EP0247135A1 - A method and an arrangement for control and guidance of the extent of the injection zone when a curable binder is jet injected in soils - Google Patents

Abstract

Method and device for controlling and monitoring the extent of an injection zone in the longitudinal direction during the jet injection of a polymerizable binder into on-site soils in order to produce load-bearing or support structures , for example piles, pillars, panels, shields, preferably made of cement, by means of a jet injection head (A) mounted on a rod and comprising an upper nozzle (11) delivering a jet of water surrounded air, and a lower nozzle (13) for injecting said polymerizable binder. The jet injection head (A) provided with excavation blades (17) is used to dig a pilot hole (P) in the ground. As we slowly lift and inject a jet of water / air, the soil of the pilot hole (P) disintegrates and said hole expands to become a larger injection area (I) cross section. Said polymerizable binder is injected via the nozzle (13). A transceiver (12) located between the nozzles (11 and 13) transmits and receives signals which are reflected by the walls of the injection area (I). The processed reflected signals provide a continuous graphical representation on a display (14) of the shape and extent of the injection area (I) and, thus, of the bearing or support structure (K) formed during of the injection operation.

Description

A method and an arrangement for control and guidance of the extent of the injection zone when a curable binder is jet injected in soils.

** ₅ The present invention relates to a method for control and

Λ guidance of the extent of an injection zone across its long¬ itudinal direction when a curable binder is jet injected in soils at a site for erecting carrying or support structures, e.g. piles, piers, wainscots, shields, preferably of cement,

10 with use of a jet injection head of the kind, and used in the manner as stated in the introductory part of the follow¬ ing independent method claim 1.

The invention, furthermore, relates to an arrangement of the ₁₅ above mentioned jet injection head for carrying out said method, and as stated in the introductory part of the follow¬ ing dependent claim 4.

Jet injection is a method for sealing off and strengthening

20 various soils at a site. This method involves loosening the soil structure by the aid of a high pressure water beam sur¬ rounded by air (jet beam), at the same time as a binder, commonly cement grout, is injected. Said binder will displace the loosened material (slurry) flowing up to the surface.

25 It is, thus, possible to build relatively thin panels (thick¬ ness 5-30 cm), piles (diamter 0.8-4.0 ), or to seal up around structures in the soil.

Jet injecting can be carried out in all soils the grain

30 structure of which can be broken down by a jet of water sur¬ rounded by air to permit cement to be injected between the grains. This method is, thus, utilizable in clay as well as

Λ

^■ silt, sand, and gravel, as well as most kinds of fillers and moraines. A high content of rocks and boulders may reduce the

35 disintegrating effect of the jet beam. It should also be possible to use jet injection in boggy soil/peat, since most of the organic material is washed away to be replaced by cement. This, however, was not tried much until now. As com- pared to traditional injection, jet injection may be describ¬ ed as an exchange of materials. Jet injection finds a large range of application and utilization of this method may be listed in three main areas:

Sealing off: When thin panels (shields) are erected in the soil to reduce the flow of water through the area, or to^* seal off around structures in the soil by injecting in zones.

Strengthening of the soil: Injection is carried out beneath existing or new foundations, commonly in the shape of piles.

Stabilization of soil: Temporarily or permanently, often in conenction with building and construction work.

This method will be especially advantageous in connection with necessary foundation work on older buildings since such work may be carried out in a precise and considerate manner and with a minimum of space needed.

For a long time it was known that a high pressure water beam (jet) is able to erode and cut through hard materials. At the end of the 1960's the Japanese and the Russians started research in order to establish whether these qualities could be utilized in building and construction work. Extensive research conducted at Kaima Institute of Construction Technology showed that it was the axial dynamic pressure from the water beam that was of most importance to the capa¬ bility of eroding in soil. Cavitation, the impact force of single drops, the resistance of the soil against dynamic loads, and their physical and chemical properties are of great importance as well.

