When building tunnels and other subterranean structures rock support is need toprevent instability or loose rock masses from falling. The most common ways todeal with rock reinforcement today in Sweden is rock bolts in combination withshotcrete. In addition to this, there are demands that require that there is a layerof mortar in between the plate of the rock bolt and the surface beneath it. Thiscomplementary grouting is supposedly done to improve the contact between plateand underlay, as well as protecting the bolt and plate from corrosion. Although itis difficult to find any clear source or reasoning for the need for this extra layer ofmortar.The purpose of this thesis is to examine the mechanical effects of the complementarygrouting on the plate and underlay. To examine this relation a numericalanalysis was done in the finite-element software COMSOL Multiphysics. Four differentcases were modeled based on examples examined during a study visit toHenriksdals water treatment plant. The cases were assumed to be worst case scenarioswhen considering the transfer of stresses and strains between the plate andthe underlay.The results from the numerical analysis showed that there were small differencesin the width of the stress zone under the plate, due to the complementary grouting.The mortar and shotcrete seem to reach failure before the rock bolt or platestarts to plasticize. However the results show that the complementary groutingdoes have some effect on the damage propagation, and maximum compressivestress shown, in the shotcrete during high loads. When considering the cost intime and resources, the effect on workplace enviorment and the negligible protectionagainst corrosion it is deemed that the positive mechanical effects fromcomplementary grouting are limited.