JP2003240701A - Evaluation method for water sealing performance of multilayer cover soil and device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method for water insulation performance of multilayer cover soil and device therefor that can evaluate the water sealing performance of a soil layer formed out of coarse grain soil and fine grain soil constituting the coarse grain layer and fine grain layer of a multilayer cover soil. <P>SOLUTION: The evaluation method in which, by performing a test using a two-dimensional test tank with the coarse grain soil and fine grain soil to be used filled in layers to the multiple cover layer formed by filling the coarse grain soil, fine grain soil, and field-generated soil in order of lower position on the upper surface of landfilled solid waste, the flow data of penetrating water is measured, is characterized in that the property values of the coarse grain soil and fine grain soil are determined by reversely analyzing the measured flow data, and then the water sealing performance of the soil layer formed with the coarse grain soil and fine grain soil is analyzed and evaluated based on the determined property values. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for evaluating the water impermeability of multi-layered soil constructed in a landfill for radioactive waste or industrial / general waste.

[0002]

2. Description of the Related Art In order to maintain a safe and comfortable environment,
It is effective to isolate the waste from the living area, and it has been a general practice to cover the landfilled waste with soil. Some rainwater that has penetrated the cover soil becomes contaminated water while passing through the waste layer, so it is necessary to purify it in the downstream area of the disposal site. In addition, if the bottom impermeable construction is incomplete, it penetrates underground and causes groundwater pollution. In order to reduce the cost of purification treatment and reduce the risk of groundwater contamination, it is effective to improve the water-blocking function of the soil cover and reduce the amount of rainfall infiltration. Therefore, the following soil covering has been conventionally performed. Single-layer soil cover 0.5-1.5 m thick soil cover that is made by compacting locally generated soil and residual soil. Water-impervious material type soil-covered soil that has improved water-impervious function by using soil and water-impervious material such as sandwiching a water-impervious sheet in the soil-covering layer or applying asphalt pavement to the surface of the soil. Mixed soil with bentonite mixed soil Covering soil with improved water impermeability by using bentonite mixed soil with mixed water with bentonite and earth and sand to enhance water impermeability as part of the soil (thickness 0.3 to 0.5 m) . Fine-grained soil (thickness 0.15 to 0.5 m) under the soil cover of the multi-layered soil,
Coarse soil with coarse-grained soil (0.15-0.3 m) placed below it with a gradient (3% or more) at the layer boundary. The water that has passed through the generated soil and infiltrated into the fine-grained soil and moved downward changes the flow direction laterally along the gradient near the boundary surface with the coarse-grained soil when the amount of infiltration is small. It is eliminated to the side through. Therefore, the amount of permeated water to the waste layer is reduced. This takes advantage of the fact that the smaller the size of the particles that make up the layer, the greater the capillary suction force and the greater the water retention, and that the particles that make up the layer are large and the water retention is small. By providing a fine-grained layer with a large water-holding capacity, it is possible to stop permeated water due to rainfall etc. in the fine-grained layer, and to add a water-conducting gradient to the cover soil to extend along the boundary surface between the coarse-grained layer and the fine-grained layer. It is made to flow down (Japanese Patent Laid-Open No. 2001-1
7933).

[0003]

However, the conventional soil covering method has the following problems. Although the water-imperviousness of single-layered soil depends largely on the nature of the soil used, it is generally said that the water-impervious property is low and that 20 to 50% of precipitation penetrates the waste layer. Has problems with durability of water-impervious sheets and asphalt pavements and reliability of joints, and the sheets themselves may become sources of pollution when they deteriorate. The bentonite mixed soil type is problematic in that its cost is higher than other soil covering methods and that construction is difficult. It is technically difficult to accurately calculate the unsaturated seepage characteristics (moisture characteristic curve and unsaturated seepage) of fine-grained soil and coarse-grained soil that affect the water impermeability of the multi-layered soil. The problem is that there is no means to evaluate and design the performance.

