8/10/2019 vertical Drainage for used

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VERTICAL DRAINAGE

Vertical drainage is defined to be a drainage system that is installed vertically into the soil in order to

improve the vertical water transport, hence accelerate settlement and gain in strength of soft soil.

The acceleration is caused by the fact that the water particle can move more easily with a vertical

drain applied. The direction of movement in poorly permeable soil change from predominantly

vertical into horizontal toward the drain. As a result the outflow of water is accelerated considerably

due to the horizontal permeability, which is generally high in soil of stratified deposits. Vertical drains

accelerate primary consolidation only, because significant water movement is associated with it.

Secondary consolidation cause only very small amounts of water from the soil.

Field of Application

A vertical drainage system is applied when problems of stability are to be expected during landfill

operations or when settlement cannot be completed entirely within the available execution time

before the construction comes into operation. This method is currently used to acceleratesettlements in the field of:

-

Road and railway construction, for example the foundation of an embankment, the widening

of a soil body

- Hydraulics structure, for an example the construction of a seawall or the reinforcement.

-

House building and utility construction, when preparing sits for building. In addition, there

are other special fields of application such as the infiltration of river water in the dunes for

the purposes of extracting drinking water.

PREFABRICATED VERTICAL DRAINAGE (PVDs)

Vertical drainage systems were mainly being applied in the form of sand drains until the seventies.

This method consisted to forming holes in the ground by means of water jets in combination with

drills or bailers, until the desired depth was reached. Those holes then filled with sand. Considering

the fact that this scope he application of geotextiles is a central issues of civil engineering, the matter

of sand drains will not be mentioned any further. Nowadays, there are many brands and types of

prefabricated drains available all with a standard width of 100 mm and 1 thickness of 3mm- 5mm.

Prefabricated drains are available in the following compositions:

-

A polyolefin extrusion wrapped in nonwoven filter fabric- A monofilament mat wrapped in a nonwoven filter fabric

- A corrugated PVC or PP pipe wrapped with a filter fabrics

-

A hollow polyolefin extrusion perforated with needles or chemicals to make outer skin

permeable.

Because of proven reliability and easy installation the first two mentioned are applied most often in

practice and all prefabricated drain installation machines are equipped to install these types of drains.