BEHAVIOUR OF skirt Raft foundation on sandy soil Using PLAXIS 2D.pptx

The skirt restrains the soil beneath laterally and acts as soil plug to transfer the load from super structure to the soil.
This foundation is commonly used for wind turbines, offshore structures, storage tank, windmill tower and oil tank.

1. BEHAVIOUR OF skirt Raft foundation on sandy soil Using PLAXIS 2D Presented by MANISH SHARMA 2020PGCEGE12 Under the Supervision of DR. A. K. SINHA

2. Introduction Literature Review Research Gap Objective Methodology Result and Discussion Conclusion Reference CONTENTS

3. Introduction: Now a days utilization of land is more important due to increase of population and less land area. Engineering’s are forced to do construction on weak soil like sand, clay, peat etc., Structure’s constructed on weak soil must be designed with good improvement techniques as required to the field conditions. The choice of ground improvement technique depends up on economic, availability of material, site restriction and environmental condition. In these modern developing days, there are lot of improvement techniques used for soil stabilization but some of them are site restriction on the field, difficult in installation and cost expansive. It is also difficult to apply on existing foundation. CIRCULAR SKIRT FOOTING

4. So that, structural skirt footing is more appropriate technique use to improve bearing capacity and reduce settlement of shallow footing resting on the soil. This technique has been using since long time to increase the Bearing Capacity of foundation in offshore areas. This technique does not require any excavation of soil. The presence of high-water table also will not affect the footing. The skirt restrains the soil beneath laterally and acts as soil plug to transfer the load from super structure to the soil. This foundation is commonly used for wind turbines, offshore structures, storage tank, windmill tower and oil tank. Confinement of soil takes places when skirts are installed

5. S.No AUTHOR REVIEW CONCLUSION 1 M. Y. Al-Aghbari (2006) Experimental test was done on circular skirt footing resting on sand to study the settlement of circular footing with and without structural skirts. Results show’s that this type of reinforcement modifies the stress-displacement behavior of the footing and reduce the settlement of subgrade. By considering various parameters that affects the settlements, the settlement reduction factor (SRF) is proposed. Depending up on stress applied and skirt depth, structural skirt produced settlement reduction of 0.1 to 1.0. SRF = 2 Amr Z. EL Wakil (2013) E xplained about the bearing capacity of shallow foundation on sandy soil using experimental test with circular skirt foundation, by changing the relative density and skirt length to footing diameter ratio. As skirt length to footing diameter ratio increases, the settlement-diameter ratio increases at failure load. Skirts are more effective solution to shallow foundation when the relative density is less than 65%. Skirts ra more beneficial in loose sand than in dense and medium sand S.No AUTHOR REVIEW CONCLUSION 1 M. Y. Al-Aghbari (2006) Experimental test was done on circular skirt footing resting on sand to study the settlement of circular footing with and without structural skirts. Results show’s that this type of reinforcement modifies the stress-displacement behavior of the footing and reduce the settlement of subgrade. By considering various parameters that affects the settlements, the settlement reduction factor (SRF) is proposed. Depending up on stress applied and skirt depth, structural skirt produced settlement reduction of 0.1 to 1.0. 2 Amr Z. EL Wakil (2013) E xplained about the bearing capacity of shallow foundation on sandy soil using experimental test with circular skirt foundation, by changing the relative density and skirt length to footing diameter ratio. As skirt length to footing diameter ratio increases, the settlement-diameter ratio increases at failure load. Skirts are more effective solution to shallow foundation when the relative density is less than 65%. Skirts ra more beneficial in loose sand than in dense and medium sand LITREATURE REVIEW :

6. S.No AUTHOR REVIEW CONCLUSION 3 Hisham T. Eid (2013) C ompared the surface foundation resting on sand with square skirt foundation and pier foundation of same size and depth with plaxis 2D. The shear strength of sand, skirt depth on bearing capacity and foundation size is evaluated. The results of this experiments of skirt and piers are almost same but not equal. Bearing capacity increases by increase in skirt depth and decreasing the relative density of sand. [q sk ] min = (1.8) D/B x q su [S sk ] max = (0.5) D/B x S su 4 Teja’s bhatkar, Sunil S. Pusadkar (2013) Explained about the raft foundation with inclined at one side, inclined at two sides and without skirt using FEM analysis. The results of the experiment explained that, increase in inclination of two sides is increasing bearing capacity and decrease in settlement, but for one side inclination both bearing capacity and settlement increases. The bearing capacity is found by keeping settlement 100mm and settlement is found by taking 1000 KN/m 2 . Inclined on two side is more effective than inclined on one side.

