JP6244280B2 - Unsaturated seepage characteristics analysis method by VG model - Google Patents

Description

  The present invention relates to an unsaturated infiltration characteristic analysis method using a VG model, and in particular, an unsaturated infiltration characteristic by VanGenuchten (hereinafter referred to as a VG model) that analyzes the infiltration characteristics of the ground in an unsaturated region using a finite element analysis program. It relates to the analysis method.

  In the Great East Japan Earthquake, soil contamination by tsunami deposits containing natural heavy metals has been reported. In the future, heavy metal materials that flow out of tsunami deposits due to rainfall, etc. are expected to cause groundwater contamination. It is also possible that man-made heavy metals will diffuse from the debris collection site that occurred in the earthquake disaster area. When considering countermeasures against such groundwater contamination, in addition to the flow of groundwater, the gap between soil particles is not filled with pore water from the ground surface to the groundwater level in the ground. It is necessary to grasp the flow of seepage water in the ground of the unsaturated region.

  In addition, various in-situ permeability test devices and in-situ permeability test methods have been proposed as devices and methods for grasping the flow of osmotic water in the ground of an unsaturated region (for example, Patent Document 1 and Patent Document 1). 2). In addition, as a test for grasping the seepage characteristics of the ground in the unsaturated region, a vertical one-dimensional unsteady seepage flow is generated in the ground, and the pressure head distribution and moisture content distribution (water content distribution) in the seepage region are Instantaneous profiling method (hereinafter referred to as IP method) that measures the unsaturated hydraulic conductivity and moisture characteristic curve of the target area from the results of measuring each time-dependent change, and preferably the volume in the depth direction of the ground From the measurement data of time-dependent changes in moisture content in the ground, measured using a commercially available insertion-type soil moisture meter capable of measuring moisture content profiling in multiple points in real time, There has also been proposed a method for analyzing the infiltration characteristics of the ground in the unsaturated region based on the unsaturated hydraulic conductivity calculated based on the model formula (for example, see Non-Patent Document 1)).

JP 2000-352042 A JP 2007-198027 A

Soil and foundation, 54-5 (580), "In-situ permeability test in unsaturated ground, measurement method of unsaturated permeability using moisture distribution meter", May 2006, Geotechnical Society

  In the method of analyzing the infiltration characteristics of the ground in the unsaturated region using the VG model, the unsaturated hydraulic conductivity k is calculated based on the following equation of [Equation 1] and divided into elements as shown in FIG. The values of the unsaturated hydraulic conductivity k and the saturation degree Se are assigned to each element of the finite element model. Further, the saturated hydraulic conductivity k0 and the unsaturated parameters α, m, and n for obtaining the unsaturated hydraulic conductivity k and the saturation degree Se are temporarily set and then obtained in the in-situ hydraulic test method, for example, as shown in FIG. As shown, it fits over time changes in moisture content at a predetermined depth (for example, GL-0.2 m) when penetrating water is infiltrated into the ground at a predetermined pressure (for example, h = 0.01 MPa). In such a reverse analysis, it is reset.

  On the other hand, in the method of analyzing the infiltration characteristics of the ground in the unsaturated region using the VG model, there is an error in the values of the saturated hydraulic conductivity k0 and the unsaturated parameters α, m, n that are set or the set values are not appropriate. The accuracy of the numerical simulation by the VG model is inferior, and it becomes difficult to accurately grasp the infiltration characteristics of the ground in the unsaturated region. For this reason, it is desired to develop a method that allows the unsaturated parameters α, m, and n to be set more appropriately and accurately.

  The present invention uses a finite element analysis program to analyze the saturation permeation coefficient and saturation degree α when calculating the infiltration characteristics of the ground in the unsaturated region by the VG model. An object of the present invention is to provide an unsaturated permeation characteristic analysis method using a VG model that can set m, n more appropriately and accurately.

