US3858398A

US3858398A - Method of and apparatus for making sand drains

Info

Publication number: US3858398A
Application number: US373920A
Authority: US
Inventors: Weele Abraham Francois Van
Original assignee: Vibroflotation Foundation Co
Current assignee: Vibroflotation Foundation Co
Priority date: 1969-08-19
Filing date: 1973-06-27
Publication date: 1975-01-07
Anticipated expiration: 1992-01-07

Abstract

Sand drains are provided in low permeability compressible stratum to accelerate drainage of water and settlement which occurs when the stratum is subjected to loading. To form the sand drain with a minimum of disturbance to the particles surrounding the drain, a heavy, elongated bailer having downwardly and upwardly directed nozzles is raised and lowered repeatedly. Such repeated motion of the bailer produces a pulsating cutting action with a water jet discharged under high pressure from the downward nozzle to remove particles of the stratum and form a hole through the stratum. The bailer motion also produces a pulsating hole cleaning action of water jets discharged under high pressure from the upward nozzles. The water jets from the upward nozzles carry the particles out of the hole and also expose the interstices between particles forming the wall of the hole. When the hole is formed to the desired depth, the bailer is kept at the bottom of the hole to flush the particles from the hole, is removed from the hole and is then lowered for another flush cycle. As the bailer is removed from the hole, water from the upward jets washes the walls of the hole to keep the interstices between the particles forming the wall of the hole open. The hole is then slowly back filled with coarse sand which fills the hole at a rate such that the interstices remain open.

Description

Van Weele tats Ptent r191 METHOD OF AND APPARATUS FOR MAKING SAND DRAllNS [75] Inventor: Abraham Francois Van Weele,

Waddinxveen, Netherlands [73] Assignee: Vibrotlotation Foundation Company, Pittsburgh, Pa.

22 Filed: June 27,1973 21 App1.No.:373,920

abandoned.

[52] 11.8. C1 61/11, 6l/53.74, 61/63 [51] Int. Cl E02b 11/00, E02d 5/34 [58] Field of Search 61/11, 10, 53.5, 53.52,

[56] References Cited UNITED STATES PATENTS 1,293,693 2/1919 Burns 61/5374 1,435,144 11/1922 Bignell 6l/53.74 3,020,965 2/1962 Keller, Jr. 61/53.74 X 3,478,524 ll/l969 Hoppe 61/63 3,608,317 9/1971 Landau 61/11 Primary Examiner.lacob Shapiro ,lan.7, 1975 [57] ABSTRACT Sand drains are provided in low permeability compressible stratum to accelerate drainage of water and settlement which occurs when the stratum is subjected to loading. To form the sand drain with a minimum of disturbance to the particles surrounding the drain, a heavy, elongated bailer having downwardly and up wardly directed nozzles is raised and lowered repeatedly. Such repeated motion of the bailer produces a pulsating cutting action with a water jet discharged under high pressure from the downward nozzle to remove particles of the stratum and form a hole through the stratum. The bailer motion also produces a pulsating hole cleaning action of water jets discharged under high pressure from the upward nozzles. The water jets from the upward nozzles carry the particles out of the hole and also expose the interstices between particles forming the wall of the hole. When the hole is formed to the desired depth, the bailer is kept at the bottom of the hole to flush the particles from the hole, is removed from the hole and is then lowered for another flush cycle. As the bailer is removed from the hole, water from the upward jets washes the walls of the hole to keep the interstices between the particles forming the wall of the hole open. The hole is then slowly back filled with coarse sand which fills the hole at a rate such that the interstices remain open.

4 Claims. 8 Drawing Figures law/jaw \s/ was Patented A Jan. 7-,- 1975.

3 finds-Shoat 1 INVENTOR ABRAHAM FRANCOIS VAN WEELE FlG.2r

BY DAVID S. UREY ATTORNEY Patented Jan. 7., 1975 3,858,398

3 Shoots-Shoo). 2

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WWW/W IQV/MQW/AQWNN NWN W4 v LAM 'I INVENTOR ABRAHAM FRANCOIS VAN WEELE BY DAVID s UREY ATTORNEY Patented Jan. 7, 1975 3,858,398

3 Shouts-Sheet 5 (PRIOR ART) r INVENTOR f ABRAHAM FRAN COIS VAN WEELE DAVID S. UREY ATTORNEY METHOD OF AND APPARATUS FOR MAKING SAND BRAINS This is a continuation of application Ser. No. 851,353, filed Aug. 19, 1969, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to methods of and apparatus for making sand drains and, more particularly, to methods of and apparatus for minimizing the effect which the method of making the sand drain has on the portion of the stratum adjacent to the drain and for enhancing the draining capability of a completed sand drain by maintaining the interstices between particles forming the wall of a sand drain hole in an open condition.

