The International Information Center for Geotechnical Engineers

Review of Polyurethane Resin Grouting for Rock Mass Stabilization



PUR has a number of advantages over other types of grouting materials. It has a low viscosity, allowing it to penetrate small fractures. It also has varied expansion properties, and set times that can be on the order of seconds, as well as its strong ability to bond to the surface of the rock (Schaller and Russell 1986). In addition, the material itself can reach strengths that are 3 to 4 times those reached by cementitious grouts (Arndt et al. 2008). Furthermore, PUR injection systems are easily mobile, making PUR injection grouting an ideal candidate for areas that are hard to access, such as underground mines. Also important is the fact that the final PUR product is environmentally inert, which makes PUR advantageous in environmentally sensitive areas.

Perhaps the biggest advantage of PUR over other types of grouting materials is the control over the properties of the material. Through chemistry of the PUR mixture alone, viscosity, set time, strength, and expansion properties can be controlled at a much higher resolution than other types of grouting materials.                 

Finally, using PUR injection grouting for support of a rock mass does not result in any blockage of pathways that are typical of structural supports, which is important in underground mining applications. It also does not require any surface hardware, which preserves the natural aesthetics of the rock mass and is important in above-ground applications, such as rock slope stability along highways.


PUR products are typically harder to pump than less viscous cementitious grouts (Arndt et al. 2008). Additionally, with water, PUR products may foam and expel through open fractures on a rock face, requiring quick cleanup of the overrun material, before it hardens and removal becomes a more difficult task. Also, PUR is typically higher in cost than other types of cementitious grouts. For this reason, PUR is sometimes used in conjunction with other types of stabilization to lower project costs. PUR can be cost effective for a project provided a good characterization of the rock mass is performed and material is not wasted on poor field implementation. Furthermore, flow of the PUR within the rock mass is unknown until after pumping has been performed and boreholes are drilled to verify infiltration. Finally, hydrofracturing and rock falls may be an issue if pressure is not adequately controlled during pumping operations.


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