As described above, there are problems in each, but since the multi-layered soil is constructed only with a long-term stable soil material, it is superior in durability and economy as compared with other soils, and can be constructed. It has the advantage of being easy to do. Furthermore, depending on the waste, a small amount of permeated water may be required to promote its decomposition and purification. In this case, it is difficult to adjust the amount of infiltrated water by covering the soil with a water-impervious sheet, but in the case of multi-layered soil, the amount of infiltrated water can be adjusted by changing the material, layer thickness, gradient, and soil cover length. , Has many advantages over other soil cover.

Therefore, the present invention has been made in order to solve the problems in the above-mentioned multi-layered soil, and is a multi-layered one for evaluating the water-impervious performance of the soil layer formed by the coarse-grained soil and the fine-grained soil used for the multi-layered soil. An object is to provide a method and apparatus for evaluating the water impermeability of soil cover.

[0006]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the method for evaluating the water-impervious property of a multi-layered soil is as follows. The flow data of the permeated water is measured by performing a test using a two-dimensional test tank in which the coarse-grained soil and the fine-grained soil that are to be used in a multi-layered soil to be formed by embedding in order from the lower side are packed. The physical properties of the coarse-grained soil and the fine-grained soil are calculated by back-analyzing the flow data, and the water impermeability of the soil layer formed by the coarse-grained soil and the fine-grained soil is determined based on the obtained physical property values. Characterized by analysis and evaluation.

In addition, the water-impervious performance evaluation apparatus for a multi-layered soil according to the present invention is characterized in that the coarse-grained soil, fine-grained soil, or locally-generated soil used for multi-layered soil laid on the upper surface of landfill waste is the above-mentioned coarse soil. The soil layer is formed in the two-dimensional test tank with the grain soil as the lower layer and the fine grain layer as the upper layer, and the water pressure gauge is embedded in the soil layer, and water is sprinkled from above the soil layer by the water supply facility. Discharge amount measuring means for measuring the pressure head of the permeated water that permeates through the water pressure gauge and measuring the discharge amount of the permeated water discharged from each drain hole provided at a constant interval on the bottom surface of the two-dimensional test tank. It is characterized by having.

[0008]

[Advantage] According to the above-mentioned structure, the coarse-grained soil, the fine-grained soil, and the locally-generated soil used for the multi-layered soil laid on the upper surface of the landfill waste are generated by the coarse-grained soil and the fine-grained soil. The soil layer with the lower layer and the fine grain soil as the upper layer is formed in the two-dimensional test tank. Water is sprinkled from the formed soil layer by a water supply facility to infiltrate the soil layer. A water pressure gauge is embedded in the soil layer, which allows the pressure head in the soil layer to be measured. In addition, drain holes are provided at regular intervals on the bottom surface of the two-dimensional test tank so that the permeated water that has permeated the inside of the test tank is discharged. The discharge amount of the permeated water discharged from each section can be measured by measuring the discharge amount of the permeated water by the discharge amount measuring means. Then, by analyzing the obtained data, it is possible to evaluate the water impermeability and water permeability of the soil layer formed by the fine-grained soil and coarse-grained soil used for the multi-layered soil, and apply it to the design of the multi-layered soil. is there.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a water barrier evaluation apparatus for a multi-layered soil according to the present invention will be described in detail with reference to the drawings. FIG. 4 shows a vertical cross-sectional view of a waste burying structure using multi-layered soil.
In FIG. 4, the multi-layered soil covering the surface of the waste is the waste 1
After applying a water-conducting gradient to the surface of the and covering it with locally generated soil 2,
The coarse particle layer 3 and the fine particle layer 4 are laid next to the coarse particle layer 3 and finally the whole is covered with locally generated soil and top soil 5 having good water-blocking properties.

In FIG. 4, the coarse particle layer 3 constituting the multi-layered soil can be formed by coarse particles such as gravel, gravel, and crushed stone. This is due to the piping rule in relation to the particle size required for the fine particle layer. Set the granularity so that Next, the fine particle layer 4 is laid on the upper surface of the coarse particle layer 3 using fine particles such as sand.

