Category DEWATERING AND GROUNDWATER CONTROL

Example of type B-3 specifications (dewatering)

a. General.

(1) The dewatering system shall be designed by the Contractor using accepted and professional methods of design and engineering consistent with the best modern practice.

(2) The dewatering system shall be of sufficient size and capacity as required to control ground and surface water flow into the excavation and to allow all work to be accomplished in the “dry.”

(3) The Contractor shall control, by acceptable means, all water regardless of source and shall be fully responsible for disposal of the water. The Contractor shall confine all discharge piping and/or ditches to the available easement or to additional easement obtained by the Contractor. All necessary means for disposal of the water, including obtaining additional easement, shall be provided by the Contractor at no additional cost to the owner.

b. Design.

(1) Contractor shall obtain the services of a qual­ified dewatering “Expert” or a firm to provide a de­tailed plan for dewatering the excavation. Contractor shall submit his or her dewatering plan to the Engi­neer for review and approval. The material to be sub­mitted shall include, but not be limited to, the follow­ing:

(a) The qualifications and experience of the se­lected dewatering “Expert” or the firm (minimum of 5 years of proven experience in the design of equivalent

system required).

(b)Drawings showing the soil conditions, strati­fication, and characteristics; location and size of berms, ditches, and deep wells; piezometers, well – points; and sumps and discharge lines or ditches.

(c) Capacities of pumps, prime movers, and standby equipment.

(d) Design calculations including design param­eters and basis of such parameters, factors of safety, characteristics of pumping equipment, piping, etc.

(e) Detailed description of procedures for in­stalling, maintaining, and monitoring performance of the system.

(2) Notice to Proceed issued by Engineer or re­ceipt of the dewatering plans and data submitted by Contractor shall not in any way be considered to re­lieve the Contractor from full responsibility for errors therein or from the entire responsibility for complete and adequate design and performance of the system in controlling the groundwater in the excavated areas, The Contractor shall be solely responsible for proper design, installation, operation, maintenance, and any failures of any component of the system.

(3) The Contractor shall be responsible for the ac­curacy of the drawings, design data, and operational records required.

c. Damages. The Contractor shall be responsible for and shall repair without cost to the Owner any damage to work in place, other Contractor’s equipment, util­ities, residences, highways, roads, railroads, private and municipal well systems, and the excavation, that may result from his or her negligence, inadequate or improper design and operation of the dewatering sys­tem, and any mechanical or electrical failure of the de­watering system.

d. Maintaining excavation in dewatered condition, Subsequent to completion of excavation and during the installation of all work in the excavated area, the Contractor shall maintain the excavations to a de­watered condition. System maintenance shall include but not be limited to 24-hour supervision by personnel skilled in the operation, maintenance, and replace­ment of system components, and any other work re­quired to maintain the excavation in a dewatered con­dition. Dewatering shall be a continuous operation and interruptions due to outages, or any other reason, shall not be permitted.

e. System removal. The Contractor shall remove all dewatering equipment from the site, including related temporary electrical service. All wells shall be re­moved or cut off a minimum of 3 feet below the final ground surface and capped. Holes left from pulling wells or wells that are capped shall be grouted in a manner approved by the Engineer.

Подпись: The proponent agency of this publication is the Office of the Chief of Engineers, United States Army. Users are invited to send comments and suggested improvements on DA Form 2028 (Recommended Changes to Publications and Blank Forms) direct toHQDA (DAEN-ECE-G), WASH DC 20314.

By Order of the Secretaries of the Army, the Air Force, and the Navy:

JOHN A. WICKHAM, JR.
General, United States Army

Official: Chief of Staff

ROBERT M. JOYCE

Major General, United States Army
The Adjutant General

CHARLES A. GABRIEL, General, USAF

Official: Chief of Staff

JAMES H. DELANEY, Colonel, USAF
Director of Administration

W. M.ZOBEL

Rear Admiral, CEC, US. Navy Commander, Naval Facilities
Engineering Command

Distribution:

Army: To be distributed in accordance with DA Form 12-34B, requirements for TM 5-800 Series: Engineer­ing and Design for Real Property Facilities.

