WO1986003532A1

WO1986003532A1 - Grout stabilisation

Info

Publication number: WO1986003532A1
Application number: PCT/EP1985/000668
Authority: WO
Inventors: Klaus Esters; Herbert Samol
Original assignee: Gkn Keller Gmbh
Priority date: 1984-12-07
Filing date: 1985-12-05
Publication date: 1986-06-19
Also published as: AT398594B; GB8618148D0; GB2188351B; ATA904885A; GB2188351A

Abstract

A method of jet grouting in which a monitor tube (25) is used to make a bore (31) and is then withdrawn to make a grouted panel (29). Before the grout in the bore (31) has set an apertured (13) grouting tube (12) is inserted into the bore. When the grout in the bore (31) has solidified, further grout is supplied to the tube (12) under such pressure as to fracture the grout in the bore (31) and so as to permeate into the surrounding ground.

Description

GROUT STABILISATION

This invention relates to a process known as jet grouting. In such a process the ground below the surface is eroded by a high pressure fluid jet and the void created is filled with a grout comprising cement and water and optionally other ingredients depending on the purpose for which the grouting is being carried out.

Two methods of jet grouting are described in British Patent Specifications Nos. 1,358,431 and 1,558,694 respectively. In each case it is possible to produce flat panels or columns.

In the method described in Specification No. 1,358,431 a hole is bored in the ground and a tube is inserted into the hole with a nozzle assembly adjacent to its end. A jet of grout surrounded by a jet of high pressure air are injected radially from the nozzle into the ground as the tube is lifted. The jets s erve simultaneously to erode the soil and to fill the void with grout. The hole may be bored by a high pressure jet of water discharged from a nozzle at the end of the tube.

In Specification No. 1,558,694 a similar arrangement is disclosed except that adjacent the bottom of the tube there is an upper nozzle assembly which discharges high pressure water and air to erode the ground and at a lower position of the tube there is a separate nozzle for supplying grout. Thus as the tube is lifted the air and water from the upper nozzle create a void which is subsequently filled with grout from the lower nozzle. In either of the above arrangements the tube can either be rotated while it is being lifted thus to produce a generally cylindrical column or the tube may be lifted without rotation. In the latter case a substantially vertical panel is formed. Normally the columns or panels are disposed vertically but they may also be disposed longitudinally in which case, of course, the tubes would be moved horizontally.

British Patent Specification No. 1,358,431 corresponds to U.S. Patent No. 3,802,203 of Ichise et al issued April 9th, 1984 and British Patent Specification No. 1,558,694 corresponds to U.S. Patents Nos. 4,047,580 and 4,084,648 of Yahiro et al issued September 13, 1977 and April 18th, 1978 respectively.

In addition it is known, inter alia from U.S. Patent No. 3,800,544 of Nakashini, issued April 2nd, 1974 to carry out jet grouting without the use of compressed air, the high-pressure grout itself serving to erode the ground and simultaneously filling the void produced therein.

In all jet grouting, not all the eroded soil is removed, the larger pieces remain and serve as aggregate in the injected grout.

Normally panels are used for ground water control since they do not have any great load-bearing strength. An object of the invention is to provide a jet grouting process in which panels are formed as described above and in which the ground surrounding the panels is additionally strengthened with an economical use of grout to increase the volume and thus the load-bearing capacity of the strengthened ground. According to the invention we provide a method of ground stabilisation by jet grouting comprising the steps of:

producing an elongated bore in the ground;

eroding the ground in a radial direction from the bore in a progressive manner from one end of the bore towards the other end thereof and injecting a first grout into the eroded ground and the bore to form a panel;

subsequently inserting a grouting tube into the bore before the first grout therein has solidified, the grouting tube having outlets spaced along its length,

permitting the first grout in the bore to solidify to an extent such that sufficient pressure can be generated in the tube to cause rupture of the solidified grout in the bore;

and supplying a second grout to said tube at or above such pressure to rupture the solidified first grout in the bore and to cause the second grout to permeate the ground adjacent to the panel and to form therewith an enlarged, stabilised volume of ground.

The method enables a given volume of stabilised ground to be produced with an economical use of grout and by use of panels which have not heretofore been used for load-bearing.

Preferably the pressure in the grouting tube to rupture the solidified first grout is generated sequentially in discrete lengths of the grouting tube preferably by the use of a packer which is moved progressively from one end of the grouting tube to the other. Thus the first grout is ruptured progressively along the length of the bore.

