Permeable conduits for disbursing fluids

Integral conduits to disburse fluids along their length, fabricated out of two materials, and a method for manufacturing such structures with permeable wall parts; characterized by extruding a profile of thermoplastic material with a lengthwise extended slitted wall (10), and where this longitudinal slit is being outfitted with a permeable material consisting of one or more layers of fabric (12, 13, 13A, 13B, 14); the sides of the fabric strips being imbedded and sandwiched in the thermoplastic wall of the conduit, lengthwise along both sides of the slit; resulting in a hollow conduit with a lengthwise extended permeable wall section. Additionally, predetermined sections of the permeable fabric can be coated to block fluid emission from these selected sections (17, 19, 21). Fabrics of varying porosity are used to control emission of fluid. A longitudinal reinforcing element (23) may be captured within the structure (24) for securement purposes.

BACKGROUND OF THE INVENTION 
The present invention relates to a variety of partial permeable conduits 
and other hollow structures to disburse fluids in controlled amounts in 
small to large volumes of porous or liquid matter, such as soils and water 
bodies, including a method to fabricate such permeable conduits. 
BACKGROUND DESCRIPTION OF PRIOR ART 
Considerable effort has been made to produce and use porous pipes for 
various applications, as appears from the sizable number of related 
patents. Many of these products are intended for irrigation, some as 
soaker hoses, other mainly for subsurface use. Some have been also 
proposed for the aeration of water, to enhance aquatic life or to treat 
waste water. 
Irrigated agriculture worldwide is by far the largest consumer of fresh 
water, but the overall efficiency is low. Competition for diminishing 
fresh water resources compels the research and development of more 
efficient irrigation systems. Subsurface irrigation can eliminate most 
irrigation water losses due to evaporation and deep percolation inherent 
for nearly all now practiced systems. Greatly increasing the efficiency of 
the water, makes the same quantity available to a larger crop culture. 
Subsurface application of irrigation water, has also the ability to 
maintain a much more constant moisture content in the root zone--without 
blocking air exchange. Moisture stress can be fully eliminated--or, if 
desired, induced--thus promoting higher plant production and an ability to 
influence blooming. 
However, due to existing shortcomings of the present available subsurface 
products, these have not been able to gain wide acceptance in the agri- 
and horticulture endeavours. 
Several patents are based on extruded porous pipes consisting of 
combinations of elastomer particles dispersed in a thermoplastic resin, 
sometimes with additives to improve one or another property. Generally the 
elastomeric particles consist of crumb rubber originating from discarded 
tires, and polyethylene types are used as the thermoplastic binder. 
Resulting porosity--when explained at all--is most often attributed to 
volatile matter, escaping from the hot extrudate, forming tortuous paths 
in the pipe-wall. Apart from certain distinctions in the manufacturing 
equipment to fabricate such pipes, the patent claims are divergent and 
even contradictory. They run from non-specified volatile matter and/or 
residual moisture (Turner U.S. Pat. Nos. 4,110,420 and 4,168,799), to 
seemingly controlled moisture levels, including a two-stage process (Mason 
U.S. Pat. Nos. 4,517,316 and 4,615,642). In contrast, another patent 
claims the use of essential moisture-free material to obtain uniform 
porous pipes (Mitchell, U.S. Pat. No. 4,958,770). In others patents claims 
for the use of blowing agents or moisture controlling additives to support 
and regulate the forming of pores are made (Hettinga, U.S. Pat. No. 
4,931,236, Franz, U.S. Pat. Nos. 5,462,092 and 5,462,092). 
More recently a patent is issued, where an extruded inner porous layer is 
reinforced with a spiral wound webbing, followed by a porous outer layer. 
Porosity of the first extrudate is increased by a pressurized fluid. 
Sizers are used to draw down the pipes after each extrusion (Creed, U.S. 
Pat. No. 5,417,997). 
Various additives to improve processing and/or to obtain a smoother 
interior wall are claimed by Turner, Mason and Creed. Improved 
weatherability by adding UV-stabilizer is claimed by Prassas (U.S. Pat. 
Nos. 5,299,885, 5,445,775 and 5,474,398). 
