Air force-feed tester for soil layer, and air force-feed test method for soil layer

Abstract

To provide an air force-feed tester for a soil layer and an air force-feed test method for a soil layer which enable ground investigation to be carried out easily even on a slope.SOLUTION: An air force-feed tester for a soil layer comprises: an air force-feed pipe 2 having an air inlet port 21b at the top and an air outlet hole 22b at the bottom; a pump 3 for force-feeding air to the air inlet port 21b; and a pressure gauge 4 for measuring air pressure in the soil layer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an air blowing test device for a soil layer and an air blowing test method for a soil layer, which are used in ground surveys to grasp the properties of the soil layer. [Background technology]

[0002] In order to construct appropriate slope stabilization works on slopes, it is necessary to understand the properties of the soil layer at the surface of the slope in advance. For this reason, various ground investigation methods are applied to slopes.

[0003] As an example of such a ground investigation method, a simplified dynamic cone penetration test (JGS-1433, Geotechnical Society) has been conventionally applied, as shown in Non-Patent Document 1. In the simplified dynamic cone penetration test, a hammer with a mass of 5±0.05 kg is allowed to freely fall from a height of 500±10 mm to transmit the impact energy of the hammer to a rod, causing the rod to penetrate vertically, and information on the strength and strength distribution of the ground is obtained from the relationship between the amount of penetration and the number of blows.

[0004] As an example of such technology, the Civil Engineering Research Institute automatic penetration tester shown in Patent Document 1 has been developed. The Civil Engineering Research Institute automatic penetration tester shown in Patent Document 1 lifts a weight with an engaging piece of a chain that is rotated endlessly by a drive motor attached to the main body of the tester, and releases the weight at the top to allow the weight to fall freely, driving a penetration bar into the soil with the impact of the falling weight, while also counting the number of drives and displaying the accumulated value.

[0005] As another example of a ground investigation method, a single-hole permeability test (JGS-1314, Geotechnical Society) has been used in the past, as shown in Non-Patent Document 2. A single-hole permeability test is one of the in-situ permeability tests, which uses a single borehole to find the permeability coefficient of the ground, and there are steady-state and non-steady-state tests.

[0006] Among these, the non-steady-state permeability test determines the permeability coefficient by temporarily lowering or raising the water level in the borehole and measuring the change in the water level over time until it returns to the equilibrium water level. Non-steady-state permeability tests include the piezometer method (casing method), tube method, and auger method, and the piezometer method has two types of measurement methods: the recovery method and the water injection method.

[0007] The recovery method involves inserting a casing pipe into the borehole to prevent groundwater from flowing into the hole from above the test section of the permeability test, then removing slime from the hole, cleaning the hole, pumping water from the hole using a pump or other device, measuring the change in water level over time as the water level drops to the equilibrium water level, and determining the permeability coefficient. On the other hand, the water injection method involves injecting water into the borehole, measuring the change in water level over time as the water level drops to the equilibrium water level, and determining the permeability coefficient.

[0008] As a technique for conducting a permeability test using such a non-steady method, for example, an in-situ permeability test method and a permeability test device have been developed as shown in Patent Document 2. The in-situ permeability test method and the permeability test device shown in Patent Document 2 insert a rod-shaped body and a pressure gauge attached to one end of an electric signal lead wire passing axially through the inside of the rod-shaped body into water in a casing pipe, and measure the change in the water level over time while the water level, which has risen due to the insertion, falls to the equilibrium water level, using the pressure gauge to determine the permeability coefficient, or insert the rod-shaped body and the electric pressure gauge into water in a casing pipe, and after the water level, which has risen due to the insertion, falls to the equilibrium water level, only the rod-shaped body is pulled up, and the change in the water level over time while the water level, which has fallen due to the pulling up of the rod, rises to the equilibrium water level, using the pressure gauge to determine the permeability coefficient. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP-A-7-113733 (pages 2-3, FIG. 1) [Patent Document 2] JP-A-9-88051 (pages 5-6, Figs. 6 and 7) [Non-patent literature]

[0010] [Non-Patent Document 1] "Methods and Explanations of Ground Investigation" by the Geotechnical Society of Japan, revised 4th edition published on March 25, 2020 (pages 317-323, Geotechnical Society of Japan Standards: Simplified Dynamic Cone Penetration Test Method) [Non-Patent Document 2] "Methods and Explanations of Ground Investigation" by the Geotechnical Society of Japan, revised 4th edition published on March 25, 2020 (pages 515-531, Geotechnical Society of Japan Standards: Permeability Test Methods Using a Single Hole) Summary of the Invention [Problem to be solved by the invention]

[0011] The PWB-type automatic penetration tester shown in Patent Document 1 is effective in that it can reduce the burden on the worker because the penetration bar can be automatically driven into the ground by the weight operated by the drive motor as long as the worker holds the tester while maintaining its verticality. However, there is a problem that it is often difficult for the worker to hold the tester while maintaining the verticality of the penetration bar on a slope because the footing is unstable on a slope. In addition, there is a problem that the worker has to bear a lot of burden in transporting a tester with a weight on a slope.

