Grouting in Karst — Time for New Thinking

Pressure grouting is often called for in treating Karst for one of two possible objectives; prevent or arrest surface settlement as a result of sinkholes, or stop the movement of water through Karstic voids. For arresting loss of soil, the throats of karst features must be sealed which might be through injection of low mobility, compaction, or permeation grout. Rarely is it reasonable to fill large Karstic spaces although many contractors favor such, especially with payment based on the volume of grout pumped. Conversely, in water control it is necessary to fill sufficient voids to create a continuous impermeable curtain. Very large grout quantities are often required, so the lowest cost, effective mixture available, should be injected at the highest pumping rates and pressures that can be safely used. The grout must be resistant to washout which can be readily achieved with standard concrete admixtures. To stop rapid flows of moving water, a pumping rate sufficiently fast to literally overwhelm the water flow should be used. While past practice has often employed expensive special grout materials and unique injection equipment to slowly build up plugs in the formation, available concrete pumps and advanced concrete mix design, now allow placement of very large quantities of cohesive, stable, grout material very quickly. This allows us to virtually overwhelm even massive flows of water rapidly, while using readily available resources.