GB2067233A

GB2067233A - A method of constructing a collector well

Info

Publication number: GB2067233A
Application number: GB8041371A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-12-29
Filing date: 1980-12-29
Publication date: 1981-07-22
Also published as: GB2067233B; JPS5697025A

Abstract

A method of constructing a collector well comprises embedding in the ground a chamber V one end of which includes connecting means for connecting a casing C, a lower end of which is open and a side wall of which is provided with port-holes. A first one of a set of casing lengths C is then connected to the connecting means, the casing being of smaller cross- section than the chamber V. Other casing lengths are then successively connected to the first casing length and to each other in sequence and embedded in the ground until the chamber V is at a depth where a suitable water bearing stratum occurs. Next, water collector tubes F are introduced into the water bearing stratum through the portholes. The chamber V and casing L are embedded on the ground by removing earth and mud from within the chamber and the casing lengths of the casing and by forcing the chamber and casing lengths into the ground, the water collector tubes being introduced into the water bearing stratum by force. <IMAGE>

Description

SPECIFICATION A method of constructing a collector well This invention relates to a method of constructing a so-called collector well having a casing embedded in the ground and connected at its bottom end to a chamber from which water collector tubes extend into a water bearing stratum of the ground.

It is a well known fact that collector wells possess a water yield that is several times the yield achieved by regular vertical wells. The constructional configuration of a conventional collector well is shown in Figures 1 and 2 of the accompanying drawings, wherein 1 denotes the casing and 2 the water collector tubes.

Hitherto, the construction of conventional collector wells has been as task involving several difficulties. The major difficulties can be grasped by examining the steps entailed in the construction of such a well. Figure 3 describes the steps in a commonly employed construction method, the sinking method. The first length 3 of a set of concrete casing lengths is placed on the ground where the well is to be constructed, this length being provided with a number of port-holes 7 for passing the water collector tubes therethrough into the water bearing stratum of the ground, and the earth within the casing is removed employing the claim shell 4, as in step (a) of Figure 2. The removal of earth causes the concrete casing length to sink under gravity into the pit formed, as in step (b).The removal of earth is continued until the same concrete casing length is completely sunk into the ground, a second length 5 of the set of concrete casing lengths then being placed on top of the first and the removal of earth continued, as in step (c). The process is repeated for each successive concrete casing length until a well depth is reached at which a suitable water bearing stratum S occurs in the ground, as in step (d). Finally, concrete is poured into the well to form a thick concrete plug 6 to seal the well bottom, and the water collector tubes are driven into the water bearing stratum through the port-holes 7.

One major problem often encountered in the sinking method is the difficulty in sinking the casing, in the manner desired, under the weight of the casing alone, for the friction between the casing and the surrounding soil is quite large. To obviate this, the usual practice is to remove more earth than is theoretically necessary. Even then, it may happen that the casing cannot be sunk as desired. It must be noted that one highly undesirable consequence of the removal of an excessive amount of earth is the resulting ground settlement which, with the passage of time, becomes serious and extends even to regions 10 to 20 meters away from the well. If measures are taken to avoid ground settlement, the costs involved become extremely high.

Another major problem is the upward movement of the casing concrete plug assemblage upon removal of the water which accumulates within the assemblage during the construction to allow the water collector tubes to be extended into the water bearing stratum of the ground. This upward movement is caused by the buoyancy exerted on the assemblage by ground water accumulating outside the assemblage, the buoyancy here being larger than the weight of the assemblage, and by the pressure of the ground water, which is usually high. To obviate this problem, the usual practice is to increase the weight of the assemblage by increasing the thickness of the casing. Again, this practice inevitably makes the costs in constructing the well high.However, if alternatively the outside diameter of the casing is made small to decrease costs and also minimise buoyancy, the weight of the casing will be insufficient to allow the casing to be sunk solely under its own weight.

In addition to these difficulties and high costs, the construction period for such wells is necessarily long.

According to the present invention, there is provided a method of constructing collector wells comprising: embedding in the ground a chamber an upper end of which includes a connecting means for connecting a casing, a lower end of which is being open and a side wall of which is provided with portholes; connecting a first one of a set of casing lengths to be the connecting means, the cross-section of the casing being smaller than the cross-section of the chamber and embedding the casing together with the chamber on the ground; connecting other casing lengths to the first casing length and to each other in sequence and embedding in the ground together with the chamber until the last of the casing lengths is embedded in the ground and the chamber is at a depth where a suitable water bearing stratum occurs; and introducing water collector tubes into the water bearing stratum through the port-holes in the chamber; the embedding of the chamber and the casing being effected by removing earth and mud from within the chamber and the casing lengths of the casing and by forcing the chamber and the casing lengths of said casing into the ground and the water collector tubes being introduced into the water bearing stratum by forcing the water collector tubes into said water bearing stratum of the ground.