With such a layer structure, the coarse-grained layer 3 having large voids exists in the upper layer of the locally-generated soil layer 2, but the fine-grained layer 4 having small voids exists in the upper layer side thereof. Then, this becomes a water retention layer for seepage water due to rainfall.
What is important here is that the fine grain layer 4 is laid on the upper layer of the coarse grain layer 3 so that the permeated water due to rainfall or the like is stopped in the fine grain layer 4 by the capillary phenomenon, and the lower coarse particle layer 3 absorbs the permeated water. It is to have a function of disconnecting so as not to seep out to the water-blocking layer 2 side. This function has a function that the water moves in the moist cloth, because the wiping cloth (fine particle layer 4) is placed on the slatted sludge (coarse water guiding gradient) (coarse particle layer 3). It can be compared to having it. Therefore, as the fine particle layer 4, a material having a large water retention property and a water permeability capable of laterally removing the permeated water is used, and the coarse particle layer 3 has a small capillary water zone and exhibits a low water permeability on the negative pressure side. The material may be a material that can suppress the infiltration of permeated water. If this is shown in a figure, it will become what is shown in FIG. FIG. 3 (1) shows a general relationship between the pressure head and the volumetric water content. Compared with the coarse-grained material, the fine-grained material is less likely to have reduced water content even when the negative pressure is increased, that is, Large water retention capacity. Also, FIG.
(2) shows the general relationship between the pressure head and the unsaturated hydraulic conductivity. The permeability of coarse-grained materials decreases sharply when the negative pressure head increases, whereas the permeability of fine-grained materials decreases. The deterioration of the property is gradual, and therefore the water permeability of both materials is reversed at the boundary of the pressure head in (a) in the figure. Although the cohesive soil shows the same qualitative tendency as the fine-grained material shown in FIG. 3, it is not suitable as a fine-grained material for the multi-layered soil because of its poor water permeability (small unsaturated hydraulic conductivity).

Further, since the fine grain layer 4 is laid on the coarse grain layer 3, it is necessary to prevent the boundary portion of these layers from being mixed. Therefore, in principle, both layers are set to satisfy the piping rule. That is, the grain size distributions of the coarse grain layer 3 and the fine grain layer 4 are adjusted so that the layer boundary becomes clear.

As described above, when water is shielded by the multi-layered soil, it is important to select and combine the coarse-grained soil and the fine-grained soil constituting the coarse-grained layer and the fine-grained layer. In view of this, in the water barrier performance evaluation apparatus for a multi-layered soil according to the present invention, the materials and their combinations that form the coarse-grained layer and the fine-grained layer are evaluated in the configurations described below.

FIG. 1 shows an apparatus for evaluating water impermeability of a multilayered soil according to this embodiment. In FIG. 1, 10 is a two-dimensional test tank, and 12 is a water supply facility for supplying water from the upper end of the two-dimensional test tank. The data for material evaluation is that the soil layers of the coarse-grained soil 14 and the fine-grained soil 16 are formed in this two-dimensional test tank, and water is supplied from the water supply equipment 12 to spread permeated water into the soil layer. The behavior is measured by measuring the discharge amount of the seepage water discharged from the drainage hole provided on the bottom of the two-dimensional test tank by the water pressure gauge 18 (tensiometer) with the pressure head of the seepage water buried in the soil layer. It is measured by an electronic balance 26.

The two-dimensional test tank 10 uses acrylic plates on the lower side and side surfaces so that the inside can be observed. A jack (not shown) is installed under one end of the two-dimensional test tank 10 so that the gradient can be changed. Further, partition plates 20 are provided on the lower side of the two-dimensional test tank 10 at regular intervals so that the permeated water that has reached the lower side can be laterally divided into fixed regions and sampled. Is provided with a drainage hole 22. A tube 24 is connected to the drain hole 22, and the permeated water discharged from the drain hole 22 flows into the beaker 28 mounted on the electronic balance 26 through the tube 24. With such a configuration, the infiltrated water reaching the lower side of the two-dimensional test tank is sampled in the lateral direction of the two-dimensional test tank 10 for each section that requires data, so that the flow state of the infiltrated water in the soil layer Information can be obtained for analysis.

In the water supply equipment 12, nozzles are attached to the bottom surface of an acrylic tank at regular intervals, and water is evenly sprayed from each nozzle by the pressure of water sent from the metering pump 30. The water supply amount can be controlled by the rotation speed of the metering pump 30. As a result, a fixed amount of water can be supplied at a fixed time, and the amount of water supplied can be freely changed.

