FIELD OF INVENTION

The present invention relates to a ground stabilization method and system thereof used in the areas of excavation and tunnelling works, and in particular but not exclusively, to a chamber pressure grouting method and system thereof for ground stabilization that is low in cost, effective and creates a safe and workable chamber environment underground for tunnel boring machine (TBM) interventions for maintenance, replacement and repair works. BACKGROUND TO THE INVENTION

The following discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was published, known or part of the common general knowledge in any jurisdiction as at the priority date of the application.

Grouting is typically used in excavation and tunnelling works. Conventional grouting methods include Tube-A-Manchette (TAM) grouting, fissure grouting and jet grouting. Since the introduction of tunnel boring machines (TBM) in the 1980s, digging under pressure has been substantially reduced. However, the cutter-head and/or cutter-head related tools of the TBM would undergo wear and tear, which then requires replacement or repair, and it would be necessary for workers to enter working chambers underground to carry out inspections, maintenance, replacement or repair works. Such activities usually disturb ground conditions and cause ground surface settlement. Hence, it is important to create working chambers underground that are safe and workable for TBM cutter intervention.

Conventional grouting methods and also ground freezing can be used to create working chambers underground for workers to carry out the necessary work by stabilising the ground surrounding the desired area. However, such methods require access to the underground works from the ground surface. In other words, each time there is a need to employ such methods to create a safe and workable working chamber for workers to carry out inspections, maintenance, replacement or repair works, drilling from the surface to reach the TBM underground is required. Hence, while such methods create working chambers that are safe and workable, such methods are also cumbersome and time consuming. Furthermore, the associated cost of employing such methods is also very high. These disadvantages are further enhanced when the excavation depth is very deep going beyond the typical depth associated with such methods.

An alternative to conventional grouting methods and ground freezing described above which does not require having to access the TBM underground via the surface of the ground is to create working chambers underground by compressed air. Compressed air can be used to create working chambers underground by direct access from the TBM. Hence, working chambers can be created quickly and at a lower cost as compared to conventional grouting methods and ground freezing.

However, for workers who work in working chambers underground created by compressed air, their physical bodies are subjected to very high pressure each time they carry out work in such chambers, which puts their lives at risk each time they work. Being subjected to a working environment with such high pressure would also affect their health in the long run. Furthermore, the compressed air working chamber environment restricts the tools and the number of working hours that a worker can work inside the chamber due to hyperbaric exposure. Therefore, there is an urgent need for a cost effective, efficient and effective ground stabilization method and system to address the aforementioned disadvantages. The present invention seeks to provide such a method and system thereof for creating safe and workable chamber environments underground for TBM interventions for maintenance, replacement and repair works to overcome at least in part some of the aforementioned disadvantages.

SUMMARY OF THE INVENTION

Throughout this document, unless otherwise indicated to the contrary, the terms "comprising", "consisting of, and the like, are to be construed as non-exhaustive, or in other words, as meaning "including, but not limited to". The present invention relates to a ground stabilization method and system thereof which enables the creation of a safe and workable chamber environment underground for tunnel boring machine (TBM) interventions for maintenance, replacement or repair works.

Advantageously, the TBM chamber is pressurized above natural water pressure or ground water pressure with grout materials which are mixed by the TBM cutter rotation or pump flow circulation to directly improve the excavation face and the surrounding TBM body cutting face. This enables reducing water inflow to the desired area, improving the cutting face and improving on the surrounding ground stability. Advantageously, surface settlement will also be reduced. In accordance with a first aspect of the present invention, there is provided a method for creating safe environment for intervention by a tunnel boring machine, the method comprising the step of:

(i) Determining grout pressure by assessing soil condition;

(ii) Assessing machine design pressure, wherein the design pressure is higher than the grout pressure;

(iii) Assessing water ingress to determine the grout flow and volume, wherein at least one of direction of the water ingress, flow rate of the water ingress or a combination thereof indicates presence of the water ingress;

(iv) Replacing slurry to water or a mixture of slurry and water in an excavation chamber for maintaining constant or above natural water pressure;

(v) Injecting grout into the excavation chamber such that the machine face pressure is increasing towards a predetermined target pressure;

(vi) Grouting is carried out at controlled flow rate to achieve the predetermined target pressure; Wherein when maintaining pressure in the excavation chamber with a pressurized mixture of water and grout, said mixture is injectable to excavation face and enabling the mixture to travel through cracks in a body of soil to prevent the water ingress when cured, thereby creating a stabilized body of soil at the excavation face. The ground stabilization method further provides replacement of slurry to grout material for grouting under unstable ground condition.

