Faculty of Science & Engineering
School of Environment & Technology
Final Year Individual Project
in part fulfillment of requirements for the degree of
BEng (Hons) in Civil Engineering
Static Soil Structure Interaction for random soil
19-11-2015
Abstract
The interaction of the foundation of structures for heterogeneous soils involves the analysis of an interactive procedure of evaluating stresses and strains relationship. The stress and strains developed because of the forces induced into the soil are complex during their analysis. This is due to the mutual effect experienced between the foundation structure and the soil. The interaction of the foundation of building structures with heterogeneous soils is analyzed using the numerical modeling, charts, and programs for mechanics. An example of the numerical modeling approach used is the 3D-Nonlinear Finite Element Analysis (Ritz & Young 2009). The forces exerted by the structures and soil settlement in this paper are addressed fully, and their numerical computation is evaluated. The paper also includes the parameters such as phases involved in the construction process, the order of loading, building ratios, soil failures and proportions in thickness of soil.
Introduction
The interaction between the foundation structures and the heterogeneous soils is complex. Complexity comes, as a result of the loads exerted by the structures cannot only be considered the soil layers and the foundation but also the foundation structures and the superstructures(Ahmed, 2015). Soil distortion influences the stress and strain distribution between the interaction of the foundation structure and the superstructure. The analysis, therefore, involves the interaction of the foundation structures and the heterogeneous soils. The underground soil is heterogeneous that is the soil layers have varying characteristics that need to examine for quality assessment of the building structures. The foundation structures are constructed deep in the soil affecting the interaction between the structure and soil layers and the foundation with the superstructures. The analysis of the foundation structures aides in determining the responses in the soil behaviors and the structures. Before construction of the foundation structure, reliable advanced computational analysis capable of simulating the non-linear soil characteristics and the relationship between the soil layers and the foundation is carried out. Numerical models, charts, and the mechanical programs are presented in this paper precisely to analyze, design, and construct the foundation system (Santos, 2008).
The uniform vertical loading of the foundation system in the subsoil with its associated soil settlement, bending moment are key factors in the construction of the structures. Their analysis involves advance formulations and calculations to estimate the magnitude and the effects it will have on the soil layers. It also helps in determining the force distribution and the consequential effects on the soil behaviors. The methods involved in the analysis should take into consideration the construction phases, soil failure, the building ratios, and the stress-strain distribution within the foundation structures and the soil layers.
The paper presents the parametric study of the foundation structures design. They include the length and space of the pile, a number of piles, thickness of the raft, pile-soil and raft-soil stiffness and the pile-raft relationship. The analysis of the aforementioned parameters leads to an estimation of correct soil settlement and accurate approximation of raft bending moments and loads exerted by the piles (Bivand et.al 2008). The pile raft foundations determine the stiffness of the foundation. Therefore careful consideration is paid to the pile raft elements. The analysis is simplified by considering the vertical loading of the foundation systems with its associated interaction effects. Numerical methods employed in the analysis include Finite Element Method, Boundary Element Method, and hybrid method (Ahmed, 2015). The finite element method is used to analyze complex structures or geometry simplifying them as far as possible (Bivand et.al 2008). It further discretizes the structure for the efficient study of various parameters used in its evaluation.
The dynamic analysis involving the soil-foundation-structure interaction relationships play mutual interdependence by considering the structural behavior of the soil in 3D non-linear and interface boundaries. The interaction of the foundation structures with the soil survey design also takes into consideration of the role played by the superstructures (Ahmed, 2015). The factors considered include its loading and the bending moment of the elements within the foundation system that are examined using the finite element approach (Bivand et.al 2008). The paper presents factors influencing the foundation structure-soil relationship that include construction phases, soil failure modes of soil field, building ratios, load distribution on both the foundation system and the soil (Ahmed, 2015). Numerical methods employed while analyzing the interaction of the foundation structures and the soil are discussed in details. The finite element method, building element method and the hybrid method are examples of the numerical methods applied in the analysis of the foundation system in civil engineering. The methods are helpful since they reduce the complexity involved during the analysis process. The soil layers below the foundation system influence the soil field response. The mode of loading in the foundation structure influences the deflection and force distribution within the superstructure elements in the soil-foundation interaction evaluation.
