Section 2112. Wick Drains
A. Furnish all necessary labor, equipment, and materials and perform operations necessary for installation of prefabricated vertical drainage wicks (wick drains) according to the contract documents.
B. Wick drains consist of a band-shaped plastic case which permits continuous vertical drainage, wrapped in a filter material, installed in the subsoils by displacement methods, and spaced and arranged as shown on the plans.
2112.02 Materials and Equipment.
At the Preconstruction Conference, submit to the Engineer for review details of the sequence and method of installation, including installation equipment, anchoring, manufacturer’s splicing method, certification indicating source of wick drain material, drain layout, and numbering plan. Review by the Engineer does not relieve the Contractor of the responsibility of installing the wick drains according to the contract documents.
Install prefabricated wick drains consisting of a plastic drainage core encased in or integrated with a filter jacket. Inspection and acceptance of wick drain materials will be according to Materials I.M. 442.01.
1. Core
Meet the following requirements:
· Provide continuous vertical drainage.
· Continuous plastic material (excluding splice area) fabricated to promote drainage along the axis of the vertical drain.
2. Jacket.
a. Install a jacket that allows free passage of pore water to the core without loss of soil material or piping. Meet the following requirements for jacket material:
· Manufactured from a synthetic non-woven geotextile capable of resisting all bending, punching, and tensile forces imposed during installation and during the design life of the drain.
· Sufficiently rigid to withstand lateral earth pressures due to embedment and surcharge so that the vertical flow capacity through the core will not be adversely affected.
· Sufficiently flexible to bend smoothly during installation and induced consolidation settlement without damage.
· Comply with the following specifications:
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Table 2112.02-1: Wick Drain Jacket Specifications |
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Test Item |
Designation |
Minimum Average Roll Value1 |
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Grab Tensile Strength2 |
ASTM D 4632 |
125 lb. |
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Trapezoidal Tear3 |
ASTM D 4533 |
55 lb. |
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Permittivity |
ASTM D 4491 |
0.7 sec-1 |
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Apparent Opening Size (max.) |
ASTM D 4751 |
60 sieve |
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1 Ensure the jacket material is tested in saturated and dry conditions. |
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2 For bonded drains, tensile strength test may be conducted on assembled drain using ASTM D 4595. |
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3 For bonded drains, trapezoidal tear test is waived. |
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b. Do not allow the jacket material to be subject to localized damage (for example, punching through the filter by sand/gravel particles). Ensure the jacket material does not undergo cracking and peeling during installation of the drain.
3. Assembled Drain.
Meet the requirements below. The Engineer may reject material that is damaged during shipment, storage, or handling, or which does not meet the minimum requirements of the drain material.
· One single type of assembled drain used on the project, unless the Engineer approves otherwise.
· Mechanical properties (strength and modulus) of the assembled vertical drain equal to or greater than those specified for the component jacket and core.
· Resistant against wet rot, mildew, bacterial action, insects, salts in solution in the groundwater, acids, alkalis, solvents, and any other significant components in the site groundwater.
· Minimum discharge capacity of 1.5 gallons per minute when measured under a gradient of one at a minimum lateral confining pressure of 25 psi according to ASTM D 4716.
· Ensure it is band-shaped with an aspect ratio (width divided by thickness) not exceeding 50.
· Minimum equivalent diameter of 2 inches using the following definition of equivalent diameter:
dw = (a+b)/2.
dw = diameter of a circular drain equivalent to the band shaped drain (inches).
a = width of the band shaped drain (inches).
b = thickness of the band shaped drain (inches).
· Drain material labeled or tagged in such a manner that the information for sample identification and other quality control purposes can be read from the label. Ensure, as a minimum, each roll is identified by the manufacturer as to lot or control numbers, individual roll number, date of manufacture, manufacturer, and product identification of the jacket and core.
· Ensure during shipment and storage the drain is wrapped in heavy paper, burlap, or similar heavy duty protective covering and according to the manufacturer’s recommendations.
1. Install wick drains using equipment of a type that will cause minimum disturbance of the subsoil during the installation operation.
2. Install the wick drains using a mandrel. Push (in one continuous movement) the mandrel through the sand blanket (if required by the contract documents) and into the soil. Obtain the Engineer’s approval for use of vibratory methods. Driving or jetting installation methods are not permitted. Ensure the mandrel:
· Protects the wick material from tears, cuts, and abrasions during installation,
· Is rectangular or rhombic in shape and of a cross sectional area not to exceed 10 square inches, and
· Is provided with an “anchor” rod or plate at the bottom to prevent soil from entering the bottom of the mandrel during installation of the drain and to anchor the bottom of the drain at the required depth at the time of mandrel removal.