Air Force; F

Navy: Special distribution.

☆ U. S. GOVERNMENT PRINTING OFFICE : 19 9 6 – 406-421 (50184)

1. A pH less than 7

[1] Dissolved oxygen in

Well discharge header system

(а) No measurement will be made for the well discharge header system.

(б) Payment for the well discharge header sys­tem will be made at the lump sum price and shall con­stitute full compensation for furnishing all plant, labor, materials, and equipment necessary to install the system. The system includes, but is not limited to, header pipe, valves, fittings, outfall structures, and ac­cessories.

(7) Jet-eductor wells.

(a) Jet-eductor wells will be measured for pay­ment by the linear foot to the nearest foot from the (berm) ground surface to the bottom of the PVC pipe as installed.

Ф) Payment at the contract unit price for instal­lation ofjet-eductor wells shall constitute full compen­sation for all plant, labor, header pipe, pumps, engines, tanks, valves, connections, materials, and equipment for performing all operations necessary to install the jet eductors and pumping system as shown on the drawings.

(8) Piezometers.

(a) M, R, S, T, and N piezometers will be meas­ured for payment on the basis of each piezometer suc-

cessfully installed and tested.

(b) Payment at the contract unit price for instal­lation of M, R, S, and T piezometers shall constitute full compensation for furnishing all plant, labor, mate­rials, and equipment for performing all operations necessary to install, develop, and test the M, R, S, and T piezometers.

(c) Payment at the contract unit price for instal­lation of N piezometers shall constitute full compensa­tion for furnishing all plant, labor, materials, and equipment for performing all operations necessary to install, develop, and test N piezometers.

(9) Testing, operation, and maintenance of de­watering sys terns.

(a) No measurements will be made for testing, operation, and maintenance of the deep-well and jet- eductor well systems.

(b) Payment for testing, operations, and mainte­nance of the dewatering systems as specified will be made at the lump sum price and shall constitute full compensation for the duration of this contract and un­til the systems are transferred to the Phase III Con­tractor or the Government.

Measurement and payment

(1) Unwatering Phase I excavation.

(a) No measurement will be made for unwater­ing Phase I excavation.

(b) Payment for unwatering Phase I excavation will be made at the lump sum price and shall consti­tute full compensation for furnishing all plant, labor, materials, and equipment necessary to unwater Phase I excavation.

(2) Surface water control and sump pumping.

(a) No measurement will be made for surface water control and sump pumping.

(b) Payment for surface water control and sump pumping will be made at the lump sum price and shall constitute full compensation for furnishing all plant, labor, materials, and equipment for surface water con­trol and sump pumping, irregardless of the source of water.

(3) Deep dewatering wells.

(a) Dewatering wells will be measured for pay­ment on the basis of each well successfully completed and accepted by the Government.

(b) Payment at the contract unit price for instal­lation of dewatering wells shall constitute full compen­sation for furnishing all plant, labor, materials, and equipment for performing all operations necessary to install, develop, and test pump each well.

(4) Dewatering turbine pumps, engines, and acces­sories. /

(a) Dewatering turbine ршпріз, engines, and ac­cessories as specified on the drawings will be measured

for payment on the basis of each pump properly in­stalled and fully operational.

(b) Payment at the contract unit price for instal­lation of dewatering turbine pumps, engines, and ac­cessories shall constitute full compensation for fur­nishing all plant, labor, materials, and equipment for furnishing and installing the pumps and engines.

(5) Standby turbine pumps,

(a) Standby turbine pumps will be measured for payment on the basis of each complete pump placed on the jobsite.

ф) Payment at the contract unit price for fur­nishing standby turbine pumps shall constitute full compensation for furnishing the pumps and placing in appropriate storage. Each standby turbine pump shall include all components shown on the drawings includ­ing, but not limited to, 130 feet of column pipe and shafting, pump bowls, suction pipe, pump head, gear drive, and flexible coupling.

(6) Standby dieselpower units.

(а) Standby diesel power units will be measured for payment on the basis of each complete power unit placed on the jobsite.