The interaction of the foundation structure with the heterogeneous is best understood by considering the following methods.
1.1 Direct Method
This method involves the relationship between the concepts of inertia and kinematics. The interaction of the two concepts is approximated by modeling soil and foundation structure (Ahmed, 2015). The vibrations from the soil mass supporting the foundation structures lead to kinematic interactions and the induced vibrations within the structure by the vibrations reaching the base of the foundation structure cause inertial interactions. The following equation is used in the evaluation of the combined response of inertial and kinematic interactions
Where M, C, and K are the mass, damping and stiffness matrices of the whole system including both the soil and foundation structure.
1.2 Substructure Method
The interaction of foundation structure and the heterogeneous soil analysis involving dividing the steps involved. The final response is evaluated by adding together the response of individual steps by the principal of superposition. Unlike in the direct method, the inertial and kinematic interactions are evaluated independently and later superimpose to obtain the response of the system. The equation above in the direct method now takes into consideration of the inertial interactions and the kinematic interactions. The final equation then will contain both the inertial and kinematic interactions equation.
1.3 Analytical Method
Numerical method used in the analysis of the interaction between the foundation structures and the soil are commonly used. This is because of the easy approach and simple criteria they use while analyzing the relationship. Three methods used include; finite element method, boundary element method and the hybrid method (Ahmed, 2015). The approaches used by these methods in establishing the interaction between foundation structures and the soil behaviors is discussed in details in the following sections. The numerical analysis methods involved include both the old and the current ones that have made it easier in the analyzing the interactions. They include the following:
1.3.1 Winkler Approach
Winkler approach method is referred to as sub grade reaction theory (Dean, 2010). This is one of the ancient methods used to determine the bending moments and deflections in the pile. Series of springs represents the soil whose spring constant is equivalent to the soil subgrade reaction. The results can be evaluated theoretically or by use of experiments (Dean, 2010). Standard charts are available that can be used to predict the deflections and bending moments of pile subjected to both static and dynamic loading. The limitation of the Winkler approach is that the approximation of the spring constant depends on the pile behaviors and size of deflection. The response, therefore, calculated is not realistic.
1.3.2 p-y Method
This is an improvement of the Winkler approach applied in the evaluation of the horizontally loaded piles (Ahmed, 2015). In the p-y method, p represents the soil pressure while y represents the deflection of the pile. In this method, the soil model is obtained by evaluating bending equations to get non-linear load against deflection curves. The p-y curves represent the soil and these curves changes with the soli type and depth (Miller et.al 2010).
1.3.3 Elastic Continuum Approach
This method is applicable where the soil is homogeneous. Therefore, it cannot be used in the analysis of the interaction between the foundation structures and heterogeneous soil. The method is used to analyze the characteristics of the laterally loaded piles. The assumption made in the elastic continuum approach is that the piles are rectangular vertical strips. The strip elements are under the influence of horizontal forces.
In the elastic continuum method, the size of the load, the height of overhang of the pile, pile, and soil stiffness are factors that determine the load-displacement characteristics of the foundation system.
1.3.4 Finite Element Method (FEM)
The finite element method applies the concept of the continuum approach. The method is used in the numerical analysis of the complex geometry of foundation systems. In this approach, the system is discretized into finite elements whose loading characteristics can then be analyzed. The advantage of the finite element method can be used in the analysis of large-scale model. The soil is modeled as a continuum and numerical methods like Galerkin, Rayleigh is applied to solve for individual finite properties (Dean, 2010). The soil non-linearity in this approach is converted to linear form and simulations are possible by use of programs like MATLAB. The stresses, strain, and deflections of the pile are analyzed by the help of beam bending equation to represent structural elements and soil interactions (Hicks, 2007).
Conclusion
The numerical methods applied in the analysis of the soil- foundation structure interaction are very efficient. The methods can be used to analyze even complex structures and make decisive recommendations. Finite element method and boundary element method are combined together for easier analysis of the interaction of structures and the soil. FEM is only discretizing the whole system into finite elements whose behavioral properties are then determined.
REFERENCES
Ahmed, M. (2015). Soil-Foundation-Structure Interaction analysis using Finite Elements. Saarbrücken: LAP LAMBERT Academic Publishing.
Bivand, R., Pebesma, E. & Rubio, V. (2008). Applied spatial data analysis with R. New York London: Springer.
