Interesting issue on consolidation tests

[paganel]

Our lab contractor is doing some consolidation tests on silty clay.
Step 1 load the sample to in-situ stress to reduce some disturbance.
Step 2unload to 5kpa then reload to 3200kpa.
They encountered some problem on reporting t50 and cv.
In some cases the deformation happens very quickly(especially the first 1or 2 reloading step). Almost 50%deformation finished even before the 1 reading(6seconds since the step started). So it not possible to determine t50 on e log t curve based on the traditional method from BS due to the limitation on the graph method.
The consultant even wants the t50 and cv for the unloading phase!!! For me it does not make any sense,as it is nothing related to consolidation,so the theory based on it is not relevant at all. Maybe I am wrong. I hope I can get some ideas from you and fight with the stupid consultant.
Thanks a lot!

 

[fattdad]

if your'e right, all you can report is a T50 that's lower than the accuracy of your quickest reading. The strain would be accordingly measured.

Jam a dilatometer in the ground and measure modulus.

Is it really a silty clay, per ASTM D-2487?

f-d

¡papá gordo ain’t no madre flaca!

 

[paganel]

Thanks fattdad!

One of the samples is described according to BS as "Firm, grey, slightly sandy CLAY ",just check with ASTM it could be classified as lean clay. Others mostly could be classfied as clay or just sandy clay.

What I concern is that reason why half or more consolidation is finished before the reading it due to the reload-unload-reload steps carried out. When at the first a few step with relative low stres level, it may could happen.

 

[paganel]

Is it reasonable to calculate consolidation coeffcient for unloading phase in oedometer test? Is it possible to use it to estimate the unloading behaviour? Please give some advice?

 

[fattdad]

I think if you read the ASTM Standard for consolidation testing, you'll have a better understanding.

f-d

¡papá gordo ain’t no madre flaca!

 

[molerat2210]

There is nothing wrong with wanting to know the T50 and Cv from the unload curve. Maybe the client wants to know how long a rebound swell is going to take. There should be no relationsip with this info to the compression T50 and Cv.

Does not sound unreasonable to me that T50 is less than 6 seconds especially since it is sandy. The Cv values will be high though.