CN102608013A - Method for measuring porosity in piping development process - Google Patents

Abstract

The invention discloses a method for measuring the porosity in the piping development process, and determines the porosity at a certain moment in the piping development process by testing parameters such as initial porosity, volume strain, and fine particle loss. The method for measuring the porosity in the piping development process provided by the invention can solve the old problem that the soil porosity evolution process cannot be determined during the piping development process, and will provide an important theoretical basis for establishing a mathematical model for predicting the piping development process.

Description

A Method for Measuring Porosity During Piping Development

technical field

The invention relates to a method for measuring the porosity in the piping development process.

Background technique

Piping is a very important form of dam seepage failure, and its development process involves many complex mechanical behaviors such as pore water seepage, movable fine particle erosion migration, porous medium deformation, etc., and is accompanied by continuous changes in porosity. Determining the porosity of the soil at any time during the piping development process is the key to accurately predicting the piping development process. It has very important theoretical and practical significance for comprehensively and objectively understanding the piping mechanism and correctly predicting the piping development process.

However, due to the concealment of the piping development process, there is no report on the porosity change law in the piping development process, and the porosity models commonly used in the seepage stress coupling research have not addressed the particularity of the piping problem, and have not considered The problem of mass loss caused by the loss of movable fine particles during the piping development process cannot be used for piping research.

The inventor submitted a patent application for "A Seepage Erosion Stress Coupling Piping Test Device" on August 23, 2011, with the application number 201110242127.0. In this application, the inventor provided a seepage erosion stress coupling piping test device, as shown in Figure 1, including a base 1, a porous steel plate 11, a pressure chamber 2, a sample 3, a heat shrinkable tube 4, a cap 5, a pebble filter Layer 6, top cover 7, axial pressure rod 8, axial pressure device 9, water outlet pipe 10, photoelectric sensor 12, resistance strain gauge 13, measuring cup 14. The drain groove is arranged in the base 1, the pressure chamber 2 is arranged on the upper part of the base 1, and the top cover 7 is arranged on the upper part of the pressure chamber 2; one end of the outlet pipe 10 is connected to the bottom outlet of the base 1, and the other end extends into the measuring cup 14; The chamber 2 is built on the base 1, and the porous steel plate 11 is arranged between the sample 3 and the base 1. The outer side of the sample 3 is tightly wrapped with a heat-shrinkable tube 4, and a cap 5 is arranged on the top, and the pebble filter layer 6 is filled in the cap 5; One end of the pressure rod 8 passes through the top cover 7 to contact the cap 5, and the other end is connected to the axial presser 9; the photoelectric sensor 12 is arranged on the body of the water outlet pipe 10; The hole diameter of the porous steel plate 11 is 0.075mm-5mm. Generally, through holes with a diameter of 0.075 mm, a diameter of 2 mm, and a diameter of 5 mm are used for experiments. The osmotic pressurizer is connected to the cap 5 through pipelines, the confining pressure pressurizer is connected to the bottom of the base 1 through pipelines, and communicates with the pressure chamber 2, the displacement sensor is arranged at the top of the axial compression rod 8, and the strain data collector It is connected with the resistance strain gauge 13, and the pore water pressure sensor is connected with the porous steel plate 11 above the base 1 through a pipeline.

The device can consider the influence of multi-phase and multi-field coupling effects such as pore water seepage-fine particle erosion migration-soil deformation on the development process of soil piping, and can track and monitor the soil under three-dimensional compression. , in which the dynamic change process of movable fine particle content, porosity, permeability, settlement and other indicators. However, due to the limitations of the inventor's research, the inventor has not been able to accurately grasp the method of measuring the porosity during the piping development process, thus restricting the in-depth research on the piping development mechanism.

Contents of the invention

Purpose of the invention: The purpose of the present invention is to address the deficiencies of the prior art and on the basis of further research by the inventors, to provide a method for measuring the porosity during the development of piping using a seepage erosion stress coupling piping test device.

Technical solution: The method for measuring the porosity in the process of piping development according to the present invention is carried out by using the seepage erosion stress coupled piping test device invented by the inventor, which mainly includes the following steps:

为0；确定试验初始时刻细颗粒流失量

为0；(1) Determine the initial porosity φ ₀ of the filling sample according to the filling dry density of the sample and the saturated water demand; determine the volume strain at the initial moment of the sample test

is 0; determine the loss of fine particles at the initial moment of the test

is 0;

确定t₀时刻试样的体积应变

(2) During the period from 0 to t ₀ , the axial strain ε ₁ is obtained by dividing the settlement monitored by the displacement sensor by the sample height; the hoop strain ε ₂ is obtained by collecting the resistance strain gauge pasted in the middle of the sample; The relationship between volume strain ε _v , axial strain ε ₁ and hoop strain ε ₂ in the test:

Determine the volumetric strain of the sample at time t ₀

(3) During the period from 0 to t ₀ , collect the loss of fine particles at time t ₀

(4) According to the following formula, calculate the porosity at time t ₀ in the period from 0 to t ₀

In the formula, ρ ^sR represents the density of soil particles.

