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  3. Increasing the bearing capacity of porous granular soils under wide foundations by means of geosynthetics

Increasing the bearing capacity of porous granular soils under wide foundations by means of geosynthetics

Number of pages: 83 File Format: word File Code: 31321
Year: 2013 University Degree: Master's degree Category: Civil Engineering
Tags/Keywords: Barari P - Carrying granular soils - Geosynthetics - Geotechnics - Granular soils - Polymer products - Porous granular soils - Porous granular soils under the foundation - Reinforced soil, geogrid - Soil and foundation mechanics
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  • Summary of Increasing the bearing capacity of porous granular soils under wide foundations by means of geosynthetics

    Master's Thesis (M.sc)

    Soil and Foundation Mechanics Department

    Abstract

    In this research, the stability of geogrid-reinforced soil located on an underground cavity was analyzed using plaxis software, and the effect of several factors such as the number of geogrid layers, the length of the geogrid layer, the hardness of the geogrid layer, the optimal location of the geogrid layer under the foundation, and the influence of the location The placement of the hole under the foundation was checked on the bearing capacity.

    Reinforcement can significantly improve the bearing capacity of the soil and reduce the settlement of the foundation. Also, with the increase in the number of geogrid layers, the amount of settlements has decreased, and with the increase in the length of the geogrid layer, the amount of settlements has decreased. Therefore, as the length of the geogrid increases, the bearing capacity ratio (BCR) increases. For soil with special characteristics, there is an optimal place for placing the first geosynthetic layer, and it is the place where the lowest settlement and the highest bearing capacity are observed. In general, by increasing the axial stiffness of geogrid (EA), the amount of settlements decreases. With the increase of EA geogrid (BCR) [1] increases. The study of the effect of the location of the hole showed that, by placing the hole at a depth of more than 3B, the rate of settlement increases and the amount of settlement is confirmed.

    Keywords: reinforced soil, geogrid, cavity, finite elements, settlement

    Chapter 1

    Overview

    Introduction

    Soil is a material that resists pressure and shear well, but is not able to resist tensile force of its own. to show Since ancient times, it has been experimentally seen that the roots of trees or plants have been effective in strengthening the soil mass. Reinforced soil is a composite building material in which elements with tensile strength are placed as reinforcement in the soil mass. The new concept of reinforced soil was first introduced by French architect Henri Vidal in 1965. Since then, this technique has been widely used in geotechnical engineering works, and in the last half century, a significant trend has been achieved in the research and use of reinforced earth structures. Today, soil reinforcement is technically an effective and reliable system for increasing the strength and stability of soil masses [1].

    The superiority of the behavior of reinforced soil is mostly due to the increase in shear strength in reinforced soil, which is due to the increase in the modulus of elasticity of the soil and the high resistance of the reinforcement in tension. It is used as a rough or smooth surface and in terms of relative hardness, i.e. with high relative hardness like steel or with low hardness like polymer textiles. Since the 80s, the use of synthetic polymers called geosynthetics [1] has become widely used. The reason for this problem can be due to the better performance of these products with low relative hardness, which have a better harmony with the soil, compared to metal reinforcement materials with high hardness. Due to their low relative hardness, these polymeric or synthetic textiles are more compatible with the soil in terms of deformability. In addition, permeable textiles are resistant to corrosion and some types are resistant to bacterial and acid attacks and are non-toxic. Artificial (canals), especially in urban areas, may be located near or under structures. When these holes are located at a depth that is within the range of the stress bubble under the foundation of the structures, in this case, the probability of the soil settling under the foundation is very high. In order to solve this problem, different methods of soil improvement are used. With the introduction of new geosynthetic materials to civil engineering, the application of these products has been considered to solve the above-mentioned problem. In this research, by using geosynthetics as reinforcement and considering the axial stiffness, length, number of layers and distances of the reinforcement, the location of the holes, the bearing capacity of the wide foundation located on the granular soil has been evaluated. 1-3- Objectives Research

    Considering that polymer products are expanding rapidly and also such products such as geosynthetics and their types such as geogrids have good compatibility with the soil.. They are also very economical. Therefore, this research aims to investigate and evaluate how to use geosynthetic reinforcement in order to increase the bearing capacity of porous granular soils under wide foundations. 1-4- Research questions and hypotheses In this research, plaxis software has been used to investigate the stability of reinforced soil on underground cavities. This software is able to perform analysis in two-dimensional and three-dimensional space by numerical method of finite elements.