Dean, E. (2010). Offshore geotechnical engineering principles and practice. London: Thomas Telford.
Hicks, M. (2007). Risk and variability in geotechnical engineering. London: Thomas Telford.
Miller, R., Bradford, J., Holliger, K. & Latimer, R. (2010). Advances in near-surface seismology and ground-penetrating radar. Tulsa, Okla. Washington, D.C. Denver, Colo: Society of Exploration Geophysicists American Geophysical Union Environmental and Engineering Geophysical Society.
Ritz, K. & Young, I. (2009). The architecture and biology of soils : life in inner space. Wallingford: CABI.
Santos, J. (2008). The application of stress-wave theory to piles : science, technology and practice : proceedings of the 8th International Conference on the Application of Stress-Wave Theory to Piles : Lisbon, Portugal, 8-10 September 2008. Amsterdam, Netherlands Fairfax, VA: IOS Press Distributor in the USA and Canada, IOS Press.
Ulitsky, V., Lisyuk, M. & Shashkin, A. (2014). Soil-structure interaction, underground structures and retaining walls : proceedings of the ISSMGE Technical Committee 207 International Conference on Geotechnical Engineering. Amsterdam: IOS Press.
Ethics Checklist
Section A: Project details – to be completed by the project student
1. Name of student/s:
Agnelo Paulo Augusto da Cunha
2. Name of supervisor:
Dr Pierfrancesco Cacciola
3. Title of project (no more than 20 words): Static Soil Structure Interaction for random soil
4. Outline of the research (1-2 sentences):
Numerical Analysis of the interaction of the static structures foundation and different soil using different methods
5. Timescale and date of completion:
1 month completed on 19-11-2015
6. Location of research:
Books and Journals
7. Course module code for which research is undertaken:
CN301
8. Email address:
A.Cunha2@uni.brighton.ac.uk
9. Contact address:
Penthouse, 13 Wilbury Road, Hove BN33JJ
10. Telephone number:
07516814771
Section B: Ethics Checklist questions
Please tick the appropriate box
Yes
No
1. Is this research likely to have significant negative impacts on the environment? (For example, the release of dangerous substances or damaging intrusions into protected habitats.)
N
2. Does the study involve participants who might be considered vulnerable due to age or to a social, psychological or medical condition? (Examples include children, people with learning disabilities or mental health problems, but participants who may be considered vulnerable are not confined to these groups.)
N
3. Does the study require the co-operation of an individual to gain access to the participants? (e.g. a teacher at a school or a manager of sheltered housing)
N
4. Will the participants be asked to discuss what might be perceived as sensitive topics? (e.g. sexual behaviour, drug use, religious belief, detailed financial matters)
N
5. Will individual participants be involved in repetitive or prolonged testing?
N
6. Could participants experience psychological stress, anxiety or other negative consequences (beyond what would be expected to be encountered in normal life)?
N
7. Will any participants be likely to undergo vigorous physical activity, pain, or exposure to dangerous situations, environments or materials as part of the research?
N
8. Will photographic or video recordings of research participants be collected as part of the research?
N
9. Will any participants receive financial reimbursement for their time? (excluding reasonable expenses to cover travel and other costs)
N
10. Will members of the public be indirectly involved in the research without their knowledge at the time? (e.g. covert observation of people in non-public places, the use of methods that will affect privacy)
N
11. Does this research include secondary data that may carry personal or sensitive organisational information? (Secondary data refers to any data you plan to use that you did not collect yourself. Examples of sensitive secondary data include datasets held by organisations, patient records, confidential minutes of meetings, personal diary entries. These are only examples and not an exhaustive list).
N
12. Are there any other ethical concerns associated with the research that are not covered in the questions above?
N
All Undergraduate and Masters level projects or dissertations in the School of Environment and Technology must adhere to the following procedures on data storage and confidentiality:
Once a mark for the project or dissertation has been published, all data must be removed from personal computers, and original questionnaires and consent forms should be destroyed unless the research is likely to be published or data re-used.
Please sign below to confirm that you have completed the Ethics Checklist and will adhere to these procedures on data storage and confidentiality. Then give this form to your supervisor to complete their checklist.
Signed (Student): Agnelo Paulo Augusto da Cunha
Date: 19-11-2015
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