In carrying out the method the ground may be eroded and jet grouted from the bore in two opposed or inclined radial directions simultaneously so as to form a flat or V-shaped panel with the bore substantially in the centre thereof, alternatively two panels may be formed in the shape of an X, with the bore in the centre thereof, by repeating the grouting step.

In another way of carrying out the method the panel is formed by eroding the ground between said bore and a second bore parallel to the first-mentioned bore and the grouting tube is inserted in to either one of the bores and second grout supplied to said tube in such manner as to permeate the ground adjacent the panel. Alternatively the method may be carried out by inserting a grouting tube into each bore and second grout is supplied to each of said tubes in such manner as to permeate the ground adjacent to the panel.

The method may be carried out to produce a number of panels from first grout starting from separate bores and arranging the panels in the ground so that the panels intersect to form a substantially continuous structure and then injecting second grout into the ground from at least some of the bores to positions adjacent to said structure to form therewith an enlarged stabilised volume of ground. The panels may be arranged to form an array of continguous tubes which touch where the bores are situated and the second grout may be injected into areas on one or both sides of said array. Preferably, during production of the or each bore a thixotropic flushing agent is used to remove the spoil and to stabilise the bore. The flushing agent may comprise a mixture of water, bentonite and cement.

The second grout may be introduced into the grouting tube at a pressure of between 20 and 50 bar. The first grout may be caused to form the or each panel at a pressure of between 50 and 100 bar. When ground erosion is effected by a high pressure water jet this may move at a speed of between 150 and 250 metres per second.

The invention will now be described in detail by way of example with reference to the accompanying diagrammatic drawings in which:-

Figures 1 and 2 illustrate the use of the process to produce a stabilising structure under ari existing building, Figure 2 being a section on the line 2-2 of Figure 1 ;

Figure 3 illustrates the production of the structure by jet grouting;

Figure 4 is a view on a larger scale of part of Figure 3;

Figure 5 is a cut-away perspective view showing the structure in position;

Figure 6 is a section through a grouting tube;

Figure 7 is a diagrammatic section showing additional grouting after the structure of Figure 5 has been produced; Figures 8 and 9 show cross sections of other structures which may be produced;

Figure 10 is a diagram similar to Figure 7 of additional grouting from the structure of Figure 9; and

Figure 11 is a diagram showing another method of making a panel by jet grouting.

Referring first to Figures 1 .and 2 the lower part of a building is indicated at 1 and ground level at 20. A subterranean tunnel 2 is located under the building and a structure 3, as will be described, is interposed between the building and the tunnel 2 to prevent settlement of the building. The structure is made by jet grouting as will now be described.

Firstly, shafts 21 are sunk into the ground at a spacing greater than the length of the building and at positions offset therefrom as shown in Figure 2. A tunnel or gallery 4 is then driven between the shafts 21 so as to lie alongside, but below the level of, the building's foundation. A tunnel such as 4 may be provided on each of two opposite sides of the building if required and a structure such as 3 made from each tunnel.

Referring to Figures 3 and 4, the tunnel 4 is shown as containing vari ous conduits indicated generally at 22 for providing compressed air, water and grout as will be described. Mounted on a carriage 23 which is movable longitudinally of the tunnel 4 is a monitor-handling machine 24. The monitor-handling machine has secured thereto a sectional monitor tube 25 whose length can be increased or decreased by adding or removing sections. As described in the aforementioned patent specifications the monitor tube has, at its ends, a pair of jets 26, 26 a which are arranged to discharge liquid and air with the air being discharged as a collar around the liquid. Discharged from each jet is a stream of grout surrounded by a stream of compressed air.

However, as described in British Patent Specification No. 1,558,694 the monitor tube may have two sets of nozzles at its end, one set nearer to the tunnel 4 for discharging high pressure water with a surrounding collar of air and one near the end 27 of the tube for discharging grout. The monitor tube 25 is received in a guide tube 5 which passes through the wall of the tunnel being sealed thereto by a labyrinth seal 5 a . The tube 25 is first moved in the direction of arrow 28 to form a bore 31 in the subsoil 30. This may be done by providing a drill at the end of the tube or by providing a high pressure jet (not shown) at the end of the tube as described in said prior specifications. The length of the tube 25 will be increased as required by adding sections.

