US3875751A

US3875751A - Strengthening cohesive soils

Info

Publication number: US3875751A
Application number: US334316A
Authority: US
Inventors: Kjeld F W Paus
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-06-14
Filing date: 1973-02-21
Publication date: 1975-04-08
Anticipated expiration: 1992-04-08

Abstract

The present invention is concerned with the technique of strengthening subsurface cohesive soil formations (such as clay and silt) by admixing into the soil in situ a strengthening or binder material by means of a helical drill structure designed as an injection and mixing tool.

Description

United States Patent 1 1 Paus 1 STRENGTHENING COHESIVE SOILS [76] Inventor: Kjeld F. W. Paus, Tjadervagen 28,

181-40 Lidingo. Sweden [221 Filed: Feb. 21.1973 121] App]. No.: 334,316

Related U.S. Application Data [63] Continuation-impart of Ser. No. 254.324. May 17.

1972, which is a continuation of Ser. No. 29,728, April 23. 1970, which is a continuation of Ser. No. 737.225. June 14. 1968. abandoned.

(in 3,875,751 1 1 Apr. 8, 1975 2.782.605 2/1957 Wcrtz et a1. 61/36 R 2.830.443 4/1958 Burrell 61/536 X 2.920.455 1/1960 Ryser et a1 61/5364 3.023.585 3/1962 Liver 61/36 R 3.074.240 1/1963 Elliott t. til/53.6 X 3.206.936 9/1965 Moor 61/5364 3.336.760 11/1967 Landau..... 61/5364 X 3.391.544 7/1968 Daczko 61/63 X 3.430.449 3/1969 Novotny et a1 61/45 8 3.529.428 9/1970 Batten 61/36 R X Primary Examiner-Philip C. Kannan Attorney. Agent. or Firm-Fred C. Phi1pitt 57] ABSTRACT The present invention is concerned with the technique of strengthening subsurface cohesive soil formations (such as clay and silt) by admixing into the soil in situ a strengthening or binder material by means of a helical drill structure designed as an injection and mixing tool.

16 Claims, 19 Drawing Figures PATEN'IEDAPR' ems o 9 mo 8 a Fig. 15

STRENGTHENING COI-IESIVE SOILS RELATED CASES This is a continuation-in-part of Ser. No. 254,324 filed May 17, I972, which in turn is a continuation of Ser. No. 29,728 filed Apr. 23, I970 and which was in turn a continuation of Ser. No. 737,225 filed June 14, 1968 all now abandoned.

BACKGROUND Methods and apparatus for strengthening comparatively coarse-grained, so-called frictional soil, such as gravel, sand and fine sand, are previously known, according to which a comparatively large amount of strengthening material, such as cement, is admixed with the cylindrical column of soil to be strengthened, the added strengthening material generally constituting about 30 percent or more of the strengthened column. On account of the relatively large amount of strengthening material supplied to the soil material and the nature of the soil itself, it is a comparatively easy matter to secure the desired distribution of the strengthening or binder material by the mixing action effected by the helical screw in connection with the withdrawal of the screw with a reduced axial feed movement.

It has been found that the known methods of strengthening a comparatively coarse-grained subsoil formation cannot be applied when it is desired to strengthen a cohesive subsoil formation consisting only, or to a great proportion, of fine-grained or very fine-grained soil, such as silt and clay, where only a comparatively small amount of strengthening material, in the first instance chemically active material such as slaked or unslaked lime, is required to give the desired strengthening effect. Since the required amount of strengthening material generally amounts to only 3 7 percent of the volume of the column of soil to be strengthened and never exceeds 10 percent, and since, furthermore. such strengthening materials as slaked or unslaked lime are chemically active only up to a rather short distance. the desired even distribution through the entire volume of the column of soil to be strengthened cannot be attained only by the conventional mixing action effected by the helices of the helical drill structure during withdrawal with a reduced axial feed movement.

It is an object of the present invention to provide an effective method of strengthening to a considerable depth a column of a cohesive subsoil formation by the even distribution therein of a comparatively small amount of a strengthening material or binder, preferably a chemically active strengthening material such as slaked or unslaked lime.

It is a further object of the invention to provide an apparatus. including a helical drill structure designed for the introduction of the strengthening material into the soil, which is particularly adapted to be used in the carrying out of the novel method of strengthening a cohesive subsoil material formation to a considerable depth.