As the cross-section of the casing is smaller than that of the chamber, and the cross-section of the casing possibly decreases away from the chamber, the heaving which is prevalent in well constructions is prevented.

Preferably, the forcing of the chamber and the casing is effected by employing a forcing cap capable of moving freely upwardly and downwardly and included in a forcing rig secured in place on the ground by two or more anchors buried in the ground.

Conveniently, the forcing cap is hollow and of an annular configuration and includes a plurality of vibrator means arranged in a closed loop within the forcing cap so as to produce a vibratory force to assist in the forcing of the chamber and the casing into the ground, or alternatively the plurality of vibrator means may be arranged in a closed loop on an upper exposed surface of the forcing cap so as to produce a vibratory force to assist in the forcing of the chamber and the casing into the ground.

Generally, earth and mud removing means are introduced into the chamber and the casing through an opening provided in the forcing cap so that earth and mud in said chamber and said casing can be removed at the same time as the chamber and the casing are forced into the ground.

Preferabiy, at least two water collector tubes are simultaneously forced in opposite directions into the water bearing stratum of the ground through two of the port-holes provided in the chamber.

Conveniently, sealing means are provided in the port-holes to prevent entry of ground water into the chamber during the forcing of the chamber on to the ground and the water collector tube and into into the water bearing stratum of the ground and further the exterior of each water collector tube may be covered with a water soluble material to prevent entry of ground water into the chamber during the forcing of the water collector tubes into the water bearing stratum of the ground.Also, the interior of each collector tube may be covered with a water soluble material to prevent entry of ground water into the chamber during the forcing of the water collector tubes into the water bearing stratum and preferably the interior of each water collector tube is provided with a sealing member to prevent entry of ground water into the chamber during the forcing of the water collector tubes into the water bearing stratum of the ground.

In order that the invention may be readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a longitudinal sectional view of a conventional collector well; FIGURE 2 is a plan view showing the arrangement of the water collector tubes of the collector well of Figure 1; FIGURE 3 is a diagrammatic view showing the stages in the construction of the conventional collector well of Figures 1 and 2; FIGURES 4 and 5 are diagrammatic views showing various stages in the construction of collector wells in accordance with respective construction methods embodying the present invention; FIGURE 6 is a side view of a preferred embodiment of the forcing rig for carrying out a method in accordance with the present invention;; FIGURE 7 is a sectional view of the forcing rig of Figure 6, taken along the line A-A of Figure 6; FIGURE 8 is a plan view of a preferred forcing cap for carrying out a method in accordance with the present invention; FIGURE 9 is a cross-sectional view of the forcing cap of Figure 8; FIGURE 10 is a plan view taken along the line B-B of Figure 11, showing the interior of the forcing cap when vibrator means is included in the cap; FIGURE 11 is a cross-sectional view of the forcing cap incorporating vibrator means; FIGURE 12 shows diagrammatically the direction of the force produced when eccentric weights of the vibrator means assume the position shown;; FIGURE 13 is a longitudinal sectional view of a well formed by a method in accordance with the invention, in which well the nature of the decrement in diameter along the axes of the diameter of the casing decreases in a stepwise manner with each succeeding casing length.

