FOUNDATION FOR DRILLING RIG

[Aldar]

i was assigned with a project to design a precast foundation for a drilling rig.
the tower of the rig, the hook load is supported by a truss substructure which lies on concrete foundation.
because i need to design it precast, i am constraint by dimensions (not to exceed the foundation weight of 25t for transportation reason).
Has anybody designed this kind of foundation? the whole structure is supported by 4 beams. i am thinking to divide the foundation in 2 or three pieces.
however, i'm not sure about the settlements in this case. Any comments , thoughts?

 

[Ron]

Why?

 

[dhengr]

Because!

 

[Aldar]

because the client wants to reuse them. now, the client makes them cast in place, and when he finishes he needs to demolish foundations.

 

[Ron]

Consider using concrete dragline mats.

 

[BUGGAR]

The purpose of your foundation is to support loads. What are your loads? This is significant depending upon the type of drill rig you are using.

Your sketch looks like the churn drills we used to use in New York. These have significant dynamic loads. Or is it a rotary rig?

A geotech should provide you with foundation soils requirements. You will likely have a varying load which may require reduce soil bearing.

I really like Ron's idea of dragline mats.


Bob

 

[Aldar]

they are rotary rigs. for the loads i have tower load 750kN (168.6kips) and 3600kN (809.3kips) hook load. I distributed them linearly on 4 line supports.
as these foundations will be used in different sites, i need to assign maximum allowable stress on soil, so that the geotechnical engineer should verify if soil of a specific site can support those stresses.
i attached of my idea, which looks like what Ron suggested.
anybody has any contraindications /comments/ suggestions?

 

[dhengr]

Aldar:
You really have to put some dimensions and details on you sketches, and you have to show where the loads are actually applied, so we can see what you are dealing with. I assume the four sets of beams B/1 & B/2 are part of the drilling rig. But, that the loads are actually applied at a few discrete points on those beams. You are basically right about the need for some GeoTech involvement, and to develop your design for some basic (allowable) soil pressure. But, I think you should turn your thinking around a little. Talk with some local GeoTech guys, right now and learn something about the soil conditions in a given drilling region, and use their info. as the basis for your allowable design soil loads. Then have a local precasting company make the planks for you with some sort of lifting features on them. You will still want the GeoTech guy to look at each drilling site to confirm the soil conditions before you put down your foundation pad.

 

[BUGGAR]

I agree that a Geotech is a good idea. We've used precast trench covers, some up to two feet thick to support crane pads over utility trenches on wharves. Depending on your precaster, consider prestressed (pretensioned) pads, especially if they are to be handled and moved around. Use a good pick up detail - we used coil rod inserts with cover plugs but the plugs always got lost and the holes plugged. If you have a solution for this, I'm buying. Don't let the precaster talk you into looped strand for picking.

I did a job where we carefully designed a bearing pad installation for some very poor soils. The contractor brought in a crane to place the pads, but he set up in the poor soil and almost toppled the erection crane.