The research also showed that the jet effect is much weaker in water than in air, whereas changes of the viscosity of the water have a very slight influence. Most of jet inject¬ ion work will be done below ground-water table. In order to achieve the desired effect the water jet is, thus, surrounded by a concentric air beam.

On the basis of the above mentioned a jet injection head was, thus, developed with three different nozzles, i.e. one nozzle

5 for water, e.g. having a diameter of 1-2 mm, which is sur¬ rounded by an air nozzle, and an injection nozzle, e.g. having a diameter of 7-8 mm. Water, air, and injecting agent are supplied from the surface of the site to said jet inject¬ ion head via a swivel, through a pipe having three separate

10 ducts. The combination of volume and pressure of the differ¬ ent components are adapted to the kind of soil, kind of construction, etc. The technically/economically most advant¬ ageous binder until now proved to be a mixture of cement and water with a ratio of 1:1 and up to 1:2. Borth standard and

15 rapidly curing cement may be used.. In case there are strict requirements as to the density of the injected material, cement may be mixed with bentonite.

It is often difficult to define the exact dimension of the 20 injection zone, i.e. the cross section of the injected binder since the transition between binder and the surrounding soil is usually diffuse. However, directive dimensions may be indicated below:

25 Piles with a diameter of 0.8-2.5 m in cohesive soils, and 1.0-3.5 m i frictional soils.

Panels with a thickness from 5 ti 10 cm in cohesive soils, and from 15 to 30 cm in frictional soils.

30 When jet injected constructions were dug out and measured for control the shape and surface of the injection zone, and thus the injected and hardened body, also often proved

^T to be very irregular and rugged. This is due to local variations of homogeneity and of the compactness of the soil.

35 Smaller local variations of homogeneity can never be consider¬ ed during jet injection, in case of larger variations of homogeneity itmight be possible to adapt the injection process on the basis of previous soil exploration. The homogeneity of the injection zone depends on how well the injected agent will mix with the original soil. In frictional soils where there is no adherence between grains, the grainy structure is readily broken down by jet washing, and intimate mixing with the injected agent is achieved. In such material the homogeneity will, thus, normally be good. Pebbles not being thrown up through the pilot hole during jet injection will stay in the injection zone. Larger rocks will not in¬ fluence the quality of the injection zone if homogeneity is otherwise satisfactory.

In conhesive soils the homogeneity of the injection zone will be more variable. Especially in soils having a high clay content. Previously, it was not possible to break down the structure of the soil completely by the aid of the jet, and portions of clay would stay intact in the shape of large and small lumps. The lumps not driven up to the surface via the pilot hole will become embedded in the injection zone. ^* The content of such lumps of clay will reduce the quality of the injection zone, i.e. the final hardened body of binder and broken dowm components from the soil.

Another cause of inhomogeneities of the structures formed in the injection zone, e.g. jet piles, is the difficulty of maintaining the desired injection values. A decrease of the injection pressure, blocking up of cement injection, as well as irregular periods of rotation of the injection head, are problems which reduced the quality of the final product. This is directly related to the fact that the known jet in- jection equipment is imperfect and not very reliable. In addition to a demand for increased flexibility of the equip¬ ment to make it adaptable to different conditions, there is especially a highly felt lack of recording equipment permitt¬ ing the operator to read the rotational speed, and injection pressure whenever this is required, and especially a lack of equipment for reading/determining the extent of the inject- . ion zone across its longitudinal direction. For quality control of jet piles produced by the method and with the arrangement disclosed above it is known to use sounding, coring ,and if desired, geophysical measuring.

Amongsounding methods, mainly "Heja sounding " (Sweden),

"Standard Penetration Test" (japan), and possibly "Pressure sounding" (Sweden) are used. It is common to said methods that they only record relative solidity and homogeneity in the injection zone, but not the absolute stregth of the pile produced in the soil.

