JP4802813B2 - Underground drilling hole backfilling method - Google Patents

Description

  The present invention relates to a method for refilling excavation holes generated by excavating underground, and particularly to a method for refilling an impermeable layer whose upper and lower sides are sandwiched between aquifers.

  2. Description of the Related Art Conventionally, underground work for drilling underground has been performed for the purpose of purifying soil contaminated with harmful substances and groundwater flowing through contaminated soil. The hole generated by excavation is backfilled using a material selected as appropriate in consideration of the properties of the surrounding soil. For example, when the excavation hole penetrating the aquifer through which groundwater flows is backfilled, the backfilled portion is filled with sand or the like so as to become a water-permeable layer. On the other hand, when refilling a hole made in an impermeable layer (also referred to as a “non-permeable layer”) under the aquifer, the backfilled portion is made water-impervious by using a water-impervious material such as clay. (For example, Patent Document 1).

In the above-mentioned underground excavation work, it penetrates the aquifer below the saturated layer near the surface covered with surface soil, the impermeable layer below the aquifer, and further under the impermeable layer There are cases where excavation reaches the aquifer (contained aquifer). For example, if contamination by harmful substances extends to the groundwater of the confined aquifer, deep excavation reaching the confined aquifer is performed, and a purifying material having a purifying function is introduced into the excavation hole and the purification wall is Construction to install is performed.
Japanese Patent No. 3071308

  By the way, when performing deep excavation to reach the confined aquifer, the pressure applied to the groundwater flowing through the confined aquifer exceeds the force applied to the impermeable layer due to the soil weight, and the impermeable layer is pushed up. A phenomenon called “board bulge” may occur. The “board bulge” phenomenon also occurs when a drilling hole formed by deep excavation is backfilled with sand or the like, and an impermeable layer above a pressure-bearing aquifer is backfilled with a water-impervious material. In particular, when a material that quickly solidifies, such as cement milk, is used as a material for backfilling the impermeable layer, a water-impervious layer can be formed instantaneously, but before the solidified material is completely solidified, There is a possibility that the water shielding layer may be destroyed due to the lift from the pressurized water being applied to the water shielding layer.

  In this way, when the impermeable layer formed by backfilling the excavation hole with the impermeable material is pushed up by the pressurized water and the impermeable layer breaks, the aquifer layer and the impermeable layer above the impermeable layer Groundwater flows between the lower confined aquifer. For this reason, in underground construction that involves excavation leading to a confined aquifer, it is necessary to prevent the blistering phenomenon. In addition, when purifying groundwater in a pressured aquifer contaminated with harmful substances in situ, prevent the flow of groundwater between the aquifer above and below the impermeable layer and the pressured aquifer. Is required.

  The present invention has been made in view of the above problems, and when the excavation hole reaching the confined aquifer is backfilled, the impermeable layer formed by backfilling the excavation hole of the impermeable layer with a water-impervious material is An object of the present invention is to provide a method for backfilling an underground excavation hole that can be prevented from being destroyed by the pushing-up force.

  In the present invention, the excavation hole of the aquifer above and below the impermeable layer is backfilled with sand or the like and the hole of the impermeable layer is backfilled with dry water-absorbing expansive granular material, Gradually balance the lifting pressure from and the force to hold back the impermeable layer. More specifically, the present invention provides the following.

(1) Filling an underground excavation hole that penetrates the aquifer and the impermeable layer located under the aquifer and reaches the confined aquifer located under the impermeable layer and through which the pressurized water flows In the return method, a portion of the excavation hole located in the pressured aquifer is mixed with a purifying material having a function of purifying contaminated groundwater and granular material for water permeability that is substantially non-water-absorbable and expandable. A pressured aquifer backfilling step for forming a pressured water permeable layer and a portion of the excavation hole located in the water impermeable layer were dried with granular bentonite having a water content ratio of 15% or less and a particle size of 5 to 30 mm . by filling a water-swellable in water-blocking particulates to form a water shield layer; backfilled impermeable layer you flowable groundwater to the water shield layer between after forming up to 1 hour, the wellbore a portion located on the aquifer, the purification material and water permeation for granules having a purification function of groundwater contaminated by mixing Hama and underground borehole comprising the steps backfill aquifer to form a water-permeable layer, a buried back method.
(2) The backfilling method for an underground excavation hole according to (1), further comprising a first rolling step for rolling the pressure-permeable water layer and then flattening the upper surface of the pressure-permeable water layer.
(3) The backfilling method for an underground excavation hole according to (1) or (2), further comprising a second rolling step for rolling the upper surface of the water shielding layer and flattening the upper surface of the water shielding layer after forming the water shielding layer. .
(4 ) The underground digging hole backfilling method according to any one of (1) to ( 3 ), wherein the water-permeable granular material is gravel having a particle size of 0.01 to 50 mm .

