Advances in Grouting Technology Applicable to Dam Construction and Repair

Questions about the effectiveness and the long-term performance of grouting have persisted over the years. In addition to this, there have long been questions as to where grout goes, what it is doing to the rock or the soil, and what changes in pressure and flow rates mean. And then there are the questions about grout mixes – how can you fill a void in rock with a grout mix that has more than 50 percent shrinkage and high water bleed? There have been tremendous advances in grouting technology in the past 20 years that involve two primary elements of this practice: the use of stabilized low/non-shrink grouts with viscosities previously unachievable, and the application of state-of-the-art computer technology to grouting. Grouting in the past was primarily based upon pumping thin mixes of portland cement grout and water into the subsurface through boreholes targeting joints and discontinuities in the hope that by filling these potential pathways, the adverse effect of seepage would be mitigated. The major difficulties in achieving “closure” or control of seepage in this manner is that the mixes used had to be thin enough to readily pump, and thin enough to flow through the cracks, joints, or fractures in the rock. To do this, the mixes were of relatively high water to cement ratios, and these grouts were mixes that, when cured, shrank, and had significant bleed associated with the separation of excess water from the cured grout. Advances in additives have made it possible to now use grouts that have essentially little or no shrinkage and very low bleed, with much lower water to solids ratios, yet are no more viscous than the old-style mixes of much higher ratios. Another problem often plaguing grouters was the phenomenon of premature closure of grout holes. In the era of hand measured grout flows, readings were taken by inspectors at intervals, and by the time a hole was prematurely blocked or plugged, it was often too late to make adjustments and save it. With continuously monitored grouting, through computers, we can now monitor and make adjustments immediately in response to premature closure. We can also terminate grouting immediately when closure is achieved, or in immediate response to undesired fracturing, uplift or leakage, without having to wait until the next reading interval for detection of these circumstances. The newly-prepared U.S. Army Corps of Engineers Engineering Manual EM 1110-2-3506: Grouting Technology presents these advances and the current state-of-the-art approaches to grouting for seepage control and remediation of foundation issues. 10 pp., 5 references.