Commonly, sounding is carried out in the centre of the pile and as far outwards that the prescribed diameter can be checked. Sounding is a simple, not very time consuming, and inexpensive method. In Sweden it was, until now, considered the best method of checking the homogeneity and extension of the pile. Unfortunately, erroneous drilling may readily occur due to the fact that the pipe wrenches are diverted to less solid zones, resulting in miscalculations.

Coring comprises removal of core samples from the injection zone. A common diameter is 50 mm and the samples are, as a matter of routine, taken from the centre of the piles and 80 cm outwards from the centre, in all three core samples from each test pile. Commonly, only the axial compressive strength and homogeneity of the sample is examined, but it is possible to make other examinations of a special kind or as a matter of routine, e.g. as to fatigue, water content, or make cutting experiments, etc. The advantage of this method is that samples are taken from the injection zone for control and further examination. Coring is obviously a complicated and expensive method and, additionally, it is doubtful whether core samples are representative of the quality of the injection zone. Examinations of the strength of jet injected soil should, in fact, be made with the largest possible samples.

In view of the present requirements to ensured quality the present methods for checking jet injected soil are not satis¬ factory. Optimal dimensioning, technically and economically, requires a rational method for checking the shape, dimensions, and homogeneity of the injection zone.

In view of the above mentioned it is an object of the present invention to provide an improved and much more reliable and efficient method of control permitting continuous control of the shape, homogeneity, and width of the pile during jet washing of the injection zone and injection of a curable binder into said zone. According to the present invention this is achiev¬ ed by the features appearing from the characterizing part of the following independent claim 1, and the following depend¬ ent claims.

The present invention also provides an arrangement in connect¬ ion with a jet injection head for use when the above method is carried out, and said arrangement is achieved by the features appearing from the characterizing part of the following arrangement claim 4 and the following claims.

Control of the extend of an injection zone across its longi¬ tudinal direction is, thus, achieved by the aid of ultrasonic waves. By the aid of electronic modules, an emitter, a re- ceiver, a digital indicator, a printer, and an electro- acoustic converter provided in said injection head with the water nozzle, and the cement nozzle the extent of the inject¬ ion zone may be determined.

Said electroacoustic converter, a so called oscillator, will emit ultrasonic signals which are reflected from the wall of said injection zone, and are received by the receiver. The velocity of reflection depends on the solidity of the medium in the wall of said injection zone. Said signals are process- ed to form a continuous graphic representation of the shape and extent of the pile simultaneously with the running injection operations. Jet injection parameters, e.g. pressure, water/ cement ratio and lifting velocity of said jet injection head may be adjusted during operations to provide for the prescrib¬ ed pile diameter and to avoid variations of homogeneity, e.g. "lenses", lumps, etc. in the produced jet pile.

An embodiment of the arrangement according to the invention will be disclosed in more detail below with reference to the drawing, where

Figure 1 shows a jet injection head with a rod having three passages and a swivel joint with connections for said passages and a display conencted with said injection head,

Figure 2 shows a collar/container surrounding said rod with three passages of said jet injection head, with a mump and a flowmeter,

Figures 3a, b, c show an example of production of jet piles,

and Figures 4a,b,c show an example of production of panels (shields) .

It will appear from Figure 1 that a jet injection head A comp¬ rises an uupper nozzle 11 for a jet of water surrounded by air, and a lower nozzle 13 for injection of a curable binder. Jet injector head A is provided at the end of a rod 16 having three passages for supply of highpressure water, compressed air, and a curable binder under pressure to said nozzles 11 and 13, respectively. Between said nozzles 11 and 13 emitter/ receiver equipment 12 is provided and is connected with signal processing equipment, and a display 14 via a line 14a. Jet injection head A has excavating claws 17 provided in a ring at the lower portion of said head, and having an ex¬ ternal ring diameter which is larger than that of the jet injection head A. Jet injection head A with rod 16 is placed in a pilot hole P indicated with dotted lines. The lower portion of said hole is enlarged to an injection zone I by jets of water and air from top nozzle 11 during rotation and lifting of said jet injection head A.

