The influence of soil geotechnical parameters on the design of circular foundations, a case study of the cooling towers of Kazerun power plant.

Number of pages: 106 File Format: word File Code: 31457
Year: 2010 University Degree: Master's degree Category: Civil Engineering
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  • Summary of The influence of soil geotechnical parameters on the design of circular foundations, a case study of the cooling towers of Kazerun power plant.

    In order to obtain a master's degree

    Civil engineering field - soil and foundation orientation

    Abstract

    Nowadays, circular foundations are more or less used for structures, especially structures that have axial symmetry. In this research, a numerical study was carried out on bearing capacity and settlement of annular foundation. PLAXIS software was used for modeling. The parameters of the materials were selected from the characteristics of the clay of the construction site of the cooling towers of the combined cycle of the Kazeroon power plant. Moore-Coulomb model was used to model materials. Bearing capacity calculations were done in two cases of smooth foundation and rough foundation, and bearing capacity coefficients were calculated based on that. The settlement of the annular foundation of the cooling tower of Kazerun power plant was calculated. Then, based on the bearing capacity and settlement calculations, the permissible bearing capacity of the annular foundation of Kazeroon power plant was calculated. From the results, it was found that the bearing capacity of the rough foundation is significantly higher than the bearing capacity of the smooth foundation. It was also found that with the increase of ri/ro (the ratio of the inner radius to the outer radius of the annular foundation), the behavior of the annular foundation approaches that of the strip foundation. The results obtained from calculations of bearing capacity and settlement have been compared with the results of existing theories and relations. Keywords: annular foundation, radius ratio, bearing capacity, settlement. Chapter 1. Chapter 1. General. Introduction: Construction projects consist of two parts: superstructure and substructure. Substructure often refers to a part that is in contact with the soil and participates in the process of directly transferring the load of the pavement to the underlying or surrounding soil. The load is transferred from the surface of the structure to the ground by a member called the foundation. The role of the foundation as a transitional part in the building can withstand relatively large stresses in the implementation of the basement of the structure such as a column, foundation or wall for the soil. Soils and natural materials available on the surface of the earth have relatively low resistance and bearing capacity compared to the pavement components such as common construction materials, such as concrete and steel. Foundation engineering is the art of applying structural science, geotechnics and engineering judgment in relation to foundation analysis and implementation in such a way that an optimal foundation system is finally obtained by observing the technical, operational, sustainability and economic principles. In order to achieve the above goals, the foundation engineer must have a proper understanding of the mutual behavior and performance, in other words, the interaction of soil and bedrock, as well as the conditions of the pavement.

    One of the basic requirements of foundation analysis and design is to determine the bearing capacity (evaluation of soil and rock resistance), estimate the volume changes and compression of the bed due to loading (estimation of the amount of soil settlement) and design a structure that is determined in the first two steps of the foundation geometry in the plan and the depth of its installation, and then design A structure or internal design is based on internal stresses caused by external forces, which includes the selection of materials, determining the thickness of the foundation and, if necessary, how to reinforce it. Stability control and external design are also essential for analysis and design, and finally the adequacy of the designed system is evaluated in terms of implementation and economy[1]. Surface foundations are one of the most common foundations, especially for construction projects, which are often less deep than their width. Surface foundations include single, compound, strip and wide foundations. Nowadays, circular and annular foundations are used for the cases where there is axial symmetry. For foundations of structures such as bridge foundations, water towers, silos, etc. Circular foundations are used. Economically, the use of circular foundations reduces the amount of materials used. In the countries where the primary materials for construction create a high price in terms of cost, the use of circular foundations is more widespread.

    In our country, Iran, circular foundations are also used. Annular foundations are used for the cooling towers and HRSG unit of the combined cycle of the Kazeroon power plant.

    1-2- The location of the Kazeroon power plant

    The location of the Kazeroon power plant is at km 10 of the Kazeroon-Farashband road (Belyan village) and km 4 of the exclusive road of the Kazeroon combined cycle power plant. The geographic position of the place is shown in Figure (1-1)[2].

    (images are available in the main file)

    1-3- General geology of the area

    The studied area is a part of the Geological Unit of Folded Zagros, which is located in the southwest of Iran.The width of this unit is estimated to be 150 to 250 km. The general trend of this area is northwest-southeast, and Paleozoic, Mesozoic, and Tertiary sediments lie on top of each other. These sediments have covered the continental margin of the eastern Arabian platform[2].

