Quality control method for bentonite-containing water barrier layers

Abstract

To provide a quality control method for a bentonite-containing impervious layer ensures quality control by measuring the penetration resistance force of the bentonite-containing impervious layer, even at a slope face or a narrow part.SOLUTION: A quality control method for a bentonite-containing impervious layer comprises: an abutting step 6 for bringing a penetration resistance force detection device, which has a penetration part penetrated into an impervious layer containing bentonite ballast or bentonite mixed soil and a resistance force detection part for detecting the penetration resistance force which the penetration part receives from the impervious layer and is usable in a gripped state in the hand, into contact with the target impervious layer so as to allow the penetration part to penetrate roughly orthogonally into the impervious layer; a resistance force detection step 7 which makes the penetration part enter into the impervious layer and detects the penetration resistance force received by the penetration part through the resistance force detection part; a water permeability coefficient conversion step 9 in which a conversion device receives the penetration resistance force detected in the resistance force detection step 7 and in which the conversion device calculates a water permeability coefficient from the penetration resistance force; and a determination step 11 in which a determining device determines that the water permeability coefficient calculated in the water permeability coefficient conversion step 9 is equal to or less than a threshold value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a quality control method for a bentonite-containing water impermeable layer, which can measure the penetration resistance of the bentonite-containing water impermeable layer on a slope or in a narrow area, and calculate the permeability coefficient from the penetration resistance to control the quality. [Background technology]

[0002] Conventionally, as a quality control technology relating to low-permeability crushed natural clay mineral material used in locations that must be permanently watertight, such as river blankets, paddy field bases, reservoirs, watertight structures at disposal sites, or overcover bases for former sites, and a method for measuring the density of such material, a quality control method for bentonite-containing watertight layers is known, for example, as described in Patent Document 1. This quality control method described in Patent Document 1 is intended to provide a low-permeability crushed natural clay mineral material of uniform quality that can be permanently watertight using a simple bearing capacity measuring device (Caspol), and a method for measuring the density of such material, since the quality varies depending on the raw soil, as it is not possible to mix the material uniformly.

[0003] The quality of a bentonite-containing impermeable layer using crushed bentonite or bentonite-mixed soil as a water impermeable layer is generally controlled by the degree of compaction and the hydraulic conductivity. For example, the degree of compaction is measured using a simple bearing capacity measuring device or an RI measuring device as shown in Patent Document 1.

[0004] The simple bearing capacity measuring device is a gravity acceleration simple compaction measuring device, but because this device measures impact using the gravity acceleration of free fall, it is practically impossible to measure unless the impacted surface is approximately horizontal. In addition, there is a problem that it cannot be used to measure on slopes or inclines. There is also a problem that it cannot be used in narrow spaces where a tripod cannot be set up.

[0005] On the other hand, RI measuring devices measure the degree of compaction by inserting a radioisotope and a source rod, but the length of the source rod is generally 20 cm or more. As a result, like the simple bearing capacity measuring device, it is not possible to measure the compaction of slopes, inclines, or thin layers of 20 cm or less. In addition, there are problems such as the measurement time taking about 30 minutes from setup to measurement, and the measurement locations being limited.

[0006] For this reason, when using these measuring devices, it is not possible to measure the penetration resistance of bentonite-containing impermeable layers on slopes or in narrow places, making quality control of the impermeable layers extremely difficult. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-130149 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above-mentioned drawbacks of conventional measuring devices, an object of the present invention is to provide a quality control method for a bentonite-containing water impermeable layer that can measure the penetration resistance of a bentonite-containing water impermeable layer even on a slope or in a narrow space, and can control the quality of the water impermeable layer. [Means for solving the problem]

