Example of type B-2 specifications (dewatering and pressure relief)
a. Scope. This section covers: furnishing, installing, operating, and maintaining the dewatering systems shown on the drawings and specified herein; unwatering the Phase I excavation; installing any additional dewatering wells, pumps, and appurtenances, if necessary, to lower and maintain the hydrostatic water level in the sand formation beneath the excavation to a level at least 5 feet beneath any Phase II excavated surfaces, and have the capacity to lower the water level to elevations – 29.0 and – 35.0 feet beneath the chamber and gate bay sections, respectively, of the lock for a Red River stage of elevation 60.0 feet; and controlling seepage from the soils above and below the bottom of the excavation, not intercepted by the specified well and jet-eductor systems, by installing additional jet-eductor wells, wellpoints, pumps, and appurtenances if necessary, so as to assure a stable bottom at grade for the Phase II excavation and prevent any significant seepage or raveling of excavated slopes. The dewatering systems shall include deep wells; jet-eductor wells; wellpoints and/or sand drains if required; pumps, engines, and piping; and related appurtenances; and dikes, ditches, sumps, and pumps necessary for control of surface water. The dewatering systems shall remain in continuous operation, as specified, until completion of this (Phase II) Contract and the systems are transferred to the Phase III Contractor or to the Government.
b. Compliance with specifications and drawings.
The contractor shall designate a representative or engineer experienced in dewatering large excavations whose responsibility will be to assure that thedewater – ing systems comply with the contract plans and specifications with respect to materials, installation, maintenance, and operation of the dewatering systems so as to control subsurface pressures, groundwater and seepage, and surface water, and maintain records as specified herein. The “dewatering” engineer’s duties shall include the following:
(1) Materials and equipment. The Contractor’s “dewatering” engineer shall obtain all specified data and supervise making all tests and/or measurements to determine that all materials incorporated in the work are in accordance with the plans and specifications. Materials and equipment to be checked shall include, but not be limited to, well screens, riser pipes, filter sand, pumps, column pipe, gear drives, couplings, diesel engines, well discharge pipe and fittings, header pipe, valves, discharge system outlet structures, piezometers, and related appurtenances.
(2) Installation. The Contractor’s “dewatering” engineer shall check to be sure that specified procedures and methods for installing wells, pumps, jet – eductor wells, piezometers, and any other supplemental dewatering or groundwater control system required are installed in accordance with the specifications and drawings.
(3) Operation and maintenance. The Contractor’s “dewatering” engineer shall supervise the operation and maintenance of the dewatering systems, supplemental groundwater control facilities if any, surface water control systems, and shall assist with obtaining all required piezometric, well performance, and flow data. The Contractor shall inspect the test starting of each nonoperating dewatering pump and engine installed in a well or on the system on a weekly basis and include in a daily report reference to the conduct of the test, the number of pumps and engines tested, and any unsatisfactory performance data and remedial action taken. The Contractor’s “dewatering” engineer shall notify the Contractor and the Contracting Officer’s Representative (C. O.R.) immediately of any event or information not in accordance with the specifications. Thirty days prior to completion of the work under this contract, the Contractor shall furnish to the Government a complete set of “as-built” drawings of the dewatering facilities installed, and all significant operational, maintenance, and performance data and records.
(4) Records. A copy of all inspection and test data relating to materials, installation, operation and maintenance, and performance of the dewatering systems, and supplemental groundwater control facilities if any, as required, shall be promptly furnished to the Contracting Officer.
c. General. The dewatering systems shall be installed, operated, and maintained so as to reduce the artesian pressure in the sand formation below the excavation, and control seepage from any excavated slopes or into the bottom of the excavation as specified below, so that the work covered under this contract can be accomplished in stable areas free of water and without heaving of soil strata overlying the sand aquifer within the cofferdammed area.
