasticity of foundation material”, “Column load”, “Foundation aspect ratio”, and “Foundation thickness” are used as the input variables and “Maximum deflection of the mat foundation” is used as the output response. The results show how the foundation deflection is affected by the design variables. “Modulus of elasticity of soil”, “Modules of elasticity of foundation material” and “Column load” are used as the input variables and “Maximum deflection of the Mat foundation” is used as the output response. The results show that Maximum deflection of the Mat foundation is sensitive to “Modulus of elasticity of soil”, “Column load” and “Modules of elasticity of foundation material” from the most to the least