JPH0128165B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a landslide suppression method implemented in a landslide zone.

[Background of the invention and prior art]

The Japanese archipelago, which is located within the Pacific Rim orogenic belt, has a complex geological structure, and Neogene rocks and wide-area metamorphic rocks that are prone to landslides are widely distributed. Disasters caused by landslides, slope failures, and debris flows are caused not only by topographical factors but also by regional development, but based on past statistics, precipitation and snowmelt are the most important triggers. Japan is located in such a geographical, social, and meteorological environment. Currently, there are approximately 70,000 locations at risk of such disasters.

Many landslides occur due to heavy rain, prolonged rain, or during the snowmelt season. This shows that the occurrence of landslides is closely related to groundwater, that is, the pore water pressure in the soil (slide surface), and conversely, the treatment of groundwater controls the occurrence of landslides.

Horizontal borings, water collection wells, and drainage tunnels (used in combination with drainage borings) for the purpose of removing groundwater (lowering the groundwater level) as a method to prevent landslides from occurring or to suppress their activity after they have occurred. There is. Horizontal boring is done gently at a horizontal angle of 0° to 15° from the ground surface, and the volume of each hole is small, so the possibility that it will encounter a water path is extremely small. Therefore, it is necessary to provide several lines, but 1
The drilling length of the book is about 20m to 60m, and if it is longer than this, the drilling error will increase. In addition, there is a risk of clogging and breaking due to landslides, so it cannot be considered permanent, and is only suitable for temporary (short-term) and small-scale installations.

Water collection wells pose problems in how the groundwater collected here is drained. In other words, if pump drainage is used, there are maintenance problems, and if long boreholes with large diameters are used as drainage holes, a hydraulic gradient is required to allow natural drainage, and similar to horizontal boring, landslides are a problem. There is a problem that the pipes may slip and break off, making it impossible to drain water.

Drainage tunnels must be dug outside the landslide area for maintenance and safety reasons. Therefore, the drilling length becomes long, which is economically very disadvantageous.

[Principle of the invention]

The soil composition of the landslide area is composed of topsoil, relatively permeable borax, and several alternating clay layers, with the landslide layer (clay) located in the area of geological change beneath the topsoil, and a weathered zone. , bedrock, and aquifers.
Groundwater that affects landslide occurrence is near the sliding surface. Water in this area is affected by seepage water from the ground surface, but it also depends on the water level and volume of recharge sources (e.g., ponds, river water) upstream. Therefore, there are places where the pore water pressure is higher than in the strata above the landslide surface, and landslides are more likely to occur at such times. Although the weathered zone and bedrock below the landslide surface do not allow water to pass through themselves, there are water passages (good permeability) such as joints and cracks within the layer, and as a result, the pore water pressure in these areas increases. is often near the slip surface or lower than the ground surface. Therefore, in order to lower the pore water pressure at the landslide surface, it is sufficient to install a device that feeds water into the low-pressure area in the lower layer.

[Structure of the invention]

For the reasons mentioned above, the method invented here was developed to improve the shortcomings of conventional methods by utilizing natural soil hydraulics.
Landslide surface (landslide clay) at intervals of 30m to 150m
3m in diameter to lower the nearby groundwater level
A reinforced concrete well, 6m long and 10m to 80m deep, will be installed for both water collection and injection purposes. A water collection/injection well has an upper water collection part and a lower water injection part in a single well, collects water from above, and uses the natural water head difference to transfer groundwater accumulated in the water collection part to the water injection part. Water is injected into the ground from below, reducing pore water pressure near the slip surface.
The size of the water injection part will be determined based on the amount of natural water that can be injected from near the slip surface through a preliminary survey. In addition, depending on the ground condition,
An effective method is to create a drainage borehole near the landslide surface of the caisson and insert a water collection pipe, and to create a water injection borehole below the landslide surface and insert the water injection pipe.

〔Example〕

The drawing shows one embodiment. First, a water collection and injection well 1 is provided that penetrates a landslide surface s where a landslide is expected. This water collection/injection well 1 has a diameter of 3m.
~6m. A plurality of water collection pipes 3 inserted into boreholes are installed near the landslide surface s where pore water pressure reduction is most required, and this part is used as a water collection part 2 and the collected groundwater is transferred to a water injection part 4 below.
send to The water injection part 4 has a sliding surface s, for example, as shown in the figure.
It is located in the base rock d that exists further down or the aquifer e below it, and the groundwater collected by the plurality of water injection pipes 5 inserted into the borehole is now returned to the aquifer below. There is. These water collection pipe 3 and water injection pipe 5 are provided with a large number of small holes, so that water can be collected or injected as a whole.

In the figure, a indicates a layer with good water permeability such as a sand layer, b indicates a layer with poor water permeability such as a clay layer, and c indicates a weathered zone.

〔Effect of the invention〕

By collecting groundwater near the sliding surface, which is the main cause of landslides, and installing water collection and injection wells at specified intervals, which flow the collected groundwater deep underground, it is possible to reduce the pore water pressure near the landslide surface and prevent landslides. In addition to effectively suppressing water pollution, it does not require any drainage equipment and is relatively easy to construct, reducing construction and maintenance costs compared to conventional construction methods.

[Brief explanation of drawings]

The drawing is a longitudinal sectional view showing an embodiment of the present invention. 1...Water collection and injection well, 2...Water collection section, 3...Water collection pipe, 4...Water injection section, 5...Water injection pipe, s
...slip surface, a...layer with good permeability, b...layer with poor permeability, c...weathered zone, d...base rock, e...
...Aquifer.

Claims (1)

[Claims] 1. In areas where landslides are expected, a water collection and injection well will be installed that penetrates the landslide's sliding surface and reaches deep underground, and a drainage bore hole will be provided in the water collection and injection well near the slip surface, and water will be injected downward. A borehole is provided, and in order to reduce the pore water pressure of groundwater near the sliding surface, the groundwater collected from the drainage borehole is allowed to flow through the water injection borehole deep underground where it will not affect the landslide, thereby reducing natural water movement. A landslide prevention method characterized by injection into the ground using the slope.