1.GENERAL
Prefabricated Vertical Drain (PVD) is artificially - created drainage path which can be installed by one of several methods and which can have a variety of physical characteristic. A PVD can be defined as any prefabricated material or product having the following characteristics:
1.1.Ability to be installed vertically into compressible subsurface soil strata under field conditions
1.2.Ability to permit pore water in the soil to seep into drain, and
1.3.A means by which the collected pore water can be transmitted up and down the length of the drain
For a particular project, the performance of the PVD will be influenced by the soil conditions, type of PVD, equipment, and construction technique (i.e. contractor). The Specialist contractor shall carry out the installation of PVD.
2.MATERIALS
2.1.The Prefabricated Vertical Drain (PVD) shall be of newly manufactured materials and shall consist of a core enclosed in a non-woven filter jacket. The jacket shall allow free passage of pore water to the core without loss of soil material or piping. The core shall provide continuous vertical drainage.
2.2.The PVD shall be band-shaped with an aspect ratio (width divided by thickness) exceeding 50.
3.INSTALLATION EQUIPMENT
3.1.Prefabricated Vertical Drain (PVD) shall be installed with approved modern equipment of a type, which will cause minimum disturbances to the sub soil during the installation operation and maintain the mandrel in a vertical position.
3.2.PVD shall be installed using a mandrel or sleeve, which shall be inserted (i.e. pushed or vibrated) into the soil. The mandrel or sleeve shall protect the drain material from tears, cuts and abrasion during installation, and shall be retracted after each drain is installed.
3.3.To minimize disturbance of the sub soil, the mandrel or sleeve shall have a maximum cross-sectional area of approximately 65 sq centimeter (cm2). The mandrel or sleeve shall be sufficiently stiff to prevent wobble or deflection during installation.
3.4.The mandrel or sleeve shall be provided with an anchor plate or similar arrangement at the bottom to prevent the soil from entering the bottom of the mandrel during the installation of PVD and to anchor the drain tip at the required depth at the time of mandrel withdrawal. The dimensions of the anchor plate shall conform as closely as possible to the dimensions of the mandrel so as to minimize soil disturbance. The engineer shall determine the acceptability of the anchorage system and procedure.
3.5.The mandrel or sleeve shall have visible external markings at maximum one (1) meter increments to enable measurement of penetration depth of PVD.
4.SITE CONDITIONS
4.1.Sub grade where PVD will be installed should not be puddle area; both tide water nor land water.
4.2.Sub grade where PVD will be installed is soft soil (with maximum value of qc < 10 kg/cm2 and SPT value < 5). During penetrated mandrel shall not meet hard soil layer, or obstacle such as boulder, wooden, both surface nor sub surface.
4.3.Sub grade is in settled condition for a 50 tons crawler crane and 10 tons rig in maximum capacity.
5.INSTALLATION PROCEDURES
5.1.Prior to the commencement of the PVD installation, the specialist contractor shall submit full details on the materials, equipment, sequence and method proposed for PVD installation to the Engineer for review and approval. Approval by the Engineer of installation sequence and methods shall not relieve the Specialist contractor of its responsibility to install drains in accordance with the plans and specifications.
5.2.Prior to the installation of PVD, the Specialist contractor shall demonstrate that its equipment, methods and materials produce a satisfactory installation in accordance with these specifications. The Specialist contractor may be given instruction be the Engineer to carry out trial installation of PVD at designated locations.
5.3.PVD shall be clearly located, numbered and stacked out by the Specialist contractor using a baseline and benchmark provided by the Engineer or Client. The Specialist contractor shall take all reasonable precautions to preserve the stakes and is responsible for any necessary re-staking. The as-built location of the PVD shall not vary by more than 250 mm from the plan locations designated on the drawings.
5.4.PVD shall be installed from the working platform to the depth shown on the drawings, or to such depth as directed by the Engineer. The Engineer may vary depth, spacing or the number of drains to be installed, and may revise the plan limits for this work necessary.
5.5.Equipment for installing PVD shall be plumbed prior to installing such drain.
5.6.PVD shall be installed during a continuous push using static weight.
5.7.The installation shall be performed without any damaged to the PVD during advancement or retraction of the mandrel. In no case will alternate raising or lowering of the mandrel will only be permitted after completion of a drain installation.
5.8.The completed PVD shall be cut off neatly 200 mm above the working platform, or as otherwise specified on the contract drawings.
6.SPLICING OF PVD
6.1.Splicing of PVD material shall be done by stapling a workmanlike manner and so as to ensure structural and hydraulic continuity of the drain.
6.2.A maximum of one (1) splice per drain installed will be permitted without specific permissions from the Engineer.
6.3.The jacket and core shall be overlapped a minimum of 150 mm at any splice.
7.OBSTRUCTION
7.1.Where obstruction are encountered below the working platform which cannot be penetrated by the PVD installation equipment, the specialist contractor shall complete the drain from the elevation of the working platform to the obstruction and notify the Superintendent Officer (S.O) or Engineer. At the direction of the S.O. or Engineer and under his review, the specialist contractor shall attempt to install a new drain within 500 mm horizontally from the obstructed drain. A maximum of two attempts shall be made as directed by the S.O. or Engineer. If the drain still cannot be installed to the design tip elevation, the drain location shall be abandoned and the installation equipment shall be moved to the next location, or other action shall be taken as directed by the S.O. or Engineer.
7.2.If directed by S.O. or Engineer, the specialist contractor may use auguring, spud ding, preboring or other methods to penetrate through the obstruction. The cost incurred by the Specialist contractor to penetrate through the obstruction shall be compensated based on the contract unit price per linear meter.