(б) Payment at the contract unit price for fur­nishing standby diesel power units shall constitute full compensation for furnishing all plant, labor, mate­rials, and equipment for furnishing the diesel engines and placing in appropriate storage. Each standby die­sel power unit shall include all components shown on the drawings including the 110-horsepower diesel en­gine with clutch power takeoff and fuel tank.

Operation and maintenance of dewatering and surface water control systems

(1) Supervision. Supervisory personnel shall be present onsite during normal working hours and shall

be available on call 24 hours a day, 7 days per week, in­cluding holidays.

(2) Operating personnel. Sufficient personnel skilled in the operation, maintenance, and replace­ment of the dewatering and surface water control sys­tems, components, and equipment shall be onsite 24

hours a day, 7 days per week, including holidays, at all times when the systems are in operation.

(3) Well pumping restriction. The pumping rate of any dewatering (deep) well shall be adjusted, if neces­sary, by adjustment of engine speed or valving so that the water level in no well is lowered below the pump

bowl. With approval of the C. O.R., the pump bowl may be lowered. In order to maintain maximum well effi­ciency, the deep-well system shall be operated by pumping whatever number of wells are required to achieve the specified water level lowering in the deep sand formation without pumping any well more than 1200 gallons per minute except in an emergency or if required to achieve the specified water level lowering.

(4) Responsibility. Dewatering the excavation in­cludes the control of seepage and artesian pressure in the deep sand stratum underlying the site and the con­trol of seepage from the upper silts and silty sand for the duration of this contract. Included are the opera­tion and maintenance of the deep-well, jet-eductor well, and surface water control systems.

(5) Repair and replacement. The specified number of wells and pumps shall be available for use at all times. All damaged or malfunctioning wells or well components shall be repaired or renewed as expedi­tiously as possible while continuing to maintain the re­quired water levels. The Contractor shall be responsi­ble for all replacement equipment and the repair and maintenance of all system components so as hmain – tain the system fully operational. Replacement equip­ment and materials shall conform to the requirements of these specifications.

(6) Maintenance criteria. The Contractor shall maintain a regularly scheduled maintenance program which shall conform with the equipment manufac­turer’s recommendations and include all other work necessary to maintain all components fully operation­al. The maintenance program shall include, but not be limited to, checking the flow rate and water elevation in each well. All data and records shall be submitted to the C. O.R. at the completion of this contract. The Con­tractor shall also maintain any nonoperating pumps and engines. Maintenance shall include, but not be limited to, starting each nonoperating pump and en­gine on a weekly basis and operating the pump for a minimum of 15 minutes. All pumps, both operating and nonoperating, shall be tested for wear, independ­ently, on a monthly basis. The Contractor shall con­duct a shutoff head test and a test to verify that the pump is capable of operating at its rated head capac­ity. The Contractor shall renew all pumps having a test result less than 75 percent of the manufacturer’s rated shutoff head or rated capacity. The maintenance tests shall be conducted under the supervision of the Contractor Quality Control representative and under the observation of the C. O.R.

j. Damages. The Contractor shall be responsible and shall repair without cost to the Government, any work in place, another contractor’s equipment, and any damage to the excavation, including damage to the bottom due to heave that may result from his negli­gence, improper operationand/or maintenance of the

dewatering system, and any mechanical failure of the system.

k. Transfer of system. The succeeding Contractor for Phase III construction, or the Government, shall take title to the complete surface and dewatering sys­tems when the Contractor for Phase II completes his or her work. The facilities to be transferred include all dewatering wells, jet-eductor wells, pumps, engines, gear drives, piezometers, header pipe, valves, and all spare parts and standby equipment pertinent to the surface and groundwater control systems. The de­watering systems shall be continuously operated dur­ing the transfer of the system to either the Phase III Contractor or to the Government. The (succeeding) Contractor for Phase III work, or the Government, shall take title to the complete dewatering well, jet – eductor, and surface water control systems as installed when either assumes responsibility for maintaining the excavation dewatered. The Contractor (Phase II) shall not be responsible for removing any of the de­watering systems or grouting of wells or supplemental dewatering facilities, if any, installed by him or her, at the end of his or her contract or subsequently there­after.

