GB2026574A - A method of, and apparatus for laying a series of interconnected tunnel sections - Google Patents

Abstract

The present invention is directed to a method of, and apparatus for, laying a series of interconnected tunnel sections. The apparatus comprises an excavation compartment (10) formed by a plurality of interconnected walls (14, 16) at least one of the walls being partly hollow and jetting pipes (15) positioned adjacent the lower ends of the walls to facilitate entry and removal of the compartment into, and from, the sea-bed (22). The apparatus also comprises a tunnel section supporting and aligning frame (12) comprising a longitudinally extending main beam (30) provided with tunnel section lifting arrangements (32) which are movable longitudinally of the main beam (30) by means of a hydraulic piston-and-cylinder arrangement (38). A pair of spaced transversely extending beams (48) are provided which support the main beam (30) for movement thereover. A piston-and-cylinder arrangement is associated with each transversely extending beam for effecting the movement of the main beam (30). <IMAGE>

Description

SPECIFICATION A method of, and apparatus for laying a series of interconnected tunnel sections The present invention relates to a method of, and apparatus for laying a series of interconnected tunnel sections. In particular, the invention is directed to the laying of such tunnel sections in a "soft" under-water bed. This latter term covers river, lake and sea-beds, hereinafter referred to for convenience as "sea-bed".

Underwater tunnels are often constructed by the immersed tube method, whereby tunnel sections are pre-fabricated on land, then launched into the water, towed out to the line of the tunnel and lowered into a pre-dredged trench in the sea-bed. The section is then joined up to the previously laid sections.

Such laying of a tunnel beneath the level of a soft sea-bed is particularly difficult in that the excavation of a trench by dredging to receive the tunnel inevit ably results in the collapse of the sides of the trench during the dredging operation which necessitates the removal of an increased volume of sea-bed in order to reach the necessary depth. This difficulty is aggravated when such dredging operations are carried out in tidal waters due to the effect of the current.

In calm water the lowering of a tunnel section directly into position can be effected by a lifting vessel floating on the surface of the water, but if there is any swell on the water this method is impractical since movement of the vessel is transmitted to the tunnel section, so that alignment thereof with previously laid sections is extremely difficult.

Due to this difficulty floating craft are seldom used for placing the sections; instead, barges provided with support legs which engage the sea-bed are used or the sections are lowered onto prepared supports set in the trench and subsequently moved into position.

However, such techniques are very expensive and difficult in deep water and the specialised vessels and equipment required are not readily available.

Thus, the object of the present invention is to provide a method of, and apparatus for, laying a series of interconnected tunnel sections which overcome the difficulties and disadvantages referred to above.

It is to be understood that throughout the following specification such terms as "vertical", "horizontal", "longitudinal" and "transverse" are used for convenience and such terms are not to be contrued as limitative.

The present invention consists in a method of laying a series of interconnected tunnel sections comprising the steps of isolating a volume of the sea-bed adjacent the last laid tunnel section by means of a plurality of walls, excavating said volume of the sea-bed, supporting and lowering a further tunnel section from support means, aligning the further tunnel section with the last laid tunnel section, connecting said last-mentioned tunnel sections together and thereafter removing said walls.

The invention further consists in an excavation compartment formed by a plurality of interconnected walls, at least one of said walls being partly hollow and jetting pipes positioned adjacent the lower ends of the walls to facilitate entry and removal of the compartment into, and from, the sea-bed.

The invention still further consists in a tunnel section supporting and aligning frame comprising a longitudinally extending main beam provided with tunnel section lifting means which are movable longitudinally of the main beam, means for effecting said movement of the lifting means, spaced transversely extending beams which support the main beam for movement thereover and means for effecting said movement of the main beam.

The accompanying drawing is a perspective view of the tunnel section supporting and aligning frame, also the excavation compartment according to the present invention, the latter compartment being shown partly in section.

In carrying the invention into effect according to one convenient mode by way of example, the apparatus basically comprises a prefabricated, reusable, excavation compartment 10, a tunnel section supporting and aligning frame 12 and an apparatus (not shown) for injecting sand beneath the tunnel section.

The excavation compartment 10 comprises spaced substantially parallel side walls 14 and spaced substantially parallel end walls 16, one of the end walls 16 being provided adjacent its lower surface with a rectangular aperture 18 for a purpose hereinafter described. The upper part of each wall 14, 16 is of hollow box-like construction and the lower edge 20 provides a relatively narrow surface which can readily enter a soft sea-bed 22. Conveniently, the lower part of each wall is formed by a stiffened steel plate 24 connected to the upper part.

Jet pipes 15 are provided around the lower, narrow edge 20 of each wall to assist in the entry of the excavation compartment 10 into the bed 22 and also to assist in the removal of same when required. If desired, the apertured end wall 16 referred to above may be in the form of a lattice beam or girder which interconnects the adjacent upper portions of the two side walls 14.

