CPT - allowable rod deflection 2

[georay]

Is there a criterion for the maximum I.D. of a casing if CPT testing (GEOTECH electric cone) has to be done below the bottom of a drill hole?

 

[coneboy]

There is no "set-in-stone" criteria for casing ID.
Many companies have set standards for conducting CPT tests in a cased hole while others will just push the cone blindly through a drilled out hole.

Typically, the drillers, CPT operators and on site engineer will jointly discuss how deep and what kind of soils will be expected beyond the cased interval. These factors will determine what style of casing should be used.

If soft soils are expected below the cased interval then the CPT rig/drill won't have to push too hard. You might be able to just use large casing for this scenario.

If fairly dense soils are expected or a deep test is required then a second set of nested casing maybe necessary. Often we have placed BQ casing inside the outer casing as BQ provides a fairly snug fit for the cone and rods while still maintaining a good level of rod support.
On some really deep tests we have also used a third set of casing due to the large diameter of the outer casing.

Hope this helps

Coneboy