Dewatering system flow

(a) Flow measurements. The flow from individ­ual dewatering wells will be measured by means of a pitometer installed in the discharge pipe from the well. As a check on the pitometer measurements and on the performance of the well pump, the rate of flow being pumped will also be estimated from the pump

characteristic curve, engine speed, static lift of the

water, and the pressure in the discharge pipe at the top of the well. Flow from the entire dewatering sys­tem will also be measured by means of a pitometer. All flow measurements will be made by the C. O.R. as­sisted by the Contractor’s “dewatering” engineer.

(b) Frequency of measurement. The total flow from the dewatering system shall be measured once or twice a week and the flow from individual wells week­ly or biweekly, as appears appropriate.

(c) Records. All flow measurements will be re­corded by the C. O.R. and a copy of the data furnished to the Contractor within 24 hours. The C. O.R. will be

responsible for reading the river gage and recording

the data; a copy of the river gage reading will be fur­nished to the Contractor each day.

(3) Sanding. The flow from each dewatering well will be monitored for sanding. The rate of sanding will be determined by taking a measured amount of water being pumped from each well and the sand content de­termined. The maximum rate of sanding acceptable will be 5 parts per million. The rate of sanding will be checked once a week by the C. O.R. and the data re­corded. A copy of the data will be furnished to the Con­tractor within 24 hours.

Piezometers

(a) Locations. The M, R, S, and T piezometers shall be installed to measure the groundwater table in the deep sand formation beneath the excavation, be­tween the dewatering wells, and on three lines out from the excavation at the approximate locations shown on the drawings. The N piezometers shall be in­stalled to measure the groundwater table in semiper­vious strata in the bottom of the excavation and mid­way between jet-eductor wells at the approximate loca­tions. The Contractor shall stake the piezometers at designated locations. The tips of M, R, S, and T pie­zometers for measuring the groundwater table in the deep sand formation shall be set in clean sand at eleva­tion -80.0 feet or below as necessary; the tips of the N piezometers for measuring the groundwater table in semipervious strata in the top stratum shall be set at the bottom of the semipervious strata.

(b) Piezometer materials. The N piezometers shall consist of a 1.50-inch I. D. (Schedule 80) PVC screen with 0.025-inch slots connected to a 1.50-inch

I. D. (Schedule 80) PVC riser pipe. The screens shall be 10 feet long. The joints of the screen and riser shall be flush (inside and outside) and shall be glued together with PVC pipe cement. The filter sand (B) shall meet the specifications set forth for jet-eductor wells. De­pending upon the method of installation, the riser and screens for the M, R, S, and T piezometers shall be as specified above, or 1.5-inch galvanized iron riser pipe connected to a 1.5- by 30-inch self-jetting wellpoint with a 30- to 40-mesh stainless steel screen.

(c) Installation of piezometers. Holes for pie­zometers may be advanced by either: using an S-inch O. D. continuous flight auger with a 3%-inch I. D. hol­low stem with the hollow stem plugged at the bottom with a removable plug; augering and more or less simultaneous installation of a 6-inch casing; or using a rotary wash drilling procedure (6-inch diameter) and an organic drilling fluid, such as Revert, if necessary, to keep the drilled hole open. The tip of the piezom­eters shall be installed at approximate depths or eleva­tions as approved by the C. O.R.; piezometers shall also be installed as instructed. The hole for a piezometer shall be kept filled with water or an approved organic drilling fluid at all times. Bentonitic drilling mud shall not be used. Any auger used in advancing the hole shall be withdrawn slowly from the hole so as to mini­mize any suction effect caused by withdrawing the auger. (Hollow-stem augers shall be filled with drilling fluid before pulling the plug in the bottom of the auger.) Drilling and installation procedures shall be as specified below and shall be in accordance with ac­cepted practice and to the satisfaction of the C. O.R.

