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PREFABRICATED VERTICAL DRAINS (PVD) In construction of various structures on compressible, saturated soils like soft clay, excessive settlement is a common problem to deal with. The ground improvement technique using prefabricated vertical drains (PVD) is one of the most suitable methods to overcome this problem. The sole purpose of vertical drain system is to shorten the drainage path of the pore water from a low permeable layer to free water sur- face or to pre-installed drainage layer, thereby accelerating the rate of primary consolidation or the proc- ess of settlement. Application of ground improvement method using prefabricated vertical drains (PVD) coupled with surcharge or pre- loading can significantly shorten the period of primary settlement. SEAFCO 144 Prayasuren Road, Bangchan, Khlong Sam Wah, Bangkok 10510. Tel. (662) 919 0090-7, Fax. (662) 919 0098 EQUIPMENT PVD installation equipment can be developed to suit the soil condition, installation depth, specified scope of work and re- quired production rate. Technical data of typical medium-sized PVD installation equipment and accessories are shown below. Installation Rig Type of Base Machine : Excavator of suitable model CAT EL200B or larger model Size (CAT EL200B) : 3.18m x 4.45m Weight (CAT EL200B) : 20 ton Pushing Force : 5.5 – 20 ton Mandrel Lifting and Pushing : Hydraulic gear drive Mast Height : 8m Typical Mandrel Dimensions Weight of Guide and Mandrel : 1.5 to 4 ton Length of Mandrel : 12 to 20m Cross-sectional Area of Mandrel : 60 to 70 cm 2 Maximum Installation Depth : 11 to 19m CHARACTERISTICS OF PVD PVD is a prefabricated material consisting of a plastic core covered by synthetic geotextile “filter jacket”. Two main components of PVD serve the following functions; • Core serves as a longitudinal flow path along the drain • Filter jacket allows water to pass into the core while restrict- ing intrusion of soil particles Time settlement curve of soft clay showing significant time reduction achieved by applying PVD with surcharge loading TYPICAL APPLICATIONS PVDs with surcharge as pre-loading method has been successfully ap- plied in various projects. PVDs are typically used as ground improve- ment system in - • Construction of road, railway, embankment, airport and ports • Industrial projects • Land reclamation projects Application of PVD with surcharge loading for ground improvement work of road embankment Time Settlement without PVD PVD without surcharge PVD with surcharge required settlement Surcharge Final Road Level Drainage Sand Blanket Pumping Well PVD SOFT CLAY

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Page 1: P-V-D

PREFABRICATED VERTICAL DRAINS (PVD) In construction of various structures on compressible, saturated soils like soft clay, excessive settlement is a common problem to deal with. The ground improvement technique using prefabricated vertical drains (PVD) is one of the most suitable methods to overcome this problem. The sole purpose of vertical drain system is to shorten the drainage path of the pore water from a low permeable layer to free water sur-face or to pre-installed drainage layer, thereby accelerating the rate of primary consolidation or the proc-ess of settlement. Application of ground improvement method using prefabricated vertical drains (PVD) coupled with surcharge or pre-loading can significantly shorten the period of primary settlement.

SEAFCO

144 Prayasuren Road, Bangchan, Khlong Sam Wah, Bangkok 10510. Tel. (662) 919 0090-7, Fax. (662) 919 0098

EQUIPMENT PVD installation equipment can be developed to suit the soil condition, installation depth, specified scope of work and re-quired production rate. Technical data of typical medium-sized PVD installation equipment and accessories are shown below. Installation Rig Type of Base Machine : Excavator of suitable model CAT EL200B or larger model Size (CAT EL200B) : 3.18m x 4.45m Weight (CAT EL200B) : 20 ton Pushing Force : 5.5 – 20 ton Mandrel Lifting and Pushing : Hydraulic gear drive Mast Height : 8m Typical Mandrel Dimensions Weight of Guide and Mandrel : 1.5 to 4 ton Length of Mandrel : 12 to 20m Cross-sectional Area of Mandrel : 60 to 70 cm2 Maximum Installation Depth : 11 to 19m

CHARACTERISTICS OF PVD PVD is a prefabricated material consisting of a plastic core covered by synthetic geotextile “filter jacket”. Two main components of PVD serve the following functions;

• Core serves as a longitudinal flow path along the drain

• Filter jacket allows water to pass into the core while restrict- ing intrusion of soil particles

Time settlement curve of soft clay showing significant time reduction achieved by applying PVD with surcharge loading

TYPICAL APPLICATIONS PVDs with surcharge as pre-loading method has been successfully ap-plied in various projects. PVDs are typically used as ground improve-ment system in -

• Construction of road, railway, embankment, airport and ports • Industrial projects • Land reclamation projects

Application of PVD with surcharge loading for ground improvement work of road embankment

Time

Set

tlem

ent

w ithout PVD

PVD w ithout surcharge

PVD w ith surchargerequired settlem ent

S u rc h a rg eF in a l R o a d L e v e l

D ra in a g e S a n d B la n k e t P u m p in g W e ll

P V DS O F T C L A Y

Page 2: P-V-D

Close-up view of PVD installation

144 Prayasuren Road, Bangchan, Khlong Sam Wah, Bangkok 10510. Tel. (662) 919 0090-7, Fax. (662) 919 0098

SEAFCO

Reference: • Hansbo, S. (1993), “Band Drains”, Ground Improvement, Blackie Academic Professional, U.K • Center for Civil Engineering Research and Code (1996), Building on Soft Soils, A.A. Balkema, Rotterdam, The

Netherlands

All rights reserved. No part of this publication may be reproduced in any form or by any means, with-out the prior written permission of SEAFCO PUBLIC CO., LTD.

QUALITY CONTROL IN INSTALLATION • Use appropriate size of

Mandrel and anchor plate to minimize soil distur-bance

• Use Mandrel with adequate stiffness to maintain verti-cality

• Apply appropriate penetra-tion rate to avoid significant bending

• Check verticality during in-stallation

LAYOUT CONFIGURATION AND DRAIN INFLUENCE ZONE PVDs are installed in either square or triangular patterns. A square pattern is more simple for setting out in the field. Triangular pattern however provides more uniform consolidation between drains.

Relationship of drain influence zone (D) to drain spacing (S) can be expressed by;

For square pattern D = 1.13 S

For triangular pattern D = 1.05 S PVD equipment in operation

QUALITY CONTROL TEST FOR PVD MATERIAL • Apparent opening size • Puncture resistance • Burst strength • Trapezoidal tear strength • Grab tensile strength • Discharge capacity (plain

and triaxial) • Density of filter fabric

Installation sequence

Typical PVD layouts and drainage influence

AnchorPlate

Position equipment andanchor plate installation

Mandrel driving Mandrel extraction PVD cutting

D = 1.13 SD = 1.05 STriangular Pattern Square Pattern

PVDPVD


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