THE PRESENT INVENTION According to the present invention strengthening material is introduced during withdrawal of the helical drill structure after the said structure has been screwed down into the soil to the desired depth, by rotating the drill structure in an unscrewing direction and simultaneously imparting thereto an enforced feed of strengthening material which for each revolution of the drill amounts to only a fraction of the pitch. The strengthening material is delivered into the soil distributed over the entire cross section of the column of soil so that it will be strengthened in rather closely positioned layers, and so that the mixing action which the helical drill is called upon to effect is limited to a further distribution of the strengthening material through the nearest portions of the soil only.

The diameter of the column of cohesive soil to be strengthened in commercial situations is always rather large, generally amounting to 800 mm or more. The present invention is based upon the concept that the required even distribution of the small amount of strengthening material through the soil column to be strengthened can be effected only by initially delivering the strengthening material into the soil distributed as evenly as possible over the entire cross section of the column of soil to be strengthened, thus depositing the material in rather close layers so that the drill will be called upon to effect by a rotary action only a final distribution of a local character.

The strengthening material can be introduced into the soil either in a fluid or in a powdered solid form. When using slaked lime as a binder, a lime slurry consisting of about 45 percent of calcium hydrate and 55 percent water by weight is a suitable mixture. Another suitable strengthening agent is a sulfonated petroleum water soluble oil which acts as a catalyst and through an electro-chemical action stabilizes the soils and clays. A proper ratio when stabilizing a soil consisting of clay, as a rule is about kgs oflime slurry to 1 cubic meter of clay. In certain cases, however, it would be suitable to increase this ratio, depending on the nature of the soil to be stabilized.

A more rapid and pronounced strengthening of the soil can often be secured by supplying the strengthening material without simultaneously supplying water. When powdered unslaked lime is used as a binder in a moist or watery cohesive soil, heat is produced when the unslaked lime is slaked by reaction with the water. and the heat thus produced speeds up the strengthening process.

THE DRAWINGS The invention will now be described more in detail in conjunction with the accompanying drawings illustrating some preferred embodiments of my invention:

FIG. 1 is a side elevation and FIG. 2 a front elevation of a complete stabilizing unit;

FIG. 3 is a plan view (on a larger scale) of the platform forming part of the unit shown in FIG. 2 and carrying certain mechanical equipment;

FIG. 4 is a side view of the unit of FIGS. I 2 carrying the platform shown in FIG. 3;

FIG. 5, on a still larger scale, illustrates the drill head of the earth drill forming part of the unit of FIGS. 1 4;

FIG. 6, partly in section. shows the drill head in a side view at right angles to that of FIG. 5;

FIG. 7 is a cross section taken along VII-VII of FIG. 6;

FIGS. 8 and 9 are cross sections taken. respectively, along VIIIVII| and lX-IX of FIG. 6;

FIG. 10 is a side view, partly in axial section, of an earth drill designed for supplying a powdered binder;

FIG. 11 is a side view, perpendicular to the side view of FIG. II], of the drill head and the adjacent part of the drill rod, partly in axial section;

FIG. 12 is a view of the drill head according to FIGS. I and 11, as seen from below;

FIG. I3 is a sectional view, perpendicular to the cut ting edge shown in FIG. 11; through an outlet aperture having a closing means formed as a cutting knife;

FIG. 14 is a side view, partly in axial section, of an earth drill designed for supplying encapsulated powdered binder;

FIG. is a schematic side view ofa device for transporting capsules to an earth drill from a hopper;

FIG. I6 shows in side view an earth drill of modified design;

FIG. I7 is an end view of the drill head of FIG. 16 taken along 17 I7.

FIG. I8 is a cross section taken along line 18 I8 in FIG I6;

FIG. I9 is a cross section along line 19 I9 in FIG. 16 and through the drill shaft showing the drill head from above.

THE INVENTION IN GREATER DETAIL As illustrated in the drawings. the drilling and injection unit is mounted on a conventional caterpillar/- crane excavator. Connected to the pivotable superstructure 10 of the excavator by two tie bars 1] in a manner known per se is a machine platform I2 which is suspended on two fixed wire stays 13 secured to the top end of the crane beam or boom 14. Independently of any slope of the ground, platform 12 is maintained in a horizontal position by the aid of a hydraulic cylinder l5. Numeral l6 denotes a guide column which is suspended at its top end from the wire tackle 17 of the crane beam or boom, and the foot end of which is hinged to the platform 12. The guide column 16 forms guiding means for the drill rod 18 having its top end rotatably mounted in a slide 19 displaceable along the guide column and being guided intermediate its ends in a mechanism which serves at the same time for transferring rotary motion to the drill rod. The rotary motion is derived from a horizontally extending drive shaft 20 which is journalled in two bearings 21 and 22 mounted on platform I2, through a bevel gearing haw ing its driving gear 23 cantilever mounted to the drive shaft beyond the bearing 21, while its driven gear 24, being substantially larger, is journalled in a cross member 25 interconnecting the ends of the