Method 1. Hollow-stem auger. After advancing the hole for the piezometer to grade (1 to 2 feet below the piezometer tip), or after taking the last sample in a hole to receive a piezometer, the hollow-stem auger shall be flushed clean with water and the plug rein­serted at the bottom of the auger. The auger shall then be slowly raised to the elevation that the piezometer tip is to be installed. At this elevation the hollow stem shall be filled with clean water and the plug removed. Water shall be added to keep the stem full of water during withdrawal of the plug. The hole shall then be sounded to determine whether or not the hollow stem is open to the bottom of the auger. If material has en­tered the hollow stem of the auger, the hollow stem shall be cleaned by flushing with clear water, or clean Revert drilling fluid, if necessary, to stabilize the bot­tom of the hole, through a bit designed to deflect the flow of water upward, until the discharge is free of soil particles. The piezometer screen and riser shall then be lowered to the proper depth inside the hollow stem and the filter sand placed. (A wire spider of design ap­proved by the C. O.R. shall be attached to the bottom of the piezometer screen so as to center the piezometer screen in the hole in which it is to be placed. Use two crossed wires just above the plug in the tip.) Filter sand shall be poured down the hollow stem around the riser at a rate (determined in the field) that will ensure continuous filter sand flow down the hollow stem around the riser and piezometer, and will keep the 8- inch hole below the auger filled with filter sand as the auger is withdrawn. Withdrawal of the auger and fill­ing the space around the piezometer tip and riser with filter sand shall continue until the hole is filled to a point about 5 feet above the top of the piezometer screen. Above this elevation, the space around the riser pipe may be filled with any clean, uniform sand with less than 5 percent passing a No. 100 U. S. Stand­ard sieve up to within 20 feet of the ground or exca­vated surface. An impervious grout seal shall be placed around the top 20 feet of the ground or excavated sur­face. An impervious grout seal shall be placed around the top 20 feet of the hole for the M, R, S, and T pie-

zometers, and 5 feet for the N piezometers.

Method 2. Casing. The hole for a piezometer may be formed by setting a 6-inch casing to an elevation 1 to 2 feet deeper than the elevation of the piezometer tip. The casing may be set by a combination of rotary drilling and driving the casing. The casing shall be kept filled with water, or organic drilling fluid if necessary, to keep the bottom of the hole from ‘blow­ing.” After the casing has been set to grade, it shall be flushed with water or (clean) drilling fluid until clear of any sand. The piezometer tip and riser pipe shall then be installed and the filter sand poured in around the riser at a rate (to be determined in the field) which will insure a continuous flow of filter sand down the casing that will keep the hole around the riser pipe and below the casing filled with filter sand as the casing is withdrawn without “sand-locking” the casing and riser pipe. (Placement of the filter sand and withdrawal of the casing may be accomplished in steps as long as the top of the filter sand is maintained above the bottom of the casing but not so much as to “sand-lock” the riser pipe and casing.) Filling the space around the pie­zometer tip and riser with filter sand shall continue until the hole is filled to a point about 5 feet above the top of the piezometer screen. Above this elevation, the space around the riser pipe may be filled with any clean, uniform sand and the hole grouted as specified in Method 1 above.

Method 3. Rotary. The hole for a piezometer may be advanced by the hydraulic rotary method using water or an organic drilling fluid. The hole shall have a minimum diameter of 6 inches. After the hole has been advanced to a depth of 1 or 2 feet below the pie­zometer tip elevation, it shall be flushed with clear water or clean drilling fluid, and the piezometer, filter sand, sand backfill, and grout placed as specified in Method 2 above, except there will be no casing to pull.

Method 4. Self-jetting. The M, R, S, and T piezom­eters may be drilled to within 4 feet of planned total depth, then clean water used to advance the self-jet­ting wellpoint to the design grade without the use of filter sand around the wellpoint. The seal and backfill for the piezometers shall consist of a pumpable cementbentonite grout, with a ratio of 1 gallon of ben­tonite per bag of cement, or equivalent cement grout approved by the C. O.R. (Only enough water shall be added to make the grout pumpable.) The tops of the risers shall be cut off 36 inches above the ground sur­face. The upper part of the piezometer shall be pro­tected by installing a 6-inch I. D. PVC or corrugated metal pipe around the riser cemented in to a depth of 3 feet below the ground surface. The number of the pie­zometer shall be marked with 3-inch-high black letters on the pipe guard around the riser pipe.