[0009] In order to achieve the above object, a quality control method for a bentonite-containing water impermeable layer according to claim 1 of the present invention is a quality control method for a bentonite-containing water impermeable layer that controls the quality of a water impermeable layer that contains crushed bentonite or bentonite-mixed soil, and is characterized by comprising: an abutting step of a penetration resistance detection device that can be held by hand and includes a penetrating portion to be inserted into the water impermeable layer containing crushed bentonite or bentonite-mixed soil and a resistance detection unit that detects a penetration resistance force that the penetrating portion receives from the water impermeable layer, the penetration resistance detection device being able to be handled in a handheld state, and abutting the penetration portion against the water impermeable layer to be investigated so that the penetration portion can penetrate at a substantially right angle; a resistance detection step of inserting the penetrating portion into the water impermeable layer and detecting the penetration resistance force that the penetrating portion receives with the resistance detection unit; a permeability conversion step of receiving the penetration resistance force detected in the resistance detection step with a conversion device and converting the penetration resistance force into a permeability coefficient; and a determination step of determining whether the permeability coefficient calculated in the permeability conversion step is equal to or less than a threshold value.

[0010] The penetration resistance force detection device of the quality control method for bentonite-containing water impermeable layers according to claim 2 is characterized in that the penetration resistance force detection device comprises: a penetration portion having an increasing cross-sectional area portion in which the cross-sectional area of ​​a cross section perpendicular to the axial direction increases as the penetration portion progresses from the tip end to the base end in the axial direction, and at least the increasing cross-sectional area portion penetrates the water impermeable layer; a moving mechanism that moves the penetration portion along the axial direction to cause the penetration portion to penetrate the water impermeable layer; a housing that holds the moving mechanism; the resistance force detection unit that continuously detects the penetration resistance force that the penetration portion receives from the water impermeable layer; and an installation unit that is provided in the housing and defines a ground reference plane perpendicular to the axial direction, and the penetration portion is located inside the housing in a normal state. [Effects of the Invention]

[0011] As is clear from the above description, the present invention provides the following effects. (1) In each of the inventions described in claims 1 and 2, the penetration resistance force can be detected by the resistance force detection unit of the penetration resistance force detection device, so that the permeability coefficient of the water-impermeable layer can be easily calculated from the penetration resistance force. (2) In addition, since the penetration resistance can be measured using a penetration resistance detection device that can be handled while being held in the hand, the penetration resistance of the water-impermeable layer can be measured even on inclined surfaces such as slopes or in narrow places. Therefore, the permeability coefficient can be calculated even on inclined surfaces such as slopes or in narrow places, and the quality of the water shielding layer can be controlled. (3) Since the penetration resistance force can be measured using a penetration resistance force detection device that can be held in the hand, the penetration resistance force can be measured easily and at many measurement points in a short period of time. [Brief explanation of the drawings]

[0012] 1 to 7 are explanatory diagrams showing a first embodiment of the present invention. [Figure 1] FIG. 1 is a process diagram of a quality control method for a bentonite-containing water impermeable layer according to a first embodiment. [Figure 2] Schematic diagram of a penetration resistance force detection device. [Figure 3] FIG. 2 is a block diagram of a penetration resistance force detection device, a conversion device, and a determination device. [Figure 4] FIG. [Figure 5] Table showing the relationship between penetration resistance and compaction degree. [Figure 6] A table showing the relationship between the water content of the water-impermeable layer and the compaction density. [Figure 7] Table showing the relationship between penetration resistance and compaction density. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings showing preferred embodiments of the present invention.

[0014] In a first embodiment of the present invention shown in FIGS. 1 to 7, reference numeral 1 denotes a quality control method for a bentonite-containing water impermeable layer (hereinafter referred to as the quality control method) that can control the quality of a water impermeable layer using bentonite crushed stone or bentonite-mixed soil in a water impermeable earth structure or the like.