FIGURE 14 is a longitudinal sectional view showing the casing lengths of Figure 13 placed in a telescopic fashion inside the chamber for the purpose of transportation; FIGURE 15 is a longitudinal sectional view of a well casing, wherein the casing lengths are so shaped as to form a casing tapering away from the chamber; FIGURE 16 is a longitudinal sectional view of a preferred chamber for use in a method embodying the present invention; Figure 17 is a partial sectional view of a port-hole closed by a plug during the forcing of the chamber into the ground; FIGURE 18 is a partial sectional view showing the stages involving in forcing the water collector tubes into the water bearing stratum through the port-holes, and securing the tubes in place using the tube retainer;; FIGURE 1 9 is a partial cross sectional view of a water collector tube, showing the details of the fore end thereof; FIGURE 20 is a transverse sectional view of the water collector tube of Figure 19, taken along the line L-L of Figure 19; FIGURE 21 is a longitudinal sectional view of a single port-hole in the water of the chamber, showing the construction of a rubber seal for preventing any entry of ground water into the chamber during the forcing of the water collector tube into the water bearing stratum of the ground and a cock for controlling the flow of ground water into the well after the completion of the well; ; FIGURE 22 is a partial longitudinal sectional view showing stopper rodds installed in a water collecting tube for preventing the entry of ground water into the chamber through the water collector tube when said tube is being forced into the water bearing stratum of the ground; FIGURE 23 is a transverse sectional view taken along the line M-M of Figure 22; FIGURE 24 is a plane view of a preferred water collector tube forcing means for use in a method embodying the present invention to force two lengths of water collector tube simultaneously in opposite directions into the water bearing stratum of the ground; FIGURE 25 is a longitudinal sectional view of the preferred chamber for use in a method embodying the present invention when the upper strata of the ground are of a weak nature;; FIGURE 26 is a transverse sectional view of the chamber of Figure 25, taken along the line N-N of Figure 25; and FIGURE 27 is a longitudinal sectional view of a preferred chamber and casing assembly for use in a method in accordance with the present invention when the level of ground water is low.

One preferred embodiment of the method of constructing collector wells according to the present invention will now be described with reference to Figure 4.

Referring to steps (a), (b) and (c) illustrated by Figure 4, a steel chamber V having a diameter of between 2 and 3 metres and completely open at a lower end 8 is placed upright on the ground G where the collector well is to be constructed, and a first length 9 of a set of casing lengths C of approximately 1 metre diameter is placed over the chamber V and welded along the junction 10. A jetting arrangement Q for cutting and removing the earth from with and around the chamber V is then introduced into the chamber V through the casing C, the said jetting arrangement comprising at the lower end thereof a slurry pump 11, a slurry discharge pipe 12 connected to the slurry pump 11, a water ejector pipe 13 and vibrator means 14 attached to a forcing cap 1 5 placed at the upper end of the casing C.The forcing cap also supports the water ejector pipe 13 and the water discharge pipe 12. The resulting casing length and chamber assemblage is driven into the ground by ejecting water through the water ejector pipe 13 and actuating, at the same time, the slurry pump 11 and the vibrator means 14. The water jet from the water ejector pipe 13 cuts and washes away the earth while the slurry pump 11 removes through the slurry discharge pipe 12 the slurry formed within the chamber V so that the casing length and chamber assemblage sinks under gravity into the pit formed, which pit is deepened progressively by the slurry removal. A space 1 6 outside the casing length and chamber assemblage is now filled with gravel 18 as the deepening of the pit continues.When the first casing length has been driven completely into the ground, a second casing length is connected to the first casing length and driven as before. The process is repeated with the other casing lengths until the requisite well depth is reached, that is the depth of a water bearing stratum 22, at which point concrete is poured into the casing to form at the bottom of the well a thick concrete plug 17, the space exterior to the casing and surrounded by soil strata 21 is filled with gravel 18, the jetting arrangement Q is removed, and water collector tubes F are introduced into the water bearing stratum 22 after removal of all the water which has accumulated within the chamber V, as illustrated at (d) in Figure 4. Finally, water pump 19 and water delivery pump 20 are installed and the well is completed, as shown at (e) in Figure 4.

In a second embodiment of the method of constructing collector wells according to the present invention, anchors 105 are buried at the corners of a square encompassing the well location, as shown at (a) in Figure 5. A forcing rig M for forcing the casing length and chamber assemblage into the ground is placed at the well located and secured in place using the previously buried anchors 105 buring previously as shown at (b) in Figure 5. The chamber V is then placed inside the forcing rig M and a forcing cap P is set over the chamber V, as shown at (c) in Figure 5. A clam shell 106 is introduced into the chamber V and the chamber V is forced into the ground by actuating the forcing rig M and removing the earth by the clamshell 106, as shown in (d) in Figure 5.

After the chamber V is forced completely into the ground, the first casing length 107 is connected to the chamber V and the resulting casing length and chamber assemblage is forced into the ground, as shown at (e) in Figure 5. Once this casing length and chamber assemblage has been forced completely into the ground, a second casing length 108 is connected to the first and the resulting casing length and chamber assemblage W is forced into the ground, as before. The process is repeated with a third casing length 109 and other lengths until the requisite well depth is reached, as shown at (f) and (g) in Figure 5 the well depth then reaching a water bearing stratum Y (the soil strata X above this being nonpermeable).Concrete is next poured into the well to form a concrete plue 110 at the bottom of the well and finally water collector tubes are introduced into the water bearing stratum Y as described in connection with the previous embodiment.