In Figure 2 a combined collar and container 4 is shown. It is intended for surrounding rod 16 of jet injection head A at the upper end of pilot hole P for collection of liquid matter flowing up to and out of pilot hole p during- production of injection zone I by jet treatment and simultaneous injection of binder.

In connection with said collar/container 4 a pump 2 is pro¬ vided and is connected with the interior space of container 4 by the aid of a diver 3. Pump 2 is, furthermore, provided with a flow meter 1 for measuring the liquid matter conveyed by said pump.

The liquid matter flowing out of the upper end of pilot hole P can, thus, be measured as regards volume and, if desired, as regards composition as well, for controlling the composit¬ ion and volume of material of the carrying or supporting structure K.

With reference to Figures 3a,b,α, the procedure for producing jet piles will be disclosed below.

Figure 3a shows drilling of a pilot hole P by the aid of excavating blades 17 of jet injection head A, rod 16 of jet injection head A, which rod may be compared to a drill pipe, being attached to a drill tool feeder 18 on a vehicle 19. Said pilot hole, e.g. having a diameter of approximately 150 mm is drilled down to the desired level of the bottom of a pile. The bore hole walls may, if desired, be stabilized by a casing or a heavy liquid.

Figure 3b: Injection head A is then slowly lifted upwards being simultaneously rotated, and with top nozzle 11 working the wall of pilot hole P with a jet of water surrounded by air to extend said pilot hole so as to form an injection zone with a larger diameter, and with simultaneous injection of an agent, e.g. in the form of cement and water, through lower nozzle 13 to fill up injection zone I. During said slow rotation and pulling up of jet injection head A water and air will, thus, under high pressure break down the grainy structure and loosen the soil to a distance fron the centre of pilot hole P simultaneously with said injection agent being injected into the broken down volume of soil which is, thus urged upwards through pilot hole P.

Figure 3c shows continued lifting and rotation of jet inject¬ ion head A with simultaneous jet washing with water and air under high pressure, as well as injection of binder. Liquid matter will continue to flow up through pilot hole P to the surface. This liquid flowing matter consists of soil, water, and some cement. It may be collected in a sedimentation basin, or it may be collected in containers to be removed. According to the present invention the liquid matter is removed via collar/container 4, shown in Figure 2, a portion 7 of said collar depending from container 4 extending into pilot hole P or a casing inside said hole for collecting the -liquid matter flowing upwards.* Said liquid matter may be conveyed by pump 2 provided on container 4 with simultaneous measuring by the aid of flow meter 1. As mentioned above, it will also be possible to take samples of said liquid matter to determine the consistency of the injected curable binder which is part¬ ly mixed with soil particles, and possibly water from the jet. By such a method piles having a diameter of approximately 0.8 -4 m may be produced, depending on the kind of soil and the process, and this may be carried out during continuous monitoring via said graphic representation on display 14 showing the width of injection zone I in relation to the centre of pilot hole P.

In Figures 4a, b, and c the procedure of building panels (shields) is shown. Said procedure has several features in common with the procedure of building piles, as shown in Figure 3. This procedure can also be divided into three phases, i.e. A: Drilling of several pilot holes P, e.g. with a dia¬ meter of 150 mm along a desired direction of the panel to be produced in the soil. The distance between pilot holes is adapted to the conditions of the soil, and may vary between 0.5 and 3 m. After drilling said pilot holes by the aid of a special drill steel and drill ring, if desired,by the aid of jet injection head A with excavation blades 17, said jet injection head A is lowered in a first pilot hole P. Jet injection head A is oriented with nozzle 11 for water/air jet towards adjacent pilot hole P. While jet injection head A is slowly pulled up the soil between said two adjacent pilot holes P is washed off with simultaneous injection of binder into the formed injection zone I. The formed liquid matter or slugde consisting of water and washed out soil matter, and some binder will rise through adjacent pilot hole P to the surface and may be collected as mentioned above. Said sludge may, if desired, be collected in a collar/container 4 which is provided in the mouth of said pilot hole P, to be measured and removed. In this case the through collar portion 7 must be closed at its upper opening provided with a gasket 6. B. Thus, a panel or a shield is erected between said two adjacent pilot holes P. C. When a panel 20 is completed between two pilot holes P,P, jet injector head A and the remaining equipment is moved to . next pilot hole P, and the prosedure is repeated.