[0015] As shown in Figure 1, this quality control method 1 includes the following steps: an abutment step 6 in which a penetration resistance detection device 5, which can be held by hand and includes a penetration portion 3 that penetrates a water-impermeable layer 2 containing crushed bentonite or bentonite-mixed soil, and a resistance detection unit 4 that detects the penetration resistance force that the penetration portion 3 receives from the water-impermeable layer 2, is abutted against the surface of the water-impermeable layer 2 to be inspected so that the penetration portion 3 penetrates the surface at approximately right angles; a resistance detection step 7 in which the penetration portion 3 is advanced into the water-impermeable layer 2 and the resistance detection unit 4 detects the penetration resistance force that the penetration portion 3 receives; a permeability coefficient conversion step 9 in which a conversion device 8 receives the penetration resistance force detected in the resistance detection step 7 and converts the penetration resistance force into a permeability coefficient; and a determination step 11 in which a determination device 10 determines whether the permeability coefficient calculated in the permeability coefficient conversion step 9 is equal to or less than a threshold value.

[0016] In this embodiment, the penetration resistance force detection device 5 includes a penetration portion 3 having an increasing cross-sectional area portion 3a in which the cross-sectional area of ​​a cross section perpendicular to the axial direction increases as the device moves from the tip end to the base end in the axial direction, as shown in FIG. 2, and in which at least the increasing cross-sectional area portion 3a penetrates into a water-impermeable layer; a moving mechanism 12 that moves the penetration portion 3 along the axial direction to cause the penetration portion 3 to penetrate into the water-impermeable layer; a housing 13 that holds the moving mechanism 12 and the penetration portion 3; the resistance force detection unit 4 that continuously detects the penetration resistance force that the penetration portion 3 receives from the water-impermeable layer 2; and an installation unit 14 that is provided at the lower end of the housing 13 and defines a ground reference plane perpendicular to the axial direction.

[0017] The penetration part 3 is a cone-shaped part with a pointed tip, and the vicinity of the upper end part when in use is connected to the movement mechanism 12 via a resistance force detection part 4 such as a load cell.

[0018] In this embodiment, the housing 13 is a cylindrical member that is open at the bottom end when in use, with the movement mechanism 12 provided on the top end side and the penetration portion 3 provided on the bottom end side. In this embodiment, this movement mechanism 12 is made up of a ball screw mechanism 16 that is connected to a rotation source 15 so that the penetration portion 3 is synchronized with the rotation source 15, and by rotating the rotation source 15, the ball screw mechanism 16 is displaced up and down, and the penetration portion 3 is synchronized with this displacement, so that the penetration portion 3 is displaced in the up and down direction.

[0019] In addition, in a normal state (a state in which the ball screw mechanism is located at the upper limit portion and the abutment step 6 is being performed), the penetration portion 3 is located inside the cylindrical housing 13. In addition, in a normal state, the tip of the penetration portion 3 is buried inside the housing 13.

[0020] The installation portion 14 is a flange-like portion formed at the tip (lower end when in use) of the cylindrical housing 13, and by abutting this portion against the surface of the water-shielding layer 2, the penetration portion 3 is formed so as to be approximately perpendicular to the water-shielding layer 2.

[0021] This penetration resistance force detection device 5 is formed to a size and weight that allows it to be held in the hand and used, so it can detect the penetration resistance of a water-impermeable layer 2 that is in an inclined position, such as on a slope or inclined surface, or in a narrow area of ​​the water-impermeable layer 2, allowing for quality control of such areas.

[0022] In the contacting step 6, the tip of the penetration part 3 is contacted at a substantially right angle to the water-impermeable layer 2 containing crushed bentonite stone or bentonite-mixed soil that is the target of the quality control test, while the penetration resistance force detecting device 5 is held by hand, as shown in Fig. 4. Here, as described above, by contacting the installation part 14 with the surface of the water-impermeable layer 2, the penetration part 3 becomes substantially perpendicular to the water-impermeable layer 2.

[0023] In the resistance force detection step 7, the movement mechanism 12 is operated while the penetration resistance force detection device 5 is held by hand to cause the penetration part 3 to enter the water impermeable layer, and the penetration resistance force received by the penetration part 3 is detected by the resistance force detection unit 4. The detected penetration resistance force is transmitted to a conversion device 8 connected by wire or wirelessly.

[0024] FIG. 5 shows the correlation between the impact acceleration Ia and the penetration resistance force Pc measured by the penetration resistance force detector 5 and Caspol, and the correlation between the penetration resistance force detector 5 and the cone index qc.

