SYSTEM THEREOF

FIELD OF THE INVENTION

The present invention relates generally to a method and system thereof for reinforcing excavated ground used in the areas of excavation and tunneling works, and in particular but not exclusively, to a body grouting method and system thereof for reinforcing the excavated ground which provides in-situ support to freshly excavated earth immediately during excavation by the tunnel boring machine (TBM).

BACKGROUND TO THE INVENTION

The following discussion of the background to the invention is intended to facilitate the understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement 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.

In modern construction, tunnels of large diameters are commonly excavated by means of a tunnel boring machine (TBM). When tunneling using these machines, overcutting is necessary to permit the advancing of the machine, and the excavation diameter is usually larger than the external diameter of the final lining due to technological considerations. However, this overcutting cannot be readily maintained due to fall of earthen material. While the volume of earth lost may not be significant in good soil condition, a considerable amount of soil displacement can occur when tunnel boring under areas of relatively unstable earth. Once the overcutting arch is lost, soil stability will be lost which leads to collapse or settlement.

Grouting works are a significant part in excavation and tunneling works. One of the numerous purposes of grout is the backfilling of tail voids in the TBM, an operation of paramount importance for tunneling procedure. Generally, backfill grouting is used to prevent ground settlement due to any over-excavation generated by the passage of the TBM. This carried out by injecting grout to fill the void between the lining and the ground (tail void). In addition to preventing ground settlement, the backfilling operation has to lock the segmental lining into position, ensure a uniform and homogeneous contact between the ground and the lining, and reduce the surface settlement over the tunnel. It is recognized that failure to carry out sufficient grouting, hence resulting in inadequately filled voids has ultimately led to tunneling faults. Therefore, sufficient grouting by forming areas for effective grouting with timely or immediate application of grout to these unstable areas is necessary to maintain a stable underground environment for TBM excavation and cutter head interventions.

Conventional TBMs are equipped with a back filling system where grouting is carried out at the grout ports at the tail voids. While excavation using this system attempts to reduce settlement over the tunnels, grouting usually cannot be carried out until the grout port has moved past the initial cutting area for subsequent tail void grouting. As a result, unstable ground is likely to collapse before grouting can be carried out.

Furthermore, during excavation of unstable ground, TBM may encounter falling soil and collapse material. In such situations, the effects of grouting would be largely negated due to ineffective grouting or a delay in provision of effective support which may eventually lead to collapse and settlement. Critical failures due to such events may result in undesirable consequences, such as damage to third parties, additional costs and delays in completion of the tunnel project, injuries or even loss of life. While existing methods allow directed application of grout to be applied directly into cracks behind the cutting face of the TBM, the reinforcement of the excavated ground by providing an active support has proven far more effective in providing support and preventing ground settlement to better cope with adverse conditions onsite.

Hence, there is an urgent need for an efficient and effective method and system to address the aforementioned disadvantages. The present invention seeks to provide such a method and system thereof for reinforcing the excavated tunnel against the surrounding geological formation, to enable forming a layer of grout over a portion of the excavated ground which obviate delay in providing support and ensuring a workable underground environment for TBM excavation. SUMMARY OF THE INVENTION

Throughout this document, unless otherwise indicate 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 method and system for reinforcing excavated ground which provides in- situ support to freshly excavated ground immediately after cutting by the tunnel boring machine (TBM). In particular, a method and system that enables grouting of adjacent subsurface simultaneously with the advance of the TBM.

In accordance with a first aspect of the present invention, there is provided a method for reinforcing at least a portion of ground excavated by a tunnel boring machine, comprising: determining TBM face pressure of the excavated ground; determining a target pressure for applying grout materials to at least the portion of the excavated ground, wherein the target pressure is greater than the TBM face pressure; applying the grout materials to at least the portion of the excavated ground at a pressure, wherein the pressure starts at the TBM face pressure and is increased to the target pressure for forming a layer over at least the portion of the excavated ground which reinforces the excavated ground.

The target pressure for applying the grout materials is from 0.5 to 2 bars, preferably 1 to 1.5 bars greater than the TBM face pressure. The grout materials is applied at a flow rate of at least from 5 to 20 L/min.

The tunnel boring machine continuously excavates the ground when the grout materials are being applied.

The grout gelling time can be controlled for maintaining the formed layer over at least the portion of the excavated ground. The grout gelling time can be controlled by varying at least one component of the grout materials used. The grout materials used can be a 2-component grouting liquid. The at least a portion of the excavated ground can comprise from 5% to 40%, and preferably 8% to 35% of total perimeter of the excavated ground. Preferably, at least the portion of the excavated ground comprises less than 50% of the total perimeter of the excavated ground.