The ground stabilization method further provides a predetermined pressure for grouting subject to soil pressure, capability of tunnel boring machine and the water ingress. The grout pressure is at least 1.5 times lower than passive soil pressure and the machine design pressure is at least 1.25 times higher than natural water pressure.

The ground stabilization method provides mixing materials in the excavation chamber by at least one of a rotating cutter head or a pump.

The ground stabilization method further comprises a supplementary grouting prior to the grouting to improve the excavation face.

The supplementary grouting comprises grouting surrounding machine body cutting face wherein a plurality of grout blocks is formed within an annulus, for which the plurality of grout blocks is regularly formable from the base of the annulus and extending upwardly.

The formation of the plurality of grout blocks further comprises: (i) A volume control step, wherein grout is injectable at a predetermined volume to enable filling of void and clearance gap; and

(ii) A pressure control step to ascertain whether a further grouting via the volume control step is required.

Preferably, the curing step is carried out by maintaining the predetermined target pressure. Preferably, the predetermined target pressure is maintained by injecting grout or water.

Preferably, there is a cleaning step by maintaining at least the natural water pressure.

The cleaning is carried out by at least one of: circulating the slurry or discharging chamber remains.

A post-grouting step is provided for assessing the water ingress to ascertain whether a further grouting is required.

The grout material for use in grouting can be at least one of: Micro fine cement, OPC cement, chemical grout, or a combination thereof. In accordance to a second aspect of the present invention, there is provided a ground stabilization method for creating safe underground environment for intervention by a tunnel boring machine, comprising:

(i) Determining grout pressure by assessing soil condition; (ii) Assessing machine design pressure, wherein the design pressure is higher than grout pressure;

(iii) Assessing water ingress to determine grout flow and volume, wherein at least one of direction of the water ingress, flow rate of the water ingress or a combination thereof indicates presence of the water ingress; (iv) Replacing slurry to water or a mixture of slurry and water in excavation chamber for maintaining constant or above machine face pressure;

(v) Injecting grout into the excavation chamber such that the machine face pressure is increasing towards a predetermined target pressure;

(vi) Supplementary grouting of surrounding machine body cutting face, comprising injecting a plurality of grout blocks, wherein the grout blocks are regularly formable from base of an annulus and extending upwardly;

(vii) Grouting excavation face, wherein the grouting is operable at controlled flow rate to achieve the predetermined target pressure;

Wherein a supplementary grouting of the surrounding machine body cutting face is operable to prevent water ingress prior to grouting the excavation face, wherein when maintaining pressure in the excavation chamber with a pressurized mixture of water and grout, said mixture is injectable to the excavation face and enabling the mixture to travel through cracks in a body of soil to prevent the water ingress when cured, thereby creating a stabilized body of soil at the excavation face. In accordance with a third aspect of the present invention, there is provided a ground stabilization system for creating safe underground environment for intervention by a tunnel boring machine, comprising:

(i) A pressurized chamber containing mixed grout material; (ii) A slurry replacement system, wherein slurry is replaceable with water or a mixture of slurry and water in one operation and injection of grout into excavation chamber in a second operation;

(iii) A plurality of ports, regularly distributed circumferentially on the chamber, for enabling grouting at controlled flow rate to achieve a predetermined target pressure;

Wherein maintaining pressure in the excavation chamber with a pressurized mixture of water and grout, said mixture is injectable to the excavation face and enabling the mixture to travel through cracks in a body of soil to prevent water ingress when cured, thereby creating a stabilized body of soil at the excavation face. The ground stabilization system further provides replacement of slurry with grout material for grouting under unstable ground condition.

The ground stabilization system further provides a predetermined pressure for grouting subject to soil pressure, capability of tunnel boring machine and the water ingress.

