Thank you very much for raising the issue and paying attention to the details. I had a quick look at the input files and also Beier’s paper. I also remembered that I had the same problem couple of years ago when setting up this benchmark.
Short answer to your question:
Table 1 in Beier’s paper is wrong. The values were given in diameter, not radius.
Assuming the U-tube pipe has a outer radius of 3.34 cm, then you have 6.68 cm outer diameter for 1 pipe. As we have 2 pipe in the cross section, we need at least a borehole of 2 x 6.68 = 13.36 diameter. In this case we can not insert 2 x 6.68 pipes in the 12.6 cm borehole. This actually gave me trouble when calculating the thermal resistance. I got a Non-a-Number (NaN) error when blindly put those values into OGS. Then the program crashed.
This forced me to dig around the internet, trying to understand what exactly is the dimension of those pipes. Please have a look at this webpage, which explains what a SDR 11 pipe is. The following table lists the specifications of these pipes.
So we are talking about 1 inch SDR 11 pipe. According to the above table, it has a outer diameter of 1.310 - 1.320 inch, which is about 3.34 cm. That confirms my suspicion that it should be diameter in Beier’s table.
According to the webpage, SDR 11 means: SDR = Diameter / Wall Thickness = 11
Assuming it’s a diameter of 3.34 cm, then we have wall thickness of 3.34 / 11 = 0.3035 cm. That’s exactly what we have adopted (or 0.003035 m as in OGS prj file).
I hope the above info helps to resolve your puzzle.