Differential Settlement of Interconnected Structures

[S R P]

Hi,

I am assigned to design an underground tank, which connects into two other large underground tanks from both sides. All together, they are going to be in a straight line and the distance from one end to the other of interconnected structure would be about 500 ft. The one that I am going to design is about 25 ft * 50 ft. This is possibly going to be on highly or medium active clayey soil. Even collapsible soil can appear. (I haven't received the soil report yet). Therefore I am curious what kind of major facts I should be careful. Please help me.

The tank is going to be about 50 ft under ground and will be about 10 feet deep. What kind of special considerations should I make in design procedure?

 

[JedClampett]

How are they connected to each other? I'd rather see piped connections. A lot of pipe connections (push on, mechanical, etc.) have some tolerance to movement. If you add up 2% rotation over a bunch of joints, you can tolerate a lot of movement in either direction.
Flanged joints and cast in place tunnels need special care, like expansion joints or ball joints in pipes.
Get the Geotechnical Report and pay attention. If they say over excavate and backfill, over excavate and backfill. If they say to lime condition the soil, well you get the idea. Make sure they understand your concerns.

 

[S R P]

Jed,

Thank you for your quick response, it helps me a lot. Yes, there are pipes connecting each tank. Bigger tanks are going to be pre-stressed (designed by someone else). As I understood, i would be able to use a exp. joint. However, if the relative settlement will be higher depending on soil condition and loads, I may need a larger tolerance. As you said, I can use multiple joints in such case.

I have used soil reports for few of building structures, but this is a different case, I am new for. Is there any special information that I need to ask from geotechnical engineer?

 

[dik]

Just a caution about changing the loading condition of the existing structure.