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Combined drainage excavation procedure

The entire combined drainage excavation procedure includes the following work activities:

  • Drilling operations: preparatory work; drilling; landing of well screen column; filling up annular space with sand & gravel mixture and construction pumping down;
  • Earth works: excavation of a communication trench for connecting a vertical blow-out well to the horizontal network; manual finishing and preparation of places for arrangement of interface elements; disassembling of filter package and back-filling of soil;
  • Erection works: cut of vertical column pipe and assembly of its junctions with the connecting water diversion pipe and horizontal drain (of nonperforated dead water conduit).

Since drilling by using FA-12 type machine-tools without mud solution by backwashing method, the most efficient method for drilling vertical drainage wells, proved to be technologically unacceptable for installation of combined drainage wells characterized by shallow depth and close spacing because of a number of technical-organizational difficulties (necessity to install a basin with large and constant volume of water; risk of water inrush into closed drains when wells-amplifiers are connected to them; etc.), the direct flushing method by means of a URB-ZAM type drill unit was recommended.

At that, low parameters of the amplifiers and shorter duration of their installation allow carrying out drilling with pure water ensuring steadiness of well walls by thinned drilling mud produced at drifting overlaying fine grained soil. In this case, construction exhaustion implemented after pipe casing and packaging by filter mixture is intended not for deargillization of the well walls, but only for forming of steady water-intake section of the amplifiers that has minimal resistance.

The final stage of the construction works consists in connecting prepared vertical wells-amplifiers to horizontal open or closed drain (surface inlet) or collector. To excavate a connecting trench that goes down to the level of the water-intake section of drains, it is better to use more exactly operating hydraulic excavators.

The procedure of connection of blow-out wells-amplifiers is implemented as a rule under conditions of permanent inflow of groundwater and flooding of the communication trench, especially when coupling with closed horizontal drain requires continuity and operational efficiency when performing the works.

Therefore, to connect wells-amplifiers to horizontal network they use handy and reliably operating structures. They allow executing fast coupling of the vertical and horizontal components of combined drainage even under continuous water inflow from the cut (at the drain level) vertical column pipe of the blow-out well. The big advantage of the recommended connecting structures is that they allow controlling the wells functionality during their acceptance and operation as well as ensuring reliability of combined drainage and its maintainability.

Source: agronews.uz

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