SETTLEMENT EVALUATION OF SHALLOW FOUNDATION SUBJECTED TO VERTICAL LOAD ON THE MULTI-LAYER SOIL

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 12, December 18, pp , Article ID: IJCIET_09_12_105 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed SETTLEMENT EVALUATION OF SHALLOW FOUNDATION SUBJECTED TO VERTICAL LOAD ON THE MULTI-LAYER SOIL Jasim M Abbas Assistant Professor, Department of Civil Engineering, College of Engineering, Diyala University, Iraq ABSTRACT In general, the building foundation rest of the layered soil, which was not covered enough in previous studies that were taken only into account one dimensional or two dimensional soil layer system. While in this study mainly taken into account the three dimensional effect on soil layers which that usually closed to the field condition. Therefore, the behavior of shallow foundation constructed over multi layered soil has been presented in this study. Finite element method has been used to achieve the goal obtained from this study. The soil material and concrete part used in this simulation has been modeled as Mohr-Columb and linear elastic models, respectively. It can be concluded that the foundation settlement changed when changing the soil layer system and therefore this issue should take into account when analysis and design for such kind of foundation. Key words: shallow foundation, FEM, 3D soil profile, settlement Cite this Article: Jasim M Abbas, Settlement Evaluation of Shallow Foundation Subjected to Vertical Load on the Multi-Layer Soil, International Journal of Civil Engineering and Technology (IJCIET) 9(12), 18, pp INTRODUCTION In most numerical and/or analytical solutions for shallow foundation, the soil layers were represented used only one bore hole (i.e. horizontal soil profile), even as the other using two bore holes. While the soil profile is really in three dimensional shape. This phenomenon, which has not been studied in detail previously, can have an effect on the behavior of foundations and therefore the results should be used from such studies in foundation analysis and design in the future. In general, analysis of such problems cannot be in the field of great difficulty which will certainly occur in such cases. In addition, in the case of analysis by traditional analytical methods that there are many variables, which cannot be any way to find solutions to them, for example the study [1, 2]. Therefore, After looking at the previous research related to consideration of the soil in the case of 3D it was found to be limited and did not cover all the important criteria to be editor@iaeme.com

2 Settlement Evaluation of Shallow Foundation Subjected to Vertical Load on the Multi-Layer Soil provided. This was first studied by [3] where FEM was used and the representation was approximated to the nearest reality, but soil layers were not taken and the real representation as well as the soil modeling.the finite element method will be the ideal way to find a close representation of the truth for such problems. number of studies were used this powerful technique to simulation and analysis of geotechnical system [4, 5, 6 and 7]. On this basis, this study used the FEM for the purpose of representing the soil and the foundation and taking into account that there is a real effect of the soil layers on the partial settlement that occurs at the base of the foundation. The Plaxis program was used to implement the study objective with a number of characteristics that became necessary to study. 2. DESCRIPTION OF THE CASE STUDY Figure 1 describe the case study that included all dimensions. It is assumed that the foundation base is 0.7 from the ground surface elevation and from subase material under the base of foundation. The water table is 1.5 from ground surface that obtained from the real case. The external loads are divided into 12 point load. Every point load carried 1000 kn Figure 1 Profile and plane views of case study 1 3. ANALYSIS METHODOLOGY AND LAYOUT In fact, the representation used in the Plaxis 3D program (Brinkgreve & Broere 04) mainly contains concrete representation by linear-elastic model with -node wedge elements as well as soil representation by the Mohr-Columb model as well as the representation of the interface zone by zero thickness element. This is a comprehensive representation of the entire system in terms of geometry. In order to complete the second step of the analysis, Table 1 includes a definition of all the materials used in this study editor@iaeme.com

3 Jasim M Abbas Table 1 Soil layers in four Bore holes BH1 Brown sandy silt Brown clay sandy Brown clay silt Brown silt sand with amount of clay Elev γ E v c φ BH2 Brown sandy silt with amount of clay and gravel Brown clay sandy silt Brown silt sandy with clay Brown clayey sand silt Brown clayey silt sand Brown silt sandy with clay BH3 Brown sandy silt Brown clay sandy Brown clay silt Brown silt sand with amount of clay BH4 Brown sandy silt with amount of clay and gravel Brown clay sandy silt Brown silt sandy with clay Brown clayey sand silt Brown clayey silt sand Brown silt sandy with clay Three-dimensional model that resulted from finite element program included mainly the mesh of shallow foundation and surrounded the soil mass is shown in Figure 2. The boundary of the whole system extends in all directions with 5m. in this case, the trial method for mesh selection is used to fix that until the result been closed with several trails. the mesh usually more finer when reaches the foundation. the nodes on the outside boundary except the top surface are restrained from moving. Figure 2 Three dimension finite element mesh of case study editor@iaeme.com

