CN103163055B - A kind of resistivity imaging consolidometer detecting unsaturated soil infiltration coefficient - Google Patents

Abstract

The invention discloses a kind of resistivity imaging consolidometer evaluating unsaturated soil infiltration coefficient, comprise top cover, side ring and chassis, described side ring is located on chassis, top cover is inserted in side ring, the top of described top cover is stainless steel cover, and bottom is plastic cylinder, is evenly distributed with multiple copper electrode in described plastic cylinder, also be provided with flexure element and detection instrument, described plastic cylinder is provided with drainage channel and is attached thereto logical draining donut simultaneously; Described side ring is lined with the stainless steel ring of plastic circle ring in being, equally spacedly on sidewall be provided with multiple copper electrode; Described chassis comprises stainless steel cask and is located at the plastic inner lining of stainless steel cask inwall, and described plastic inner lining is arranged arranges corresponding with plastic cylinder.Instant invention overcomes prior art and can not consider the defect that anisotropy, nonuniformity and test size are little, by causing the change of soil body resistivity along with pore water flows out in test consolidation test, carrying out cheapness, evaluating unsaturated soil infiltration coefficient quickly and easily.

Description

A Resistivity Imaging Consolidation Instrument for Detecting the Permeability Coefficient of Unsaturated Soil

technical field

The invention belongs to the technical field of civil engineering, in particular to a resistivity imaging consolidation instrument for detecting the permeability coefficient of unsaturated soil.

Background technique

With the development of my country's economy, the pollution of urban groundwater resources is becoming more and more serious. Pollutants tend to migrate from shallow unsaturated soil to saturated soil. Therefore, the study of pollutant migration rules first needs to determine the seepage characteristics of unsaturated soil. Seepage characteristics in unsaturated soil can usually be obtained by direct test methods and indirect methods, and direct test methods include field tests and laboratory tests. Field tests such as tension infiltration test are limited to shallow areas above the surface, and the test time is long and the workload is heavy. Indoor test methods usually use consolidation tests or constant head and variable head tests to measure the permeability coefficient of soil. This method regards all indoor samples as homogeneous and isotropic units, and ignores the influence of the remodeling process on the isotropic properties of the samples. Due to the influence of heterogeneity, and the sample volume is small, the size effect makes the measured seepage characteristics of unsaturated soil unreliable. The latest research trend is to use indirect methods to detect the seepage characteristics of unsaturated soil, among which the most commonly used and simple method is the numerical inversion method. The numerical inversion method first assumes that the permeability coefficient function k can be approximately expressed by the analytical formula of several finite unknown parameters, and assigns initial values to these unknown parameters, and then substitutes the initial value k into the control equation that characterizes the instantaneous flow, and combines Test the controllable boundary conditions and initial conditions to form a mathematical model that can fully describe the seepage state, and finally solve the mathematical model. The solution of the seepage equation is compared and analyzed with the experimental observations, the assignment of unknown parameters is improved and optimized, and the above steps are repeated until the error between the simulated value and the measured value is minimized, thereby determining the expression of k. Numerical inversion methods also require indoor model tests or field tests to provide actual observations for comparison. Resistivity imaging technology is a new experimental technology that reflects the properties of soil by testing the resistivity value of the soil. It has been developed rapidly due to its advantages of fast, reliable, and low cost. It can be used to monitor the distribution range of pollutants and the degree of pollution. Division, soil anisotropy identification and foundation treatment quality inspection and other fields. In the consolidation test, as the load acts, the pore water flows out, the pore volume changes, and the resistivity of the soil changes accordingly. Therefore, the soil permeability coefficient can be obtained by inversion by using the change of resistivity. Using numerical inversion method and resistivity imaging technology, combined with indoor conventional consolidation instrument, the present invention proposes a resistivity imaging consolidation instrument which can use numerical inversion method to detect seepage characteristics of unsaturated soil.

Utility model content

Purpose of the invention: In order to overcome the above-mentioned problems and defects, the present invention proposes a resistivity imaging consolidation instrument that can be used to detect the permeability coefficient of unsaturated soil.