The excavated ground can be reinforced by applying the grout materials to at least the portion of the excavated grout until a target volume of the grout materials is reached. The target volume can be determined from over-excavation volume of the TBM, when the actual excavated volume exceeds projected excavation volume during excavation. Under manageable or stable ground conditions, the target volume can be calculated based on the following formula:

V= ((D + 2R)* (D + 2R) x π I - D* D x π /4) x Θ / 360° x L wherein, D = diameter of body of the tunnel boring machine (TBM body), θ = angle of reinforced portion of excavated ground; R = overcutting clearance and/or collapse; L = excavation distance.

The invention method and system are directed to an application in which the purpose is to stabilize/reinforce a freshly excavated body of earth, susceptible to settlement.

The invention has at least the following advantages:

1. The present invention permits creation of safe underground work site, which sufficiently reinforces the overcutting clearance, which enables the TBM to simultaneously advance. This continuous excavation by the TBM, advantageously leads to efficient and more cost-effective tunneling.

2. The present invention obviates the limitations of delay in time in supporting freshly excavated ground by present grouting systems by immediate application of grout directly to any voids/fissures or unstable earth with the passage of the TBM. Advantageously, this is very effective for minimizing risks of ground settlement during excavation.

3. The present invention can be used with existing TBMs and does not require customization, which advantageously operates at a low cost.

4. The present invention offers the direct application of grout to any earthen material around the TBM body which advantageously is effective for alignment control of the TBM. This provides ease of positioning the TBM in a convenient and practical manner during excavation.

5. The present invention provides improved ground stability to freshly excavated areas around the TBM with minimum or no disturbance to the TBM during excavation works and without the need for specialized equipment.

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 illustrates a flowchart of a method of grouting the body and rear end of the tunnel boring machine (TBM) in accordance with an embodiment of the present invention; FIG. 2 is a perspective view of the TBM with grouting around the body and rear end of the TBM in accordance with an embodiment of the present invention;

FIG. 3A is an illustration of the grouting method for filing collapse void in which grout is delivered to void via the TBM body as the TBM advances in accordance with an embodiment of the present invention; FIG. 3B is a perspective view of the TBM of FIG. 3A, wherein grout is applied via a pump and moves to a region of lower pressure to fill the void; the grout stops flowing due to gelling of the same;

FIG. 4 illustrates the TBM of FIG. 2 for reinforcing the unstable excavated ground, wherein the unstable ground around the TBM body region has been reinforced by the grouting layer and the back of the TBM supported by backfill grout in accordance with an embodiment of the present invention;

FIG. 5 is a cross-sectional view of the TBM similar to FIG. 2 illustrating the reinforced ground during excavation by forming the grouting layer for providing support to the excavated ground, whereby grout is applied from the top of the body and backfill grout at the rear end of the TBM in accordance with an embodiment of the present invention;

FIG. 6 illustrates the TBM of FIG. 2, being in operation to control the steering of the TBM in accordance with an embodiment of the present invention; FIG. 7 is a side view of a perspective view of the TBM of FIG. 5, in which grout is applied via the TBM body along with backfill grouting in accordance with an embodiment of the present invention;

FIG. 8 is another cross- sectional view of the TBM similar to FIG. 5 illustrating the movement of the grout in the cutting clearance for forming the grouting layer for reinforcing the excavated ground; and

FIG. 9 illustrates the TBM of FIG. 2 and the cutting clearance created, in which the grout is applied to form the layer over the excavated ground for reinforcing the same 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.

Reference made to the use of "TBM Body Grout" in the present document refers to the system and method for reinforcing the excavated ground in accordance with the present invention. With reference to Figures 1 to 9, there is a method and system for reinforcing the excavated ground in accordance with embodiments of the present invention. The method and system of the present invention enables continuous excavation by simultaneously boring and reinforcing the excavated ground by a tunnel boring machine (TBM) 10. Advantageously, grout materials are pressurized above the TBM face pressure for reinforcing the excavated ground behind the cutter head 11 to support the surrounding ground around the TBM body region 12. This enables maintaining the overcut as the excavated ground is continuously reinforced as the cutter head 11 advances and continues boring. Advantageously, friction between ambient grout and the TBM body will also be reduced.

Figure 2 illustrates a TBM 10 with grouting behind the cutter head around the body region 12 of the TBM 10. The TBM body is equipped with a plurality of grout ports 13. Grout is pressurized and applied to the excavated ground. This pressure is maintained slightly higher than the TBM face pressure to allow the grout material to form a predetermined layer in the excavated tunnel.