4 Settlement Evaluation of Shallow Foundation Subjected to Vertical Load on the Multi-Layer Soil 4. RESULTS AND DISCUSSIONS In order to achieve the objective of this study, four bore holes have been assigned with layers in different depth and also different properties. In the first phase, only one bore hole was used for the study. while in the second, third and fourth stages were used 2, 3 and 4 bore holes, respectively, and a comparison was made between the results obtained from these cases. In addition, four sections were assigned in this foundation, two of them were longitudinal section and others were along the width, as shown in Figure2. Figure 2 horizontal and vertical sections used in this study and bore hole distribution 5. SETTLEMENT ANALYSIS USED ONE BOREHOLE Initially, for the purpose of the initial analysis, which can be used to compare with other cases, the definition of the soil was determined by a sample obtained from a single bore hole (i.e. BH1, BH2, BH3 and BH4). This assumption was usually used in previous studies and hence the idea used to improve the new finding of this study that taking more than one bore hole in the analysis at the same time. Figure 3 (a and b) shows the distribution of foundation settlement along its length (i.e. Section A1-A1 and Section A2-A2). It can be observed that the highest settlement of the foundation was in the center and gradually decreases down to the both sides, which is known in the fundamental of the foundation engineering. in addition, it can be seems that the highest settlement was in the section A2-A2 compared to the second section in most cases. It can also be noted that there is a clear difference in the magnitude of the settlement when comparing several types of soils and this is attributed to the difference properties of each soil and there before its impact on the amount of displacement. In addition, the settlement analysis for shallow foundation in vertical sections (section B1- B1 and section B2-B2) is illustrated in Figure 3 (c and d). It is clear that there is a great similarity with the behavior of the previous cases with the significant differences in the settlement values. This part will be clear from the taking of cases coming from the selection of more than a bore hole analysis, and that the differential settlement will be different between one section and another editor@iaeme.com

5 Jasim M Abbas Figure 3 Settlement distribution along foundation length and width for one bore hole, (a) section A1- A1, (b) section A2-A2, (c) section B1-B1 and (d) section B2-B2 6. SETTLEMENT ANALYSIS USED TWO BORE HOLES This part included the assessment of foundation settlement used two bore holes. This type of analysis probably closed to the real cases. This analysis was resulted based on four bore holes as follows (i.e. BH1+BH2, BH1+BH3, BH1+BH4). Figure 4 shows 3D soil mass that generated depend on two bore holes. Here it can see the change of soil layers below the foundation which can affect the behavior. Figure 5 (a and b) shows the distribution of foundation settlement along its length (i.e. Section A1-A1 and Section A2-A2). In addition, the settlement analysis for shallow editor@iaeme.com

6 Settlement Evaluation of Shallow Foundation Subjected to Vertical Load on the Multi-Layer Soil foundation in vertical sections (section B1-B1 and section B2-B2) is illustrated in Figure 5 (c and d). It can be noted also that the highest value of the settlement was at the center of the foundation and that the maximum value was near to the middle sections (i.e. sections A2-A2 and B2-B2) and usually move to the right side. However, the deformation was not equal when moving away from the center, in this case the effect of the layers on the overall behavior of the system is clearly demonstrated here. Where the difference in the decline between the sides is up to 5%. This is serious and needs to be taken into consideration in analysis or design. While the difference in settlement between the center and left side reached 9%, while with the right side it reached 4%. This is due to the change in response of soil under foundation when change the properties and depth of layers. While when compared to the section B-B, it is clear that this difference is less and this is because of used only two holes, which affected the first section clearly. Where it is found that the highest value of the settlement was in the middle and gradually decreasing until reaching the sides which were almost equally. Figure 4 Three dimension finite element mesh of case study used two bore hole 10 editor@iaeme.com

