Grout curtain

Plume Containment. WeUs can be placed at a contaminated site to prevent the contamination from spreading further or migrating offsite. In the past, containment efforts often reHed on physical methods such as bentonite slurry trenches, grout curtains, sheet pilings, weU points, and fixative injections. Containment by judiciously placed weUs generally costs less, takes less time to install, and is more flexible because pumping rates and locations can be varied. 

In earth fill dams, grout curtains placed for preventive purposes are completed before or during the very early fill stages. For remedial purposes, curtains can be placed from the crest of the dam, if it isn t too high, or from the downstream slope. 

Figure 9.8 Location of grout curtain under a concrete dam.

At gel times of 4min and lOmin (Figs. 13.30c and d), effects were very severe. For both these injections virtually all the grout was washed out of the two coarser sands. The stabilized masses that remain have volumes of half or less of those obtained with the shorter gel times and represent a very inefficient use of material. Further, this would also be an extremely ineffective attempt at erecting a grout curtain. 

Figure 13.31 Grout curtain in stratified deposits using two- and three-row patterns.

Figure 13.32 Grout curtain in stratified deposits made with single row or holes.

Field and laboratory experience continually emphasize the need for three-row grout patterns in linear cutoff grouting. In terms of resistance to extrusion and reduction of permeability, very thin cut-off walls would suffice. (A 6- to 12-in.-thick grouted curtain in sands and silts will support unbalanced hydrostatic heads of several hundred pounds per square inch. This is reflected in the fact that slurry trenches are generally very thin also.)... 

Figure 13.33 Outer row of three-row grout curtain pattern.

Grout curtains or cut-off walls are constructed to create an impervious barrier in permeable formations. Generally, such curtains must be virtually complete in order to be effective. The use of short gel times is further enhanced by multiple rows of grout holes and the sequence in which each hole is grouted. 

The depth of a grout curtain is determined by the soil profile. Unless the bottom of the curtain reaches relatively impervious material, the curtain will be ineffective if shallow and very expensive if deep. 

This is a Basic program to compute the most economical spacing of chemical grouting holes for a Grout Curtain, which will cut off the flow of ground water. 

Assume it is necessary to place a 100 long cut-off (grout curtain) through a 20 foot depth of granular materials, overlain by 5 feet of clayey silt and underlain by rock. 

When a grout curtain is built for a dam prior to the full impounding of water behind the dam, there may be no way to evaluate performance of the curtain for a long time after its completion. Even when performance can be evaluated quickly, there is often no way to relate poor performance to faulty... 

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