7. S.NO AUTHOR REVIEW CONCLUSION 5 W. R. Azzam (2014) Focused on the skirt foundation of four stored reinforced building adjacent to sand slope under earthquake loading using palxis 2D. The results declared that Skirt foundation stabilized the seismic slope, decrease the slope deformation and excess pore water pressure. The increasing skirt thickness will increase the subgrade thickness. Great effectiveness in increasing the stability of the slope and foundation. 6 Kangkan sarma, Dr. Nayanmoni Chetia (2016) Explained about the raft foundation with and without skirt on plaxis 2D under both Mohr’s column model and Hardening soil model. The geometry of raft foundation is 15BX20B with draft size of B= 10m, 15m, 20m with different skirt depth ratio. The results showed that bearing capacity increases and settlement decreases for both models but performance is better in Hardening soil model . Hardening soil model slightly better than Mohr’s coulomb model.

8. S.No AUTHOR REVIEW CONCLUSION 7 Vishwas N. K., S.P. Debbarma, Rakesh Kumar (2017) Done laboratory test on square and rectangular with and without skirt footing rest on sand to find bearing capacity and settlement behavior. The results of experiments given that the bearing capacity improved by 33.3% to 68.5%, 68.9% to 127% & 146.7% to 262% for skirt depth of 0.25b, 0.5b & 1.0B of skirted footing on footing without skirt. For relative density of sand at 30% and 50% are more effective than 70% and 87%. Improvement bearing capacity factor is used. 8 T. Gnananandarao, Vishwas N. K., Rakesh Kumar (2017) Explored about the improvement of pressure settlement behavior of sand on skirt footing with square shape and H shape by conducting series of plate load test. The parameters used are skirt depth and relative density. The bearing capacity of H plan shaped footing is slightly better than square footing, when relative density is same. H shape is better than Square footing 9 Rishma Hussain, Mrs. N. Chetia (2017) Explored the performance by experimental test on circular skirt foundation with Medium Dense Sand. The parameters used for the test are Improvement factor and skirt depth ratio. For maximum length of confinement, the improvement factor is 3.25 for bearing capacity out of various test. Settlement is decreased for skirt depth ratio increases and skirt diameter decreases. Reduction in settlement is 12% and increasing in BC is 3.25.

9. S.No AUTHOR REVIEW CONCLUSION 10 Lujain Haider, Haider M. Mekkiyah (2018) Explored the performance by experimental method considering 21 tests on circular skirt foundation with both closed end and open end on Dry Medium Dense Sand with different skirt length, foundation size and skirt conditions at relative density is equal to 60%. The test results declared that, by increasing skirt depth or foundation size the load carrying capacity of foundation has increased. The closed end is more effective than open end for load carrying capacity. Closed end is more better in load carrying capacity than open end. 11 D A W Gautama, B S Supanji and W Rahayu (2020) Explained about the skirt footings on peat soil to determine the settlement for consolidation of 5 days and 365 days on plaxis 2D. Compared the results of 16 variants skirt footing with unskirt footing and mini piles by using variants of skirt length and skirt diameter. For better holding loads skirt footing is good compared to unskirt footing. Vertical deformation of skirt footing has stabilized than the mini piles for concentered the load on an area of land. Circular footings plays a role in reducing the effect of settlement.

