Hydraulic and earth engineering – Drainage or irrigation – Porous waterway – e.g. – sand drain – etc.
Patent
1982-01-20
1984-06-19
Taylor, Dennis L.
Hydraulic and earth engineering
Drainage or irrigation
Porous waterway, e.g., sand drain, etc.
83444, 83639, 405 36, E02B 1100
Patent
active
044551053
DESCRIPTION:
BRIEF SUMMARY
The present invention is applied when using prefabricated drains to the purpose of compacting water-carrying, fine-grained and poorly water-permeable soil, such as clay, silt, etc. by carrying out dewatering of the soil material with the aid of vertical draining and thereby reducing the water content of the soil material. Hereby one improves the bearing capacity of the ground and accelerates the settlings that can be expected to take place, while at the same time the shearing strength of the soil increases.
Various kinds of prefabricated drains have been developed for vertical draining, consisting of a profiled strip e.g. of plastic with about 10 cm width, and of porous paper or another similar, draining material wound around it which is permeable to water.
A prefabricated drain is installed in the ground by pushing it with the aid of a special insertion tube to desired depth, usually in vertical direction. The prefabricated drain is held in the insertion tube, and the lower end of the prefabricated drain becomes anchored in position with the aid of a special anchoring member. The insertion tube is pulled out on completed installation, thus leaving the vertical prefabricated drain in the ground. The prefabricated drain is cut off a short distance over the ground surface. Such prefabricated drains are provided at a suitable spacing depending on the ground conditions and on the objective in mind, e.g. with 1-2 m spacing, in the area which one desires to compact. The water from the soil material drains through the porous paper into the passages in the prefabricated drain, rises to the ground surface and runs off.
A procedure of this kind is indicated when the layer which has to be dried/compacted, e.g. a clay stratum, lies on the ground surface or close thereto. Often, however, the clay bed is overlaid by coarser, readily water-conducting soil in the natural state or by earth filling, such as sand or gravel. It would not be necessary in such cases to raise the water from the clay bed all the way up to the ground surface: lifting the water into the sand layer over the clay course would be fully enough.
The same situation is also encountered when vertical draining is used to dry, to compact, a clay and mud layer on the bottom of a sea or lake and which may have a thickness of tens of meters. Vertical draining is required when the intention is to fill up e.g. a lake or sea at the point in question for the construction of a road, railway or even an air field. If the soft, compressible clay or mud layer is not vertically drained prior to the filling operation, the settling of the compressible strata under effect of the earth fill and other loads imposed on them takes many decades. The settling can be accelerated by vertical draining so that it is accomplished within a year or two, or even in a few months, depending on the subsoil conditions and the spacing of the vertical drains. Depending on the soil conditions and on the load, the settling may amount to several meters. When nowadays prefabricated drains are used towards the vertical draining of clay and mud layers, the procedure is to extend the prefabricated drains from the solid bottom through the clay course up to the water surface, where they are cut off.
The purpose of the present invention is to further develop the procedure known in the art. Thus the object of the invention is a procedure for creating a vertical drain by pushing into the soil an insertion tube housing in its interior a prefabricated drain, by pulling out the insertion tube and by cutting off the prefabricated drain. The invention is characterized in that the prefabricated drain is cut off with the aid of a cross-cutting means located within the insertion tube, at such height, or in such a layer as for instance a sand layer, which accepts the water conveyed by the prefabricated drain.
Certain remarkable advantages are gained by the aid of the invention. Since the top end of the prefabricated drain is located at a level lower than known heretofore, the hydrostatic pressure counteracting the
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