The present invention is an unsaturated infiltration characteristic analysis method for analyzing the infiltration characteristics of the ground in an unsaturated region using a finite element analysis program, and a model expression based on a VG model is used as an expression for calculating the unsaturated hydraulic conductivity. The saturated moisture permeability and the unsaturated parameter of the model formula based on the VG model are obtained by the in-situ unsaturated permeability test, and the moisture content at a given depth when penetrating water is infiltrated into the ground at a given pressure. It is set by inverse analysis from the change over time of the soil, and by calculating the unsaturated hydraulic conductivity using the set saturated hydraulic conductivity and unsaturated parameters, the infiltration characteristics of the ground in the unsaturated region The change in moisture content over time for setting the saturated hydraulic conductivity and the unsaturated parameter obtained in the in-situ unsaturated hydraulic permeability test is stepwise A plurality of different pressures with increased, the osmosis water to penetrate into the ground and aging of the resulting water water content, to penetrate the penetration water into the ground with a predetermined pressure in situ unsaturated permeability test From the initial moisture content and initial suction measured or estimated before, setting the provisional value of the unsaturated parameter, estimating the saturated hydraulic conductivity, temporarily setting the measurement conditions by performing a preliminary analysis, Based on the temporarily set measurement conditions, permeated water is infiltrated into the ground in the in-situ unsaturated water permeation test at a plurality of different pressures increased stepwise to obtain the change in moisture content with time. The above-described object is achieved by providing a method for analyzing unsaturated permeation characteristics using the VG model.

  According to the unsaturated osmotic property analysis method using the VG model of the present invention, the unsaturated permeability coefficient and the saturation degree are calculated when analyzing the osmotic property of the ground in the unsaturated region by the VG model using a finite element analysis program. Therefore, the saturated hydraulic conductivity k0 and the unsaturated parameters α, m, and n can be set appropriately and accurately.

It is a flowchart explaining the unsaturated osmosis | permeation characteristic analysis method by VG model which concerns on preferable one Embodiment of this invention. It is sectional drawing explaining the structure of the test apparatus used for an in-situ unsaturated water permeability test. It is explanatory drawing of the finite element model of the ground of the unsaturated area | region divided into elements. It is a chart which illustrates the time-dependent change of the moisture content obtained when penetrating water is infiltrated by increasing the pressure stepwise. It is a chart which illustrates the time-dependent change of the moisture content obtained when the permeated water was permeated at a predetermined pressure without changing the pressure. It is a chart which illustrates the unsaturated characteristic curve of a VG model.

  In the unsaturated osmotic property analysis method using a VG model according to a preferred embodiment of the present invention, a model formula based on a VG model incorporated in a computer is solved at each node and each element of a finite element model (see FIG. 3). Using a known finite element analysis program that is possible, as an analysis method to enable the computer to accurately simulate the time-dependent change in moisture content (volumetric moisture content) due to seepage water in the ground of unsaturated regions It has been adopted. Further, the unsaturated infiltration characteristic analysis method of the present embodiment uses the saturated hydraulic conductivity k0 and the unsaturated parameters α, m, and n of the VG model, which are temporarily set to calculate the unsaturated hydraulic conductivity and the saturation, Saturation permeability coefficient k0 and unsaturation parameters α, m, and n are more accurately accurate when resetting by reverse analysis to fit the time-dependent change of moisture content actually obtained in the position unsaturated permeability test It has a function to make it reset well.

Here, in the unsaturated osmosis characteristic analysis method using the VG model, as described above, the unsaturated hydraulic conductivity k is calculated based on the model formula shown in [Equation 1], and the elements are divided as shown in FIG. The values of the unsaturated hydraulic conductivity k and the saturation degree Se are assigned to each element of the finite element model. In addition, from equation (1) in [ Equation 1], α can be back-calculated as in Equation (4) in [ Equation 2] , and in parentheses in Equation (1) in [Equation 1] From the relationship between m and n, if one of m and n is set, the other can be automatically set. Therefore, by appropriately setting either the saturated hydraulic conductivity k0, the unsaturated parameter α, or the unsaturated parameter m or n, the water content of the permeated water in the ground of the unsaturated region can be calculated by the computer. It is possible to accurately simulate the change with time.

