EP2286037A1

EP2286037A1 - Pit and related covered filter tube

Info

Publication number: EP2286037A1
Application number: EP09724951A
Authority: EP
Inventors: Lukas Schoenmakers
Original assignee: VISSER AND SMIT HANAB BV
Current assignee: VISSER AND SMIT HANAB BV
Priority date: 2008-03-22
Filing date: 2009-03-23
Publication date: 2011-02-23
Also published as: NL2003708C2; US20110017451A1; WO2009120070A1; AU2009229585A1; NL2003708A1; NL2002653A1; NL2002653C2

Abstract

This invention relates to a method to make a pit to withdraw or store or infiltrate water; a pit to withdraw or store or infiltrate water; a method to withdraw water from a water bearing package or to store or infiltrate water, particularly wherein use is made of a filter tube contrary to a drainage tube. The filter tube can be provided with a sheath/ jacket of filter sand of gravel.

Description

Title: Pit and related covered filter tube.

Introduction

The invention relates to fabricating a pit for water production or -stowing or -infiltration, to a pit for water production or -stowing or -infiltration and to a method to produce water from a water bearing package or to stbwe ^~~or ^~iή^~fϊϊtrate^~"of^~ water,^{" "} in^" particular wherein:^~ use is made of a filter tube contrary to a drainage tube. As a rule, when use is made of a filter tube, development of the system is carried out after it is installed, i.e. during some time preliminary purging is carried out to ensure a high capacity at a high water quality (little or no dragged contaminating particles such as sand) for a long time, while the water obtains a subsequent use. On the contrary, with a drainage tube one is merely interested to ensure a minimum water draining capacity to protect a soil package sufficiently against (rain) water annoyance or to control contaminated locations.

Several design principles are known to make a pit for withdrawal or stowage or -infiltration of water. Three principles are disclosed in Sass en Treskatis, Grundwasser - Zeitschrift der Fachsektion Hydrogeologie 1/2000, p 17- 23. E.g. the withdrawal of ground water, particularly ground water to produce drink water, is carried out in classical manner by making use of a vertical pit or in some cases a collector well with radial strands (Radial Collector Well, RCW) . The capacity of a vertical pit is relatively small, such that in general many pits are required for large scale water recovery. Thus for large scale water recovery many pumps, pipes etc. are required. A radial pit (RCW) consists of a deep, vertical shaft to 80 meters at the most below the surface, from which several horizontal filter tubes can be located in the water bearing package in the ground. With the horizontal filter tubes of a radial pit one can obtain a larger capacity per pit compared to vertical pits/ but a radial pit (RCW) is in general relatively expensive and, based on the costs of this_, _pi_.t_ type,, limited in depth and length of the horizontal filter tubes. An alternative to a RCW is application of a horizontal pit which is drilled by means of the HDD technigue, which is principally more effective. A horizontal pit of this type (HDD-pit) comprises in general a (preferably at least substantially liquid tight) input line which from the surface is under an angle or horizontally drilled into the ground until a water bearing package. In the water bearing package the input line merges into a water permeable filter tube which extends through the water bearing package. Principally the filter tube can extend in a curve or diagonally through the water bearing package, although the filter tube typically extends at least substantially in a horizontal direction due to practical reasons.

This invention is applicable to any pit type, both of the above type and other types. It is expected that the best advantages are obtained by application of the invention to a horizontal pit, particularly the HDD-pit.

Compared to vertical pits, with horizontal pits (both the radial pit (RCW) and the with HDD technique drilled pit) in principal there is a larger risk for plugging due to the remained lining of the drill hole such that capacity can decrease. Lining of the drill hole is applied during drilling to stabilise the wall of the drilled hole for collapsing. Also sand supply and/or ensuring of the biological quality of the water can be a problem, in particular if the pit is designed to obtain drinking water. Particularly application of horizontal pits in ground with a relatively low permeability, such as mode_rate to fine sandy soils,, in which disposal of the lining with conventional techniques is difficult, thus is generally regarded in the field as unrealistic due to too high risks.