    According to the conditions of the problem, in order to perform the required analysis on the built models, plane strain mode is considered. In order to study the mutual influence of soil with reinforcement and their combined geometry, in the stability of the reinforced soil cover on the hole, various parameters that characterize the characteristics of each of the above factors will be investigated. In examining the impact of each parameter, other parameters will be kept constant. Variable parameters include axial stiffness, geosynthetic length, number of reinforcing layers, and the distance of the first layer from the foundation. Fixed parameters include foundation type, number of holes, soil type, soil conditions and static loading. It should be noted that the distance between the geosynthetics is considered fixed.

    1-5-Research model

    In this research, the dimensions of the considered model are 70 meters long and 40 meters high. The considered hole has a radius of 1.5 meters, the width of the wide foundation is 10 meters and its depth is 1 meter. According to the conditions of the problem, in order to perform the required analyzes on the built patterns, the plane strain mode is considered and to form the finite element network and perform the calculations, 15-node triangular elements have been used for the soil layer and 5-node elements for the geogrid element. Two types of soil cover of the type of grains with Moore-Coulomb behavioral pattern are considered on the hole.

    The parameters with abbreviations used in the present research which seem to be the main parameters affecting the bearing capacity of reinforced soil are as follows:

    The vertical distance from the foundation to the first reinforcing layer (u)

    The number of reinforcing layers (N)

    The total thickness Reinforced soil (d)

    Vertical distance between layers (h)

    Reinforcement length (Lr)

    Foundation width B

    Foundation depth (Df)

    Soil characteristics including soil specific gravity, soil adhesion (c) and soil internal friction angle

    Reinforcement characteristics

    1-7-Research method

    In this research, using the finite element numerical method, according to the considered variables, various models were first built and then analyzed. In the third chapter, the background of the research has been examined and in the fourth chapter, a brief introduction of plaxis software and validation has been discussed. In the fifth chapter, the characteristics of materials and modeling methods have been described, and in the sixth chapter, the analysis of the models and the examination of the results of the models have been discussed and investigated. Finally, in the seventh chapter, summaries, conclusions and suggestions have been presented for those who are interested in continuing the research of this topic.

    Chapter 2

    Bearing capacity of foundations and applications of geosynthetics

    1 Introduction

    The ultimate bearing capacity of foundations has been considered for a long time, and among many factors and parameters, including parameters of soil shear strength, foundation shape and dimensions, foundation depth, slope of the ground, slope of the foundation itself, inclination or Load eccentricity, underground water level, layered soil and soil compaction are effective on its value. In between, there are other factors that, despite the few cases of dealing with them, have a great impact on the final carrying capacity. Among these cases, we can mention the presence of underground holes in the soil, which, if adjacent to the foundation, will be one of the determining factors in the final bearing capacity of the foundation. Today, the construction of underground buildings has been widely developed, so that due to the ever-increasing needs of mankind and with the advancement of knowledge and technology, the scope of human activity has reached the underground and even under the existing structures in urban areas. In this regard, there are many examples of structures located on holes and tunnels. These holes can be the result of activities such as mine exploration or tunnel digging.

