Pre Fabricated Vertical Drain (PVD)

EDTP –N5/S16 (SITE ENGINEER- ALSON CHIN)

Perfabricated Vertical Drain ( PVD)  Commonly used to accelerate the rate of consolidation and is use in conjunction with surcharging  Monitoring to validate design and performance  Design criteria: stability and settlement control  Successfully used worldwide  Cost effective

This treatment is widely use for sites which consist of fine grained, saturated soils that have poor drainage properties. These soil properties are exactly match the marine clay at my site condition. Then normal surcharging might take few years surcharge period to complete the consolidation process, use of PVD might accelerate by provide the drain out system and time saving yet cost saving compared to sand drain/ sand column system. It is critical that the excess water to expelled form the soil before construction begin, it will increase the bearing strength of the soil and allow supporting the weight of new structures. However fine grained, compression soils have a low permeability and therefore take a long time to consolidate. The PVD provide a shorter and easier drainage path through which the can escape. Performance of vertical drains During the consolidate process the vertical drains are subjected to both tensile and compressive forces as the soil shifts and settles. This can severely affect the ability of the drains to function as intended: Lateral soil displacement can cause certain drains to elongate beyond their rupture point Vertical soil compression (settlement) has been shown to cause some drain to pinch off, as they experience folding and buckling of the core.

EDTP –N5/S16 (SITE ENGINEER- ALSON CHIN)

EDTP –N5/S16 (SITE ENGINEER- ALSON CHIN)

INSTALLATION OF PVD

Mandrel

PVD Roll

Steel Plate

EDTP –N5/S16 (SITE ENGINEER- ALSON CHIN)

INSTALLATION OF PVD 1. Setting out of the reference line carried out by the survey team, then setting out for each PVD point shall be measure by tape or offsetting from the reference line according to the shop drawing. 2. PVD shall install with the approved modern equipment, which will cause minimum disturbance to the subsoil during the installation operation in and maintaining the mandrel in a vertical position within tolerance of the specification. 3. PVD shall be installed using a mandrel or sleeve, provided with the anchor plate to prevent soil from the entering the bottom of mandrel and to assist to anchor the PVD at the required installation depth. 4. The contractor shall provide he SE with suitable means of the depth of advancing drain at any given time and the length of drain installation at each point. 5. Equipment for installation of PVD shall be plumbed prior to installing each drain and not deviate from the vertical by more than 1:50 during installation of drain. 6. PVD shall be installed from the working surface to the required depth in the drawing. A continuous push using static weight or vibration methods. 7. The installation shall be performed without any damage to the drain during advancement or retraction of the mandrel. Alternate rising or lowering of the mandrel during advancement will not be permitted. Raising of the mandrel will only be permitted after completion of a drain installation. 8. The completed PVD shall be cut off neatly about 300mm above the working grade pr as otherwise specified on the contract drawings. 9. Splicing of PVD drain material shall be done by stapling in a manner acceptable to ensure structural and hydraulic continuity of the drain.