In use, a surface vessel is employed in lowering and subsequently removing the excavation compartment 10. The compartment 10 is lowered onto the sea-bed 22 with the aperture 18 in one end wall 16 directly over the end portion of the last laid tunnel section 26, the hollow walls 14, 16 being water filled through openings (not shown) to increase the effective weight of the compartment 10. By water jetting through the pipes 15 positioned adjacent the lower end of the walls 14, 16 and internal excavation, the compartment 10 sinks to a depth which will support further excavation to a specified depth suitable to receive the next tunnel section 28 to be laid, at which depth the aperture 18 in the end wall 16 surrounds the sides and top of the last laid tunnel section 26.

During this operation the excavated material is used to fill over the previously laid tunnel sections which obviates the necessity for disposing of the excavated material and the importing of additional filling materials.

With the excavation complete, a fresh tunnel section 28 can be lowered into the compartment under the direction of divers who align the section with previously laid sections by means of the frame 12 now to be described and then connect the sections together with sealing means interposed therebetween. The excavation compartment 10 is then removed with the aid of fluid passing through the jet pipes and/or air pumped into the hollow parts of the walls 14, 16 in addition to lifting means suspended from the lifting vessel.

The tunnel section supporting and aligning frame 12 comprises a longitudinally extending main beam 30 provided with a pair of vertically disposed, hydraulic piston-and-cylinder lifting arrangements 32, which respectively, extend through spaced, longitudinally extending slots 34 in the beam 30 and are mounted on wheeled trollies 36 so that the lifting arrangements 32 can be moved along the beam 30 by means of a further, horizontally disposed, hydraulic piston-and-cyinder arrangement 38, the cylinder of which is fixedly connected to the beam 30, whilst the ends of the piston rod which extend from opposite ends of the cylinder are connected, respectively, to the trollies 36.

Each end of the beam 30 is provided with an upstanding inverted 'U'-shaped bracket 40 in which a double flanged wheel 42 is rotatably mounted. Each bracket 40 is also provided with a pulley block 44 around which a lifting cable 46 passes from a surface vessel (not shown).

The main beam 30 is also provided with a pair of transversely extending beams 48 postioned, respectively, through the brackets 40 on the main beam 30.

Each double flanged wheel 42 is aligned with and engages a rail 50 on the top surface of each of the transverse beams 48. Each transverse beam 48 is provided with a hydraulic piston-and-cylinder arrangement 52, the cylinder of which is pivotally mounted at 54 on the beam 48, whilst its piston rod is pivotally connected at 56 to the associated bracket 40 on the main beam 30 thus, the latter can be moved relatively to the transverse beams 48 upon extension and retraction of the piston-and-cylinder arrangement 52, such movement being facilitated by the double-flange wheels 42 mounted in the brackets 40 engaging the rails 50 on the transverse beams 48.

In use, initially each end of the longitudinally extending main beam 30 is suspended from a lifting vessel (not shown) by means of the cables 46 attached to the respective brackets 40 through the pulley blocks 44. Preferably, the lifting vessel is of the catamaran type so that the frame 12 can be held above the water between the two hulls, in which position the next tunnel section 28 to be laid can be floated beneath the frame 12 and connected by chains 58 to the two vertically disposed piston-andcylinder lifting arrangements 32 mounted on the trollies 36. The arrangements 32 are then fully extended and the frame 12 together with the attached tunnel section 28 is lowered by winches until the tunnel section 28 comes to rest in the excavated portion defined by the excavation compartment 10 referred to above.The tunnel section 28 is then in approximate alignment with the previously laid tunnel section 26 and spaced approximately one to two metres therefrom. In this position the transverse beams 48 of the frame 12 are positioned slightly above the top of the spaced side walls 14 of the excavation compart ment 10 so that any dynamic loads due to movement of the tunnel section 28 react on the sea-bed 22 and not on the frame 12.

The cables 46 from the lifting vessel are then slackened completely so that the transversely extending beams 48 of the frame 12 rest on the top of the sides 14 of the excavation compartment 10 and the longitudinally extending main beam 30 is suspended therefrom, the double-flange wheels 42 engaging the rails 50 on the transverse beams 48.

The two vertically disposed piston-and-cylinder lifting arrangements 32 are then retracted to lift the tunnel section 28 from the sea-bed to approximately its correct height, whereupon the horizontally disposed pistion-and-cylinder arrangement 38 mounted on the main beam 30 is then actuated to bring the tunnel section 28 adjacent the previously laid section 26 so that the alignment thereof can be checked by the divers.Any transverse adjustment of the tunnel section 28 which may be required is then effected by the piston-and-cylinder arrangements 52 mounted on the transverse beams 48, the extension or retraction of these arrangements 52 effecting a transverse movement of the main beam 30. Thetun- nel section 28 is then finally aligned with the previously laid sections and the sections are bolted together in known manner with a sealing member (not shown) interposed therebetween.

