a. Wellpoint systems are installed by first laying the header at the location and elevation called for by the plans as illustrated in figure 5-1. After the header pipe is laid, the stopcock portion of the swing connection should be connected to the header on the spacing called for by the design, and all fittings and plugs in the header made airtight using a pipe joint compound to prevent leakage. Installation of the wellpoints generally follows layout of the header pipe.
b. Self-jetting wellpoints are installed by jetting them into the ground by forcing water out the tip of the wellpoint under high pressure. The jetting action of a typical self-jetting wellpoint is illustrated in fig-
ure 5-2. Self-jetting wellpoints can be installed in medium and fine sand with water pressures of about 50 pounds per square inch. Wellpoints jetted into coarse sand and gravel require considerably more water and higher water pressures (about 125 pounds per square inch) to carry out the heavier particles; either a hydrant or a jetting pump of appropriate size for the pressures and quantities of jetting water required can be used. The jetting hose, usually 2 to 3 inches in diameter, is attached to the wellpoint riser, which is picked up either by a crane or by hand and held in a vertical position as the jet water is turned on. The wellpoint is allowed to sink slowly into the ground and is slowly raised and lowered during sinking to ensure that all fine sand and dirt are washed out of the hole. Care should be taken to ensure that a return of jet water to the surface is maintained; otherwise, the point may “freeze” before it reaches grade. If the return of jet water disappears, the point should be quickly raised until circulation is restored and then slowly relowered. In gravelly soils, it may be necessary to supplement the jet water with a separate air supply at about 125 pounds per square inch to lift the gravel to the surface. If filter sand is required around the wellpoint to increase its efficiency or prevent infiltration of foundation soils, the wellpoints generally should be installed
using a hole puncher and a jet casing to form the hole for the wellpoint and filter. When the wellpoint reaches grade and before the water is turned off, the two halves of a swing connection, if used, should be lined up for easy connection when the jet water is turned off and the jetting hose disconnected.
c. Where a wellpoint is to be installed with a filter (i. e. “sanded”), generally the wellpoint should be installed in a hole formed by jetting down a 10- to 12- inch heavy steel casing. The casing may be fitted with a removable cap at the top through which air and water may be introduced. The casing is jetted into the ground with a return of air and water along the outside of the casing. Jetting pressures of 125 pounds per square inch are commonly used; where resistant strata are encountered, the casing may have to be raised and dropped with a crane to chop through and penetrate to the required depth. A casing may also be installed using a combination jetting and driving tool, equipped with both water and air lines, which fits inside the casing and extends to the bottom of the casing. Most of the return water from a ‘hole puncher” rises inside the casing, causing considerably less disturbance of the adjacent foundation soils. After the casing is installed to a depth of 1 to 3 feet greater than the length of the as-
sembled wellpoint, the jet is allowed to run until the casing is flushed clean with clear water.
d. The wellpoint is placed in the casing, the sand fd – ter tremied or poured in, and the casing pulled. Care should be taken to center the wellpoint in the casing so that it is completely surrounded with filter material. Before the wellpoint is connected to the header, it should be pumped to flush it and the filter and to check it for “sanding.” All joints connecting wellpoints to the header should be made airtight to obtain the maximum needed vacuum.
e. Wellpoint pumps, similar to that shown in figure
5- 3, are used to provide the vacuum and to remove water flowing to the system. To obtain the maximum
possible vacuum, the suction intake of the pump should be set level with the header pipe, Wellpoint pumps should be protected from the weather by a shelter and from surface water or sloughing slopes by ditches and dikes. The discharge pipe should be watertight and supported independently of the pump.
f. Vacuum wellpoint systems are installed in the same manner as ordinary wellpoint systems using a jet casing and filter, except the upper 5 feet of the riser is sealed airtight to maintain the vacuum in the filter.
g. Jet-eductor wellpoints are usually installed using a hole puncher and surrounding the wellpoint and riser pipe with filter sand. Jet eductors are connected to two headers-one for pressure to the eductors and
9, Air Suction line Wiper Float Chamber to Vacuum Pump 10. Discharge Check Valve 1 1. Vacuum Pump Exhaust
12. Oil Reclaimer for Vacuum Pump
13. Discharge Connection 14 . Flexible Coupling
I 5. Engine
16, Cooling Water line for Vacuum Pump
17. Be It Guard
|8. Vacuum Pump Pulley
19* MT7l~*t Rotary-Type Vacuum Pump
20. Vacuum Pump Rocker-Type Base
21. Vacuum Pump Exhaust Thermometer
22. Vacuum Pump Oil Supply Lines
23. Oil Dripper/Lubricator for Vacuum Pump
(Courtesy of Moretrench American Corp.)
another for return flow from the eductors and the wellpoints back to the recirculation tank and pressure pump.
5-4. Vertical sand drains. Vertical sand drains can be installed by jetting a 12- to 18-inch casing into the soil to be drained; thoroughly flushing the casing with clear water; filling it with clean, properly graded filter sand; and pulling the casing similar to installing “sanded” wellpoints. It is preferable to place the filter sand through a tremie to prevent segregation, which may result in portions of the filter being too coarse to filter fine-grained soils and too fine to permit vertical drainage. Sand drains should penetrate into the underlying pervious aquifer to be drained by means of wells or wellpoints.
5- 5. cutoff s.