fork legs

26 and 27 of guide column I6. From gear 24 the torque is transmitted to the square-sectioned drill rod I8 in a conventional way by means of four rollers 28 journalled in brackets secured to the gear body. The guide column has one fork leg 27 thereof supported on the drive shaft 20 inwardly of the driving bevel gear 23, while its other fork leg 26 is formed with a pin 29 which isjournalled in a bearing 30. Pin 29 is in axial alignment with drive shaft 20, thereby enabling the guide column to be folded to any desired position ofinclination without affecting the power transmission to the drill rod I8.

The driving power for drive shaft 20 is derived from a diesel engine 31 mounted on platform 12, through a hydraulic torque converter 32 and a gearbox 33 the output shaft of which can be connected to the drive shaft through a disengaging coupling 35. Gearbox 33, in the embodiment shown, has a reversible output with three speeds in both directions.

The feed movement of the drill rod 18 is derived from the drive shaft through a variator 36 mounted on the guide column and adapted to be connected to the drive shaft by means of a disengaging coupling 37. The variator is structurally integrated with an intermediate gearing 34 carrying a sprocket 39 on its output shaft 38, and journalled on the guide column, at the top end thereof, is a similar sprocket, not shown. Running about the two sprockets is a roller chain 41 having its two ends secured to bearing slide I9. Obviously, when the coupling 37 is engaged, the feed rate of the drill rod 18 will be directly proportional to its speed of rotation.

Extending from a countershaft in gearbox 33 is an output shaft 42 which is connected to a pump 46 through an over-running clutch 43, a variator 44 and a flexible coupling 45. The pump is of the kind discharging a predetermined volume per revolution. The inlet side of the pump is connected through a flexible pipe 47 to a supply tank 48 suspended from beneath the platform 12 and containing lime slurry or other injection fluid, while its outlet side communicates through a flexible pipe 49 with a tube 50 extending down the bore of the hollow drill rod IS.

The drill head 55 is carried at the lower end of the drill rod I8 through the intermediary of a dog clutch 56 having substantial clearance between its cooperating dogsv The drill spindle 57 has a longitudinally extending injection fluid passageway 58 which connects to the tube 50 within the drill rod. Secured to the drill spindle 57 are two

helical flights

59 and 60 each having an axial length corresponding to half the pitch of the helix. The helices at thier lower ends are straightly cut off along a plane perpendicular to the drill axis and have hinged to the straight edges thus formed replaceable cutters 61. The flow passageway 58 of the drill spindle at the lower end of the drill connects to branch passages 62 opening into slot-shaped outlet apertures 63 distributed radially over the lower end face of each helix, When screwing down the drill, the cutters 61, owing to the cutting pressure, will be urged against the end faces of the helices to thereby close off the outlet apertures 63, whereas, upon screwing the drill upwardly, the cutters will turn about their axes thereby exposing said apertures. At their upper ends each helix is also cut off along a plane which is perpendicular to the axis of the drill, so that the two scraping edges are formed.

To prevent injection fluid from being supplied during the screwing-down operation, a throttle valve 64 is disposed within the upper member of the dog clutch S6 and has its actuating element adapted to be acted on in such a way upon relative angular movement between the two members of the dog clutch, that said valve will be closed during power transmission in the direction corresponding to the screwing-down motion of the drill, but will be opened when the drill is rotated in the opposite sense. A spring 65 inserted in the clutch automatically returns the clutch members to the position thereof corresponding to closed valve as the drill is lifted free from ground.

The operation of the apparatus thus descirbed is as follows,

After the apparatus has been moved to the desired site, the machine platform 12 has been adjusted into horizontal position, and the guide column 16, by means of the crane beam or boom 14, has been caused to oc cupy a vertical, or any desired inclined position, the diesel engine 31 is started with

couplings

35 and 37 disengaged. The gearbox 33 is set for power transmission in a direction corresponding to screwing the drill head 55 downwardly, and in a speed position which is deemed to be suitable having regard to the nature of the earth concerned. The variator 36 is set to a position which will cause a vertical downward feed of the drill rod 18 equal to the pitch of the

drill head helices

59 and 60. Then first coupling 37 and thereafter coupling is engaged. As a result, through drill rod 18 a rotational movement and at the same time a vertical feed will be transmitted to the drill head 55, whereby the latter will screw itself down through the earth to rigid bottom. Upon rotation of the drill head in this sense, the overrunning clutch 43 cannot transmit any torque, so that the pump 46 will remain inoperativev Further, the cut-off valve 64 in the binder fluid supply conduit is closed and due to the cutting pressure, the cutters 61 are pressed against the outlet apertures 63 thereby closing off the latter.

