GB1558694A - Consolidation of underground masses - Google Patents

Description

(54) CONSOLIDATION OF UNDERGROUND MASSES (71) We, KAJIMA CORPORATION of No. 2-7, Moto-Akasaka l-chome, Minato-ku, Tokyo, Japan and CHEMICAL GROUT COMPANY LIMITED of No.

1-1, Nishi-Shinjuku 2-chome, Shinjuku-ku, Tokyo, Japan, both Japanese companies, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the consolidation of underground masses and in particular to a method and apparatus for forming a cemented structure underground.

Before initiating a grouting or consolidation process, it is necessary to dig or bore mechanically or hydromechanically a vertical hole into the earth.

It is known to construct sand seams and solidified bodies such as watertight walls by the so-called chemical grouting after digging, crushing, piercing and injecting with high-velocity jets of liquid such as water discharged from nozzles. Highvelocity liquid jets are utilized in various construction techniques known as jet grouting, sand draining, jet piling, etc.

These methods are effectively used because they are high in digging efficiency, provide high energy-density rates and require only a relatively small and simple device for producing a high-velocity liquid jet. It is usually in strata with subterranean water or in the sea floor that high-velocity liquid jets are used for piercing and crushing. The water encountered in such locations rapidly slows down the velocity of jet liquid to reduce the working efficiency of the jet.

Specifically, the in-water distance that the liquid jet can traverse ranges from about 1/10 to 1/15 of the in-air distance that the jet can traverse. This accounts for the inability of a high-velocity liquid jet to perform well when the jet of liquid is directed into a zone df water.

In order to increase the in-water distance that the high-velocity liquid jet traverses, it has been proposed in the prior art that an air jet discharged from a ring-shaped nozzle surrounding the liquid jet nozzle so that the air jet will envelop the high-velocity liquid jet. Devices implementing this proposition have been successful in increasing the distance traversed by high-velocity liquid jets in water and, moreover, the air jet facilitates removal of loosened or crushed sand or the like because of its air lifting effect. An example of such a practice known in connection with jet grouting is disclosed in U.S. Patent 3,802,203 which is incorporated herein as known reference. In this known technique, a pair of coaxial jet nozzles is provided for supplying two liquid chemicals.We have experienced that with such known technique, the effective distance of these liquid jets is rather limited.

Even -with a high-velocity liquid jet enveloped by air jet, a drawback has been noted in that there are fluctuations in the distance traversed by the liquid jet, termed the liquid jet distance in this specification, thus introducing discontinuous portions in watertight wall construction, or producing an anisotropic or non-homogeneous deposition of the cementing agent in solidifying work.

It is an object of the invention to provide an improved method of chemical grouting or consolidation wherein the liquid jet-piercing distance into the earth is substantially improved for the purpose of enlarging the grouting zone.

It is a further object to provide an improved method of the above kind providing a possibility for solidifying crushed earth masses, even with use of common cement milk in place of the high price resin based solidifier. It is a further object to provide a relatively high efficiency and low cost method of the above kind.

According to a first aspect of the invention a process for the formation of a consolidated underground mass, comprises the steps of injecting separate jets of liquid and gas arranged concentric to one another laterally within the earth from a elevating first point to fluidically penetrate into the earth and cut the earth, and grouting continuously from a second point with a cementing agent separately from said jets and at a lower level than the jets to solidify a mixture of the earth and the liquid, said second point being elevated concurrently with said first point.

According to a second aspect of the invention apparatus for the formation of a consolidated underground mass comprises a concentric triple-walled pipe rod fitted at its upper end with a swivel and supply assembly arranged to receive separate supplies of compressed air, pressure liquid and pressurized comenting agent and supported for vertical and rotational movement, the pipe rod being fitted at its lower end with a working head comprising a laterally directed double jet nozzle, one nozzle element being concentrically arranged within the other nozzle element, the inner nozzle element being arranged to discharge a liquid jet containing no earth-solidifying agent and the outer nozzle element being arranged to eject a gas jet surrounding the liquid jet, the ejection velocity of said gas jet being at least a half the sonic velocity, the working head being provided with cementing agent discharge means positioned at a lower level than the double jet nozzle.