There is a plurality of injecting ports regularly distributed circumferentially around the machine body to enable supplementary grouting.

The ground stabilization system further provides forming a plurality of grout blocks within an annulus, wherein the blocks are formable from the base of the annulus and extending upwardly.

The grout material for use in grouting can be at least one of: Micro fine cement, OPC cement, chemical grout, or a combination thereof.

The present invention has at least the following advantages:

1. The present invention does not pose any restriction as to the surface condition that is above an underground work site with a TBM, as the method for ground stabilization is advantageously carried out directly at the location of the TBM and no drilling from the ground surface is required.

2. The present invention advantageously utilizes the existing grout pump system of a TBM, which reduces overall system downtime and minimizes grouting time as less preparation work is required as compared to conventional methods. 3. The present invention enables the direct application of grout to any cutting face cracks around the TBM which advantageously is very effective for improving the area required for creating a safe and workable chamber environment underground. Furthermore, when the desired result of ground stabilization has not been achieved, it is easy to apply repeatedly the grout so as to achieve the desired result.

4. The present invention minimizes and controls ground surface settlement and structure damage, which advantageously contributes to safety and productivity. The present invention also improves the advance ground condition for improving unstable excavation condition when the geology is difficult.

5. The present invention operates at a very low cost as compared to conventional methods.

6. The present invention creates a safe and workable chamber environment with a reduced need for compressed air or without the need for compressed air, which advantageously does not compromise the health and safety of workers.

Other aspects and advantages of the invention will become apparent to those skilled in the art from a review of the ensuing description, which proceeds with reference to the following illustrative drawings of various embodiments of the invention.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of illustrative example only, with reference to the accompanying drawings, of which:

FIG. 1 is a perspective view of a tunnel boring machine (TBM) 10 with grouting around the front body 12 and rear body 13 of the TBM in accordance with an embodiment of the present invention;

FIG. 2 is a cross section of the front body of the TBM 10 of FIG. 1;

FIG. 3 is a schematic diagram of a ground stabilization system where the feeding line 15 is supplied with slurry, in accordance with an embodiment of the present invention; FIG. 4 is a schematic diagram of the system of FIG. 3 where (A) the feeding line 15 is supplied with water in accordance with an all slurry replace method; and (B) the feeding line 15 is replaced with a grout pump 17 in accordance with a chamber slurry replace method; FIG. 5 is an illustration of the TBM cutter rotation of the TBM 10 of FIG. 1 ;

FIG. 6 is an illustration of the ground stabilization system with grouting at the TBM front body 12 where blocks of grout are applied to fill the clearance between the TBM 10 and cutter face in accordance with an embodiment of the present invention;

FIG. 7 is an illustration of the ground stabilization system of FIG. 6 with grouting at the front of the TBM 11 where grout is injected in accordance with an embodiment of the present invention after filling the clearance with grout;

FIG. 8 is an illustration of a ground stabilization system for controlling settlement in accordance with an embodiment of the present invention;

FIG. 9 is an illustration of the system of FIG. 6, in which advance grout is applied for unstable ground condition; and

FIG. 10 is an outline of the process work flow of the ground stabilization of FIG. 7 in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Particular embodiments of the present invention will now be described with reference to the accompanying drawings. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention. Additionally, unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. The use of the singular forms "a", an", and "the" include both singular and plural referents unless the context clearly indicates otherwise. The use of "or", "/" means "and/or" unless stated otherwise. Furthermore, the use of the terms "including" and "having" as well as other forms of those terms, such as "includes", "included", "has", and "have" are not limiting.

The use of "excavation chamber materials", "excavation materials" or "chamber materials" as used herein refer to slurry, water, grout, a combination thereof, or any other substances that can be found in a TBM excavation chamber, unless the context clearly indicates otherwise.

The use of "annulus" as used herein refers to a ring shaped structure or region, unless the context clearly indicates otherwise. With reference to Figures 1 to 10, there is described a ground stabilization (or a chamber pressure grout) method and system thereof in accordance with embodiments of the present invention. The ground stabilization method and system thereof of the present invention enables the creation of a safe and workable chamber environment underground for tunnel boring machine (TBM) interventions for maintenance, replacement or repair works.

