JP3006993B2 - Groundwater level lowering method for permeable ground - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to permanent groundwater control for structures installed on permeable ground, and more particularly to buoyancy reduction measures for buildings of nuclear power plants and other structures important for earthquake resistance. It is.

[0002]

2. Description of the Related Art Conventionally, for structures that are important for seismic resistance, such as nuclear power plant buildings, always take measures to reduce buoyancy against expected seismic force to ensure stability during earthquakes. Is kept. As a conventional buoyancy reduction measure, it is common to provide drainage around the building by forced drainage and also to provide the drainage facilities with an earthquake-resistant design equivalent to that of the building. This is because conventional nuclear power plants are based on bedrock, and buildings are installed or buried in low-permeability bedrock. This is because it is said that there is little time to recover the water level, and that the function can be fully recovered after the emergency drainage is added.

[0003] From the viewpoint of expanding the location of a nuclear power plant, even if the above-mentioned rock mass is changed to a quaternary stratum (gravel layer), the stratum has a sufficient bearing capacity because there are many strata. However, there is no problem in terms of the bearing capacity of the structure. However, since the Quaternary ground (gravel layer) has a higher permeability than ground rock and abundant groundwater, measures to eliminate groundwater are important issues. In other words, in addition to having to install a deep drain,
This is because the amount of pumped water is considerably increased, and the operating cost of the drainage equipment is increased.

The groundwater level lowering method shown in FIG. 2 is a combination of a building 1 installed on a permeable ground 2 and a drainage device 5 and a water blocking wall 8, which is an extension of conventional buoyancy reduction measures. It is thought that there is. However,
In this construction method, first, when there is no impermeable ground 3 such as a bedrock, the effect of the water blocking wall 8 cannot be expected, and the generality and adaptability of the system are limited. Also,
There is a high possibility that the impermeable ground 3 for embedding the water blocking wall 8 is deep, and there is a problem that construction of the water blocking wall 8 requires excessive cost.

[0005]

An object of the present invention is to provide a permanent groundwater measure for a structure installed on a permeable ground,
It is intended to provide a highly feasible groundwater level lowering method that is excellent in terms of safety and cost.

[0006]

In the method for lowering the groundwater level of a water-permeable ground according to the present invention, a water-permeable layer is formed around the bottom and side surfaces of a structure installed on the water-permeable ground, and the inside and outside of the water-permeable layer are formed. It is characterized by providing drainage equipment on the ground. In addition, the method of lowering the groundwater level of the permeable ground according to the present invention is to form a poorly permeable layer with clay and other fine particle suspension grout around the bottom and side surfaces of the structure installed on the permeable ground, Drainage equipment is provided on the ground inside and / or outside the poorly permeable layer.

[0007]

[Function] In the above groundwater level lowering method, in normal times,
The groundwater inside the poorly permeable layer is discharged outside from the permeable ground by the function of the inside drainage facility. Further, the groundwater level is always lower than the poorly permeable layer due to the function of the outer drainage facility.

In the event of an earthquake, even if the function of the inner drainage system stops, the poorly permeable layer blocks the rise of groundwater, so that the rise of the lowered groundwater level can be delayed. On the other hand, even when the function of the outer drainage facility is stopped, since the impervious layer functions in the same manner, there is ample time until the function of the stopped drainage facility is restored, and a highly safe permanent Groundwater countermeasures.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the method for lowering the groundwater level of a permeable ground according to the present invention is applied to a measure for reducing the buoyancy of a building of a nuclear power plant will be described below with reference to FIG. In FIG. 1, a building 1 is installed on a gravelly ground 2 as a permeable ground, and an impermeable ground 3 such as a bedrock is located below and at a large depth below the gravelly ground 2.

Reference numeral 4 denotes an impervious layer formed by surrounding the bottom and side surfaces of the building 1. The ground immediately below and on the side of the building 1 is improved to an impervious layer using clay grout or the like. Here, the clay grout can be used by mixing fine particles obtained by appropriately pulverizing naturally occurring clay or the like with water. The cohesive soil is preferably one that does not cause clogging and does not swell when injected into the gravel ground 2, and examples thereof include volcanic ash cohesive soil such as Kanto loam and Masa soil.

The purpose of using clay grout in this embodiment is to fill the voids of the permeable gravel ground 2 with fine clay particles so as to make the gravel ground 2 less permeable. It is also possible to use a suspension grout consisting of fine particles of sand, cement, lime or the like, which has the same effect as the grout. However, in terms of cost, clay grout is the best. On the other hand, a bentonite stabilizing solution used in the underground continuous wall construction method or the like, a chemical solution and other ground injecting agents that are commonly used for the purpose of consolidating the ground and the like are unsuitable.