  And in this embodiment, an in-situ unsaturated water-permeable device 10 as shown in FIG. 2 can be used as a device for performing an in-situ unsaturated water-permeable test. That is, the in-situ unsaturated water-permeable device 10 shown in FIG. 2 acquires data relating to the moisture content (volume moisture content) of the soil for grasping the seepage characteristics of the ground 30 in the unsaturated region to be measured. It is. The in-situ unsaturated water-permeable device 10 is installed in a state where the outer peripheral portion is in close water-tight contact with the ground surface 30a with the laying adhesive material 17 interposed therebetween, The soil moisture meter 12 having a plurality of moisture sensors 12a, extending downward from the central portion of the sealed water-filling lid 11 and arranged in the ground, the inside of the sealed water-filling lid 11, the feed pipe 13, and the return pipe 14, the water supply is connected to the inside of the sealed water injection lid 11, and the pressure water is supplied to the inside of the closed water injection lid 11 while circulating the pressure water to and from the water supply tank 16 in a state where the inside of the closed water injection lid 11 is filled with the pressure water. And a pump 15.

  Further, the in-situ unsaturated water permeability test apparatus 10 has a sealed water pouring cover 11 integrally provided with a flange plate 11a provided with a plurality of anchor holes 11b provided to project outward from the opening edge of the opening surface of the lower surface. The sealing water pouring lid 11 is placed on the outer peripheral portion by placing the flange plate 11a on the upper surface of the laying adhesion material 17 and driving the anchor member 19 toward the laying adhesion material 17 and the ground 30. It is installed in a state where the flange plate 11a is in close contact with the ground surface 30a in a watertight manner.

  The sealed water pouring lid 11 constituting the in-situ unsaturated water permeability test apparatus 10 can be easily formed by subjecting a metal plate having a thickness of, for example, about 5 mm to bending or welding. The sealed water filling lid 11 is formed, for example, by joining a strip-shaped peripheral wall plate 11d having a height of about 30 mm along the periphery of a substantially square upper surface plate 11c having a size of about 300 mm in length and width. A flat convex lid body 11e whose bottom surface is an open surface, and an outer surface projecting outward from the lower end edge of the peripheral wall plate 11d of the lid body 11e and joined together, for example, with a width of about 100 mm It consists of a flange plate 11a. As a result, the sealed water-injecting lid 11 as a whole is formed to have a substantially square planar shape having a size of about 500 mm in length and width, for example, and has a height of about 30 mm, for example.

  In addition, a plurality of anchor holes 11b having a size of about φ7 mm, for example, are formed through the flange plate 11a of the sealed water pouring lid 11. A large number of anchor holes 11b are preferably formed on the entire surface of the flange plate 11a in a substantially uniformly distributed state. The number and arrangement positions of the anchor holes 11b can be appropriately designed in consideration of the pressure of the pressure water filled in the sealed water-injecting lid 11, the length of the anchor member 19, the soil quality of the ground 30, and the like.

  Further, a known penetrating metal fitting 21 having a sealing function for penetrating the soil moisture meter 12 in a watertight state is attached to the upper surface plate 11c of the sealed water pouring lid 11. Moreover, well-known joint metal fittings 22a, 22b, and 22c for connecting the feed pipe 13 and the return pipe 14 and a drain pipe 24, which will be described later, to the inside of the sealed water-filling lid 11 are attached by a known method. For example, a known small pressure gauge 23 is attached to a joint fitting 22 a that connects the feed pipe 13 to the inside of the sealed water-filling lid 11. The pressure of the pressure water filled in the sealed water injection lid 11 is measured by the small pressure gauge 23 so that the pressure of the pressure water can be easily managed.

  The through metal fitting 21 has, for example, an inner diameter similar to the outer diameter of the guide tube 12c of the moisture meter 12 in the soil, and an annular outer side from the lower end portion of the cylindrical sleeve portion 21a. It is composed of a joint flange portion 21b provided so as to overhang. The through metal fitting 21 integrally joins the joining flange portion 21b to the opening peripheral edge portion of the circular rod insertion hole 11f having an inner diameter of about 27 mm, which is formed through the central portion of the upper surface plate 11c. Is attached to the sealed water-injecting lid 11 in a state in which it is erected from the upper surface plate 11b. When installing the sealed water-filling lid 11 on the ground surface 30a of the ground 30 to be measured, the guide tube 12c of the soil moisture meter 12 is buried in the ground prior to this, so that the guide is erected from the ground surface 30a. The upper end portion of the tube 12c is inserted into the cylindrical sleeve portion 21a from below. By inserting the soil moisture meter 12 into the guide tube 12c, the soil moisture meter 12 penetrates the central portion of the sealed water-filling lid 11 in a water-tight state and is inserted into the ground, and the upper end portion of the soil moisture meter 12 extends upward from the upper surface plate 11c. It will be installed protruding.

