The amount of grout to be pumped into the foundation may in many cases be so small that a hand force pump such as is made especially to handle grout will be ample for the purpose. (See Plate VI, Fig. C.) Where the anticipated amount of grout is large it will be better to arrange for forcing it in by using compressed air.

A very satisfactory apparatus for the purpose is the Caniff grouting machine. (See Fig. 18.) Cement and water are introduced through the inward swinging door on top, agitated and mixed by blowing in compressed air at the bottom, and then, after shutting the door, blown into the hole by air entering the tank near the top. The necessary manipulations of the valves and their sequence should be obvious from the illustration. The machine is double in order that one tank may be rilled as the other is being emptied. In addition to doubling the capacity of the grouting gang, continuity of the operation is often highly desirable or necessary to obtain the best results.

It is assumed that a pipe has been connected with the hole to be grouted, and the connection secured by cementing the pipe into the hole; or in case of a pipe leading from a seam, the connection is secured by having built a sufficient depth of masonry around and above it. To this pipe, which should be 2 in. in diameter, connect the outlet pipe from the tank, put the grout into the tank, close the grout inlet and apply the air pressure through the top of the tank. While using a grout pump or tank, it should be occasionally washed out to prevent clogging up. Of course, it should also be cleaned most thoroughly on discontinuing work.

The hole may first be tested by forcing in clear water; the Tate at which water can be forced in being some index of the amount of cement required for a suitable grout. A free open bole may first be treated with a heavy grout, finishing up with a thinner mixture, such as would be properly used in a relatively tight hole. It will usually not be necessary to force into every pipe, as when forcing into one the grout will make its appearance at any adjacent pipe or pipes which connect with the same system of seams. Any such pipe or pipes from which grout is issuing in such volume and of such consistency as to make it apparent that the intermediate seams are well filled, may be shut off at once, as the purpose is accomplished, thus forcing the grout on its way to the next outlet.

Fig. 18. The Caniff grouting machine.

Where the connections (via seams) between pipes are reasonably direct and free several pipes may be satisfactorily filled by forcing into one. Should the connection be indirect or not so free, the fact will be apparent from the quantity and character of whatever grout issues from the pipe. In that case the first set of pipes may be closed and the pump or tank moved to another pipe on what may be called another system. It is always well to go over the holes a second time after the grout has had time to set, say the next day, and test the completeness of the first work; often some additional grout (even if thin grout) can be forced in. Each set or system of holes should be tested, preferably by pumping into some hole from which the grout issued the first time.

The entire operation is important enough to justify some study in order to secure the best results, the data being the behavior of the water in the various pipes as they are brought up, supplemented if desirable by such tests as forcing into some of them water so colored that its outlet may be readily and positively discerned.

If holes are tested by forcing in water or air at the time the foundation is being prepared, and again (as a preliminary to grouting operations) after much masonry has been laid, there may be observed an effect due to the weight of masonry tending to close the seams in the rock. This is said to have been quite distinctly the case at the Kensico dam where some masonry 100 ft. in depth was laid in the deepest part of the gorge, before certain holes in the rock were grouted. Whether the holes are grouted before or after such a settlement would seem to be immaterial, for the only essential point is that the weight of rock or masonry above the seam being grouted should be so ample that the opening of the seam under the applied pressure will be absolutely prevented.

While some foundations have been thus grouted over their entire area, and while in the future there may be others where such procedure may be proper, still the thing which is logical and in consonance with recent practice in draining foundations would be to grout a zone along the upstream face, leaving the remainder open so as to pass any water which may penetrate that zone. If similar treatment is given to the entire area, it may result in making the downstream portion the tightest portion, conducting to an uplift pressure. The matter is further discussed under Drainage of Foundations, pages 105-106.