Sass and Treskatis disclose in Grundwasser - Zeitschrift der Fachsektion Hydrogeologie 1/200, pp 24-34 the fabrication of a curved horizontal pit to obtain drinking water in a highly permeable water bearing package (coarse sand/gravel, with a typical permeability of more than 150 m/day) . The pit is drilled by a directional horizontal drilling technique, which technique is known in the field as HDD {"horizontal directional drilling") . During drilling use is made of a drill liquid/drill fluid which, a.o., contains drill clay.

A drill clay, e.g. bentonite in the drill liquid can cause a limitation of the production capacity or infiltration capacity, which is undesirable, particularly if a pit has to be installed in a water bearing package with a relatively low permeability compared to coarse sand, e.g. less than 100 m/day and particularly less than 80 m/day. In Netherlands, e.g., the water permeability is typically less than 100 m/day, particularly about 10-50 m/day. Also a drill clay, like bentonite, after drilling not completely removable, which is a disadvantage for the capacity of the pit, particularly in a relatively low permeable water bearing package, such as e.g. in Netherlands typically.

In stead of a drill clay, as the drill liquid use can be made of a decomposable agent, e.g. of organic type, like a polymer. It is e.g. soluble in water or chemically or biologically decomposable. However care should be given that .the .decomposing, process_. in_ the_. often anoxic g_rqund water of the water bearing package will be slow or even not significantly demonstrable/detectable. Alternatively a drill liquid can be used which is decomposed by an agent (e.g. oxidiser} with which the water pit after drilling (e.g. during development) is treated, e.g. by injection. E.g. the drill liquid contains at least one oxidisable polysaccharide (preferably chemically unmodified) and during development of the pit it is decomposed in the presence of at least one oxidiser which is supplied for that. The polysaccharide can be a gum, preferably a gum from the group containing xanthene gum, guar gum and its combinations. The drill liquid could also contain carboxymethylcellulose (CMC) .

The oxidiser can be a peroxide, e.g. hydrogen peroxide, or bleekloog or ozone.

The drill fluid further contains typically ground water and drilled soil (a.o. sand, clay, silt and/or peat) .

OBJECT OF THE INVENTION

The object of the invention is, in case of a water pit, particularly a by HDD technique installed horizontal water pit, to provide one or more of the following: a new method to make a water pit, as alternative to the known method; a proper capacity, particularly an increased capacity compared to a similar pit of the same type and made conventionally; a capacity which is maintained for a long time span; from which ground water can be obtained which is substantially free of sand; a method wherein the ground and the ground water during drilling and developing are as little as possible contaminated with foreign matter, particularly the _..soil contaminating or for drinking water undesired matter; a water pit from which ground water with a biologically reliable quality can be obtained; a method to obtain ground water of a biologically reliable quality; a water pit in a relatively shallow and/or unconsolidated soil layer (contrary to a consolidated soil layer in which typically mining, like oil or gas winning from a pit is carried out) ; a water pit to obtain drink water and/or to store water for the application fields energy storage (heat/cold storage by storing hot or cold water, i.e. water with a temperature below or above, respectively the mean soil temperature) and/or water buffering and/or infiltration of rain water; a method designed to apply in any water bearing package, i.e. a soil layer from which water can be produced or into which water can be stored or infiltrated; the original water bearing package can be relatively highly permeable, like in coarse sand or gravel, or relatively low permeable, like in moderate fine to fine sand; applicable in soils with a high water permeability, like a permeability of more than 100 m/day, e.g. 150 m/day or more; applicable in a relatively low permeable package, such as a package with a water permeability of 100 m/day of less, particularly less than 80 m/day at the most, more particularly 50 m/day at the most, wherein based on practical capacity considerations, the water permeability is preferably at least 10 m/day, particularly at least 20 m/day; a horizontal water pit wherein typically at least the part of the pit designed to allow passage of water {the filter tube) in the water bearing package extends substantially in a horizontal direction; along the length of the part of the pit designed to allow passage of water {de filter tube), the permeability of the original substrate can vary, e.g. with at least a factor 10 or 50 or 100 or 200 or 500 or 1000; due to installing the filter tube or such, preferably the rate of the variation of the water capacity along the length of the filter tube is made smaller or larger with preferably at least a factor 10 or 50 or 100. One or more different objects will be clear from the description and/or claims, which follow. DEFINITION OF THE INVENTION GENERAL

