Caisson Design Standards/ Guidelines for Sinking Procedure 3

[bejotycox]

I am looking for a good reference or design standards for circular caisson reinforcement and sinking procedures. Specifically looking for guidelines for prevention of tipping during the sinking sequence.

Wanting to sink a 30 ft diameter concrete caisson to approximately 90 ft, but there is a possiblity of an unbalanced load, which could lead to excessive tipping and possibly create a dangerous situation if not prevented or mitigated.

Any suggestions?

 

[Zambo]

This is about 9m diameter by 27m deep. Not a huge job but certainly interesting. What soil type are you excavating in?

I will check my bookshelf tonight to see if there is anything useful.

Are you precasting sections or casting in situ as you sink? It will depend on the soil conditions but in general I would suggest sinking in 3m lifts.

Are you using bentonite against the excavation face? It all depends on the soils but probably you will need a cutting shoe at the base which is thicker than the shaft wall. Then you can fill the anulus with bentonite to help overcome the friction.

Why do you think there is a danger of tipping. If you keep to 3m lifts and use a guide ring at the surface there shouldn't be a problem.

 

[bejotycox]

Will be excavating in about 5m of sand overlying stiff clay and casting in place as we excavate.

This is my first caisson sinking project so I have be doing quite a bit of research and looking at case studies. I was told about a project similar to this where the caisson tilted just above the clay layer. Apparently the sand on one side flowed under the cutting edge causing the caisson to tip.

We are working with an experienced contractor, but I would like to find some good references on procedure so I am aware of these potential problems.

 

[BigH]

Do a search of Indian specifications, etc. Indians call these kind of caissons "Well Foundations." Som and Das put out a book "Theory and Practice of Foundation Design" (Prentice-Hall India, 2003) that has a full chapter on the design and sinking of well foundations. MORTH's Specifications for Road and Bridge Works has a full specification on Well Foundations - it is actually quite informative - almost like a how to do - includes how to measure tilt, etc. Talks about cutting edge, steining, sinking of wells, how to adjust tilt by kentledge, gives a well installation record format, etc. MJ Tomlinson's book Foundation Design and Construction also speaks about your type of well foundations.

 

[bejotycox]

Thank you so much for the information. Those pictures are great.

 

[caissonsinker]

The following is a good practical paper on caisson sinking. Examples of Caisson Sinking in Scotland, D.Allenby,G.Waley and D.Kilburn. Published by the Institution of Civil Engineers in Geotechnical Engineering 162, February 2009, Issue GEI, pages 59 to 70.