As ground collapse typically occurs due to unstable soil located overhead of the overcutting clearance, the reinforced layer can be formed by applying grout to the overhead region of the tunnel. To prevent the TBM getting jammed, the reinforced portion of the excavated ground is less than 50% of the total perimeter of the excavated area. This reinforced portion of the excavated ground comprises from 5% to 40%, and preferably 8% to 35% of total perimeter of the excavated ground.

This reinforced portion may be derived from a ratio of the reinforced layer with respect to the cross section of the excavated tunnel (see Figure 5). The angle of the reinforced layer can comprise at least 20° to 130°, preferably 30° to 120° about the axis of rotation of a TBM relative to the cross section of the excavated tunnel. This angle of the reinforced portion can be less than 180° of the total diameter of the excavated tunnel.

The method of the present invention enables grouting at the TBM body region 12 by applying grout to form a layer comprising at least a portion of the excavated ground for reinforcing the excavated area as the TBM 10 advances. Advantageously, grout materials can be applied timely for reinforcing once the cutter head 11 advances ahead of the excavated ground. Furthermore, the grouting method enables maintaining or adjusting the overcutting region in relation to the ground conditions and is advantageous for steering the TBM 10 for negotiating a curve during tunnelling operation (see Figure 6).

With reference to Figure 7, backfill grouting 14 can be carried out simultaneously when the TBM 10 advances during tunnelling work. This specific combination advantageously provides effective reinforcement to the freshly excavated ground around the TBM body and the TBM segment area 15 and reduces the risk of ground settlement.

Prior to the actual body grouting work by the TBM 10 which provides in-situ support immediately to freshly excavated ground so as to ensure a workable underground environment for TBM excavation, certain conditions must be assessed first under the design stage.

Design Stage

1. Geological Condition

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

2. TBM Design Pressure

The design pressure of the TBM 10 may be assessed. Preferably, the design pressure of the TBM cutter seal, articulation seal, and TBM body capacity is higher than the grout pressure that is to be applied. Preferably, the design pressure of the TBM is controlled and adjusted based on the grout pressure that is applied.

3. Grout Pressure

The grout pressure may be assessed in order to determine the groutability of the ground. During TBM operations, the grouting distance is controlled by the grout pressure and gel time.

For example, a long gel time grout requires low grout pressure, while a short gel time grout requires high grout pressure. This results from friction generated from gelling of the grout. It would be appreciated that a long gel time grout covers more ground than a short gel time grout under same grout pressure.

The grout pressure is typically from 0.5 to 2 bars, and preferably 1.0 to 1.5 bars higher than the TBM face pressure, which enables filing of overcut gap and/or void. The TBM face pressure is slightly higher than the natural water pressure and/or the surrounding geological pressure.

Grouting Flow Rate

The grouting flow may be assessed to determine the ability of the grout to flow into the desired area and is controlled so as to reach a predetermined target pressure and volume. The predetermined target pressure and volume are subject to the geology condition and TBM cutting clearance, collapse distance, grouting port distance from cutter head, advancing speed of TBM. Generally, grout material is applied at low grout flow rate for effective grouting and also minimize the risk of TBM 10 jamming.

Grout Material

The grout material advantageously contributes to ground reinforcement and support. The grout material is assessed in accordance with the surrounding geological condition and the grouting technique in order to ensure the groutability of the ground. Preferably, the grout material is a 2-component grout, which allows easy control of the flowability and gel time. The 2-component grout consists of an A-Liquid and a B-Liquid, in which the A-Liquid comprises OPC cement based liquid and the B-Liquid comprises sodium silicate. It would be appreciated that other grout materials, such as chemical grout, micro fine cement, OPC cement, can be used as desired depending on system requirements. Preferably, the grout material used can be the same as the backfill grout materials.

Controlling the gel time is critical for reducing the frictional resistance between TBM 10 and the excavated ground during its advance and preventing TBM 10 jamming. When the TBM gets stuck, this inevitably causes delays which would impose heavy and expensive burdens on the tunneling operation. To reduce the possibility of machine jamming, choosing a suitable gel time is essential. The gel time can be controlled by adjusting the mixing ratio of the 2 components in the grout material.

Grout Mix Ratio The mixing ratio is controlled so as to provide the grouting material that is required. The grout mix can comprise the composition of Liquid A and Liquid B. One possible mix of the components is given in Table 1 below.

Table 1

The recommended grout mix can comprise Liquid A and Liquid B in 15 vol%. The ensuing grout mix provides longer gel time and advantageously, offers significant benefits for voids/fissures when combined with the body grouting method.

