GB2137675A - Improvement in thrusting means using inflatable bladders - Google Patents

Abstract

In a method of lining a tunnel or shaft which includes the steps of arranging an assembly of annular lining sections (a), (b) in longitudinal juxtaposition and advancing said sections worm-like along the tunnel or shaft by inflating and deflating in sequence inflatable tori (d) located between the juxtaposed ends of respective pairs of lining sections, the thrusting characteristics of the torus are improved by providing the respective ends (x), (y) of the lining sections (a), (b) with inter-engaging profiled surfaces such that at least during initial inflation of the torus (d) a greater area of surface contact is maintained between the torus (d) and the lining sections (a), (b) whilst the lining sections move apart. Preferably, the profiled surfaces are respectively convex and concave in axial cross-section, the concave end of the section (a) being fitted with a collar (s), and may be arcuate or hyperbolic. The length (l) of the arcuate profile in the radial direction should be substantially equal to the corresponding dimension of the uninflated torus (d). <IMAGE>

Description

SPECIFICATION An improvement in thrusting means using inflatable bladders There are known methods for the worm-like non-disruptive installation of tunnel linking sections underground utilising inflatable tori as thrusting means. One such method is described in European Patent Application No: 80301938.9 which is a method of tunnel construction utilising inflatable tori interposed between adjacent tunnel lining sections. By inflating and deflating the tori in a special sequence an overall forward worm-like motion of the tunnel as a whole is created.

The torus material commonly used comprises an inner thin rubber lining surrounded with a helically wound plastics fiber wound in clock and anti-clockwise direction so as to produce a criss-cross pattern set at the optimum angle to give longitudinal and circumferential reinforcement. There is then provided an outer rubber protective coating. The natural shape of the material when manufactured can be circular in cross-section or flattened.

The tunnel lining sections are maintained in longitudinal reciprocating alignment by means of a thin collar fitted to the extrados of and extending rearwardly from the rearward of the forward section into which the forward end of the rearward section can slidingly fit. The corresponding ends of the forward and rearward sections are formed with flat radially extending surfaces between which are interposed the inflatable tori.

There are certain disadvantages in using inflatable tori interposed between flat ended tunnel lining units which are related to the trust to stroke characteristics of the torus.

When the torus is in a flat condition when the joint is closed, and a driving fluid admitted, the torus produces its maximum thrust because the thrust generated is the product of the flattened depth of the bladder and the pressure of the driving fluid. As the joint opens so the area of contact of the wall of the torus with the end of the section decreases reducing the thrust generated until the torus is fully inflated and in its unconfined inflated circular shape. At this stage the thrust is zero.

At any given working pressure it can be seen that the thrust generated varies from a maximum when the torus is fully squashed, to zero when it is fully inflated in an unconfined configuration. This reduction of thrust is linear with respect to the increasing stroke of the joint and this characteristic is unsatisfactory.

First, if a stroke of a desired magnitude and thrust is needed then the torus requires a working pressure higher initially than that required to generate the desired thrust value at the working stroke. For example, if it is required to generate a certain thrust at a stroke equivalent to one half of the internal diameter of the torus material inflated in an unconstrained condition, then it will be necessary to provide a driving fluid at twice the pressure required to- produce the thrust when the joint is closed. This high start up thrust can cause inertial kick-back in the joint.

A second further disadvantage of the known methods is related to the driving of curved tunnels wherein the adjacent ends of the tunnel lining units become inclined to each other. For example, the inner side of the curve of the tunnel will have joints between the lining sections closer together than the corresponding joints on the outside of the curve of the tunnel.

The difference in the width of joint across the diameter of the tunnel is known as joint lead and it can be seen that the part of the thrusting bladder working on the inside of the curve of the tunnel will be operating at a significantly less width than that part working on the outside of the curve. The difference of lead causes the section of the torus on the outside of the curve to operate at a lesser unit thrust than the inner section thereby debilitating the total thrust of the torus. For example, if the sum of the length of the working stroke and the lead equals the inner cross sectional diameter of the torus material then the torus as a whole will operate at only one half of the thrust that it would were no lead present.

This thrust sensitivity of known tori severely limits the scope of the known methods of tunnel construction by means of worm-like and similar progression.

This present invention largely overcomes the problems are relates-to a means whereby the thrust to stroke relationship is modified to produce characteristics more suited to known methods of tunnel construction and improves the scope of these tunnel methods.