In the selection of sites and rights-of-way for constructing buildings and highways, adverse subsurface soil conditions are often encountered. For example, highly compressible, relatively impermeable subsurface strata are often found at locations where construction specifications require significant subsurface load bearing capacity. In particular, clay, which is a highly con pEssibIefr ela t iveIy impermeable material, consists mainly of very small, particles which are interconnected by microscopically small pores. If the pores are filled with water, the clay stratum can be compressed only if the water is drained off. When a downward load is applied to the clay stratum, the pore water will be subjected to increased pressure. Consolidation will then take place, i.e., under constant load there will be a gradual decrease in the size of the pores between the particles of the clay stratum as the pore water flows very slowly to strata under nonloaded areas of the site.

The consolidation of the loaded stratum will take place during the time that it takes the water under excess pressure to flow from the pores. When such stratum is horizontally layered, the permeability thereof may be as much as ten times greater in the horizontal direction as in the vertical direction, thus the horizontal distance .to coarse-grained, easily drained strata is an important factor in determining time necessary to consolidate such a clay stratum. If the impermeable stratum is subjected to significant loading before it consolidates, it is likely that shear failure of the stratum will occur. As a result, the load and the stratum may become inverted, for example. Obviously, such inversion or other failure must be avoided. Thus, the achievement of relatively rapid consolidation is essential to minimizing construction time.

Vertical holes formed at spaced locations in the ground and extending through impermeable strata are filled with coarse, highly permeable sand to receive water from the impermeable strata and drain the water upwardly and downwardly to permeable strata. When properly installed, sand drains are effective to substantially reduce the time required to consolidate the impermeable strata.

2. Description of the Prior Art Vertical sand drains have been formed in the past using a variety of methods and apparatus. In particular, rotary drills have been used to form sand drain holes. Further, rotating water jet heads having a downwardly directed nozzle have been lowered into the ground to form sand drain holes.

Also, in sand drains formed by the displacement method, a hollow pipe having a closed lower end has been driven into the ground by displacing the existing soil, the pipe filled with sand, the lower end opened, and the pipe withdrawn to leave the sand in the hole formed by displacement. Driven sand drains have also been formed by forcing cardboard wick-like elements into the ground.

As known to applicant, with the exception of the driven wick method, all of these methods utilize a hollow, sand filled casing which is pulled from a sand drain hole leaving the sand in the hole. The removal of the casing smears the walls of the sand drain hole.

These prior methods and apparatus have been used at various times since the first sand drain was installed in 1934. As indicated in over papers which have been published on the sand drain installations, these methods have not been reliable in that numerous sand drain installations have not successfully assisted in the consolidation process. Moreover, although some of the causes for the ineffectiveness of sand drains formed using certain of the prior methods were identified over twenty years ago, methods currently used for installing sand drains include the steps which have been identified as contributing to such ineffectiveness.

SUMMARY OF THE INVENTION Research conducted in endeavor to provide sand drains which are reliable and provide maximum drainage from impermeable strata indicates that methods of and apparatus for installing sand drains should have a minimum effect on the soil between adjacent sand drains and should leave the interstices between soil particles forming the wall of sand drains in an open condition. To achieve these objectives, the soil adjacent to a sand drain hole is subject to a minimum of vibration during formation of the hole so that the permeability of such soil is not reduced. Further the hole is both formed and filled with sand without smearing the walls of the hole so that the interstices between particles of soil which form the walls remain open to provide relatively easy passage for water draining from the adjacent soil. I

With these objectives in view, the present invention may be practiced with a bailer provided with an elon gated body section having a central bore for supplying water. At the lower end of the bailer there is a jet head having a cavity for receiving water from the central bore. The cavity feeds water to a first downwardly directed nozzle and a first group of upwardly directed nozzles. In addition, toward the mid point of the bailer a second group of upwardly directed nozzles is provided in communication with the central bore.