Thus the present invention is directed to a method to produce a horizontal water pit, comprising drilling, preferably by means of HDD-technique, of a pit in a water bearing package in the presence of a drill fluid, locating within the drill hole of a filter tube and developing of the pit. SPECIFICALLY

Preferably the filter tube is used which is above the ground already sheathed/enveloped/jacketed/covered by a layer of coherent and preferably at the outer side of the filter tube mounted material, which layer after installing has or obtains a filtering property and/or function, e.g. comparable to a natural or artificial surrounding filling. This enveloping layer can vary in thickness between very thin, preferably between 50 micron and 1 millimetre, e.g. 100 micron, like a plastic muff, or substantially thicker, like between 0,5 and 10 cm or more, like a with binding agent bound layer of granular material, like filter sand and/or filter gravel. The sheath/jacket is porous or water permeable or is designed to obtain this property in the soil^ The sheath is designed to, during use of the filter tube in the ground, be sustainable permanently coherent, like with a polymer foil, or become completely or partly incoherent (to become like a surrounding/external filling) , like with a layer of by binding agent mutually bound granules .

The sheath can substantially with the complete surface of its inner side be mounted to the filter tube, e.g. in case the sheath contains granular material, or can with intervals in the direction of the length and/or circumference of the filter tube be mounted to it, e.g. in ring shaped areas with a spacing of at least 10 centimetre in the direction of the length of the filter tube in case of a foil or cloth like sheath.

The external surface of the sheath is preferably smooth walled to install the assembly of filter tube and sheath with the least friction in the ground, and for that provides preferably a substantially closed external surface, substantially free from relief. The sheath fits preferably tightly around the filter tube, in case of a foil or cloth like sheath it is preferably elastically yields at the filter tube such that it is mounted with pre tension. In an embodiment the sheath is after installation of the filter tube in the ground treated, e.g. released from the filter tube, to obtain the properties as desired for filtering. E.g. such that a regeneratable external filling around the filter tube is created. E.g. after the sheathed filter tube is installed in the ground, the mutually and to the filter tubes bound or adhered granules are loosened from each other and from the filter tube by breaking the binding or adhesion by e.g. chemical or mechanical treatment, e.g. by exposing of the sheath to an indeed or not pulsating liquid stream and/or a the binding or adhesion decreasing or removing solvent. E.g. in the filter tube in the ground a liquid of high pressure is injected, which flows to the outside through the wall of the filter tube, and arrives into the sheath.

The binding agent is e.g. based on gypsum or water- glass or some different material with a convenient adhering property. Preferably the binding agent is not epoxy or a binding agent with an adhering property equal to or better than that of epoxy. Since, a binder with a too high adhering property avoids that, in the ground, the granules can easily be mutually loosened by mechanical and/or chemical influence externally from the filter tube.

