EP3250353A1

EP3250353A1 - Grout preparation and administration

Info

Publication number: EP3250353A1
Application number: EP16743791.2A
Authority: EP
Inventors: Stefan SANDMAN
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-01-27
Filing date: 2016-01-26
Publication date: 2017-12-06
Also published as: SE1550080A1; WO2016122381A1; EP3250353A4; SE538466C2

Abstract

A method of preparing and administering grout (G) for injection into multiple or large diameter boreholes in rock or soil, whereby a batch of grout having a predetermined composition is prepared by controlled addition of predetermined quantities of ingredients, such as water, cement and additives, from a respective supply (2-5) to two or more mixers (6A-6N) for mixing therein, a prepared grout quantity is detected by positive weighing of the grout prepared in a mixer and prepared grout is then fed to an agitator (7) from which grout is pumped on demand to injection equipment (8) for injection into boreholes. The method includes a continuous detection of the output quantity of grout from the agitator and thereby of the grout supplied to the injection equipment by negative weighing, i.e. weighing of remaining grout in the agitator to thereby enable calculation of a mass flow rate, e.g. the amount of grout withdrawn from the agitator in a given time and thereby of the required total mixer capacity for a specific batch. An apparatus for performing the method is also provided.

Description

TITLE: GROUT PREPARATION AND ADMINISTRATION

TECHNICAL FIELD

The present technology generally concerns the reduction of water flows in cracks and dis- continuities in rock and/or soil by grouting, namely by injecting cementitious and/or non- cementitious grouts into an open end of injection and sealing pipes introduced into pre-drilled boreholes formed in the rock/soil. The technology has its primary field of application in association with drilling for tunnelling etc. In particular the technology concerns a method and equipment for preparing and administering grout for such rock/soil grouting.

BACKGROUND

Grouting is commonly performed for the general purpose of sealing soil and rock formations. Common applications for such grouting is found within normal civil engineering, such as in projects for reducing permeability of and prevent settlement in granular soils, generally known as permeation grouting, or for reducing water flow in fissured rock, generally known as rock grouting. Grouting is frequently performed in association with work such as by tunnelling projects or for stabilizing soil formations below basements and other foundations.

Normally, grout is injected into soil or rock formations by pumping prepared grout into steel pipes or casings that have been introduced into boreholes that are pre-formed in the soil/rock formations. For a specific application, grout is prepared in batches of a predetermined composition or formulation that for cementitious grouts consists of ingredients such as water, cement and additives, although other non- cementitious grouts are used for certain applications. The ingredients are added to a mixer in predetermined quantities, fed from a respective supply and mixed therein. After a set mixing time prepared grout is fed to an agitator from which it is then pumped on demand to injection equipment for injection into the boreholes.

In existing systems the grout batches are basically prepared in a separate mixer that supplies the prepared grout to one or two agitators from which grout is alternatingly withdrawn to be injected into boreholes in the soil/rock formation. In such systems the size of the mixer must be increased dramatically to meet increased grout demands. Such increased mixer size has several drawbacks among which may be specifically mentioned the additional preparation time for each batch and also the problem of large amounts of unused grout mix in the event that the grouting operation is finished prematurely or is changed. Alternatively several smaller mixers may be used that all supply their prepared grout mix to one or more associated agitators and all mixers and agitators must be equipped with their own semi-automatic control system controlling preparation of grout mix of a specific batch. SUMMARY

It is a general object of the present technology to provide an improved solution to the above discussed problems and shortcomings of conventional grout mix preparation and administration in association with rock/soil grouting. In particular it is an object of the technology to suggest an improved method of preparing and administering grout mix for injection into multiple or large diameter boreholes in rock or soil.

It is another object of the technology to suggest an improved apparatus for preparing and administering grout mix for injection into multiple or large diameter boreholes in rock or soil.

These and other objects are met by the technology as defined by the accompanying claims.

The technology generally relates to grouting, namely the injection of cementitious and/or non- cementitious grouts into an open end of injection and sealing pipes introduced into pre-drilled boreholes formed in rock/soil. Grout is prepared at site and is prepared and administered into the boreholes in a quantity required by the circumstances.

