Compensation Grouting
COMPENSATION GROUTING, A TECHNIQUE USED TO DENSIFY SOILS WHILE SOIL DECOMPRESSION IS OCCURING. COMPENSATION GROUTING USES A VARIETY OF GROUTING APPLICATIONS INCLUDING CHEMICAL, COMPACTION, AND SLURRY GROUTING TO PROTECT STRUCTURES FROM SETTLEMENT.
- GROUTING APPLICATION
- CHEMICAL GROUTING
Compensation grouting injects calculated quantities of grout between a tunnel or pipe and the foundations or surface structures to offset the effects of soil decompression and the material removed for the tunnel. Successful application of Compensation Grouting depends not only on utilization of the appropriate monitoring equipment in the field, but also fundamental understanding of grout-soil interaction. This technique uses hydraulic fracturing to get a heave that can compensate the settlement or to get compaction to densify the soils to improve its characteristics. Compensation grouting is up to now predominantly an empirical procedure. It is qualitatively know that the necessary injection pressure depends on the over-burden pressure, the density of the material, and the properties of the grout. Here are some additional facts about the procedure:
- The properties of the grout mixture have an influence on the fractures that occur. Both injection pressure and shape of the fractures depend on the properties of the mixture.
- Both leak off and grout bleeding seem to be importance for the shape of the fractures. Fine particles at the boundary between the fluid and the material to be grouted can hamper the formation of fractures.
- There appears to be an optimum in the efficiency of the compensation grouting process. The optimum typically reached at 10% cement-leading to more bleeding.
- When the injection pressure is close to maximum according to cavity expansion theory, then quite wide fractures will occur. Fractures will be thinner for lower injection pressures.
- Performing an injection at a constant volume rate makes it possible to determine leak off from the pressure reading. A fluctuating pressure indicates leak off.
Grouting techniques to perform Compensation Grouting include Compaction, Chemical and Slurry Grouting applications. Grouting can be performed through steel grout pipes placed directly above or between the structures being protected. Manchette tubes can also be placed in similar locations or paralleling above and alongside the tunnel or pipe.
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