Principle installation of PVD

Principle installation of Prefabricated Vertical drains

• Specialized rig
• Mandrill supported inside a leader held by crane or hydraulic excavator
• Mandrill pushed into soil by chains/cables driven by hydraulic engines.
• PVD installed inside a mandrill
• Rhombic mandrill less disturbance (Often rectangular mandrill)

Installation methods of prefabricated vertical drains (PVD's)

Wickdrains - Methods of installation

• Water Jetting
• Ramming
• Pushing, modern preferred method
• Pushing + vibration
• Pushing + water jetting

A Soil consolidation project

In this project about 700.000 meters of wickdrains (prefabricated vertical drains-PVD) were specified.

Working with sand drains need more time and work.

The soil should be consolidated quickly, and the road is near the sea.

It was like draining the sea.

At the top of the soft soil a sand layer was placed to move the machines and also for drainage.

The contractor preferred a special soil consolidation composite - Colbonddrain.

At the top of the soil there were a 1 meter thick soil which was difficult to penetrate in some areas. The bottom was very soft.

A simple wickdrain installation equipment attached to an excavator worked well.

The wick drains installed upto 18 meters depth.

At the end the consolidation was done succesfully.

Applications of uniaxial geogrids

Some Applications of uniaxial geogrids

• Bridge abutments
• Steep slopes
• Walls
• Embankments
• Segmental retaining walls
• Landfill capping
• Landfill foundation
• Topsoil stabilization
• Structures over mining areas

Findrains to stabilise water saturated river banks

Geocomposite prefabricated findrains can be used to stabilise the water-saturated banks of various drainage ditches.

The 1 meter high drainage screens can be installed at 1.25 m from the crests of the banks to intercept the groundwater flows.

Hydrostatic pressure causes horizontal displacement of the entire bank.

The geocomposite findrain contains an 80 mm perforated collector drain.








The prefabricated findrain can be installed in the 0.40 m wide trenches easily.

Calculation of band drains (PVD) 4 - Drain spacing

1)triangular spacing standard

2)for a square grid :
D = 1.128 S

S : spacing of drains

D : diameter of the equivalent cylindrical column of soil, drained by each drain.

For more information about the calculation of prefabricated vertical drains (wickdrains) please also see other posts.

Calculation of PVD's 3 - Kjellman formula

where:
t = consolidation period (years)
D = diameter of drained soil cylinder (m)
d = equivalent diameter of drain (m)
Ch = horizontal consolidation coefficient (m2/year)
Uh = average horizontal consolidation degree

Calculation of Prefabricated wick drains 1

VERTICAL DRAINAGE DESIGNS
An assessment of the effect of vertical drains on the consolidation process may be made using the method proposed by Kjellman.
This method is based on the assumption that the drains are placed in a regular pattern and that each drain serves a cylindrical soil column of exactly the same length as the drain (colbonddrain) . it is assumed that the increase in vertical load is evenly distributed over the consolidation area and that horizontal layers remain horizontal throughout the consolidation process. It is been assumed
that the permeability of the cohesive soil remains unchanged throughout the consolidation period and that the internal resistance of the drain is negligible. Practical experiments have shown that although these assumptions are not always applicable, in majority of cases their influence on the ultimate results is of little significance. The exception is where drains without a "high flow" core are used for thick highly compressible strata. In such cases the internal resistance of the drain can have a substantial effect on the consolidation period.

Geogrid with a filter layer

Kocaeli free zone project has a harbour inside the project. There is a heavy traffic of trucks. To prevent or reduce partial settlements on the roads due to the heavy truck traffic special geogrid was used.

This multifunctional geogrid delivers reinforcement, separation and filtration in one easy-install product for paved roads, parking areas, platforms and building/structure foundations. In the project it reduced the required subbase thickness.

Due to the special manufacturing method Enkagrid TRC has very low elongation properties.

It helps to reduce the partial settlements.

Beside the reinforcing Trc geogrid also provides a filter layer. So it works like a geogrid and a nonwoven .

This type of geogrids work as reinforcement, separation and filtration layers.

Reinforcement of roads by geogrids

On weak soils, for road construction contractors generally need a thick layer of base course.

Using geogrids as reinforcing layers can help to reduce the required thickness of the unbound base course stabilizing structures on soft ground or in unsettled areas.

Another problem is the forces coming from the traffic causes crack on the surface of the road. Geogrid reinforcing layers can absorb the forces and delay propagation of cracks the life of the structure may be increased.

In railway construction multiple layers of geogrid reinforcements can be used to provide more effective stabilization.

Soil consolidation

Civil Engineers, planners and contractors aim for direct economic highways, airports and other traffic routes using natural resources as efficiently as possible in their construction: this often means having to build on poor soils and sometimes even to reclaim land. In many cases, the sub-grade is too weak to allow construction to proceed at a normal rate. Soft, cohesive soils are very slow to consolidate. 90% settlement often takes 20-25 years without the use of Prefabricated Vertical Drains (PVD's).
Prefabricated vertical drain (PVD), provides an economical solution to this issue. The principle feature of prefabricated vertical drain (Colbonddrain) lies in providing much shorter and highly permeable drainage paths for the dissipation of excess porewater pressure, allowing 90% consolidation in a time period of months, rather than years.