  In the present embodiment, the flow rate adjusting valve 20 is preferably attached to the joint fitting 22b that connects the return pipe 14 to the inside of the sealed water-injection lid 11. The flow rate adjustment valve 20 uses a valve member having a known mechanism capable of adjusting the cross-sectional area of the flow path of the pressure water and controlling the flow rate of the pressure water passing through the flow rate adjustment valve 20. it can. By controlling the flow rate of the pressure water returned from the inside of the sealed water filling lid 11 to the water supply tank 16 via the return pipe 14 by the flow rate adjusting valve 20, it is pumped from the water supply pump 15 via the feed pipe 13 and sealed. The pressure of the pressure water filled in the water injection lid 11 can be easily adjusted within a range of, for example, about 0.001 MPa to 0.1 MPa.

  Furthermore, in the present embodiment, a drain pipe 24 is provided so as to be connected to the inside of the sealed water pouring lid 11 via a joint fitting 22 c attached to the upper surface plate 11 c of the sealed water pouring lid 11. The drain pipe 24 is supported by the auxiliary stand 25, and its tip is disposed at a position considerably higher than the ground surface 30a. The drain pipe 24 functions as a safety valve by opening the valve 22c to open the pressure water inside the sealed water-filling lid 11 to the atmosphere, and when the pressure water pressure is unexpectedly increased. The inside of the sealed water injection lid 11 can be urgently depressurized.

  A feed pipe 13 and a return pipe 14 that allow the inside of the sealed water injection lid 11 to communicate with a water supply tank 16 and a water supply pump 15 and circulate pressure water between them, and a drain pipe 24 have a thickness of about φ10 mm, for example. Various known pressure-resistant hoses having flexibility can be used. As the feed water pump 15, for example, various known feed water pumps that can supply pressure water having a maximum pressure of about 0.2 MPa can be used. As the water supply tank 16, a known simple water supply tank having a capacity of about 20 L, such as a polyethylene tank, can be used. Since the water supply tank 16 can be appropriately replenished with water, the amount of water required to permeate the water to the depth of the moisture sensor 12a can be easily supplied. A filter 26 for removing soil particles and the like contained in the pressure water returned from the sealed water-filling lid 11 is provided at a portion where the return pipe 14 is connected to the water supply tank 16.

  The soil moisture meter 12 that constitutes the in-situ unsaturated permeability test apparatus 10 is a variety of commercially available various insertion types capable of measuring volume moisture content profiling at multiple points in real time in the depth direction of the ground. A soil moisture meter can be used. More specifically, for example, “profile probe PR2 / 6” manufactured by Delta-T can be preferably used. By using the “profile probe PR2 / 6”, it becomes possible to measure the volumetric water content at a depth of 10 cm, 20 cm, 30 cm, 40 cm, 60 cm, and 100 cm from the ground surface.

  The soil moisture meter 12 is formed, for example, by attaching a plurality of moisture sensors 12a at predetermined intervals to a lower part of a polycarbonate rod portion 12b having a length of about 1350 mm and a thickness of about φ25 mm. Yes. The soil moisture meter 12 uses a dedicated auger to provide a measurement hole having an inner diameter of, for example, about 25 mm in the ground 30 prior to the installation of the sealed water-filling lid 11 on the ground surface 30a of the ground 30 to be measured. After forming in the vertical direction up to the depth, the lower end of the rod portion 12b to which a plurality of moisture sensors 12a are attached is inserted into the formed measurement hole in a state protected by the guide tube 12c, thereby the upper end of the rod portion 12b. The portion can be installed on the ground 30 with the portion standing from the ground surface 30a. After that, installation work of the sealed water pouring lid 11 is performed.