  As the “water-permeable granular material”, any granular material that has substantially no water-swelling property and forms a layer (water-permeable layer) that does not impede the fluidity of water when filled in the excavation hole can be used. “Substantially no water-absorbing expansibility” means, for example, that the water-absorbing expansion rate is less than 10%, particularly less than 5% when water is absorbed to the maximum, and more specifically, JGSJ standard JGS It is only necessary that the water absorption expansion coefficient is less than 10%, particularly less than 5%, when measured by the water expansion test according to the number 2121-1998.

Specific examples of the water-permeable granular material include gravel (hereinafter, “sand” having a particle diameter of 0.4 mm or more and less than 2 mm, gravel or gravel having a particle diameter of 2 mm or more, and a particle diameter exceeding 10 mm. May be referred to as bean gravel), granulated slag, and glass particles. The water-permeable granular material preferably has a water permeability coefficient of the order of 10 ⁻² to 10 ⁻³ cm ² / s. As the water-permeable granular material, those having a particle diameter of 0.01 to 50 mm can be suitably used, and particularly gravel can be suitably used. Sand (gravel) includes river sand (river gravel), mountain sand (mountain gravel), sea sand (sea gravel), land sand (land gravel), and crushed sand (crushed stone).

The water-absorbing expansibility of the “water-absorbing expansible water-impervious granular material” includes, for example, the water-absorbing expansivity when water is absorbed to the maximum, particularly the water-absorbing expansivity measured by a water-absorbing expansibility test according to JGS No. 2121-1998 Is preferably 20% or more, more preferably 30% or more. Moreover, it is preferable that a water permeability coefficient is 10 ^<-6 > ^-10 < ^-8 > cm ^{< 2} > / s order as water-imperviousness.

  The water-impervious granular material preferably has a particle size of 5 to 30 mm, particularly 15 to 25 mm. If the particle size is too small, it is difficult to gently lift the pressurized water. On the other hand, if the particle size is too large, there is a possibility that water shielding cannot be ensured. Specific examples of the water-impervious granular material include granular materials containing smectite-based swellable clay minerals such as montmorillonite, beidellite, saponite, hectorite, and saconite. In particular, bentonite mainly composed of montmorillonite has a high water-swelling property and can be suitably used. Granular clay minerals may be natural (substantially unprocessed) obtained by crushing and drying mined materials, or those subjected to processing such as expansion control agent addition or molding May be.

  The water-impervious granular material is put into the excavation hole in a dry state. Specifically, in the case of a clay-like granular material such as granular bentonite, the water content is preferably 15% or less, particularly preferably about 5 to 10%. If the water content is high, a water-impervious layer having high water-imperviousness is formed immediately after being introduced into the excavation hole, and the water-impervious layer may be destroyed as in the case where the particle size is too small.

  After filling the drilling hole with water-permeable granular material or water-impervious granular material, the layers filled with water-permeable granular material or water-impervious granular material can be compacted by pressing with a heavy object having a flat surface, respectively. Good. By performing such rolling, the backfill portion of the excavation hole can be stabilized at an early stage, and the backfill portion can be prevented from sinking unexpectedly after the backfill work.

  In the present invention, the impermeable layer sandwiched between the two upper and lower aquifers is backfilled with a dry granular water-impervious material, so that the impermeable layer is backfilled as in the case of using a slurry-like water-impervious material. Avoid that the water-permeable layer becomes instantaneously water-impervious. And before the impervious layer gradually increases the water barrier and the impermeable layer is destroyed by the pressurized water, the backwater material is filled on the impermeable layer so that the pressurized water in the pressurized aquifer becomes The force with which the backfill material filled on the water-impervious layer presses the water-impervious layer downward can be made larger than the force that pushes up the water-impervious layer formed on the impermeable layer. As a result, it is possible to prevent the destruction of the water-impervious layer due to the board bulge, and to form a water-impervious layer that is water-impervious enough to gradually improve the water-impervious property and prevent movement in the vertical direction of groundwater.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In the following, the same members are denoted by the same reference numerals, and description thereof is omitted or simplified.