In the use of the bailer in practicing the present invention, the bailer is hung in a vertical position from a cable in vertical alignment with a location at which it is desired to install a sand drain to consolidate an impermeable stratum. Water is supplied to the central bore and the bailer is lowered so that a water jet from the first nozzle commences the formation of a sand drain hole. Water jets from the first group of nozzles establish an upward flow of water to flush particles out of the hole and to actively erode the walls of the hole so that the interstices between the particles which form the walls of the hole remain open rather than being smeared closed. As the hole is formed, the bailer is reciprocated to create the pulsating cutting action.

When the hole has been jetted through the impermeable stratum, the reciprocation of the bailer is stopped and the bailer is maintained at the bottom of the hole with the water supply on. Particles are flushed from the hole for a given time period whereafter the bailer is slowly raised and then lowered to repeat the flushing cycle until the water flowing from the hole is relatively clear. After the bailer has been removed from the sand drain hole, batches of coarse sand are placed in the hole at such a rate that the interstices remain relatively undisturbed and open.

Because the bailer is effective to form the sand drain hole without compacting the soil adjacent to the hole, there will be no impediment to the flow of subsurface water through such soil. Further, the bailer is not rotated so that a minimum of smearing of the wall of the hole occurs. Also, because the upward water jets erode the walls of the hole and keep the interstices open, the flow of subsurface water in the impermeable stratum will be free to pass therethrough and into the sand for drainage. Further, by avoiding the use of a casing which is pulled from the sand drain hole, the sand filling step does not smear the wall of the hole. In particular, by not exceeding the selected rate of placing sand in the hole, the water remaining in the hole after jetting is displaced relatively slowly to permit the sand to settle without wiping the wall of the hole. Also, by back filling at such a rate, voids are not formed in the sand, thus there is no tendency for large sections of sand to shift downwardly in the hole (to fill the voids) and smear the wall of the hole.

An object of the present invention resides in a new and improved method of and apparatus for making sand drains.

A further object of the present invention is to provide methods of and apparatus for minimizing the effect which sand drain installation has on soil adjacent to the sand drain.

Another object of the present invention resides in the provision of methods of and apparatus for making sand drains in which the draining capability of the sand drain is improved by maintaining the interstices between particles forming the wall of the sand drain in an open condition.

A further object of the present invention resides in the method of making a sand drain in which a sand drain hole is filled by hand shovelling with batches of sand sequentially placed in the hole at such a rate that the interstices between particles forming the wall of the hole remain relatively undisturbed and open.

An additional object of the present invention is to provide a bailer having vertically spaced groups of upwardly directed nozzles which provide upward water jets for eroding the walls of a sand drain hole to maintain the interstices between particles forming the wall of the hole in an open condition to permit water to flow into sand received in the hole.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects of the present invention may be appreciated upon reference to the following description of the preferred embodiments when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross sectional view of a low permeability, compressible stratum provided with sand drains ac cording to the principles of the present invention to accelerate consolidation of the stratum under load;

FIG. 2 is a cross sectional view of a bailer of the present invention having a downwardly directed nozzle and spaced groups of upwardly directed nozzles for providing waterjets according to the principles of the present invention; I

FIG. 3 is a sectional view taken along line 33 in FIG. 2 illustrating the spacing of the first group of nozzles relative to an annular knife edge provided on the lower end of the bailer;

FIG. 4 is a sectional view taken along line 4-4 in FIG. 2 showing the location of the second group of nozzles relative to an elongated body section of the bailer;

FIG. 5 is an elevational view ofa machine for moving the bailer and supplying water thereto for making sand drain holes according to the principles of the present invention;

FIG. 6 is a cross section of adjacent sand drains formed by a prior art method and apparatus illustrating relatively compacted particles forming the wall of the hole and a smeared layer of particles on the wall;

FIG. 7 is a cross section of a sand drain hole formed by the present invention; and

