GB2088935A - A Collapsible Flexible Membrane Dam - Google Patents

Abstract

The dam comprises a rigid foundation having a bottom 4 and a pair of side walls 5, and an envelope which is (1) formed of a flexible membrane (2) secured to the bottom and side walls, and (3) provided with a hole 6 so as to be inflatable by filling with fluid. The membrane is secured to the bottom 4 over an upstream bottom line a-i and a downstream bottom line b-j and is secured to each side wall over an upstream side line a-g, a downstream side line b-f and a further side line g-d. The upstream and downstream side lines a-g and b-f extending upwardly from the ends a and b of the respective upstream and downstream bottom lines a-i and b-i in a plane perpendicular to said bottom 4. The further side line g-d connects an upper end g of the upstream side line a-g with a point d on the downstream side line b-f which is higher than the upper end g. A portion of the membrane which, when said dam collapses downstream, engages a part of each side wall 5 downstream of the downstream side line b-f is polygonal and at least triangular (preferably pentagonal), whereby said dam is collapsible both upstream and downstream. <IMAGE>

Description

SPECIFICATION Collapsible Flexible Membrane Dam The present invention relates to a collapsible, flexible membrane dam.

As is well known in the art, a collapsible flexible dam is assembled by securing to a concrete foundation formed on a river bed or the like, an envelope in the form of a cylinder or a bag which is made of non-stretchable sheet material such as rubber-coated fabric. The envelope is inflated by filling it with water or air. Such arrangements are described, for instance, in Published Japanese Applications Nos.

11702/1965 and 2371/1969. Such a collapsible dam is, however, disadvantageous in that, as will be described hereinafter in detail, it is not sufficiently protected from the backstream pressure which is continuously present.

Accordingly, an object of the invention is to provide an improved collapsible flexible dam which can collapse both upstream and downstream.

According to the present invention, there is provided a collapsible dam comprising a rigid foundation having a bottom and a pair of side walls, and an envelope which is (1) formed of a flexible membrane (2) secured to the bottom and side walls, and (3) adapted to be inflated by filling with fluid; said flexible membrane being secured to the bottom over an upstream bottom line and a downstream bottom line and being secured to each side wall over an upstream side line, a downstream side line and a further side line; the upstream and downstream side lines extending upwardly from the ends of the respective upstream and downstream bottom lines in a plane perpendicular to said bottom; said further side line connecting an upper end of the upstream side line with a point on the downstream side line which is higher than said upper end; and a portion of said membrane which, when said dam collapses downstream, engages a part of each side wall downstream of said downstream side line being polygonal and at least triangular, whereby said dam is collapsible both upstream and downstream.

Preferably, said portion of said membrane is pentagonal and, more preferably, is also divisible into at least three triangles.

The expressions "upstream" and "downstream" are used in relation to the direction of flow over the dam from the side thereof at which water is retained in use.

In the accompanying drawings:- Figs. 1 A and 1 B are perspective and schematic sectional views respectively, showing a conventional collapsible dam, wherein in Fig. 1 B the solid lines indicate a collapsed state of the dam and the dotted lines indicate the dam in an inflated state; Figure 2 is a view showing in an unfolded state, portion of rubber-coated fabric which forms the dam shown in Fig. 1; Figs. 3, 4 and 5 are sectional views taken respectively along lines C-C, B-B and A-A in Fig. 1 A; Fig. 6 is a perspective view of the collapsible dam of Fig. 1 in the inflated state; Fig. 7 is a diagram illustrating the problems which arise from the collapsible dam of Fig. 1 when water flows upstream;; Fig. 8 is a perspective view of the dam in Fig. 1 which has been improved so that it can collapse both upstream and downstream, the dam being illustrated in a collapsed state; Figs. 9 and 10 are sectional views taken respectively along lines B-B and A-A in Fig. 8; Fig. 11 is a view showing, in an unfolded state, a portion of rubber-coated fabric which forms the dam of Fig. 8; Figs. 1 2A-1 2C are diagrams showing a first preferred embodiment of a collapsible dam according to the invention, wherein Fig. 1 2A is a perspective view of the dam in a collapsed state, Fig. 1 2B is a sectional view of the dam as it collapses upstream, and Fig. 1 2C is a sectional view of the dam as it falls downstream;; Fig. 1 3 is a schematic view showing, in an unfolded state, a portion of rubber-coated fabric which forms the dam of Figs. 1 2A-1 2C; Figs. 14 and Figs. 1 SA and 1 SB are diagrams showing another embodiment of a collapsible dam according to the invention in the case where the configuration of a vertical surface of the dam is not divisible into triangles.