None of these various patents based on porous pipes made from crumb 
rubber-thermoplastic polymer combinations teaches how to obtain specific 
porosity, e.g., how to influence the pore sizes and pore size 
distribution. Mason (in U.S. Pat. Nos. 4,161,055 and 4,615,642) claims, 
that the porosity is influenced by changes in die temperature, and the 
rate of pull-off of the hot extrudate. In the earlier patent it is found 
that a lower die temperature results in a lower porosity. On the contrary, 
in the later patent it is mentioned, that a 20.degree. F. decrease in die 
temperature increases porosity nearly three times| Such erratic results 
seem to emphasize, that more relevant factors influencing porosity have 
escaped attention. 
There exist many factors that thwart the efforts to manufacture and 
replicate such porous pipe with a constant uniform porosity. The major 
component, rubber crumb, is generally obtained by grinding discarded 
tires. Car tires differ from manufacturer to manufacturer, in type and 
application, in age, exposure and wear. Tires are composed of various 
layers, each layer to accomplish a specific function. The grinding 
procedures, whether cryogenic or under ambient temperature, need high 
energy input. Much of the energy to shred rubber is transformed into heat. 
This causes fluctuations in the process operating temperatures, which, 
together with the wear of the cutting and impact tools affects the 
resulting particle shapes, size and particle size distribution. Screening 
of ground rubber is also not without its problems. The ability to produce 
identical batches of rubber crumb, with the same overall properties, has 
its limitations. Mixing the crumb rubber with the polyolefine pellets 
homogeneously, and then feeding this mix into the feed zone, e.g., screw 
channel of an extruder, without segregation, is the next hurdle. Apart 
from transport through the extruder and die, where other complications may 
appear, a porosity resulting from escaping gas is hard to control. An 
unknown portion of water vapour or other volatile matter may escape 
backwards through the screw channel and feed hopper, and is lost for 
causing porosity by evaporating from the extrudate. The hot extrudate is 
very fragile, due to the high elastomer-load, even very slight 
fluctuations in sizing or in pull-off speed or force, show consequences in 
porosity, as Mason shows also. These phenomenonna frustrate efforts to 
produce pipes with uniform and reproducible porosity. A two-stage process 
like Creed's (U.S. Pat. No. 5,417,997), which may enhance mechanical 
properties, compounds these problems. 
Even thorough quality control of the raw materials, and monitoring every 
step of the operation, can not eliminate all inherent causes which foil 
the best intentions. Such non-reinforced pipes do not inherently have good 
mechanical properties. For a mechanical field installation, a relative 
substantial pipe wall thickness is mandatory to ensure the necessary 
tensile strength. Even so, impact strength of these pipes remains 
borderline. Stress cracking resistance remains a serious problem. The high 
particle load and erratic pore configuration which offers vulnerable 
points for attack, lower greatly the threshold for failure. Especially the 
locations were such pipes are stressed--pulled over and clamped on 
inserts--are highly vulnerable, and often show premature failure. 
Obtaining just the right type of porosity for industrial applications, that 
is for long laterals, is a balancing act. Too porous an irrigation pipe, 
and the water may never reach the end of the line, or at least not in the 
desired quantity. Less porous, supplying water uniformly over the length 
of a longer pipe, dictates less or smaller pores. Consequently, this 
implies the demand for a higher than usual quality of irrigation water, to 
prevent clogging of small pores. Due to the expected, claimed, and 
demonstrated tortuous paths of the pores in the pipe-wall (see: Mason, 
U.S. Pat. No. 4,616,055, FIG. 9 and 10), filtration at least better than 
20 micron is necessary to prevent blocking of most of the larger pores. It 
appears not practical, to try to protect smaller pores from becoming 
clogged by intensified filtration. The poorly uniform porosity, and the 
demand for high water quality, limit dramatically the marketability and 
acceptance of these types for industrial irrigation. 
Another approach to obtain a porous irrigation pipe, using a blowing agent 
to foam a flexible PVC-pipe, and drawing down the hot extruded material to 
rupture the cell-walls to obtain an open-pored structure (Dorrn, U.S. Pat. 
No 4,577,998), suffers from similar problems as described earlier. These 
pipes, with an initial probably acceptable porosity, show a large and 
inadmissible drop in emission rate after running these only for a short 
period with water passed through a 100 micron filter. The products do not 
appear to be fitted for professional applications. 
An interesting method to fabricate porous pipes proposes the use of a 
meltable polymer--such as polypropylene--and an only partly compatible 
fluid, which combination shows a certain immiscibility gap (Stohr, U.S. 
