CPT or DMT

[valebvd]

Hello,

I am an geotechnical engineer from Romania and I need an advice. I've never used either CPT nor dilatometer, but i'd want to buy one (i can afford only one of the above two). Can anyone, who has used both, advise me wich is the best? I must say that I allready have an dynamic penetration rig, wich I intend to use in inserting the DMT blade.

Thank you in advance.
Best regards.

 

[jdonville]

valebvd,

It depends on what you want to do. I would imagine that an electronic CPT apparatus, sometimes referred to as CPTu, would be more versatile and give you more performance for the money spent. However, in the right circumstances, the dilatometer may provide information that the CPT cannot. Your call.

Jeff

 

[dgillette]

I'm with Jeff. The CPTu can be used for general stratigraphy and soil classification, undrained shear strength of clays, liquefaction potential, density of sands, settlement estimates, etc. It is about the fastest way I know to get detailed information about a site.

Either CPTu or DMT needs to be accompanied by a little drilling to verify material types and other info. There is nothing that can beat holding the sample in your hand and poking it with your finger.

DRG

 

[Mccoy]

My opinion is that you should go for the CPTU, as Jdonville and dgillette say it's more versatile and less costly (per meter) then DTM. CPTU gives you a far higher data density then DTM, and you can have a pretty accurate estimate of the lithological column (true enough, nothing beats direct sampling , but using Zhang & Tumay probabilistic method plus porewater dissipation monitoring results in a fair degree of reliability, plus you may have some prior knowledge of the succession).
As far as I know, the DTM is very good for the evaluation of the edometric modulus (dilatometer modulus) so if settlements considerations prevail in your job that might be a choice of selection. Beware, though, you must be sure to use it, since usually it costs about twice to the contractor with respect to the DTM, and might be out of the market. Some people here bought it and never used it (they intended to couple it to a dynamic penetrometer rig, as you are thinking about). Same thing happened to some American colleaugues, as I discovered in this or other forum.
Which projects do you plan to investigate for?

 

[coneboy]

Another item to think about that favors the CPT approach is the maximum depth you may achieve.
The DMT has a larger end profile than a 10 sq cm electronic cone. If you are doing a deep sounding you should be able to push the CPT farther than the DMT.
Pushing power is generally not an issue with purpose built cone trucks, but with a drill rig your safe pushing capacity can sometimes be a limiting factor.

Coneboy (a some what biasedopinion, just like the name)