According to the present invention there is a method of improving the thrusting characteristics of an inflatable torus (as hereinbefore described) used in the worm-like installation of a tunnel or shaft lining by longitudinally advancing an assembly of tunnel lining sections arranged in end to end relationship which comprises a joint between the ends of two adjacent tunnel lining sections which are maintained in longitudinal reciprocating alignment arranged such that the rear end of the forward section is formed with a radially extending concave surface and the forward end of the rearward section is formed with a radially extending convex surface to engage with the said concave surface about an inflatable bladder, the length of the squashed cross section of the interposed bladder being substantially the length of the said radially extending concave surface.

The tunnel lining sections may comprise right or circular cross-sections units wherein the corresponding convex and concave surfaces will form the corresponding rearward and forward end of the lining units as described in European Patent Application No 80301938.9.

The radius of curvature of the corresponding convex and concave surfaces is determined by the flat deflated depth of the torus material, by the desired thrusting characteristics of the arrangement and also by the structural wall thickness of the tunnel lining sections.

In the case of tunnel lining sections a preferred embodiment of the invention is that in which the concave surface has a radius one half that of the structural thickness of the forward end of the lining units and the flat deflated torus section a length slightly shorter than the distance along the radially extending length of the concave surface, and the convex surface a radius of curvature equal to one half of the said structural depth plus the thickness of the flat torus material section. When in the close configuration the preferred arrangement provides a convenient sandwiching of the bladder between the two corresponding curved surfaces providing a passive thrust transmitting means from the forward to the rearward unit when this feature is compatible with the means of tunnelling in use.

Some embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which Fig. 181) represents a preferred embodiment of the invention related to the use in tunnel installation being a vertical longitudinal part section through the walls of identical tunnel lining units at their adjacent ends.

Fig. 1(2) is the same joint in a partially open configuration. Fig. 2 is a graphical representation of the variation of bladder thrust measured against joint width (w) when inflated with a driving fluid and for a variety of configurations of the invention including known arrangements for comparison purposes.

Fig 3(1) and 3(2) show an arrangement as in Fig. 1(1) and 1(2) in which the concave and convex surfaces have a hyperbolic shape.

Fig. 4 is a longitudinal section through two identical lining units when they have been finally jointed. Fig. 5 is an embodiment of the invention arranged to minimise stress in the extreme folds of the torus when the joint is in a closed position.

Fig. 1 is shown an operating joint between two identical tunnel lining sections. The forward section (a) has a rearward- end (x) formed to a concave radius R(o). The rearward section (b) has a forward face (y) formed with a convex radius R(i). Interposed between the faces (x) and (y) is an inflatable torus (d) whose natural deflated shape is flat or may be curved to the mean radius of the said faces (x) and (y). The thickness of the deflated and flat torus is nominally the same as the difference of the radial lengths (Ro) and (Ri). Means are provided whereby a driving fluid may be admitted to and exhausted from the torus (d) and which is not shown in the figure.

It will be noted that in this condition, the flattened torus (d) evenly distributes thrust from one lining section to the other over the projected length (1). The rear of the foward lining section (a) may be provided with a rearwardly extending metal collar (s) into which the front of the rearward lining unit (b) which may be provided with a corresponding rebate (t) can slidingly reciprocate coaxially with the lining section (a).

When a driving fluid is admitted to the torus (d) at a pressure (p) the initiai thrust generated upon the corresponding forward and rearward faces (x) and (y) is the product of the fluid pressure and the projected length of contact (1) of the torus (d). If the pressure is such that this resulting product acting over the whole toral length of the torus is sufficient to overcome the soil friction acting upon the outside of the tunnel lining section the forward section (a) will move forward if sufficient reaction is provided by the rearward unit (b) by an amount corresponding to the quantity of driving fluid admitted to the torus (d).

Fig. 1(2) shows the arrangement when the joint has opened a distance (w) and it can be seen that as the unit (a) moves forward the length of contact of the rearward face of the torus (d) with the surface (y) has significantly reduced in length whereas the length of contact between the forward surface of the torus (d) and the surface (x) has not significantly reduced.

This phenomena is a result of the geometrical properties given to the forward and rearward faces (x) and (y) and the fact that the parts of the torus wall not in contact with either of the surfaces (x) and (y) form a circular configuration between the points of contact with the said surfaces with which they ae tangential at the point contact.

