Hydraulic and earth engineering – Underground passageway – e.g. – tunnel – Lining
Reexamination Certificate
1999-02-22
2001-02-27
Bagnell, David (Department: 3673)
Hydraulic and earth engineering
Underground passageway, e.g., tunnel
Lining
C405S150100, C405S146000
Reexamination Certificate
active
06193439
ABSTRACT:
This invention relates to a process for cladding partially-overhanging substrates, and to constructions produced thereby.
By “partially-overhanging substrates” is simply meant substrates which partially overhang. The most obvious type is a tunnel which has an overhanging roof and non-overhanging walls, as well as other excavations. Alternatively, the “partially-overhanging substrate” can also be a building or concrete construction, such as an arch.
When a tunnel is driven underground, it is generally required that the rock surface left exposed be clad, for either or both of waterproofness or structural integrity. The traditional way of doing this has been to apply a sealing layer to the rock face, followed by a supporting layer. First of all, the rock surface of the tunnel is coated with an initial concrete layer by any convenient method, such as by shotcreting or spraying, or by applying prefabricated sections which are grouted. To this is applied the sealing layer, typically a waterproofing membrane consisting of welded, prefabricated sheets of a flexible plastic material, typically a synthetic polymer materials such as polyvinyl chloride (PVC) or polyethylene. This sheeting is held in place by suitable anchoring means. Finally, there is applied a supporting layer, generally by means of formwork or prefabricated sections. Steel reinforcement is usually included in this final layer.
While this type of structure has worked well and has been widely used, it suffers from a number of flaws. These include
the considerable expense and effort used to form the initial layer is largely wasted as it plays no part in the structural integrity of the completed cladding; moreover, the sheet separates the initial layer from the final supporting layer, and the two exist as separate entities with an unstable zone in between them, this unstable zone being unable to take shearing stress;
the application of the waterproofing membrane is very time-consuming and expensive;
the waterproofing membrane is easily damaged, for example by the insertion of steel reinforcing in the supporting layer;
it is particularly difficult to form properly the roof of the tunnel with concrete of sufficient quality;
it is difficult to achieve small radii with this method.
In addition, where tunnels are being bored by machines such as shield tunnel boring machines with long supply and cladding vehicles following them, especially those which are fitting prefabricated elements on the initial layer, it is very difficult and expensive to fit the waterproofing membrane.
It has now been discovered that these problems can be at least substantially overcome by the use of a novel structure and a novel way of applying this structure. The invention therefore provides a construction applied to a partially-overhanging substrate, the construction comprising
(a) a sealing first layer applied directly to a surface of the partially-overhanging substrate; and
(b) a non-deformable second layer applied to the first layer,
characterised in that the sealing first layer is a plastics material and its surface is so configured as to provide anchoring means which anchor together the first layer and the applied second layer to form in effect a single layer capable of withstanding shearing stress.
The invention further provides a method for cladding a partially-overhanging substrate, comprising the steps of applying to a surface of the partially-overhanging substrate at least one sealing first layer, followed by the application of at least one non-deformable second layer, characterised in that anchoring means formed in the surface of the first layer anchor the first and second layers together to form in effect a single layer.
By “a surface of the partially-overhanging substrate” is meant either the substrate itself or an initial layer already applied to that substrate, as mentioned hereinabove in the discussion of the prior art. In this invention, the initial layer, when present, is preferably shotcrete.
The sealing first layer may be any suitable plastics or synthetic polymeric material known to the art which can be applied by spraying, one example being a thermosetting polyurethane.
An essential feature of the invention is the configuring of the surface of this first layer to provide anchoring means, so that it forms with the subsequently-applied non-deformable second layer what is in effect a single layer. This can be achieved by several methods. One possibility is to modify the surface by mechanical means before it has fully hardened. These modifications could take the form of irregularities such as webs and grooves formed in the layer, shapes to which the second layer will conform to anchor the two layers together. A further possibility is to include in the first layer, usually by embedding after layer formation, solid material which will cause suitable irregularities in the surface. A typical suitable material is a granulate, especially stone chips. A still further possibility may be used when, as hereinabove described, there is applied to the substrate an initial layer of concrete to which the sealing first layer is then applied. The surface of this initial layer may be provided with anchoring means. The sealing first layer applied thereto can then itself be provided with anchoring means. However, the first layer will preferably be so thin that it will also bear the profile of the initial layer on its external surface and the second layer will therefore conform to it. In such a case, this initial layer is preferably shotcrete. It is of course possible and permissible to use combinations of these methods.
The non-deformable second layer is preferably a sprayed concrete (shotcrete). Into this layer can be incorporated reinforcing, preferably by including suitable fibres in the material to be applied. It is preferred that such fibres be present.
The construction of the present invention has numerous advantages. Because the two layers behave as one entity, the sealing film more readily retains its integrity and therefore watertightness, and is less prone to mechanical damage and is capable of coping with shearing stress. This is also true when an initial layer is applied to the rock face—all three act as a single layer, and all contribute to the support of the rock. As a result, the thickness of construction needed can be considerably less than that of a conventional construction.
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Bagnell David
Fish & Richardson P.C.
MBT Holding AG
Singh Sunil
LandOfFree
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