Phicometer

[genomty]

Is anybody familiar with the use of a device called phicometer? I understand that, this is a device used in connection with the Menard pressuremeter to obtain shear strength and phi values, unfortunatly that is all I know about this test. The firm I'm working for, is providing CMT services to a building construction, as part of the works to be performed an anchored, shotcreted excavation of about 30 feet is being developed. The Geotechnical study performed by another firm, refers that slope stability analyses were based on data obtained using a phicometer, my concern about this issue is that report refers a phi of about 43 degrees and a cohesion of about 820 psi, now for the soils that are being excavated (mostly clayey soils firm to stiff with some lenses of clayey gravel) cohesion does not seem to be high, however phi looks huge for this kind of soils. So I'm looking for some references about the test method, the reliabilityof test results and the cases where this test is applicable.

Thanks in advance for your valuable cooperation.

Best Regards

 

[BigHarvey]

The phicometer test is an in-situ direct shear test. it was developed in France but is not widely used. The only paper I know about it is in "Revue française de Géotechnique" N°35 pp49-65 title " The phicometer : in-situ direct shear test".
Basically , you insert a probe in a 60 to 64 mm diameter borehole. The probe has two half shells that can move laterally like a pressuremeter and you then pull on the pobe and repeat this for increasing lateral pressures.
It is an undrained non consolidated test. The article gives an example of tests carried out in a 0/150 mm backfill ( no lab test possible ) and compares values obtained in-situ and in the lab for a clay, a clayey sand and sand. Its main advantage is to obtain values where you can't get samples for the lab.The tool is sold by a company called APAGEO ( they have a web site )

 

[fattdad]

I have nothing to add, but have to wonder is this tool even applicable for overconsolidated clays? While I've never heard of it before, the mechanics of the tool make it seem much more applicable for use in granular soils.

f-d

¡papá gordo ain’t no madre flaca!

 

[BigHarvey]

The article I mentioned clearly indicates that this test is not intended to replace a lab test but is a way to obtaine reliable results when representative sampling is not easy to obtain.

 

[genomty]

So, if I correctly understand, and my poor engineering judgment is still working, in a site where soils are normally consolidated sandy clay soil (stratum thickness of about 8 feet), interbedded or interstratified with stratums consisting of boulders, cobbles and gravel clayey in some cases and, in others there is no fine matrix -apparently due to former groundwater flow, some cementation due to carbonatation was noted- (stratum thickness is about 2 or 3 feet), I would take some undisturbed samples of the clayey soils and use test results as parameters for designing an anchored cut instead using the phicometer with the abovementioned parameters, which might be badly interpretated if test was performed in the interface of two diferent strata, Am I right, or shall turn back.

 

[BigHarvey]

If getting undisturbed samples is not a problem on your site ,you will definitely feel more secure with lab results than with phicometer results. Phicometer is to be used where it's better to have an approximative value than nothing at all !