[0025] The coefficient of determination obtained from the relationship between qc and Ia, which was measured at a total of 12 points with different water content and compaction levels, was R2 = 0.924, and the coefficient of determination for Pc and Ia using the penetration resistance force detection device 5 was R2 = 0.908, so it is thought that these measuring devices are correlated.

[0026] On the other hand, the coefficient of determination obtained from the relationship between qc and Pc was R2 = 0.800, which shows some variation compared to the former, but when Pc is 260N or less, it shows a very high correlation with R2 = 0.998.

[0027] Therefore, it can be inferred that measurements and construction management are possible using the penetration resistance force detection device 5.

[0028] The Japan Road Association's "Guidelines for Road Earthworks" state that the cone index qc required for the operation of construction machinery (dump trucks) is 1200 kN / m2 or more, whereas the impact acceleration is Ia = 12.9 and the penetration resistance force at this time is Pc = 164.7 N. In the case of the aforementioned Pc of 260 N or less, Pc = 150.3 N, so it is thought that this is within the range where the reaction force can be generated by human power.

[0029] From the above, the penetration resistance force detection device 5 can measure penetration resistance with sensitivity equal to or higher than the existing measurement outputs, such as the impact acceleration impact value and cone index.

[0030] As such, there is a high correlation with the output values ​​of conventional methods such as Caspol and cone penetration tests, and the measurement time can be measured within 10 seconds after setting, which allows for more frequent measurements and a larger sample size, improving the accuracy of quality control and making it possible to measure the penetration resistance of slopes and other inclined surfaces and narrow areas, which was previously impossible.

[0031] Furthermore, the measurement time is shorter than that of Caspol even on flat surfaces, and the measurement time can be reduced.

[0032] In the permeability coefficient conversion step 9, the conversion device 8 receives the penetration resistance force detected in the resistance force detection step 7 and calculates the permeability coefficient from this penetration resistance force. This conversion device 8 stores a conversion formula that can calculate the permeability coefficient from the compaction density, which is obtained by measuring the relationship between the permeability coefficient and compaction density in advance through a laboratory test for the soil containing bentonite used in the water barrier layer 2.

[0033] Upon receiving the penetration resistance force, the conversion device 8 first calculates the compaction density of the water shield layer 2 from the penetration resistance force.

[0034] Once the compacted density is calculated from the penetration resistance, the permeability coefficient is then calculated from the compacted density using a conversion formula derived from the relationship between the permeability coefficient and the compacted density, which was previously measured in a laboratory test.

[0035] In the determination step 11, the permeability coefficient calculated by the conversion device 8 is received by the determination device 10, which determines whether the permeability coefficient of the water shielding layer 2 satisfies a predetermined quality. The conversion device 8 and the determination device 10 may be separate devices, or the conversion and determination may be performed by an indicator 17 that includes the conversion device 8 and the determination device 10, as in this embodiment.

[0036] The determining device 10 stores an upper limit value of the permeability coefficient determined for each structure forming the water-blocking layer 2, and determines whether the permeability coefficient calculated by the conversion device 8 is below this upper limit value, which is used as a threshold value. Note that the permeability coefficient is an index that indicates the amount of water that passes through per second, so if it is below the upper limit value, it means that water is less likely to permeate (good water-blocking properties).

[0037] The hydraulic conductivity is judged by the judgment device 10, and if it is below the upper limit, it displays that the hydraulic conductivity is good, and if it is above the upper limit, it displays that it is unsuitable. This display can be changed as appropriate, and it is sufficient if it allows the administrator or the like to determine whether the hydraulic conductivity meets the threshold value (below the upper limit).

[0038] Regarding the permeability coefficient conversion process 9 and the determination process 11, the greater the compaction density of the water-blocking layer 2, the lower the permeability coefficient. This is because the denser the soil, the smaller the voids between the soil particles, and when it comes into contact with water, it swells and blocks the voids, thereby blocking water. Furthermore, water is trapped between the bentonite crystals in the bentonite plate-like crystalline structure, which acts as a water barrier. These two water-blocking mechanisms are used to block water.