Advantageously, the TBM chamber is pressurized above natural water pressure or ground water pressure with grout materials which are mixed by the TBM cutter rotation or pump flow circulation to directly improve the excavation face and the surrounding TBM body cutting face. This enables reducing water inflow to the desired area, improving the cutting face and improving on the surrounding ground stability. Advantageously, surface settlement will also be reduced.

Figure 1 illustrates a TBM 10 with grouting around the chamber 11 and the front body 12 of the TBM. The chamber and/or the cutter head are equipped with a plurality of grout ports. Grout is injected to the fractures 13 with high pressure and this pressure is maintained slightly higher than natural hydrostatic pressure to allow the grout to set inside the fractures 13 without washing out. Grouting can also be carried out around the TBM body 12 region, which prevents water ingress from bypassing the cutting clearance, which is generally larger than ground fractures. The cutting clearance gap is filled by injecting a plurality of grout blocks 14. The combination of grouting via the front body 11 and the body 12 enables water tightness around the excavation face and improves the surrounding ground stability.

Prior to the actual site work where the TBM 10 is located and where the desired area for creating a safe and workable chamber environment underground will take place, certain conditions must be assessed first under the design stage.

Design Stage

1. Ground Condition

The ground condition must be assessed in order to determine the grout pressure that is required. The passive ground pressure should be higher than the grout pressure that is be applied. Preferably, the passive ground pressure is 1.5 times higher than the grout pressure that is to be applied. It would be appreciated that 1.5 times is the safety factor of the grouting work.

2. TBM Design Pressure The design pressure of the TBM 10 must be assessed. The design pressure of the

TBM 10 should be higher than the grout pressure that is to be applied. Preferably, the design pressure of the TBM 10 is greater than 1.25 times that of natural water pressure.

It would be appreciated that the design pressure of the TBM can be lower than 1.25 times that of the natural water pressure, and is subject to the TBM design. Where limited by the TBM design and a lower predetermined target pressure is required, it would be necessary to increase the curing time.

In another embodiment where the geological condition provides a constraint on the predetermined target pressure to be lower than 1.25 times that of the natural water pressure, it would be necessary to increase the curing time.

3. Geological Condition

The geological condition must be assessed. The surrounding geological condition should be checked and research has to be carried out to determine the likelihood of risk of leakage of grout materials. Preferably, mitigation measurements are also prepared.

Site Work

1. Water Ingress Checks

Deviation flow, which is detected from slurry transportation system, and physical water ingress are both assessed. In another embodiment, a TBM 10 with a bubble chamber system, water ingress can be detectable from bubble level increasement under checking pressure.

2. Slurry Replacement

The slurry is replaced with water without changing the face pressure or if necessary, with a change in the face pressure. The water may comprise rocks, fractured rocks and other geology. The replacement of slurry with water provides an improved bond between the grout and cracks. A pump 18 or a grout pump which is equipped for back fill grout is used to perform the replacement of slurry with water.

Preferably, only the slurry in the chamber is replaced. It is also possible to replace the slurry in the chamber, pipelines and slurry regulation tank 16. Whilst this would be easier to carry out as compared to the replacement of slurry restricted to only the chamber, there is a high wastage of good slurry.

In another embodiment, the slurry is replaced with grout. The grout may comprise soil, weather rock, mix ground, other geology.

3. Injection of Grout Materials

The injection of grout materials advantageously contributes to ground improvement. Grout materials can be selected from the following:

(a) OPC cement

(b) Micro fine cement

(c) OPC cement and micro fine cement (d) Chemical grout method

The grout materials can be mixed by TBM cutter rotation. The grout materials can also be mixed by flow circulation using a pump or similar equipment.

In one example, micro fine cement is selected to penetrate small ingress in rocks and weathered rocks. A 200 kg/m of micro fine cement in water was mixed in the tank equipped with an agitator. An assessment is carried out before grouting and after grouting. The initial water inflow of 40 L/min has been reduced to approximately 0 L/min.

In another example, OPC cement is selected for reducing heavy water ingress. A 2- component mixture of 260 kg/m OPC cement based liquid and 30 kg bentonite was used. The initial water flow under water pressure of 187 kPa per 1.37 m /min is reduced to free air and leakage of 109 L/min.

