A COLLAPSIBLE DAM The invention concerns a collapsible dam for restraining the waters in canals and basins, particularly suited to regulate the water flow in the Venetian lagoon. It is a known fact that, for restraining and regulating the water flow in canals, basins and similar some movable dams are used consisting of a plurality of adjustable floodgates which allows either to restrain or to regulate the flow of the waters, according to the position they acquire when they are activated by operating mechanisms. Within the sphere of the studies for restraining and regu- lating the water flow in the basins, are particularly important those carried out on the basin of the Venetian lagoon, aiming to solve the problem of high water by regu- lating the water flow through the use of movable dams. Among the various systems being studied and tested, the tendency of the experts is to look toward a solution which foresees a series of floodgates hinged to the bottom of the lagoon, which are lifted until they emerge over the surface of the water at adjustable heights by means of operating units which cause them to rotate around the hinge of the fulcrum. Such a solution, however, implies some problems related to the particular configuration of the hinge which joins each floodgate with the bottom, in that sand and other organic and/or inorganic substances can easily penetrate into said hinge and in the course of time compromise the functionali- ty of the hinge itself and consequently, also the operating reliability of the floodgates. Therefore, periodical maintenance operations are necessary which, given the size of the equipment and the environment wherein it operates, are difficult to carry out and are, therefore, costly. The present invention proposes to eliminate such inconveniences.

The main purpose of the invention is to obtain a collapsi- ble dam for restraining and regulating the water flow in canals and basins which is more reliable as compared with the dams of the known type. It is another purpose that the dam according to the inven- tion is practically maintenance-free. The purposes now described are achieved by a collapsible dam for restraining and regulating the water flow in ca- nals, basins and similar comprising one or more floodgates having a prevalently vertical development, lined up one next to the other and connected with one another, and is characterized in that each of said floodgates consists of two or more walls arranged one behind the other, slidingly and firmly connected to one another through guiding ele- ments belonging to them, said walls co-operating with thrusting means suited to drive their mutual sliding motion along a common longitudinal axis. According to one prefe ^' r- red embodiment each of said floodgates consists of three walls, one of them being arranged on the bottom and atta- ched to it, while the other two walls slide vertically upwards when they are pushed by a hydraulic telescopic cylinder attached to the wall arranged on the bottom, and presenting the other two telescopic elements, each of them being connected to each of the other two walls. The telescopic cylinder is filled with oil and its opera- tion occurs by pumping into its interior and under the surface of the oil itself, water under pressure injected through tubes connected with a pumping system. The dam according to the invention can be employed with great advantage to restrain the water flow in the basin of the Venetian lagoon in order to solve the problem of high water. Another important advantage of the dam according to the invention is given by the fact that the dam has no mutually rotating elements and for this reason jammings will rarely

occur, giving more reliability than the dams of known type. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed descrip- tion and specific examples, while indicating preferred embodiments of the invention, are given by way of illustra- tion only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description and from the drawings, wherein: - Fig. 1 shows one of the floodgates, which form the dam in the exploded view of its components; - Fig. 2 shows the floodgate of Fig.l after it has been assembled; - Fig. 3 shows the floodgate of Fig.2 in a cross section; - Fig. 4 shows the floodgate of Fig.2 with the walls arra ^' n- ged one behind the other; - Fig. 5 shows the floodgate of Fig. 4 seen in a top view; - Fig. 6 shows a pair of floodgates coupled together; - Fig. 7 shows a dam consisting of eight floodgates, two of which are opened; - Fig. 8 shows another configuration of the dam shown in Fig. 7 presenting four open floodgates. The collapsible dam according to the invention, which is shown in the Figs. 7 and 8 and indicated as a whole with 1, consists of a plurality of mobile floodgates 3, lined up one next to the other, one of which is represented in an axonometric exploded view in Fig. 1 and in an axonometric assembled view in Fig. 2. Referring to Fig. 1 it can be observed that said floodgate 3 consists of one bottom wall 31, one intermediate wall 32 and one upper wall 33, each of them consisting of a pair of plates 131, 132 and 133 respectively, which are linked together by means of a guiding element, which is located

centrally in relation to said walls. As can be observed in the Figs. 2,3,4,5, said guiding elements consist of a tubular bottom element 231 belonging to the bottom wall 31, an intermediate shell 232 belonging to the intermediate wall 32 and an upper shell 233 belon- ging to the upper wall 33, wherein said tubular bottom element 231 and said shells 232 and 233 present in a cross section respectively a total or partial circular shape suited to obtain their mutual coupling inside one another, as shown in detail in Fig. 4 and Fig. 5. It can be observed in fact in Fig. 5 that the outer diame- ter 331 of said tubular bottom element 231 is the same as the inner diameter of the intermediate shell 232 so that said intermediate shell 232 slidingly couples outside the tubular bottom element 231. Similarly, the outer diameter 332 of said intermediate shell 232 is the same as the inner diameter of the upper shell 233 and is, therefore, suited to couple inside the latter. The walls 31, 32 and 33, therefore, are connected with one another, and are arranged one behind the other in corre- spondence with the plates 131, 132 and 133 respectively, being vertically kept in guide following the direction of the common axis 34 along which said tubular bottom element 231 and said intermediate and upper shells 232, 233 respec- tively, are telescopically coupled. It can be observed also in Fig. 5 that the perimetrical development of each of said intermediate and upper shells is larger than a semicircle since, as can be observed, the plates 132 and 133 which belong to said shells are attached to them and are off-set by a thickness 35 and 36 respecti- vely, in relation to their common centre through which runs the longitudinal common axis 34. In such a way the walls themselves are prevented from coming apart because of their mutual radial off-set posi-