Referring now to Figs. 1 A, 1 B and 2 to 7, a dam 1, which is made of a piece of rubber-coated fabric, is secured to a concrete foundation on a river bed. The concrete foundation has a bottom 4 and side walls 5. A water supplying and draining hole 6 is formed in the bottom 4 for enabling the dam 1 to be inflated and deflated. During construction of the concrete foundation, anchor bolts or the like for securing the dam 1 are embedded therein.

The piece of rubber-coated fabric forming the dam 1 is fixedly secured to the concrete foundation by means of the anchor bolts and metal retainer strips 2 and 3. Edges d-c at the ends of the piece of rubber-coated fabric are bonded together before securing the dam 1 to the concrete foundation.

The part of the piece of rubber-coated fabric which is fixedly secured to the concrete foundation with the anchor bolts and the metal retainer strips 2 and 3 (hereinafter referred to as "a securing peripheral part" where applicable) is bordered (i) by upstream and downstream, mutually parallel bottom lines a-i and b-j on the bottom 4, and (ii) on each side wall 5, by a downstream side line b-f rising from the point b in a plane which is perpendicular to the bottom 4 and which includes the line b-j and by a side a g-f-e-d, the line a--gg--ff-e-d rising vertically from the point a to the point g and then extending downstream, or rising obliquely from upstream to downstream.

As shown in Figs. 3, 4 and 5, the piece of rubber-coated fabric is fixedly secured to the anchor bolts on the concrete foundation by means of the metal retainer strips 2 and 3 thus forming a bag shape whose cross-sectional shape decreases in width decreases towards the top at the side wall.

In general, for a collapsible dam of this type, there is provided a water level controlling device on the river bank (not described in detail herein).

The water level controlling devices used to control the height of the dam. Furthermore, when the flow rate of water from upstream increases to such an extent that the level of water greatly exceeds the height of the dam, the water level controlling device operates to collapse the dam 1 as shown in Fig. 1. As water or air is injected into the collapsed dam through the water supplying and draining holes 6 by the water level controlling device, the height of the dam is gradually increased to a desired value (as indicated by a dotted line in the Fig. 1 B). As a result, the amount of water retained by the dam increases until it finally flows downstream over the dam. Fig. 6 shows the dam in the inflated state.

Fig. 7 shows the dam in a state where the water flows upstream. As the level of the water downstream increases, the dam changes its configuration as if it were a sail filled with wind.

As a result, a strong force is exerted in the region of the point P as the level of the water increases.

Finally, the dam may in its entirety be pushed upstream, and at worst it may be broken.

In order to eliminate this difficulty, the lines along which the dam is secured to the foundation have been modified in various ways. An example of such a modification is disclosed by Japanese Published Patent Application No. 28498/1973 and is shown in Figs. 8 to 11. In this modification, like the dam of Fig. 1, the portions of the piece of rubber-coated fabric which are secured to the bottom 4 are fixed along upstream and downstream, mutually parallel bottom lines a-i and bj. However, it should be noted that the parts which are adjacent each side wall 5 are secured thereto along upstream and downstream side lines a-g and b--9.

The edges gHi and gHJ at each end of the rubber-coated fabric shown in Fig. 11 are bonded together and afterwards the dam 1 is fixedly secured to the concrete foundation along the bottom and side lines a-i, b-j, a-g and b-g, as noted above. After the dam has been secured tothe concrete foundation, it can fall downstream as shown in Figs. 9 and 10. In securing the dam, the dam 1 is not secured to the side walls 5 along the lines g--d so that a bag-shaped portion h is formed downstream of one end g of the line a-g.

In the case of the conventional collapsible dam shown in Fig. 1 , the lines e--d which serve as the bases for defining the upper edge of the dam 1 when the dam is inflated or when the water flows upstream are fixedly secured to the side walls. On the other hand, in the collapsible dam shown in Fig. 8, the dam is not secured along such lines.

Thus with the collapsible dam of Fig. 8, the bag-like portion h serves to provide slack. When the water flows upstream, the dam 1 turns around the lines g-b-j and g-a-i upstream by the force of the water as a result of which the dam 1 is collapsed upstream onto the bottom 4 and side walls 5. In this operation, the bagshaped portion h is deformed, and therefore the dam thus collapsed is somewhat bent around the bag-shaped portion h. However, no abnormal tension is applied to any point of the bag because the lines b-g are suitably inclined. However, the dam of Fig. 8 still suffers from difficulties. In inflating the dam, it is not satisfactorily inflated around the vertical portion. That is, the inflated dam has a poor appearance.If the dam is modified so that its appearance is acceptable when inflated, then water can leak into the dam through creases in the vertical portion.