[0012] The in-situ permeability test method and permeability test device shown in Patent Document 2 are effective in that they can perform permeability tests by the water injection method and the recovery method by inserting a rod-shaped body and a pressure gauge into a casing pipe, eliminating the need to procure water injection equipment and water, and to pump water from inside the casing pipe. However, the permeability test shown in Patent Document 2 requires a boring machine to open boreholes, which is problematic in that it is often difficult to perform permeability tests at many measurement points on slopes.

[0013] The present invention has been made in consideration of these problems, and aims to provide an air pumping test device for soil layers and an air pumping test method for soil layers that can easily conduct ground investigations even on sloping ground. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides a soil layer air blowing tester, This device is characterized by comprising an air pressure delivery pipe with an air inlet at the top and an air outlet hole at the bottom, a pump that pressure-feeds air to the air inlet, and a pressure gauge for measuring the air pressure in the soil layer. According to this feature, the air pressure pipe can be inserted into the soil layer from any direction, not necessarily vertically, and the air pressure within the soil layer can be measured, making it easy to conduct ground surveys to understand the properties of the soil layer even on sloping ground with poor footing.

[0015] The air pressure supply pipe is characterized in that a sharp tip is provided at the lower end thereof, and the air supply hole is provided at the sharp tip. According to this feature, since the lower end of the air pressure delivery pipe is sharpened, it is easy to penetrate the air pressure delivery pipe into the soil layer.

[0016] The tip is characterized in that it is formed by an oblique flat surface. According to this feature, the air is pumped in a direction intersecting the direction of the air pump pipe in the soil layer, so that leakage of the pumped air from the boundary between the side of the pipe and the surrounding ground is suppressed. Also, the pressure of the pumped air makes it difficult for the air pump pipe to come out of the soil layer.

[0017] The air delivery hole is characterized in that it is provided on the side surface of the lower end of the air pressure delivery pipe. According to this feature, the air blowing holes can be prevented from being blocked by soil when penetrating into the soil layer.

[0018] The air inlet is provided on a side surface of the air pressure delivery pipe. According to this feature, since a force can be applied to the upper end of the air pressure delivery pipe, it becomes easier to penetrate the air pressure delivery pipe into the soil layer.

[0019] The air pump is characterized in that an anvil is provided at the upper end of the air pump pipe for transmitting impact energy to the air pump pipe. According to this feature, by striking the anvil with a hammer or the like, striking energy can be efficiently transmitted to the air pressure feeding pipe, making it easier to penetrate the air pressure feeding pipe further into the soil layer.

[0020] In order to solve the above problems, the soil layer air pumping test method of the present invention comprises: The method is characterized in that the lower end of an air pressure pipe is inserted into the soil layer, air is pumped from the lower end of the air pressure pipe into the soil layer using a pump, and the air pressure inside the soil layer is measured using a pressure gauge, thereby estimating the properties of the soil layer. According to this feature, since only the air pressure needs to be measured on-site, it is possible to easily estimate at least one of the properties of a soil layer, including permeability coefficient, dry density, void ratio, degree of saturation, and fine particle mass percentage, even on sloping land.

[0021] The property of the soil layer is estimated based on whether the soil is fine-grained or coarse-grained, in addition to the air pressure. According to this feature, the properties of the soil layer can be accurately estimated by selecting at least one of the soil properties, which are highly correlated with air pressure, from among the permeability coefficient, dry density, void ratio, degree of saturation, and fine particle mass percentage, depending on whether the soil is fine-grained or coarse-grained at the site.

[0022] The soil layer is fine-grained soil, and the properties of the soil layer are characterized by at least one of dry density and degree of saturation. According to this feature, since there is a stronger correlation between maximum air pressure and dry density and degree of saturation in fine-grained soil, it is possible to accurately estimate the properties of at least one of the soil layers, namely dry density and degree of saturation, on sloping land consisting of fine-grained soil.