FIG. 8 is an exploded cross sectional view of the sand drain hole shown in FIG. 7 representing a relatively undisturbed soil condition adjacent to the hole and relatively open interstices between particles forming the wall of the sand drain hole.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings wherein like reference characters are used throughout to designate like elements, the illustrative and preferred embodiments of the present invention may be understood by referring to FIG. 1 which illustrates a construction site 10 having a subsurface stratum 11 provided with sand drains I2 according to the method and apparatus of the present inventions. While the stratum 11 is shown extending from the surface 14 to a depth defined by the line 16, the stratum may also be located completely beneath the surface 14. Although sand drains 12 may be effective in strata characterized by various soil conditions, the stratum 11 may be formed from a highly compressible and relatively permeable material, such as clay. The stratum may also consist of silt, silty clay, clayey silt, peat, or sand and layered layers of all these materials, especially laminated cohesive materials with thin layers of sand. Referring also to FIG. 8, in its natural, undisturbed condition, the clay consists of very small porous particles 16 whichare interconnected by microscopically small pores 18. The pores 18 may be filled with water such that the stratum 11 may be compressed, such as by a surface load 20 (FIG. 1) only if the water is drained off. When the load 20 is applied over the stratum 11 in the absence of the sand drains 12, the pore water will be subjected to increased pressure and consolidation will take place very slowly. For purposes of reference herein, the term consolidation is used to indicate the gradual decrease in pore size of a stratum subject to a relatively constant load as the pore water flows very slowly to strata under unloaded areas of the site 10. Without the sand drains 12, complete consolidation of an impermeable, compressible stratum may take a number of years. Obviously, a construction project planned for erection on the site 10 would be delayed substantially in the absence of a method of accelerating the drainage and promoting rapid settlement of the particles 16.

The sand drains 12 decrease the time required for consolidation by decreasing the distance which the pore water must travel before reaching a relatively highly permeable soil condition. By providing a series of the sand drains 12 according to the principles of the present invention, maximum pore water drainage into the sand drains 12 will be promoted so as to provide conditions contributing to minimizing the time required for complete consolidation of the stratum 11.

As shown in FIG. 1, the pore water flows horizontally (see arrows 24) to the sand drains l2 and either upwardly to the surface 14 into the load and/or downwardly to a permeable lower stratum 26.

Referring to FIG. 6, there are shown adjacent prior art sand drains 28. While such prior art sand drains 28 have been effective to reduce the time required for consolidation of a porous, impermeable stratum 11, it has also been found that many of such sand drains 28 have not decreased, but have increased, the length of time required for consolidation. It has been observed that such sand drain failures may be caused by smearing of the walls 30 of the sand drains 28 (as shown in FIG. 6 by the heavy lines 32). The smeared walls form a barrier to the flow of pore water from the stratum 11 to the sand 34 within the sand drain 28.

Also, prior sand drains 28 have been installed by methods which compact the particles adjacent to the sand drain holes 30. Thus, as shown in FIG. 6,

annular zones

36 and 38 next to the wall 30 are compacted and impair the flow of pore water from the stratum 11 to the sand 34 within the sand drain 28.

The method and apparatus of the present invention have been developed in an endeavor to eliminate the problems encountered in prior sand drains 28 by maintaining during sand drain installation, relatively undisturbed soil conditions adjacent to the wall 42 (FIG. 8) of the sand drain hole 44 and by maintaining interstices 46 between the particles 16 which define the wall 42 open. In this manner, pore water is relatively freeto flow from the stratum 11 to the sand drain 12.

Referring now toFIG. 5, apparatus for practicing the present invention includes a crane or derrick 48 which may be moved along the surface 14 to locate an end 50 of a boom 52 in generally vertical alignment with the central axis 54 of a sand drain 12 which is to be formed in the stratum 11. The crane 48 is supplied with water under pressure, such as up to 270 psi, through a conduit, such as a Zia-inch pipe or hose 56, for example, to a valve 58. A hose 60, having a 2-inch diameter, for example, extends to a tension device 62 which permits the hose 60 to be payed out from and reeled onto pulleys 64.

The tension device 62 includes a slide 65 for supporting the upper pulley 64 for substantially vertical movement to pay out and reel the hose 60 onto the pulleys 64. The slide 65 is biased toward the end 50 of the boom 52 with a force sufficient to maintain the hose under tension between the pulleys 64.

The crane 48 is also provided with a cable 68 which passes around a pulley 70 for supporting a bailer or hole drilling head 72 of the present invention. As shown also in FIG. 2, the bailer 72 is provided with an elongated body section 74 having a central bore 76 formed therethrough. At the upper end 78 of the bailer 72 the hose 60 is connected to the bore 76 to supply the high pressure water to the bailer 72.

Referring to FIG. 5, the bailer 72 is shown in general provided with a downwardly directed nozzle 82 for producing a water jet 84 which forms the sand drain hole 44 in the stratum 11. The hole forming action of the nozzle 82 is assisted by an annular knife edge 88 secured to the bailer 72. The bailer 72 also includes a first, lower group of nozzles 86 and a second, upper group of nozzles 90 which are directed upwardly to produce water jets 92 (FIG. 7) which flow upwardly as the hole 44 is formed.