Preferably, the recommended grout mix can comprise Liquid A and Liquid B in the range between 8 to 10 vol%. The ensuing grout mix provides shorter gel time, which avoids having excessive grout around the surface of the TBM body surface which leads to high thrust force. Advantageously, a shorter gel time is desirous for providing the required support to unstable body of earth, susceptible to collapse, thereby minimizing risk of settlement when combined with the body grouting method.

However, it would be appreciated that this mix ratio may vary, depending on the subject to the geological condition and TBM overcutting clearance.

Grout Ports

A plurality of grout ports 13 are positioned on the TBM body for injecting the grout materials.

The injection of grout materials from the grout ports 13 advantageously contribute to reinforcing the excavated ground for providing support. A plurality of grout ports 13 are mounted on the exterior of the TBM 10. Preferably, each of the grout ports 13 is positioned within 2 m interval on the circumference of the TBM body. Generally, a TBM 10 can experience ground collapse from one or sometimes more than one direction during excavation. For reinforcing the excavated ground, the grout ports 13 on the TBM 10 that are facing the collapse directions are typically used for grouting the excavated ground. Body Grouting Methodology

The body grouting methodology of the system comprises the following:

1) Equipping a plurality of grout ports 13 on the top part of the TBM body, wherein each of the grout ports are positioned approximately 2.0 m interval and connected to a pump (not shown) via connecting means such as pipes or conduits, for providing pressurized grout material to the grout ports 13. Preferably, the pressure of the grout should be lower than the TBM seals on the cutter head drive and articulation seal capacity.

2) Providing grout material to the plurality of grout ports 13 in point (1) above. The grout material is injected into the adjacent subsurface behind the TBM cutter head 11, with grouting around the TBM body region 12. The injection of the grout material is triggered when an abnormal excavation volume is detected or when the actual excavated volume deviates significantly from the planned excavation volume. The volume of excavated material is measured during excavation to estimate the volume loss, which serves to provide prediction of ground collapse deformation and as a means of quality control. It would be appreciated that the abnormal excavation volume that is required to trigger the grout injection may vary, depending on the different ground condition and void.

The triggering can also be performed when the TBM 10 excavates and advances. Grouting stops when the target pressure is achieved and the projected excavation volume is achieved.

Referring back to Figure 1, the method for reinforcing the excavated ground comprises assessing the ground condition to determine the geological pressure and/or natural hydrostatic pressure 1; determining an overcutting clearance created by the TBM 10; determining a target pressure for grouting based on TBM face pressure which is derived from the geological pressure and/or natural hydrostatic pressure 3, whereby the target pressure for grouting is higher than the TBM face pressure; continuously applying grout materials at a pressure higher than the TBM face pressure to fill the overcutting clearance, the grout pressure increases until the target pressure is reached whereby the applied grout covers a layer over the portion of the excavated ground for reinforcing the excavated ground, the pressure increase enables forming at least the portion of the excavated ground and the pressure increase starts when the applied grout flows in the overcut area; applying grout at controlled flow rate to provide grout flowability so that the grout covers at least a portion of the grouting area 4, whereby the excavated ground can be reinforced as the TBM 10 continuously advances and excavates; grouting discontinues when the target grouting pressure is achieved 5.

Application of grout materials may continue as the TBM advances along the excavation route, which when the pressure decreases below the target pressure triggers the application of grout and continues reinforcing the portion of the ground excavated.

The pressure increase to reach the target pressure can improve grout flowability to form the reinforced portion of the excavated ground, which comprises between 5% to 40%, and preferably 8% to 35% of the total perimeter of the excavated ground (see Figure 5). This pressure increase starts when the applied grout flows in the overcut area. For example, when the grout flow rate is high, pressure can increase sharply to ensure that the pressurized grout materials do not extend beyond the portion of the excavated ground to be reinforced. When the grout flow rate is adequate, pressure can increase gradually to enable the pressurized grout materials to cover the portion of the excavated ground.

Generally, if the target pressure is achieved before the target volume, the advancing TBM 10 may continue grouting so that the target volume may be reached. Preferably, under unstable ground condition with over-excavation, this over-excavation volume can be detected by the TBM system, when the actual excavated volume exceeds projected excavation volume during excavation.