The forcing rig M, forcing cap P and earth removal arrangement will now be described in more detail.

Referring to Figure 6 and 7, the forcing rig M comprises: a rig formed by erecting each of four columns 119 at the corners of a square base 120 and connecting the upper ends of the columns to a frame 121 to form a rigid structure; and a forcing cap P which is capable of sliding vertically upwardly and downwardly guided by the columns 119 and which is actuated by two endless wire loops 122 and 122' connected to the cap P at diametrically opposite points on the top and bottom surfaces thereof.

The upper parts of the endless wire loops pass over two freely rotatable pulleys 123 and 123' suspended from the frame 121, and the lower parts pass around the drums of two winches 124 and 124' such that two endless wire loops 122 and 122' undergo identical and simultaneous motions, enabling the forcing cap to slide vertically upwardly and downwardly freely without any transverse and angular motions. Those parts of the endless wire loops 122 and 122' engaging in the downward pulling of the forcing cap P are provided with the springs 125 and 125' to ensure uniform pull and to absorb excessive shocks occurring during the forcing operation.

The forcing cap P is made of steel and, as shown in Figures 8 and 9, is of an annular configuration having a central opening 126 for permitting the introduction of the clamshell 106 into the chamber of the well, a hollow internal space 127 and a ring 138 at a bottom external surface 138 thereof for engaging with the bore of the chamber or the casing lengths of the well. The diameter of the ring 138 is variable, the variation being effected by using an adaptor ring of the requisite diameter, replacing the ring 138 with a ring of requisite diameter or employing any of the known or available methods to make the diameter of the ring 138 adjustable.

An estimate of the force necessary for forcing the chamber and the casing lengths into the ground in the embodiment just mentioned will now be derived. If the bore diameter and the length of the chamber are respectively 2.5 and 4.0 metres, the bore diameter and the length of each casing length respectively 2 and 16 metres, the depth of the well 30 metres, the mean soil pressure on the surfaces of the chamber and the casing lengths 5 t/m2, and the coefficient of friction 0.3, the effective force necessary for forcing the chamber and the casing lengths into the ground then becomes ((2.5 x 4) + (2 x 26)) x 76 X 5 X 0.3, that is, 292 tonnes.

To produce such a force, it is necessary that the anchors withstand a pull equal to this force.

However, taking the weight of the forcing rig into account and assuming it as, say, 20 tonnes, the minimum pull the four anchors must withstand together becomes (292 -20) tonnes, that us, 272 tonnes; or 68 tonnes per anchor. If the anchors are buried at a depth of 30 metres, this pull can be easily withstood as, with the anchoring techniques available today, a single anchor at such a depth can be made to withstand a pull of about 100 tonnes. If the pull cannot be withstood by a single anchor, two anchors may be employed at each of the four points. This reasoning is valid for well depth up to 50 metres.

Particularly, for well depths greater than 50 metres, the vibrator V1, the details of which are as shown in Figures 10 and 11, is attached inside the hollow space 127 of the forcing cap.

Two electric motors 129 and 129' running in opposite directions are mounted at diametrically opposite points on a base 133 of the forcing cap, which is a circular steel plate having a central opening. Four unbalanced rotatable weights 131, 131 132 and 132' of the same shape, size and weight are freely rotatably mounted on suitable bearings on the base 133, two of the weights being separated from the other two by the electric motors 129 and 129'. The weights and motors form a closed loop in the space 127. Rotation of the unbalanced weights is effected by bevel gears 130 and 130' having equal numbers of teeth and fixedly incorporated one at each end of the shafts of each motors. The unbalanced weights are arranged so that all the weights point in the same direction.Once the motors are running and the weights are in motion, the forcing cap experiences an upward force when the weights point downwardly as is shown at (a) in Figure 12 and a downward force when the weights point upwards as shown at (b) in Figure 12. If the vibrator is attached firmly to the forcing cap, the cap undergoes a vibration of the same frequency as the vibrator; but, if the vibrator is merely placed inside the cap an elastic element is disposed between the two, the cap undergoes irregular vibration at a particular frequency dependent upon the nature of the elastic element. Although the two types of vibrations are effective, the latter is known to be more effective in producing strong repetitive impulses in, for example, impact rammers.