These and further objects, features and advantages of the invention will become more apparent in the following detailed description of the invention given with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of apparatus according to the present invention in use, Fig. 2 is a side elevation of apparatus according to the invention to a larger scale than that of Fig. 1, Fig. 3 is a similar view to Fig. 2, showing the apparatus at a later step of the process, Fig. 4 is a schematic representation of part of the apparatus of the invention Fig. 5 is a schematic sectional view of a nozzle unit of the invention, Fig. 6 is a vertical section of another part of the apparatus, Fig. 7 is a vertical section of a further part of the apparatus, and Figs. 8-11 are several diagrams illustrative of the functional effects of the method of the invention.

A portable combined digging and grouting machine is shown at 1 in Fig. 1. An elongated pipe rod 3 of a predetermined length, say 30 metres, is mounted at an intermiediate point of its length to be vertically movable in the machine 1. This pipe rod can be rotated around its own central axis when occasion desires.

The machine 1 is at ground level G. The pipe rod comprises a number of pipe rod elements detachably joined one after another by screw coupling means or the like, (not shown). The pipe rod extends into a hole 2 previously formed in the earth by an auger or like means. A working head W' is detachably attached to the lower end of the pipe rod.

The machine 1 comprises an air compressor and a pump which are shown only schematically in the form of a block diagram in Fig. 4. An air pipe 5 extending from the compressor C and a liquid pipe 6 extending from the pump P are connected to a combined swivel and supply assembly S (see Figs. 2, 3 and 6) attached to the top end of pipe rod 3, the working head W' being positioned at the lower end of the latter.

Fig. 5 shows a nozzle 4 of the head W' in longitudinal section, wherein at the centre of the nozzle is a liquid-jet passage 7 to which liquid pipe 6 conveys the liquid. Note in Fig. 5 that the centre passage 7 is surrounded by air-jet passage 8 which is annular in its traverse cross section and to which air pipe 5 conveys air, as will be more fully described hereinafter.

The air supplied by compressor C is released from the air-jet passage 8 while the liquid is discharged from liquid-jet passage 7, so that, when both air and liquid are being discharged, the stream of jet liquid becomes surrounded by the annular stream of air.

When the working head W', and thus the nozzle 4 is immersed in water, the stream of air from passage 8 surrounds the liquid jet from the centre passage 7, isolating the water jet from the surrounding water in the hole so that it is discharged as if the nozzle were being used immersed in air. This manner of discharge from the nozzle enables a highvelocity liquid jet to be generated and maintained to traverse a greater distance in the water than is otherwise possible.

We have discovered that there is a close relationship between the distance traversed by the high-velocity liquid jet of the above kind and the velocity of the enveloping ring air jet issuing from the outer air-jet passage 8 of the nozzle assembly 4. The basis of this relationship will be explained hereinbelow with reference to Fig. 8.

In Fig. 8, the jet stream J emerging from a nozzle N increases its transverse crosssectional area as the liquid advances from the nozzle tip. A position X1 of the stream is assumed to be located at a given distance from the nozzle tip and its cross-sectional area is further assumed to have a value A, the corresponding stream velocity being expressed by U. At another position X2, separated by an infinitesimally small distance from the said position X1, dA represents an increment of cross-sectional area and dU the corresponding reduction in velocity, both occurring over the small distance between these two positions under consideration. Then, we obtain the following equation: dU/U=(dA/A)/( 1 -M2) where M stands for a Mach number.

Theoreticalls. the denominator in the right-hand part of the above equation approaches zero if the velocity of the discharging air stream approaches the unit Mach nnumber 1; and, since dU/U is finite, dA too must also approach zero. Stated differently, if Ml, then dA4), meaning that there is no increase in the crosssectional area of the jet stream. Applying this relationship to the air jet produced by the ejection of air from the outer air jet passage 8 of the combined nozzle 4, it will be seen that, if the air is ejected at a velocity equal to its unit Mach number, the air jet surrounds the core liquid jet and rushes forward with the central jet; Consequently, the liquid jet does not increase its cross section and is thus forced to traverse a greater distance.