Directing attention to FIG. 2, the bailer 72 is shown in detail as including the elongated section 74 having an outer diameter of 5% inches, for example, and a length of 27 feet, for example, for forming holes 44 having a l2-inch diameter. The section 74 is shown including the bore 76 which supplies the high pressure water to a cavity 102 provided in a jet head 104 secured to the bailer 72. The nozzle 82 is formed in the jet head 104 with a l-inch diameter, for example, so as to produce the water jet 84 having a volume of from about 50-60 percent of the total water supplied to the bore 76. For example, up to 250-300 gpm of water may be supplied to the bore 76, with up to I gpm being discharged through the nozzle 82.

The jet head 104 is also provided with the first group of nozzles 86. Each nozzle 86 may have a %-inch diameter opening 106 connected to the cavity 102 to provide the upwardly directed water jets 92 (FIG. 7).

As shown in FIG. 3, three equally spaced nozzles 86 may be provided to produce jets 92 which act on the entire circumference of the wall of the hole 44.

Referring to FIGS. 2 and 3, the annular knife edge 88 is shown supported by arms 108 which depend from an internally threaded member 110 secured to the bailer 72. The arms 108 are spaced so as to avoid interference with the water jets 92 from the nozzles 86.

The body section 74 of the bailer 72 is alsoprovided with passages 114 connected to the bore 76 to supply water to the upper group of nozzles 90. The nozzles are located approximately from 10 to 12 feet from the lower end of the bailer 72 and may each have an exit diameter of three-eighths inch to provide the water jets 92. As shown'in FIG. 4, three nozzles may be provided.

In the use of the crane 48 and the bailer 72 to install sand drains 12 according to the method of the present invention, the crane 48 is moved over the surface 14 to position the bailer 72 in vertical alignment with the sand drain axis 54. The cable 68 is payed out until the knife edge 88 of the bailer 72 gently rests on the surface 14. The valve 58 is opened slowly to establish the water jet 84 and initially erode the surface 14 to form the first few feetof the hole 44. As the bailer 72 is lowered into the hole 44, the valve 58 is opened further to supply up to 300 gpm of water to the bore 76 to form the high

pressure water jets

84 and 92. Once the combined action of the jet 84 and the edge 88 have formed the hole 44 to a sufficient depth to insert the second group of nozzles 90 in the hole 44, the cable 68 is reeled in and payed out to repeatedly raise and lower the bailer 72 in the hole 44 to accelerate the formation and washing of the hole 44.

The combined action of the jet 84 and the knife edge 88 form a major portion of the final diameter of the sand drain hole 44 through combined erosion and physical loosening of the particles 16 of the stratum 11. Such combined action does not compact or compress the particles 16 adjacent the hole 44 as in the prior art techniques in which hollow mandrels are driven into the stratum 11. Thus, the particles 16 adjacent to the hole 44 are maintained relatively uninfluenced by the action of the jet 84 and the edge 88.

As the bailer 72 is lowered into the hole 44, the water jet 84 impinges against the bottom of the hole 44 and is turned upwardly. The upward flow of water from the jet 84 initiates upward movement of particles 16 which have been eroded. The jets 92 not only enable the upward flow of water and particles 16 to reach the surface 14, but are also effective to wash and erode the wall 42 to the final diameter of the hole so as to expose the interstices 46 between the particles 16 which define the wall of the hole 44. In this manner the hole 44 is formed without smeared walls 42 so that in the use of the sand drain 12 pore water can flow relatively easily from the stratum 11, through the wall 42 into the hole 44.

Once the hole 44 extends through the stratum 11 into the adjoining permeable stratum 26, a flushing cycle is commenced by maintaining the bailer 72 at the bottom of the hole for a selected period of time, such as l minute, for a l2-inch diameter by 40 foot deep hole 44 while the full flow of water is supplied to the bore 76. The water flushes the eroded particles away from the bottom of the hole 44 and out of the hole. The bailer 72 is then slowly raised until the upper group of nozzles 90 is exposed and is then lowered to the bottom of the hole 44 where it remains for another 1 minute at the full water flow so that the resulting sand drain 12 will be capable of draining water downwardly to the stratum 26. The bailer 72 is then slowly withdrawn from the hole 44 to enable the water jets 92 to make a final pass relative to the wall 42 of the hole so that the interstices 46 remain open.