A beaker 28 into which the permeated water discharged from the lower side of the two-dimensional test tank 10 flows is placed on the electronic balance 26, and the amount of discharged water is measured. The electronic balance 26 is connected to the information processing terminal 32, and records the drainage amount at intervals of 5 minutes under the control of the information processing terminal 32. The data of the pressure head measured by the water pressure gauge 18 is recorded by the data recorder 34 at 5 minute intervals. With this configuration, it is possible to continuously obtain data on the behavior of seepage water in the soil layer.

Next, the evaluation procedure will be described. First,
As shown in FIG. 2 (a), the coarse-grained soil 14 is packed to a thickness of about 0.2 m in a two-dimensional test tank 10 which is entirely inclined by a jack (not shown), leaving a part of the downstream end. After filling the part of the remaining downstream end with the fine-grained soil 16, the coarse-grained soil 14
A water pressure gauge (tensiometer) 18 is installed on the surface of the, and the whole surface is filled with the fine-grained soil 16 in a thickness of 0.1 to 0.3 m. At this time, gravel, gravel, crushed stone, or the like can be used for the coarse-grained soil 14, and fine-grained material such as sand can be used for the fine-grained soil 16. Next, from the upper end of the two-dimensional test tank 10, the water supply equipment 1
2. A constant flow rate of water is supplied by 2, and the change over time of the pressure head of the permeated water at the layer boundary is measured by the water pressure gauge 18, and the measurement results are recorded at 5 minute intervals by the data recorder 34 connected to the water pressure gauge 18. .

The permeated water that has reached the layer boundary is shown in FIG.
As shown in (c), it flows down and permeates along the water transfer gradient along the boundary surface, and is discharged from the drain holes 22 provided on the lower side of the two-dimensional test tank 10. The behavior of the permeated water at this time depends on parameters such as the difference in physical properties between the coarse-grained soil 14 and the fine-grained soil, the magnitude of the water guiding gradient, and the amount of water supplied per hour. That is, for example, when the fine-grained soil 16 is superior in water retention and water permeability to the coarse-grained soil 14 and has a sufficient capacity for removing permeated water, most of the permeated water reaching the layer boundary is the coarse-grained soil 14. It does not permeate into the water and flows downward near the boundary, and most of it is discharged from the drainage hole at the lower part of the fine grain layer at the downstream end. On the other hand, if the material selection is inappropriate or the amount of water supplied per hour exceeds the exclusion capacity, the amount of permeated water that moves to the coarse-grained soil 14 will increase, and it will also be discharged from the drainage holes below the coarse-grained layer. become.
The permeated water drained from the drain hole 22 in this manner passes through the tube 24 and is placed on the electronic balance 28.
Inflow to 6. The electronic balance 28 measures the inflow amount at any time, whereby the position of the lower side drainage and the change over time in the flow rate are measured, and the data measured by the connected information processing terminal 32 is recorded at 5-minute intervals.

The test is repeated by changing the amount of water supplied per hour, and the limit of the amount of water supplied per hour at which discharge from the drainage hole on the lower side of the coarse-grained soil begins, and the amount of water supplied when the amount of water supplied per hour is increased beyond that Calculate the ratio of bottom drainage from (coarse-grained soil / fine-grained soil).

Next, the physical property values (moisture characteristic curve) of the fine-grained material (fine-grained soil) and the coarse-grained material (coarse-grained soil) were analyzed while conducting a simulation analysis of the behaviors of the pressure head and the bottom drainage obtained in these tests. , Unsaturated hydraulic conductivity, etc.) are finely adjusted to obtain physical properties that can accurately reproduce the behavior.

