group 9 sbc of soil.pptx

safe bearing capacity of soil

1. UMA CHARAN PAATTNAIK ENGINEERING SCHOOL BERHAMPUR regd no:- f20012001002 f20012001001 l2001200100 3 f20012001025 TOPIC:- Safe bearing capacity PRESENTED BY;- name:- Akash kumar panda A.sritam patro g OURG opal jena etishree nayak guided by:- Er.Deeptirani mishra

2. Title and Content Layout with List Introduction Literature review soil bearing capacity of soil Requirements of SaFE bearing capacity objective Methodology FACTORS AFFECTING SAFE BEARING Reference 11/5/2023 Add a footer 2

3. Introduction The safe bearing capacity of soil field test is performed to verify the soil’s ability to support loads.Let’s consider an example of a small plastic chair. The small plastic chair made for children and can support a capacity of 10 kg. Suppose, if an adult has sat down, the chair will be broken. The same case is applied to the soil. The bearing capacity of soil may be explained as the capacity of the soil to hold the loads transferring from the foundation 11/5/2023 Add a footer 3

4. Foundation design consists of two distinct parts: the ultimate bearing capacity of the soil under the foundation, and the tolerable settlement that the footing can undergo without affecting the superstructure They investigated the ultimate bearing capacity of footings on a sand layer overlying a clay layer in order to study its influence on the ultimate bearing capacity of footings Hamzah M. Beakawi Al- Hashemi Oda and Win 11/5/2023 Add a footer 4 Literature review

5.   He analyzed the bearing capacity of a strip footing resting on two layers of clay. He assumed that the cohesive soils in both layers are consolidated approximately to the same degree. In order to determine the ultimate bearing capacity of the foundation, he assumed that the failure surface at the ultimate load is cylindrical, where the curve lies at the edge of the footing. Button (1953) 11/5/2023 Add a footer 5 Literature review

6. Foundation design consists of two distinct parts: the ultimate bearing capacity of the soil under the foundation, and the tolerable settlement that the footing can undergo without affecting the superstructure   Hamzah M. Beakawi Al- Hashemi (1999) 11/5/2023 Add a footer 6 Literature review

7. What is soil and what is its use in civil engineering world T he soil is a mixture that contains minerals, organic matter, and living organisms. But broadly speaking, soil can refer to any loose sediment.  Soil is a natural material with mechanical properties that allows it to be handled by construction equipment designed for handling soil. 11/5/2023 Add a footer 7

8. BEARING CAPACITY OF SOIL   1. Introduction   The bearing capacity of soil may be explained as the capacity of the soil to hold the loads transferring from the foundation. The pressure that the soil can easily resist against load is called allowable bearing pressure. 11/5/2023 Add a footer 8

9. TYPES OF BEARING CAPACITY OF SOIL   3. Types of Bearing Capacity   The capacity of Soil Following are some types of bearing capacity of soil:- 1. Ultimate bearing capacity (qu) 2. Net ultimate bearing capacity (qnu) 3. Net safe bearing capacity (qns) 4. Gross safe bearing capacity (qs)  Ultimate  Ultimate bearing capacity ( q u )   Ultimate bearing capacity ( q u )  bearing capacity ( q u )    Ultimate bearing capacity ( q u )   11/5/2023 Add a footer 9

10. 1. Ultimate bearing capacity The gross pressure at the base of the foundation at which soil fails is called ultimate bearing capacity. It helps us to know how much pressure can a structure bear till its failure 11/5/2023 Add a footer 10

11. 2. Net ultimate bearing capacity By neglecting the overburden pressure from ultimate bearing capacity we will get net ultimate bearing capacity. 11/5/2023 Add a footer 11

12. 3. Net safe bearing capacity By considering only shear failure, net ultimate bearing capacity is divided by certain factor of safety will give the net safe bearing capacity.
Qns = qnu/ F Where F = factor of safety = 3 (usual value) 11/5/2023 Add a footer 12

13. 4. Gross safe bearing capacity When ultimate bearing capacity is divided by factor of safety it will give gross safe bearing capacity. Gross SBC means, adding additional soil bearing capacity with net bearing capacity. This additional bearing capacity density of filling material above the footing 11/5/2023 Add a footer 13

14. REQUIREMENT OF SAFE BEARING CAPACITY The first test to be carried out before construction is the soil’s safe bearing capacity. It is a preliminary test that must be carried out before the construction of any structure . It is recommended that the safe bearing capacity of the ground be tested at all points of the foot. The safe bearing capacity of the soil is enough at one part of the building, but not the other part. It is recommended to check the SBC of soil at all footing positions to overcome the Soil Liquefaction. And the perfect type of footings is chosen by checking the Safe bearing capacity of the soil 11/5/2023 Add a footer 14