10. Research gap : Considering previous journals, I found that most of the experiment models and numerical models are done by using sand. We can use silt , clay or any combination of soil like silty clay, sandy clay, etc., The vertical skirts are placed in few papers but we can use inclined skirt with respect to vertical. The skirt inclination can be placed in clockwise direction with respect to vertical. Material model in plaxis can be changed other than Mohr’s coulomb and hardening soil we can also use soft soil for clay soils and Soft soil Creep Modeling for peat soils. The load applied on foundation can be horizontal, vertical with eccentricity or inclined load. Keeping all conditions same, we can compare the results of skirt foundation and any other ground improvement technique like stone column, mini piles, geogrid etc., Shape of footing can also be changed to I shape, etc.,

11. OBJECTIVE : From the above research gaps, I am interested to make the numerical modeling on Skirt Raft foundation placed on Sandy Soil. Structural skirts are placed inclined to the square footing by changing there skirt depth ratio, different Loads, inclination angle, and inclination position . The Skirt are placed inclined with respect to the vertical and a skirt placed at centre of the footing for both interior and exterior I will find the percentage of settlement for various loads acting on the footing for different widths, skirt angle, and skirt depth ratio. This numerical analysis has been done using PLAXIS 2D.

12. METHODOLOGY : The dimensions of soil model is considered as 20BX20B with different raft sizes are 15m, 20m, 25m, and 30m to analyze the settlement of Skirts The Skirt depth ratio is taken from 0.5, 1, 1.5, 2, and 2.5 are placed at the corner with the inclination of 5 ° and 10 ° and a vertical skirt at the center of the raft foundation for both interior and exterior of the footing.

13. Different Stages used in PLAXIS 2D The line load applied on the raft foundation varies from 0 kN/m 2 to 1000 kN/m 2 gradually. The Soil and Skirt parameter are used in this model can be seen in Table 1 & 2. For every change in parameter, the settlement values as be noted and percentage of settlement is calculated. Higher percentage of Settlement values signifies the lower settlement values. Percentage of Settlement = Settlement without Skirt – Settlement with Skirt Settlement without Skirt X 100

14. Table 1.Geometrical Properties of Sand PARAMETERS VALUE MATERIAL PLATE Material type ELASTIC Axial Stiffness of Steel Skirt, EA (kN/m) 31500 Flexural Rigidity, EI (kN-m 2 /m) 0.5 Table 2.Geometrical Properties of Skirt PARAMETERS VALUE Type of material Sand Material model Mohr coulomb Material behavior Drained E 50 (kN/mm 2 ) 40000  Unsat (kN/m 3 ) 20  Sat (kN/m 3 ) 20 Cohesion(c) 0.1 Poisson’s ratio(υ) 0.3 Friction Angle(φ) 35 Angle of Dilatancy(ψ) 2 Interface Reduction Factor ( R inter ) 0.7

15. VALIDATION : In this section, a model that was used in Kanga Sarma , et.al, research's is verified. They investigated the load-displacement behavior of the skirt raft foundation on sandy soil. The variable parameters used by Kangkan Sarma, et.al. (2016) were the depth of skirt D s = 0B, 0.5B, 1B, 1.5B, 2B, 2.5B, and 3B. The geometry of the finite element soil model taken for the analysis is 15BX15B with different raft sizes of B=10m, 15m, and 20m. Kanga Sarma et, al. did this by using the materials model of Mohr-Coulomb and the Hardening Soil model. In the analysis, for the maximum applied pressure of 1000 (kN/m 2 ) the corresponding settlement is measured.

16. SKIRT RATIO D s /B SETTELEMENT FOR 1000 (kN/m 2 ) AS PER KANGA SARMA et al. SETTELEMENT FOR 1000 (kN/m 2 ) AS PER PLAXIS 557 574 0.5 561 558 1 562 558 1.5 531 517 2 494 500 2.5 450 472 3 427 488 SKIRT RATIO D s /B SETTELEMENT FOR 1000 (kN/m 2 ) AS PER KANGA SARMA et al. SETTELEMENT FOR 1000 (kN/m 2 ) AS PER PLAXIS 2D 1055 994 0.5 1065 968 1 1156 996 1.5 1077 940 2 994 925 2.5 847 928 3 795 916 Settlement Results as per Researcher and by PLAXIS for Hardening Soil Model. Settlement Results as per Researcher and by PLAXIS for Mohr's Coulomb Model.