In the water impermeability evaluation of the soil cover, firstly, the highest level locally generated soil is modeled in one dimension, and the daily change model of precipitation and evapotranspiration at the planned construction site is analyzed as an input value.
The daily change in the amount of water that passes through the generated soil and permeates downward is calculated for one year. Next, the fine-grained soil and coarse-grained soil that make up the cover soil were modeled in a two-dimensional cross-section, and the upper surface of the fine-grained soil was analyzed by giving a diurnal change in the amount of infiltrated water passing through the locally generated soil obtained in the above analysis , Calculate the amount of water discharged laterally through the fine-grained soil.
These analyzes can be easily performed by saturated unsaturated permeation particle analysis by the finite element method.

By performing the above-described evaluation, the lateral drainage behavior of the fine-grained soil is actually confirmed by using the target soil material, and the unsaturated permeation characteristics are obtained through the simulation, so that the reliability is high. Unsaturated penetration characteristics are obtained. In addition, since the non-steady state analysis of unsaturated regions where the nonlinearity of physical properties is strong is performed in the evaluation of the water impermeability of the soil cover, a large calculation is required if the entire soil cover consisting of locally generated soil, fine-grained soil and coarse-grained soil is modeled and analyzed. Although there is a problem that it takes time, as described above, by performing analysis separately for locally generated soil and analysis for fine-grained soil and coarse-grained soil,
The calculation time can be greatly shortened, and the effect of various structural conditions such as layer thickness and gradient on the impermeable performance can be efficiently compared and studied. In addition, the analysis result of such division analysis is
No significant difference is observed when modeling the entire cover soil.

[0024]

As described above, according to the method and apparatus for evaluating the water impermeability of a multi-layered soil according to the present invention, the lateral drainage behavior of fine-grained soil used for the multi-layered soil is confirmed, and unsaturated is obtained through the simulation. Since the permeation characteristics are obtained, highly reliable unsaturated permeation characteristics can be obtained. This makes it possible to evaluate the water impermeability and water permeability of the soil layer formed by the fine-grained soil and the coarse-grained soil used for the multi-layered soil and apply it to the design of the multi-layered soil.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a water-impervious performance evaluation device for multi-layered soil according to the present invention.

FIG. 2 is an explanatory diagram showing a flow state of permeated water in a soil layer.

FIG. 3 is a graph showing physical properties of a fine-grained material and a coarse-grained material.

FIG. 4 is a vertical cross-sectional view of a waste burying structure using multi-layered soil.

[Explanation of symbols]

1 ………… Waste, 2 ・ ・ ・ …… Soil generated locally, 3 ……… Coarse-grained layer, 4 ……… Fine-grained layer, 10 ……… Two-dimensional test tank, 12…
…… Water supply device, 14 ………… Coarse grain soil, 16 ………… Fine grain soil,
18 ... Water pressure gauge, 20 ... Partition plate, 22 ... Drain hole, 24 ... Tube, 26 ... Electronic balance, 28 ...
...... Beaker, 30 ………… Metering pump, 32 ………… Information processing terminal, 34 ………… Data recorder.

Claims (2)

[Claims] 1. A layered structure of the coarse-grained soil and the fine-grained soil to be used for a multi-layered cover formed by embedding coarse-grained soil, fine-grained soil, and locally-generated soil in order from the bottom on the upper surface of landfill waste. To measure the flow data of the permeated water by performing a test using a two-dimensional test tank packed in, to obtain the physical property values of the coarse-grained soil and the fine-grained soil by back-analyzing the flow data, and obtain the determined physical properties. A method of evaluating water-imperviousness of a multi-layered soil, characterized by analyzing and evaluating the water-imperviousness of a soil layer formed by the coarse-grained soil and the fine-grained soil based on the values. 2. The coarse-grained soil and the fine-grained soil, which are to be used for a multi-layered soil formed by stacking coarse-grained soil, fine-grained soil, and locally-generated soil in order from the bottom on the upper surface of landfill waste, By forming a soil layer in a two-dimensional test tank with coarse-grained soil as the lower layer and fine-grained soil as the upper layer, and embedding a water pressure gauge in the soil layer, and by performing watering from the soil layer with a water supply facility, Discharge to measure the pressure head of the permeated water that permeates the soil layer with the water pressure gauge and to measure the amount of permeated water discharged from the drain holes provided at regular intervals on the bottom surface of the two-dimensional test tank. A water-impervious performance evaluation device for multi-layered soil, comprising a measuring means.