Although the vibrator was mentioned as being incorporated inside the hollow space of the forcing cap, it may also be attached to or placed on the top surface of the cap (in this case the cap need not be hollow if this is convenient.

Referring to Figure 6, the earth removing arrangement comprises a derrick 134, a wire 135, a winch 136 and clamshell 106. A boom 137 of the derrick134 is capable of moving sideways and vertically so as to transfer, lower or raise the clamshell, the chamber or the casing lengths.

Alternatively, instead of the above described earth removing arrangement, an arrangement somewhat similar to a reverse circulation drill may bs used. The arrangement should be such that it permits a swift and easy addition of the casing lengths during the forcing of the chamber and the casing lengths into the ground.

The forcing cap here should be such that it can be easily removed whenever a new casing length is to be added, and its construction of sufficient strength to withstand the forces occurring during the forcing of the chamber and the casing lengths into the ground.

Referring to Figure 13, the casing is preferable so formed that the diameter of each successive casing length is smaller than that of the preceding length.

A first length C1 of the casing is welded to a flange 209 of the chamber V along a junction 208, a second length C2 is welded to a flange 210 of the first length, the second length being of a slightiy larger diameter than that of the first. The process is repeated for all successive lengths.

The reason for giving the casing such a shape is that during the digging of the well pit, the wall R of the pit undergoes gradual heaving so that the diameter of the pit becomes gradually smaller towards the top end giving the pit a somewhat conical form; this causes an increase in the frictional resistance during the forcing of the casing lengths into the pit, owing to an increase in the soil pressure caused by the heaving. Thus if the casing is of a conical configuration, less frictional resistance occurs during the forcing operation than if the casing is of the same diameter throughout the entire length thereof.

Referring to Figure 16, a preferred chamber V for use in the above embodiments comprises a steel cylinder 214, open at both ends, the upper end being provided with a stepped flange 212 for connecting an inner surface 21 3 of the first casing length 107 by welding 211 to the steel cylinder, and the lower end with a cutter shoe 21 5 for cutting the soil while the chamber is being forced into the ground. Wedges 21 6 are attached to the steel cylinder at a height 1 from the lower end thereof to break up any soil left undug by the clamshell at the internal periphery of the chamber V and to prevent the concrete plug (poured to a thickness 1, after the chamber and the casing lengths are forced completely into the ground, to serve as a bottom) from getting displaced upwards.Brackets 2 8 and 218' are provided in the chamber to support the means for forcing the water collector tubes into the water bearing stratum of the ground through port-holes 217 and 21 7' formed in the side wall of the chambers.

Plugs 225 and 225' are provided in the port-holes to prevent the entry of ground water into the chamber through the port-holes while the chamber is being forced into the ground.

The diameter of the chamber should be sufficient to provide space for two men to operate the means for forcing the water collector tubes into the ground, when at least two water tubes are being simultaneously forced into the ground in opposite directions.

The difference in the diameters of the first casing length and the chamber should be appropriate, as too large a difference in the two diameters would result in a large gap between the well pit wall and the casing, allowing ground water to accumulate in the gap and resulting in soild flowage, or even soil failure in the well pit while the casing lengths are being forced into the ground. A gap of say 20 cm is considered appropriate.

The provision of a step-wise decrement in the diameter of the casing also produces advantages as regards transportation. Referring now to Figure 14, the casing lengths C1, C2 and C3 have diameters such that they can be placed inside the chamber in a telescopic fashion whereby space, time and money can be saved substantially in transportation, compared to conventional collector well casings.

Alternatively, the chamber and the casing may linearly decrease in diameter to produce a conical configuration, as shown in Figure 1 5.

As evident from the descriptions given so far, the construction of collector wells by a method embodying the present invention entails a short period of construction as the quantity of soil to be removed is small even for wells having depths of about 30 metres, this being attributable to the small diameter of the casing as compared to that of convention collector wells. A short period of construction undoubtedly implies reduced construction costs.

It should be noted that the preferred embodiments of the method of constructing collector wells according to the present invention described so far applies to soils where the water bearing stratum is preceded by a hard soil stratum.

A fourthe embodiment of a method of constructing collector wells in accordance with the present invention is as described below, and suitable for use where the water bearing stratum is preceded by a soft soil will now be described with reference to Figures 25 and 26. A casing 236, with casing lengths all of about 1 metre diameter, is connected to a chamber 237 having a diameter of about 2 to 3 metres by the brackets 238. When the chamber and the casing lengths are forced into the soil, the fir.st casing length and the chamber are welded together with the brackets to form a single assemblage, and this assemblage is driven into the ground employing a driving means like that employed in pile driving.

