2. dr. isam jardaneh / foundation engineering / 2010

10.  If weak soil layer is shallow, then remove it and let the foundation be supported on the strong layer.  If weak soil layer is deep, then consider the foundation to be supported on the weak soil only.

12. The ultimate bearing capacity is the smallest of the two values as follows:

13. First value: if the depth H is relatively small compared with the foundation width B, a punching shear failure will occur in the top soil layer, followed by a general shear failure in The bottom soil layer.

14. Second value: if the depth H is relatively large, then the failure surface will be completely located in the top soil layer

15. Cases for layered soil

16. Case # 1: Top layer is strong sand and bottom layer is saturated soft clay dr. isam jardaneh / foundation engineering / 2010

19. Case # 2: Top layer is stronger sand and bottom layer is weak sand.

21. Case # 3: Top layer is strong saturated clay and bottom layer is weaker saturated clay.

22. dr. isam jardaneh / foundation engineering / 2010

24. Remember select the smallest of the two values.

33. A theoretical solution for the ultimate bearing capacity of a shallow foundation located on the face of a slope was developed by Meyerhof 1957.

34. Figure below shows the nature of plastic zone developed under a rough continuous foundation of width B.  abc is an elastic zone  acd is a radial shear zone  ade is a passive zone

35. The ultimate bearing capacity can be expressed as

38. The pressure at Z Ơ = --------------------- + ----------------------- ≤ q all soil B1+ZB2+Z Q2Q1 B1B2 Z Q2Q1 Square footings (B1+Z)(B2+Z)(B1+Z)(B2+Z)

39. When Ơ ≤ q all soil, use separate footings Ơ ≥ q all soil, use combined footings

40. Problem #1 – Problem #3: for the three figures shown, determine the a- gross allowable bearing capacity. b- How much increase in the bearing capacity for each problem? Square footing

42. Problem #4

43. Problem #5