Technical solution: In order to solve the above technical problems, the present invention adopts the following technical solution: a resistivity imaging consolidation instrument for detecting the permeability coefficient of unsaturated soil, including a top cover, a side ring and a chassis, and the side ring is arranged on the chassis, The top cover is inserted into the side ring, wherein: the upper part of the top cover is a stainless steel cover, and the lower part is a plastic cylinder, and a plurality of copper electrodes are evenly distributed in the plastic cylinder, and a bending element and a wave detector are also provided at the same time , the plastic cylinder is provided with drainage channels and drainage concentric rings, and the drainage concentric rings communicate with the drainage channels; the side rings are stainless steel rings lined with plastic rings, and the side walls of the side rings are also A plurality of copper electrodes are provided at intervals; the chassis includes a stainless steel barrel and a plastic lining arranged on the inner wall of the stainless steel barrel, and the plastic lining is also provided with copper electrodes, bending elements, wave detectors and drainage concentric rings, and respectively Corresponding to the copper electrode, bending element, wave detector and drainage concentric ring in the plastic cylinder; meanwhile, the plastic lining is also provided with a drainage channel, which communicates with the drainage concentric circle.

As a further improvement, the copper electrode includes a copper electrode rod, a polyamide fiber plastic sleeve, a stainless steel handle and a wire, the tail end of the copper electrode rod is connected to the wire, and the polyamide fiber plastic sleeve is sleeved on the copper electrode rod, The wire is buried in the stainless steel handle and a lead wire is left; meanwhile, a sealing ring is arranged between the copper electrode rod and the polyamide plastic sleeve.

Further, the top cover and the chassis are respectively provided with 13 copper electrodes, and 8 of them are evenly distributed on the circumference concentric with the top cover and the chassis, and the other 5 copper electrodes are installed on the top cover and the chassis respectively. central part of .

Further, a sealing ring is provided on the contact surface between the top cover and the side ring, and the contact surface between the side ring and the chassis; at the same time, a sealing ring is provided on the contact surface between the copper electrode and the plastic cylinder or plastic lining.

Preferably, 16 copper electrodes are arranged on the side ring.

Preferably, the plastic cylinder and the plastic lining are made of polyamide fiber, and the resistivity is 1×10 ¹³ Ω·m˜9×10 ¹³ Ω·m.

Preferably, the outer wall of the chassis is provided with a pressure valve connected to the drainage channel.

Beneficial effects: Compared with the prior art, the present invention has the following advantages: Pollutants tend to migrate from shallow unsaturated soil to saturated soil. Therefore, the study of pollutant migration law first needs to determine the seepage of unsaturated soil feature. The invention solves the defects that anisotropy, heterogeneity and small test size cannot be considered when the existing domestic consolidation instrument detects the seepage characteristics of unsaturated soil, and the soil resistance caused by the outflow of pore water in the consolidation test is tested. Low-cost, convenient and fast detection of unsaturated soil permeability coefficient. The technology is reliable, economical, fast and repeatable.

Description of drawings

Fig. 1 is the structural representation of resistivity imaging consolidation instrument of the present invention;

Fig. 2 is a schematic structural view of the side ring of the present invention;

Fig. 3 is a schematic structural view of the chassis of the present invention;

Fig. 4 is a schematic structural view of the copper electrode of the present invention.

Among them, stainless steel cover 1, plastic cylinder 2, copper electrode 3, bending element 4, detector 5, drainage channel 6, drainage concentric ring 7, stainless steel ring 8, plastic ring 9, stainless steel barrel 10, plastic lining 11 , pressure valve 12, sealing ring 13, copper electrode rod 31, polyamide fiber plastic sleeve 32, stainless steel handle 33, wire 34,