[0023] The soil layer is characterized in that it is a coarse-grained soil, and the property of the soil layer is the hydraulic conductivity. According to this feature, since the correlation between maximum air pressure and permeability coefficient is more pronounced in coarse-grained soil, the permeability coefficient, which is one of the properties of a soil layer, can be accurately estimated in sloping land consisting of coarse-grained soil. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram showing an air-feeding tester in Example 1 of the present invention. [Diagram 2] FIG. 1 is a perspective view showing a pressurized air-feeding pipe constituting a pressurized air-feeding tester in Example 1 of the present invention. [Diagram 3] FIG. 2 is a diagram showing measurement points in an air pressure feeding test. [Figure 4] FIG. 4 is a schematic diagram showing a method for measuring air pressure. [Diagram 5] FIG. 11 is a diagram showing the measurement results at each measurement point. [Figure 6] FIG. 1 is a schematic diagram showing the steps of a method for collecting soil samples. [Figure 7] FIG. 13 is a diagram showing the correlation between maximum air pressure and ground constant. [Figure 8] FIG. 13 shows a scatter plot and linear regression of maximum pressure values ​​and each ground constant using all samples. [Figure 9] FIG. 13 shows a scatter plot and linear regression of maximum pressure values ​​and each ground constant using fine-grained soil samples. [Figure 10] FIG. 13 shows a scatter plot and linear regression of maximum pressure values ​​and each ground constant using coarse soil samples. [Figure 11] FIG. 1 shows measurement locations on the surface layer of clayey soil. [Figure 12] FIG. 13 is a diagram showing the relationship between air pressure and measurement time at a measurement point on the surface layer of clayey soil. [Figure 13] FIG. 11 is a schematic diagram for explaining an earthen tank experiment in Example 2 of the present invention. [Figure 14] FIG. 13 is a graph showing time-air pressure curves obtained in a soil tank experiment. [Figure 15] FIG. 13 is a diagram showing a scatter diagram and linear regression of maximum air pressure and degree of compaction using model ground. [Figure 16] FIG. 13 is a diagram showing the correlation between maximum air pressure and ground constants using a model ground. [Figure 17] FIG. 13 is a perspective view showing a modified example of the air pressure feeding pipe. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment for carrying out the soil layer air blowing test device and soil layer air blowing test method according to the present invention will be described below with reference to the examples. EXAMPLES

[0026] A soil layer air blowing test device and a soil layer air blowing test method according to a first embodiment will be described with reference to Figs.

[0027] The air pumping tester 1 of the present invention is used for ground surveys to grasp the properties of the surface layer of the ground, and estimates the ground constants by penetrating an air pumping pipe 2 into the ground Gs, pumping air into the ground from a pump 3 connected to the air pumping pipe 2, and measuring the maximum air pressure.

[0028] As shown in FIG. 1, the air pressure delivery tester 1 is mainly composed of an air pressure delivery pipe 2, a pump 3 connected to the air pressure delivery pipe 2, and a pressure gauge 4 also connected to the air pressure delivery pipe 2.

[0029] 2, the pressurized air sending pipe 2 is composed of a hollow pipe made of stainless steel. Note that the material of the pressurized air sending pipe 2 is not limited to stainless steel, and it may be freely changed to a material such as resin.

[0030] The air pressure delivery pipe 2 in this embodiment is configured by vertically connecting the female threaded portion 21c of the upper split pipe 21 and the male threaded portion 22c of the lower split pipe 22 by screwing them together. If it is desired to increase the penetration depth of the air pressure delivery pipe 2 into the ground Gs, the length of the air pressure delivery pipe 2 can be changed by connecting an additional air pressure delivery pipe (not shown) between the upper split pipe 21 and the lower split pipe 22 by screwing them together.

[0031] Incidentally, the air pressure sending pipe 2 is not limited to a divided structure, but may be made up of a single member.

[0032] 1 and 2, a sharpened portion 22A that tapers downward is formed at the lower end of the lower split pipe 22. This sharpened portion 22A is composed of a flat inclined surface 22a. This makes it easier to insert the air pressure delivery pipe 2 into the ground Gs.

[0033] In this embodiment, three air outlet holes 22b are provided on the inclined surface 22a. This allows the air pressurized by the pump 3 (described later) to be delivered to the ground. The number, size, shape, etc. of the air outlet holes 22b may be freely changed.