During the drilling or eroding of the hole 31 a thixotropic flushing medium may be used which advantageously comprises water, 8% of bentonite and some cement. The flushing medium removes the spoil which can flow up the tube 5 into the tunnel and, depending on the soil structure, can solidify in the bore to hold it open for the next stage of the method or may form a lining in the bore to stabilise it if the soil is porous. Alternatively the tube 5 may be advanced to the bottom of the bore 31 during its formation and a non-thixotropic flushing agent may be used. After the bore 31 has been produced the tube 25 is retracted in the direction of the arrows 28 a by shortening the tube while grout is injected as indicated at 7. It will be seen that the grout is injected in two opposite directions thus producing two panels in the soil as indicated at 29 and referred to below.

Excess grout carrying the eroded soil returns up the bore 31 and the tube 5 as indicated by the arrows 7 a in Figure 4. The excess grout leaves the tube 5 via preventers 5 b of known construction and the resistance to flow of the grout can be adjusted by the preventers to adjust the pressure at which the grouting takes place which is advantageously between 50 and 100 bar. If a water and air jet is used to erode the soil as described in British Specification No. 1,558,694, the speed of the water may advantageously be between 150/250 metres per second. If a thixotropic flushing agent has been used during production of the bore 31, this is removed with the excess grout during formation of the panels.

Referring to Figure 5, the operations described in relation to Figures 3 and 4 are repeated to produce a cell like structure as will now be described. Thus referring to the right-hand part of Figure 5, the bore 31 is indicated and panels 29 which have been formed by withdrawing the monitor tube 25 as described in Figures 3 and 4. The material in the bore 31 still being in an unset state, the monitor tube 25 is then returned to the bottom of the bore 31 and turned through 90 degrees and again moved in the direction of the arrows 28 a to provide two further panels 32 which are at right angles to the panels 29. The above operations are repeated from a bore 33 to form panels 34 and 35. The panel 29 intersects with the panel 34 at 36 and the panel 32 intersects with the panel 35 at 37. A still further bore 38 is provided and further panels 39 and 40 are produced as described, the panels 35 and 39 intersecting at 41 and the panels 34 and 40 intersecting at 42. It will be seen that there is thus produced a horizontal structure consisting of a number of generally square-section tubes arranged with their cross-sectional diagonals vertical and horizontal and touching at the bores 33 and 38.

Into the bore 31, before the material therein has solidified, there are inserted two grouting tubes 1 2 as shown in Figure 5. One of the tubes is illustrated in detail in Figure 6. The tube is closed at one end at 43 and is provided, along its length, with spaced apertures some of which are indicated at 13. The apertures are closed by rubber sleeves 14 closely fitting over the tube. The sleeves prevent the ingress of grout or water into the tube 12 as it is inserted into the bore 31. Instead of sleeves 14, the apertures 13 may contain non-return valves or be replaced by weakened wall portions of the tube wall which will rupture under a predetermined pressure. Arranged within the tube is a packer consisting of a cylindrical member 44 closed at one end at 45 and carrying 0-rings 46 which seal with the internal surface of the tube 1 2. The cylindrical member 44 is provided with apertures 47 which communicate with the cylindrical space between the tube 12, the member 44 and the 0-rings 46 and thus with the apertures 13. The member 44 is secured to a tube 48 along which grout can be supplied from the conduits 22 as will be described below. As shown in Figure 5, two tubes such as 12 are inserted into each of the bores 31 , 33 and 38. The bore 31 is shown by way of example in Figure 7 with the two tubes 12 in position. The grout in the bore 31 is now allowed to solidify to at least an extent that it grips the tubes 12 in a substantially liquid-tight manner. Further grout is now supplied down the tube 48; if the pressure is sufficient, e.g. a pressure of 20 to 50 bar, the grout will lift the rubber sleeves 14 away from the tube 12 and the grout will pass through the apertures 13. Because the grout in the bore 31 is solid the liquid grout delivered from the apertures 13 cannot flow up outside the tubes 12 but will rupture the grout in the bore 31 in its weakest positions 49 and 50 as shown in Figure 7. The liquid grout will thus be delivered at 51 into the ground surrounding the panel structure. The grout thus being forced into the ground strengthens it and the escape of the grout from its injected positions is controlled by the configuration of the panels. The formation of the latter has prefractured the ground making it easier for the liquid grout to enter the interstices thereof.

The packer is moved progressively along the tube 12 so that the grout in the bore 31 is progressively ruptured along the length of the bore and the ground alongside each panel progressively solidified along the length thereof. It will be seen from Figure 7 that grout supplied to the upper tube 12 is injected upwardly and grout from the lower tube 12 is injected downwardly, thus the apertures 13 advantageously point in the direction that it is desired the grout will travel in the ground.