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figure 1, a resistivity imaging consolidation instrument for detecting the permeability coefficient of unsaturated soil, the device is divided into three parts: top cover, side ring and chassis; the upper part of the top cover is a stainless steel cover 1, which withstands the consolidation test The applied load, the lower part of the top cover is a polyamide fiber plastic cylinder 2, which insulates the current inside the resistivity imaging consolidation instrument from the stainless steel cover 1, and 13 copper electrodes 3 are arranged inside the top cover, and the copper electrodes 3 are made of copper Made of electrode rod 3.1, O-shaped sealing ring 3.2, polyamide fiber plastic 3.3, stainless steel handle 3.4 and wire 3.5, wherein 8 copper electrodes 3 are equally spaced on the circumference of the same circle as the polyamide fiber plastic cylinder 2, and Near the center of the polyamide fiber plastic cylinder 2, 5 copper electrodes 3, 1 bending element 4 and 1 geophone 6 are concentratedly installed, and the inside of the polyamide fiber plastic cylinder 2 is provided with a drainage channel 5 and 3 drainage concentric Circular rings 7.1, 7.2, 7.3 are equipped with O-shaped sealing rings 8 above the drainage channel 5, inside the bending element 4 and the geophone 6, to prevent the water flow inside the consolidation instrument from causing a short circuit; the outer wall of the side ring of the device is made of stainless steel Ring 9, the inner wall is a polyamide fiber plastic ring 10 for insulation, and 16 copper electrodes 3 are arranged at equal intervals on the circumference of the side wall concentric with the side ring; the design of the chassis of the device is similar to that of the top cover, and the lower part of the chassis is made of stainless steel Barrel 11, the inner wall of the stainless steel barrel 11 is covered by polyamide fiber plastic 12, 13 copper electrodes 3, 1 bending element 4, 1 geophone 6 and 3 drainage concentric rings 7.1, 7.2, 7.3 are arranged inside the chassis , each component is directly opposite to the components in the top cover, and a drainage channel 5 is also provided inside the chassis, and a pressure valve 13 is installed opposite the outer wall of the stainless steel barrel 11 to adjust and control the drainage and stress conditions in the consolidation instrument, An O-ring seal 8 is provided in the groove of the polyamide fiber plastic 12 corresponding to the polyamide fiber plastic ring 10 .

The diameter of the polyamide fiber plastic cylinder is designed to be 130 mm, and the resistivity is about 10 ¹³ Ω·m.

The outer diameter of the stainless steel ring of the side ring is 150mm, the inner diameter is 135mm, the outer diameter of the polyamide fiber plastic ring of the side ring is 135mm, the inner diameter is 130mm, and the height of the side ring is 100mm.

The diameter of the copper electrode rod at the head of the copper electrode is 2 mm, and the distance between the 16 copper electrodes in the side ring and the bottom surface of the side ring is 20 mm.

The diameters of the three drainage concentric rings are 70mm, 90mm and 130mm respectively, and the tolerance is 2mm.

The stainless steel barrel of the chassis has an outer diameter of 170mm and an inner diameter of 150mm, and the polyamide fiber plastic of the chassis has an outer diameter of 150mm and an inner diameter of 130mm.

In the resistivity imaging consolidation test, the distance between the polyamide fiber plastic cylinder and the surface of the polyamide fiber plastic in the chassis is 20-60 mm, that is, the height of the tested soil sample should be 20-60 mm.

The electrical resistivity imaging consolidation instrument that can be used to detect the permeability coefficient of unsaturated soil of the present invention, its permeability characteristic testing part is mainly made up of the stainless steel cover of top cover and polyamide fiber plastic cylinder, the stainless steel ring of side ring and polyamide fiber plastic circle Ring, chassis stainless steel barrel and polyamide fiber plastic, copper electrodes, drainage channels, 3 drainage concentric rings, O-ring seals and pressure valves. The stainless steel cover of the top cover, the stainless steel ring of the side ring and the stainless steel barrel of the chassis can withstand the load imposed by the consolidation test. The polyamide fiber plastic cylinder of the top cover, the polyamide fiber plastic ring of the side ring, and the polyamide fiber plastic of the chassis insulate the internal circuit of the resistivity imaging consolidation instrument from the stainless steel of the outer wall to ensure the correct measurement of the potential and reduce the resistance at the same time The friction effect between the inner wall of the imaging consolidation instrument and the soil sample. 42 copper electrodes are set on the inner boundary of the resistivity imaging consolidation instrument, 16 electrodes are arranged at equal intervals on the inner wall of the side ring, and the distance from the bottom surface of the inner wall of the resistivity imaging consolidation instrument is 20mm, and the top cover and the chassis are respectively placed 13 root electrode. The 5 copper electrodes centrally placed on the top cover and the chassis increase the resistivity information in the middle of the soil sample, because the resolution of the inversion analysis there is usually poor, and the centralized installation can further increase the sensitivity and accuracy of the electrical inversion. sex. During the test, a voltage is applied to two of the copper electrodes in the side ring, and the distribution of the potential difference can be obtained on the other copper electrodes, so as to obtain the resistivity of each part of the soil, and the resistivity can be measured from the vertical and horizontal directions at the same time , taking fully into account the anisotropy and heterogeneity of soil samples. The drainage channel and three drainage concentric rings provide the drainage path required for the consolidation test, and in order to avoid the short circuit caused by the flow of pore water, O-ring seals are installed near the drainage channel, inside the bending element and the geophone , so as to ensure that pore water always flows in the designed drainage path. The pressure valve controls the consolidation pressure required for the consolidation test and provides a drainage channel. The permeability coefficient function k of unsaturated soil can be obtained through numerical simulation technology combined with inversion analysis.