8.SITE RECORDS
The Specialist contractor shall provide competent personnel to continuously supervise and observe the installation of PVD, and furnish the Daily Record Sheets (Electronic and Manual) to the S.O. or Engineer each week. The Daily Record Sheets signed by the Specialist contractor representative and the S.O. shall contain the following information:
8.1.Date and time of installation
8.2.Type of PVD
8.3.Location of PVD (installation point)
8.4.Depth of length of PVD installed at each location
8.5.Details of obstruction, delays and any usual ground conditions.
Tuesday, April 3, 2007
About Prefabricated Vertical Drain
At times, Engineers are required to build on sites which are founded on soft compressible soils in the construction of buildings, infrastructures and other structures. In such instances, it would be necessary to improve the soft compressible soils before constructing any structures on them.
Presently, there are various methods available to improve the soft compressible soils. Soil improvement with Prefabricated Vertical Drain (PVD) or sometimes known as wick drains, is among the most economical method to expedite the consolidation process.
The Consolidation Process
In saturated soils such as clay and silty clay, which have a large percentage of voids or pores usually filled with water, large settlement will occur over a long period of time when a load such as a road embankment is placed on top of the soil. The load will result in an initial increase in pore water pressure which will dissipate slowly as the pore water drains off.
During this process called consolidation, the load is gradually transferred to the soil particles as the volume of the voids are reduced and this culminates in the form of settlement.
Acceleration of Consolidation Using Vertical Drains
Due to the very low permeability of clay soil and silty clay soil, the consolidation process will take many years. In order to accelerate and reduce the consolidation time, vertical drains are installed at regular close spacing to the full depth of the compressible layer, to create artificial and shorter horizontal drainage paths for the pore water to drain off. In addition, this will also take advantage of the higher permeability of the soil strata or sand lenses in the horizontal direction. During this accelerated process, the soil will gain an increase in shear strength.
Normally, vertical drains are used in conjunction with pre loading by surcharge with soil or vacuum pressure. In some projects like tank farm, water can also be used as surcharge.
Prefabricated Vertical Drain
. Drain body
a unique high density polyethylene cuspate core or continuous channels polypropylene core to provide high discharge capacity, high tensile and compressive strength
. Filter jacket
a non woven spunbonded polypropelene or polyester fabric with high tensile strength, high permeability and effective filtering properties.
By combining both the features of the unique cores and highly permeable filter jacket, is effective, fast and reliable performance for soil improvement.
Benefits of Using Prefabricated Vertical Drain
. High water discharge capacity to ensure sound safety factor
. The unique and flexible core will not pinch off or flatten when the drains bends and folds during the consolidation of the soils
. High compressive strength of the core to prevent the collapse of the flow path
. Deep installation exceeding 40 m depth
. Light weight
. Customized core and filter jacket to suit particular soil conditions
. Minimum disturbance to the soil during installation
. Fast installation
. Short consolidation period
. Well proven performance in many projects under different soil condition soil conditions
Performance of Prefabricated Vertical Drain
The type of projects where it has been used successfully are :
. Construction of roads, highways and expressways
. Treatment of ex-mining areas for housing development.
. Container yards and harbor construction
. Land reclamation for the construction of airport runways and buildings
. Construction of tank farms
. Commercial development in ex-agriculture land
Presently, there are various methods available to improve the soft compressible soils. Soil improvement with Prefabricated Vertical Drain (PVD) or sometimes known as wick drains, is among the most economical method to expedite the consolidation process.
The Consolidation Process
In saturated soils such as clay and silty clay, which have a large percentage of voids or pores usually filled with water, large settlement will occur over a long period of time when a load such as a road embankment is placed on top of the soil. The load will result in an initial increase in pore water pressure which will dissipate slowly as the pore water drains off.
During this process called consolidation, the load is gradually transferred to the soil particles as the volume of the voids are reduced and this culminates in the form of settlement.
Acceleration of Consolidation Using Vertical Drains
Due to the very low permeability of clay soil and silty clay soil, the consolidation process will take many years. In order to accelerate and reduce the consolidation time, vertical drains are installed at regular close spacing to the full depth of the compressible layer, to create artificial and shorter horizontal drainage paths for the pore water to drain off. In addition, this will also take advantage of the higher permeability of the soil strata or sand lenses in the horizontal direction. During this accelerated process, the soil will gain an increase in shear strength.
Normally, vertical drains are used in conjunction with pre loading by surcharge with soil or vacuum pressure. In some projects like tank farm, water can also be used as surcharge.
Prefabricated Vertical Drain
. Drain body
a unique high density polyethylene cuspate core or continuous channels polypropylene core to provide high discharge capacity, high tensile and compressive strength
. Filter jacket
a non woven spunbonded polypropelene or polyester fabric with high tensile strength, high permeability and effective filtering properties.
By combining both the features of the unique cores and highly permeable filter jacket, is effective, fast and reliable performance for soil improvement.
Benefits of Using Prefabricated Vertical Drain
. High water discharge capacity to ensure sound safety factor
. The unique and flexible core will not pinch off or flatten when the drains bends and folds during the consolidation of the soils
. High compressive strength of the core to prevent the collapse of the flow path
. Deep installation exceeding 40 m depth
. Light weight
. Customized core and filter jacket to suit particular soil conditions
. Minimum disturbance to the soil during installation
. Fast installation
. Short consolidation period
. Well proven performance in many projects under different soil condition soil conditions
Performance of Prefabricated Vertical Drain
The type of projects where it has been used successfully are :
. Construction of roads, highways and expressways
. Treatment of ex-mining areas for housing development.
. Container yards and harbor construction
. Land reclamation for the construction of airport runways and buildings
. Construction of tank farms
. Commercial development in ex-agriculture land
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