Wellpoint systems

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-

Plan of a typical wellpoint system.

Wellpoint systems

(From “Foundarion Engineering, ” (i. A. Leonards, ed., 1962, McGraw-Hill Book Company. Used with permission of McGraw-Hill Book Company.)

Figure 5-І. Plan of a typical wellpoint system.

 

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-

IPointed tip of wellpoint with high pressure jet stream

 

(Courtesy of Griffin Wellpoint Corp.)

 

Wellpoint systems

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

Wellpoint systems

Подпись: 1. Centrifugal Pump Volute 2. Cleanout 3- Screenbox k. Suction or Header Connection 5. Wiper Float Drain Line 6. Scrubber Float Chamber 7. Wiper Float Chamber 8. Air Vent Valve

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.