[0034] A hose 6 extending from the pump 3 is connected in a sealed manner to the inner diameter side of the male thread portion 22c provided at the upper end portion of the lower split pipe 22.

[0035] An anvil 21a is provided at the upper end of the upper split pipe 21. The anvil 21a is a part that is struck with a hammer or the like when the air pressure feeding pipe 2 is penetrated into the ground, and is a stainless steel plate material that is generally circular in plan view and thicker than the plate thickness of the side wall that constitutes the upper split pipe 21. By providing the anvil 21a, striking energy can be efficiently transmitted to the air pressure feeding pipe 2, making it easier to penetrate the air pressure feeding pipe 2 into the ground Gs. The shape of the anvil 21a can be freely changed. Furthermore, the anvil 21a is not limited to being made of stainless steel, and may be freely changed to a material such as resin, and the shape may also be freely changed.

[0036] An air inlet 21b is provided on a side surface near the upper end of the upper split pipe 21. The air inlet 21b is for inserting a hose 6 extending from the pump 3 into the air pressurized feeding pipe 2. The hose 6 extending from the pump 3 passes through the air inlet 21b and the upper split pipe 21, and is connected to the inner diameter side of the male thread portion 22c of the lower split pipe 22.

[0037] Returning to Fig. 1, the pump 3 pumps air into the ground. In this embodiment, a rechargeable air pump MP100D manufactured by Makita Corporation, which is an electric pump, is used as the pump. Note that a manual pump may be used as the pump instead of the electric pump.

[0038] The pressure gauge 4 is connected to a branch hose 7 that branches off from the hose 6. The pressure gauge 4 measures the pressure of the air pumped into the ground. In this embodiment, a high-precision digital pressure gauge KDM30 manufactured by Krone Corporation is used as the pressure gauge.

[0039] Moreover, the pressure gauge 4 transmits the measured air pressure by wireless communication. A personal computer or a mobile terminal that receives this signal records the air pressure over time, and it is possible to confirm the air pressure of the air pumped from the pump 3 to the ground and the change over time of the air pressure measured by the pressure gauge 4. In this embodiment, the pressure gauge 4 is wirelessly connected to the terminal, but a wired connection is also possible. Also, the pressure gauge 4 may transmit the measured air pressure to a cloud server, record the air pressure over time on the cloud server, and access the cloud server from the terminal via an Internet line to confirm the air pressure of the air pumped to the ground and the change over time of the air pressure.

[0040] Next, the air pressure feeding test method will be described.

[0041] As shown in Fig. 3, the slope to be measured in this example is a slope in the Tano Field of the Field Science Education and Research Center attached to the Faculty of Agriculture, University of Miyazaki, in Tano Town, Miyazaki City, Miyazaki Prefecture. According to the legend of the seamless geological map provided by the Geological Survey of Japan, National Research and Development Agency, National Institute of Advanced Industrial Science and Technology, the geology of the slope to be measured is confirmed to be sandstone deposited in the Tertiary Period of the Cenozoic Era. The slope to be measured faces approximately northwest, and the slope gradient is approximately 20° to 35°. Collapsed soil caused by rainwater surface runoff has accumulated in part of the slope to be measured.

[0042] On the slope to be measured, four side lines, numbered No. 1 to No. 4, were set up along the contour lines. Measurements were taken at approximately 1m intervals on each side line. The measurement points on each side line were numbered No. 1-1 to 6 on side line No. 1, No. 2-1 to 10 on side line No. 2, No. 3-1 to 8 on side line No. 3, and No. 4-1 to 13 on side line No. 4, for a total of 37 points. The number of measurement points differs for each side line because measurements were taken in locations where footholds could be secured.

[0043] Next, a method for measuring the air pressure in the ground at each measurement point will be described. As shown in FIG. 4, first, the sharp tip 22A of the air pressure pipe 2 is grounded at the measurement point of the sloping ground, and the anvil 21a is struck with a hammer to penetrate the sharp tip 22A of the air pressure pipe 2 into the ground Gs to a desired depth. In this embodiment, the air pressure pipe 2 is penetrated to a depth of 40 to 50 cm from a direction approximately normal to the ground surface. The air pressure pipe 2 does not necessarily need to be penetrated into the ground Gs from a vertical direction, and can be penetrated from any direction, so that it can be easily penetrated even in sloping ground.

