Raft Foundations - Depth below footing

[ONENGINEER]

For pad foundations they usually take into acount soil parameters within 2B below the footing. When it is a raft foundation 2B becoming a great number. What would be the depth to consider for soil parameters. (Although for geotechnical investigation one may go to deeper depth)

 

[FixedEarth]

I use a depth equal to B^0.7 for settlement calculation. Bearing capacity is rarely an issue in Mats due due to large B value. See more discussion in Chapter 10 Bowles foundation book. If you prefer to go into more depth, there are a collection of great papers in this book: "Design and Performance of Mat Foundations: State-Of-The-Art Review/Sp-152", 1995 by ACI.