dr. isam jardaneh / foundation engineering / 2010

 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.

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

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.

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

Cases for layered soil

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

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

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

dr. isam jardaneh / foundation engineering / 2010

Remember select the smallest of the two values.

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

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

The ultimate bearing capacity can be expressed as

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)

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

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

Problem #4

Problem #5