17. The Different Types of Effects are : Effect of Load. Effect of Foundation Width. Effect of Skirt Angle. Effect of Skirt Depth Ratio. RESULTS AND DISSCUSION: Geometry of Skirt Raft Foundation (a) Exterior Skirt Angle (b) Interior Skirt Angle

18. EFFECT OF LOAD : Load vs settlement for B=15m, Interior Skirt Angle 5 ° LOAD (kN/m 2 ) SETTLEMENT (mm) D=0B D=0.5B D=1B D=1.5B D=2B D=2.5B 100 -89.76 -86.7 -85.96 -85.57 -85.32 -85.14 200 -179.6 -173.3 -172 -171.2 -170.2 -169.7 300 -269.5 -259.7 -258.1 -256.9 -256.1 -255.6 400 -362.1 -348.1 -346.2 -343.6 -342.6 -341.8 500 -459.8 -441.5 -439 -434.1 -432.4 -431.8 600 -564.8 -541.8 -538 -531.2 -528.4 -526.3 700 -674.4 -646.6 -640.6 -632.2 -629.9 -625.2 800 -799 -761.4 -755 -747.1 -739.9 -730.1 900 -953.4 -901.3 -891.5 -880 -856.8 -837.4 1000 -1100 -1037.3 -1022 -1009 -987.5 -951.5 Settlement for B=15m, Interior Skirt Angle 5 ° Interior Skirt

19. Load vs Percentage of settlement for B=15m, Skirt Angle 10 ° Load vs Percentage of settlement for B=15m, Skirt Angle 5 °

20. Load vs Percentage of settlement for B=20m, Skirt Angle 5 ° Load vs Percentage of settlement for B=20m, Skirt Angle 10 °

21. Load vs Percentage of settlement for B=25m, Skirt Angle 5 ° Load vs Percentage of settlement for B=25m, Skirt Angle 10 °

22. LOAD D=0B D=0.5B D=1B D=1.5B D=2B D=2.5B 100 -179.5 -169.8 -169.1 -168.7 -168.5 -168.3 200 -359 -339.6 -338.2 -337.5 -337 -336.6 300 -538.6 -509.4 -507.5 -506.3 -505.5 -505 400 -718.3 -679.4 -676.8 -675.3 -674.2 -673.5 500 -898 -849.4 -846.3 -844.3 -843.1 -842.2 600 -1078 -1020 -1016 -1013 -1012 -1011 700 -1261 -1192 -1187 -1183 -1182 -1180 800 -1450 -1369 -1361 -1357 -1354 -1351 900 -1642 -1548 -1540 -1535 -1530 -1527 1000 -1839 -1730 -1724 -1716 -1712 -1708 Load and Settlement Load Vs Settlement for B=30m, Interior Skirt angle 10 ° When B=30m, Interior Skirt Angle 10 °

23. Load Vs Percentage of Settlement for B=30m, Interior Skirt angle 5 ° LOAD (kN/m 2 ) PERCENTAGE OF SETTLEMENT (%) D=0.5B D=1B D=1.5B D=2B D=2.5B 100 5.18 5.74 6.02 6.13 6.24 200 5.13 5.77 5.99 6.13 6.21 300 5.12 5.76 6.00 6.13 6.22 400 5.23 5.75 5.99 6.13 6.22 500 5.28 5.75 5.98 6.12 6.21 600 5.33 5.75 5.94 6.12 6.22 700 5.35 5.87 6.11 6.26 6.34 800 5.38 6.07 6.30 6.55 6.62 900 5.36 6.09 6.39 6.76 6.82 1000 5.44 6.09 6.47 6.80 6.91 Load and Percentage of Settlement

24. Exterior Skirt Load vs Percentage of settlement for B=15m, Skirt Angle 5 ° Load vs Percentage of settlement for B=15m, Skirt Angle 10 °

25. Load vs Percentage of settlement for B=20m, Skirt Angle 5 ° Load vs Percentage of settlement for B=20m, Skirt Angle 10 °

26. Load vs Percentage of settlement for B=25m, Skirt Angle 5 ° Load vs Percentage of settlement for B=25m, Skirt Angle 5 °

27. Load vs Percentage of settlement for B=30m, Skirt Angle 5 ° Load vs Percentage of settlement for B=30m, Skirt Angle 10 °

28. EFFECT OF FOUNDATION WIDTH : Skirt Angle 10 ° Skirt Depth Ratio Vs Percentage of Settlement for Exterior Skirt Depth Ratio Vs Percentage of Settlement for Interior