tion, while they are only allowed to move following the vertical direction of the longitudinal common axis 34. Always in Fig. 1 and also in detail in Fig.3, it can be observed that inside the tubular bottom element 231 a telescopic cylinder indicated as a whole with 5 is inser- ted. This consists of a bottom element 51, internally locked within the tubular bottom element 231, an interme- diate element 52, the upper extremity of which contrasts against the intermediate thrust ring 432 attached to the upper part of the intermediate shell 232 and a third ele- ment 53 which contrasts with its upper part against the upper thrust disc 433 attached to the upper shell 233. It can also be observed that the bottom element 51 of said telescopic cylinder 5 is equipped with a connection 54 for the injection of fluid under pressure, suited to drive telescopically the motion of the elements of the cylinder and, therefore, to cause the movement of the walls which form each floodgate. Each of said floodgates 3 presents then a position wherein all the walls composing it are arranged one behind the other as represented in Fig.4 and that is achieved when the elements of the telescopic cylinder 5 are all inserted one within the other, and a position wherein all the walls are one on top of the other, as represented in Fig. 2 and in Fig. 6, which is obtained when the telescopic cylinder 5 is arranged in the position of its maximum extension. The walls which form the floodgate can also acquire other infinite partial opening positions, each of them being obtained by modifying their mutual height by adjusting the amount of fluid under pressure which is pumped into the telescopic cylinder 5. In particular, the telescopic cylinder is filled with oil and it is operated by pumping into its interior and under the surface of the oil, any kind of fluid under pressure which can even be water drawn from the same basin or canal

where the dam is installed. Since oil is lighter than water, the blending of the two fluids will not occur, thus obtaining the advantage that the inner walls of the telescopic cylinder and the sliding surfaces of its cylindrical elements in particular are constantly lubricated. Several floodgates are lined up one next to the other and connected with one another since each of the walls which composes them presents in correspondence with its ends a female coupling 6 on one side and a male coupling 7 on the other side that can be joined together so as to obtain the dams represented in Figs. 7 and 8 by way of illustration. Moreover, said couplings present in a cross section a profile having essentially the shape of an arc of a circle 61 and 71 respectively, which permits the mutual rotation, so that two or more floodgates can be joined together, lined up following any type of line which can also be' a broken, eventually closed line. With regard to the possible compositions that said floodga- tes can acquire when joined together, the Figs. 7 and 8 represent by way of illustration only, two possible confi- gurations of a dam composed by eight floodgates attached to the lateral walls 8 of an hypothetical canal 9. In particular, it can be observed that in Fig. 7 the dam is represented with the central floodgates lowered so as to allow the flow and the downflow of the water inside the space 11, while in Fig. 8 the same dam is represented with the 2nd, 4th, 6th and 8th floodgates lowered so as to realize a corresponding number of passages, indicated with 12, for the flow and the downflow of the water. It is evident, however, that according to the use, many other solutions are possible. With regard to the securing of the dam to the bottom this is obtained by means of the bottom plate 331, belonging to the bottom wall 31, which is attached through log bolts.

should the bottom be rocky, or through uprights which penetrate into the ground if the bottom is sandy. In this second case, the weight of the dam helps the stabi- lity of the anchorage. According to what has been described, it is then understood how the collapsible dam according to the invention achieves the proposed purposes. In particular the main purpose has been achieved, that is to obtain a dam presenting a higher reliability of opera- tion as compared with dams similar to it and of the known type. It could be seen in fact, that the walls which compose each floodgate forming said dam, do not foresee mutually rota- ting elements and consequently there are no chances for the floodgates to malfunction, due to jammings of the rotating elements. Moreover, since the elements of the telescopic cylinder are constantly lubricated, no lubrication and maintenance is necessary. Different solutions from the described embodiment, can foresee a different number of walls which compose each floodgate and said walls can also foresee different profi- les of the guiding elements which connect them together and that allow their mutual sliding. Lastly, with regard to the telescopic cylinders which operate the lifting and lowering of the walls, these could be operated one independently from the other or in parallel with one another. It is understood, however, that all said possible modifica- tions fall within the spirit and scope of the present invention.