[0044] Next, the pump 3 is operated to pump air into the ground from the air outlet hole 22b through the inside of the air pumping pipe 2. Next, while checking the air pressure on the screen of the personal computer connected to the pressure gauge 4, the pumping of air continues until the maximum air pressure is measured, and after the maximum air pressure is reached, the pumping of air stops. As another example, the measurement may be terminated when the measured value reaches or exceeds the pressure that is the maximum capacity of the pump 3. In this case, the air pressure in the ground at that measurement point is evaluated to be equal to or greater than the maximum capacity value of the pump 3.

[0045] This allows obtaining the maximum air pressure of the air stored inside the ground and the change over time in pressure dissipation from the maximum air pressure, so that the correlation between the maximum air pressure and the ground constants, or the correlation between the change over time in pressure dissipation and the ground constants, can be examined and a relational equation can be obtained. Figure 5 shows the maximum air pressure (shown as "peak pressure" in Figure 5) at each measurement point. Note that, although this embodiment describes an example in which the relational equation is obtained using the maximum air pressure, the air pressure used is not limited to the maximum.

[0046] Next, the method of collecting soil samples from the ground at each measurement point will be described. After the air pressure pipe 2 is inserted 40 cm into the ground and air pressure is pumped (see FIG. 6(a)), the air pressure pipe 2 is pulled out from the ground, and the hole created by the pulling out is excavated concentrically using the auger 8. The excavation depth at this time is 40 cm, and the diameter of the excavated hole is about 6 cm (see FIG. 6(b)). Next, the soil sampler 10 with a 5 cm diameter sample mold 9 attached to its tip is inserted until it touches the bottom of the hole (see FIG. 6(c)). Next, the top of the soil sampler 10 is struck to penetrate the sample mold 9 into the ground, and then the soil sampler 10 is pulled out, and a soil sample with little disturbance is collected in the sample mold 9 (see FIG. 6(d)). Next, the auger 8 is inserted into the hole again, excavates the bottom and is pulled up, and the disturbed soil sample attached to the rotor of the auger 8 is collected (see FIG. 6(e)). The excavation and pulling up by the auger 8 is repeated several times until a soil sample of a quantity required for measuring the soil constants is obtained.

[0047] The sample collected in the sample collection mold 9 was used to measure density (JIS A 1225) because its volume can be considered to be equivalent to the internal volume of the mold. It was then attached to a variable head permeability tester (DIK-4050) made by Daiki Rika Kogyo Co., Ltd., and the hydraulic conductivity was measured. The natural moisture content, density of soil particles, and particle size distribution were measured from the sample collected from the rotor of the auger 8. Experiments were carried out in accordance with JIS A 1203, JIS A 1202, and JIS A 1204, respectively. Based on these, the wet density, dry density, void ratio, degree of saturation, and fine particle mass percentage (shown as "fine particle" in Figure 5) were calculated. These results are shown in Figure 5.

[0048] For No. 3-1 to 3-5, the mass of the samples in the mold could not be measured, and the wet density, dry density, void ratio, and degree of saturation could not be calculated. For No. 1-4 to 1-6, No. 3-1 to 3-8, No. 4-4, 4-7, and 4-10, the collected soil samples were used up, and the density of the soil particles could not be measured, so measurements were made using the samples in the mold and the median value of the actual measurements was provisionally adopted. For No. 1-4 and No. 2-9, a measurement error resulted in the degree of saturation exceeding 100%. Furthermore, the sample for No. 2-2 was very fragile, and a permeability test could not be performed.

[0049] Next, the correlation between the maximum air pressure (maximum pressure value) and soil constants (permeability coefficient, dry density, void ratio, degree of saturation, and fine particle mass percentage) was investigated.

[0050] The measured values ​​and experimental results summarized in Figure 5 were plotted in a scatter diagram with the physical properties for which correlations were to be confirmed and the maximum pressure values, and a regression equation and correlation coefficient were obtained by linear regression. The results are shown in Figure 7. The scatter diagrams are also shown in Figures 8 to 10.

[0051] Figures 8(a), 9(a), and 10(a) show scatter plots of the maximum pressure value and the hydraulic conductivity, Figures 8(b), 9(b), and 10(b)1 show scatter plots of the maximum pressure value and the dry density, Figures 8(c), 9(c), and 10(c) show scatter plots of the maximum pressure value and the void ratio, Figures 8(d), 9(d), and 10(d) show scatter plots of the maximum pressure value and the degree of saturation, and Figures 8(e), 9(e), and 10(e) show scatter plots of the maximum pressure value and the fines mass percentage.