The thickness of the water-impermeable layer 4 is determined in consideration of the properties of the gravel ground 2 and the cohesive soil used, but is generally about several meters. In addition, instead of the fine particle suspension grout, the poorly permeable layer 4 formed on the side surface of the building 1 is
The retaining wall having water blocking properties of the building 1 may be used as it is.

A drainage device 5 is provided between the building 1 and the gravel ground 2 inside the poorly permeable layer 4. The drainage device 5 collects groundwater that has passed through the poorly permeable layer 4 and ascended around the building 1, and forcibly drains it with a pump (not shown). The arrangement is appropriately determined according to the properties of the gravel ground 2 and the like.

Reference numeral 6 denotes a water permeable layer provided between the bottom surface of the building 1 and the poorly permeable layer 4 for enhancing the effect of collecting the groundwater that has passed through the poorly permeable layer 4. is there. Generally, sand or gravel can be used as the permeable layer 6, and depending on the nature of the gravel ground 2 on which the building 1 is installed, it can be used as it is.

On the other hand, reference numeral 7 denotes a drainage facility provided on the gravel ground 2 outside the poorly permeable layer 4, and the groundwater level is set at the poorly permeable layer 4.
It plays a role of always lowering it. Therefore, the drainage of the drainage equipment 7 does not need to be provided to the impermeable ground 3 and may be provided to a position slightly deeper than the poorly permeable layer 4. In buildings other than the nuclear power plant building, such a double drainage system 5 and drainage system 7 are not required, and either one of the drainage systems is sufficient. In that case, drainage equipment 5
It is more advantageous to provide.

In the above embodiment, the groundwater inside the poorly permeable layer 4 is discharged outside from the gravel ground 2 by the operation of the drainage equipment 5 in normal times. The groundwater level is always lower than the poorly permeable layer 4 due to the function of the drainage device 7.

In the event of an earthquake, even if the function of the drainage equipment 5 is stopped, the poorly permeable layer 4 blocks the rise of the groundwater, so that the rise of the lowered groundwater level can be delayed. On the other hand, even when the function of the drainage equipment 7 is stopped, the poorly permeable layer 4 functions similarly. In other words, by operating the drainage system 5 or the drainage system 7 in preparation for the same degree of aftershocks after the earthquake, until the function of the stopped drainage system is restored,
It is possible to provide sufficient time and secure sufficient safety against the assumed seismic force.

[0018]

The method for lowering the groundwater level according to claim 1 is excellent in function, safety and cost. Specifically, (1) It is not necessary to install a deep water stop wall or drain even in permeable ground,
It can be kept low. (2) Permanent groundwater countermeasures that do not depend on the permeability of the gravel ground or the depth of the rock below, and the generality and adaptability of the system will be wide. (3) High safety can be ensured by the double structure of the shallow drainage equipment.

Therefore, it is extremely effective as a permanent countermeasure against groundwater for structures installed on the permeable ground. Examples of such a structure include a structure buried underground and having a large buoyancy, such as a deep underground structure, an underground shopping mall constructed in an urban area, a subway, and an underpass.

In particular, as described above, even if a permeable ground with abundant groundwater is selected as the location of the nuclear power plant, sufficient safety against the assumed seismic force can be guaranteed. In addition to the effect, the same effect can be expected in the case of constructing a nuclear power plant by constructing an artificial island in the coastal sea area.

According to the second aspect of the present invention, the impervious layer can be easily formed with a low-cost material, and the fine-particle suspension grout can be formed by the mechanical characteristics of the gravel ground to be injected. Therefore, there is an effect that the reliability in construction is high.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment in which the method of the present invention is applied as a buoyancy reduction measure for a nuclear power plant building.

FIG. 2 is an explanatory diagram of a groundwater level lowering method which is considered to be on an extension of a conventional buoyancy reduction measure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Building 2 Gravel ground as permeable ground 3 Impervious ground such as rocks 4 Impervious layer 5 Drainage facility 6 Drainage facility 7 Drainage facility

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) E02D 31/10-31/12 E02D 27/32 E02D 27/34

Claims (2)

(57) [Claims] 1. A with surrounds the bottom and sides of the structure to be installed in a water-permeable ground to form the impermeable layer, in that a drainage inside Oyo beauty outside side ground of the flame aquifer Characteristic method of lowering the groundwater level of permeable ground. 2. An impervious layer is formed by fine particle suspension grout around the bottom and side surfaces of a structure installed on the permeable ground, and drainage equipment is provided on the ground inside and / or outside the impervious layer. A method of lowering the groundwater level of permeable ground, characterized by the provision of