Fig. 9 represents a graph showing the results of experimental tests in which the velocity of the air jet is varied. In this graph, the distance expressed in centimetres from the nozzle is plotted against the air jet velocity in cm/second. In addition, the pressure reduction ratio Pm/Pe is taken as a parameter, Pm representing the pressure in the axial direction of the air jet flow appearing at a variable distance measured from the nozzle outlet and P0 representing the pressure measured at the nozzle outlet.

These pressures are in the direction of liquid flow. Curves V, W, X, Y and Z are plotted for Pm/Po ratios of 1/100, 1/50, 1/10, 1/5 and 1/2, respectively, in that order. The vertical broken lines R1 to R7, inclusive, represent several selected ratios of the variable air velocity U to the maximum air velocity U to the maximum air velocity Urn (of which mention will be made hereinafter).

Specifically, these selected ratios are 8/10 for R1, 7/10 for R2, 6/10 for R3, 5/10 for R4, 4/10 for R5, 3/10 for R6, and 2/10 for R,. On the other hand, the sonic speed of air varies with temperature and its range is normally between 330 and 345 m/sec. In the present experiment, May=329 m/sec. is adopted so that one-half the sonic speed amounts to 165 m/sec. The nearly vertically extending broken line curves P, to P5, inclusive, represent the ratio of traversed distance to the maximum distance Xmax, the ratio being 0.9 for P1, 0.8 for P2, 0.7 for P3, 0.6 for P4 and 0.5 for P5, respectively.

It will be seen in Fig. 9 that the higher the velocity of the air jet, the greater will be the distance traversed by this jet. Curves V to Z, inclusive, flatten out or level off in the region of higher air jet velocity U. In order to secure a traversed distance which is, say, 900/, of the maximum traverse distance Xmax corresponding to the maximum air jet velocity Umax, the air jet must take a velocity value appearing at the right hand region from curve P,. This means that the air velocity in this case must be at least half the sonic speed.

Referring to Fig. 6, a preferred embodiment of the combined swivel and supply assembly S is shown.

This assembly S comprises a stationary outer sleeve unit 30 consisting several sleeve parts screw-coupled one to another as shown, a rotatable outer sleeve unit 34 being partially held in and by the said stationary unit 30 through anti-friction bearings 32.

The assembly S further comprises a rotatable and concentric intermediate sleeve unit 20 consisting of several sleeve elements screw-coupled one to another as shown.

An outer cementing agent passage 36 is formed between the outer and intermidiate sleeve units 34 and 20 and communicates with a lowermost inlet socket 42 made integral with the outer sleeve unit 30 for receiving a cementing agent preferably a cement milk having a cement/water ratio, say 50:50. A compressed air passage 38 is formed between the rotatable intermediate and core sleeve units and communicates with an intermediate inlet socket 44 made integral with the stationary outer sleeve unit for receiving compressed air from the compressor C. A high pressure water passage 40 is provided by the interior space of the core sleeve unit 25 and communicates with an upper socket 48 made integral with the said stationary outer sleeve unit, for receiving pressurized water from the pump P.

Although not specifically shown, pipe rod 3 is built into a triple-walled structure comprising an outer pipe, an intermediate pipe and a core pipe being rotatable in unison and each of the pipes comprising a number of pipe elements coupled together.

The upper most pipe elements of these pipes are detachably coupled with respective lower ends of the outer, intermediate and core sleeve units, in known manner.

Referring to Fig. 7, the working head W' comprises an outer sleeve 52 having a female-screwed upper end coupled with the outer pipe of the rotatable pipe rod 3. There is provided an intermediate sleeve 53 which is integral at its lower end with the said outer sleeve. An auxiliary smaller sleeve 57 is attached fixedly to the sleeve 53 by pressure fitting, or welding, or like conventional fixing technique. This auxiliary sleeve is adapted for sealingly receiving the lowermost end of the intermediate pipe of the pipe rod 3, as clearly shown.

The head S is further provided with a sleeve 55 for sealingly receiving the lower end of the centre pipe of the pipe rod.

There is a mounting piece 59 positioned within and at the centre of the head S, and receiving snugly and axially the lower end of the core sleeve 55 and at the same time, mounting laterally the double nozzle 4 already referred to.

A cement milk passage 54 is formed between outer sleeve 52 and intermediate sleeve 53, thus leading to the corresponding inlet socket 42.

