RQD is an indicator of how solid or unfractured the rock mass is. If you are drilling in a boulder field, you have no RQD, even if you have long pieces of core retrieved.
If you have an RQD of 0.25, but a strength of 100 MPa, you need to really look at how fractured and deteriorated the rock actually is.
You need to find a k factor that is appropriate for your local. In literature k is often presented as 16-24 for most rocks however this isnt true.
We have thousands of UCS and PLTs at the same depth in rock strata. k is typically between 4-6, so a lot less than 16.
Our rocks are extremely week to weak, design UCS of 1MPa is common.
And TG brings up a valid point when assessing rock strength. UCS testing is on a discrete intact piece of rock. The discontinuities dictate the performance of the rock mass as a whole.
You need to be considering the Hoek Brown GSI method to properly assess your rock. Note, its only applicable to jointed rock mass so if RQD is near 100 then your UCS test results are applicable to your whole rock mass.