  In order to install the sealed water filling lid 11 on the ground surface 30a of the ground 30 to be measured, first, the upper end portion of the rod portion 12b and the guide tube 12c of the installed soil moisture meter 12 standing from the ground surface 30a. As a center, the ground surface 30a around the ground is leveled, and the flange plate 11a is disposed at a position away from the rod portion 12b and the guide tube 12c and at which the flange plate 11a of the sealed water-filling lid 11 is disposed. The laying adhesion material 17 is laid in a substantially square annular shape with the same width as. Here, as the laying adhesion material 17, the laying adhesion material 17 absorbs the unevenness of the ground surface 30 a and the lower surface of the flange plate 11 a by solidifying from a soft state such as bentonite and water-expandable material. Various well-known laying adhesive materials 17 capable of bringing them into close contact with each other can be used. In addition, the laying adhesion material 17 is laid with a water shielding sheet interposed between the ground surface 30a and the lower surface of the flange plate 11a, thereby improving the water tightness around the installed water-sealing lid 11. It becomes possible to hold firmly. Furthermore, the pressure of the pressure water inside the sealed water-filling lid 11 is preferably increased by forming a solidified layer 30b by infiltrating a known ground surface solidifying agent into the ground 30 of the surface portion immediately below the laying adhesive material 17. When raised, it is possible to more effectively prevent the formation of a water channel on the ground surface 30b. As the ground surface solidifying agent, for example, “Flynet R” manufactured by Fuji Sash Corporation can be preferably used.

  If the laying adhesive material 17 is laid at the position where the flange plate 11a of the sealed water pouring lid 11 around the rod portion 12b is disposed, the sealing water pouring lid 11 as described above before the laying adhesive material 17 is not yet solidified. The rod insertion hole 11f and the cylindrical sleeve portion 21a of the through metal fitting 21 are inserted on the upper surface of the laying adhesive material 17 on which the flange plate 11a is laid while inserting the upper end portion of the rod portion 12b standing from the ground surface 30a. Then, the sealed water pouring lid 11 is installed on the ground surface 30a of the ground 30 to be measured. After that, a plurality of anchor members 19 are driven toward the laying contact material 17 and the ground 30 through the plurality of anchor holes 11b formed in the flange plate 11a. Then, when the inside of the hermetically sealed water filling lid 11 is filled with water, the water oozes out into the laying adhesive material 17 where the laying adhesive material 17 is solidified. It can be installed in a state of being in close contact with the surface 30a in a watertight manner.

  When the sealed water pouring lid 11 is installed on the ground surface 30 a of the ground 30 to be measured, the feed pipe 13, the return pipe 14 and the drain pipe 24 are connected to the installed air pouring lid 11, and By circulating the pressure water between the inside and the water supply pump 15 or the water supply tank 16 and filling the inside of the sealed water filling lid 11 with the pressure water, the filled pressure water is grounded on the ground 30 to be measured. It will be in the state which can be permeated as osmotic water inside. In addition, the soil moisture meter 12, the small pressure gauge 23, the water supply pump 15 and the like are connected to a data processing unit (not shown) including a data logger and a personal computer via wirings, thereby measuring various kinds of measured values. The measurement data can be processed. Furthermore, the personal computer incorporates a known finite element analysis program capable of analyzing the infiltration characteristics of the ground in the unsaturated region using the VG model. By this finite element analysis program, the soil moisture meter 12, Based on the measurement data sent from the small pressure gauge 23, the feed pump 15, etc., the saturated hydraulic conductivity k0 and the unsaturated parameters α, m, n of the VG model are set more appropriately and accurately, It is possible to analyze the penetration characteristics.

  And the unsaturated infiltration characteristic analysis method by the VG model of this embodiment is an analysis method for analyzing the infiltration characteristic of the ground in the unsaturated region using a finite element analysis program, and is an expression for calculating the unsaturated hydraulic conductivity. , [Equation 1] is used, and a model equation based on the VG model is used, and the saturated hydraulic conductivity k0 and the unsaturated parameters α, m, n of the model equation based on the VG model are obtained by the in-situ unsaturated hydraulic permeability test. From the time-dependent change of moisture content at a given depth when penetrating water penetrates into the ground, it is set by inverse analysis, and the set saturated permeability coefficient k0 and unsaturated parameter By calculating the unsaturated hydraulic conductivity using α, m, and n, the infiltration characteristics of the ground in the unsaturated region are analyzed, and the saturated permeability obtained in the in-situ unsaturated hydraulic test is obtained. As shown in FIG. 4, the time-dependent change in the moisture content for setting the coefficient k0 and the unsaturated parameters α, m, n is infiltrated into the ground with a plurality of different pressures increased stepwise. It is assumed that the moisture content of the water obtained by the change over time.