Referring now to Figs. 1 2A to 1 2C, the dam 1 according to an embodiment of the present invention is secured to the bottom 4 of the foundation along mutually parallel upstream and downstream bottom lines a-i and b--j, respectively. To each side wall 5, the dam 1 is secured along a downstream side line b-f, an upstream side line a-g and a further side line g-s. The downstream side line b-f extends upwardly from point b at the end of bottom line b-j in a plane which is perpendicular to the bottom 4 and which includes the line b-j. The bottom line b-f terminates at point f.The upstream side line a-g extends upwardly from point a at the end of the bottom line a-i in a plane which is perpendicular to the bottom 4 and which includes the bottom line a-i. The upstream side line a-g terminates at point g which is lower than point f. The further side line g-s extends obliquely upwardly from point g in the downstream direction to terminate at point s which, in this embodiment, lie on the downstream side line b-f just below point f to facilitate urging of the dam by gas or water against the side walls 5. However, in another embodiment, points coincides with point f. In either event point s is higher than point g.The portion of the membrane which, when the dam collapses downstream, engages against the side wall 5 downstream of the downstream side line bf is polygonally shaped and at least triangular. Most advantageously, this portion is at least pentagonal and of a form which can be divided into at least three non-superimposed triangles by lines drawn from point b to the other corners of the pentagon.

Figs. 1 2A to C show the case where the aforementioned portion of the dam is of a configuration which can be divided into three triangles defined by points b, c and f; b, e and d, and b, c and d, respectively. Both of the upper and lower sides of the folded dam in the region of the portion s-f are secured to the side wail 5. For instance, the upper and lower sides of the folded dam are secured to the line b-f.

In Fig. 1 3 the reference characters correspond to those in Figs. 1 2A-1 2C. Line c-h is the line along which the centre portion of the dam is folded double when collapsed downstream.

Further in Fig. 13, a line corresponding to the join line between the bottom 4 and each side wall 5 passes through points a, b', c and b.

The above-described rubber-coated fabric can be fabricated as follows:- First, draw a line b'-j' to the left-hand side of the line c-h so that it is symmetrical with the downstream side line b--j with respect to the line c-h. Mark points k, m and n on the line f-c so that the distances f-k, k-m, m-n and n--e are equal. Draw a line perpendicular to the line f-c from the point m so that it intersects the line ab'-c-b at a point 0. Draw an arc centred on the point 0 through points f and c.Draw perpendiculars to the line f-c from the points k and n so that they intersect said arc at points e and d, respectively. Thus, the configuration of the vertical or side surface is defined by triangles b'ef, b'de and b'cd and triangles pef, qde and rcd which are symmetrical with the former triangles with respect to the respective lines f-e, e-d and c-d at which the dam is folded double on the side wall.

In operation, the lines e-p and e-q, d-q and d-r, and d-r and c-r are bonded together, as a result of which the portion of the dam which confronts the side wall is shaped substantially into a bag.

If the vertical portion were not divided into triangles, unlike the above-described case, a collapsible dam would be formed as shown in Fig.

14, which is drawn in correspondance to Fig.

1 2A, or as shown in Fig. 1 SA or 1 SB, which is drawn in correspondance to Fig. 13. This embodiment of a dam of the invention is somewhat unsatisfactory in configuration; however, it is effective similarly as in the first embodiment described above.

As is apparent from the above description, in the collapsible dam according to the invention, the straight clampline extending to the top of the vertical surface is disposed on the downstream side, and the vertical surface configuration is made larger than that of a dam which can collapse onto one side so that the dam can fall either upstream or downstream. Accordingly, the dam maintains a good configuration when inflated. In addition, even if the water or tide flows upstream towards the dam, there is no concentration of stress at any particular point on the dam.

Claims (4)

Claims

1. A collapsible dam comprising a rigid foundation having a bottom and a pair of side walls, and an envelope which is 11 ) formed of a flexible membrane (2) secured to the bottom and side walls, and (3) adapted to be inflated by filling with fluid, said flexible membrane being secured to the bottom over an upstream bottom line and a downstream bottom line and being secured to each side wall over an upstream side line, a downstream side line and a further side line; the upstream and downstream side lines extending upwardly from the ends of the respective upstream and downstream bottom lines in a plane perpendicular to said bottom, said further side line connecting an upper end of the upstream side line with a point on the downstream side line which is higher than said upper end, and a portion of said membrane which, when said dam collapses downstream, engages a part of each side wall downstream of said downstream side line being polygonal and at least triangular, whereby said dam is collapsible both upstream and downstream.

2. A dam as claimed in claim 1, wherein said portion of said membrane is pentagonal.

3. A dam as claimed in claim 1, wherein said portion of said membrane is pentagonal and is divisible into at least three triangles.

4. A collapsible dam substantially as hereinbefore described with reference to Figs.

12Ato 12Cand 13, or Figs. 14, 15Aand 15Bof the accompanving drawings.