Grouting Flow Control

The grouting flow is controlled so as to reach a predetermined target pressure. The predetermined target pressure is subject to geology, TBM capacity and ingress condition. The curing time of the grout is subject to grout type, the required or desired water tightness and ingress condition. During the grouting and curing periods, there is a need to check the viscosity which may cause clogging in the chamber and TBM body.

Procedure for Chamber Pressure Grout (Slurry and EPB)

1) Water ingress check to decide method and target pressure and flow rate

Example 1

Case Condition

Natural Water Pressure: 500kpa

TBM design Pressure: 700kpa allowable up to 800kpa; 700/500=1.4 times

Water ingress check: under 200kpa water pressure ; observed 600L/min,

Water ingress Projection will be 600L/min/(500kpa-200kpa)*500kpa=1000L/min under free air condition. 2) Decide target chamber grout pressure

Target chamber grout pressure: 700kpa

start grout flow is 200L/min, then increase chamber pressure 500kpa up to 700kpa by cement grout (such as Aliquid)

In summary, where the water ingress is high, there is a need to increase cement content in the chamber.

3) Chamber pressure control

Control the chamber pressure by pressurize grout or pressurize water flow rate. For example:

Start to lhour lOOL/min; keep 700kpa lhour to 2hour 40L/min; keep 700kpa 2hour to 3hour lOL/min; keep 700kpa

Basically the target chamber pressure flow rate reduces with time due to choke of crack and water pass.

4) End target flow rate

Free air condition target water ingress, if less than WI=50L/min Safety factor 2 FS=2 WI/FP*(CP-FP)/SF=50/500*(700-500)/FS=10L/min Target flow rate should be below lOL/min

In the above case, grout injection is about 3hours, curing time is about 12 hours under the pressure of 700kpa.

Total 15 hours (This excludes the replacement of slurry to water)

To ensure that there is less water ingress than the target, it is recommended to increase curing time and reduce target flow rate. . Block Body grout

The block body grout uses a 2-component grout (backfill grout A+ B) to fill the gap between the TBM body and the cutting face as illustrated in Figure 2. Advantageously, this enables efficient grouting of remote and distal areas when used in combination with the chamber pressure grouting method. Preferably, grouting is carried out from the base of the profile and upward by forming a plurality of blocks of grout, thereby minimizing grout block volume.

For example, if the direction of water ingress is behind TBM or TBM body area, the application of the TBM block body grout is recommended as follows:

Inject Back fill grout A+B to TBM body surrounding injection port.

1 ^st step: Inject fix volume grout to each port to make block. This is carried out under the same pressure as chamber pressure grout or if necessary, to be carried out separately and under different pressure. Preferably, the pressure is above natural water pressure.

2 ^nd step: Inject grout from injection port in each of the areas which has not reached target pressure. This is carried out under the same pressure as chamber pressure grout or if necessary, to be carried out separately and under different pressure. Preferably, pressure is applied above natural water pressure.

3 step: Curing 6 hours under same pressure as chamber pressure grout (depends on ingress amount and target ingress flow). In another embodiment where a different pressure is applied, apply same pressure as grouting period TBM face pressure.

The above-mentioned grout is to support the cutter head behind water ingress and in combination with chamber pressure grout, to easily seal up wide gap area such as TBM surrounding over cut area.

Cleaning Chamber

Slurry TBM

After grouting, the cleaning process is initiated immediately by starting circulation slurry in the chamber to cleaning any remaining grout. EPB

Discharge chamber materials into a muck car. Preferably, there is provided a screw conveyor to keep excavation materials for making a plug zone in the event of emergency pressurize situations. 7. Water Ingress Checks After Grouting

Water ingress checks should be performed after grouting to determine whether there is water ingress. Preferably, the checks reveal a rate more than target water ingress. In such a situation, the grouting step can be repeated. Alternatively, block body grout and/or polyurethane grout can be added. It is to be understood that the above embodiments have been provided only by way of exemplification of this invention, and that further modifications and improvements thereto, as would be apparent to persons skilled in the relevant art, are deemed to fall within the broad scope and ambit of the present invention described herein. It is further to be understood that features from one or more of the described embodiments may be combined to form further embodiments.