JPH047405A - Drifting wood stopping work - Google Patents

Abstract

PURPOSE:To surely catch drifting wood having lengths largely affecting the occurrence of disasters by designing a drifting wood stopping work by appropriately setting spans between horizontal beams and between pillars from results of drifting wood catching tests and materials indicating the length distribution of drifting wood. CONSTITUTION:The span between each pillars 1 installed to the downstream side of a river in an inclined state is set at b2 and the outermost pillars 1 are respectively supported by stays 2. At the same time, a plurality of horizontal beams 3 are installed to the pillars 1 at prescribed spans. This drifting wood stopping work is designed by setting the spans between horizontal beams 3 at 0.3 m<=b1<=2.0 m and the spans between pillars 1 at 0.4 m<=b2<=4.0 m from results of drifting wood catching tests and materials indicating the distribution of the length L of drifting wood. With this drifting wood stopping work, at least drifting wood having length exceeding the spans between the pillars is caught. Therefore, drifting wood having length largely affecting the occurrence of disasters can be caught surely with this constitution having no structural uselessness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention particularly relates to a driftwood stopper that effectively traps driftwood of a predetermined length or more.

[Conventional technology]

Driftwood gets entangled and accumulates in curved parts of mountain streams, narrow parts of rivers, places with little space between bridge girders and riverbeds, and bridge piers. As a result, the following debris becomes blocked by the accumulated driftwood.

If this happens, the river bed will rise, causing disasters such as flood flow and overflow of gravel in the upper reaches of the river.

Furthermore, when the accumulated driftwood rots and collapses, there is a risk that the earth and gravel that is being dammed will flow down all at once, causing a disaster in the downstream area of the river.

Therefore, in order to prevent such disasters, it is necessary to capture the above-mentioned driftwood.

Incidentally, sabo dams have traditionally been built on rivers, but with these dams, the driftwood that floats in the flowing water exceeds the top of the dam, so the effectiveness of trapping the driftwood is close to zero. Therefore, something with a lattice structure that allows water to flow down but only stops the driftwood is required.

In order to increase the driftwood capture rate, for example, it would be possible to narrow the spacing between the supports and cross beams that make up the lattice, but this would be economically unfavorable from the perspective of the amount of materials used, and from the perspective of the purpose, it would not have an impact on disasters. There is no need to capture small pieces of driftwood that are rarely distributed.

In other words, from the above point of view, it is desirable to have a configuration that can only stop driftwood that is longer than a predetermined length.

However, the design of such structures has relied heavily on empirical rules.

Of course, when designing any structure, the rules of thumb are extremely important and cannot be ignored, but adding a theoretical basis to these rules of thumb will make it possible to design more rationally. Become.

Regarding tests related to driftwood stoppers that attempted to take this kind of consideration into consideration, for example, the effect of a permeable erosion control dam on trapping driftwood (
This is stated in a paper entitled Civil Engineering Materials, 30-11.1988).

Below, Fig. 5 is a front view of the model as seen from the upstream side of the river, Fig. 6 is a view from the ■ arrow in Fig. 5, and Fig. 7 is a front view of the model as seen from the upstream side of the river. Figure 8 of the ■arrow view in Figure 7 and the ratio of the pure spacing bt of the supports to the length L of the driftwood, that is, b
2/ Referring to FIG. 9, which is a graph of the relationship between L and driftwood capture rate T, what is shown in FIG. 5.6 is as follows.
The pillar (1) is provided inclined toward the downstream side, and the net distance between this pillar (1) and the pillar (1) adjacent thereto is b2. Also, the outermost pillar (1)
Each of the pillars (1) is supported by a stay (2), and each pillar (1) is provided with a horizontal beam (3) at a predetermined pure interval (hereinafter referred to as type A).

In addition, the model shown in Fig. 7.8 has the same configuration as the above-mentioned A type model, and has a configuration in which the net spacing b1 between the cross beams (3) is set wide (hereinafter referred to as B type model). type).

Next, a trapping test was conducted using two types of driftwood models with different diameters, and the results shown in FIG. 9 were obtained.

In other words, in Fig. 9, the case where the diameter of the driftwood caught by type A is 0.8 cm is indicated by a white circle, and the case where the diameter of the driftwood is 0.3 cm.
The case of m is shown with a square square mark, the case where the diameter of the driftwood captured by type B is 0.8 cm is shown with a black circle mark, and the case where the diameter of the driftwood is 0.3 cm is shown with a black = square mark, respectively. From this figure, bz/L is about 0.4 to 0.5,
In other words, the net spacing b2 between the supports (1) is 0 of the length of the driftwood.
．． The results show that most of the driftwood can be captured by increasing the amount by 4 to 0.5 times.

[Problem B that the invention attempts to solve]

However, the above results show that the driftwood capture rate T tends to improve as b2/L becomes smaller and the spacing b2 between the supports becomes narrower, but the range of b2 where the driftwood capture rate T is significantly affected is clearly defined. Therefore, even if a driftwood stopper is manufactured, its effectiveness in trapping driftwood is questionable.

The reason for this is that bz/L is a dimensionless value, and the range of driftwood length that causes actual disasters is unclear, so in addition to the fact that the pure spacing between columns cannot be determined, This is because the pure interval S, /L related to S, is also unknown.

Therefore, an object of the present invention is to provide a driftwood stopper that can catch driftwood reliably at low cost by understanding the range of driftwood length that is the main cause of disasters.

[Means to solve the problem]

The driftwood stopper according to the present invention has been made in view of the above-mentioned circumstances, and therefore, the structure of the driftwood stopper according to the present invention includes a support installed in a river and a cross beam supported by the support. In the driftwood stopper, the net spacing between the pillars is 0.4 m or more and 4.0 m or less, and the net spacing between the horizontal beams is 0.3 m or more and 2.0 m or less. Features.