In the similar way as before, compressed air passage 56 and high pressure water passage 58 are formed, leading to the respective inlet sockets 44 and 48, respectively. The bottom end of the intermediate sleeve is tightly closed by a screw plug 61 which has a screwed connection at 62. This plug serves at the same time for mounting the mounting piece 59.

The working head W' is further provided with a hollow tip member 66 which is screwed at 63 into the lower end of outer sleeve 52, the inside space 64 of the tip member serving as a part of the cement milk passage kept in fluid communication with passage 54. Two or more inclined outlet passages 68 are provided within the tip member which permanently communicates the inside space 64. As an alternative measure, a plurality of lateral outlet passages may be provided as at 68a shown by broken lines.

The operation of the foregoing machine is as follows: It is assumed that a water tight barrier wall is ta be constructed in the earth and along the plane of the paper of Fig. 1.

At first, a number of vertical holes or shafts are dug or bored into the earth, only three of which are shown at 2a; 2 and 2b in Fig. 1.

In practice the machine 1 may be separated into a crane vehicle 24 and a stationary supporting device 22, as shown in Fig. 2, the device 22 being fitted with an engine and transmission means, not shown, for rotating the pipe rod 3, in addition to driving said compressor C and pump P.

These mechanical devices are of conventional form.

For initiating the method of the invention, crane vehicle 24 and supporting device 22 are positioned in proximity to a selected one of the holes or shafts above referred to, and then a crane 18 of a conventional telescopic kind is extended from the vehicle 24 for suspending the swivel and supply unit S coupled with the pipe rod 3 and working head W', by means of its hoisting wire cable 19 and its suspension hook 17.

Then, the crane 18 is sa operated to lower the pipe rod assembly 3 into the selected shaft 2 until the working head W' is positioned nearly at the lower end of the shaft 2. A certain rotational movement is applied to pipe rod 3 through a rotatable and releasable grip 22a of conventional design, so as to direct the double nozzle towards the neighboring shaft 2a, for example.

Next, compressor C supplies compressed air, say at 7 kg/cm2, through the corresponding air passage in the assembly S, pipe rod 3 and working head W' towards the outer nozzle 8 of the double nozzle assembly 4 for the delivery of a ring air jet and then the pump P is driven to feed high pressure water through liquid passages in the assembly S, pipe rod 3 and working head W' towards the core nozzle 7 for the injection of a water jet surrounded by the ring air jet.

By these jet actions, the ground between the lower ends of both shafts 2 and 2a is fluidically penetrated to communicate with each other. Then, the latter hole or shaft 2a acts as a slime discharge passage, working on the principle of a bubble pump. Even if such slime discharge shaft 2a is not provided, the whole plant can function, because the space defined by and between the shaft wall 2 and the pipe rod 3 serves for the similar slime discharge passage.

Then, the crane 24 is started to gradually elevate the pipe rod and associated assembly and at the same time, the cement milk supply pump is operated to feed such milk through the corresponding passages in the unit S, pipe rod 3 and working head W' towards the outlet openings 68 or 68a, as required and at a lower level than the axis of core water jet. Then, the broken ground in the bottom of the hole crushed and sedimented by the water jet is solidified into a gradual upwardly developing cemented wall. For this purpose, the cement is preferably of rapidly solidifiable character.

This earth-solidifying process at its intermediate step is shown only schematically in Fig. 1 at 100. A slime mass appearing on the ground level G after passage through the neighboring slime shaft 2a, conveyed in the form of a liquid suspension and under the action of a kind of bubble pump and assisted by the pressurized liquid-air-earth mixture prevailing in the upper part of the liquid-cut space 100 in the ground, is shown at 101 in Fig. 1.

The process is continued until the working head W' appears at ground level G.

Then, the machine 1 is moved to a next position in proximity to the next shaft 2b and the pipe rod is again lowered until its working head W' is brought to its initial working position, as shown in Fig. 2, and so on.

In the foregoing operational mode, rotational motion is not applied to the pipe rod assembly including the unit S and head W'. In this case, the cemented barrier wall will be formed within a rather limited space range, connecting the shafts 2a; 2 and 2b.

The cement milk, may be added with any commercial solidification accelerating agent, if necessary. Core water supply pressure may be in the range 400-500 kg/cm2. Milk supply pressure may preferably be 1050 kg/cm2.