    - Geotechnical studies

    According to field observations, examination of samples and the results of laboratory tests, the underground crusts in the target area mainly include low plasticity clay in brown color. These layers are associated with a small amount of sand in some depths. It is based on the unified soil classification of CL type. The underground water level has been accurately measured using a piezometer. Due to the presence of a piezometer at the location, it was possible to measure the water level during the implementation of the project. Before the implementation of the project, the underground water level was at a depth of 26 meters from the ground surface.

    Geotechnical studies of the said power plant were first conducted by drilling 3 boreholes at the site of the cooling tower structure, and then to complete the above studies, another 9 boreholes were examined, and finally, in order to determine the physical properties of the soil, granulation, hydrometry, Etterberg limits, density, triaxial, uniaxial, consolidation and direct cutting tests were carried out on the Representative samples were taken from the site and the characteristics of the layers were determined based on this. According to the results of laboratory tests, observations and field tests as well as engineering judgment and assuming a constant Poisson's ratio for the soil layers, the local soil parameters are summarized in Table (1-1).

    In order to determine the relative density of the underground layers, standard impact and penetration tests have been performed at different depths in all boreholes. In this test, the number of blows resulting from a weight of 64 kg falling from a height of 76 cm, which penetrates 30 cm, is recorded. Figure (1-3) shows the changes in the number of blows according to depth for several boreholes. Lufran test was used to determine the permeability coefficient of the layers. Due to the low level of underground water, the method of testing was fixed head and falling head. The test should be done separately in each borehole to determine permeability in the horizontal direction and permeability in the vertical direction [2].

    (images are available in the main file)

    1-5- Necessity of conducting research

    The progress of geotechnical engineering science in the use of special foundations has opened a new chapter in engineering designs. For the geotechnical design of the foundation, i.e. determining its depth and dimensions, relationships are needed to calculate the bearing capacity and settlement. Determining the bearing capacity of the foundation correctly can have a high economic impact. Considering the special form of circular foundations, it does not seem correct to use the bearing capacity relations presented in the existing theories. Therefore, there is a need to present relationships for calculating the bearing capacity of the annular foundation. 1-6- Research objectives In this research, the bearing capacity of the annular foundation is calculated at different depths and dimensions, and then the amount of settlement of the cooling towers of the HRSG unit of the combined cycle of Kazaron power plant is discussed. In general, the objectives of this research can be stated as follows:- Calculation of the final bearing capacity of the annular foundation

    - Calculation of the bearing capacity coefficients using the calculated bearing capacity

    - Comparison of the calculated bearing capacity coefficients with existing theories

    - Investigation of the foundation settlement of the cooling towers of the combined cycle HRSG unit of the Kazron Power Plant

    - Calculation of the permissible bearing capacity of the annular foundations of the towers Kazerun power plant cooling

    (images are available in the main file)

    1-7- Thesis structure

    In the second chapter, different methods of calculating carrying capacity and different relationships for calculating carrying capacity are presented. Also, in this chapter, various relationships are presented for calculating the settlement of foundations. In the third chapter, the method of modeling circular foundations in PLAXIS software, including geometric modeling, material modeling, meshing, determination of initial conditions and how to perform calculations is examined.

    The fourth chapter is the analysis of the results of modeling and the comparison of the results obtained from the numerical method with the classical methods.

    Chapter 2

    Research conducted

    - Introduction:

    Mainly in the design of surface foundations, the control factor is allowed to determine the bearing capacity.

  • Contents & References of The influence of soil geotechnical parameters on the design of circular foundations, a case study of the cooling towers of Kazerun power plant.

    List:

    Chapter One: Generalities

    1

    1-1- Introduction

    2

    1-2- Location of Kazeron power plant

    3

    1-3- Geology of the area

    3

    1-4- Geotechnical studies

    5

    1-5- Necessity of conducting research

    8

    1-6- Research objectives

    8

    1-7- Dissertation structure

    9

    Chapter Two: Conducted research

    10

    2-1- Introduction

    11

    2-2- Types of subsoil rupture P

    12

    2-2-1- General shear failure

    12

    2-2-2- Local shear failure

    13

    2-2-3- Punching shear failure

    14

    2-3- Types of analytical methods for calculating bearing capacity

    14

    2-3-1- Limit equilibrium method

    14

    2-3-2- Slip-line method

    15

    2-3-3- Upper bound method

    15

    2-3-4- Numerical methods

    16

    2-4- Capacity calculation Loading

    16

    2-5- Settlement of foundations

    28

    2-5-1- Instant settlement

    28

    2-5-2- Consolidation settlement

    32

    Chapter three: Modeling

    34

    3-1- Introduction

    35

    3-2- Reasons for choosing PLAXIS software for conducting research

    36

    Title

    Page

    3-3- General about PLAXIS

    37

    3-3-1- Introduction of input data

    37

    3-3-2- Selection of model type

    37

    3-3-3- Element type selection

    38

    3-4- Geometric modeling

    40

    3-5- Material modeling

    42

    3-6- Meshing

    46

    3-7- Applying initial conditions

    48

    3-8- Calculations 50

    3-9- Output data

    53

    3-10- Curve presentation

    54

    3-11- Software flowchart

    55

    Chapter four: calculations and analysis of results

    57

    4-1- Introduction

    58

    4-2- Review Correctness of software operation

    58

    4-3- How to load pi

    60

    4-3-1- Smooth pi

    60

    4-3-2- Rough pi

    61

    4-4- Dimension of pi

    62

    4-5- Strain stress chart

    62

    4-6- Bearing capacity results

    67

    4-7- Calculation of bearing capacity coefficients

    68

    4-8- Comparison of the present work with past theories

    71

    Title

    Page

    4-9- Calculation of foundation settlement of Kazron cooling tower

    74

    4-9-1- How to perform calculations

    74

    4-9-2- Calculated settlement

    75

    4-10- Comparison with past theories

    76

    4-10-1- Instant settlement

    77

    4-10-2- Settlement Consolidation

    79

    4-11- Calculate the allowable stress of annular foundation

    82

    Chapter five: results and suggestions

    84

    5-1- Introduction

    85

    5-1- Results

    85

    5-2- Suggestions

    86

    Resources

    87

     

     

    Source:

     

    [1] Eslami, Abulfazl (1385), Engineering P: design and implementation, building and housing research center

    [2] Boland Bayah company, final report of on-site geotechnical studies and research Construction of cooling towers and combined cycle HRSG unit of Kazeroon power plant [3] Das, Bara (1380), principles of geotechnical engineering, Shapour Tahoni, 6th, Tehran, Pars Ain Publishing Institute

    [4] Vesic, A.S. (1972), Expansion of cavities in infinite soil mass, Jour. Of the Soil Mechanics and Foundations div., ASCE, Vol.98, 265-290

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    [6] Hjiaj, M., Lyamin, A.V. and Sloan, S.W.(2004), Numerical limit analysis solutions for the bearing capacity factor N?, International Journal of Solids and Structures 42 (2005) 1681–1704

    [7] Terzaghi(1943), Theoretical soil mechanics, New York: John Wiley and Sons

     

    [8] Meyerhof G.G. (1951), The ultimate bearing capacity of footings. Geotechnique; 2(4):301-32.

    [9] Hansen, J.B. (1970), A revised and extended formula for bearing capacity. Bulletin of the Danish Geotechnical Institute 28, 5–11.

     

    [10] Manoharan N, Dasgupta SP.(1995), Bearing capacity of surface footings by finite elements. Comput Struct;54(4):563–86.

     

    [11] Kumar J, Ghosh P.(2005), Bearing capacity factor N? for ring footings using the method of characteristics. Can Geotech J;40(3):1474–84.

     

    [12] Boushehrian, J.H. and Hataf, N. (2002), Experimental and numerical investigation of the bearing capacity of model circular and ring footings on reinforced sand

     

    [13] Hataf, N., Razavi, M.R. (2003), Behavior of ring footing on sand. Iranian Journal of Science and Technology, Transaction B, Vol. 27, pp. 47–56. [14] Zhao, L. and. Wang, J.H.(2007), Vertical bearing capacity for ring footings, Computers and Geotechnics 35 (2008) 292–304

     

    [15] Craig, R.F. (1983). 16, Norwegian Geotechnical Institute, pp. 30-32

     

    [17] Bowles, J.E., (1997), Foundation Analysis and Design, 5th Edition. McGraw-Hill, New York.

     

    [18] Eslami, Abulfazl (2005), Wide Foundations: Analysis, Design and Performance, First Edition, Gilan University Publications

     

    [19] DAS / Som(2003), Theory and Practice of Foundation Design, ISBN-81-203-2190-1, New Delhi, Prentice-Hall of India Private Limited

     

    [20] Skempton, A.W. and Bjerrum, L. (1957), A contribution to settlement analysis of foundations in clay, Geotechnique, London, Vol. 7, p. 178

     

    [21] Brinkgreve RB, Vermeer PA.(1998), Plaxis-finite element code for soil and rocks analysis. Version 8. Rotterdam Brookfield: AA. Balkema

     

    [22] De Beer, E.E. (1970), Experimental determination of the shape factors and bearing capacity factors of sand, Geotechnigue, Vol. 20, No. 4, pp. 124-128.

The influence of soil geotechnical parameters on the design of circular foundations, a case study of the cooling towers of Kazerun power plant.