To effect the correct transverse alignment it will be appreciated that it may be necessary to extend or retract the piston-and-cylinder arrangements 52 on the transverse beams 48 by different amounts, or even in opposite directions. Thus the transverse beams 48 are not always at right angles to the main beam 30 and to permit this, clearance must be provided between the transverse beams 48 and the brackets 40 mounted on the main beam 30.

However, it is important that the main and transverse beams 30 and 48 are at right angles to each other at the commencement of the operation, otherwise there would be insufficient clearance for subsequent alignment correction. To ensure this condition, small wedge shaped blocks (not shown) are used to locate the transverse beams 48 while these are supported on the main beam 30 during the lowering of the tunnel sections.

When the transverse beams 48 are supported on the top of the excavation compartment 10, the load is transferred so that the main beam 30 and the tunnel section 28 are supported by the transverse beams 48 and the clearance enables the beams 48 to pivot through a small angle.

After connection of the tunnel sections, sand or grout is injected beneath the last laid section to provide a permanent support through pipes (not shown) from both sides of the tunnel section simultaneously in such a manner that the sand or grout extends across the full width of the tunnel section in one operation, ensuring that voids or soft patches are obviated. If the tunnel section is of considerable length it must remain supported bytheframe 12 while sand or grout is injected.

If the method of the present invention utilises a barge with support legs, the tunnel sections are supported and lowered directly from the barge into the excavation compartment. Likewise, if the nature of the sea-bed is sufficiently firm to render use of the compartment 10 unnecessary, it will be appreciated that the frame 12 may be supported in any convenient manner, for example, the ends of each of the transverse beams 48 may be provided with support legs.

Claims (18)

1. A method of laying a series of interconnected tunnel sections comprising the steps of isolating a volume of the sea-bed adjacent the last tunnel section by means of a plurality of walls, excavating said volume of the sea-bed, supporting and lowering a further tunnel section from support means, aligning the further tunnel section with the last laid tunnel section, connecting the last-mentioned tunnel sections together and thereafter removing said walls.

2. A method as claimed in claim 1, including the step of using the excavated volume of sea-bed to cover over previously laid tunnel sections.

3. A method as claimed in claim 1 or 2, including the step of directing jets of fluid adjacent the lower edges of said walls to facilitate entry and removal of the wall into, and from, the sea-bed.

4. A method as claimed in any of claims 1 to 3, including the step of injecting sand or grout beneath the last laid section simultaneously from both sides of the section so that the sand or grout extends across the full width of the section.

5. An excavation compartment formed bya plurality of interconnected walls, at least one of said walls being partly hollow and jetting pipes positioned adjacent the lower ends of the walls to facilitate entry and removal of the compartment into, and from, the sea-bed.

6. An excavation compartment as claimed in claim 5, including spaced side and end walls, one of the latter being provided adjacent its lower surface with an aperture which, in use, surrounds the sides and top of a previously laid tunnel section.

7. An excavation compartment as claimed in claim 6, wherein the upper part of each wall is of hollow box-like construction and the lower edge thereof provides a relatively narrow surface.

8. An excavation compartment as claimed in claim 5, including spaced side and end walls, one of the latter being in the form of a lattice beam or girder which interconnects the adjacent upper portions of the side walls.

9. Atunnet section supporting and aligning frame comprising a longitudinally extending main beam provided with tunnel section lifting means which are movable longitudinally of the main beam, means for effecting said movement of the lifting means, spaced transversely extending beams which support the main beam for movement thereover and means for effecting said movement of the main beam.

10. Aframe as claimed in claim 9, wherein said tunnel section lifting means comprises at least one, vertically disposed, extensible arrangement which passes through a longitudinally extending slot in the main beam and is mounted on a trolley for movement therealong.

11. Aframe as claimed in claim 10, wherein the, or each, extensible arrangement comprises a hydraulic piston-and-cylinder arrangement.

12. A frame as claimed in any one of claims 9 to 11, wherein the means for effecting the movement of the lifting means comprises a hydraulic piston-andcylinder arrangement.

13. A frame as claimed in any one of claims 9 to 12, wherein the transverse beams extend, respectively, through brackets provided at each end of the main beam, each bracket has at least one flanged wheel rotatably mounted therein which is aligned with and engages a rail extending longitudinally of the associated transverse beam for movement of the main beam thereover.

14. A frame as claimed in claim 13, wherein each transverse beam is provided with a hydraulic piston-and-cylinder arrangement interconnecting the transverse and main beam for effecting said movement of the main beam.

15. A frame as claimed in claim 13 or 14, wherein each bracket is provided with a pulley block around which, in use, a lifting cable passes from a surface vessel.

16. A method of laying a series of interconnected tunnel sections substantially as described with reference to the accompanying drawing.

17. An excavation compartment substantially as described with reference to, and as illustrated in, the accompanying drawing.

18. A tunnel section supporting and aligning frame substantially as described with reference to, and as illustrated in, the accompanying drawing.