When rotational movement is applied to the pipe rod assembly, the earth-solidifying space can be enlarged into a cylindrical space around the vertical axis of the selected shaft as at 2, as schematically shown at 70 in Fig. 3.

Although not shown, the cement milk feed pump is preferably mounted on the support device 22, and a feed hose or pipe 16, only partially and schematically shown in Figs. 2 and 3, extends from the delivery outlet of the pump to the lowest socket inlet 42 of the assembly S. Pipes or hoses 5, 6 and 16 are conveniently handled together as at 50 in Figs. 2 and 3, for convenience of handling thereof during the lowering and raising operation of the pipe rod assembly.

For this purpose, part of the pipes schematically shown in Fig. 4 may be replaced by hoses.

The rate of slime discharged through the slime shaft and appearing on the ground surface G may amount to about 50 sÓ of the liquid-crushed earth mass. More specifically, the resultant slime is forced to appear at the ground surface through guide hole 2a or 2b, and is continuously discharged. While this process is in progres, the cement milk is injected into the growing columnar cavity from outlet openings 68 or 68a of the working head. The supplied milk mixes with part of the earth being crushed, and the mixture increases in volume to fill up the cavity. After a certain time lapse the mixture solidifies and thus changes to a cemented mass 100 or 70.This mass 100 or 70 is much like conventional piles driven into the ground, and may serve well as a supporting structure for a building or oil tank In the graph of Fig. 10, comparison is made of the data taken on a high-velocity liquid jet discharged into the air with that enveloped with a ring air jet directed into a water mass according to the method according to this invention. Curve M represents the former experiment, while curve N the latter. These two curves must not be construed as determining the distance traversed by either jet as a function of Pm/P0; they tell at what point in the length of the jet a certain pressure drop occurs.

note that Pm/Po is scaled on the vertical axis of the graph, and the ratio of actual jet penetration distance (or jet length) to the initial region lo of the jet is scaled on the horizontal axis. The portion of primary interest of the curve is the flat portion (Fig.

11). It will be seen that the length of initial region lo is practically the same for the two identical liquid jets, one being directed into the air without any protecting air jet and the other being directed into the water and accompanying a protecting air jet.

The meaning of the "initial region lo" will become apparent with reference to Fig. 11.

The curves X and Y stand for the same high-velocity liquid jet, having an initial (nozzle outlet) pressure of 200 kg/cm2.

Curve X refers to the jet directed into the air and curve Y to the same without any assistance of the protecting air jet directed into the water. In the latter case, jet pressure Pm starts to fall earlier than in the former, resulting in a shorter initial region lo Comparison of curve Y (of Fig. 11) with curve N (of Fig. 10) clearly suggests superior merits of the method of this invention.

As an example of the merit of the present invention, it should be noted the resulting column like cemented cylindrical mass will have a diameter of 0.8-1.6 metres when the pipe rod is rotated around together with its working head W'.

The pipe rod 3 comprises three concentric passages wherein the central passage allows passage of said liquid, the intermediate passage is used for compressed air and the outermost passage is used for said cement milk. It is seen that in this way, the medium at lowest pressure flows in the outermost passage, while the medium at highest pressure flows through the central passage. In this way, most effecient design for rigidity of the pipe rod is positively assured.

With the separate and independent extrusion of the cement milk and the liquidair combined jet with the milk discharged at a lower level than the latter, earthpenetration and cement milk-application can be executed concurrently, yet separately. In this way, the desired slimedischarging effect is positively assured, At the same time, the earth-cutting operation is improved, by virtue of the provision of a kind of liquid-and-gas purging means. When utilizing such combined and concentric liquid-air jet as conventionally known by the teachings of U.S. Patent 3,802,203 wherein at least part of liquid jet contains earthsolidifying agent, slime could be discharged, since any discharge of the liquid will invite a considerable loss of the solidifying agent which is costly.In the process according to the invention, the liquid containing no such agent will act to cut into the earth for crushing same, while the resulting bubbled water-and-earth mixture is gradually discharged through the slime shaft or the like and the remaining mixture will gradually solidify and become cemented from below.