The water remaining in the hole 44 after the bailer 72 has been removed is clear relative to the original water which is discharged from the hole 44 during the hole forming operation. The degree of clarity of the remaining water may be established by local standards, for example.

According to the present invention, after the bailer 72 has been removed from the hole 44, the hole 44 is carefully filled with coarse sand so as to avoid disturb ing the open interstices 46 of the wall 42 of the hole 44. In particular, in one embodiment of the present invention, batches of coarse sand, such as sand used in the manufacture of concrete, are sequentially placed in the hole 44 to sequentially displace the water which remains in the hole 44. For example, for a 12-inch diameter sand drain hole, the batches of sand may be from one-quarter to one-half cubic foot in volume and may be conveniently measured by the amount of sand which may be carried on a standard long handle, round, point shovel. Further, for such a hole, thebatches of sand are sequentially placed in the hole 44 at a rate of from about one batch every 3 seconds to about one batch every 5 seconds so that each batch settles slowly to the bottom of the hole 44.

Alternatively, the slow filling of the sand drain hole 44 may be accomplished by directing a relatively thin, continuous stream of sand into the top of the hole 44. For example, the batches of sand may be placed in a funnel located over the hole 44 so that the sand continuously flows into the hole 44 at a rate of from about 3 cubic feet to about 12 cubic feet per minute.

The step of slowly filling the hole 44 has been found effective to completely fill the'hole 44 without leaving voids in the hole 44. If voids are formed, the weight of the sand above the void may become sufficient to cause the sand above the void to slide downwardly and fill the void. Such sliding would wipe the wall of the hole 44 and establish a barrier to the flow of pore water to the sand in the hole 44.

It may be appreciated that the combination of the steps of the present invention avoids forming the sand drain hole 44 by the mandrel driving method and avoids filling the sand drain hole by the casing pulling method. Further, the present invention subjects the wall 42 to the cleansing erosive action of the upwardly flowing water jets 92 so that the particles adjacent the hole 44 are not compacted and the interstices 46 are maintained open. Moreover, the upward flow of water keeps the hole open by counteracting the tendency of an uncased hole formed through clay to cave in, even when stratum of sand or silt are located in the main clay stratum. Also, with the interstices 46 open, the slow filling of the hole 44 with sand permits the sand to settle slowly at the bottom of the hole 44 and to move into contact with the particles 16 which define the wall 42 without smearing the wall 42. As a result of these combined steps, the pore water in the stratum 11 may under the pressure caused by the load 20 flow horizontally in the portion of the stratum 11 which is adjacent to the hole 44 and may flow more easily through the walls 42 into the coarse sand.

It is to be understood that the above described arrangements are simply illustrative of the application of the principles of this invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is: 1. The method of installing a sand drain in a stratum of impervious material so that the portion of said stratum adjacent to the drain remains relatively undisturbed and the wall of said sand drain relatively free to permit water to flow into sand within said drain with a bailer provided with at least one downwardly directed nozzle, a plurality of upwardly directed nozzles, and an annular knife edge positioned axially ahead of said downwardly directed nozzle, which method comprises the steps of:

directing a first water jet from said downwardly directed nozzle into said stratum to form a hole therethrough, said hole being formed in the absence of a casing or mandrel for supporting the wall of the hole so formed, and in the absence of an axially extending vane or flute on said bailer,

directing a plurality of additional water jets upwardly in said hole from said upwardly directed nozzles for removing particles of said stratum from said hole and for erroding the surface of said hole to form said wall of the said drain,

reciprocating the bailer in said hole to produce a pulsating action of said water jets in said hole and to provide a cutting action with said annular knife until said hole reaches the desired depth,

slowly raising said bailer to the top of said hole,

lowering said bailer to the bottom of said hole,

maintaining said bailer in the bottom of said hole until the water issuing from the top of said hole is relatively clear of particles,

again slowly raising said bailer to the top of the hole and removing the bailer therefrom, and

filling said hole with sand by slowly depositing said sand into the top of said hole and allowing the sand to sink slowly to the bottom of the hole.

2. The method of claim 1 further comprising the step of maintaining said bailer in the bottom of said hole for a given time period to flush said particles from the hole prior to raising said bailer for the first time.

3. The method of claim 1 wherein the volume of water issuing from said downwardly directed nozzle comprises 50-60 percent of the total volume of water supplied to said nozzles carried by said bailer.