The volume of the grout material is advantageous for controlling grout application when reinforcing the excavated ground, such that the grout layer does not exceed at least the portion on the overcutting clearance for reinforcing the excavated tunnel. The projected volume of grout material can be determined from the size of the overcut, the TBM diameter, the excavated distance, collapse. The target volume of grout materials can be calculated based on the following formulae:

V= ((D + 2R)* (D + 2R)x π /4- D* D x π /4)x Θ / 360° x L

0Γ Υ = ϋ χ π χ θ / 360° x R x L

wherein, D = diameter of the body of the tunnel boring machine (TBM Body), θ = angle of reinforced portion of excavated ground; R = overcutting clearance and/or collapse; L = excavation distance. If the target grout volume is achieved before the target pressure can be reached, it is preferable to review the target grout volume, flow rate, gel time. For a manageable ground condition, grouting may stop while the overcutting clearance is being produced by the TBM cutter head. For unstable ground condition with collapse or over-excavation, the TBM system detects that the actual excavated volume exceeds the projected excavation volume, and applies grout continuously until the target pressure is reached.

The examples below describe reinforcing excavated ground under various conditions. During unstable ground conditions, grouting is carried out under volume and pressure control for reinforcing ground collapse. Depending on the size of the collapse, more time may be taken for the grout materials to form the reinforced layer in the clearance. In this case, grout can be applied under controlled grout flow or controlled speed of the advancing TBM 10 to form a portion of the reinforced layer.

Procedure for forming the layer for reinforcing the excavated ground Example 1

For stable ground condition, grout is applied using volume and pressure control. TBM diameter: 6.6 m

TBM advancing speed: 20 mm/min

Overcut: 0.05 m

Grout applied to cover 120° over the excavated ground

Grout flow rate: 15 L/min Required grout volume for 1 m advance of TBM: 6.6m* π* 120/360*0.05m = 0.345 m3/m Time required for pressure to reach target pressure: 0.345/0.015 = 23 min (time for grout to cover 1 m)

Time required for TBM advancing at 20 mm/s to excavate lm: 1000 mm/20 mm/min = 50min (>23 min less than the time taken for grout to cover lm excavated ground)

During excavation, grouting stops when the target pressure is reached or when the grout volume is reached.

Example 2(a)

For unstable ground condition, grout is applied using pressure control and when advancing speed of TBM is adjusted.

TBM diameter: 6.6 m

Collapse overhead: 0.5 m

Grout applied to cover 120° overhead for support

Grout flow rate: 15 L/min

Required grout volume for 1 m advance of TBM: 6.6m* ^* 120/360*0.5m = 3.45 m3/m Time required for grout to reach target pressure: 3.45/0.015 = 230 min (too long)

Need to control TBM speed: 1000mm/230min = 4.3 mm/min

For a TBM excavating at lOmm/min, grout flow rate must increase so that the target volume can be reached.

Adjusted flow rate = 3.45 m3/l 000mm/ lOmm/min = 34.5 L/min

Example 2(b)

For unstable ground condition, grout is applied using pressure and volume control under controlled grout flow rate.

Change grout flow rate

TBM advancing speed: 20 mm/min

Time taken for TBM to excavate lm: 1000 mm/20 mm/min = 50 min

Target grout flow: 3.45 m3/50 min = 69 L/min Grout continuously to reach target volume or target pressure. Grout flow rate depends on the diameter of the TBM, the overcut and/or collapse size and the advancing speed of the TBM.

With reference to Figure 6, the body grouting system can be applied for steering the TBM 10. This steering operation may be carried out by applying grout via the plurality of grout ports 13 which may be mounted along the TBM body on each of the top face, bottom face and sides. The direction of the grout ports 13 from which grout is applied may depend on the steering direction of the TBM 10. During the steering operation of the TBM 10 in a first intended direction, grout can be applied to a second direction that is 180° to the first intended direction.

For example, upwards steering of the TBM 10 may be induced by applying grout from the grout ports 13 that are positioned at the bottom face of the TBM 10. Conversely, to steer the TBM 10 downwards, grout can be applied via the grout ports 13 that are positioned at the top face of the TBM body. Sideways steering of the TBM 10 can be achieved in a similar effect. For example, to steer the TBM 10 to the left may be induced by applying grout via the grout ports 13 on the right side of the TBM body; steering the TBM 10 to the right may be achieved by applying grout via the grout ports 13 positioned on the left side of the TBM body.

Advantageously, the present invention allows for steering control of the TBM 10 when the machine deviates from the planned tunnel alignments, and particularly useful for maneuvering the TBM 10 when negotiating a curve during excavation.

Steering of a TBM 10 is site sensitive. In unstable soil condition, the weak layers will get sheared off by the cutting edge. The invention advantageously enables ground stabilization during steering of the TBM 10 and keeping the alignment difference at a minimum.

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.