This grouting from the tubes 12 can be carried out in one or a number of stages . Differ ent compositions of grout can be used in the different stages if desired.

Where a dual jet grouting system such as described in British Patent Specification No. 1,558,694 is used and there is a separate water jet for eroding the soil this may have a speed of between 150 and 250 metres per second. In either process the grout used to make the panels may be injected at a pressure of between 50 and 100 bar.

The advantage of the invention is that one can produce strip like panels by jet grouting which, although they do not have a great deal of inherent strength, may be arranged in a cell like form as described in relation to Figure 3 and then further strengthened by injecting grout surrounding the cells. By downward injection an upward pressure may be induced in the ground with a tendency to lift a building above the structure.

Figure 8 shows a different form of horizontal panel structure which can be provided by forming pairs of panels in a V-shaped orientation. Thus panels 60 and 61 are produced from a bore 62 and panels 63 and 64 from a bore 65. A single tube such as 12 may be inserted into the bore 62 to provide grout injection 66 and two tubes such as 12 may be inserted in bore 65 to produce grout injection 67 and 68.

Figure 9 shows a similar arrangement to Figure 8 but with the bores at the bottom of the V-shaped structure. Thus from bores 69 and 70 are produced panels 71 and 72 respectively. One or more tubes such as 12 inserted into the bore 71 can produce a grouting pattern such as shown at 72. Figure 10 shows this in more detail. Although the invention has been described in detail in relation to a horizontal structure; a vertical load bearing structure could also be made in the same manner.

Figure 11 illustrates a further method of making vertical panels in a known way. Two bores 75 and 76 are used. A monitor tube 77 is lowered down the bore 75 by a monitor tube handling machine 78 and a water and air jet 79 is used to erode the space between the bores 75, 76 which is then filled with grout by a jet 80. After the panel is complete, tubes such as 12 may be inserted into either or both of the bores 75 and 76 and after the grout therein has solidified further grouting may take place from the tubes. This method may also be used to provide horizontally extending panels as described above.

Claims

1. A method of ground stabilisation by jet grouting comprising the steps of:

producing an elongated bore in the ground;

2. A method according to Claim 1 wherein said pressure is generated sequentially in discrete lengths of the grouting tube.

3. A method according to Claim 2 wherein said pressure is limited to said discrete lengths of the grouting tube by the use of a packer which is moved progressively from one end of the grouting tube to the other.

4. A method according to any one of Claims 1 to 3 wherein the ground is eroded and jet grouted from the bore in two opposed or inclined radial directions simultaneously so as to form a flat or V-shaped panel with the bore substantially in the centre thereof.

5. A method according to Claim 4 wherein two panels are formed in shape of an X with the bore in the centre thereof by repeating the grouting step.

6. A method according to any one of Claims 1 to 3 wherein the panel is formed by eroding the ground between said bore and a second bore parallel to the first-mentioned bore and wherein the grouting tube is inserted in to either one of the bores and second grout is supplied to said tube in such manner as to permeate the ground adjacent the panel.

7. A method according to Claim 6 wherein a grouting tube is inserted into each bore and second grout is supplied to each of said tubes in such manner as to permeate the ground adjacent to the panel.

8. A method comprising producing a number of panels from first grout and starting from separate bores according to any one of the preceding claims, arranging the panels in the ground so that the panels intersect to form a substantially continuous structure and then injecting second grout into the ground from at least some of the bores to positions adjacent to said structure to form therewith an enlarged stabilised volume of ground.

9. A method according to Claim 8 wherein the panels are arranged to form an array of continguous tubes which touch where the bores are situated and wherein the second grout is injected into areas on one or both sides of said array.

10. A method according to any one of the preceding claims wherein during production of the or each bore a thixotropic flushing agent is used to remove the spoil and to stabilise the bore.

11. A method according to Claim 10 wherein the flushing agent comprises a mixture of water, bentonite and cement.

12. A method according to any one of the preceding claims wherein the second grout is introduced into the grouting tube at a pressure of between 20 and 50 bar.

13_' A method according to any one of the preceding claims wherein the first grout is caused to form the or each panel at a pressure of between 50 and 100 bar.

14. A method according to any one of the preceding claims wherein the ground erosion is effected by a high pressure water jet moving at a speed of between 150 and 250 metres per second.

15. A method of ground stabilisation substantially as hereinbefore described with reference to the accompanying drawings.