The driving is continued welding the successive casing lengths on one at a time. Once the driving of the chamber and the casing lengths to the required depth is completed, the soil within the chamber and the casing is removed using a grab bucket. The space 239 between the chamber and the casing, at the lower end of the latter, is then covered by attaching plates 240 welding or some other method, and concrete is poured into the well bottom to form a thick concrete plug. The water collector tubes are driven into the water bearing stratum as described above with reference to the other embodiments.

Noteworthy features in the embodiment just described are that the chamber and the casing can be easily driven into the soil employing a driving means like that employed in pile driving; the soil within the casing and the chamber can be removed using a grab bucket or other similar means; and the casing the chamber cannot undergo any displacement upwards as the chamber, being of a diameter larger than that of the casing, serves as an anchor to prevent such displacement.

When the water content of the soil is not high and the level of the ground water is a little above -the water bearing stratum, it is preferable, as shown in Figure 27, for the chamber 241 and casing 242 to be of the same diameter.

Detailed descriptions of the forcing of the water collector tubes in the above described embodiments will now be given.

The port-holes which allow the water collector tubes to pass through the chamber are made in the chamber wall at the time of constructing the chambers. Therefore, water effuses through these holes once the chamber is forced into the water bearing stratum, making work within the chamber during forcing of the water collector tubes into the water bearing stratum difficult. Thus it becomes necessary to have all the port-holes plugged or closed while the chamber is being forced into the ground.

Referring to Figure 17, the plugging of the port holes is done by providing the chamber wall 223 with an internal thread 224 and by screwing a plug 225 made of steel onto this thread. When forcing a water collector tube into the water bearing bearing stratum, the plug 225 is first removed and, as shown at (a) and (b) in Figure 18, a steel bush 227 provided with a rubber seal packing 226 is screwed onto the thread 224 of the chamber wall 223 and the water collector tube F is forced into the water bearing stratum through the rubber seal. The rubber seal is provided with holes N, including one running longitudinally, so that water-tight sealing is produced when the water collector tube is being forced through it.

After the water collector tube has been forced into the water bearing stratum, the steel bush 227 together with a rubber seal 226 may be either retained, or replaced by a lock bush 228, as shown at (c) in Figure 1 8, for securing the water collector tube in place screwing onto the thread 224 of the chamber wall 223.

Referring to Figures 19 and 20, a forward end of the water collector tube F has a conical head 229 and a suitable number of intake slits 230 are formed in the tube wall 231 of the tube F to permit the entry of ground water into the tube.

The intake slits 230 are so dimensioned that the strength of the water collector tube is not affected and the entry of sand and mud through same is prevented. Also each water collector tube is an assemblage of several tube lengths, each length having a length less than the internal diameter of the chamber and taking into account the allowance necessary for forcing two tube lengths at a time in opposite directions. The forcing of the water collector tubes in a single direction is effected by forcing the tube lengths into the water bearing stratum one by one after connecting the one to be forced to that already forced. The rear end of the last tube length is fitted with a cock 318, as shown at (c) in Figure 21, to allow work to continue inside the chamber if ground water effuses in such quantities as to affect the continuation of work inside the chamber.

Alternatively, as shown at (a), (b) and (c) in Figure 21, in order to prevent entry of ground water through the port-holes a rubber seal 308 having the illustrated cross-section is attached to a port-hole 307 of chamber wall 306 by an annular piate 309 and screws 310, indicated at (a) in Figure 21. The seal 308 prevents the entry of ground water into the chamber while the chamber is being forced into the ground. When a water collector tube F is forced into the water bearing stratum, conical head 311 of the tube pierces thin central region 312 of the rubber seal and the seal assumes a shape which provides highly watertight sealing, as shown at (b) in Figure 21 (b).

Referring to (c) in Figure 21, the entry of ground water through the inlet slits of the water collector tubes into the chamber while the water collector tubes are being forced into the water bearing stratum is prevented by covering the exterior of the tubes with a water soluble tape 313 and bonding the tape to the tube by means of a water soluble adhesive. The water soluble tape and adhesive are such that they begin to dissolve in the surrounding ground water to permit the entry of the water into the tube through intake slits 305 only a few hours after forcing of the tubes into the water bearing stratum thereby enabling the forcing of the tubes into the water bearing stratum to be effected conveniently and efficiently. The water soluble tape and adhesive referred here are preferably made of vegetable starch, such as pullulan.The time at which dissolution begins is prolonged by the addition of a suitable delaying agent. The entry of ground water through the intake slits may also be prevented by coating the water collector tubes externally and/or internally with only the vegetable starch as to fill the intake slits completely.

