SPT or Pocket Pen for Su Estimation?

[moe333]

Hi All-
In the absence of lab testing, what do you think is the preferred correlation to Su of CL material: SPT or Pocket Pen/Torvane on a sample from an SPT or CalMod sampler?

Also (dgillette if you are out there); looking for USBR criteria for seismic loading for simplified seismic deformation of new or existing canal embankment? Site in Central Valley CA...475/950/2475 return period? I assume USBR would use ~ 95% of Std. Proctor for compacted embankment fill?

Thanks!

 

[GeoPaveTraffic]

I typically take an average of both the SPT and Pocket Pen(PP), normally do not have torvane values. If something looks off about one of the values, I exclude it from the average.

If the clay contains any sand or gravel, then the PP values really become suspect. Same thing if the material becomes very silty since the amount of confinement put on the sample while taking the PP can really effect the reading.

Mike Lambert

 

[moe333]

I generally tend to trust the SPT over the PP. The SPT is testing a larger interval...less prone to random variations.

 

[oldestguy]

If the samples are on hand, and assuming sealed jars, I have found a valve spring tester gives a form of unconfined comprehensive strength that I trust more than blows or pocket pen. It takes just less than a minute to trim sample and squash. Pick the value off a chart of typical diameters and loads., Heck you have the sample out of the jar anyhow to verify classification. For jars, use olive jars to get some height.

 

[BigH]

SPT and miniature vanes over the pp.

 

[Okiryu]

moe333, what is the correlation that you use for Su and N values? Su=6.25N (KPa)?

For our overconsolidated unsaturated residual clays, PP are always much higher than the above correlation. PP readings are also higher than the Su obtained from say unconfined compression test. Typically, the above correlation is conservative for our residual clays. So, if there is not lab data, I try to use an average between SPTs and PP readings.

Torvane is not available here in Japan...

 

[fattdad]

I'd consider the PP over the SPT for fine-grained soils - especially marine clays!

I'd consider the SPT over the PP for residual soils that are fine-grained.

More than likely, I'd consider one data set and I'd consider the other data set and then I'd make up my mind.

f-d

ípapß gordo ainÆt no madre flaca!