Method 5. Sampling. Split-barrel samples shall be obtained at 5-foot intervals and at every strata change for the N piezometers. Samples shall be obtained using a 1%-inch (minimum) I. D. split-barrel or З-inch Shelby tube sampler by driving or pushing. The length of drive or push shall not be less than 3 inches. If there is insufficient sample recovery to identify the soil prop­erly, another sample shall be obtained immediately be­low the missed sample. If desired, the sampler may be advanced using driving jars on a wireline.

(d) Development and testing. After each pie­zometer is installed, it shall be promptly flushed with clean water, developed, and pumped to determine if it is functioning properly. (If an organic drilling fluid has been used, Johnson’s Fast Break, or equivalent, shall be added in accordance with the manufacturer’s rec­ommendations to break down the drilling fluid,) A 10- foot minimum positive head shall be maintained in the piezometer following addition of the Fast Break. After at least 30 minutes has elapsed, the piezometer shall be flushed with clear water and pumped. The piezom­eter may be pumped with either a suction pump or by means of compressed air. The approximate rate of pumping during development shall be measured, Pie­zometers installed in the deep sand formation will be considered acceptable if they will pump at a rate of 2 to 5 gallons per minute or more. Piezometers installed in the semipervious strata within the top strata will be considered acceptable if they will pump at a rate of at least 0.5 gallon per minute, or when the piezometer is filled with water, the water level falls approximately half the distance of the groundwater table in a time less than the time given below for various types of soil:

Approximate

Type of soil in Period of time of

which piezometer observation 5Opercent fall

screen is set minutes minutes

Sandy silt (> 50% silt) 30 30

Silty sand (< 50% silt, > 12% silt) 10 5

Fine sand (<12% silt) 5 1

If the piezometer does not function properly, it shall be developed by a combination of air surging and pump­ing with air as necessary to make it perform properly. If the piezometer still will not perform properly, it shall be reinstalled at a nearby location selected by the C. O.R.

(e) Monitoring groundwater table. The Contrac­tor shall read all M and N piezometers at least once a week, selected piezometers at least twice a week, some of the piezometers in the deep sand formation daily, and the water level in the dewatering and the jet-educ­tor wells at least once a week for his or her informa­tion and use in operation of the dewatering systems and control of groundwater as specified. The Contrac­tor shall record what deep well and jet-eductor wells are being pumped when he takes his piezometer or water level readings. The C. O.R. will also read the M

and N piezometers on a schedule similar to the above for his own check and evaluation purposes.

f) Records, The Contractor shall furnish copies of all piezometer and water level readings to the C. O.R. within 24 hours of being taken. Copies of pie­zometer, water level, and flow measurements made by the C. O.R. will be furnished to the Contractor within 24 hours.

Monitoring dewatering systems

(1) General. Continuous control of seepage into and artesian pressure beneath the excavation is essen­tial for driving the test and foundation piles for the dam, and subsequent construction of the lock and dam. It is therefore imperative that the dewatering systems have adequate capacity to control the ground­water beneath the slopes and the excavation as speci­fied at all times, In order to check the adequacy and performance of the dewatering systems, the Govern­ment will make the following measurements and eval­uate the data:

(a) Measure the groundwater table beneath the bottom of the excavation by means of M, R, S, and T piezometers installed in the deep sand aquifer that underlies the site at specified locations.

(b) Measure the groundwater table at selected locations where the excavation penetrates silts and silty sands in the top stratum overlying the deep sand formation by means of N piezometers installed at the locations.

(c) Measure the flow from individual wells and from the complete dewatering system.

(d) Measure the water level in the dewatering

wells.

(e) Measure sand in the flow from dewatering

wells.

(/) Measure the head loss through the filter and well screen for selected wells.

(g) Read river stages.