WHAT WE CLAIM IS: 1. A process for the formation of a consolidated undergound mass, comprising the steps of injecting separate jets of liquid and gas arranged concentric to one another laterally within the earth from a elevating first point to fluidically penetrate into the earth and cut the earth, and grouting continuously from a second point with a cementing agent separately from said jet and at a lower level than the jets to solidify a mixture of the earth and the liquid, said second point being elevated concurrently with said first point.

2. A process according to claim 1, comprising purging part of the earth and liquid mixture for reducing the accumulated pressure in the cavity formed by the injected liquid jet.

3. A process according to claim 1 or 2, comprising simultaneously rotating said first and second points in phase and at the same rotational speed and about a vertical axis.

4. A process according to claim 1, 2 or 3 wherein the liquid is water, and the gas is air.

5. A process according to any one of the preceding claims wherein the ejection velocity of the gas jet is at least a half the sonic velocity.

6. Apparatus for the formation of a consolidated underground mass comprising a concentric triple-walled pipe rod fitted at its upper end with a swivel and supply assembly arranged to receive separate supplies of compressed air, pressure liquid and pressurized cementing agent and supported for vertical and rotational movement, the pipe rod being fitted at its lower end with a working head comprising a laterally directed double jet nozzle, one nozzle element being concentrically arranged within the other nozzle element, the inner nozzle element being arranged to discharge a liquid jet containing no earth-solidifying agent and the outer nozzle element being arranged to eject a gas jet surrounding the liquid jet, the ejection velocity of said gas jet being at least a half the sonic velocity, the working head being provided with cementing agent discharge means positioned at a lower level than the double jet nozzle.

7. Apparatus according to claim 6 wherein the triple-walled pipe rod comprises three concentric passages, a central passage for said liquid, an intermediate passage for compressed air, and an outer passage for said cementing agent.

8. Apparatus for the formation of a consolidated underground mass substantially as described with reference to Figs. 1 to 7 of the accompanying drawings.

9. A process for the formation of a consolidated underground mass substantially as described and with reference to Figs. 8 to 11 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. agent will act to cut into the earth for crushing same, while the resulting bubbled water-and-earth mixture is gradually discharged through the slime shaft or the like and the remaining mixture will gradually solidify and become cemented from below. WHAT WE CLAIM IS:

1. A process for the formation of a consolidated undergound mass, comprising the steps of injecting separate jets of liquid and gas arranged concentric to one another laterally within the earth from a elevating first point to fluidically penetrate into the earth and cut the earth, and grouting continuously from a second point with a cementing agent separately from said jet and at a lower level than the jets to solidify a mixture of the earth and the liquid, said second point being elevated concurrently with said first point.

2. A process according to claim 1, comprising purging part of the earth and liquid mixture for reducing the accumulated pressure in the cavity formed by the injected liquid jet.

3. A process according to claim 1 or 2, comprising simultaneously rotating said first and second points in phase and at the same rotational speed and about a vertical axis.

4. A process according to claim 1, 2 or 3 wherein the liquid is water, and the gas is air.

5. A process according to any one of the preceding claims wherein the ejection velocity of the gas jet is at least a half the sonic velocity.

6. Apparatus for the formation of a consolidated underground mass comprising a concentric triple-walled pipe rod fitted at its upper end with a swivel and supply assembly arranged to receive separate supplies of compressed air, pressure liquid and pressurized cementing agent and supported for vertical and rotational movement, the pipe rod being fitted at its lower end with a working head comprising a laterally directed double jet nozzle, one nozzle element being concentrically arranged within the other nozzle element, the inner nozzle element being arranged to discharge a liquid jet containing no earth-solidifying agent and the outer nozzle element being arranged to eject a gas jet surrounding the liquid jet, the ejection velocity of said gas jet being at least a half the sonic velocity, the working head being provided with cementing agent discharge means positioned at a lower level than the double jet nozzle.

7. Apparatus according to claim 6 wherein the triple-walled pipe rod comprises three concentric passages, a central passage for said liquid, an intermediate passage for compressed air, and an outer passage for said cementing agent.

8. Apparatus for the formation of a consolidated underground mass substantially as described with reference to Figs. 1 to 7 of the accompanying drawings.

9. A process for the formation of a consolidated underground mass substantially as described and with reference to Figs. 8 to 11 of the accompanying drawings.