Pat. No. 4,740,104). The melt is extruded into a spin bath to coagulate 
the mix into a pipe with a high pore cavity. The resulting pore sizes from 
this process however, are for the largest part less than 4 microns. This 
pore size puts extremely high demands on the filtration of any water to be 
applied, and is not economically feasible for irrigation. 
Leaching of soluble particles dispersed in thermoplastic wall strips of a 
co-extruded pipe is another proposition (Youval, U.S. Pat. No. 4,182,582). 
Variations in porosity over the length of the pipe are obtained by 
increasing or decreasing the width of the relevant wall strips. The 
proposed method for the production of such pipes is cumbersome and 
includes four to five separate steps. The leaching process, essential to 
cause microporosity, demands several days, underlining that this 
proposition is highly unpractical, and not cost effective. 
A complex and rather murky proposition embodies a seeping hosepipe with an 
integral textile core, embedded in a mixture of resin, an odd kind of 
plasticizer, carbon black, bactericides, fungicides, algicides and 
thickeners. This coating is claimed to show water absorbing capacity 
(Maso, U.S. Pat. No. 5,152,634). No information is provided how the pipe 
is made, nor how water is transferred through the pipe. 
A system, based on ceramic elements, baked from clay mixed with plastic 
powders (Saburi, U.S. Pat. No. 4,221,501), demands many additional parts 
for installation and appears very labor intensive and expensive. 
Coils of hollow cellulose acetate fibers are suggested to addresses the 
watering need of individual plants (Patterson, U.S. Pat. No. 4,928,427). 
Fibers are limited in their ability to carry water over any significant 
distance. Industrial applications based on coiled fiber seem hardly 
feasible. 
An at least two compartmental extruded conduit, in cross section preferab 
like a figure eight with an open top, where the upper compartment is fill 
with a spongelike polyurethane foam, extending outside this compartment 
along the length of the conduit to provide capillary type action (Winston 
U.S. Pat. No. 4,061,272) has in principle more potential. Controlling the 
foaming operation and preventing accidental clogging of the lower, water 
supplying conduit will be a problem. Capillary type transport through this 
kind of barrier presumes small pores and therefore the need for protection 
against clogging, implying adequate water treatment. 
A method whereby a perforated pipe is covered with fibrous material, and 
this configuration is confined in a second casing pipe, which, except for 
a lengthwise slit, encases the perforated pipe completely (Pramsoler, U.S. 
Pat. No. 4,948,295), may conclude this review of prior art. In this case 
water is supplied to the soil via the perforations and slit; the fibrous 
material serves to prevent soil particles and roots penetrating this pipe. 
Although this system shows conceptual merits, it does not offer any real 
practical advantages in comparison to its competitors. Producing such pipe 
is cumbersome, and has to be carried out in successive steps. The inner 
pipe has to be extruded, pulled through a cooling bath and mechanically 
provided with orifices. Next this pipe is wrapped with one or more layers 
of fibrous fleece, and then the casing pipe with slit needs to be extruded 
around this composition. Consequently, the final product will have a 
relative large wall thickness and limited flexibility, is costly in 
material and difficult to handle in longer dimensions. Subsurface 
mechanical installation seems highly impractical. This proposed system 
also does not provide for any control of the emission and emission rate 
over longer laterals, nor does it teach how to manipulate the various 
parameters to obtain a desired porosity. 
None of the known porous pipes, including the above mentioned patented 
propositions, possess exactly defined and unequivocal uniform porosities, 
adaptability in porosity and design to accommodate existing conditions, 
together with an uncomplicated and flexible manufacturing process 
SUMMARY OF THE INVENTION 
This invention presents viable procedures for the manufacturing and 
application of a variety of irrigation and aeration conduits with 
pre-designed porosities, by incorporating one or more strips of 
prefabricated fabric materials in hereto reserved slits, in structures 
otherwise made of impervious flexible material. The elementary design 
consists of a lengthwise slitted thermoplastic pipe, in which the slit is 
bridged by a strip of fabric, and where the edges of the fabric are 
imbedded in the sidewalls along the slit. Varying the width of the slit 
and/or the using types of fabric with diverging permeabilities, allow an 
uncomplicated method to modify porosity and rate of emission, to meet the 
specific requirements for a given situation. 