  FIG. 1 is a cross-sectional view of a formation in which excavation holes H to be backfilled by a backfilling method according to an embodiment of the present invention are formed. In this example, a saturated layer 1 composed of surface soil exists at a depth of about 2 m below the ground surface 11, and a first aquifer 2 and a first aquifer 2 in which groundwater flows below the saturated layer 1. A first impermeable layer 3 in which clay or the like is deposited below, and a second aquifer (pressured aquifer) 4 exists under the first impermeable layer 3.

  A second impermeable layer 5 exists below the pressurized aquifer 4, and further, a third aquifer (pressured aquifer), a third impermeable layer 5 exist below the second impermeable layer 5. There may be a water permeable layer or the like. In the following, the case where underground excavation reaching the lower part of the confined aquifer 4 is taken as an example, and it is sandwiched between the first aquifer 2 and the second aquifer 4 that is the confined aquifer. A case where the backfilling work is performed while avoiding the bulging of the first impermeable layer 3 will be described. However, the present invention is not limited to this, and can also be applied to backfilling an arbitrary impermeable layer above the pressurized aquifer, for example, the second impermeable layer 5.

The first aquifer 2 has a thickness of about 8 m, the first impermeable layer 3 has a thickness of about 2 m, the pressured aquifer 4 has a thickness of about 6 m, and the borehole H has a depth of about 18 m. It is formed by excavation, and the deepest part is at the same depth as the lower interface of the confined aquifer 4. In this formation, the water level (first water level) 12 flowing through the first aquifer 2 is about 2 m deep. The water level (second water level) 14 of the groundwater (pressured water) flowing through the pressured aquifer 4 is essentially the same height as the upper interface of the pressured aquifer 4 as shown in FIG. It is in. However, in this example, the aquifer aquifer 4 is pressurized at a pressure of 58.8 kN / m ^{2 due to} the soil weight of the upper layer, and the second water level 14 is about 4 m below the ground considering the lift due to this pressure. Become. And the underground water level HW in the excavation hole H is about 5 m underground.

  2-5 is explanatory drawing of the implementation procedure of the backfilling construction method which concerns on one Embodiment of this invention, FIG. 2 shows the state which implemented the pressurized aquifer backfilling process. In the present embodiment, first, as the pressured aquifer backfilling step, the river sand S as the permeable granular material is filled into the excavation hole H as shown in FIG. As a result, a water-permeable backfill layer (pressured water layer) 24 is formed in a portion (pressured water layer hole) where the pressured aquifer 4 is excavated.

In this embodiment, river sand S having a particle size of about 0.4 to 2 mm and a water absorption expansion rate of less than 0.5% is used as the water-permeable granular material. The pressurized permeable layer 24 formed by filling the river sand S has a water permeability equivalent to that of a general aquifer, that is, a water permeability coefficient of the order of 10 ⁻² to 10 ⁻³ cm ² / s.

  The filling amount of the river sand S is such that the height of the pressurized permeable layer 24 is substantially the same as the upper interface of the pressurized aquifer 4, that is, the thickness of the pressurized permeable layer 24 is about 6 m. And After performing the pressure-bearing aquifer backfilling process in which the amount of the river sand S is thrown into the excavation hole H, the compacting process (first rolling process) for flattening the upper surface of the pressurized water-permeable layer 24 is performed. It is preferable.

  In the rolling step, a heavy object having a flat surface at the tip is attached to a crane or a pile driving machine, and the heavy object is dropped into the excavation hole H to roll the surface of the pressurized water permeable layer 24. FIG. 3 is a schematic diagram showing an execution procedure of the first rolling step. As shown in FIG. 3, in this embodiment, a heavy object G having a disk-shaped flat surface is attached to the pile driving machine C by cutting out the top of the cone, and the heavy object G is attached to the inside of the excavation hole H. The surface of the pressurized water-permeable layer 24 is compacted and flattened.

  As a result of performing the first rolling step, river sand S may be additionally filled when the upper surface position of the pressurized water-permeable layer 24 becomes deeper than the upper surface of the pressurized aquifer 4. When carrying out the rolling step, if a tape measure is attached to the tip of the heavy object G, the underground depth of the upper surface of the pressurized water permeable layer 24 can be measured. In this case, it becomes easy to make the upper surface of the pressurized water-permeable layer 24 flush with the upper surface of the pressurized aquifer 4. Note that the first rolling step may be performed after the entire amount of river sand S necessary for forming the pressurized water-permeable layer 24 is input to the excavation hole H, and the number of times the river sand S is input to the excavation hole H is determined. There may be a plurality, and the rolling process may be performed after each injection.