The entry of ground water through the inlet slits may be prevented by stopper rods T as shown in Figures 22 and 23. The stopper rod T comprises the a rubber seal 314 which come into contact with the inner wall of the water collector tube to produce water-tight sealing when the rod T is placed inside the water collector tube F, which is also covered with water soluble tape 313. A tube 315 is provided for holding the rubber seal 314, and hinges 316 and 317 are provided at both ends of the tube 315 to flexibly connect the stopper rods to any desired length. The stopper rods can also be pulled and pushed through the water collector tube no matter what degree of bending the latter may undergo during the forcing thereof into the water bearing stratum.Before forcing a water collector tube into the water bearing stratum, a suitable number of the stopper rods connected end to end are inserted into the water collector tube and the forcing operation then performed. Upon completion of the forcing operation, the stopper rods are removed by pulling same by a rope attached to the eye of the hinge 317 of the last stopper rod.

Once the water collector tube is completely forced into the water bearing stratum, a cock 318 is fitted to the tube, as shown at (c) in Figure 21, for the purpose of regulating the flow of ground water into the chamber.

Figure 24 shows in detail the means for forcing the water collecting tubes into the water bearing stratum. The forcing means K comprises the oil hydraulic cylinders 232 and 232' for forcing the water collector tubes F and F', forcing shoes 234 and 234' attached to the piston rods 233 and 233' of the hydraulic cylinders and the frame 235 for holding the hydraulic cylinders rigid.

In operation, the forcing means K is placed inside the chamber such that the centres of the hydraulic cylinders 232 and 232' coincide with those of two port-holes of the chamber, and secured firmly. Then two lengths of the water collector tubes F and F' are placed between the forcing shoes 234 and 234' and the port-holes of the chamber V after extending the two piston rods to their maximum lengths. The hydraulic cylinders are then actuated and the two water collector tube lengths are simultaneously forced by the shoes 234 and 234' into the water bearing stratum piercing through the rubber seals of the port-holes in the chamber, in respective diametrically opposite directions, parallel to the diameter of the chamber.

The forcing of a single length of water collector tube into the water bearing stratum is done in two stages, first by forcing the tube length through a distance equal to the stroke of the oil hydraulic cylinder, and second by forcing the tube length through an equal distance into the water bearing stratum using a spacer rod, so that the fuil length of the water collector tube is forced into the water bearing stratum. When forcing further tube lengths, each of a pair of additional lengths is first connected to a respective one of the lengths already forced into the water bearing stratum, When the last lengths of the water collector tube have been installed their rear ends are secured in place using the lock bush 228 described previously and shown at (c) in Figure 1 8.

The forcing means just mentioned enables the small and limited space available inside the chamber to be used effectively and allows two water collector tubes to be forced into the water bearing stratum at the same time in opposite directions safely and efficiently. When only a single water collector tube is driven at a time, as in conventional methods they employ impact hammers, such as diesel hammer, an impulse equal to or less than that with which the tube is driven into the water bearing stratum acts on the part of the chamber wall against which the driving means rebounds. To withstand the impulse, the chamber has to be reinforced, for the chamber wall is relatively thin, and the reinforcement necessitates a large number of structural members that entail high costs and occupy a large space within the chamber.Thus, if the water collector tubes are forced two at a time in opposite directions, the impulses due to reaction are counter-balanced and no resultant horizontal forces act on the chamber wall.

In another embodiment the water collector tubes may be driven into the water bearing stratum using means such as impact hammers.

When employing impact hammers, two such hammers are arranged so that two lengths of water collector tube can be driven into the water bearing stratum at the same time in opposite directions as in the case of the forcing means described previously. However, in such an arrangement, differences in the times at which the hammers strike the tube length ends can occur, producing reactions that are out of phase and may even be different in magnitude, causing the chamber to experience shocks and vibrations. This defect is eliminated by having two hammers mounted over an elastic material like rubber, or over springs. The positioning and operation of the hammers is analogous to that of the forcing means described before.

