Concrete-concrete interface stiffness

Hi Itascans, I have a model that represents the joints between concrete segments for a tunnel lining as shown:

For the interface stiffness properties I am using the Kn and Ks formula from the FLAC3D manual

resulting Ks = kn = 1040 GPa/m

The values seems a bit high however I will justify them referring the FLAC3D manual.
Anyone could give me any advise on those values? Thanks

The equation you posted in a typical way to determine the stiffness of an interface