In a first aspect of the technology, there is provided an improved method of preparing and administering grout for injection into multiple or large diameter boreholes formed in rock/soil whereby a batch of grout having a predetermined composition is prepared by controlled addition of predetermined quantities of ingredients from a respective supply to several mixers for mixing therein. A prepared grout quantity is detected by positive weighing of the grout prepared in a mixer and prepared grout is fed to an agitator from which grout is pumped on demand to injection equipment for injection into boreholes. In a basic configuration the output of grout from the agitator and thereby of grout supplied to the injection equipment is continuously detected by negative weighing, i.e. weighing of remaining grout in the agitator. This enables calculation of a mass flow rate, e.g. the amount of grout withdrawn from the agitator in a given time and thereby of the required total mixer capacity for a specific batch. According to another aspect of the technology there is provided an improved apparatus for preparing and administering grout for injection into multiple or large diameter boreholes in rock/soil and including respective supplies for grout ingredients, several mixers for mixing the grout ingredients therein and a load cell for positive weighing associated with each mixer. An agitator is also provided to which the prepared grout is fed and from which grout is then pumped on demand to injection equipment for injection into the boreholes. In a basic configuration of the apparatus load cells for negative weighing are associated with the agitator. A control system is also provided for individually controlling and logging the grout preparation in each of the mixers and for administration of the prepared grout to the agitator in amounts based on a withdrawal of grout from the agitator, as calculated from the negative weighing of the amount of grout withdrawn from the agitator.

Preferred further developments of the basic inventive idea as well as embodiments thereof are specified in the dependent subclaims.

Advantages offered by the present invention, in addition to those described above, will be appreciated upon reading the below detailed description of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its further objects and advantages will be best understood by reference to the following description taken together with the accompanying drawings, in which:

Fig. 1 is an illustration of a prior art apparatus for grout preparation and administration and a variation thereof;

Fig. 2 is a schematic illustration of a an apparatus for grout preparation and administration in accordance with the present technology;

Fig. 3 is a schematical diagram of a grout preparation and administration control unit of the present technology; and

Fig. 4 is a schematic flow diagram of a grout preparation and administration control method according to the present technology. DETAILED DESCRIPTION

The present technology will be explained below with reference to exemplifying embodiments of a method of preparing and administering grout for injection into boreholes in rock/soil and an apparatus for preparing and administering such grout. The discussed and shown embodi- ments relate to an application of the technology in particular to the injection of cementitious grout into multiple injection pipes, such as by tunnelling work. The present teclinology may be applied generally in the field of grouting and it is emphasized that all employed equipment and components that are well known within this field are therefore not illustrated in detail in the attached drawing figures. The described technology is equally well suited for application to other types of environments and for other specific types of grouting work. Thus, the drawings are included for the sole purpose of describing preferred embodiments of the present technology and are not intended to limit the teclinology to details or to any specific field of application. It shall be realized that the disclosure covers the incorporation of features related to other applications and any combination of features disclosed herein.

In Fig. 1 is depicted an example of a partially and schematically outlined conventional grout preparation and administration system/apparatus 100 with the above mentioned, presently used type of mixer 106 A and agitator 107 combination. Specifically, Fig. 1 shows in full lines a basic prior art apparatus 100 that is controlled (control units 120A, 120B) in a semi-automatic manner and that has one mixer 106 A supplying grout to two agitators 107. Of these agitators 107 one serves as a buffer for prepared grout and does therefore in continuous operation not add to the capacity of the system. In such a system ingredients, such as water, additives and cement are sequentially fed from respective supplies 104, 102, 103 and 105 to the mixer 106A in quantities prescribed by the composition of the prepared batch and controlled by appropriate valves 113, 114, 115 and 117. The conformance of the prepared grout to the composition is controlled by positive weighing (load cells 1 12) of the additive supply/supplies in combination with positive weighing (load cells 1 10) of the mixer during and after supply and preparation. The known systems use positive weighing (load cells 1 1 1) of the/each agitator 107, but the only purpose of this weighing is to determine how much prepared grout is available to the systems. The systems further employ magnetic inductive flow meters 118 to determine flow of prepared grout from the agitators, and thereby to determine the continuous grout consumption. In the long run such a detection provides insufficient accuracy for the operation control since the valves will inevitably become fouled after some time in operation. Such fouling will have the effect that the detected delivered grout quantity is higher than the actual amount. The described system relies to a significant part on manual input, such as a manual start of each batch or series of batches, a manual choice of which agitator 107 to supply with prepared grout and a manual input of the ingredients having been added to detemiine the sum of the pumped grout. The conventional system is therefore very exposed to malfunctions due to human errors.