The piezometers for monitoring the groundwater table beneath the slopes and bottom of the excavation shall be installed by the Contractor. The pitometers for measuring the flow from individual wells and from the complete system will be furnished by the Government. Copies of the data obtained by the Government will be promptly furnished to the Contractor. The Contractor will furnish and install the pitometer inserts. Opera­tion and maintenance of the dewatering systems, any supplemental groundwater control facilities if re­quired, and surface water control facilities shall be su­pervised by someone trained and with at least 5 years of actual experience in managing large dewatering sys – terns and operating pumps and engines.

Surface water control

(1) The Contractor shall be fully responsible for designing all features of the system for unwatering the excavation and controlling surface water that may fall into the excavation. The sump pumping system shall be designed with sufficient storage and pumping ca­pacity to prevent flooding the bottom of the excava­tion for the dam for at least a 1 in lo-year rainfall in­tensity, assuming 100 percent runoff, for the follow­ing periods:

Period 30 minutes

1 hour

2 hours

In any event, the Contractor shall be responsible for controlling whatever surface runoff occurs, regardless of rainfall intensity, so as to protect the area for pile driving and testing from flooding.

(2) The Contractor shall submit for approval with­in 15 calendar days, after he or she has received a No­tice to Proceed, drawings, design data, and charac­teristics of the equipment he proposes to utilize in unwatering and controlling surface water. The data

and drawings to be submitted shall include, but not necessarily be limited to:

(a) Location and size of sumps, pumps, and

dikes.

(b) Height and elevation of dike around excavation.

(c) Characteristics of sump pumps and horsepower of engines.

(d) Location and size of discharge piping. (Sur­face water shall not be pumped into the discharge header for the dewatering (well) sys­tem.) g. Dewatering perched groundwater in lower part or bottom of excavation. The Contractor shall be fully responsible for design and installation of any sup­plemental dewatering facilities that may be required to control any seepage or groundwater in the bottom or lower part of the excavation in order to assure a sta­ble subbase and permit work to be conducted in the “dry.” These supplemental measures may include well – points, sand drains, French drains, and appropriate pumps, piping, and appurtenances as necessary and approved by the C. O.R. subject to satisfactory perfor­mance of the facility installed. Pay for any such sup­plemental dewatering, if required, for the lower or bot­tom part of the excavation should be included in the price for excavation. There will be no charges or claims for extra compensation or time extension for any sup­plemental dewatering performed in the bottom or lower part of the excavation.

Materials

(а) Riser pipe. The riser pipe and the 2-foot blank pipe on the bottom of the screen shall be 4-inch diameter, flush-joint Schedule 80, type 2110 PVC pipe.

(б) Screen. The screen shall be 4-inch, Schedule 80, type 2110 PVC screen. The screen shall be slotted with.025-inch slots in sufficient numbers to give a minimum area of opening of 5 percent. The screen sec­tion of the well shall extend from the top of any semi-

Подпись: Rainfall Intensity, inch/hour Amount, inches 4.5 2.25 3.0 3.00 2.0 4.00

pervious strata as shown by the boring logs, or as en­countered, to the depth specified.

(c) Filter sand. Filter sand around the well screen shall be washed (clean) uniform sand or crushed stone composed of hard, tough, and durable particles free from any adherent coating. The filter sand shall contain no detrimental quantities of vegetable matter, nor soft, friable, thin, or elongated particles, and shall meet the following gradation requirements:

Filter Sand B

U. S. Standard

Percent by weight

Sieve No.

passing

8

95-100

10

92-100

14

75-100

16

65-95

20

30-77

30

10-30

40

1-13

50

0-5

(5) Jet-eductor pumps and header pipe. The jet- eductor pumps shall have the specified pumping ca­pacities, The pressure pumps for operating the jet – eductor pumps shall have a diesel engine with a horse­power of at least 110 and a capacity of 1800 gallons per minute at a total dynamic head of at least 150 feet on a continuous basis. The standby pumps shall have the same horsepower and capacity. The pressure header pipe shall be Schedule 40; the return header pipe shall have a minimum wall thickness of 0.20 inch. The sump pumps for the jet-eductor systems shall be an electric, automatic priming type, with a capacity of pumping 600 gallons per minute at TDH = 50 feet.