As the drill head 55 has been driven down to the desired depth,

couplings

35 and 37 are disengaged thereby interrupting the power transmission to the drill rod 18. Gearbox 33 is then shifted for power transmission in the reverse direction, and variator 36 is reversed for upward feed by increments which, for each revolution of drill rod l8, are essentially smaller than the pitch of the helices of the drill head. Thereupon the

couplings

35 and 37 are reengaged. As a result, an oppositely directed torque will now be transmitted to drill rod 18. Actually the two members of dog clutch 56 will now initially rotate relative to each other to their opposite limit position, thereby opening valve 64. For this direction of rotation, the over-running clutch 43 is operative to transmit rotational movement to pump 46 which, during each revolution of the driving shaft, will press a predetermined volume of binder fluid to and out through the outlet openings 63 formed in the helices of the drill head. The cutters 61 protrude slightly downward beyond the end faces of

helices

59 and 60 in a manner to cause the cutters during the operation of screwing the drill in an upward direction to pivot into a position in which the apertures 63 are exposed. Thus, during each revolution of drill head 55 a predetermined quantity of binder fluid will be discharged through apertures 63 and will penetrate into the surrounding earth.

As already mentioned, the drill head has an upward feed rate. which is only a fraction of the pitch of the helical flights, say only about 4 cm. for each revolution of the drill. The lower edges of the flights will thus each follow an imaginary helical surface the convolutions of which are very close together. the binding material leaving the outlet openings being deposited along said helical surface in coaxial spiral-shaped strings, the convolutions of which are very close together both in a radial and in an axial direction. Since the drill head has two flights, the axial distance between two layers" of string may be only 2 cm apart. By means of the apparatus described the binder material is thus, as desired, delivered into the soil fairly evenly distributed through the entire volume of the column of soil to be strengthened.

In this connection it should also be noted that during withdrawal of the earth drill while rotating the drill in the unscrewing sense, the upper edges 63a of the helical flights will work through soil material above the drill head, so that the binder material will be deposited in a rather loose soil. Furthermore, it should be noted that the flights of the drill head will stir or agitate the material between and around the flights, causing the binder material deposited in the soil to be distributed over the entire cross section of the column and thus become still better mixed.

As soon as the drill head 55 is raised free above the ground the coupling is disengaged causing the pump 46 to stop. Spring 65 will return the two members of dog clutch 56 into their normal relative position, thereby resetting the throttle valve 64 to its closed position. As the drill head 55 has been raised to a sufficient height above the ground the diesel engine 31 is stopped, and the apparatus is moved for use at another place.

Screwing down the drill head 55 at a rate corresponding to the pitch of the

helices

59 and 61 will subject the earth material to a minimum of disturbance. This is generally an advantage, for instance in the case where the earth material is a clay. On the other hand, if it is desired to effect a loosening of the earth material during the operation of screwing down the drill head, then the variator 36 is preset to cause the downward vertical feed during each revolution of the drill head rotation to be substantially smaller than the pitch of the helices. Under these conditions the cutters 61, so to say, can break loose material and agitate the same as the drill head is moving down into the earth.

In the embodiment according to FIGS. 10 13 the drill head 55 is designed for supply and admixing in the earth of powdered injection substance. To the drill spindle 69, which is a direct extension of the hollow drill rod 18, are attached two helices and 71, the axial length of which correspond to the pitch. The bell ces are straight cut at the lower edge where they have their maximum cutting breadth. From the straight cut ting edges 72 and 73 the radial breadth of the helices decreases so that the breadth after half a turn is zero. The successive decrease of the breadth of the helices is so designed that the

outer edges

74 and 75 of the helices in an end view ofthe drill (See FIG. 12) follow Archimedian helical curves. The upper portion of each helix has a