E.g. in the factory the filter tube is equipped with the aid of cement (a binder) , lime, chalk, gypsum, water and sand with a gradation of 0, 5-5 nun, with a sheath with a thickness of 0,5-lOcm. The filter tube including sheath is pulled (possibly within a casing tube) into the drill hole. After pulling in, the casing tube is removed from the drill hole. This casing tube carries a device to disturb the drill hole mechanically during pulling out, e.g. by one or more projections at the mantel tube and penetrating the wall of the drill hole to treat material of said wall. After removal of the casing tube the connections between the sand granules of the sheath of cement, lime, chalk, gypsum water and sand by means of a high pressure liquid between 5 and 400 bar are destroyed. Depending from the situation a strong oxidiser is added to this liquid. Because, of _this a loo_se_ sand package is created with the properties of a natural surrounding filling. According to another embodiment the permanent coherent sheath is foil like, e.g. of nylon or another polymer, however can also be of different material, e.g. metal, such as steel. In stead of foil like the sheath can be made of fibres, such as cloth, gaze, fabric, tissue or braid. If from fibres, the sheath will have in many cases naturally the desired porousness or water permeability. If from foil the sheath has pores of small holes or slits made in it. Preferably the sheath is not made of a muff from fibres of jute, such as known as such from drainage tubes. Since such an already known muff is not mounted to the filter tube, is relatively thick walled and has a relatively rough external surface, such that it is unsuited to be brought into the ground by making use of HDD- technique. The dimension of the openings in the sheath are preferably at least 20 micron, e.g. 100 micron. The open surface of the sheath measures preferably at least 10% or 20%. The thickness measures preferably 0,5 or 1 millimetre at the most. The permanent coherent sheath is preferably at mutually spaced locations fixed to the external side of the filter tube, e.g. in the direction of the length of the filter tube an spacing of 1 meter. The permanent coherent sheath offers the possibility to create a very fine filter. The mean dimension of the pores of the wall of the filter tube against which the sheath bears or adjacent which it is located, is preferably larger, more preferably at least 10% larger, than the mean dimension of the pores within the sheath. FURTHER MEASUREMENTS TO BE COMBINED WITH THE INVENTION The drill fluid preferably meets the generally known requirements which are required to make a HDD drilling, preferably without the requirement of bentonite or another drill clay. One of the important things is that the drill hole is maintained during drilling. Maintaining the hole is, a.o., important such that during drilling the drilling equipment will not get stuck in a collapsed drill hole, to be able to locate a filter within the hole after drilling, if required. Besides the drill fluid can provide for a good plastering/lining of the drill hole such that loss of drill liquid during drilling is limited and/or the drill hole does not collapse.

Preferably during the method the drill hole is temporarily lined, which is desired during drilling. Subsequently the lining is removed in a relatively short time span. Removal is important to realise a desired high water producing capacity.

The invention is possibly combined with the creation of a so called natural (gravel) surrounding filling of the well/filter tube during development of the pit. With a natural surrounding (or external) filling the space around a filter tube is not really filled with gravel/sand but a filtering layer around the filter tube is created by, after installing of the filter tube, removing from the naturally present soil around the filter tube, of smaller soil-, gravel- and sand particles during development of the well. The fine particles within the ground around the filter tube are flushed away from the ground and are dispensed through the drill hole of the filter tube. A grove fraction (coarse sand, gravel etc.) remains behind around at least a part of the filter tube. This fraction makes a so called natural filling around the filter tube, functioning as a filter layer.

Or the invention is combined with the provision of an artificial souurounding (or external) filling. With an artificial filling preferably in the drill hole a filter tube is located with a diameter (substantially) smaller than that of the drill hole, preferably such that around the filter tube within the drill hole a ring space {also called oversnijding) with a thickness at least 2 or 5 or 10 or 15 cm is made. The space around filter tube within the drill hole is subsequently filled with filter gravel. The filter gravel provides that no sand from the natural soil enters the filter, said differently the filter gravel prevent sand supply. Maintenance is also improved.

By providing a filling the effective diameter of the filter tube is virtually increased, by which its capacity for water passage increases, such that for a predetermined capacity a lower flowing speed at the external circumference of the filling suffices, such that the chance for contamination decreases. The invention also relates to a pit to remove water, which can e.g. be obtained by means of a method according to the invention. Such a pit is generally substantially free from lining agent and/or contains a natural or artificial filling.