[0052] As shown in Figures 7 and 8, the maximum correlation coefficient of regression for all samples was 0.28838, and the correlation between the maximum pressure value and the soil constants was not necessarily high. Therefore, the inventors focused on the grain size and attempted to separate the soil into fine grained soil and coarse grained soil.

[0053] As shown in Figures 7 and 9, when the correlation between the maximum pressure value and each ground constant was examined for fine-grained soil, the correlation coefficient between the maximum pressure value and the degree of saturation (0.51172) was the highest (see Figure 9(d)). The correlation coefficient between the maximum pressure value and the dry density (0.50397) was also the second highest (see Figure 9(b)).

[0054] As shown in Figures 7 and 10, when the correlation between the maximum pressure value and each ground constant was examined for coarse-grained soil, the correlation coefficient (0.44453) between the maximum pressure value and the hydraulic conductivity was the largest (see Figure 10(a)).

[0055] In addition, when measurements were taken at the surface layer of the slope (see Fig. 11), which is made of clay and has a different soil quality from the measurement points shown in Fig. 3, the air pressure was as shown in Fig. 12. The maximum air pressure was about 700 to 900 kPa.

[0056] The soil at the measurement point shown in Figure 3 contains about 20 to 50% gravel even in fine-grained soil, but the measurement point in Figure 11 contains almost no gravel. The wet density of the sample is 2.991 g / cm 3 The hydraulic conductivity was 2.1×10 -7The value was extremely low at only cm / sec, more than one order of magnitude lower than the measured value in Figure 5. Therefore, the maximum air pressure was also approximately 250 kPa at the measurement point in Figure 3, but approximately 700-900 kPa at the measurement point in Figure 11. From the above, it was found that the measurement of maximum air pressure makes it possible to distinguish between clayey soil containing almost no gravel and other soils.

[0057] As described above, the air pressure delivery tester 1 can penetrate the air pressure delivery pipe 2 into the soil layer from any direction, not necessarily vertically, and measure the air pressure within the soil layer to grasp the properties of the soil layer, making it possible to easily conduct ground surveys to grasp the properties of the soil layer even on sloping ground with poor footing.

[0058] In addition, since the lower end of the air pressure delivery pipe 2 is formed into the sharp tip 22A, the air pressure delivery pipe 2 can be easily inserted into the soil layer.

[0059] In addition, the sharpened portion 22A is formed by an inclined flat surface, i.e., an inclined surface 22a, and since the inclined surface 22a is formed with the air delivery holes 22b, the air is delivered in a direction intersecting the direction of the penetration of the air delivery pipe 2 in the soil layer, and the leakage of the delivered air from the boundary between the side surface of the pipe and the surrounding ground is suppressed. Also, the pressure of the delivered air makes it difficult for the air delivery pipe 2 to come out of the soil layer.

[0060] Also, the air inlet 21b is provided on the side surface of the pressurized air feeding pipe 2. This allows a force to be applied to the upper end of the pressurized air feeding pipe 2, making it easier to penetrate the pressurized air feeding pipe 2 into the soil layer.

[0061] In addition, an anvil 21a for transmitting impact energy to the air pressure delivery pipe 2 is provided at the upper end of the air pressure delivery pipe 2, and by striking the anvil 21a with a hammer or the like, the impact energy can be efficiently transmitted to the air pressure delivery pipe 2, making it easier to penetrate the air pressure delivery pipe 2 further into the soil layer. In addition, the anvil 21a is thicker than the plate thickness of the side surface of the air pressure delivery pipe 2 and has high strength, so it will not be damaged by being struck by a hammer or the like.

[0062] In addition, in the air pressure test method using the air pressure tester 1, the lower end of the air pressure pipe 2 is inserted into the soil layer and only the air pressure is measured, so that the soil layer properties such as the permeability coefficient, dry density, void ratio, saturation degree, fine grain mass percentage, etc. can be easily estimated even on a slope. Measuring the change in pressure over time (chronological change) as in this embodiment is preferable because it allows evaluation of various soil layers. In this embodiment, the form of measuring the maximum air pressure is mainly exemplified, but as described above, the change in air pressure over time may be measured, and the relationship between the maximum capacity value of the discharge pressure of the pump 3 and the measured air pressure may be specified. When the maximum capacity value of the discharge pressure of the pump 3 is used as in this embodiment, the configuration of the air pressure tester is simple, which is preferable.