  After the upper surface of the pressurized water-permeable layer 24 is rolled and flattened, natural granular bentonite B obtained by crushing and drying bentonite ore as a water-absorbing expandable granular material in the excavation hole H as shown in FIG. The impervious layer back-filling step of forming the water-impervious layer 23 by filling with water. The granular bentonite B of this embodiment has a particle size of 15 to 25 mm (average particle size of about 20 mm), a water content ratio of 5%, and a water absorption expansion coefficient of about 30%.

  In the impervious layer backfilling step, the granular bentonite B is introduced into the excavation hole H so that such granular bentonite B is deposited on the flattened river sand S layer constituting the pressurized water permeable layer 24. The amount of the granular bentonite B is such that the height of the water-impervious layer 23 is substantially the same height as the upper interface of the first impermeable layer 3, that is, the amount of the thickness of the water-impervious layer 23 is about 2 m. To do. After the amount of granular bentonite B is charged into the excavation hole H or in the process of charging, a rolling step (second rolling step) for flattening the surface of the layer on which the granular bentonite B is deposited may be performed. preferable.

  The second rolling step can be performed in the same procedure as the first rolling step that is performed in conjunction with the above-described pressurized aquifer backfilling step. Moreover, when the upper surface position of the water-impervious layer 23 sinks as a result of performing the second rolling step, the granular bentonite B may be additionally filled. After forming the water-impervious layer 23 and rolling the surface as necessary to flatten the upper surface, as shown in FIG. 5, the river sand S as the water-permeable granular material is filled in the excavation hole H to form the water-permeable layer 22. The aquifer backfilling step to be formed is performed.

  In the present embodiment, the river sand S that forms the water permeable layer 22 is the same as the river sand S used to form the pressurized water permeable layer 24. However, depending on the thickness of the water permeable layer 22 and the pressure applied to the groundwater flowing through the pressurized aquifer 4, the water permeable granular material constituting the water permeable layer 22 is different from the water permeable granular material constituting the pressure permeable water layer 24. May be used. For example, when the water-permeable layer 22 is thin or when the pressure of pressurized water is high, the true specific gravity of the water-permeable granular material constituting the water-permeable layer 24 is 0. You may use a large thing about 1-0.5. By doing so, the force applied to the water shielding layer 23 is increased by the weight of the water permeable layer 22 more quickly than the force caused by the pressurized water, and the destruction of the water shielding layer 23 is more effectively avoided. it can.

  In the aquifer backfilling step, the river sand S is introduced into the excavation hole H, and the river sand S is deposited on the water shielding layer 23 composed of the granular bentonite B. The amount of river sand S introduced is such that the height of the water permeable layer 22 is substantially the same as the upper interface of the aquifer 2, that is, the thickness of the water permeable layer 22 is about 8 m. It is preferable that the upper surface of the water permeable layer 22 formed by depositing the river sand S is flattened by rolling with the heavy material G described above. What is necessary is just to make the rolling process in the case of rolling the water-permeable layer 22 the same as the 1st and 2nd rolling process mentioned above.

  The upper part of the water permeable layer 22 may be formed with a surface layer having the same properties as the saturated layer 1 by covering with soil or the like, and depending on the construction purpose, the river layer S is continuously filled instead of forming the surface layer. The upper interface of the layer 22 may be exposed to the ground.

In the backfilling method according to the embodiment of the present invention described above, the granular bentonite B is dried when it is put into the excavation hole H, and the water shielding layer 23 is in a state having many gaps, so The water permeability is higher than that of the impermeable layer 3. For example, when the second rolling step is not performed, the water permeability coefficient of the water shielding layer 23 may be, for example, on the order of 10 ⁻² to 10 ⁻³ cm ² / s. The water permeability of the water layer 23 is on the order of 10 ⁻³ to 10 ⁻⁵ cm ² / s.

  For this reason, groundwater can flow between the impermeable layers 23 for about 1 to 5 hours after forming the impermeable layers 23. That is, during or immediately after the backfilling method, the pressurized water in the pressurized aquifer 4 passes through the impermeable layer 23 and moves to the permeable layer 22, so that the pressurized permeable layer 24 Lifting by the pressurized water applied upward with respect to the water shielding layer 23 is released.

