Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention i9 applied when using prefabricated drains to the
purpose of compacting water-carrying, fine-grained and poorly water-per-
meable 90il, such as clay, silt, etc. by carrying out dewatering of thesoil material with the aid of vertical draining and thereby reducing the
water content of the soil material. Hereby one improves the bearing ca-
pacity of the ground and accelerates the settlings that can be expected to
take place, while at the same time the shearing strength of the 90il in-
creases .
Various kinds of prefabricated drains have been developed for verticaldraining, 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 i9 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 i9 held in the insertion tube, and the
lower end of the prefabricated drain becomes snchored in position ~ith 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 i~ 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 stratum1 lies on the ground ~urface or olose
thereto. Often, however, the clay bed is overlaid by coarser, readily
water-conducting 30il in the natural state or by earth filline, such as
sand or gravel. It would not be nece3sary in such cases to rai~e the water
from the clay bed all the way up to the eround surface: lifting the water
into the sand layer over the clay cour~e 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
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which may have a thickness of tens of ~etres. Vertic~l draining i9 re-
quired when the intention is to fill up e.g. a la`~e or sea at the point in
que3tion for the construction of a road, railway or aven 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 ta'~es many
decades. The settling can be accelerated by vertical draining so that it
i8 accomplished within a year or two, or even in a few months, depending
on the subsoil conditions and the spacing of the vertical drains. Depend-
ing on the 80il conditions and on the load, the settling may amount to
several metres. 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 i8 to further develop the procedure
known in the art. Thus the object of the invention i3 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 inser-
tion tube and by cutting off the prefabricated drain. The invention i8
characteriæed 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
ir, 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 e~d of the prefabricated drain is located at a level loYer
than known heretofore, the hydrostatic pressure counteracting the flow in
the prefabricated drain i9 correspondingly reduced, while at the same time
the internal resistance to flow (the well resistance) in the vertical
drain will be less~ This accelerates the flow in the prefabricated drain
and improves the operability of the drain. On the other ha~d this also
implies that less prefabricated drain material is required, which as a
rule comes in rolls. Assuming for in~tance that the area that has to be
provided with vertical drains is 10 hectare3, that the spacing of the
prefabricated drains is 1.5 m and that it is possible to save 5 m of the
length of each prefabricated drain, the total savings in the area will
then be 220,000 metres of prefabricated drain.
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The invention al80 concerns a mean~ for carrying out the procedure just
described. ~he means is characterized in that it compri~es, located within
the tube, a cutting blade movable in a direction tran~versal to the tube,
and a counterblade located opposite to this first bla~e, and the prefab-
ricated drain being located between these blades.
Fig. 1 illustrates the situ~tion which i8 pre~ent when the prefabricated
drains are inserted, from dry land, into a clay or mu~ layer.
Fig. 2 illustrates a situation in which the prefabricated drains are in-
serted in the clay or mud layer, operating on the water surface.
Fig. 3 shows the section alore the line III-III in Fig. 1.
Fig. 4 shows the section along the line IV-IV in Fig. 3.
Fig. 5 is equivalent to Fig. 4 and presents another embodiment of the in-
vention.
FiB. 1 illustrates the case that there is, lowermoat, the hard bottom 1,
thereupon a clay course 2, and upon this there i9 water-permeable natural
soil or earth fillins 3, which lets water pass through. The installation
of the prefabricated drains 9 takes place with the aid of an insertion
tube 7 mounted on a working machine 32 moving on the ground surface 10.
While the insertion tube is in its top position, whereby its lower end 33
is above ground, the prefabricated drain 9 obtained from a ~torage coil 6
is affixed to the lower end of the ins_ertion tube. The insertion tube 7
is then pushed through the layers 3 and 2 all the way to the hard bottom
1. The lower end of the prefabricated drain 9 is secured to the hard
bottom 1 with a special anchorin~ device (not depicted). ~he insertion
tube is pulled up enough to bring the cross-cutting means in the tube a
small distance over the top of the clay layer 2. The prefabricated drain 9
is cut off and the insertion tube raised to its top position. The working
machine 32 is then sliehtly displaced, and another prefabricated drain 9
is introduced into the clay layer 2.
The cros3-cutting means within the insertion tube 7 is located close to
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the lo-~er end of the insertion tube so that it is easily acces3ible for
servicing, repairs or replacement.
Fig. 2 illustrates the case in which the prefabricated drains 9 are in-stalled in a clay course 2 in the bottom of a water body, such as a sea
for instance, with the aid of a worXing mschine ~2 floating on a pontoon
8. The operation is similar to th~t described in connection with Fig. 1.
It is possible, before the operation is commenced, to deposit on the sea
bottom a water-permeable sand cou.se 3. After the prefabricated drains 9
have been instslled, the earth filling 30 is run into the sea. It is
moreo~er possible to cart an excess embankment 31 upon the earth filling,
to speed up the settling. In the embodiment of Fig. 1 an excess embankment
31 may likewise be added.
Fig. 3 shows the cross section of the insertion tube 7 at the point where
the prefabricated drain cross-cutting means is located. The cross-cutting
means comprises a cylin~ body 12 with three cylinders 13 transversal
to the insertion tube 7. The cylind~r body 12 carries on its bottom a
cutting blade 14, transversal to the insertion tube 7. Each cylinder 13 is
guided on a stationary piston 15 affixed to the wall of the insertion tube
7. Each cylinder 13 has been connected to a pressure fluid-carrying tube
11 entering through the top end of the insertion tube 7. ~hen pressure
fluid i9 admitted into the cylinders, the cylinder body 12 will move to
the right in Figs 3 and 4. Hereby it will push the prefabricated drain 9
against the counterblade 16 and cut ths prefabricated drain off. Both ends
of the bottom of the cylind~r body 12 are acted on by a spring 17,
which returns the cutting blade into its initial position as soon as the
cylinders 1~ are depressurized. The cutting blade protector 18 and the
counterblade protector 19 protect the prefabricated drain 9 durin6 the
pulling up of the insertion tube 7.
In the embodiment of Fig. 5, the cutting blade 20 is journalled by its
ends to be carried by two opposite -~alls of the insertion tube 7. For
cross-cutting the prefabricated drain 9, the cutting blade 20 i8 rotated
from the position shown in Fig. 4, clockwise, through about 90 degrees,
whereby it meets the counterblade 21 and cuts the prefabricated drain. The
cutting bladb 20 carries on its end a sprocket wheel 22 cooperating with a
chain 11 entering the insertion tube 7 through its top end. The members
24, 25, 2v an~ 27 serve to protect the prefabricated drain 9 while the
insertion tube 7 is being pulled up.
It i9 obvious to a person skilled in the art that different embodiments of
the invention may vary within the scope of the claims stated below. This
concerns, above all, the construction of the cross-cutting means within
the in~ertion tube 7 and its mode of operation. This means may operate
mechanically, hydraulically,.pneumatically o- electrically.