The Archie equation gives the measured conductivity versus saturation for porous media:

$\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; p</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; q</span>}}$

In the formula, ρ and ρ _w are the resistivity of soil and pore water, respectively; n is the porosity; p and q are empirical parameters, which reflect the connection characteristics of internal pores. When the porosity and salinity in water are kept constant, the Archie method can be written as:

$\frac{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; t</span>}}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; q</span>}}$

In the formula, ρ _sat is the resistivity of the saturated soil sample.

Then the saturation of the reshaped soil sample can be written as:

S _r ＝(σ/σ _sat ) ^1/q

With copper electrodes mounted on all boundaries of the Resistivity Imaging Consolidator, a large number of resistivity measurements can be performed and changes in pore water are reflected.

According to the mass conservation law of continuum, the flow partial differential equations of pore water and air are expressed as follows:

$\frac{<span\; class="notranslate">\; \&part;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; wxya</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; \&part;</span>\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&dtri;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}$

$\frac{<span\; class="notranslate">\; \&part;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; \&part;</span>\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&dtri;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}$

In the formula, γ _i is the soil bulk density of the i-th phase; q _i is the specific flow rate; n is the porosity; S _r is the saturation; i=w or a, w represents the water phase, and a represents the gas phase.

The flow of pore water and air can be described by Darcy's law:

${\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&dtri;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; q</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&dtri;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}\mathrm{<span\; class="notranslate">\; g</span>}}<span\; class="notranslate">\; )</span>$

In the formula, k _a and k _w are the permeability coefficients of gas and water respectively, which are functions of saturation; u _w and u _a are the pressures of water and gas, respectively. _kw is the permeability coefficient of unsaturated soil.

Brooks and Corey established a relationship with saturation: where k _w ^sat is the permeability coefficient of saturated soil. β is the empirical coefficient.

Corey gave an expression for the permeability coefficient of pore gas:

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; r</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

where k _a ^dry is the permeability coefficient of gas in the soil under completely dry conditions.

According to the van Genuchten relationship, the soil water holding curve is:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; S</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; S</span>}}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&lsqb;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; \&rsqb;</span>}^{\mathrm{<span\; class="notranslate">\; m</span>}}$

In the formula, Se is effective saturation; S _r ^RES is residual saturation; α, _n , m are empirical coefficients; s=u _a -u _w is matrix suction. The hysteresis of the soil-water characteristic curve was ignored because the experiment experienced multiple water additions.

Accordingly, the constitutive equations of water and air are:

γ _w ＝γ _w0 exp(B _w u _w )

${\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}\mathrm{<span\; class="notranslate">\; T</span>}\mathrm{<span\; class="notranslate">\; g</span>}}$

In the formula, γ _w0 is the bulk density of water under standard atmospheric pressure, γ _w0 = 10kN/m ³ ; B _w is the volumetric compressibility coefficient of water, B _w = 1×10 ^-6 kPa ^-1 ; ma is air as _an ideal gas mass fraction at , ma ₌ 28.96kg/mol; R is ideal gas constant, R=8.31432J/(mol K); T is absolute temperature, T=298.23K; g is gravitational acceleration, g=9.8m/ ^s2 .