cylindrical edge surface

76 and 77 respectively. with a diameter corresponding to the maximum cutting breadth. This portion is straight cut both at its lower end and at its upper end so that lower and upper cutting edges 78, 79 respectively 80, 81 having maximal cutting breadth are formed. A central channel 82 in the drill sprindle 69 forming a direct extension of the axial channel in the drill rod 18 is bifurcated downwards into two

channels

83 and 84 which pass out into the

lower cutting edges

78 and 80, respectively, close to the drill spindle, i.e., at a place where the lower portions of the helices have their smallest radial breadth. Cooperating with the outlet apertures of the

channels

83 and 84 are cutters 8S and 86 which during the screwing down of the drill are forced against the end surfaces of the helices, under the action of the cutting pressure. and close the outlet apertures, while during the screwing up ofthe drill the cutters turn around their suspension axis and open the apertures.

The tube 87 for supply of powdered injection substance is gas-tightly inserted in the drill rod 18 through a cross wall 88 positioned in the upper portion of the drill rod, and the tube emerges at the lower end freely in the central channel 82 in the drill spindle. The drill bar wall is just below the cross wall 88 provided with outlet apertures which are controlled by an adjustable throttle valve 89. The powdered binder is blown by means of compressed air from a magazine for injection substance through a flexible tube to and through the tube 87 in the drill rod. After having left the mouth of the tube 87 the rapidly flowing air carrying the powder flows with considerably reduced speed up through the ring-shaped channel 90 between the tube 87 and the surrounding drill bar wall, said channel having substantially greater cross sectional area than the tube 87, and leaves through the throttle valve 89. When the air speed decreases, the air can no longer carry the powder, which separates and accumulates at the bottom of the central channel 82 and is then forced, under the action of the air pressure, through the

channels

83 and 84 into the soil, when the drill is screwed upwards.

The powder forced into the soil during the screwing up of the drill is deposited as two helical bands or strings around the drill bar in a soil which has been loosened by action of the upper sections of the

helices

70 and 71. The lower helix sections, which during the screwing up of the drill follow the upper sections, force by means of their curved

outer edges

74 and 75 the deposited injection substance radially outwardly so that it is distributed over the entire cross section of the drill hole. The injection substance is simultaneously admixed into the surrounding earth mass by means of the screw surfaces of the helices in the same way as in the embodiment shown in FIGS. 1-4, the lower helix sections also effecting a packing action on the column of soil admixed with binder below the drill head. By suitable adjustment of the throttle valve 89, the desired overpressure can always be maintained above the powder accumulated in the channel 82, and by means of an adjustable pressure reduction valve between the air pressure chamber and the air feeding device the necessary flowing speed of the carrier air can always be maintained.

1n the embodiment according to FIG. 14, the powdered injection substance is supplied to the drill equip ment encapsulated in cylindrical capsules of paper. plastic or any other easily breakable material. The

helices

70 and 71 on the drill spindle 69 have the same shape as in the embodiment according to FlGS. 12. The supply tube 87 for the injection substance, inserted in the drill rod 18. is here designed with comparatively greater diameter and is. with a helical bend at the lower end connected to a channel 92, which is bent in a corresponding way. in one of the two upper helix sections, said channel emerging in the lower cutting edge 80 of the upper portion of each helix. The channel mouth is closed by a swingably mounted cutter 93, which exposes the mouth when the drill is screwed upwards. A number of air outlet apertures 94 are provided in the wall of the tube 87 at some distance from the lower end. During the screwing up of the drill the comparatively short capsules 95 containing injection sunstance are supplied. one at a time, to the upper end of the tube 87. The capsules are fed to the tube 87 by compressed air from a magazine through a flexible tube 96 connected to the upper portion of the tube 87. and are pushed by the air along cutters 97 on the inner side of the tube. said cutters breaking the capsules so as to re lease the powdered contents. The injection powder supplied to the earth mass is deposited in the soil as a spiral'shaped band with small pitch around the drill spindle in the same way as in the embodiment according to FIGS. 1012 and is after a short while distributed by the edge portions of the lower helix section radially over the whole cross section of the drill hole under simultaneous admixing with the soil.