A. Familiarity with site conditions and the available geotechnical information is a necessity. Select the equipment, method, and materials: 1) suitable for the existing site conditions; and 2) capable of producing a satisfactory drain installation to the minimum elevation. This may require the contractor to drill additional soil borings. Demonstrate the equipment, method, and materials produce a satisfactory drain installation by installing a trial drain at the location of the first production drain.
B. The Engineer’s review of the method and equipment used to install the trial drains does not constitute acceptance of the method for the remainder of the project. If the Engineer considers that the method of installation does not produce a wick drain that satisfies the requirements of the contract documents, alter the method or equipment, or both, in order to achieve compliance.
C. Prior to installing the drains, grade the site sufficiently level (at no additional cost to the Contracting Authority) to allow vertical and proper drain installation.
D. Install the wick drains following placement of the sand blanket (if required by the contract documents). Install a granular blanket of sufficiently coarse material and compact to provide a stable working surface.
E. Locate, number, and stake wick drains. Take all reasonable precautions to preserve the stakes. Ensure drain locations vary by no more than 3 inches from the locations indicated on the drawings.
F. Auguring or other methods may be used to loosen stiff upper soils prior to the installation of the drains, provided such operations do not extend more than 2 feet into underlying compressible soils. After the wick drain has been satisfactorily installed, fill all holes or voids created by such operations with sand.
G. Check the installation equipment for plumbness prior to advancing each drain. Ensure the plumbness of the mandrel does not deviate more than 1/4 inch per foot from vertical. Install the drains to the minimum elevation as shown on the plans. If the penetration shown on the plans is more than 1 foot into the underlying foundation layer and difficulties are encountered prior to achieving the indicated depths, install the drains to a depth of 1 foot below the bottom of the soil layer(s) being improved by wick drain installation as shown on the plans.
H. Raising the mandrel is permitted only after completion of drain installation.
I. The Engineer will reject wick drains that vary from their proper location by more than 6 inches at the ground surface, drains that are damaged during installation or subsequent construction, or drains that are improperly completed. No compensation will be allowed for any materials furnished or for any work performed on such drains.
J. During installation, provide the Engineer with suitable means of measuring the vertical length of each wick drain installed at a given location and deriving a tip elevation for each drain.
K. Provide splices with structural and hydraulic continuity of the drain. A maximum of one splice, constructed according to manufacturer’s splicing method, per drain is allowed. Ensure manufacturer’s splicing method is compatible with installation equipment.
L. When obstructions that cannot be penetrated by the drain installation equipment are encountered below the working surface, notify the Engineer and complete the drain from the elevation of the obstruction to the working surface. At the direction of the Engineer, attempt to install a new drain (maximum of two attempts, as directed by the Engineer) within an 18 inch radius from the obstructed drain. The Contractor will be compensated for each obstructed drain unless the drain is improperly completed, in which case no compensation will be allowed.
M. After installation, cut each drain horizontally such that approximately 6 inches of drain material extends above the top of the sand blanket or as otherwise specified by the contract documents.
N. The Contractor shall keep a daily log which lists for each drain the date of installation, top elevation, tip elevation, and pay length. A copy of each daily log shall be provided to the Engineer.
2112.04 Method of Measurement.
A. Measurement for Wick Drain (including trial wick drain) will be feet installed according to the contract documents, calculated from measurements taken from the top of the drain to the tip elevation of the drain.
B. In the case of obstructions, the Engineer will
calculate the number of feet from measurements taken from the top of the drain
to the elevation at which the obstruction was encountered.
A. Payment for Wick Drain will be the contract unit price per foot.
· Field staking for the location of wick drains, and
· All labor, equipment, and materials necessary to complete the installation according to the contract documents.
C. No payment will be made for unacceptable drain or trial drain installations.
D. In instances where pre-auguring is permitted, the cost of pre-auguring and subsequent placing of sand backfill material is incidental to the price bid for Wick Drains.
E. The cost of borings drilled to select the equipment, method, and materials suitable for the existing site conditions to produce a satisfactory drain installation is incidental to the price bid for Wick Drains.
F. No payment will be made for constructing any work platform other than that shown in the contract documents.