Well construction
The wells used for the construction of structures to promote and monitor the groundwater . These structures usually include wells and groundwater measuring points .
The following types are common:
Shaft well
A vertical shaft is built into the groundwater body by manual or mechanical excavation . In the course of going deeper , the shaft is secured with masonry or precast concrete parts that were prefabricated from (steel) concrete . The inflow of the groundwater to the well takes place through the bottom of the shaft and / or a vertical filter section. The method is only suitable for shallow depths (mostly much less than 40 m).
Usually, the construction of a shaft well with a simple construction method for small depths and individual objects is carried out as follows (this work is dangerous and should be carried out by a specialist company ):
- There are concrete manhole rings (diameter z. B. 1.000 mm) was used.
- A small amount of earth is excavated on which the first manhole ring (without crampons) is placed exactly horizontally. This first ring can be provided with a steel blade on the underside.
- The soil under the first manhole ring is excavated, the manhole ring sinks, and further manhole rings can be added.
This form of well construction is also used for masonry wells and is called a sink well. Instead of prefabricated concrete rings, a well rim is bricked up and this is continuously sunk until the groundwater is reached. After each sinking, the wall wreath is built up again at the top.
The Kanat is a special form of the shaft well . Castle wells are very often shaft wells.
Ramming and impact wells
A pipe with a tip and a filter section at the bottom (open part of the pipe) is driven into the groundwater by ramming. This method is particularly used by hobbyists for small systems and shallow depths. The blow well is also known as the Abyssinian well or Norton well . Advantage: easy and inexpensive to build. Disadvantage: the delivery rate is low due to the small filter surface. If the flow rate at the filter is too high due to excessive water withdrawal, deposits quickly form which, depending on the nature of the soil, can reduce the service life to a few years.
Drilling wells
A borehole is driven into the aquifer . A filter section is provided in the area of the water-bearing layer. The filter section is usually formed through the gravel pack , which can be carried out at cased and uncased bore. Often a single or multiple graded pouring takes place, with the largest grain size lying directly on the filter tube. Even when drilling into solid rock, gravel is often brought in, but here primarily with a support function and preventive with regard to erosion. Alternatively, glass balls are also used. This method can be used at great depths (over 1,000 m).
Drainage pipes
Horizontal drainage pipelines, originally developed from open drainage trenches, serve to develop shallow and slightly thick, but extensive water-bearing layers. For this purpose, well filter pipes are usually used at a depth of at least 4 to 5 meters, which are completely permeable in length and circumference.
Source versions
A potential source should, if possible, be caught at the outlet point, protected from contamination, without damming. Source fittings are often problematic from a hygienic point of view.
Horizontal filter well
Starting from a shaft, horizontal boreholes with filter sections are driven into the groundwater body ( horizontal well construction ). These wells allow large quantities to be withdrawn. The wells are to be secured against the ingress of contaminants by a cover and a lateral seal of the shaft or the bore against the surface.
Water production, by sucking pumps or submersible pumps and submersible pumps done. The water extraction depends on the yield of the basic water resources and the performance of the filter section, which is to prevent flushing of the bottom of the well.
Design and execution
The maximum suction lift of a pump corresponds to the air pressure of the atmosphere minus the vapor pressure of water (rule of thumb for cold groundwater: 5–12 Torr at 5–12 ° C). At sea level, this corresponds to the pressure of a 10.13 meter high water column. For this reason, water can theoretically only be pumped from a depth of up to 10.13 meters with a suction pump , in practice only from a depth of around seven to eight meters.
As late as 1970, centrifugal pumps driven by electric motors for domestic water systems were typically set up at the bottom of an accessible shaft with a diameter of about 1 m. The bottom of the shaft should be permanently above the fluctuating groundwater level, as the electric motor was not waterproof and a person should be able to work standing or crouching here.
The actual well pipe is usually made of steel, has a diameter of around 12-20 cm, is a maximum of 10 m long and is sunk below the lowest expected groundwater level. It is useful to have lateral bores, slits or fine wire grids in the area immersed in the groundwater to allow the groundwater to enter while sand and gravel are kept outside.
The suction pipe, a threaded pipe with a diameter of about 3 cm, for the motor pump is lowered into the well pipe. At the lower end of the pipe there is a suction strainer with a diameter of about 6 cm (slotted cast iron or sieve grille) and a check valve that keeps the water column in the pipe when the pump is at a standstill.
The suction pipe can be held at the top by crossbars above the well pipe. The depth of the suction tube is set so that the suction strainer is above the bottom of the well sump in order to prevent fine particles from being sucked in. The suction pipe is connected to the pump , for example via a Dutch or flange .
Self-priming pumps can generate a vacuum that is sufficient to lift the water column up to the pump even without water filling. In simple pumps, several liters of water must first be poured through an overhead filler neck (with screw plug) in order to fill the suction tube and vent the pump. Only when the pump is filled with water does it work effectively and reach the intended pressure.
Submersible pumps, which are located below the water table, can be driven by an electric motor installed in the dry via an extended axle.
Corrosion- resistant and sealed subsea pumps are widely used today. These have the shape of a cylinder and are available from 75 mm in diameter. A diameter of 93 mm is typical for use with well pipes with an inner diameter of 100 mm. They are lowered on a rope to about 1 m above the well sump or the end of the well pipe in order not to suck in any sand particles that could cause pump mechanics and pipe fittings to wear out.
If a thin-walled polypropylene pipe is used as the pressure pipe, a soft start pump should be used to reduce pressure surges on the pipe. During operation, ensure that the water-bearing elements are free from frost. Even if the bottom of the well shaft lies in the ground in a frost-free depth, the stationary pump can freeze within several hours due to the cold air penetrating the shaft. When it is very cold, the heat loss through the manhole cover can be sufficient for this.
Hand pumps with a pump handle dip into the groundwater with their pipe with a typical 1¼ inch nominal diameter. A check valve is installed at or near the top of the pipe. A cast iron cylinder with an internal diameter of around 75 mm sits on it, in which the piston with leather seal and valve is moved up and down by a connecting rod through the handle. If the suction lift is higher, it is helpful to first fill the cylinder of the pump manually with water.
In order to achieve a more even pressure curve and to avoid the pump starting up too frequently, pressure vessels ( membrane or air vessels ) are used, which can also be accommodated in the well shaft.
See also
literature
- Erich Bieske, Wilhelm Rubbert and Christoph Treskatis: Bohrbrunnen . R. Oldenbourg Verlag Munich, Vienna 1998.
- Edward E. Johnson, Inc .: Ground Water and Wells. Saint Paul, Minnesota 1966.
- Raymond Rowles: Drilling for Water- A Practical Manual. Cranfield Press, Bedford UK 1990.
- Drilling: the manual of methods, applications and management / produced by the Australian Drilling Industry Training Committee Limited, - 4th edition, 1997.
- Bohrtechnik: Norms Ed .: DIN, German Institute for Standardization eV, 1st edition. Stand of the signed Standards: August 1998, Berlin, Vienna; Zurich: Beuth, 1999 (DIN Taschenbuch; 272).
- Specialist magazine bbr Pipeline construction, well construction, geothermal energy , wvgw Wirtschafts- und Verlagsgesellschaft Gas und Wasser mbh, Bonn.
Individual evidence
- ^ Well construction with glass balls , accessed on April 17, 2017
- ↑ Installation instructions for deep well pumps .