  Moreover, the unsaturated osmotic property analysis method by the VG model of this embodiment is the initial moisture content and the initial suction measured or estimated before infiltrating the osmotic water into the ground at a predetermined pressure in the in-situ unsaturated permeability test. From the above, the provisional values of the unsaturated parameters α, m, n are set, the saturated hydraulic conductivity is estimated, the measurement conditions are provisionally set by performing a preliminary analysis, and based on the provisionally set measurement conditions, In the in-situ unsaturated water permeability test, the permeated water is infiltrated into the ground at a plurality of different pressures increased in stages to obtain a change in moisture content with time.

  The unsaturated infiltration characteristic analysis method based on the VG model of the present embodiment can be preferably performed according to the flowchart shown in FIG. 1 using a computer (personal computer) incorporating a known finite element analysis program. That is, in this embodiment, first, in the in situ unsaturated permeability test, a measurement hole for installing the moisture meter 12 in the soil is drilled using a dedicated auger, and the soil moisture meter 12 as a measurement device is formed. If it installs, it will measure the initial volume moisture content of the ground 30 used as a measuring object with the soil moisture meter 12 installed before penetrating osmotic water in the ground.

  Next, the presence or absence of groundwater in the ground 30 to be measured is determined, and the initial suction (initial negative pressure head) of the ground 30 is estimated or measured. That is, for example, the presence or absence of groundwater in the ground 30 is determined from the nearby borehole data or the borehole data obtained during the in-situ unsaturated permeability test. If the groundwater level is clear and shallow, the hydrostatic pressure is assumed. Then, the initial suction is estimated by a known estimation formula. When the groundwater level is unknown or deep, the initial suction cannot be estimated. For example, the initial suction is measured using a known tensiometer. When the initial suction is estimated or measured, for example, a provisional value of the unsaturation parameter n is set from the initial suction and the initial saturation based on the initial volume moisture content measured by the soil moisture meter 12. ) To set a provisional value for the unsaturated parameter α.

  When the provisional value of the unsaturated parameter α is set, for example, a well-known Creager is obtained from the soil quality and particle size distribution of the drilling shear obtained when drilling the measurement hole in which the soil moisture meter 12 is installed. Estimate the saturated hydraulic conductivity k0 of the ground 30 to be measured using the equation, and perform preliminary analysis using a finite element analysis program to temporarily set the measurement conditions such as water pressure when penetrating water into the ground To do.

  After preliminary analysis by the finite element analysis program and temporarily setting the measurement conditions, in the in-situ unsaturated permeation test, the permeated water was discharged at different pressures increased in stages based on the temporarily set measurement conditions. Infiltrate into the ground so that the moisture content over time can be obtained. That is, while the pressure is controlled by the small pressure gauge 23 using the above-mentioned in-situ unsaturated water permeability test apparatus 10, the inside of the sealed water filling lid 11 is controlled by the flow rate adjusting valve 20 or the water supply pump 15 provided in the return pipe 14. The pressure of the pressure water filled in is adjusted, and a predetermined water pressure P is loaded inside the sealed water injection lid 11 of the test apparatus 10. Further, every time a predetermined time elapses, the pressure P of the pressure water that permeates into the ground as permeated water while circulating the pressure water between the inside of the sealed water filling lid 11 and the water supply pump 15 or the water supply tank 16. Then, it is increased stepwise and the moisture content at each measurement point in the ground is measured by the soil moisture meter 12.