(1) Dewatering requirements. Construction dewatering to be performed by the Contractor shall consist of:
(а) Dewatering lock and dam excavation by pumping from deep wells; jet-eductor wells; and any other supplemental groundwater control facilities if required.
(б) Unwatering the Phase I excavation.
(c) Testing adequacy of deep-well system prior to and after unwatering the Phase I excavation. Evaluation of the adequacy of the jeteductor system after unwatering the excavation.
(d) Controlling and removing of surface water falling into the excavation.
The dewatering systems for Phase II excavation for the lock and dam shall be constructed in accordance with the details shown on the drawings and the requirements herein specified. The dewatering systems shall be installed and operated by the Contractor to control seepage from any excavated slopes or the bottom of the excavation so as to assure a stable work area at grade and prevent raveling or sloughing of excavated slopes, and to lower the hydrostatic water level in the deep underlying sand formation so that as the excavation progresses the piezometric heads and groundwater table are maintained at least 5 feet below the bottom of the excavation and 3 feet below the slopes at all times, as measured by construction piezometers. After the hydrostatic water level in the deep sand formation has been lowered to the required levels beneath the excavation, it shall be maintained at the required elevations so that all testing and construction operations can be performed in the dry without interruption.
(2) Design of dewatering systems. The (dewatering) well system has been designed to lower the hydrostatic water level to elevation -26.0 feet in the deep sand formation beneath the excavation for the dam and to elevation – 35.0 feet beneath the lock (or below) with a river stage at elevation 60.0 feet, with as many as two to five well pumps off depending on their location.
(a) The jet-eductor wells (indicated by borings made in and around the excavation) have been designed to drain semipervious soils in the top stratum to prevent or minimize any detrimental seepage from the (main) excavated slopes around the excavation. Additional jet-eductor wells may be required to control seepage from other sections of the slopes around the excavation. As shown by the boring logs and subsequently referenced reports, the stratification of the top stratum soils above the deep sands is erratic (more so in some areas than others). The deep wells and jet – eductor wells, subsequently installed around the top or upper berm for the excavation, may or may not completely dewater or stabilize all slopes or areas in the bottom of the excavation. Dewatering facilities for control of groundwater in the lower part or bottom of the excavation, if required, shall be designed by the Contractor subject to approval of the Contracting Officer. Facilities for unwatering the Phase II excavation, and controlling and sump pumping surface water, shall be designed by the Contractor.
(b) The Contractor shall submit for approval by the C. O. within 15 calendar days after receipt of Notice to Proceed complete information regarding methods and equipment he or she proposes to utilize for installing the jet-eductor wells and pumping the dewatering wells required by these specifications. The Contractor shall at the same time submit detailed design data and drawings for the system he or she plans for controlling surface water and unwatering the excavation for the Phase I work. The material to be submitted shall include, but not necessarily be limited to, the following: capacities and characteristics of all well and jeteductor pumps, engines, gear heads, flexible couplings, and standby equipment; description of equipment and procedures he or she proposes to use for installing the dewatering wells, jet-eductor wells, and any supplemental dewatering facilities, if required, in the bottom or lower part of the excavation; calculations and drawings of dikes, ditches, sumps, pumps, and discharge piping for unwatering the Phase I excavation and for controlling surface water; and a detailed description of his or her procedures and plans for supervising the installation, operation, and maintenance of the dewatering systems to insure that the systems are installed as specified herein and that they are operated and maintained so as to preserve the systems in first class working conditions subject to normal wear, throughout the life of this contract.
(c) Approval by the Contracting Officer of the plans and data submitted by the Contractor shall not relieve the Contractor from the responsibility for controlling surface water, seepage, and artesian head and groundwater levels in the excavated areas as, and to the extent, specified herein.