FIG. 15 shows a device which was previously largely known for feeding capsules through a tube by means of compressed air. A capsule 95 is by means ofa piston 101 belonging to an air cylinder 102 supplied from a magazine or hopper into a tubular lock chamber 103 which is provided with a fore lock valve 104, open during the feeding process, and a rear lock valve 105, closed during the feeding process. A tube 107, which is provided with a closing valve 106 and connected to a pressure air supply, emerges in the lock chamber 103 and pressure air tube provided with a closing valve 109 emerges in the lock chamber extension 108 to which the flexible feeding tube 96 is connected. During the feeding of the capsules into the lock chamber the air valve 106 is closed but the air valve 109 is open so that the desired over-pressure can be maintained in the capsule feeding tube 87 which is inserted in the drill bar. When the capsule 95 has been fed to the lock chamber 103 and the feeding piston 101 has been retracted, the fore lock valve 104 and the air supply valve 109 are closed and the rear lock valve 105 is opened. After this the air valve 106 is opened. The pressure air supplied behind the capsule 95 pushes the capsule through the lock chamber extension into and through the flexible feeding tube 96 connected to this extension, and into the feeding tube 87 inserted in the drill bar. All valves are preferably controlled. in connection with the screwing up of the drill, from the driving mechanism of the drill bar in such a way that a new capsule is fed into the feeding tube just before the content of the previously supplied capsule is forced into the surrounding earth mass.

The drill head illustrated in FIGS. 16 19 has a single helical flight which extends about five quarters of one turn around the drill hub 116. The single flight is composed of two sections spaced from one another, viz a lower flight section 117 and an upper flight section 118. The lower section 117 has a straight lower cutting edge 119 extending perpendicularly to the axis of the drill head, the width of the lower flight section decreasing gradually from the cutting edge to zero. the broadened outer edge 120 of the section following an Archimedian curve. The upper flight section 118 has a straight lower cutting edge 121 and a straight upper cutting or scraping edge 122, the outer edge of the upper flight section following a circular cylinder. The binder substance is delivered through an outlet opening 123 positioned close to the hub of the drill head between the two flight sections, the said opening being closed by a swingable lid 124 when screwing down the earth drill into the ground. When screwing the drill into the ground the cutting edge 119 will cut through the ground material along a helical surface having the pitch of the single flight, meaning that the upper flight 118 will enter and move along the helix of loosened ground material provided by the lower flight section.

When withdrawing the earth drill from the ground with a reduced axial feed movement while rotating the drill in an unscrewing direction, the upper flight section 118 loosens by means of its cutting edge 122 the undisturbed soil above the drill head and feeds the loosened soil downwards The lid 124 swings open and the binder material is deposited as a string spirally around the hub On further rotation of the drill head the lower flight section 117 moves, by means of its broadened curved outer edge 120, the deposited binder material radially outwards, thereby effecting a positive distribution of the binder material over the entire cross section of the column of soil to be strengthened. At the same time the lower flight section 117 by means of its helical lower surface will stir and mix the soil with the roughly distributed strengthening material. The lower flight section 117 also effects a packing action on the underlying column of soil mixed with stengthening material aided by the upper flight section 118.

in FIG. 16, the drill is shown in a position taken up during a stabilizing operation. The drill has been screwed up from its lower-most position with a pitch considerably smaller than the pitch of the helical flight on the drill head, and it is assumed to take up a position at about half the height of the column of soil to be stabilized. The helix which a point on the circumference of the drill head describes during the screwing down operation is illustrated by the curve 125, whereas the helix described by the same point during the unscrewing operation is illustrated by the dotted curve 126.

In FIGS. 17 19, the cross-hatched surface illustrates the spreading of the binder material over the crosssection of the column of soil to be stabilized. In FIG. 17 the binder material has merely been deposited as a string around the hub. According to FIG. 18, which shows a section taken about midway between the upper and lower ends of the lower flight section, the binder material has been distributed over about half the cross section of the column of soil to be strengthened. When the drill head has left the section through the column of soil being stabilized, the distribution of the binder material over the entire cross section ofthe column has been completed as indicated in FIG, 19.

The tool illustrated in FIGS. 16 19 effects a very rapid and yet very intimate mixing of the binder material with the soil to be stabilized. This is of great importance when attempting to stabilize cohesive soils with small quantities of rapidly binding stabilizing agents In conclusion, while the foregoing specification and drawing describe the construction, operation and use of some preferred embodiments of the instant invention, it is to be understood that I do not intend to limit myself to the precise constructions and arrangements herein disclosed, since the various details of construction, form and arrangement may obviously be varied to a considerable extent by anyone skilled in the art without really departing from the basic principles and novel teachings of this invention, and without sacrificing any of the advantages of the invention, and accordingly, it is intended to encompass all changes, variations. modifications and equivalents falling within the scope of the appended claims.

