In RS2, users have the option to apply additional pressure inside a joint, and there is also the option to apply the pressure to the liner side only.
Apply Pressure to Liner Side Only feature: Define Joint Properties dialog in RS2
Consider the case of a model having a primary liner, a secondary liner, and a joint.
If the joint is between the rock and the primary liner, and the Apply Pressure to Liner Side Only option is checked on in the Joint Properties dialog, the pressure is applied to both the primary and secondary liner and not the rock.
If Apply Pressure to Liner Side Only is not checked, then the pressure is applied to both the liners and the rock. Since the liners use beam elements, and the beam elements (primary and secondary beam elements) share nodes on one side of the joint element, the pressure gets applied to both. The beam elements are really two dimensional with no thickness except in the formulation. There are numerous resources available with regards to Timoshenko beam elements.
Joint between rock and primary liner: Pressure will be applied to both liners
If the joint is between the primary liner and the secondary liner, and the Apply Pressure to Liner Side Only option is checked, then the pressure is only applied to the secondary liner.
Joint between primary and secondary liners: Pressure will be applied to Liner 2 only