(3) Responsibility. The Contractor shall be fully responsible for furnishing, installing, operating, and maintaining the dewatering and jet-eductor well sys – terns, as specified, and any other seepage and surface water control systems required for control of groundwater as herein specified. However, any jet-eductor or
dewatering wells, pumps, piping, etc., required to control groundwater in the main excavated slopes around the excavation and in the deep sand stratum below the bottom of the excavation will be paid for as an extra. Any supplemental measures for control of seepage, whether perched or otherwise, in the bottom of the Phase II excavation or from excavated slopes in the bottom of the excavation, will not be paid for as an extra.
(o) The Contractor shall be responsible for: installing and testing the dewatering well and jet-eductor system as specified prior to and after unwatering the Phase I excavation; unwatering the Phase I excavation; dewatering and/or controlling any seepage from specified excavated slopes or in the bottom of the excavation so as to prevent any raveling or other instability of the slopes while unwatering of the Phase I excavation and driving the test and foundation piling under this contract; maintaining the hydrostatic water level in the deep sand formation at least 5 feet below the bottom of the excavation and any excavated slopes, and controlling any detrimental seepage emerging from pervious soils in the top stratum; lowering the groundwater table in pervious or semipervious strata in the top stratum at least 3 feet below any excavated slopes except at the contact with an underlying impervious stratum; maintaining the bottom of the excavation free of all seepage or surface water until the end of this contract; and operating and maintaining the dewatering systems.
ф) The Contractor shall be responsible for installing and operating continuously the dewatering well systems specified herein, and any other supplemental wells, pumps, and engines, necessary to lower and maintain the hydrostatic head in the deep underlying sand formation 5 feet or more below any Phase II excavation, and with the capacity of lowering the groundwater table below elevation -29.0 feet in the chamber and elevation -35.0 feet in the gate bay areas for the lock, for a projected Red River stage of elevation 60.0 feet. The Contractor shall also be responsible for maintaining the groundwater table in silt, silty sand, and sand strata, penetrated by the Phase I or Phase II excavation at least 3 feet below the surface of the slope, and shall control any seepage at the contact between seeping soil strata and impervious strata occurring at any time which might otherwise cause raveling or instability of the slope at that level. Any noncompliance with the above specified groundwater control requirements shall be promptly rectified in accordance with these specifications.
(c) The Contractor shall be responsible for all damage to work in excavated areas caused by failure to maintain and operate the dewatering systems as specified.
(4) Installation sequence. Prior to installation of
the deep and jet-eductors dewatering wells, the Contractor shall submit a plan of his or her procedures and equipment for accomplishing the work within fifteen (15) days of his or her Notice to Proceed. After receiving approval of such procedures and equipment, he or she shall install and test the above dewatering system, including unwatering the Phase I excavation, within 120 calendar days. Any apparent deficiencies in the deep or jet-eductor well systems for whatever cause shall be corrected within 15 calendar days after evaluation of the pumping tests made on the systems and notification by the Contracting Officer. There shall be no unwatering of the Phase I excavation until the deep-well system has been installed and tested, and no unwatering of the excavation more than 3 to 5 feet below any reach of the uppermost berm, where jet-eductor wells are to be installed, until all of the jet-eductor wells specified are installed.
(5) Testing dewatering system. After the deep – well dewatering system has been completely installed, its adequacy shall be checked by the Contractor making a pumping test on the entire system, as directed by the C. O.R., prior to unwatering the Phase I excavation and at the completion of unwatering the Phase I excavation. The jet-eductor systems shall be continuously operated while unwatering the Phase I excavation and the adequacy of its performance evaluated after completion of unwatering and as the excavation for Phase II is carried to grade. The performance of the dewatering systems will be evaluated by the Government. If the dewatering well system and jet-eductor wells are found to be inadequate to control the groundwater and artesian head below the excavation, they shall be supplemented as provided for subsequently in these specifications.
(6) Operation during contract. The Contractor shall operate and maintain the specified dewatering well and jet-eductor systems and any supplementary wells or seepage control measures that may have been installed, as needed to comply with these specifications during the complete period of this contract.