4. Apparatus for making a hole through an impervious stratum in the installation of a sand drain, said hole being characterized by a wall which is relatively open and a portion around said hole which is relatively undisturbed from the condition thereof prior to making said hole, which comprises:

an elongated member having a central bore formed therethrough,

a first nozzle located on the axis of said central bore, said first nozzle communicating with said bore and directed downwardly parallel to said bore,

a plurality of second nozzles communicating with said bore and directed upwardly parallel to said bore, said second nozzles being adjacent to said first nozzle and disposed symmetrically radially outwardly of said first nozzle,

a plurality of third nozzles communicating with said bore and directed upwardly parallel to said bore, said third nozzles being axially spaced from said second nozzles and disposed symmetrically radially outwardly of said first nozzle,

the cross-sectional area of said first nozzle being 50-60 percent of the sum total cross-sectional area of all of said nozzles so that 50-60 percent of the liquid supplied to said bore issues from said first nozzle,

an annular knife edge rigidly and non-rotatably secured to said elongated member, said knife edge being positioned axially ahead of said first nozzle for loosening the impervious: stratum in the hole while minimizing the smearing action of the wall of the hole,

means for supplying high pressure liquid to said central bore so that a jet of liquid is discharged from each of said nozzles; and

means for moving said member rapidly up and down to impart to the jet of liquid issuing from said first nozzle a pulsating action to cut said hole in stratum and to impart a pulsating action to said jets of liquid issuing from said second and third nozzles to gode the wallofsaid hole and remove particles of said stratum from said hole.

Claims

1. The method of installing a sand drain in a stratum of impErvious material so that the portion of said stratum adjacent to the drain remains relatively undisturbed and the wall of said sand drain relatively free to permit water to flow into sand within said drain with a bailer provided with at least one downwardly directed nozzle, a plurality of upwardly directed nozzles, and an annular knife edge positioned axially ahead of said downwardly directed nozzle, which method comprises the steps of: directing a first water jet from said downwardly directed nozzle into said stratum to form a hole therethrough, said hole being formed in the absence of a casing or mandrel for supporting the wall of the hole so formed, and in the absence of an axially extending vane or flute on said bailer, directing a plurality of additional water jets upwardly in said hole from said upwardly directed nozzles for removing particles of said stratum from said hole and for erroding the surface of said hole to form said wall of the said drain, reciprocating the bailer in said hole to produce a pulsating action of said water jets in said hole and to provide a cutting action with said annular knife until said hole reaches the desired depth, slowly raising said bailer to the top of said hole, lowering said bailer to the bottom of said hole, maintaining said bailer in the bottom of said hole until the water issuing from the top of said hole is relatively clear of particles, again slowly raising said bailer to the top of the hole and removing the bailer therefrom, and filling said hole with sand by slowly depositing said sand into the top of said hole and allowing the sand to sink slowly to the bottom of the hole.

4. Apparatus for making a hole through an impervious stratum in the installation of a sand drain, said hole being characterized by a wall which is relatively open and a portion around said hole which is relatively undisturbed from the condition thereof prior to making said hole, which comprises: an elongated member having a central bore formed therethrough, a first nozzle located on the axis of said central bore, said first nozzle communicating with said bore and directed downwardly parallel to said bore, a plurality of second nozzles communicating with said bore and directed upwardly parallel to said bore, said second nozzles being adjacent to said first nozzle and disposed symmetrically radially outwardly of said first nozzle, a plurality of third nozzles communicating with said bore and directed upwardly parallel to said bore, said third nozzles being axially spaced from said second nozzles and disposed symmetrically radially outwardly of said first nozzle, the cross-sectional area of said first nozzle being 50-60 percent of the sum total cross-sectional area of all of said nozzles so that 50-60 percent of the liquid supplied to said bore issues from said first nozzle, an annular knife edge rigidly and non-rotatably secured to said elongated member, said knife edge being positioned axially ahead of said first nozzle for loosening the impervious stratum in the hole while minimizing the smearing action of the wall of the hole, means for supplying high pressure liquid to said central bore so that a jet of liquid is discharged from each of said nozzles; and means for moving said member rapidly up and down to impart to the jet of liquid issuing from said first nozzle a pulsating action to cut said hole in stratum and to impart a pulsating action to said jets of liquid issuing from said second and third nozzles to errode the wall of saId hole and remove particles of said stratum from said hole.