What is claimed is:

1. Apparatus for stabilizing cohesive soil to substantial depths which involves driving down into the earth an implement designed as an injector for a binder and having binder outlet apertures formed adjacent its lower end, which appartus comprises a rotary-type earth drill having a drill head mounted on the end of a drill rod and provided with one or more helices and with a number of outlet apertures communicating with pressurized-binder supply conduit extending down wardly through the drill rod, said outlet apertures being located in a lower cutting face ofa helix and distributed radially over these faces, means for rotating the drill in LII a desired direction of rotation, means effective upon screwing the earth drill upwardly to forcibly impart thereto an upwardly directed feed movement which during each revolution of the drill is considerably smaller than the pitch of the helix or helices, the drill head being adapted to positively distribute the binder over the entire cross section of the drill head.

2. Apparatus as claimed in claim 1, characterized in that below the helix or helices provided with outlet apertures for the binder there is provided one or more further helices which have the function to mix the de posited binder with the soil and to effect a packing action on the underlying column of soil admixed with the binder.

3. Apparatus as claimed in claim 1, characterized in that the helices are straightly cut off at a lower edge provided with outlet apertures, and in that each helix carries at the said lower edge a foldable cutter which is adapted during screwing down the earth drill into the ground to occupy a position to close offthe binder fluid outlet apertures but upon rotating the drill in the opposite sense to pivot into a position to open the apertures.

4. Apparatus according to claim 1, characterized in that the drill rod is guided by a guide column, the upper end of the rod being rotatably but axially nondisplaceably mounted in a slide slidable along said guide column and having the vertical feed movement transmitted thereto by means of an endless chain extending about sprockets journalled on the guide column.

5. Apparatus according to claim 1, characterized in that the rotational movement of the drill and its vertical feed movement are derived from a common power source so that the feed movement is proportional to the rotational movement.

6. Apparatus according to claim 5, characterized in that the vertical feed movement is transmitted from a drive shaft for the drill through a change-speed gearing.

7. Apparatus according to claim 5, characterized in that the earth drill is adapted to receive air-borne binder powder.

8. Apparatus according to claim 1, characterized in that there is provided for supplying binder fluid to the outlet apertures of the drill crown a pump of a conventional type adapted to deliver a predetermined fluid volume per revolution.

9. Apparatus according to claim 8, characterized in that the pump is connected to the same source of power as the earth drill through an overrunning clutch in such a way as to be inoperative during screwing down the drill into the earth, but to deliver during the screwing withdrawal of the drill an amount of binder fluid proportional to the feed movement of the drill.

10. Apparatus for stabilizing cohesive soil to substantial depths which involves driving down into the earth an implement designed as an injector for a binder and having binder outlet apertures formed adjacent its lower end, which apparatus comprises a rotary-type earth drill having a drill head mounted on the end of a drill rod and provided with one or more helices and with a number of outlet apertures communicating with pressurized-binder supply conduit extending downward through the drill rod, means for rotating the drill in a desired direction of rotation, means effective upon screwing the earth drill upwardly to forcibly impart thereto an upwardly directed feed movement which during each revolution of the drill is considerably smaller than the pitch of the helix or helices, the drill head being adapted to positively distribute the binder over the entire cross section of the drill head, a lostmotion clutch being mounted in the drill rod and adapted, through the intermediary of a movement transmitting system, upon relative movement between the clutch members, to actuate a valve mounted in the binder fluid supply conduit so as to cause the valve to be closed during screwing down the drill into the earth but to be opened when, during its withdrawal from the earth, the drill is rotated in the opposite sense.

11. Apparatus according to claim 10, characterized in that the earth drill, working as an injection nozzle, is adapted to supply binder in the form of a dry powder.

12. Apparatus according to claim ll, characterized in that the earth drill is adapted to receive easily break able capsules, fed by means of pressure air and containing powdered binder.

13. Apparatus according to claim 11, characterized in that a gas tight supply tube for the air-borne binder is positioned above the hollow drill bar, the lower end of said supply tube freely emerging in a chamber in the drill head that communicates with outlet channels for the binder, and has a cross-sectional dimension such that between the tube and the surrounding drill bar wall an air flow channel is formed which has a ring-shaped cross-section, the area of which is substantially greater than the inner cross-section area of the tube, and which at the top communicates with the free air through preferably adjustable throttle apertures.

14. Apparatus according to claim 13 having an adjustable throttle valve for the discharging of air, characterized in that the adjustment of the throttle valve is controlled from the driving mechanism of the earth drill so that the pressure of the gas flowing through the chamber always is greater than the pressure from the earth mass or the ground water around the drill head.

