Hydraulic and earth engineering – Underground passageway – e.g. – tunnel – Cut and cover
Reexamination Certificate
1998-05-12
2001-05-22
Neuder, William (Department: 3673)
Hydraulic and earth engineering
Underground passageway, e.g., tunnel
Cut and cover
C405S239000, C014S026000, C052S087000
Reexamination Certificate
active
06234716
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to prefabricated reinforced concrete elements, whether precompressed or not, for the construction of works sunk beneath ground level such as artificial tunnels, underpasses, underground carparks and the like.
The majority of such works can be constructed only after open air excavations, and after having gone down to the level of the foundation or the floor of the work itself. Once the construction has been completed this must be covered over with earth in such a way as to form the embankment over the roof or the deck slab over the work and to sustain the supporting uprights at their flanks.
In many cases however the excavation cannot be performed in the conventional open air manner down to the base of the structure due to the lack of space for the banks at the sides thereof or else because the excavation involves risks for the stability of nearby works; in other cases the conventional excavation, with lateral banks is not economically convenient due to the large volume of ground to be excavated.
In order to avoid the formation of banks in the above-mentioned cases the sides of the excavation can be supported by means of containment structures known per se such as bentonitic diaphragms, piling, tieback pile walls, sheet piling or the like. Some of such containment structures, such as sheet piling or tieback pile walls, are used in a temporary manner only to permit the excavation to proceed, while the sides of the work to be produced, for example the walls of a tunnel or the shoulders of an underpass, are usually constructed working close to the temporary containment structure.
If it is intended to form the sides of a tunnel, the shoulder of an underpass or the wall of an underground carpark in situ, these can be constituted by bentonite diaphragms or by piling with large diameter piles. In these cases the prefabricated structure is constituted in practice only by the deck and by possible intermediate floors. The deck between two bentonite diaphragms or between two series of large diameter piles is in general formed by prefabricated rectilinear beams of precompressed reinforced concrete laid on a beam made in situ on each piling header or diaphragm header. The prefabricated deck beams are then integrated in situ by means of concrete castings which complete the cover between one beam and the next and which makes it possible to considerably improve the robustness of the individual prefabricated beams.
This arrangement, currently very widely used, has however several disadvantages. In the first place the prefabricated deck beams are not normally assigned the task of transmitting from one piling header to the next the horizontal force necessary to resist the thrust of the ground which acts on each piling so that the piling must be dimensioned in such a way as to resist these thrusts themselves.
Moreover, if the deck beams should be rigidly fixed between the two piling headers, the expansion of these beams due to thermal variations would impose on the piling headers themselves deformations which could involve excessive stresses in the pile because of the limited deformability of the ground in contact with the pilings. To overcome this problem the piling headers are fixed by anchoring them to the ground via anchors, or tie rods of precompressed reinforced concrete and often between the deck beams and the piling headers there is introduced an expansion joint which allows the effects of thermal expansion of the deck beams to be absorbed. This arrangement however weakens the hermetic seal of the work in correspondence with the roof and the deck of a road possibly overlying the work.
In the second place, the deck beams are frequently of large dimensions, which causes significant problems for their transport, because they must be simply supported both so as not to form a rigid tie with the piling headers and for constructional convenience. Because of this type of fixing between these beams and the piling headers it is not possible to take advantage of the benefits due to the embedded bending moment at the supports of the beams so that these must be dimensioned also taking this disadvantage into account.
SUMMARY OF THE INVENTION
In the structure according to the invention the deck is of much reduced thickness in that it is possible to benefit from the advantageous effect due to the embedded bending moments at the lateral ends of the deck beams; which results in a considerable reduction in the mid point bending moment. Notwithstanding the reduction in the thickness, the rigidity of the deck against vertical loads is considerably increased thanks to the embedding at the ends so that the maximum deflection of the deck under load is reduced notwithstanding the reduction in the thickness of the elements of which it is composed.
The transport of the prefabricated elements is much simplified in that the length of the longest element, generally the central portion of the deck, is equal to about 60% of the clear span instead of about 110% of the span as occurred with conventional deck beams. In practice, all the prefabricated elements can be transported by road without exceeding the shape-limit imposed by road regulations (transport regulations) to permit the construction of works with spans up to about 25 m, whilst the dimensions of conventional prefabricated beams which can be transported by road allow maximum spans of only about 12-13 m to be achieved.
According to a preferred characteristic of the invention, the lateral portions of each deck section have a substantially L-shape form with an inclined intermediate part.
The presence of these inclined parts, which permits points of negative bending moment of the deck to be eliminated, further reduces the thickness of the deck itself.
The installation of the elements which constitute each section of the deck of the construction, which form an articulated quadrilateral which is balanced but unstable before being fixed in situ with the ridigifying castings, is very much facilitated by the presence of the bodies of concrete which constitute bracing members for the deck during its assembly.
Preferably there are provided adjustable means for varying the attitude of the said side portions, interposed between these portions and the pile-like elements, to allow balancing of these portions during assembly of the deck of the work.
In this way, during assembly of the deck its L-shape side portions are fixed with respect to the adjacent concrete bodies thanks to these adjustment means, preferably constituted by sscrews engaging respective nuts incorporated in the prefabricated elements, in such a way as to prevent an articulated quadrilateral from leaning, without it being necessary to utilise underpinning flasework to support the deck during its assembly.
If an intermediate slab is present, typical of underground carparks, it can be made as a prefabricaated element to be fixed to the structure close to the walls of the work with connections which guarantee the total reliability of its connection with the structure. The certainty of the embedded bending moment permits a further considerable reductin in the thickness. In any case the speed of construction of the entire work is much increased.
The invention further has for its subject a process for the construction of underground structures, particularly for tunnels, underpasses, underground carparks or the like, as well as a prefabricated element for such a structure.
DE-A-4 302 980 discloses a prefabricated element for a containment structure having an elongate reinforcement and a concrete body anchored to an upper end of the reinforcement and facing the deck. The reinforcement body is axially aligned with respect to the reinforcement. The prefabricated element is inserted in a bore hole and concrete is cast in the lower part of the hole such as to anchor the element in the ground and to form in situ a pile element forming part of the containment structure.
REFERENCES:
patent: 1746566 (1930-02-01), Tufts
patent: 2194279 (1940-03-01), Goldsb
Neuder William
Singh Sunil
Sughrue Mion Zinn Macpeak & Seas, PLLC
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