Pad Foundation Design

Part 1: Geotechnical Verification

Aug 02, 2023

Hi friends,

I discovered that you guys are really into these quick structural design mails, as the open rates are quite high.

So today we are covering what verifications you need to do to design a pad foundation.

In this e-mail, we start with the geotechnical design and next week Wednesday, you’ll get another mail about the reinforced concrete design. So stay also tuned for that. 💯💯

You can find the in detail articles here. ⬇️⬇️

The overall step-by-step process we always follow looks like this: 👇👇

Calculate characteristic loads that act on pad foundation
Load combinations
Define properties of the sand/clay and concrete
Geotechnical design – bearing resistance verification
Geotechnical design - Sliding resistance verification (if vertical load is excentric)
Reinforced concrete design – bending verification
Reinforced concrete design – shear verification

Geotechnical design - pad foundation

1. Calculate characteristic loads that act on pad foundation

In order to verify the pad foundation, we need to know the exact loads that act on it
⬇️⬇️. We first calculate the loads and then do a vertical and horizontal load transfer By now, you should know which loads we consider in building structures. If not, then check the e-mail from 2 weeks ago.

Let us know in the comments, if you want us to show how to do a vertical load transfer. ✍️✍️

2. Load combinations

Once the characteristic loads (snow, wind, dead, live load) on the pad are found, we need to do load combinations in order to find the design load. You can check out this article about load combinations where we explained it in detail or use our 👉 load combination generator 👈.

3. Define properties of the sand/clay and concrete

Usually we design pad foundations for either sand, clay or a mix of the two. In general, we need the following parameters

Density of the soil
Density of water
Angle of friction for sand
Undrained shear strength for clay

4. Bearing resistance verification

The formulas for the bearing resistance are different for sand and clay.

Design bearing resistance sand (EN 1997-1 (D.2)):

Design bearing resistance clay (EN 1997-1 (D.1)):

Now, the design bearing resistance needs to be greater than the vertical design load that you calculate in step #2.

There are a lot of parameters in those formulas. So check our blog posts to find out what they are and how to set their values (the links are in the beginning of this mail).

5. Sliding resistance verification

The sliding verification only has to be done if there is a horizontal load acting on the pad foundation.