29. Skirt Angle 5 ° : Skirt Depth Ratio Vs Percentage of Settlement for Exterior Skirt Depth Ratio Vs Percentage of Settlement for Interior

30. EFFECT OF SKIRT ANGLE : Skirt Depth Ratio Vs Percentage of Settlement for B=15m Skirt Depth Ratio Vs Percentage of Settlement for B=20m

31. Skirt Depth Ratio Vs Percentage of Settlement for B=25m Skirt Depth Ratio Vs Percentage of Settlement for B=30m

32. EFFECT OF SKIRT DEPTH RATIO : Exterior : Width of Raft Foundation Vs Percentage of Settlement for Skirt Angle 5 ° Width of Raft Foundation Vs Percentage of Settlement for Skirt Angle 10 °

33. Interior : Fig. 3 Width of Raft Foundation Vs Percentage of Settlement for Skirt Angle 5 ° Fig. 3 Width of Raft Foundation Vs Percentage of Settlement for Skirt Angle 10 °

34. CONCLUSION : It is observed that as the skirt depth ratio increases, 15m foundation width show the highest percentage of settlement for different skirt angles, irrespective of the skirt location as compared to other foundation widths. With an increase in the skirt depth ratio the percentage settlement increases whether we are using interior or exterior skirt. The highest percentage of settlement is observed when the skirt depth ratio is 2.5. So, it must be adopted for skirt foundation. When the skirt angle is changed from 5 to 10 degree, it shows larger percentage of settlement. Therefore, it is concluded that for any type of skirt, whether exterior or interior, a larger skirt angle is preferred.

35. When the skirt angle and width of foundation is kept constant, larger percentage of settlement is observed in exterior skirt. So, exterior skirt is recommended to be used instead of interior skirt. It is observed that as the load is increased beyond 500kN/m 2 , the percentage of settlement is quite significant for all the skirt depth ratio.

36. [1] M. Y. Al- Aghbari ,(2007) “ Settlement of shallow circular foundation with structural skirt resting on sand ”. The Journal of Engineering Research Vol. 4, No.1 ,11-16. [2] Amr Z. EL Wakil, “Bearing capacity of skirt circular footing on sand”. Alexandria Engineering Journal, (2013). [3] Hisham T. Eid, (2013 ) “Bearing capacity and settlement of skirted shallow foundation on sand”. International journal of geomechanics © ASCE 645. [4] Sunil S. Pusadkar, Teja's Bhatkar, (2013) “Behavior of raft foundation with inclined skirt using plaxis 2D”. Proceedings of Indian Geotechnical Conference December 22-24, Roorkee. [5] W .R. Azzam, (2014 ) “Finite element analysis of skirted foundation adjacent to sand slope under earthquake loading”. Housing and Building National Research Center. [6] Kangkan sarma, Dr. Nayanmoni Chetia , (2016) “Load displacement behavior of skirted raft foundation sand using Plaxis 2D”. International Journal of Advanced Engineering Research and Science (IJAERS). [7] Vishwas N. K., S.P. Debbarma, Rakesh Kumar, B Mohanty, (2017) “Pressure settlement behavior of square and rectangle skirted footing resting on sand”. Geomechanics and Engineering, Vol. 12, No. 4 , 689-705. REFERNCE :

37. [8] T. Gnananandarao, Vishwas N. K., Rakesh Kumar, (2017) “ Performance of multi edged skirt footings resting on sand”. Indian Geotech J DOI 10.1007/s40098-017-0270-6. [9] Rishma Hussain, Mrs. Nayanmoni Chetia , (2017) “ A Study on the Performance of Circular Skirted Foundation on Medium Dense Sand”. Indian Geotechnical Conference GeoNEst . [10] Lujain Haider, Haider M. Mekkiyah , (2018 ) “ Response of Skirted Foundations Resting on Dry Medium Dense Sand”. Civil Engineering Journal. [11] D A W Gautama, B S Supanji and W Rahayu , (2020) “The effect of skirt footings for road settlement on peat soil”. 4th International Conference on Civil Engineering Research.

38. THANK YOU