One further, specific problem has been noted by the supply of ingredients to the mixer, namely that the system does not preclude tampering with the logged quantities of used ingredients, especially the expensive additives, in the batch being prepared. Another less desirable reality in prior art systems is that the single mixer 106 A normally needs to have a large grout preparation capacity to provide a required amount of grout to injection equipment 108 for a specific application. In addition to the initially mentioned extra preparation time for each batch and the problem of large amounts of unused grout mix, an operator must also manually switch between the agitators 107.

In attempts to increase the capacity of such conventional systems without further increasing the size of the mixer it is known to duplicate the described system by providing two separate mixers 106A, 106B each supplying prepared grout to two designated agitators 107. Such a further developed system is indicated with dash-dot lines in Fig. 1 and uses two separate con- trol units 120A, 120B, each controlling preparation of one grout composition batch for the designated mixer 106A, 106B, with no interaction there between. Thus, each mixer and control unit must completely finish the composition before the next batch or composition preparation may be started manually. For the large number of parts employed in this system it requires considerable manual input from at least 2-4 operators. Still it has a very limited grout capacity.

To overcome the above described disadvantages and problems associated with the known methods and systems, the present technology suggests a novel approach for the control and performance of a grout preparation and administration method and system intended for use in rock/soil grouting operations. The suggested grout preparation and administration approach briefly involves providing a secure control of the grout preparation and mixing by combining positive and negative weighing performed in series for one and the same grout composition and by using several mixers controlled interactively and feeding one agitator. This will enable the efficient, practical use of the system and thereby the preparation and supply of a significantly increased quantity of grout, all with the use of only one operator. At the same time the proposed improvement will provide very accurate and tamper-free logging and control of the quantities of the used additive ingredients. By allowing thorough control of the number of grout batches that the system requires per minute and thereby minimization of waste, the environmental effect will further be very advantageous. The versatility of the system as regards the change of grout composition will also be greatly improved compared to existing solutions.

The proposed new technology for preparation and administration of grout for injection into multiple or large diameter bore-holes formed in rock/soil will first be explained with reference to an exemplifying apparatus 1 illustrated in Fig. 2. The apparatus 1 is intended for the preparation and administration of grout G and includes respective level-controlled supplies 2-5 of grout ingredients that for a cementitious grout may comprise water, cement and additives. Reference numbers 2 and 3 represent supplies, normally tanks, for additives, 4 represents a water supply and 5 represents a cement supply that is normally named a bin. Separate flow control valves, 15, 17 and 13, 14 are associated with each water, cement and additive supply, and through said valves water, cement and additives are separately supplied to each mixer from the respective supplies 2-5. A hydraulic valve and motor (not shown) are activated to convey cement from the cement bin 5 via an ordinary screw feeder (not specifically denoted) and to a manifold 16 distributing the cement to the valve 17 associated with the respective mixer 6A-6N. The flow control valves 15, 17, 13, 14 for the water, cement and additive supplies are preferably pneumatically or electrically (magnetic spool) controlled. Two or more mixers 6A-6N are provided for mixing the grout G ingredients therein and the number of mixers may in this case be varied freely within reasonable numbers, such as based on required capacity and/or available space. This means that each mixer 6A-6N may have a considerably reduced size, enabling a great amount of versatility as regards the ability to shorten the lead time for each batch and the possibility to quickly change grout composition/formulation. In practical examples that shall by no means delimit the technology, the mixers may be provided in a cluster configured in pairs or in sets of four or even six mixers each having a size of approximately 100 liters. The system further includes a single agitator 7 to which prepared grout G is fed through valves (not specifically denoted) from selected mixers 6A-6N and from which grout is then pumped on demand to injection equipment 8 for injection into the boreholes (not specifically shown). For the pumping of grout G from the agitator 7 is employed a grout pump of any appropriate, not specifically named type that is able to provide an even flow of grout to the injection equipment 8.

