Tel:(852) 2437 2803
Fax:(852) 2626 9245
| |
Surface
Drainage for Recreational Areas
1.0
|
Introduction-介紹
The greatest single factor in the deterioration of recreational surfaces
is the presence of standing water on or free water beneath the surface.
Surface drainage (above ground) and subsurface drainage (below ground) are
both essential components of properly constructed recreational surfaces.
There are three basic tasks of water drainage:
1. Collect;
2. Conduct; and
3. Dispose of excess
water.
|
2.0
|
Purpose-目的
The intention of this guideline is to equip the reader with a basic
understanding of systems in order to plan properly for new construction or
to recognize and correct existing problems.
|
3.0
|
General
Requirements-一般的要求
A.
|
Subsurface
Drainage-表層下的排水
A peripheral subsurface drainage system is installed where needed to
intercept and redirect the flow of subsurface water that might
otherwise accumulate beneath recreational areas.
Where it is necessary to lower the water table at a given site, a
subsurface lateral or parallel drainage system may be required to
direct free water from the subsurface to other areas.
|
B.
|
Surface
Drainage-表面排水
Surface drainage usually consists of a series of swales or a
fabricated system designed to redirect surface water that might
otherwise flow over the recreational surface, and to prevent seepage
of water beneath the surface.
|
|
4.0
|
Procedures
-過程
|
|
A.
|
Subsurface
Drainage -表層下的排水
There are three types of subsurface drainage systems used to
redirect subsurface water:
Conventional Vertical Stone Drains常規的垂直的石塊
1.
|
This
type of drain is classified as an interceptor drain. It
intercepts subsurface water in a stone "wall" and
causes it to drain downward into a perforated pipe which
carries the water to an outlet.
|
2.
|
A
trench is dug 1’-2' wide on the full or partial perimeter of
the facility as directed by local conditions. The depth of the
trench will depend on the predetermined water level, but
should have a minimum depth of 18". Since the trench must
be sloped a minimum of 0.28% (1:360), the depth of the trench
will also be determined by the length of the trench before the
water outlet. Multiple water outlets or catch basins may be
necessary to minimize trench depths. Place 2" to 4"
of permeable aggregate in the base of the trench.
Note: Non-woven geotextiles are usually used as a filter
fabric to protect either the entire stone trench or the pipe
only. Corrugated, perforated pipe is available with a
"sock" over it. In either case, filter fabrics tend
to clog when used in clay or silty soils.
|
3.
|
A
porous or perforated pipe with a minimum diameter of 4"
should be placed on the aggregate in such a way as to have not
less than 0.28% (1:360) of pitch and not more than 0.83%
(1:120) of pitch. A larger pipe may be required as dictated by
the amount of free water to be conveyed, the surface area to
be drained, or available pitch on the pipe.
|
4.
|
Back
fill of the trenches should be of permeable aggregate of no
larger than 1 1/2" placed in 6" lifts, each of which
should be compacted to minimize the risk of subsequent
settlement.
Note: It is generally recommended when using a filter fabric
around the stone to use 1 1/2" stone size and when not
using a filter fabric, to use smaller aggregate to act as a
natural filter.
|
5.
|
The
trench is then filled to the surface with smaller washed stone
where an open drain is desirable.
|
6.
|
Where
a closed drain is desired, the trench is filled to 8"
below the surface, after which a porous type membrane is
placed over the stone, and a sod or an impervious type swale
formed over this.
|
|
|
|
|
Subsurface
Horizontal Stone Drain Layer-細長的孔道排水
This drainage layer is a "capillary breaker" used in areas
with ground water problems or heavy clay soils. When installed
properly, it prevents vertical movement of ground water under a
surfaced area. It is highly recommended that this system be used in
conjunction with a perimeter interceptor drain system.
1.
|
Installation
includes excavation of all vegetation and topsoils under the
surfaced area and to a minimum of 5' beyond. The soil subgrade
must be sloped. The slope of the stone drainage layer is then
graded to match the proposed finish slope requirements of the
surfaced area. Installation includes a 6" to 12"
stone layer of two inch (2") minimum washed aggregate
installed and compacted in 6" lifts. Compaction should be
95% of the maximum density determined by ASTM Method D1557.
|
2.
|
On
the low end of the drainage layer, a perforated pipe should be
installed with a proper slope to collect and dispose of water
at the outlet area.
|
3.
|
The
horizontal drain layer does not necessarily take the place of
subgrade gravel materials.
|
4.
|
Design
of this system should be done by a geotechnical engineer.
|
"Prefabricated
Rockless" or "Geocomposite Drain"無石預制件"及"滲透式排水"
This system is also classified as an interceptor or curtain drain.
1.
|
The
system consists of a plastic dimpled or waffle sheet that
forms a channel to permit the vertical and horizontal flow of
water on each side covered by a non-woven geotextile fabric.
Curtain drains usually have a corrugated pipe inserted along
the bottom to carry the accumulated ground water to the outlet
area.
|
2.
|
Geocomposites
are available in various heights ranging, depending on the
manufacturer, from 2" to 60'. The installation
requirements may differ from manufacturer to manufacturer but,
in general, the installation requires excavation of a trench
wide enough to install the geocomposite (usually 4" to
8"). The trench is backfilled with the excavated
material. Some clay type soils may require backfilling with a
coarse sand. Consult with your local contractor, geotechnical
engineer or architect for design and installation
specifications.
|
|
B.
|
Surface Drainage - Tennis
Courts-表面排水
There are several types of systems.
Open Drain System-開放式排水
Open drains are shallow swales using gravity to move water around
the recreational area. Swales used to collect and conduct surface
water should be a minimum of 5' wide and 6" to 8" deep in
the center. Slope requirement should be a minimum of 2% (1:50) on
grass and 0.56% (1:180) on pavement. Swales can be located on the
ends or sides of a facility and carry water to the outlet area.
Closed Drain System-隱藏式排水
A closed drain system utilizes the swale design to collect and
conduct water to inlets located (at a minimum of every 200') in the
center of the swales. The water inlets are connected below ground to
pipe (size is determined by volume of water being collected) which
carries water to catch basins or other outlet areas.
Combination Systems-結合系統
Combination systems utilize swales and/or conventional open or
closed vertical stone drains or "prefabricated rockless"
geocomposite drains as discussed in the above section on subsurface
drainage.
Prefabricated Channel Drain Systems-預制水渠通道系統
Another functional system being used for surface drainage is the
prefabricated channel drain. These vertical lineal drains have been
used for years in the track industry to drain both the field and the
track surface. Their application with tennis courts and other
related surfaces are also being used successfully. They require
shallow excavation and some manufacturers offer sections with
"built in slopes". Channel drains are available in radius,
angles and straight lengths. They also have removable grates to
allow for easy cleaning.
To obtain the correct system for your facility, you should consult
with an experienced contractor, qualified architect and/or engineer.
|
Next
|
|