  Here, the pressure of the pressurized water (water pressure P) filled in the sealed water-filling lid 11 is increased step by step every time a predetermined time elapses, and each measurement point in the ground is measured by the soil moisture meter 12. When measuring the change in the moisture content at, it is determined whether or not the rate of increase in the moisture content is appropriate. When the rate of increase in moisture content during measurement is excessively high or low, the water pressure P is corrected to ensure an appropriate measurement time. When the rate of increase in the moisture content is appropriate, after measuring the change in moisture content at each measurement point in the ground, the water pressure P is stepped up, and the predetermined water pressure P that has been stepped up is sealed in the test apparatus 10. The inside of the water injection lid 11 is loaded. And the process of measuring the change of the moisture content at each measurement point in the ground with the soil moisture meter 12 while stepping up the water pressure P in the same manner is performed until the soil at each measurement point in the ground is saturated. After repeating the number of steps, the measurement is finished. As a result, the pressure P of the pressure water to be infiltrated into the ground as osmotic water is increased stepwise, and the measurement time when measuring the moisture content change at each measurement point in the ground with the soil moisture meter 12 is shortened. Thus, it is possible to effectively improve the measurement accuracy.

  Moreover, in this embodiment, the time-dependent change of the moisture content for setting the unsaturated parameter when the water pressure P is increased stepwise while being stepped up, obtained in the in-situ unsaturated water permeability test, for example, is shown in FIG. 4 can be obtained as a change with time. For example, at a depth of GL-0.2 m, the time-dependent change in moisture content shown in FIG. 4 is as follows: 85 minutes after the start of the test, the pressure of the osmotic water is increased from 0.01 MPa to 0.02 MPa, and after 90 minutes. Temporal change in moisture content (volume moisture content) when the pressure of the permeated water was increased from 0.02 MPa to 0.03 MPa and the pressure of the permeated water was further increased from 0.03 MPa to 0.04 MPa after 60 minutes. Is shown.

  In the present embodiment, for example, as shown in FIG. 4, the saturated water permeability k0 is obtained from the change over time in the moisture content obtained by infiltrating the permeated water into the ground at a plurality of different pressures increased stepwise. The unsaturated parameter of the model formula based on the VG model can be set by inverse analysis, and the unsaturated hydraulic conductivity is calculated using the set saturated hydraulic coefficient k0 and the unsaturated parameter. It is designed to analyze the infiltration characteristics of ground in unsaturated regions.

  Then, according to the unsaturated infiltration characteristic analysis method by the VG model of the present embodiment having the above-described configuration, when analyzing the infiltration characteristic of the ground in the unsaturated region by the VG model using the finite element analysis program, The saturated hydraulic conductivity k0 and the unsaturated parameters α, m, and n for calculating the saturated hydraulic conductivity and the degree of saturation can be set more appropriately and accurately.

  That is, according to the unsaturated osmotic property analysis method based on the VG model of the present embodiment, the water content of moisture for setting the saturated hydraulic conductivity k0 and the unsaturated parameters α, m, and n obtained in the in-situ unsaturated hydraulic permeability test. As shown in FIG. 4, the time-dependent change is a time-dependent change of the moisture content obtained by infiltrating the permeated water into the ground with a plurality of different pressures increased stepwise. The curve that describes the change is also a curve that is a combination of a plurality of S-shaped curves including a portion where the shape of the S-shaped curve changes by changing in stages according to the hydraulic pressure P of the osmotic water that increases in stages. It has become.

  Therefore, according to the present embodiment, in the model formula based on the VG model, the saturated hydraulic conductivity k0 and the unsaturated parameters α, m, and n for obtaining the unsaturated hydraulic conductivity k and the saturation degree Se are temporarily set, When re-setting by reverse analysis to fit the time-dependent change of moisture content at a given depth when penetrating water is infiltrated into the ground at a given pressure obtained in the method of position permeability test In addition, by performing a reverse analysis so as to fit a plurality of S-shaped curves as shown in FIG. 4, it is more precise than in the case of performing a reverse analysis so as to fit a single S-shaped curve as shown in FIG. Since accurate back analysis will be performed, it becomes difficult to reset the saturated permeability coefficient k0 and the unsaturated parameters α, m, and n that have errors or inappropriate values, and the saturated permeability coefficient k0 and unsaturated Parameter α, m, n It becomes possible to set more appropriately and accurately. In addition, by using a finite element analysis program incorporating a model formula based on the VG model, the time-dependent change in moisture content (volume moisture content) due to seepage water in the ground of the unsaturated region is accurately simulated by a computer. It becomes possible.