For the arrangement shown, the lengths projected (1) and (1 i) remain nominally the same for the values of the stroke (w) corresponding to one third of the internal diameter of the torus cross section (d) when inflated in an unconfined condition.

For example, a torus of 3" internal diameter section when inflated to a pressure of 100 psi will exert a thrust of about 430 1 bsf per inch of its length when constrained in the arrangement shown in Fig. 1(1). When the stroke (w) is 1" the thrust will be about 420 1 bsf per inch of its length which for practical purposes means that the torus is not stroke sensitive to thrust. Known thrusting means have corresponding thrust values using a 3" diameter section of about 470 1 bsf when the joint is closed and about 31 5 1 bsf at the stroke (w) of 1". The corresponding percentage loss of thrust as a result of the increased stroke is about 2% in the former case and 33% in the latter and it can be readily seen that the invention is a substantial improvement in the use of inflatable tori as thrusting means.

Fig. (2) is a graphical representation of the thrust and stroke relationship for a variety of configurations of the invention and, for comparison, is shown the relationship for known thrusting means in which the joint has plane and parallel ends. Line (f) is the general form of the relationship for an apparatus comprising the invention as is shown in Figs. 1. Line (fi) is the form for an apparatus comprising the invention as shown in Fig. 3 yet to be described. Line (e) is the form when thrusting according to known means.

The abscissa of point (h) represents the unit thurst when the stroke (w) is equal to the full unconstrained inflated diameter of the torus section and which is zero in all cases.

It can be shown that the ordinate line extending from the abscissa position representing the stroke (w) being 30% of the bladder diameter intersects the lines (e) and (f) to produce an ordinate value (i) for the thrust which amounts to about a 40% advantage of thrust at this stroke value of the thrusting means comprising the invention over known means.

Figs. 3(1) and 3(2) show a further arrangement of a joint containing the apparatus between two adjacent tunnel lining sections and similar to that shown in Figs. 1 except that the corresponding convex and concave surfaces are hyperbolic in which case the thrust stroke relationship is modified to the shape shown as line f(i) in Fig. 2.

Tunnels constructed by the method described in European Patent Application No: 80301 938.9 are finally jointed up by first inflating the torus in the known thrusting means, deflating the said torus and removing it from the joint, cleansing the joint and applying some form of sealant material and then inflating the next rearward torus to close the joint and trap the sealant material within the two opposing faces of the ends of the lining sections.

This method has the disadvantage that should there be water pressure in the ground surrounding the tunnel then this will exert pressure on the back of the sealant which tends to push it out of the joint arrangement resulting in undesirable leakage onto the tunnel interior.

In Fig 4 is shown the arrangement when jointing up of the joints between tunnel lining sections which have been installed using the present invention as a thrusting means.

The jointing up is carried out in the same way as the known method however the final completed joint has the advantage that because the two radii R(i) and R(o) have differing values the voids formed by the corresponding forward and rearward faces of the ends of the lining units are tapered such that when exterior water pressure acts upon the sealant contained in the void area (p) the sealant contained is forced more firmly into place and will tend to seal more firmly the greater the pressure.

Conversely sealant trapped in the void area (q) will be forced more firmly into place when the tunnel is subjected to interior pressure when the tunnel-is used as a pressure carrying aqueduct.

Fig. 5 is an embodiment of the invention arranged to minimise the shear stresses caused in the extreme folds (u) of the torus material (d) when squashed flat. This embodiment is of significance when the use of bladder hose material as hereinbefore described has are carrying adequate.

Fig. 5 is an embodiment of the invention arranged to minimise the shear stresses caused in the extreme folds (u) of the torus material (d) when squashed flat. This embodiment is of significance when the use of bladder hose material as hereinbefore described has a natural circular cross-section, uninflated.

The arrangement is characterised in that the radius (Ro) is significantlty greater than the sum of the radius (Ri) and the squashed torus thickness.

When the joint is closed the arrangement cannot completely flatten the bladder at the position of the folds (u) thereby substantially reducing the amount of shear stress and subsequent delamination which occurs with known methods.

It can be readily seen that this invention is a substantial improvement over known means of thrusting using inflatable tori and in particular broadens the scope of known methods of tunnel lining installation using inflatable tori as thrusting means.