On the other hand, since the granular material which comprises the water-impervious layer 23 is a water absorption expansibility, after implementing a backfilling method, it swells by absorbing groundwater gradually, and the clearance gap between granular materials becomes small. For this reason, in about one week after the backfilling method is implemented, the water permeability of the water-impervious layer 23 decreases, and the water permeability coefficient equivalent to that of the surrounding first impermeable layer 3, for example, 10 ⁻⁶ to 10 ⁻⁸ cm ² / s. It becomes the order grade.

  According to the present invention, the stability of the pressurized water permeable layer 24 and the water permeable layer 22 sandwiching the water shielding layer 23 is increased while the water permeability of the water shielding layer 23 is gradually decreased. That is, since the fluidity of the groundwater between the pressurized aquifer 4 and the aquifer 3 gradually decreases, the force for pressing the impermeable layer 23 is greater than the upward force applied to the impermeable layer 23. While maintaining the state, the water-imperviousness of the water-impervious layer 23 gradually increases. As a result, while avoiding the destruction of the impermeable layer 23 due to the blisters, the imperviousness of the impermeable layer 23 is gradually increased. Water impermeability comparable to that of the water permeable layer 3 can be provided.

  The said embodiment can be changed suitably. In other words, it can be used not only for refilling excavation holes caused by underground work, but also for burying a purification wall for purifying contaminated groundwater. Specifically, by mixing, for example, iron powder into the river sand S, the pressurized water-permeable layer 24 and / or the water-permeable layer 22 is made to be a permeable reaction wall having a function of adsorbing and decomposing organic chlorine compounds and the like. it can. By burying such a permeable reaction wall in the ground, groundwater contaminated with organic chlorine compounds, heavy metals, etc. can be purified in situ.

  Thus, according to the present invention, when underground excavation over two or more aquifers is performed and a purification wall is formed in the generated excavation hole, or when the excavation hole is simply backfilled, it is blocked by a blister. A water permeable layer can be continuously formed in each aquifer while avoiding destruction of the water layer. For this reason, especially when embedding permeable reaction walls in each of two or more aquifers, it is possible to easily install two or more permeable reaction walls in the vertical direction by simply excavating one underground hole.

  INDUSTRIAL APPLICABILITY The present invention can be used for backfilling of excavation holes generated during underground excavation work and installation work of a purification wall for purifying contaminated groundwater.

1 is a cross-sectional view of a formation in which excavation holes to be backfilled by a backfilling method according to an embodiment of the present invention are formed. It is an implementation procedure explanatory drawing of the pressure backed aquifer backfilling process of the backfilling method. It is execution procedure explanatory drawing of the rolling pressure process of the said backfilling construction method. It is execution procedure explanatory drawing of the impermeable layer backfilling process of the said backfilling construction method. It is execution procedure explanatory drawing of the aquifer backfilling process of the said backfilling construction method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Saturation layer 2 1st aquifer 3 1st impermeable layer 4 Confined aquifer 5 5 2nd impermeable 22
B Granular bentonite (water-impervious granular material)

Claims (4)

In the backfilling method of underground excavation holes that penetrate the aquifer and the impermeable layer located under the aquifer and reach the confined aquifer located under the impermeable layer and through which the pressurized water flows There,
A portion of the excavation hole located in the pressured aquifer is mixed with a purifying material having a function of purifying contaminated groundwater and water- permeable granular material having substantially no water-swellability to form a pressurized water-permeable layer. A backwater aquifer backfilling step,
A portion of the excavation hole located in the impermeable layer is filled with a dry water-absorbing expandable water-impervious granular material composed of granular bentonite having a water content ratio of 15% or less and a particle size of 5 to 30 mm to form a water-impervious layer. a step back to the ground water fills impermeable layer you flowable to said water shield layer between after forming up to 1 hour,
An aquifer backfilling step in which a portion located in the aquifer of the excavation hole is mixed with a purification material having a purifying function for contaminated groundwater and a granular material for permeable to form a permeable layer by filling the subsurface Drilling hole backfilling method. The method for backfilling an underground excavation hole according to claim 1, further comprising a first rolling step for rolling the pressure-permeable water layer and rolling the upper surface of the pressure-permeable water layer to make it flat. The backfilling method for an underground excavation hole according to claim 1 or 2, further comprising a second rolling step for rolling and flattening the upper surface of the water shielding layer after forming the water shielding layer. The backfilling method for an underground excavation hole according to any one of claims 1 to 3 , wherein the water-permeable granular material is gravel having a particle size of 0.01 to 50 mm.

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