[0039] To compact crushed bentonite, an appropriate range of moisture content is found. If the moisture content is too low, it will be fluffy and difficult to compact, but if the moisture content is too high, it will be sticky and difficult to compact.

[0040] Therefore, a cone index of 1,200KN / m2 or higher, as indicated by the cone penetration test, is empirically considered to have good trafficability and is strong enough for compaction machines and large dump trucks to pass through, so this index is used as the basis for determining ease of compaction.

[0041] For example, if the results of a permeability test for crushed bentonite or bentonite-mixed soil at a compaction density Dc of 85% indicate a permeability coefficient of 3.6 x 10-11 m / sec, as shown in Figure 6, the degree of compaction of the crushed bentonite will vary depending on the water content, and will reach its highest value at the optimum water content, based on the penetration resistance measured by the penetration resistance detection device 5 of the water impermeable layer containing the crushed bentonite and the compaction density for each water content.

[0042] If the penetration resistance is 270.5N or more, the compaction density Dc is certainly 85% or more, and it can be determined that the impermeable layer satisfies the permeability coefficient of 3.6 x 10-11 m / sec. Furthermore, when the compaction density is 90%, the permeability coefficient is 2.0 x 10-11 m / sec, and the more compacted it is, the lower the permeability coefficient becomes, becoming more on the safe side. Figure 7 shows the maximum penetration resistance value for each degree of compaction, which is used as the calibration curve and as an on-site index, the threshold value for quality control. [Industrial Applicability]

[0043] The present invention is used in industries that perform quality control of water barrier layers of earth structures. [Explanation of symbols]

[0044] 1: Quality control method for bentonite-containing water barrier layers, 2: Water impermeable layer, 3: Penetration part, 4: Resistance force detection unit, 5: Penetration resistance force detection device, 6: contact step, 7: resistance force detection step, 8: Conversion device; 9: Permeability coefficient conversion step; 10: Determination device, 11: Determination process, 12: moving mechanism; 13: housing; 14: installation portion; 15: rotation source; 16: Ball screw mechanism, 17: Indicator.

Claims

1. 1. A quality control method for a bentonite-containing water impermeable layer that controls the quality of a water impermeable layer containing crushed bentonite or bentonite-mixed soil, the quality control method comprising: a contacting step of contacting a penetration resistance detection device that can be held by hand, the penetration resistance detection device including a penetrating portion to be inserted into the water impermeable layer containing crushed bentonite or bentonite-mixed soil and a resistance detection unit that detects a penetration resistance force that the penetrating portion receives from the water impermeable layer, the penetration resistance detection device being capable of being handled in a handheld state, so that the penetrating portion can penetrate the water impermeable layer at a substantially right angle; a resistance detection step of inserting the penetrating portion into the water impermeable layer and detecting the penetration resistance force that the penetrating portion receives with the resistance detection unit; a permeability conversion step of receiving the penetration resistance force detected in the resistance detection step with a conversion device and converting the penetration resistance force into a permeability coefficient; and a determination step of determining whether the permeability coefficient calculated in the permeability conversion step is equal to or less than a threshold value.

2. The penetration resistance force detection device includes: a penetration portion having an increasing cross-sectional area portion in which the cross-sectional area of ​​a cross section perpendicular to the axial direction increases as the penetration portion progresses from the tip end side to the base end side in the axial direction, and at least the increasing cross-sectional area portion penetrates the water-impermeable layer; a movement mechanism that moves the penetration portion along the axial direction to cause the penetration portion to penetrate the water-impermeable layer; a housing that holds the movement mechanism; the resistance force detection unit that continuously detects the penetration resistance force that the penetration portion receives from the water-impermeable layer; and an installation unit that is provided in the housing and defines a ground reference plane perpendicular to the axial direction; 2. The quality control method for a bentonite-containing water impermeable layer according to claim 1, wherein the penetration portion is located inside the housing under normal conditions.

Images