**5. Behavior of PUR resin in the grouted environment**

Grouting PUR resin enters into the borehole as a mixture. The grouting material flows through the rock mass first as a liquid. After curing reaction start, gaseous CO2 is formed, which causes foaming of the mixture. In case of contact with moisture present in the soil or rock, the foaming is more intense, because the water reacts with the present isocyanate groups. Foaming causes increase of volume of the PUR mixture. The mixture is pushed into open structures of the rock mass and the viscosity of the mixture consecutively increases. The flowing stops, when the viscosity of the material is so high that further pumping is impossible, and the resin becomes hard foam. In case, that the pump is further operated, the pressure increases and the material density increases. In practice, this situation is indicated by significant pressure increase. Increase of the pressure may sometime cause opening of new structures for the grouting and continuing of the grouting. In case of formation of new openings the pressure drops. This may occur repeatedly until full grouting of the surrounding of the borehole.

Volume weight of the grouting material increases from the front of the grouted structure towards the packer. In case of the PUR resins, when the pump is stopped, so called autogrouting continues, which is induced by the reaction of the material and formed CO2, which induces pressure of 0,1 to 0,3 MPa. In case the grouting process stops before full saturation of the environment by the grouting media, the saturation continues due to the pressure formed by CO2 until finishing of the chemical reaction. In case, that the fissure had been already filled, the pressure is higher than the pressure of CO2 and bubbles are not formed - CO2 remains dissolved in the grouting media and has minimal volume. The texture of the material is in this case compact. Formation of the bubble structure depends therefore on the pressure under which the mixture cures. Usually porous structures are formed with closed or partly closed pores during the grouting.