15. General formula of Safe Bearing Capacity is, Safe Bearing capacity of soil = Ultimate Bearing Capacity Cross Sectional Area*Factor Of Safety 11/5/2023 Add a footer 15 ME t HODOLOGY

16. OBJECTIVES If more load is applied to the soil than its resistance, the soil begins to shift or break, which leads to settlements . In order to keep the structure safe, the safe bearing capacity is calculated on the field at different points, and the foot selection is made accordingly. 11/5/2023 Add a footer 16

17. Labrotary Method Plate Load Test Field Method Drop Weight Method 11/5/2023 Add a footer 17 TESTS WE WILL DO !

18. Plate Load Test Plate load test is performed to determine the ultimate load bearing capacity of soil over the in-situ conditions. The plate load test is mandatory in case of designing foundation over the sandy and clayey soil. This test gives the highest rate of accuracy determining the safe bearing capacity of soil in case of shallow foundations. This test determines the Ultimate Bearing capacity of Soil, Settlement of foundation & Allowable bearing pressure of soil. Plate load test is suitable for Cohesionless soil as in case of Cohesion soil the settlement takes place in longer duration which this test is not suitable. 11/5/2023 Add a footer 18

19. A pparatus for Plate Load Test on Soi l Mild Steel plate Hydraulic jack Reaction beam or reaction truss Dial gauges Excavating tools 11/5/2023 Add a footer 19

20. Procedure Excavate test pit up to the desired depth. The pit size should be at least 5 times the size of the test plate ( B p ). At the center of the pit, a small hole or depression is created. The size of the hole is the same as the size of the steel plate. The bottom level of the hole should correspond to the level of the actual foundation. The depth of the hole is created such that the ratio of the depth to width of the hole is equal to the ratio of the actual depth to the actual width of the foundation . A mild steel plate is used as a load-bearing plate whose thickness should be at least 25 mm thickness and size may vary from 300 mm to 750 mm. The plate can be square or circular. Generally, a square plate is used for square footing and a circular plate is used for circular footing. 11/5/2023 Add a footer 20

21. Procedure A column is placed at the center of the plate. The load is transferred to the plate through the centrally placed column. The load can be transferred to the column either by gravity loading method or by truss method. 11/5/2023 Add a footer 21

22. Procedure For gravity loading method a platform is constructed over the column and load is applied to the platform by means of sandbags or any other dead loads. The hydraulic jack is placed in between column and loading platform for the application of gradual loading. This type of loading is called reaction loading. At least two dial gauges should be placed at diagonal corners of the plate to record the settlement. The gauges are placed on a platform so that it does not settle with the plate. Apply seating load of T/m 2  and release before the actual loading starts. The initial readings are noted. 11/5/2023 Add a footer 22

23. Procedure The load is then applied through the hydraulic jack and increased gradually. The increment is generally one-fifth of the expected safe bearing capacity or one-tenth of the ultimate bearing capacity or any other smaller value. The applied load is noted from the pressure gauge. The settlement is observed for each increment and from dial gauge. After increasing the load-settlement should be observed after 1, 10, 20 and 40 minutes or more untill the settlement upto 25 mm (For Foundation). The readings are noted in tabular form. After completing the collection of data for a particular loading, the next load increment is applied and readings are noted under new load. This increment and data collection is repeated until the maximum load is applied. The maximum load is generally 1.5 times the expected ultimate load or 3 times of the expected allowable bearing pressure. 11/5/2023 Add a footer 23

24. OBSERVATION Sl no. Time (in min) Load ( in tone) 1st Gauge Settlement (in mm) 2nd Gauge Settlement (in mm) Average Settlement ( in mm) 1 1 2 1.74 0.76 1.25 2 10 4.2 9.23 5.21 7.22 3 20 6.16 22.2 14.41 18.305 4 34 8.1 31.8 18.4 25.1 5 40 8.9 36.41 21.88 29.14 11/5/2023 Add a footer 24

25. CALCULATION i)Area of the Plate:- 0.25*0.75 m^2 ii)Final and total load applied upto 25 mm settlement =8800 kg So, Ultimate Bearing Capacity= Total Load/Area of the plate =8800/0.25*0.75 =46933.33 kg/m^2 Therefore Ultimate Bearing Capacity= 46933.33 kg/m^2 11/5/2023 Add a footer 25