15. Apparatus for stabilizing cohesive soil to substantial depths which involves moving down into the earth an implement designed as an injector for a binder and having binder outlet apertures formed adjacent its lower end, which apparatus comprises a rotary-type earth drill having a drill head mounted on the end of a drill rod and provided with one or more helices and with a number of outlet apertures communicating with pressurized-binder supply conduit extending downward through the drill rod, means for rotating the drill in a desired direction of rotation, means effective upon screwing the earth drill upwardly to forcibly impart thereto an upwardly directed feed movement which, during each revolution of the drill, is considerably smaller than the pitch of the helic or helices, said outlet apertures being positioned close to the drill head spindle below the upper end of a helix or helices, and that below the binder discharge aperture or apertures there are provided one or more further helices which have a breadth successively increasing from the drill spindle and have the function to move by their outer edges, in a radial direction, the binder material deposited in the earth mass over the cross section of the drill hole and to mix the binder with the adjacent portions of the soil filling the drill hole.

16. Apparatus for stabilizing cohesive soil to substantial depths which involves moving down into the earth an implement designed as an injector for a binder and having binder outlet apertures formed adjacent its lower end, which apparatus comprises a rotary-type earth drill having a drill head mounted on the end of a drill rod and provided with one or more helices, a capsule feeding tube being provided for the feeding of easily breakable capsules containing powdered binder to outlet apertures for the binder, provided in the drill head, said tube being gas-tight inserted in the hollow drill bar and at the lower end on its inner side provided with capsule breaking cutters, and above these cutters provided with air discharge apertures in the tube wall, and that the ring-shaped air flow channel between the tube and surrounding drill bar wall communicates with the outer air through preferably adjustable throttle apertures.

Claims

1. Apparatus for stabilizing cohesive soil to substantial depths which involves driving down into the earth an implement designed as an injector for a binder and having binder outlet apertures formed adjacent its lower end, which appartus comprises a rotarytype earth drill having a drill head mounted on the end of a drill rod and provided with one or more helices and with a number of outlet apertures communicating with pressurized-binder supply conduit extending downwardly through the drill rod, said outlet apertures being located in a lower cutting face of a helix and distributed radially over these faces, means for rotating the drill in a desired direction of rotation, means effective upon screwing the earth drill upwardly to forcibly impart thereto an upwardly directed feed movement which during each revolution of the drill is considerably smaller than the pitch of the helix or helices, the drill head being adapted to positively distribute the binder over the entire cross section of the drill head.

2. Apparatus as claimed in claim 1, characterized in that below the helix or helices provided with outlet apertures for the binder there is provided one or more further helices which have the function to mix the deposited binder with the soil and to effect a packing action on the underlying column of soil admixed with the binder.

3. Apparatus as claimed in claim 1, characterized in that the helices are straightly cut off at a lower edge provided with outlet apertures, and in that each helix carries at the said lower edge a foldable cutter which is adapted during screwing down the earth drill into the ground to occupy a position to close off the binder fluid outlet apertures but upon rotating the drill in the opposite sense to pivot into a position to open the apertures.

4. Apparatus according to claim 1, characterized in that the drill rod is guided by a guide column, the upper end of the rod being rotatably but axially non-displaceably mounted in a slide slidable along said guide column and having the vertical feed movement transmitted thereto by means of an endless chain extending about sprockets journalled on the guide column.

10. Apparatus for stabilizing cohesive soil to substantial depths which involves driving down into the earth an implement designed as an injector for a binder and having binder outlet apertures formed adjacent its lower end, which apparatus comprises a rotary-type earth drill having a drill head mounted on the end of a drill rod and provided with one or more helices and with a number of outlet apertures communicating with pressurized-binder supply conduit extending downward through the drill rod, means for rotating the drill in a desired direction of rotation, means effective upon screwing the earth drill upwardly to forcibly impart thereto an upwardly directed feed movement which during each revolution of the drill is considerably smaller than the pitch of the helix or helices, the drill head being adapted to positively distribute the binder over the entire cross section of the drill head, a lost-motion clutch being mounted in the drill rod and adapted, through the intermediary of a movement transmitting system, upon relative movement between the clutch members, to actuate a valve mounted in the binder fluid supply conduit so as to cause the valve to be closed during screwing down the drill into the earth but to be opened when, during its withdrawal from the earth, the drill is rotated in the opposite sense.

12. Apparatus according to claim 11, characterized in that the earth drill is adapted to receive easily breakable capsules, fed by means of pressure air and containing powdered binder.