7 Jasim M Abbas Figure 5 Settlement distribution along foundation length and width for two bore hole, (a) section A1- A1, (b) section A2-A2, (c) section B1-B1 and (d) section B2-B2 7. SETTLEMENT ANALYSIS USE THREE BORE HOLES This part included the assessment of foundation settlement used three bore holes (i.e. BH1+BH2+BH3, BH1+BH3+BH4). This type of analysis much near to the real cases. Figure 6 shows 3D soil mass that generated depend on three bore holes. Figure 7 (a and b) shows the distribution of foundation settlement along its length (i.e. Section A1-A1 and Section A2-A2). In addition, the settlement analysis for shallow foundation in vertical sections (section B1-B1 and section B2-B2) is illustrated in Figure 7 (c and d). The effect of the change in the soil layers can be observed in such a way that the difference between the two ends of the base is about 5% to 8%. This is due to a change in the layers below the foundation, which has different depths and properties. Figure 6 Three dimension finite element mesh of case study used three bore hole editor@iaeme.com

8 Settlement Evaluation of Shallow Foundation Subjected to Vertical Load on the Multi-Layer Soil Figure 7 Settlement distribution along foundation length and width for three bore hole, (a) section A1- A1, (b) section A2-A2, (c) section B1-B1 and (d) section B2-B2 8. SETTLEMENT ANALYSIS USED FOUR BORE HOLES This part included the assessment of foundation settlement used four bore holes. This type of analysis exactly closed to the real cases. This analysis was resulted based one four bore holes (i.e. BH1+BH2+BH3+BH4). Figure 8 shows 3D soil mass that generated depend on four bore holes. Figure 9 shows the distribution of foundation settlement along its length (i.e. Section A1-A1 and Section A2-A2) as well as its width (i.e. Section B1-B1 and Section B2-B2). It can seem that in the section A- A, the highest value of the settlement occurred in the middle area as usual, but moving from the center towards the right side slightly due to the influence of the different layers under the foundations. The difference between these higher values approximates 3% between the region editor@iaeme.com

9 Jasim M Abbas in the sectiona1-a1 and section A2-A2. in addition, the difference between the side settlement up to 4% in this section. While in the section B-B shows that there is a similar behavior in terms of the presence of the highest settlement in the center, but the foundation tends to the right side. The difference between the two sides is up to 2.%. This is certainly because of the layers below the foundation. Figure 8 Three dimension finite element mesh of case study used four bore hole Figure 9 Settlement distribution along foundation length and width used four bore hole editor@iaeme.com

10 Settlement Evaluation of Shallow Foundation Subjected to Vertical Load on the Multi-Layer Soil 9. CONCLUSIONS It is very clear that the finite element method and the Plaxis program can represent such large and complex problems that the thickness of the soil layer is taken under the foundations The difference in the number of bore holes greatly affects the behavior of the foundation, where the deferential settlement occurs under foundation of in this condition. In many cases, the foundation tends to one side when supported vertical loads and sometimes the difference between the two sides reach to 8%. This is very important because it can affect the stability of buildings, especially in the tall buildings. REFERENCES [1] M J. Cassidy, B. W. Byrne and G. T. Houlsby. Modelling the behaviour of circular footings under combined loading on loose carbonate sand. Geotechnique 52,(10): (02). [2] K. Horikoshi and M. F. Randolph,. On the defnition of raft-soil stiffness ratio for rectangular rafts. Geotechnique 47( 5): (1997). [3] G. A. Fenton, and D. V. Griffiths. Three-Dimensional Probabilistic Foundation Settlement. Journal of Geotechnical and Geoenvironmental Engineering. 131(2): 1-17 (05). [4] A. Nour,, A. Slimani, N. Laouami. Foundation settlement statistics via finite element analysis. Computers and Geotechnics 29 : (02) [5] J.M. Abbas, Z. Chik,, M.R. Taha. Influence of group configuration on the lateral pile group response subjected to lateral load. Electronic Journal of Geotechnical Engineering. (G): (10). [6] O. Enkhtur, T. D. Nguyen, J. M. Kim, and S. R. Kim. Evaluation of the Settlement Influence Factors of Shallow Foundation by Numerical Analyses. KSCE Journal of Civil Engineering. 17(1):85-95 (13). [7] J. M. Abbasa, Z. Chik, and M. R. Taha,. Influence of axial load on the lateral pile groups response in cohesionless and cohesive soil. Frontiers of Structural and Civil Engineering. 9, ( 2): pp (). [8] R.B.J. Brinkgreve, and W. Broere,. PLAXIS 3D FOUNDATION - version 1. Netherlands (04) editor@iaeme.com