Usually, the porous products intended for irrigation or aeration, by nature 
of the manufacturing process, are porous over the entire surface, in 
circumference as well lengthwise. There exist no compelling reason for the 
pores to be distributed over the whole area of the pipewall. To obtain the 
same emission rate of a fluid or gas for a given length of pipe, under 
otherwise identical conditions, a smaller area with a proportionally 
higher pore density or larger pores can perform at least equally well. The 
option for larger pores concentrated on a smaller section of the wall is 
preferable, the main reason: lesser sensitivity for possible clogging. 
An even better result can be expected, when pore size and pore form are 
fully controlled. Eliminating the small pores which are bound to clog, by 
utilizing materials of certified uniform pore sizes, provides the means 
for such control. Woven fabrics manufactured for screening and filtration 
purposes, are available in a broad variety of fiber and wire types, weave 
patterns, mesh openings and permeability. The basic manufacturing process 
consists of extruding an adequate thermoplastic profile and to encapsulate 
both edges of a fabric ribbon in the hot material, reserving a strip of 
fabric with the intrinsic uniform pore sizes and pore form free from 
thermoplastic material, in such a way the a partly permeable conduit 
results. After cooling in a water bath the product can be coiled. 
Modifications on the basic principle are part of the invention. For 
aeration fine pored fabric is to be preferred, smaller gas bubbles 
dissolve better. This type of fabric may fail to contribute sufficient 
mechanical strength to the structure, the inclusion of an additional 
coarser, more rigid fabric can correct this problem. 
Under certain conditions, a special design with a coarser fabric bridging 
the slit in the conduit to secure rigidity, with a tubular shaped finer 
pore size fabric extending over this permeable channel and outwards of the 
conduit, in such a way, that the edges of both the coarser and the finer 
fabric are imbedded in the sidewalls of the thermoplastic conduit. The 
function of the finer fabric is to prevent particles--such as 
silt--contaminating the conduit. On the other hand, to diminish the danger 
of clogging from the inside, the larger area of the finer fabric offers a 
larger filtering surface and space to form a substantial filter cake. 
Thus, the functioning of the pipe can be protected for extended periods. 
Where trees or other plants are further apart, it can be advantageous to 
not supply water in the soil between the root zones. The invention does 
provide for the manufacture of conduits with intermittent permeable and 
impervious sections, by blocking corresponding permeable sections. The 
blocking is carried out during the primary process, no additional stage is 
involved. 
It holds even for pipes with uniform porosity, that due to head loss the 
specific per unit length emission decreases. The rate of emission of 
fluids through a porous medium, keeping other parameters equal, is 
proportionate to the fluid's pressure. Head loss depends on flow rate and 
friction. Due to the high content of rubber particles, porous pipes made 
with this material show rougher walls and higher friction. Conduits of 
this invention have smooth walls, reducing friction loss. Nevertheless, 
pressure loss resulting from long conduits and high flow rates, may 
prohibit to obtain the pursued irrigation uniformity. Several measures to 
compensate fully for the drop in emission due to pressure loss are part of 
this invention. 
Corrective measures can be made, by gradually increasing the permeable 
areas along the conduit from inlet to end. The same effect is obtained by 
partly blocking the permeable areas in a gradually tapering off pattern. 
Another method to accomplish uniform emission is, to use gradual more 
permeable fabrics for successive sections. Combining the control of the 
relative permeable areas and modifying the fabrics is also an option.

DETAILED DESCRIPTION OF THE INVENTION 
The structures of the present invention consist only of two 
components--each with a specific function--which, integrally combined, 
form permeable conduits to distribute fluids along their length. Methods 
to accomplish this integration are also part of the invention. 
The impervious part of the structure--intended for the fluids or gas 
transport, is preferably extruded from a thermoplastic material as a 
hollow tubular shape with a lengthwise slit. Although other thermoplastic 
materials can be used, low density polyethylene (LDPE) or linear low 
density polyethylene (LLDPE) types, having low melt indices (M.I.&lt;1) and 
high stress cracking resistance are preferred. Such types are widely 
available at economical prices, uncomplicated to extrude, and possess 
satisfactory mechanical properties. These materials are also highly 
resistant to all conceivable environments and products with which the 
permeable pipes can be expected to become exposed. Pigmented with carbon 
black, to better protect against UV-degradation a long term functionality 
is assured in the preferred designs of this invention, the structures made 
out of LDPE or LLDPE are sufficient flexible to be coiled in a relative 
small diameter. 
The second component, the permeable element of the structure, consist of a 
screen or permeable fabric as used for sifting and filtration, inserted in 
the lengthwise slit, to complete the structure. 