The drill hole of the pit preferably has a water permeability at least substantially equal to that of the surrounding water package.

The invention also relates to a method to remove ground water, wherein ground is removed from the ground into which a pit (obtained) according to the invention is provided. Such a method is particularly suited to make drinking water, at least water of a proper microbiologically quality.

The invention also relates to a method to store/infiltrate water, wherein water is injected in a water bearing package through the pit according to the invention, e.g. obtained by means of the method of the invention. Such a method can e.g. be applied for energy storage, ground water management, soil cleaning, counteracting salinisation. Preferably the pit contains one or more of the following: within the drill hole a filter tube, such as a wound wire filter, located, e.g. at least within a part of the drill hole located in the water bearing package; close to the entrance and exit point blind tubes, if required, are located, to keep the hole open at said locations; at the entrance point and possibly at the exit point a pump room; a blind drill hole, wherein there is merely an entrance point and no exit point; a length of the part of the pit designed to allow the passage of water {the filter tube), within large limits, measuring e.g. at least 10m, at least 50 m, at least 100 m, or at least 300 m; a depth of the at least substantially horizontal part of at least 10 m, at least 30 m, or at least 100 m and/or at least 500 or 300 or 250 or 200 meter; a diameter, entrance angle, exit angle and/or other geometrical parameters selected within wide limits depending from the desired capacity; a filter tube designed to at least substantially block a relatively grove fraction {particularly with a particle size of at least 100 μm. (micrometer), more particularly at least 300 μm (micrometer) }; a filter tube which is, for proper development of the well, designed to allow passage of a fine fraction (like fine sand or a smaller fraction), e.g. with a filter opening of slit in the range from 0.1-0.4 mm, or a filter with a comparable permeability for soil particles; a relatively large open surface of the filter tube of 10% ore more, particularly to about 20% or more; a filter tube of stainless steel or plastic.

For the field of application of the invention the following applies in connection with applying a possible artificial filling around the filter tube: the available space in the drill hole is limited, such that via a tube with small diameter the filter gravel has to be supplied; since the space between the filter tube and the wall of the drill hole must be completely filled with filter gravel, the risk for blocking is large; carrying out detections and measurements at the outflow opening of the supply tube for the filter gravel within the space between the wall of the drill hole and the filter tube is problematic or even impossible such that the precise dosage of the filter gravel above the ground can not be made; the dosage point of the filter gravel within the drill hole moves during pouring out of the filter gravel across a large distance; pouring of the filter gravel in the drill hole must take place at a sufficient and controlled speed; the transport medium (water) used to supply the filter gravel through the supply tube to the drill hole, has to be able to be removed-

To solve one or more aspects of this problem, one could make use of a dispensing system for the filter gravel comprising e.g. a venturi pump. For that the venturi pump is equipped with a local restriction in a liquid transporting tube. Immediately downstream from the restriction the liquid stream creates a vacuum in the widening part of the tube. In said vacuum area the filter gravel are injected into the liquid stream. This pump type is insensitive for the abrading filter gravel, can provide a sufficient high pressure and is little sensitive for blocking and is cheap. Alternatively a (pulse free) positive displacement pump could be applied or a preferably rubbered centrifugal pump.

The dispensing system for the filter gravel can be designed to be wheeled, to be drawn with the from the drill hole coming supply tube for the filter gravel that are supplied to the drill hole.

The process of making an artificial filling can be monitored by continuously or intermittently measuring and/or controlling the weight of the above the ground present supply of filter gravel, from which filter gravel are injected into the tube to supply filter gravel to the drill hole and/or the speed with which said supply tube during supplying of the filter gravel is pulled from the drill hole. E.g. for that said supply of filter gravel is associated with a weighing device and/or the dispenser tube is associated with a velocity meter.