[0063] In addition to the maximum air pressure, by selecting the properties of the soil layer to be estimated depending on whether it is fine-grained or coarse-grained soil, it is possible to accurately estimate at least one or more of the properties of the soil layer, including the permeability coefficient, dry density, void ratio, degree of saturation, and fine particle mass percentage.

[0064] For example, in fine-grained soil, there is a stronger correlation between maximum air pressure and dry density and degree of saturation, so it is possible to accurately estimate the properties of at least one of the soil layers, namely dry density and degree of saturation, on sloping land consisting of fine-grained soil.

[0065] Furthermore, since there is a stronger correlation between maximum air pressure and permeability coefficient in coarse-grained soil, the permeability coefficient, which is one of the properties of a soil layer, can be accurately estimated on sloping land consisting of coarse-grained soil. EXAMPLES

[0066] Next, a soil layer air pressure delivery test device and a soil layer air pressure delivery test method according to Example 2 will be described with reference to Figures 13 to 16. Note that the same components as those shown in Example 1 are designated by the same reference numerals and duplicated descriptions will be omitted.

[0067] As shown in Figure 13, in this Example 2, in order to obtain the relationship between the pressure value during air pumping and the degree of compaction, a soil tank experiment was conducted in an indoor laboratory using the air pumping tester 1 of Example 1, an experimental soil tank 100, and a model ground 101.

[0068] The experimental soil tank 100 is made of three acrylic cylinders stacked vertically and connected in a sealed manner to prevent air leakage. Each cylinder has a thickness of 11 mm, a diameter of 230 mm, and a height of 250 mm.

[0069] Decomposed granite soil was used as the soil sample for the model ground 101. The decomposed granite soil used is classified as gravel-mixed fine-grained sand (SF-G) with a fine content Fc of 20.3% and an optimum water content wopt of 13.8%. The model ground 101 was created by spreading this decomposed granite soil in the experimental soil tank 100 to a thickness of about 2 to 4 cm and compacting it with a rammer weighing 4.1 kg. In the soil tank experiment of this embodiment, four types of model ground 101 with different degrees of compaction Dc (Dc = 55%, 65%, 75%, 85%) were created.

[0070] Here, the permeability radius for negative pressure propagation is said to be 10 to 20 m for sandy soil. In the main soil tank experiment, the diameter of the experimental soil tank 100 was 23 cm, and although the influence of its walls was expected, the primary aim was to understand the correlation between the degree of compaction and air pressure as ground constants by measuring them under the same conditions.

[0071] In the soil tank experiment, the center of the plan view of the model ground 101 was used as the measurement point, and the air pressure pipe 2 of the pressure tester 1 was struck vertically downward to penetrate the soil tank. The measurement point was the point where the tip of the air pressure pipe 2 reached the midpoint of the experimental soil tank 100, at a depth of 375 mm (see dashed line in Figure 13).

[0072] After reaching the measurement location, the pump 3 was operated to pump air into the model ground 101 through the inside of the air pumping pipe 2, and after the maximum air pressure was measured as in Example 1, the air pumping was stopped.

[0073] The measurements according to the above-mentioned procedure were performed five times on the model ground 101 with each degree of compaction, and the average pressure value for each degree of compaction was calculated based on the obtained pressure values ​​(see FIG. 14). Note that the model ground 101 was prepared by breaking it and compacting it again after each measurement.

[0074] As shown in Fig. 14, in the soil tank experiment, the average maximum air pressure was highest at 486 kPa when the compaction degree of the model ground 101 was Dc = 85%. Also, the average maximum air pressure was lowest at 35.8 kPa when the compaction degree was Dc = 55%. The difference between these was about 450 kPa.

[0075] Furthermore, almost no variation was observed in the five pressure values ​​measured when the compaction degree of the model ground 101 was Dc=55%. On the other hand, it was found that the variation in the pressure values ​​obtained from the five measurements increased as the compaction degree increased. This is thought to be because, when the resistance from the model ground 101 increases during penetration, the number of strikes against the air pressure supply pipe 2 increases, causing disturbances and gaps around the air pressure supply pipe 2 in the model ground 101, resulting in variation in the condition of the model ground 101 for each measurement.