[Effect]

According to the driftwood stopper according to the present invention, it is possible to capture driftwood whose length exceeds at least the pure distance between the supports.

〔Example〕

An example of the driftwood stopper according to the present invention is shown in Figure 1, which is a front view of the driftwood stopper seen from the upstream side of the river, Figure 2, which is a view in the direction of the ■ arrow in Figure 1, and b t/L. As a parameter, bl/
While referring to Figure 3, which is a relationship diagram between the driftwood capture rate T and the driftwood outflow rate with respect to L, and Figure 4, which is a driftwood length distribution graph diagram, find one that is the same as the conventional one or one that has the same function. They will be explained below using the same reference numerals.

First, the inventors began developing a driftwood stopper by investigating the distribution of driftwood lengths, and discovered materials such as the one shown in Figure 4.

This material is a distribution map related to the distribution of driftwood length, and this distribution map shows that the most common length of driftwood is 1 m to 4 m.

Next, the inventors found through visual observation that this was almost appropriate, and conducted various capture tests using the model of the driftwood stopper described below to determine the net spacing between the supports and the distance between the cross beams. We explored the pure interval between.

First, to explain the structure of the driftwood stopper, the reference numeral (1) shown in Figs. The net interval between is b
It is now 2. In addition, each of the outermost pillars (1) is supported by a stay (2), and each of the pillars (1) is provided with a plurality of horizontal beams (3) at a predetermined distance. be.

On the other hand, a model of the driftwood stopper constructed as described above was made, and a driftwood catching test was conducted using this model and the driftwood model, and the results shown in FIG. 3 were obtained.

That is, according to the same figure, when b, /L, > Q, 5, the driftwood capture rate T hardly changes, whereas when 0.26≦
It was found that as bl/L becomes smaller in the range of bl/L≦0.5, the driftwood capture rate T increases rapidly. Furthermore, as b2/L increases, the driftwood capture rate decreases dramatically, but when b2/L<0.40, the capture rate T becomes 0.72 or more regardless of /L.

In other words, the range of b2/L is between 0.4 and 0.96,
In other words, it has been found that the range of 0.4≦b2/L≦0.96 is sufficient.

Therefore, from the experimental results explained above and the data of the driftwood length between 1m and 4m, which has the largest distribution of driftwood length ■7 shown in the above materials, we can calculate the net spacing between the horizontal beams (3). 0
．． 3m≦b, ≦2.0m, and further support (1
), it was concluded that driftwood could be captured more effectively if the net distance between the pieces was 0.4 m≦b2≦4.0 m.

Therefore, if the driftwood stopper king is designed with these net spacings and b2 set to values within the above range, it becomes possible to catch driftwood more effectively.

However, in reality, even if the driftwood is long enough to be caught, it may pass through the driftwood stopper depending on the direction in which it is flowing. If you plan to install two or more, the driftwood will be caught by the driftwood stop installed downstream, so there is no particular problem with the passage of driftwood.

In addition, if the length of the driftwood is short, depending on the water level of the water stream, even if it can be caught by the cross beam (3), the capture rate T of the driftwood is low, so it is thought that most of it will pass through the driftwood stopper and be washed away. Once a piece of driftwood is caught, subsequent pieces of driftwood will be more likely to be caught by the captured piece of wood, regardless of their length, and as a result, the capture rate T will increase. Even if it passes through the stop, the impact on disaster is extremely small, so there is no need to worry about it in this case.

In addition, in the above embodiment, the support column (1) is supported by the stay (2), but this is simply a problem with the design strength of the driftwood stopper, and therefore, the stay (2) is not necessarily supported.
2) is not necessary.

It should be noted that the embodiment described above is only one specific example of the present invention, and therefore the scope of the technical idea of the present invention is not limited by this embodiment.

〔Effect of the invention〕

As detailed above, according to the driftwood stopper according to the present invention, the net spacing between the supports and the net spacing between the cross beams can be determined rationally, so that the construction is structurally efficient. In addition, it has become possible to reliably capture driftwood of a length that is considered to have a large impact on the occurrence of disasters, and has improved the economic efficiency of manufacturing driftwood stoppers and improved the driftwood capture function. We can expect extremely great effects.

[Brief explanation of the drawing]

Figures 1 to 4 relate to the present invention; Figure 1 is a front view of the driftwood stopper seen from the upstream side of the river, Figure 2 is a view in the direction of the ■ arrow in Figure 1, and Figure 3 is b 2. / With L as a parameter, b+/
Figure 4 is a graph of the length distribution of driftwood, Figures 5 to 9 are related to conventional examples, and Figure 5 is a diagram of the relationship between driftwood capture rate T and driftwood runoff rate with respect to L. Figure 6 is a front view of the first conventional example of the driftwood stopper 1 model, Figure 6 is a view from the ■ arrow in Figure 5, and Figure 7 is the second conventional example of the driftwood stopper model viewed from the upstream side of the river. Figure 8 is a front view of Figure 7,
FIG. 9 is a graph showing the relationship between the ratio of the net spacing b2 of the struts to the length of the driftwood, ie, /L, and the driftwood capture rate T. (1)... Prop, (2)... Stay, (3)...
Transverse beam, b,... Net distance between cross beams, b2... Pure distance between supports, L... Driftwood length, T... Driftwood capture rate.

Claims (1)

[Claims] (1) In a driftwood stopper that has a pillar installed in a river and a cross beam supported by the pillar, the net spacing between the pillars is set to 0.4 m or more and 4.0 m or less, and
A driftwood stopper characterized in that the net spacing between the cross beams is 0.3 m or more and 2.0 m or less.