To fill the space around the filter tube within the drill hole the filter tube could be provided with redial spacers along its length (simple embodiment) . During drawing of the filter tube into the drill tube, the spacers bear against the wall of the drill hole and keep the filter tube spaced from the wall of the drill hole. E.g. the spacers keep the filter tube substantially centred within the drill hole. These spacers are e.g. provided by along a part of the length of the fill tube extending elongated slender bodies, such as strips, which are at their ends mounted to the filter tube and from said mounting location keep an increasing distance to the filter tube, to obtain midway their length the maximum distance to the filter tube. E.g. at least three or four spacers are provided at the same location along the length of the filter tube, wherein said spacers mutually keep a substantially equal angular distance. Simultaneously with pulling in of the filter tube or after that/ preferably one or more tubes are pulled into the drill hole, to supply filter gravel to and/or sucking away of liquid/water from the drill hole, respectively. Preferably care is taken that one or more of these tubes or at least the free end of them, is present in the top half of the drill hole, such that the filter gravel are poured from above onto the filter tube in the drill hole. E.g. these tubes have for that sufficient buoyancy, e.g. by adding one or more floaters. The tubes can have this buoyancy along their length, or merely at a free end. This one or more tubes can have at their end projecting into the drill hole a injection or dispenser nozzle. Subsequently this one or more tubes of the supply system for filter gravel are pulled from the drill hole, wherein simultaneously with said tubes filter gravel are injected into and liquid is removed from the drill hole, respectively.

Possibly one or more different tubes are present at low level, e.g. in the lower half of the drill hole e.g. to remove liquid, like drill liquid, although liquid could also be removed through the filter tube, while in the filter tube a further tube could be present which along its length is indeed or not liquid permeable and is used to supply or remove liquid. Besides care can be taken that the filter tube is temporary, e.g. during installing of the pit, sealed along its length.

Alternatively for filling the space around the filter tube in the drill hole, the filter tube could be provided with means to mechanically remove or to breach the lining or to cancel it. For that use could be made of a pulling head which around the already in the drill hole present and stationary filter tube is pulled into the drill hole, e.g. at a casing tube. The pulling head provides e.g. pulling force/driving power and/or contains one or more further tubes . This pulling head is preferably provided such hat it takes care for a seal between the part of the drill hole at its front and the part of the drill hole at its back. In this manner care can be taken that the drill hole at the one side of this pulling head contains de one liquid, e.g. the drill fluid, and at the other side of this pulling head contains the other liquid, e.g. substantially clean water. Thus one can ensure that during pulling the pulling head from the drill hole, the drill liquid is by the pulling head pushed from the drill hole, or that during pulling the pulling head into the drill hole, the drill liquid by the pulling head is pushed, e.g. from the drill hole through the opposite debouching end of the drill hole at the earth surface or through a drainage tube extending through the drill hole, parallel to the filter tube and in the direction of the debouching end of the drill hole but inserted from the pulling head.

Alternatively or in combination one preferably provides that the pulling head has a feature to mechanically disturb the wall of the drill hole, e.g. by one or more convenient projections present at the pulling head and penetrating the wall of the drill hole if the pulling head is located in the drill hole to process the material of said wall. E.g. said feature provides an eroding or cutting action. Preferably the members of said feature are present in one and preferably two or more mutually movable, e.g. turnable, sets, e.g. to circumvent an underground obstacle in the edge of the drill hole. Alternatively or in combination the feature can be provided with nozzles to provide liquid jets with which the wall of the drill hole can be processed for the same purpose. Alternatively or in combination one preferably provides that the pulling head has a feature to offer protection against collapsing of the wall of the drill hole, such that in said protected area the filter gravel can be poured into the drill hole around the filter tube without disturbance. An alternative could be, to make a First drill hole after which this is completely filled with filter gravel, after which in the filling of the first drill hole a second drill hole of smaller diameter is drilled, into which subsequently a filter tube of substantially the same diameter is pulled in.