Conventional load cells 10 for positive weighing are associated with each mixer 6 A-6N and serve to provide control of the supplied water and cement quantities and a value of the total weight of the prepared grout mix supplied to the agitator 7. A load cell 12 for negative weighing is associated with each additive supply 2, 3 in order to enable accurate control of the additive supply to the mixers 6A-6N. The quantities of additives for each batch are very small and the negative weighing of withdrawn quantities will provide a very accurate result. Further load cells 1 1 for negative weighing are associated with the agitator 7. A control unit 20 is provided for individually but interactively controlling and logging the grout preparation in each of the mixers 6A, 6N and for administration of the prepared grout G to the agitator 7 in amounts based on a withdrawal of grout G from the agitator 7. A mass flow of grout from the agitator 7 per unit of time is calculated from the continuous negative weighing of the amount of grout withdrawn from the agitator.

Fig. 3 illustrates very schematically the basic components and functions of an exemplary control unit 20 being common to all mixers 6A-6N and serving to control the grout preparation apparatus 1. The common control unit 20 separately controls the supply of ingredients of a selected grout composition to one or several mixers 6A-6N, as required. It further controls the mixing operation for and withdrawal of grout G from all active mixers 6A-6N in accordance with the selected compositions and based on input values from load sensors 10, 1 1, 12, supply valves 13, 14, 15, 17 and the below described, calculated grout consumption based on withdrawal of grout G from the agitator 7. This control unit 20 provides an automatic process function by enabling control of all mixers of the apparatus 1, which means that as soon as the flow of grout G from the agitator is greater than that supplied by one mixer 6A alone, further mixers 6B-6N are activated as required. Thus, in the apparatus 1 according to this technology a number of individually but interactively controlled mixers 6A-6N are provided and the number of activated mixers depends upon the grout quantity required by the injection equipment 8. This quantity is represented by the mass flow rate of grout G as calculated from the result of the continuous negative weighing of the agitator 7.

For providing the described functions the common control unit 20 may basically include a sensor input evaluation means 21 receiving the detected values from all load cells 10, 11 , and 12. Load cell input values are then entered into a sensor input computing means 22 by which is also made a manual input 19 of a selection of grout composition or formulation. A process timer 24 is also connected to the sensor input computing means 22 to provide the time data for calculating the mass flow rate of grout from the agitator 7 based on the negative weighing. The computing means 22 is further connected to means 23 for controlling the activation of the supply of ingredients to the mixers 6A-6N as well as the activation of impellers (not specifically shown) of the mixers. An override function may also be provided at the control unit 20 for allowing the operator to make a manual mixer selection input 18.

It will be readily appreciated that the technology also concerns a method of preparing and ad- ministering grout for injection into multiple or large diameter boreholes preformed in rock or soil. Thereby a batch of grout G having a predetermined composition is prepared in a conventional manner by controlled addition of predetermined quantities of ingredients, such as water, cement and additives, from a respective supply 2-5 to two or more mixers 6A-6N for mixing therein. A grout quantity prepared in the mixer/-s is basically detected by positive weighing of the grout G prepared. Prepared grout G is then fed to an agitator 7 from which grout is pumped on demand to the injection equipment 8 for injection into boreholes. In particular, with specific reference to Fig. 4, the method includes the below described steps.

In a first step SI the grout preparation is started by supplying water pumped from the water supply 4 to one of the mixers 6A-6N and in a quantity as prescribed in the selected composition. This supply of water is controlled by positive weighing of the mixer in step S2, so that the water valve 13 closes when the mixer load cells 10 detect a preset weight for the specific grout composition being prepared. Then, in step S3, additives in quantities as prescribed in the composition are supplied from the respective additive supply 2, 3, through the designated valves 14, 15 and to the mixer. Specifically, the output quantity of one or more additives from associated additive supplies 2, 3 and thereby of the additive supplied to each mixer 6A-6N is continuously detected by negative weighing of remaining additive in the supplies/tanks during grout preparation. This supply of additives being controlled by negative weighing is performed in step S4, so that when the weight of additive in the respective supply 2, 3 has de- creased by a preset weight the corresponding additive valve 14, 15 closes. The additive tanks are pressurized and the weight of supplied additives is calculated by the loss of weight therein, as measured with the negative weighing of the quantity withdrawn from the additive supplies. In step S5 the impeller of the mixer is started in order to create a vortex therein preventing that a lump is formed when cement is then supplied to the mixer in step S6. The supply of cement to the mixer is started by the control unit 20 that activates a valve and motor causing a feed screw to convey cement from the bin 5 to the distributor 16 and from there to the mixer, through the cement supply valve 17. Mixing is now performed for a prescribed time, such as for 30 seconds, in step S7. As the control unit 20 detects that preparation of grout G in a mixer is completed the mixer weight is determined by the positive weighing of the mixer The grout quantity that is ready to be fed to the agitator 7 is calculated by deducting from the detected positive weight a weight of residual grout mix remaining on the walls of the mixer. At the same instant prepared grout from the mixer 6A is fed to the agitator 7. Since the weight of grout remaining in the agitator 7 has been checked in step S8 by negative weighing, the total quantity of grout available in the agitator 7 is determined by adding the calculated weight of grout fed from the mixer to said weight detected by the negative weighing. The calculations are being made instantaneously so that there is no need to pause the mixer or agitator before or during the feeding of grout to the agitator.