  In the present embodiment, the suction measurement performed in accordance with the measurement of the moisture content distribution performed in the IP method is omitted. However, by using a plurality of water pressures P as the measurement conditions, as a result It becomes possible to measure the moisture content distribution based on various fluctuations, and it becomes possible to set the unsaturated hydraulic conductivity more easily by supplementing the measurement conditions by not performing the suction measurement.

  In the present embodiment, provisional values of the unsaturated parameters α, m, and n are set from the initial moisture content and the initial suction, and the measurement conditions are provisionally set by performing a preliminary analysis. Based on the above, in the in situ unsaturated permeability test, the permeated water is infiltrated into the ground at different pressures increased in stages, so that the moisture content over time is obtained. Thus, it is not necessary to measure the change in the suction during the measurement of the moisture content distribution, and the initial suction is measured to set the provisional values of the unsaturated parameters α, m, n. It is possible to determine both ends of the initial value and the final value (suction at saturation is 0) for the curve of moisture content θ-suction φ. As a result, it is possible to analyze the unsaturated permeation characteristic considering suction as a measurement condition. In addition, as compared with the method of analyzing the unsaturated permeation characteristics based on the VG model from only the measurement data of the change in moisture content with time, as in Non-Patent Document 1, the suction is not considered at all. It becomes possible to analyze unsaturated permeation characteristics with high accuracy.

  The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the time-dependent change in the moisture content obtained by infiltrating the permeated water into the ground at a plurality of different pressures increased in stages is the in-situ unsaturated using the in-situ unsaturated water permeability test device. Without being limited to the permeability test, it can also be obtained by an in-situ unsaturated permeability test using other test equipment.

DESCRIPTION OF SYMBOLS 10 In-situ unsaturated water permeability test apparatus 11 Sealed water-filling lid 11a Flange plate 11b Anchor hole 11c Upper surface plate 11d Perimeter wall plate 11e Cover body 11f Rod insertion hole 12 Moisture meter 12a Moisture sensor 12b Rod part 12c Guide tube 13 Feeding tube 14 Return Pipe 15 Water supply pump 16 Water supply tank 17 Laying adhesion material 19 Anchor member 20 Flow rate adjusting valve 21 Through metal fitting 21a Cylindrical sleeve portion 21b Joint flange portions 22a, 22b, 22c Joint metal fitting 23 Small pressure gauge 24 Drain pipe 25 Auxiliary stand 26 Filter 30 Ground 30a in the unsaturated region to be measured Ground surface 30b Solidified layer

Claims (1)

An unsaturated infiltration characteristic analysis method for analyzing infiltration characteristics of ground in an unsaturated region using a finite element analysis program,
As a formula for calculating unsaturated hydraulic conductivity, a model formula based on VanGenuchten model is used.
The saturation permeability coefficient and the unsaturated parameter of the VanGenuchten model equation show that the moisture content over time at a given depth when infiltrated water is infiltrated into the ground at a given pressure obtained by an in situ unsaturated permeability test. From the change, it is set by inverse analysis. Analyzing the infiltration characteristics of the ground in the unsaturated region by calculating the unsaturated permeability coefficient using the set saturated permeability coefficient and unsaturated parameter. Is supposed to
In addition, the permeated water penetrated into the ground at a plurality of different pressures, which were obtained by gradually increasing the moisture content over time to set the saturated permeability coefficient and the unsaturated parameter obtained in the in situ unsaturated permeability test. It is not the time course of the resulting water water content,
From the initial moisture content and initial suction measured or estimated before infiltrating the seepage water into the ground at a predetermined pressure in the in-situ unsaturated permeability test, a provisional value of the unsaturation parameter is set and the saturation Estimating the permeability coefficient and performing preliminary analysis to temporarily set the measurement conditions, and based on the temporarily set measurement conditions, the in situ unsaturated permeability test at a plurality of different pressures increased in stages. Unsaturated osmotic property analysis method using a VG model in which permeated water is permeated into the ground to obtain a change with time in the moisture content .

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