Another alternative could be to make use of a flushing ring, e.g. to rescue or remove a filter tube, or to improve the soil.

Examples

Figure 1 shows a First system to make the filling around the filter tube in the drill hole (simple) ; figure 2 shows a cross section of fig. 1; figure 3 shows a second system for making the filling around the filter tube in the drill hole (firm); figure 4 shows a cross section of figure 3.

Figure 1 shows a horizontal drill hole 1 drilled according to the HDD-technique. It centrally contains a filter tube 2 of substantial smaller diameter, with along its length and spaced spacers 3 of which one is shown in the drawing. Each spacer 3 comprises four strips extending substantially parallel to the filter tube 2, which with their ends are mounted to the filter tube 2, and from the location of mounting keep an increasing distance to the filter tube to obtain halfway their length the largest distance to the filter tube. Thus the strips provide radial projections at the filter tube 2 and keep an equal angular spacing. Above the filter tube 2 a from the filter tube independent unit is present to provide around the filter tube the filling of filter gravel. This unit comprises a supply tube 4 for the mixture of filter gravel and transport liquid, and two exhaust tubes 5 to drain transport liquid. These tubes 4 and 5 debouch at substantially the same location into the drill hole 1. During provision of the filling this unit is with preferably substantially constant velocity in the direction of arrow A pulled from the drill hole 1, wherein simultaneously filter gravel come out of the in the drill hole projecting end of the tube 4 and liquid is sucked away at the adjacent openings of the tubes 5.

In stead of centring as shown in fig. 2, the filter tube 2 could be present at a different location in the drill tube 1, e.g. further down or up.

Figure 3 shows again a drill hole 1 with in it a filter tube 2. Across the filter tube 2 a pulling head 6 is pulled/ having a casing tube. The pulling head is provided with a crown 7 of knives which penetrate the wall of the drill hole 1, a crown of water jet nozzles 8 spaced from the wall of the drill hole 1 and directed towards said wall, two to the wall of the drill hole 1 engaging seals 9 and 10 axialIy spaced mutually, a crown of guides 11, a casing 12, a supply tube 4 for filter gravel and an exhaust tube 5 for liquid. The supply tube for the nozzles 8 is not visible in this drawing. While the filter tube 2 is stationary, the pulling head is in the direction of the arrow A pulled from the drill hole, while it processes the wall of the drill hole and pushes the original drill liquid forward and discharges filter gravel pouring liquid. The casing 12 ensures that the drill hole 1 is kept sufficiently opened in the area where the filter gravel are poured. In the embodiment of figure 3 the crown 7 is mounted fixedly. In an alternative embodiment it can be mounted pivotably around the centre line of the filter tube 2. Two or more such crowns 7 can be mounted to the pulling head behind each other.

Also different embodiments belonging to this invention are feasible, without going beyond the scope of the claims.. E.g. by applying a separate feature of an in here disclosed embodiment separately or in combination with one or more separate features of the same or of one or more different in here disclosed embodiments.

In connection with a filter tube which above the ground is already provided with a completely surrounding sheath/the circumference of the filter tube completely surrounding/covering jacket, preferably also one or more of the following is applicable, e.g. to lessen or avoid damage during one or more of storage, transport, handling and pulling in of the filter tube: a layer onto the outer side of the sheath, e.g. provided above the ground, wherein said layer is completely surrounding/covering the circumference of the sheath/jacket is e.g. of coherent material or prefabricated, e.g. a casing of paper or carton, or is afterwards provided at the outer side of the sheath as initially or permanently form free material, e.g. a coating or sliding agent, and provides e.g. an external reinforcement or a lost formwork or protective casing, wherein the layer can be designed to be removed from the filter tube before or after installing in the ground, e.g. by being soluble or degradable in contact with e.g. water, or to be provided with a feature to easily remove the layer, e.g. an embedded tear wire or weakening along the length of the layer; the parts of the sheath are mutually fixed by one or more of a stone like, mineral {e.g. blast furnace or Portland cement) , soil proper, brittle, weak, in water or a different solvent soluble, binding agent and/or are mutually released by one or more of enzymatic, biologic, mechanic and chemical manner (e.g. by dissolving in water of the binding agent) ; a for pulling in convenient external shape; application of slides or projecting sleeves at the external side of the sheath or a sliding agent at the internal wall of the bore in the ground or the into the bore located casing tube to lower the friction during pulling in; the sheath contains an internal reinforcement; the material around the filter tube is provided in one or more layers. To remove drill liquid or to let the drill hole collapse, application of one or more of bristles, scrapers, sprayers is preferred.