Installation of jet-eductor wells

(a) Location and depth of wells. The jet-eductor wells shall be installed at the designated locations. Soil conditions where the jet-eductor wells are to be in­stalled are depicted in a general way by the logs of bor­ings made around the excavation. The wells should extend about 2 feet below the bottom of the pervious strata being drained. The required depth of the wells may vary considerably from those indicated on the drawings.

(b) Drilling and jetting. The jet-eductor wells shall be installed in the following manner:

Step 1. Predrill a 10- or 11-inch hole 2 feet below the silt or silty sand stratum to be drained. Hy­draulic rotary, or auger, methods of drilling may be used. No drilling muds or additives, other than clear water, shall be used in drilling the hole for the well. The hole shall be kept full of water during the predrill­ing, and withdrawal of the auger, so as to minimize caving.

Step 2. After predrilling the hole to grade, it shall be washed out by driving and jetting (with clear water) a 12-inch “sanding casing” with a hole puncher to the bottom of the predrilled hole.

Step 3. After the “sanding casing” is driven and jetted to the required depth, it shall be washed clean by jetting with clear water. The jet pump, pipe, and hose shall be of sufficient capacity to produce an up­ward velocity inside the casing to efficiently remove all material in the casing, so that the well screen and riser can be set to grade. The “sanding casing” shall be kept filled with water until the well screen and filter sand have been placed so as to prevent any “blow in” of the bottom of the hole.

(c) Installation of well screen and filter sand. After the sanding casing has been cleaned by jetting and the clear depth in the casing checked by sounding with an approved device, the well screen shall be low­ered to the bottom of the casing. Particular care shall be exercised in handling and placing the screen so as not to damage it. Complete assembly of the screen and riser pipe on the ground’surface will not be permitted. Two or three connections shall be made to the assem­bly as it is placed in the casing. Approved centralizers shall be furnished and attached to the screen at inter­vals not greater than 20 feet. The design and attach­ment of the centralizers to the well screen shall be sub­mitted to the C. O.R. for approval. The top of the riser pipe shall be securely covered or capped to prevent the filter sand from falling into the well. The method of placement shall assure a fairly rapid, continuous, uni­form rate of placement of filter sand, which will evenly distribute the filter sand around the screen. The rate of placing the filter sand shall not cause bridging of the sand in the “sanding” casing. As the fil­ter material is placed in the well screen, 70 percent granular calcium hypochlorite shall be added to evenly distribute a minimum of 2 pounds per ton of filter. The method of placement shall be approved by the C. O.R.

(d) Development of jet-eductor wells. Within 12 hours after installation of each well, it shall be devel­oped by means of air-lifting. A 2-inch inner diameter air line shall be lowered in the well to within 1 foot of the bottom of the well and sufficient air be pumped through the air line to cause the well to flow. For low – yielding wells, it may be necessary to add clear water to help develop the well and remove any sand that may have entered the screen. Air-lifting shall continue un­til all sand or filter material is removed from inside the screen and water from the well flows clear. Each well shall be developed for a minimum of 20 minutes.

(e) Chlorination of well. Upon completion of in­stallation of the well and prior to installing a cap on the top of the riser, a minimum of 3 pounds of 70 per­cent granular calcium hypochlorite shall be dropped into the well,

(f) Well top. The 4-inch riser shall extend 6 inches above the ground surface and shall be sealed around the riser pipe for the jet-eductor pump. The well number shall be painted on the top of the riser pipe.

(g) Riser pipe. The 4-inch riser pipe for the wells shall be 15 feet in length. The filter sand shall extend to within 8 to 10 feet of the berm surface; the space around the riser pipe from the filter to the berm sur­face shall be grouted with an approved bentonite-ce­ment grout.

(h) Well records. A report showing depth, eleva­tions, date of installation, approximate rate of flow during development, and any other data concerning in­stallation of each well will be completed by the C. O.R. The water level in the well shall be recorded at the time of installation. The Contractor shall assist in ob­taining the installation data. If the jet-eductors or pumps appear to be losing their efficiency with the passage of time, the Contractor may be required to re­develop and/or chemically treat the wells as directed by the Contracting Officer, the cost of which will be paid for under paragraph 3 (Changes) of the General Provisions of the Contract.