The preference is to select a prefabricated woven material with uniform 
openings from the wide range of commercially available products. This 
selection offers choices in weave patterns, fibre or wire types and sizes, 
mesh openings, and open areas, that fit every imaginable application 
intended for this invention. For most applications synthetic fiber weaves 
are preferred, under some conditions woven metal wire can be used; glass 
fiber weaves are preferred where optimum resistance against chemical 
attack is needed. Natural fibers generally do not possess sufficient 
mechanical, chemical or biological resistance. The fabrics which deserve 
consideration, do not negatively affect the flexibility of the original 
thermoplastic structure, preserving the ability for coiling. 
Referring to the drawings, FIG. 1 up to and including FIG. 7 illustrate 
different embodiments of the permeable structures invented. The common 
characteristics of these embodiments are the impervious thermoplastic wall 
and wall sections generally designated 10 and the hollow conduit through 
which the media to be distributed are transported 11. 
FIGS. 1 and 1A illustrate a permeable conduit fitted with a relative small 
strip of coarse fabric with a relative large pore size 12. This embodiment 
is preferred, where there is no danger for clogging of the pores or 
conduit from the environment in which the structure is embedded. However, 
it allows the presence of larger particular impurities in the medium to be 
distributed. FIGS. 2 and 2A illustrate a permeable conduit fitted with a 
broader strip of a finer pored fabric 13 to prevent possible entry of fine 
particles from the environment into the structure. The finer pores require 
a higher quality pretreatment of the medium to be distributed with regard 
to solid impurities. 
FIG. 3 illustrates a conduit fitted with multiple permeable strips, the 
strips 13A and 13B of the same pore size differing in width, while strip 
14 is larger pored Although of no direct practical importance, it shows 
the wide versatility of possible combinations. 
FIG. 4 embodies a configuration where a combination of two types of fabric 
is of advantage. 
The fine fabric 13 prevents entry of particles from the environment into 
the structure, and/or for example assures the distribution of fine gas 
bubbles, while the coarse fabric or screen 14 improves the mechanical 
integrity of the structure. 
FIG. 5 illustrates a variation on the embodiment of FIG. 4. Here the screen 
or fabric 14 serves to stabilize the structure, but allows expected 
impurities contained in the medium to pass. The fine pored fabric 13 
spaciously extending over the lengthwise slit bridged by fabric 14, forms 
a partition 15, superimposed on the main structure. This permeable 
partition 15 has a twofold function. Primarily this conduit acts as a 
barrier to prevent the entry of particles from the environment which 
surrounds the structure. Secondly this fine fabric 13 will retain all 
particles in the medium which are too large to pass through the pores. The 
generous filter surface and ample space 15, allow for the accumulation of 
a considerable filter cake, before any real problem of clogging arises. 
The operative lifespan of the conduits under frequently encountered 
unfavourable conditions can be vastly expanded, and can be successfully 
used, where other existing system do not offer a feasible option. 
FIG. 6 illustrates by way of one example only, another variation of the 
invention, a permeable structure in which sections of the permeable strip 
have been blocked, to prevent emission in these segments. The lengths of 
successive open and blocked segments can be selected subject to 
conditions. In this illustration, permeable segments 16, 18 and 22 have 
identical lengths, but segment 20 is longer; the blocked segments 17, 19 
and 21 each differ in length. There are several ways to accomplish the 
blocking, polymer solutions or dispersions like paints, glues, printing 
inks, hot melts or other hydrocarbon derivates can be used. The preferred 
method however is, to apply strips of thermoplastic melt over the 
permeable fabric, before sizing and cooling of the structure. Application 
is preferably carried out by activating an accumulator, which is supplied 
with molten LDPE or LLDPE by a small extruder. The accumulator is operated 
by a hydraulic system and computer controlled. To clearly mark the 
segments, the blocking material is preferably of a color contrasting with 
the impervious wall material. 
FIG. 7 illustrates art embodiment where for purposes of attaching the 
structure to keep them in the desired position, a cable or wire 23 is 
incorporated in a wall thickening 24. 