In case the detection in step S9 indicates that the weight of the agitator 7 is too high the mixer 6A-6N is put on hold in step S10 and no pumping of grout G to the agitator 7 is started. If, on the other hand the value of the agitator weight detected in step Sl l is too low the control system sends a signal to the appropriate valve for conveying prepared grout G to the agitator 7 in step S I 2. In step S 13 the control unit adds the detected weight of grout removed from the mixer 6A-6N to the weight of the agitator 7. While grout G is being pumped from the agitator 7 as requested by the grouting equipment 8 the weight of the agitator 7 is continuously detected by negative weighing of the agitator in step S I 5. By this continuous negative weighing, i.e. weighing of remaining grout in the agitator, the output quantity of grout from the agitator and thereby of the grout supplied to the injection equipment is detected. Based on the result of the negative weighing by the agitator load cells 1 1 and set in relation to time a mass flow rate of the grout leaving the agitator may be calculated in step S I 6. Expressed otherwise the combined positive weighing of the mixer and negative weighing of the agitator enables calculation of the mass flow rate, e.g. the amount of grout withdrawn from the agitator in a given time and thereby of the required total mixer capacity for a specific batch. In the event that the required mass flow rate exceeds what may be prepared by one mixer 6A, that is the time required for one mixer to complete the preparation of one batch, the system may order the activation, in step 17, of another one of the mixers 6B-6N to prepare grout with the same composition. With the present technology this activation of a required further mixer or further mixers is carried out fully automatic by the control unit 20. In summary, in the described application, by detecting the positive weight of grout supplied from the mixer 6A it is likewise established what quantity was supplied to the agitator 7. By also detecting, through the negative weighing, the quantity that has been withdrawn from the agitator 7, during pausing of the mixing, the average mass flow rate may be calculated. In the present method the weighing in the form of negative weighing at the agitator 7 is thereby part of the batch system as a flow control. From the above discussion it should be clear that the calculated flow of prepared grout G from the agitator 7 is used to determine when further mixers 6A-6N, in addition to a first one, must be activated for grout preparation. Thus, mixing grout G of the same composition may be performed in a number of mixers 6A-6N that are individually but interactively controlled by the common control unit 20. To these mixers is separately supplied water, cement and additives from a common supply 2-5, through separate flow control valves 13, 14, 15, 17, and the number of activated mixers depends upon the quantity of prepared grout G required by the injection equipment 8. If the grout quantity requested by the grouting is reduced the mixers that do not have to be active stop in the phase after the supply of water. In this phase the mixers will start for approximately 3 seconds every 5 minutes to rinse down cement having become stuck on the edges and to maintain said cement active/alive. When the grout requirement increases again the supply of additives and cement etc. will simply be continued to the now required, previously stopped mixer or mixers.

In this apparatus 1 there is only one control unit 20 having several load cells, depending upon the number of mixers employed. The load cells are all working in series for one and the same grout composition. One load cell each is used for flow control and for additive weighing. This means that all load cells may work simultaneously and due to a use of several smaller mixers the lead time for each batch may be shortened., Mixing of 100 liters will require a mixing time of about 30 seconds and if the quantity is increased to 200 liters the mixing time will with a conventional system be 60 seconds and so forth. If, in a practical example of this described technology, it will take 37 seconds to prepare one grout composition, the use of e.g. six smaller mixers in the proposed configuration will make it possible to prepare six grout compositions in the same 37 seconds. This gives a theoretical value of 516 liters per minute. In practical operation the number of mixers being active will be controlled depending upon the mass flow rate, in other words upon the quantity of grout being pumped out from the agitator. Thus, the grout preparation capacity is controlled by the output from the agitator. The control unit 20 uses a completely new approach based on the idea that the possibility to provide flow control is created by mixing positive and negative weighing. Such flow control involves the negative weighing of every prepared grout mix and a calculation of over time to obtain a mass flow rate. Weighing of the batches mixed in each mixer is performed positively in order to control the consumption of the ingredient materials. This provides a double control of how much grout there is in the agitator that by its load cells governs the flow control. By using this way of controlling how many mixers that must be active it will be possible with this process to control how many batches per minute the grouting system requires. This does in turn provide further advantages from an environmental point of view since there will be less material waste.