Such jet panels 20 will have a thickness in an order of 5-30 cm and a width varying from 0.5 m to 3 m. Their height is adapted to the requirements, depending on the soil and the design. Such panels need not be completed up to the sur¬ face of the site but may, if desired, be limited between two levels below the surface.

Claims

11CLAIMS :

1. A method for control and guidance of the extent of an injection zone across its longitudinal direction by jet injection of a curable binder into soils at the site for providing carrying, or support structures, e.g. piles, piers, panels, shields, etc., preferably of cement, by use of a jet injection head (A) with an upper nozzle (11) for a jet of water surrounded by air, and a lower nozzle (13) for inject¬ ion of a curable binder, said jet injection head (A) being provided at the end of a rod (16) having three passages for supply of water, air, and a curable binder under pressure to said nozzles (11, 13), and which jet injection head (A) is lowered into a pilot hole in the soil, where the water/air jet will, during slow lifting and, if desired, turning back and forth or slow rotation of said jet injection head, break up the soil by washing towards the wall of said pilot hole, and force the resulting liquid matter up through the upper portion of pilot hole (P) with simultaneous injection of a curable binder into the pilot hole thus enlarged, i.e. injection zone (I), c h a r a c t e r i z e d i n that the width of inject¬ ion zone (I) is controlled by the aid of emitter/receiver equipment (12), which is provided in jet injection head (A) and emits signals that are reflected by the walls of inject¬ ion zone (I) back to the receiver, and which reflected signals are processed to make a continuous graphic represent¬ ation on a display (14) of injection zone (I) and, thus, the shape and extent of the produced carrying, supporting struct¬ ure (K) simultaneously with injection operations.

2. A method as defined in claim 1, c h a r a c t e r i z e d i n that ultrasonic signals are used generated by the aid of an electroacoustic converter/swinger (12), which is provided in jet injection head (A) together with water/air nozzle (11), and cement nozzle (13), preferab¬ ly between said nozzles.

3. A method as defined in claims 1 and 2, c h a r a c t e r i z e d i n that the liquid matter flowing out of the upper end of pilot hole (P) is measured as to its volume and, if desired, its composition for controlling the composition and amount of material of said carrying or supporting structure (K).

4. An arrangement in a jet injection head (A) for carrying out the method as defined in claim 1, with said head (A) comprising an upper nozzle (11) for a jet of water surrounded by air, and a lower nozzle (13) for injection of a curable binder, and being provided at the end og a rod (16) having three passages for supply of water, air, and a curable binder under pressure to said nozzles (11,13), c h a r a c t e r i z e d i n that emitter/receiver equip¬ ment (12) is provided in said jet injection head (A), and is connected with signal processing equipment and a display (14) for graphic representation of the shape and extent of injection zone (I), and the produced carrying or supporting structure (K) simultaneously with injection work.

5. An arrangement as defined in claim 4, c h a r a c t e r i z e d i n that emitter/receiver equipment (12) comprises an electroacoustic converter (swinger) (12) provided in jet injection head (A) between said water/ air nozzle (11), and said cement nozzle (13).

6. An arrangement for use in measuring liquid matter flowing out of the upper end of pilot hole (P), as defined in claim 3, c h a r a c t e r i z e d i n that it comprises a collar/holder (4) surrounding rod (16) which has three passages at the upper end of pilot hole (P) for collecting the liquid matter, and a pump (2), as well as a flowmeter (1) for further transport and measuring said liquid matter.