  • Contents & References of Increasing the bearing capacity of porous granular soils under wide foundations by means of geosynthetics

    List:

    Abstract. 1

    Chapter One: Generalities

    1-2- Necessity of doing research. 4

    1-3-Research objectives. 4

    1-4- Research questions and assumptions. 4

    1-5-Research model. 5

    1-7-Research method. 6

    1-8- thesis structure. 6

    Chapter Two: Bearing capacity of foundations and applications of geosynthetics

    2-1 Introduction. 8

    2-2- Basics of carrying capacity. 8

    2-3- Bearing capacity of porous soils. 11

    2-4- History of geosynthetic materials. 12

    2-4-1 General description of geosynthetics 12

    2-4-2 Classification of geosynthetics 13

    2-4-3- Geosynthetics 18

    Chapter three: Research background

    3-1- Introduction. 22

    3-2- Laboratory study. 25

    3-2-1- Checking the behavior of load-settlement of strip foundations installed on soil reinforced with geogrid on the hole 25

    3-2-2- Test device and material specifications. 26

    3-2-3- Experiments program 28

    3-2-4- Presentation of results and data interpretations 29

    3-2-5- Conclusion. 33

    3-3- Numerical and analytical study. 33 3-3-1- Prototyping the problem 34 3-3-2- Investigating the depth effect of placing the first geotextile layer. 35

    3-3-3- Investigating the tensile strength of geotextile. 37

    3-3-4- Investigating the effect of the number of geotextile layers. 38

    3-3-5- Investigating the effect of geotextile layer length. 40

    3-3-6- Conclusion. 42

    Chapter four: Brief introduction of PLAXIS software and accuracy of modeling

    4-1- Introduction. 44

    4-2 Introduction of Plaxis software. 45

    4-3 important features of Plaxis software version 8.2. 47

    4-4- Verification of Plaxis software. 48

     

    Chapter Five: Specifications of materials and how to model

    5-1- Introduction. 51

    5-2- Geometry of the model. 51

    5-3- Specifications of materials. 53

    5-3-1- Characteristics of soil. 53

    5-4- How to model. 56

    Sixth chapter: Modeling and results review

    6-1- Introduction 58

    6-2- Problem conditions 58

    6-3- Parametric studies. 58

    6-3-1-The effect of the number of geotextile layers. 59

    6-3-2-Effect of geogrid length 60

    6-3-3- Optimum location of the first layer of geogrid 62

    6-3-4- Effect of geogrid tensile strength 63

    6-3-5- Effect of hole location in the soil. 64

    Seventh chapter: summary and summary of results

    7-1- Introduction 67

    7-2- Summary. 67

    3-7- Conclusion. 67

    7-4- Providing suggestions for further research. 68

    List of references. 69

     

    Source:

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    [4]. Wang, M.C. and Badie, A. (1985), "Effect of Underground Void on Foundation Stability", Journal of Geotechnical Eng., ASCE, Vol.111.No. 8, August 1985, pp. 1008-1119. [5]. Binquet, J., and Lee, K.L.(1975a), "Bearing Capacity Tests on Reinforced Earth Slabs", Journal of Geotechnical Eng.Div., ASCE, Vol,101, No.12, pp 1241-1255.

    [6]. Fragaszy, R., and Lawton, E.(1984), "Bearing Capacity of Reinforced sand subgrades", Journal of Geotechnical Eng., ASCE, Vol,110,No.10,pp 1500-511.

    [7].Gudio, V.A., Chang, D.K., and sweency.M.A.(1986), "Comparison of Geogrid and Geotextile Reinforced Earth slabs", Canadian Geotechnical Journal, No. 23,pp435-440.

    [8].Akinmusuru, J.O., and Akinbolade, J.A.(1981), "Stability of Loaded Footing on Reinforced Soil", Journal of Geotechnical Eng. Div., ASCE, Vol,107,No.6,pp 819-827.

    [9].Huang, C.C., and Tatsuoka, F.(1988), "Prediction of Bearing Capacity in Level Sandy Ground Reinforced with strip Reinforcement", Proceeding International Geotechnical Symposium Theory and(1988), "Prediction of Bearing Capacity in Level Sandy Ground Reinforced with strip Reinforcement", Proceeding International Geotechnical Symposium Theory and Practice of Earth Reinforcement, Balkema, Fukuoka, Kyushu, Japan, pp.191-196.

