grout sump in addition to the pump line of the single -line system. Thus, if
the header connection to the hole is closed, grout can be continuously circu-
lated from the grout sump to the pump, through the pump line, through the
header, and back to the sump through the return line. While grouting, the
amount of grout entering the hole through the header can be varied by open-
ing or closing a valve on the return line without changing pump speed. The
double-line system is generally preferred because it permits better control
of grouting pressures and allows less material to settle out of the mix to
plug the lines.
-- . H o s e . Flexible hose is most commonly used for suction and dis-
b
c h a r g e lines. If the length of the discharge line is such that pipe is neces-
sary, a short length of hose should be provided at the pump discharge and at
the connection to the grout header. The hose should be not less than
1-1/2-in. diameter (inside) and capable of withstanding the maximum grout-
ing pressure with an ample margin of safety. The suction line from the
grout sump and water tank may be either pipe or hose of suitable diameter
and should be as short as feasible. It should be provided with fittings at both
e n d s . Hose is preferable to pipe because its flexibility permits ready inter-
change of the suction end between the sump and water tanks. Pipe; on the
other hand, requires the installation of valves that will permit the pump to
draw either grout or water as the occasion demands. It has been found that
difficulty often arises because of clogging of the water valve on the grout
line side.
c . P i p i n g . Black steel pipe and fittings 1-1/2 in. in diameter are nor-
really-suitable for pressure lines; but where large quantities of grout are to
be injected and the supply line is long, it may be desirable to provide a
larger size pipe and connection hoses. Pipe must be capable of withstanding
at least the maximum pressure to be applied in the grouting operation.
d . Grout Header. The grout header is usually assembled as a unit in
order--that it may be moved from one grout hole to another. The assembly
consists of the operating valves, a pressure gage, pipe, and the necessary
fittings to attach the header to the hole and to attach the grout supply and re-
turn lines. The gage and the valves are de scribed in more detail in e and f
b e l o w . A header assembly is shown in figure 16. It should be noted that the
pressure gage is so connected that by closing one valve it can be used for
pressure-drop observations without interrupting the circulation of grout in
the pump system.
Pressure
Gages.
--.
e
( 1 ) Reliable pressure gages are essential in pressure grouting. They
constitute the principal index to the behavior of the hole and the stresses that
are being produced in treated material. If the hole is more than 100 ft hori-
zontally or 20 ft vertically from the pump, there should be two gages in the
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