(7) Transfer of dewatering system to Phase III Contractor. Upon completion of this contract, the Contractor shall turn over the complete deep-well, jet – eductor, and surface water control systems and all standby equipment to the Phase III Contractor or the Government who will at that time assume ownership and operation of the dewatering and surface water control systems. The Phase III Contractor will be responsible for removal of the systems in accordance with his Phase III contract.
(8) Unwatering excavation for Phase I contract. It will be the responsibility of the contractor to unwater the excavation made during the Phase I contract for this project. No unwatering of the excavation shall be started until after the deep-well and jet-eductor dewa-
tering systems have been completely installed and initially tested. When, and if, the first full-scale pumping test conducted on the dewatering system shows the system adequate to lower and maintain the hydrostatic water level in the deep underlying foundation 3 to 5 feet below the water level in the excavation as it is unwatered, the Contracting Officer will advise in writing that the Contractor may proceed with unwatering the excavation The water level in the Phase I excavation shall be lowered at a rate not to exceed 1 foot per day or slower if there is any sign of raveling or instability of the excavated slopes.
(9) Surface water control. The Contractor shall install, operate, and maintain dikes, ditches, sumps, pumps, and discharge piping for controlling surface water so as to prevent flooding of the work area for driving the test and foundation piles for the dam.
(10) Available soilandpumping test data.
(a) Some of the soil test data obtained by the Government are shown on the boring logs. Additional logs of borings made for the project are plotted in____________________________
___________ The above report and additional laboratory data and samples of soils from the borings shown
____ office of_____________________
(b) Pumping tests have been performed on three wells installed at the site. One of these test wells (Well A) was installed with 190 feet of 16-inch nominal diameter well screen that more or less fully penetrated the deep sand aquifer beneath the excavation site; two of the test wells (Wells В and C) were installed to a depth of approximately 80 feet for the purpose of testing the upper top strata of silty sands and sandy silts. The locations of the test wells and some of the piezometers installed in connection with making the pumping tests are shown on the drawings. The elevation of the well screens for the test wells and piezometers and logs of borings made along the piezometer lines radiating out from the test wells were plotted. A hydrograph of the Red River and Piezometers PA9 and PA9A installed 2970 and 3970 feet from Test Well A, observed during the test on Well A, are shown on a drawing of these specifications. Plots were made of drawdown observed while pumping Test Well A, corrected for an estimated (natural) change in the groundwater table during these tests as a result of a rise on the Red River. Results of the pumping tests made on Test Wells B and C were also plotted. No correction was made for any natural change in the groundwater table during the pumping test on Wells B and C inasmuch as there was very little change in the river stage during the pumping test on these wells. A report on
the pumping test made at the site by_______________
and design of the dewatering systems may be exam-
ined at the New Orleans District Office or at the office of The Government guar
antees the accuracy of the basic river stage and pumping test data as obtained for the particular wells installed at the locations tested; however, as the logs of borings indicate, the characteristics of the subsurface soils at the site vary considerably, and therefore the Contractor should not assume that the data obtained from the pumping tests made at the locations specified are representative of all conditions that exist at the site. Therefore, it shall be the responsibility of the Contractor to make his or her own evaluation of the relation of the pumping test data to subsurface conditions at other locations at the site.
(c) The subsurface soils at the site consist of a top stratum of clays, silts, and fine sands, with widely varying degrees of arrangement and stratification, with a depth of about 80 to 120 feet. A stratum of rather pervious sand underlies the entire site with a thickness of approximately 220 feet. The top of this deep thick sand stratum varies from about elevation – 20.0 to – 70.0 feet. Logs of three borings (M-l, M-2, and M-3) made 500 feet deep indicate that this sand stratum is underlain by a clay stratum about 120 feet thick at a depth of about 290 to 380 feet. This clay stratum may or may not be continuous, It is underlain by more sand to a depth of about 400 feet.