In addition to those advantages offered by the present teclinology that have been specifically mentioned above, may be emphasized that:

- the configuration of the apparatus and the control functions of the method will make it possible to manually change the grout composition during the process, such as when grout injection into the rock is too quick, requiring a modification of the composition;

- in applications consuming large amounts of grout the mixers are operated sequentially in a number corresponding to the actual grout consumption as calculated from the result of the actual amount of grout withdrawn from the agitator;

- all mixers in a cluster are controlled in series by the same grout composition as set in the control unit;

- larger security margin through reduction of the effect of human errors;

- the teclinology is economically advantageous for contractor and entrepreneur since the actual consumption is invoiced;

- the proposed technology permits faster grout injection in rock and by tunnelling work using fewer operators and with smaller impact on the environment. In particular the proposed apparatus and method makes it possible to inject into large diameter boreholes or multiple boreholes at the same time, with the mentioned reduced personnel; and

- energy consumption to operate the equipment will be reduced. 8

12

Logging must be performed on all systems within this area to secure that the contractor and the entrepreneur may be in agreement of the actual consumption of materials. In the proposed technology the size of the composition is known and is entered as a positive factor in the negative weighing of the flow and can therefore not be manipulated in any sense. Each batch added to the mass flow detection is also logged in the system by the proper material type. This in turn means that this technology does not require a separate flow meter or separate logging instruments. The equipment may advantageously be operated by one single person since it will be fully automatic, but other restrictions may demand two persons working together, such as by tunnelling work. The apparatus will also be adapted for remote control, which means that an operator starting the grout composition may also perform manual pumping work, such as the handling of hoses. Changing of the composition being prepared is performed without stopping the preparation and thereby contributes greatly to avoiding spillage and unnecessary time loss. In practice the change of composition requires only two push-button maneuvers, selecting a preset composition number and pushing enter. This changes the composition for all mixers without delay. It is to a large extent this automation and the increased capacity that makes it possible to pump grout to multiple or large diameter boreholes and to lower the lead times for rock injection and tunnelling as requested. In alternative, but not specifically illustrated embodiments of the technology variations of the different illustrated parts of the apparatus may be employed without departing from the scope of the invention. An example of this is the use of varying numbers of mixers in a cluster controlled in series by the control unit. Likewise, varying types of containers and tanks and various types of supply control valves, motors and pumps may be used for the supply of ingredients of the grout mix and of prepared grout. It shall also be emphasized that although the invention has been described and illustrated with specific reference to an application for use with cementitious grout in connection with grouting for tunnelling operations, the invention is in no way restricted to such applications. The basic principles of the invention may be applied to other similar operations and processes.

The present technology has been described in connection with embodiments that are to be regarded as illustrative examples thereof. It will be understood by those skilled in the art that the present technology is not limited to the disclosed embodiments but is intended to cover various modifications and equivalent arrangements. The present technology likewise covers any feasible combination of features described and illustrated herein. The scope of the present technology is defined by the appended claims.

Claims

PATENT CLAIMS

1. A method of preparing and administering grout (G) for injection into multiple or large diameter boreholes formed in rock/soil, whereby a batch of grout having a selected compo- sition is prepared by controlled addition of predetermined quantities of ingredients, such as water, cement and additives, from a respective supply (2-5) to two or more mixers (6A-6N) for mixing therein, a prepared grout quantity is detected by positive weighing of the grout prepared in a mixer and prepared grout is fed to an agitator (7) from which grout is then pumped on demand to injection equipment (8) for injection into boreholes, characterized by:

(a) continuously detecting the output quantity of grout from the agitator and thereby of the grout supplied to the injection equipment by negative weighing, i.e. weighing of remaining grout in the agitator; thereby

(b) enabling calculation of a mass flow rate, e.g. the amount of grout withdrawn from the agitator in a given time and thereby of the required total mixer capacity for a specific batch.