26. CALCULATION As we know that Safe Bearing Capacity= Ultimate Bearing Capacity/Factor of Safety Here Factor of Safety is taken as 3 So SBC of that Soil is , =46933.33/3 =15644.44 kg/m^2 11/5/2023 Add a footer 26

27. Drop weight method:- Well, so many theories explained about how to find the  safe bearing capacity of the soil.  Among them,  Drop weight method  is the easiest and reliable test . This is a Field Procedure. It is also Praticed in most of the site for getting general knowledge about the bearing capacity of the soil of that construction site As a pit is digged here so mostly during finding the SBC of the ground soil it is used (At the Time of Foundation) 11/5/2023 Add a footer 27

28. procedure Firstly Excavate a pit of required depth. So we had taken the depth as 2 metre Then we have to take a square cube of known dimensions 0.15*0.15*0.15 Now drop the square-cube on the pit from the height from the normal ground level Measure the impression made on the pit by square cube using the scale and then take it as D (In our Test it is 0.02m) Note the cross section area and the weight of the cube for calculation Here we also need to find the resistance of the soil.s 11/5/2023 Add a footer 28

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30. calculation Reistance of Soil=M*H/d Where w is the weight of the cube H is depth of the pit D is the measurement of the impression on soil by Cube As we know that density of concrete cube of this dimension is 2400kg/m^2 So 0.15*0.15*0.15*2400*10*2/0.02=8100 Now Safe Bearing Capacity of that soil= R/A*FOS =8100/0.15*0.15*3 =12000 kg/m^2 11/5/2023 Add a footer 30

31. Factors affecting Safe bearing capacity Safe bearing capacity of a soil depends upon various factors as follows: Type of soil structure – soil parameters like cohesion, friction, shear strength, etc. has a direct impact on the bearing capacity of the soil. For cohesionless soil and mixed types of soils, it increases proportionally with an increase in the angle of friction. For cohesive soil, it varies linearly with the cohesion (C) value. Water table and variations – water table near the foundation is found to adversely affect the bearing capacity of the soil due to seepage and uplift problems. However, water table at considerable depth below the base of foundation does not have any significant impact on the bearing capacity of the soil 11/5/2023 Add a footer 31

32. Factors affecting Safe bearing capacity Density of the soil – denser the soil greater will it’s bearing capacity. Void ratio and porosity of soil – the presence of subsurface voids tends to decrease the bearing capacity of the soil. Voids also allow seepage of the water that can further affect the soil strength. 11/5/2023 Add a footer 32

33. reference 1] Namdar , A., Nusrath , A., foundation numerical modeling and mitigation, Frattura ed Integrità Strutturale , 12 (2010) 57-62; doi : 10.3221/IGF-ESIS.12.06. [2] Namdar , A., Pelkoo , M. K., Numerical analysis of soil bearing capacity by changing soil characteristics, Frattura ed Integrità Strutturale , 10 (2009) 37-41; doi : 10.3221/IGF-ESIS.10.05. [3] Galvín , P., Romero, Soil Dynamics and Earthquake Engineering, 57(2014) 10-14. [4] Namdar , Numerical analysis of SBC, 7(6) (2012) 636-646. 11/5/2023 Add a footer 33

34. reference Namdar , A., Pelkoo , M. K., Bearing capacity of mixed soil model, Frattura ed Integrità Strutturale , 7 (2009) 73-79; doi : 10.3221/IGF-ESIS.07.06. De Beer, EE., Bearing capacity and settlement of shallow foundations on sand, In: Proceedings of symposium on bearing capacity and settlement of shallow foundations. Duke University; (1965) 15-33. Terzaghi , K., Theoretical soil mechanics, New York: John Wiley & Sons, (1943). Meyerhof , G.G., Some recent research on the bearing capacity of foundations, Can Geotech J, 1(1) (1963) 16-26. Vesic , A.S., Analysis of ultimate loads of shallow foundations, JSMFD, ASCE 99(1) (1973) 45-73. Namdar , A., Nusrath , A., foundation numerical modeling and mitigation, Frattura ed Integrità Strutturale , 12 (2010) 57-62; doi : 10.3221/IGF-ESIS.12.06. Namdar , A., Pelkoo , M. K., Numerical analysis of soil bearing capacity by changing soil characteristics, Frattura ed Integrità Strutturale , 10 (2009) 37-41; doi : 10.3221/IGF-ESIS.10.05. Galvín , P., Romero, Soil Dynamics and Earthquake Engineering, 57(2014) 10-14. . 11/5/2023 Add a footer 34