Thus the invention preferably relates to provide a filter bed of material around the underground filter tube avoiding ingress of undesired material, such as sand, into the filter tube, but of which the components {the filter sand or gravel) mutually have sufficient movement space such that contamination settled onto the components, can be released from it by, during a cleaning cycle between two terms of removal of ground water through the filter tube, providing that the components mutually move and rub, after which the contamination is removed through the filter tube.

Fig. 5 and 6 show a side and front view of a tube 2 with sheath 20 of sand and binder, e.g. produced by locating the tube 2 concentrically into a thin walled carton tube and filling the ring shaped inner space with the initially form free material for the sheath 20. The carton tube contains a tear rope such that it is easy to tear the tube open to remove it after the sheath is cured. The tube 2 projects at both sides beyond the tube 20 such that two or more tubes 2 with each a jacket 20 can easily be mutually connected.

Claims

1. Method to remove ground water through a pit wherein above the ground a filter tube (2) is enveloped by a, preferably tightly fitting, layer of coherent material and subsequently said sheathed/jacketed filter tube is installed in the ground (1) in a water bearing ground layer to become part of the pit, after which ground water from the surrounding through the pores in the jacket/sheath (20) flows inwards into the filter tube and said ground water is filtered by the sheath/jacket from undesired components.

2. Method according to claim 1, wherein one takes care that, after the sheathed filter tube is placed in the ground, the material of the sheath looses its coherent nature .

3. Method according to claim 1 or 2, wherein after locating of the filter tube in the ground, the sheath changes in a layer of loose granules of e.g. filter sand (particle size between 0.063 en 2 millimetre) or filter gravel (particle size at least 2 millimetre) around the filter tube.

4. Method according to claim 1, 2 or 3, wherein the sheath comprises a mixture of granules and binder and the binder substantially consists of gypsum.

5. Method according to any of claims 1-4, wherein the sheath is enveloped by a material layer of eg. carton which is removed before the tube (2) is brought into the ground, which material layer is preferably not or substantially worse water permeable than the sheath.

6. Method according to any of claims 1-5, wherein after locating the tube (2) into the ground one presses a fluid from the tube (2) into the sheath (20) such that the material of the sheath becomes incoherent.

7. Method according to any of claims 1-6, wherein the sheath is permanently coherent and pliable, e.g. foil like, a cloth, fabric, gaze, weave or braid, and water permeable.

8. Method according to any of claims 1-7, wherein the sheath is locally/spotwise with a spacing of at least 10 centimetre in longitudinal direction of the filter tube mounted to it.

9. Method of making a horizontal water pit, comprising preferably by means of HDD technique drilling of a pit in a water bearing package in the presence of a drill fluid, locating within the drill hole of a filter tube and developing of the pit.

10. Method according to any of claims 1-10, wherein for making an artificial filling around the filter tube a dispensing system for the filter gravel is used which contains a venturi pump or positive displacement pump or centrifugal pomp.

11. Method according to any of claims 1-10, wherein the filter tube is provided with radial spacers (3) along its length.

12. Method according to any of claims 1-11, wherein means (7, 8) are applied to during or after locating of the filter tube into the drill hole, disturb the wall of the drill hole.