FIG. 8 is a schematic view of a system to produce the structures of the 
invention. A extruder 25 is outfitted with a motor 26, to drive an 
extrusion screw 29 in a barrel 28 via a gearbox 27. Temperatures over the 
barrel 28 and an extrusion head 32 are regulated by heating and cooling 
elements 30. A thermoplastic material is supplied via a hopper 31. A 
mandrel 33, disposed in the head 32 as part of the die assembly shaping 
the extrudate, is partly extended from said head. The thermoplastic 
material, transported and molten by the screw action, is forced downstream 
the die around the mandrel on its way outside, preferably in cross section 
as an incomplete annulus. A reel 34 contains a ribbon of fabric 35, said 
ribbon is led through a channel, which merges near the downstream end of 
the head with the die channel around the mandrel 33. Where the channels 
join, the fabric ribbon 35 is on both sides partly enveloped with molten 
thermoplastic material 48, before the thus formed structure emerges from 
the extrusion head 32. Further downstream, to correct potential minor 
imperfections in the sandwiching of the fabric in the thermoplast 
extrudate, and to smooth possible bumps resulting from the application of 
blocking strips, the structure--still supported by the extended mandrel 
33.times.is passed under a roll with adjustable pressing force 36. The 
structure is then pulled through a vacuum sizer 37, evacuated by pump 38. 
To obtain and maintain the desired degree of vacuum during sizing, and to 
prohibit cooling water being sucked upstream through the permeable 
structure, two stainless steel balls 40, kept mandrel 33, perform as 
seals. Belt puller 42 pulls the structure 50 through the sizer 37 and 
cooling bath 39. The cooling water is constantly refreshed to keep the 
water temperature low. To seal off, and squeeze out any water picked up 
from the cooling bath, a third ball 40 is kept in position inside 
structure 50 at the end of the bath, by an extension of cable 41, used for 
the other two sealing balls 40. After leaving puller 42, the now finished 
integral conduit, is wound on a reel with the help of coiler 43. 
A second small extruder 44 processes the thermoplastic material used to 
block segments of the permeable fabric. Extruder 44 is outfitted with 
motor, gearbox, barrel and screw, hopper and heating and cooling elements. 
The plastic melt is extruded into an accumulator 45, furnished with a 
nozzle 46, positioned between head 32 and pressing roll 36, directly over 
the slit outfitted with fabric 35. On demand plunger 47 is activated, and 
an exact quantity of melt 49 is forced from the nozzle and superimposed on 
the fabric to seal the pores. The to and fro movement of plunger 47 in 
accumulator 45 is realized and controlled by an assembly 51, consisting of 
a hydraulic unit commanded by a programmable computer. FIGS. 8A, 8B and 8C 
illustrate schematically successive downstream cross sections of extrusion 
head 32. 
SUMMARY 
Thus the reader will see, that the permeable conduits of this invention 
provide devices, with which distribution of fluids along their length can 
be completely controlled. These conduits can be fabricated in a 
considerable range of products of varying pore sizes and varying pore 
area, allowing for a very large flexibility in managing emission rates. 
Because of the extremely high precision in the manufacture of woven 
fabrics, these materials provide the basis for these conduits to be 
fabricated with optimum values for the manufacturer's coefficients of 
variation. This fact, together with the possibility to influence porosity 
to obtain uniform emission along even very long laterals, allow for high 
design uniformity for subsurface irrigation systems, as specified in ASAE 
Engineering Practice ASAE EP405. The ability to use only slightly treated 
waste water subsurface, eliminating the danger of contact with humans or 
animals, contributes to solving some environmental problems and can save 
fresh water. The use of fine pored fabrics, allow to aerate shallow water 
bodies, without losing input for reason of the escape of larger gas 
bubbles at the surface. The ability for long conduits, coupled with low 
emission rates, makes it feasible, to disburse substances in water bodies, 
which influence the movement of migrating fish and to protect them from 
danger. 
The availability of fabrics, based on a variety of fibers made from 
synthetic polymers, glass, carbon, metal and other, allow the 
manufacturing of special permeable conduits, resistant to chemical or 
biological active solutions for leaching and bio-remediation of soils, 
ores, slag or other porous materials. 
The invention has been described and illustrated as an embodiment of 
permeable structures, mainly for subsurface irrigation and aeration of 
water bodies. It is not intended to be limited to the described 
applications, nor to the described and illustrated method of producing 
said structures. Manufacturing of the conduits of this invention can for 
example be carried out by using flat extruded material; or; strips of 
thermoplastic material may be heated up and then paired with the fabric. 
Since various modifications and structural changes of these embodiments and 
method of production may be made, without departing in any way from the 
spirit of the present invention, the scope of this invention should be 
determined by the appended claims and their legal equivalents, rather than 
by the examples given.