[0076] In the soil tank experiment, a model ground with a compaction degree Dc=95% was prepared and the above-mentioned measurements were performed, but the maximum pressure value was 472 kPa and the average maximum pressure value was 392 kPa, both of which were lower than the values ​​obtained when the compaction degree Dc=85%. One of the causes of this is surface cracks that occurred on the soil layer surface when the air pressure pipe 2 was penetrated into the soil layer surface. Since the grain size of the decomposed granite soil used in the soil tank experiment is almost constant, the model ground with Dc=95% became a very hard soil layer due to the gaps becoming very dense due to compaction. It is considered that the driving of the air pressure pipe 2 into the soil layer caused widespread cracks on the soil layer surface, and the air escaped from these cracks, which reduced the maximum pressure value.

[0077] As shown in Figure 15, a scatter plot of the degree of compaction and the maximum pressure value was created, and the slope and correlation coefficient of the regression equation were obtained by linear regression. In the same way, the slope and correlation coefficient of the regression equation were obtained for other soil constants (degree of saturation, void ratio, air void ratio) and the maximum pressure value. These are summarized in Figure 16.

[0078] As shown in Figure 16, the highest correlation was obtained with the degree of saturation, at 0.93. The slopes of the regression equations for the degree of saturation and the degree of compaction are both positive, while the slopes for the void ratio and air void ratio are negative. From the above, it was found that the smaller the voids in the soil become, the higher the air pressure becomes, and that the air pressure increases as the degree of compaction increases.

[0079] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0080] For example, in the above-mentioned first and second embodiments, the sharpened portion is formed by an oblique flat surface, but it may be formed by a curved surface, a bent surface, etc. Furthermore, although the configuration in which the sharpened portion is provided at the lower end of the air pressure feeding pipe has been described as an example, the lower end may not be provided with a sharpened portion and may be a flat surface.

[0081] In the first and second embodiments, the air outlet holes are provided on the lower surface of the air pressure delivery pipe. However, the air outlet holes may be provided on the lower surface and the side surface of the air pressure delivery pipe, or only on the side surface.

[0082] 17, air delivery holes 220b may be provided at the lower end of the pressurized air delivery pipe 200, i.e., on the side surface of the lower divided pipe 220. With this, since the air delivery holes 220b open in a direction substantially perpendicular to the direction in which the pressurized air delivery pipe 200 penetrates, it is possible to prevent the air delivery holes 220b from being blocked by soil when the pressurized air delivery pipe 200 is penetrated into the soil layer. [Explanation of symbols]

[0083] 1. Air pressure tester 2. Air pump pipe 3. Pump 4. Pressure gauge 5 Data Logger 6 Hose 7 Branch Hose 8 Auger 9. Sampling mold 10. Pottery Sampler 11 Lead Wire 21 Upper split pipe 21a Anvil 21b Air inlet 22 Lower split pipe 22A Sharp tip 22a Slope 22b Air outlet hole

Claims

1. An air pressure pumping tester for soil layers, comprising: an air pressure pumping pipe having an air inlet at the top and an air outlet hole at the bottom; a pump for pumping air to the air inlet; and a pressure gauge for measuring the air pressure in the soil layer.

2. 2. The soil layer air pressure delivery tester according to claim 1, wherein a sharp tip is provided at a lower end of said air pressure delivery pipe, and said air delivery hole is provided at said sharp tip.

3. 3. The soil layer air blowing tester according to claim 2, wherein said sharp tip is formed by an inclined flat surface.

4. 2. The soil layer air pressure delivery tester according to claim 1, wherein the air delivery hole is provided on a side surface of a lower end of the air pressure delivery pipe.

5. 2. The soil layer air pumping tester according to claim 1, wherein the air inlet is provided on a side surface of the air pumping pipe.

6. 2. The soil layer air pumping tester according to claim 1, wherein an anvil is provided at an upper end of said air pumping pipe for transmitting impact energy to said air pumping pipe.

7. An air pressure testing method for soil layers, comprising the steps of: inserting a lower end of an air pressure pipe into a soil layer; using a pump to pump air into the soil layer from the lower end of the air pressure pipe; measuring the air pressure inside the soil layer using a pressure gauge; and estimating the properties of the soil layer.

8. 8. The method for air pumping test for soil layers according to claim 7, further comprising estimating the properties of the soil layer based on whether the soil layer is fine-grained or coarse-grained, in addition to the air pressure.

9. 9. The air pumping test method for a soil layer according to claim 8, wherein the soil layer is fine-grained soil, and the properties of the soil layer are at least one of dry density and degree of saturation.

10. 9. The method for air pumping testing of a soil layer according to claim 8, wherein the soil layer is a coarse-grained soil, and the property of the soil layer is a coefficient of permeability.

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