As is evident from the foregoing descriptions, a method of constructing wells in accordance with the present invention may provide the following advantages: a. As the peripheral length of the cross-section of the casing is smaller than that of the crosssection of the chamber, or as the casing can be of a configuration where the cross-sections of the casing decrease towards the upper end, the occurrence of heaving, which is prevalent in all well construction methods, is prevented.

b. As the forcing of the casing length and chamber assemblage into the ground is effected by including the vibrator means is the forcing cap which also permits at the same time the removal of the earth and mud within the chamber while the casing chamber assemblage is being forced into the ground, the forcing operation is both speedy and efficient, compared to that in conventional well construction methods.

c. As the forcing of the water collector tubes into the water bearing stratum is effected at a rate of at least two at a time, in opposite directions, and a vibrator means may be included in the forcing means, the forcing operation is both speedy and efficient, compared to conventional well construction methods.

d. As the entry of ground water through the port-holes or through the water collector tubes into the chamber is prevented, work inside the chamber in forcing the water collected tubes into the water bearing stratum is both speedy and convenient, compared to conventional well construction methods.

e. As the entry of ground water through the intake slits of the water collector tubes into the chamber is prevented by employing a water soluble material or stopper rods, the forcing of the water collector tubes into the water bearing stratum is speedy, efficient and convenient.

f. As the forcing operations in the method of constructing collector wells according to the present invention are speedy, efficient and convenient, the costs entailed are low and the construction period short, compared to conventional well construction methods.

Claims

1. A method of constructing collector wells comprising: embedding in the ground a chamber, an upper end of which includes a connecting means for connecting a casing, a lower end of which is being open and a side wall of which is provided with port-holes; connecting a first one of a set of casing lengths to the connecting means, the cross-section of the casing being smaller than the cross-section of the chamber and embedding the casing together with the chamber in the ground; connecting other casing lengths to the first casing length and to each other in sequence and embedding in the ground together with the chamber until the last of the casing lengths is embedded in the ground and the chamber is at a depth where a suitable water bearing stratum occurs; and, introducing water collector tubes into the water bearing stratum through the port-holes in the chamber; the embedding of the chamber and the casing being effected by removing earth and mud from within the chamber and the casing lengths of the casing and by forcing the chamber and the casing lengths of said casing into the ground and water collector tubes being introduced into the water bearing stratum by forcing the water collector tubes into said water bearing stratum of the ground.

2. A method according to Claim 1 wherein the forcing of the chamber and the casing is effected by employing a forcing cap capable of moving freely upwardly and downwardly and included in a forcing rig secured in place on the ground by two or more anchors buried in the ground.

3. A method according to Claim 2 wherein the forcing cap is hollow and of an annular configuration and includes a plurality of vibrator means arranged in a closed loop within the forcing cap so as to produce a vibratory force to assist in the forcing of the chamber and the casing into the ground.

4. A method according to Claim 2 wherein a plurality of vibrator means are arranged in a closed loop on an upper exposed surface of the forcing cap so as to produce a vibratory force to assist in the forcing of the chamber and the casing into the ground.

5. A method according to Claim 2, 3 or 4 wherein earth and mud removing means are introduced into the chamber and the casing through an opening provided in the forcing cap so that earth and mud in the same chamber and said casing can be removed at the same time as the chamber and the casing are forced into the ground.

6. A method according to any preceding claim wherein at least two water collector tubes are simultaneously forced on opposite directions into the water bearing stratum of the ground through two of the port-holes provided in the chamber.

7. A method according to any preceding claim, wherein sealing means are provided in the portholes to prevent entry of ground water into the chamber during the forcing of the chamber on to the ground and the water collector tubes and into the water bearing stratum of the ground.

8. A method according to any preceding claims, wherein the exterior of each water collector tube is connected with a water soluble material to prevent entry of ground water into the chamber during the forcing of the water collector tubes into the water bearing stratum of the ground.

9. A method according to any preceding claim, wherein the interior of each water collector tube is covered with a water soluble material.

10. A method according to Claim 8 or 9 wherein the water soluble material comprises a water soluble tape bonded to the tube by a water soluble adhesive.

11. A method according to any preceding claim, wherein the interior of each water collector tube is provided with a sealing member to prevent entry of ground water into the chamber during the forcing of the water collector tubes into the water bearing stratum of the ground.

12. A method of constructing a collector well substantially as hereinbefore described with reference to the accompanying drawings.

13. Any novel feature or combination of features disclosed herein.