After adding appropriate boundary conditions and initial conditions to the constitutive equation, it can be solved by finite element numerical simulation software. In order to simplify the calculation process, the test can be treated as an axisymmetric structure, and the grid is divided into three nodes, which are denser near the drainage channel. Except for drainage channels, the boundaries of the specimen may be impermeable to both water and air.

The solution given by the finite element is in the form of u _a and u _w at different times, and the saturation and resistivity are obtained through the water holding curve and the Archie equation. The unknowns given by the above model are five parameters α, n, m and β. The numerical simulation resistivity imaging consolidation test is used to obtain the simulated resistivity values at different times, and then the simulated resistivity values are compared with the actual observed values, and the difference between the simulated resistivity values and the observed values is represented by the objective function Φ(b).

Φ(b)＝(e ^T /ρ _m )·e

In the formula, ρ _m is the observed resistivity vector; b is the parameter vector, b=b(α,n,m,β); e is the error, e=ρ _m -ρ _s ; ρ _s is the seepage flow of numerical simulation Vector; T means transpose. When Φ(b) is minimum, the volume permeability coefficient function k of unsaturated soil can be obtained. At present, there are many methods to minimize the objective function, such as the steepest descent method, Newton method, Gaussian method, and LM method (Levenberg-Marquardt method), among which the LM method is the most widely used as a standard method.

Claims (7)

1. detect a resistivity imaging consolidometer for unsaturated soil infiltration coefficient, it is characterized in that: comprise top cover, side ring and chassis, described side ring is located on chassis, and described top cover is inserted in side ring, wherein:

The top of described top cover is stainless steel cover, bottom is plastic cylinder, multiple copper electrode is evenly distributed with in described plastic cylinder, also be provided with flexure element and detection instrument simultaneously, described plastic cylinder is provided with first row aquaporin and the first draining donut, and described first draining donut is communicated with first row aquaporin;

Described side ring is lined with the stainless steel ring of plastic circle ring in being, equally spacedly on the sidewall of simultaneously side ring be provided with multiple copper electrode;

Described chassis comprises stainless steel cask and is located at the plastic inner lining of stainless steel cask inwall, described plastic inner lining is provided with copper electrode, flexure element, detection instrument and the second draining donut equally, and corresponding with the copper electrode in plastic cylinder, flexure element, detection instrument and the first draining donut respectively; Described plastic inner lining is also provided with second row aquaporin simultaneously, and this second row aquaporin is connected with the second draining donut.

2. detect the resistivity imaging consolidometer of unsaturated soil infiltration coefficient according to claim 1, it is characterized in that: described copper electrode comprises copper electrode bar, polyamide fibre plastic jacket, stainless steel handle and wire, described copper electrode bar tail end is connected with wire, described polyamide fibre plastic jacket is enclosed within copper electrode bar, and described wire to be imbedded in stainless steel handle and left lead-in wire; Copper electrode bar and Maranyl are provided with O-ring seal between overlapping simultaneously.

3. detect the resistivity imaging consolidometer of unsaturated soil infiltration coefficient according to claim 2, it is characterized in that: described top cover and chassis are respectively equipped with 13 copper electrodes, top cover and chassis concentric be circumferentially evenly distributed with 8 copper electrodes respectively, be separately installed with 5 copper electrodes in the centre on top cover and chassis.

4. detect the resistivity imaging consolidometer of unsaturated soil infiltration coefficient according to claim 3, it is characterized in that: the surface of contact of described top cover and side ring, and the surface of contact on side ring and chassis is provided with O-ring seal; The surface of contact of described copper electrode and plastic cylinder or plastic inner lining is provided with O-ring seal simultaneously.

5. detect the resistivity imaging consolidometer of unsaturated soil infiltration coefficient according to claim 4, it is characterized in that: described side ring is provided with 16 copper electrodes.

6. detect the resistivity imaging consolidometer of unsaturated soil infiltration coefficient according to claim 5, it is characterized in that: the material of described plastic cylinder and plastic inner lining is polyamide fibre, and resistivity is 1 × 10 ¹³Ω m ~ 9 × 10 ¹³Ω m.

7. detect the resistivity imaging consolidometer of unsaturated soil infiltration coefficient according to claim 6, it is characterized in that: the outer wall on described chassis is provided with the pressure valve be connected with drainage channel.