should be well stirred while the water is being added. To prevent the grout from becoming stiff through partial set and thus becoming sluggish as well as weak, the material should be poured as soon as possible after the mixing. When poured from any height, it is desirable to employ neat cement or rich mixtures, as there is a

FIG. 122.-Grouting Machine Used by Board of Water Supply, New York.

tendency for the cement and sand to separate and form separate layers.

The quantity of water required for grout depends upon the class of work in which it is employed. Where the interstices through which it is to be poured are small, it must be made thin

About 3-10

and watery, otherwise it cannot be forced beneath the upper layers of rock. When the interstices are large or the grout is applied under pressure, a thicker mixture can be used. It is always desirable to employ as thick a grout as can be forced into the cavity which it is intended to fill, since a thin grout becomes weak and porous after the water has evaporated.

Where grout is used in large quantities, machines are employed for mixing, and the grout is forced through pipes under pressure. Grout Mixing Machines.-Grout mixing machines are of two general types: (a) tank mixers and (b) paddle mixers.

In the tank machine, grout is mixed by blowing in air at the bottom of the tank, and the material is ejected by turning the air in at the top and forcing the grout through a hole in the base. In this type, there are no stuffing-boxes or shafts carrying revolving paddles to wear out by the grinding action of the cement.

The so-called paddle-mixing machines consist in general of a closed steel box of cylindrical shape, about two feet in diameter. Through the axis of the cylinder a shaft is fitted. The shaft makes about 30 revolutions per minute and carries about six double paddles which thoroughly mix the ingredients. The time of mixing occupies about three minutes. After mixing, air pressure is admitted to the cylinder and the grout is discharged by means of a flexible hose connected with the cylinder. In grouting the dry stone packing between the tunnel and rock of the East River Tunnel for the Rapid Transit Subway between Brooklyn and New York, a pressure of 90 pounds per square inch was employed, the high pressure being required to force the grout against the hydrostatic pressure due to the depth of the working.

Cementing Joints.-Grout is employed to some extent for cementing the joints in rubble masonry, but for this purpose its use is not recommended. When so employed the interior of the wall is laid up dry. The grout is poured on top of the wall and is expected to find its way downward and fill all voids. The difficulty with this method is twofold. If the grout is made thin, it becomes porous and weak, and if made thick, it fills only the upper portions of the wall. Better results are obtained by inserting pipes into the body of the wall at several points and forcing in the grout under pressure. Grout was formerly employed in this way in the construction of

bridge piers, where it was customary after laying the large backing stones in place to fill the vacant spaces with broken stone of various size and then pour in as much grout as would work its way into the voids. Such methods are, however, no longer in vogue for firstclass structures, where each stone is thoroughly bedded in cement mortar before the next

Water

Grout

Air Inlet

Hammer

Grout Tank

Hollow Chisel on End of Jet-Pipe

Water Supply from Force
Pump for Jetting

of the pile, pipes should be inserted into the mass and the grout forced in under pressure, or else some special method adopted for obtaining this result.

In Engineering-Contracting, for May 6, 1908, is given a description of the methods employed by the U. S. Government in constructing locks and dams on the upper White River in Arkansas. Lock and dam No. 1 were located about one mile below Batesville, Ark. The locks The were of concrete masonry while the dam was a Filled with Grout. timber crib structure weighted down with stone, Showing Arrange- and provided with a concrete apron. The lock ment of Apparatus was at one end of the dam, and a concrete for Driving.

Bedrock

FIG. 123.

Clark Steel Pile

T-shaped abutment was built at the other end to

protect the shore end of the structure from erosion.

The foundation for this abutment consisted of a timber crib, formed of 10 X 10 in. squared timbers, with interior pens varying in size from 5 X 10 ft. to 10 X 12 ft. These pens were filled with "one-man" stones to weight down the structure, the filling averaging 11 ft. in depth. The stones were then consolidated by filling the interstices with Portland cement grout.

The method of applying the grout was as follows:

Before the filling was commenced, open-ended square boxes,

8 x 8 ins. inside dimensions, were perforated with 1 1/2 in. holes and placed on end about 10 ft. apart. These were the distribution boxes for the grout. Inside of the distribution boxes, smaller openended square boxes made of 1-in. boards were placed. These boxes, which were not perforated, measured 3 X 3 ins. on the inside and were at first just long enough to reach from the bottom to the top of the outside boxes. As the grout rose in the rubble, the inside boxes were raised and shortened to compensate for the depth filled. By feeding the grout through these smaller boxes, which delivered

it almost intact at the bottom of the large perforated ones, it had to enter the rubble from below upward: and being twice as heavy as water, the filling of all the voids was practically assured. The grout was a 12 mixture of Portland cement and sand, and the cost of grouting was at the rate of $3.65 per cu. yd. of stone composing the fill.

Depositing Concrete Under Water. The standard methods of depositing concrete under water are by means of a tremie or trough, by depositing in closed buckets, and by depositing in cloth or paper bags.

An older method which, however, is not recommended for first

class work, is to deposit loose stone or riprap, and to fill the interstices by forcing liquid grout into the mass by means of a pipe reaching into the interior.

The objections to this method are the impossibility of filling the voids on account of the washing away of a large part of the grout, and to the impracticability of forcing it into all of the interstices between the stones. For use in consolidating blocks employed as paving for reservoir slopes, the use of grout is, however, economical and amply sufficient for the purpose.

Grout in Tunnel Linings.-One of the most useful applications

FIG. 125.-Showing Arrangement of Grout Pipes on Catskill Water Works, New York.

of grout is for the purpose of waterproofing and increasing the strength of tunnel linings.

In tunnelling through rock, the section removed by blasting is in excess of the requirements. When lined with iron rings or concrete, a space is left over the lining which, if left unfilled, would permit the accumulation of water, causing dampness or leaks in the tunnel, and in the case of unstable rock, producing unequal pressures, or endangering the roof lining from possible slides. It is, therefore. desirable to pack the space above the lining with stone, and in submarine tunnels the stone packing is consolidated and rendered impervious by forcing in grout to fill the interstices between the stones.