Hydraulic and earth engineering – Bank – shore – or bed protection – Revetment
Reexamination Certificate
1999-06-17
2001-06-19
Will, Thomas B. (Department: 3673)
Hydraulic and earth engineering
Bank, shore, or bed protection
Revetment
C405S015000, C405S016000, C405S258100
Reexamination Certificate
active
06247873
ABSTRACT:
Construction methods for preventing land erosion and improving streams, or for revetments, and construction methods for preventing mountain landslides
TECHNICAL FIELD
The present inventions relate to a method for simply and effectively carrying out erosion preventive works, revetment works, or the like for streams or rivers, without destroying the natural environment of streams in mountains, other rivers, etc. These inventions also relate to a construction method for simply and effectively stabilizing the ground surface on mountainsides without damaging the natural environment.
BACKGROUND ART
The erosion or collapse of mountains and streams is caused by the downward travel of earth and gravel produced upon the collapse of mountains by mainly rainfall, snowfall, earthquakes, or the like, whereas erosion or collapse of ordinary rivers is caused mainly by floods. However, because there are many techniques common to the prevention of these types erosions or collapses, mountain conservancy work techniques for preventing land erosion and improving streams and for revetments conventionally applied to mountains or streams will be described below.
Obviously, the best practice for preventing such erosion and collapse and for restoration from such erosion and collapse is to make full use of the water retention and mountainside-stabilizing ability of forests by covering a mountain with a forest, thereby perfecting a mountainous and forested environment so as to permit prevention or alleviation of erosion and collapse of mountainsides and streams even when a heavy rainfall or snowfall occurs.
However since very great costs and a long period of time are required to condition and maintain such a mountainous and forested environment, many artificial works have been constructed at the same time that efforts have been made to perfect the mountainous and forested environments. These works are characterized in that an independent structure is installed at a prescribed location in a mountainous district, thereby it being attempted to reduce the velocity and quantity of flowing water, earth, and gravel by the effects of the weight of the structure, or the bearing capacity of the bedrock and the like supporting the structure. Installing a structure having these functions requires much material, labor, and costs. Their outlines are as follows (see Sadao Hagiwara, “
Forest Water Utilization and Land
-
erosion Prevention
”. (Dendrology, Vol. 9), Asakura Publishing Co., 1953; and Aritsune Takei, Ed.,
Land
-
erosion Preventive Engineering
, Eibundo Publishing Co., 1993).
1. Works for Streams
Cases of stream erosion are divided into downward erosion or vertical erosion, in which the depth of the stream bed is increased, and side erosion or horizontal erosion, in which the bank of the stream is horizontally eroded. In the both cases, the banks of streams collapse due to their own weight, leading to landslides or the like. As a result, huge quantities of earth and gravel accumulate on the stream bed. Earth and gravel that accumulate on the stream bed in large quantities are carried by floodwaters, etc. downstream, and sometimes take the form of mudflows having considerable destructive power and cause a great deal of damage to areas surrounding the downstream end. Works for streams are constructed for the purpose of preventing such erosion, and restoring such eroded material, in streams, and more specifically, are classified into the following categories (a) to (e).
(a) Soil-Saving Dam Works
The long-established and most commonly used are the soil-saving dam (barrage) works. Works of this type have as their main object preventing downward erosion by providing a weir that runs perpendicular to a stream, and retaining gravel behind such a weir to make a new stream bed having a gentler slope, thereby reducing the power of the flowing water. A plurality of dams may be provided stepwise for a single stream, depending on the inclination of the stream and the extent of the erosion. The materials and construction method used for installing the dam are selected in accordance with the strength required for the dam. The following kinds of dams have conventionally been built:
i. Stonemasonry dam Wet masonry dam: using mortar Dry masonry dam: using no mortar Mixed masonry dam: using wet masonry for the main portions, and dry masonry for the other portions
ii. Concrete dam
iii. Wooden dam
iv. Wire cylinder dam
v. Plaited fence dam
(b) Works for Groundsels
Works of this type have an object to maintain the current condition of a stream bed, whereby a bank of a stream is protected from tributary washout. This is a work of solidifying a stream bed with stones, concrete, wire cylinders, plaited fences, mattresses (timber frames filled with stones), or the like.
(c) Revetment Works
This is to provide a certain wall to protect a stream bed from side erosion. Because this wall is made to be parallel with the watercourse, it is known also as a longitudinal dike. These works use stones, concrete, wire cylinders, plaited fences, wooden fences, boards, or the like.
(d) Spur Dikes
For the purpose of changing the direction of a watercourse center, a structure projecting with an appropriate length and in an appropriate direction from one shore or from both shores toward the center is made. Masonry or wire cylinders are employed.
(e) Watercourse Works
These are watercourse alteration works for avoiding disturbances through adjustment of watercourses or directing the watercourse from a weak shore to a stronger shore. A pitching, rubble, or concrete process is employed.
2. Mountainside Works
Works of this type are divided, in terms of the object, into two types, i.e., works for shaping an irregularly eroded area and works for ground surface stabilization.
(a) Open Cuts with Sloping Slides
These are works for shaping irregularly eroded ground (into topographic features suitable for planting).
(b) Stage-Making Works
These are works for reducing the speed of runoff flowing on the surface of the ground, and for promoting water absorption by the ground by providing stages on the open-cut mountainside. To protect the steep inclined surfaces on the fronts of the stages, the following processes are adopted:
Turing (using turf)
Simple terracing works (using Japanese pampas grass, Miscanthus)
Mountainside wicker works
Mountainside masonry works
(c) Works to Cover Mountainsides
These are works for preventing raindrops from hitting the ground by covering a mountainside made of earth, which has insufficient cohesive power. Thereby the velocity of runoff flowing on the surface of the ground is reduced. In these works the entire mountain is covered. As specific examples, works in which the mountainside is covered with bundles of fascine in a net shape should be noted.
(d) Works on Mountainside Watercourses
These are sodding works or works in which stones are pitched for protecting a recess in a mountainside where water collects and flows.
3. Landslide Preventive Works
These are culvert works and the like using fascine or wire cylinders filled with stones and gravel for the purpose of excluding groundwater that may cause a landslide.
4. Mudflow Preventive Works
(a) Soil-Saving Dam Works
As described above
(b) Works for Accumulating Gravel
These are works for accumulating earth and gravel on an expanded portion of a stream watercourse. Thereby the force of a mudflow is reduced.
The conventional techniques for mountain and forest work as described above have the following problems. For most of these problems, this is also the case with flood control works for ordinary rivers.
i. Needs of high costs and much labor
As described above, some mountain and forest work is always required anywhere there is mountainous land, and for a single work, the objective area to be covered by the work usually has a large expanse. Thus, when solid structures such as dams are to be constructed at many sites that are targeted, considerable labor, materials, and funds are required. With the limited financial capabilities of the national government or local governments, sufficie
AuBuchon F. David
Brinks Hofer Gilson & Lione
Hartmann Gary S.
Will Thomas B.
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