2. A method according to claim 1, characterized by mixing grout (G) of the same composition in a number of individually controlled mixers (6A-6N), said number depending upon the quantity required by the injection equipment (8), to which water, cement and additives are separately supplied from a common supply (2-5) through separate flow control valves (13, 14, 15, 17).

3. A method according to claim 1 or 2, characterized by continuously during grout (G) preparation detecting the output quantity of one or more additives from associated additive supplies (2, 3) and thereby of the additive supplied to each mixer (6A-6N) by negative weighing of remaining additive in said container.

4. A method according to any of claims 1-3, characterized by using the calculated mass flow rate of prepared grout (G) from the agitator (7) to determine when one or several further mixers (6A-6N), in addition to a first one, must be activated for grout preparation.

5. A method according to any of claims 1-4, characterized in that based on the positive and negative weighing of ingredients and of the negative weighing of the withdrawn quantity of grout from the agitator (7), a tamper-proof control and registration is provided of the consumed quantities of the different ingredients.

6. A method according to any of claims 1-5, characterized in that water is fed from a water supply (4) to a mixer (6A-6N) in a quantity as prescribed in the composition and as measured with the positive weighing of the mixer, additives are then fed to the mixer in a quantity as prescribed in the composition and as measured with the negative weighing of the quantity withdrawn from additive supplies (2, 3), the mixer is started, cement is fed to the mixer from a cement supply (5) and the mixer is run for a set time of e.g. 30 seconds.

7. A method according to any of claims 1-6, characterized in that when preparation of grout (G) in a mixer (6A-6N) is completed the mixer weight is determined by positive weighing of the mixer, a grout quantity being ready to be fed to the agitator (7) is calculated and said prepared grout from the mixer is fed to the agitator, whereby the total quantity of grout available in the agitator is determined by adding said calculated weight of grout from the mixer to said weight detected by the negative weighing.

8. A method according to any of claims 1-7, characterized in that in applications consuming large amounts of grout (G) the mixers (6A-6N) are operated sequentially in a number corresponding to the actual grout consumption as calculated from the result of the actual mass flow rate of grout withdrawn from the agitator.

9. An apparatus (1) for preparing and administering grout (G) for injection into multiple or large diameter boreholes formed in rock/soil and including respective supplies (2-5) of grout ingredients such as water, cement and additives, two or more mixers (6A-6N) for mixing the grout ingredients therein, a load cell (10) for positive weighing associated with each mixer and an agitator (7) to which the prepared grout is fed and from which grout is then pumped on demand to injection equipment (8) for injection into the boreholes, characterized by:

- load cells (1 1) for negative weighing that are associated with the agitator; and

- a control system (20) for individually controlling and logging the grout preparation in each of the mixers and for administration of the prepared grout to the agitator in amounts based on grout consumption, as calculated from the negative weighing of the amount of grout withdrawn from the agitator.

10. An apparatus according to claim 9, characterized by a number of individually controlled mixers (6A-6N), said number depending upon the quantity required by the injection equipment (8) and by separate flow control valves (13, 14, 15, 17) associated with each water, cement and additive supply (2-5) through which water, cement and additives are separately supplied to each mixer from the respective supplies.

1 1. An apparatus according to claims 9 or 10, characterized by a load cell (12) for negative weighing associated with each additive supply (2, 3).

12. An apparatus according to any of claims 9 - 11 , characterized by a common control unit (20) separately controlling supply of ingredients to, mixing operation for and withdrawal of grout (G) from all mixers (6A-6N) in accordance with selected compositions and based on input values from load sensors, supply valves and calculated grout consumption based on withdrawal of grout from the agitator (7).

13. An apparatus according to any of claims 9 - 12, characterized in that the common control unit (20) includes:

- sensor input evaluation means (21) receiving detected values from all load cells (10, 11, 12); - sensor input computing means (22) in which load cell input values are then entered;

- a process timer (24) likewise connected to the sensor input computing means to provide time data for calculating the mass flow rate of grout from the agitator (7) based on the negative weighing; and

- control means (23) for controlling activation of the supply of ingredients to the mixers (6A- 6N) as well as the activation of mixers.