    [10]. Khing, K.H., Das, B.M., Puri, V.K., Yen, S.C., and Cook, E.E. (1994), "Foundation on Strong Sand Underlain by Weak Clay with Geogrid at the Interface", Journal of Geotextile and Geomembranes, Vol,13,No.3,pp 199-206.

    [11].Takemura,J., Okamura,M., Suesmasa,N., Kimura,T. (1992), "Bearing Capacity and Deformations of Sand Reinforced with Geogrid". Proceeding Oath Reinforcement Practice, Balkema, Fukuoa, Kyushu, Japan, pp.695-700.

    [12].Omar,M.T.,Das,B.M.,Yen,S.C.,Puri,V.K.and Cook,E.E. (1993) "Ultimate Bearing capacity of Rectangular Foundations on Geogrid-Reinforcement sand", Geotechnical Testing Joumal, Vol,15,No.2,pp 246-252.

    [13]. Christopher, B.R.  and Holtz, R.D.  (1985), "Geotextile Engineering Manual", United States Department of Transportation, Federal Highway Administration, Washington DC, Report No. FHWA-TS-86/203, 1044p.

    [14]. Mannsbart, G. and Christopher, B.R. (1996), "Long-term Performance of Nonwoven Geotextile Filters in Five Coastal and Bank Protection Projects", Proceedings of the 10th Geosynthetics Research Institute Conference on Performance of Geosynthetics and Geosynthetic Related Systems, Philadelphia, Pennsylvania, pp. 26-38.

    [15]. Bhatia, S.K. AND Suits, D., (1996), "Geotextile Filters and Prefabricated Drainage Geocomposites", American Society for Testing and Methods, STP 1281, PA, USA.

    [16]. US Army Corp of Engineers (1977), "Civil Works Construction Guide Specification for Plastic Filter Fabric", Corps of Engineer, U.S. Army Corps of Engineer Specifications No. CW-02215, Office, Chief, Chief of Engineers, U.S. Army Corp of Engineers, Washington, D.C.

    [17].  Maharaj D.K., (2003). "Nonlinear finite element analysis of stip footing on reinforced clay." The Electronic Journal of Geotechnical Engineering, Vol.8, Bundle C. [18]. Ingold, T.S., and Miller, K.S., (1992), ``Analytical and laboratory investigation of reinforced clay.'' Proceedings of the 2nd International Conference on Geotextiles, Vol.3,pp. 587-592. [19].  Khing, K.H., Das, B.M., Puri, V.K., Cook, E.E., and Yen, S.C., (1993), ‘‘The bearing capacity of a strip foundation on geogrid reinforced sand.’’ Geotextiles and Geomembranes, Vol.12, pp. 351-361.

    [20]. John, N.W.M., Geotextile, First Pub, Chapman and Hall, U.S.A., [21]. Bauer, G.E(1987)., Control of Settlement Using Geogrids, Proceeding of the Conference on Vertical and Horizontal Deformations of Foundations and Embankments, ASCE, Vol.1, (1994)

    [22]. Bauer, G.E, (1994). Control of Settlement Using Geogrids, Proceeding of the Conference on Vertical and Horizontal Deformations of Foundations and Embankments, ASCE, Vol.1.

    [23].  Michalowski, R.L., April (2004), ``Limit loads on reinforced foundation soils'', Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol.130, No.4, pp. 381-390.

    [24].  Omar, M.T., Das, B.M., Yen, S.C., Puri, and Cook, E.E., (1993a), ``Ultimate bearing capacity of rectangular foundations on geogrid-reinforced sand.'' Geotechnical Testing Journal,ASTM,Vol.16, No.2, pp. 252-246. [p>

    ]25[. Asakre, Adel, Laboratory investigation of the load-settlement behavior of strip foundations placed on soil reinforced with geogrid on a cavity, 2018, Shiraz University International Engineering Congress.

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Increasing the bearing capacity of porous granular soils under wide foundations by means of geosynthetics
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