Claims (25)

1. A method of lining a tunnel of shaft which includes the steps of arranging in longitudinal juxtaposition a plurality of annular lining sections, the juxtaposed ends of at least one pair of adjacent sections being provided with interengaging profiled surfaces, inserting between the juxtaposed ends of the or each said pair of lining sections an inflatable torus of a size and shape substantially corresponding to that of the cross-section of the lining sections, and inflating said torus to generate an axial thrust between said sections and a corresponding relative axial movement thereof, said profiled surfaces being such that, at least during initial inflation of said torus and corresponding relative axial movement of said surfaces, a greater area of surface contact is maintained between said torus and said lining sections than if said juxtaposed end surfaces lay in radial planes.

2. A method as claimed in Claim 1, characterised in that the axial cross-section of one of said profiled surfaces is concave and that of the outer surface is convex.

3. A method as claimed in Claim 2, wherein the said surfaces are of acruate profile and the radius of curvature of the convex surface is smaller than that of the concave surface by an amount at least equal to the deflated thickness of the said torus.

4. A method as claimed in Claim 3, wherein the inflatable torus has a circular radial cross-section when in the relaxed state, and the difference between said radii of curvature is substantially greater than twice the wall thickness of said torus.

5. A method as claimed in Claim 2, wherein the said surfaces are of hyperbolic profile.

6. A method as claimed in Claim 3 or 4, wherein the radius of curvature of said concave surface is substantially equal to one half of the structural thickness of the respective lining section.

7. A method as claimed in any one of Claims 2-6, wherein the radial dimension of said torus when in deflated form substantially corresponds to the length of the profile of said concave surface.

8. A method as claimed in any one of Claims 2-7, wherein that one of said pair of lining sections having the end of convex profile is restrained with respect to the bore of the tunnel or shaft with greater force than the other section so that during inflation of said torus the said other section is urged axially along the tunnel or shaft via said concave surface.

9. A method as claimed in Claim 1 and substantially as herein described.

10. A method of lining a tunnel or shaft substantially as herein described with reference to Figs. 1 (1) and (2), Figs. 3 (1) and (2), Fig. 3 and Fig. 4 of the accompanying drawings.

11. A tunnel or shaft when lined by a method as claimed in any preceding claim.

1 2. A tunnel or shaft lining section in which the profile of the axial cross-section of one end surface of the section is concave and that of the other end is convex.

1 3. A section as claimed in Claim 13, in which the said surfaces are of arcuate profile and the radius of curvature of the convex surface is smaller than that of the concave surface.

14. A section as claimed in Claim 14, in which the radius of curvature of said concave surface is substantially equal to one half of the structural thickness of the lining section.

1 5. A section as claimed in Claim 12, in which said surfaces are of hyperbolic profile.

1 6. A section as claimed in any one of Claims 12-15 and additionally comprising an axially-projecting collar received in an annular rebate formed at said one end-of the section, the section being provided at said other end wit a rebate corresponding to the projecting portion of the collar.

17. A section as claimed in Claim 12 and substantially as herein described.

18. A tunnel lining section substantially as herein described with reference to Figs. 1 (1) and (2), Figs. 3 (1) and (2) of Fig. 5 of the accompanying drawings.

1 9. A tunnel or shaft lined with a plurality of sections as claimed in any one of Claims 12-18.

20. An assembly for use in a method as claimed in Claim 1 comprising at least one pair of sections as claimed in any one of Claims 12-18 arranged in longitudinal juxtaposition and, interposed between the juxtaposed ends of the or each of said pair of sections, an inflatable torus of a size and shape substantially corresponding to that of the cross-section of the sections.

21. An assembly as claimed in Claim 20, in which said sections are as claimed in Claim 1 3 and said radius of curvature is smaller by an amount at least equal to the deflated thickness of said torus.

22. An assembly as claimed in Claim 21, in which the inflatable torus has a circular radial cross-section when in the relaxed state, and the difference between said radii of curvature is substantially greater than twice the wall thickness of said torus.

23. An assembly as claimed in any one of Claims 20-22, in which the radial dimension of said torus when in deflated form substantially corresponds to the length of the profile of said concave surface.

24. A tunnel or shaft when lined by the use of an assembly as claimed in any one of Claims 20-23.

25. The feature as herein disclosed, or their equivalents, in any novel selection.

CLAIMS Claim 1 3 has been made appendant to Claim 12 Claim 14 has been made appendant to Claim 13.