确定t₁时刻试样的体积应变

(6) During the period from t ₀ to t ₁ , the axial strain ε ₁ is obtained by dividing the settlement monitored by the displacement sensor by the sample height; the hoop strain ε ₂ is obtained by collecting the resistance strain gauge pasted in the middle of the sample; The relationship between volume strain ε _v , axial strain ε ₁ and hoop strain ε ₂ in the axial test:

Determine the volumetric strain of the sample at time t ₁

(7) During the period from t ₀ to t ₁ , test the loss of fine particles at time t ₁

(8) According to the following formula, calculate the porosity at time t ₁ in the period from t ₀ to t ₁

Beneficial effects: the method for measuring the porosity in the piping development process provided by the present invention can solve the old problem that the soil porosity evolution process cannot be determined during the piping development process, and is conducive to deepening the in-depth understanding of the piping development mechanism. Mathematical models of developmental processes provide an important theoretical basis.

Description of drawings

Figure 1 is a schematic diagram of the structure of the seepage erosion stress coupled piping test device.

In the figure, 1 is the base, 11 is the porous steel plate, 2 is the pressure chamber, 3 is the sample, 4 is the heat shrink tube, 5 is the cap, 6 is the pebble filter layer, 7 is the top cover, 8 is the axial pressure rod, 9 is an axial presser, 10 is a water outlet pipe, 12 is a photoelectric sensor, 13 is a resistance strain gauge, and 14 is a measuring cup.

Detailed ways

The technical solutions of the present invention will be described in detail below, but the protection scope of the present invention is not limited to the embodiments.

Embodiment: The present invention utilizes the seepage-erosion stress-coupled piping test device shown in FIG. 1 to measure the porosity of the soil during the piping development process.

The test method of seepage erosion stress coupled piping test device, the steps are as follows:

(1) Preparation and installation of samples. First, according to the requirements of dry density and water content, a special split mold is used to prepare the sample, and the outer surface of the sample is tightly wrapped with a heat-shrinkable tube. Secondly, place a porous steel plate with a diameter of 2mm on the base (the porous steel plate is mainly used to separate coarse and fine materials, this test assumes that the particle size of the movable fine particles is less than 2mm, that is, in the test, only fine particles with a particle size of less than 2mm can flow out of the test sample), fix the sample on the base of the instrument, and tighten the screws. Finally, put a cap on the top of the sample, and be careful to keep the sample in a vertical state at all times, so as to ensure that eccentric compression will not occur when the axial pressure is applied later, which will affect the test results.

(2) Paste the resistance strain gauge. In order to monitor the hoop strain of the sample and determine the volumetric strain of the sample during the piping development process, four resistance strain gauges are evenly pasted on the heat shrinkable tube on the same circumference near the middle of the sample, and the angle of each strain gauge is A difference of 90 degrees. During the test, the strain values of 4 resistance strain gauges were collected, and the average value was used as the hoop strain value of the sample.

(3) Apply confining pressure. First, the confining chamber is filled with water. Install the pressure chamber, pay attention to tightness. Open the air release valve on the top of the pressure chamber, and start to add water to the pressure chamber slowly. When the water is completely filled in the pressure chamber and overflows from the air release valve, tighten the air release valve and close the water inlet valve. Secondly, install the axial pressure rod to adjust the balance of the lever. Install the axial pressure rod to ensure that the axial pressure rod is just placed in the groove on the top of the cap, tighten the nut to ensure close contact, place the displacement sensor on the top of the nut to maintain close contact, and adjust the counterweight to make the lever in balance Location. Finally, open the confining pressure control valve to start applying confining pressure, and at the same time open the drain valve, the sample begins to consolidate, and the water flows through the outlet pipe and enters the measuring cup.

(4) Apply axial pressure. According to the drainage and consolidation process of the sample, start the axial pressurizer and apply axial pressure. Add weights, the lever changes from balanced to unbalanced, and the balance adjustment device is rotated until the lever changes from unbalanced to balanced again. During the loading process, it is applied in stages, and the settlement of the sample during the consolidation process is closely monitored through the displacement sensor. After the first level of pressure is applied, when the settlement of the sample no longer changes, the next level of pressure is applied until the loading reaches required axial load. After the sample settlement is stable, keep the confining pressure and axial pressure constant to simulate the three-dimensional compression state of the undisturbed soil in actual engineering.

(5) Apply osmotic pressure. Open the osmotic pressure control valve, start the osmotic pressurizer, and start to apply osmotic pressure in stages. The osmotic water flow enters the sample through the water inlet pipe, and enters the measuring cup through the water outlet pipe. During this process, the following data are closely monitored: (a) the relationship between sample flow and permeation slope; (b) the relationship between turbidity and permeation slope monitored by the photoelectric sensor, which is used to judge the critical permeation when the movable fine particles start to start. Slope; (c) fine particle loss-time relationship; (d) sample settlement-time relationship, sample circumferential strain-time relationship, sample settlement-permeation slope relationship, sample circumferential strain-permeation slope drop relationship.

The above-mentioned seepage erosion stress coupled piping test device is applied to the method of the present invention, and the specific theoretical derivation process is as follows:

Generally, soil consists of three phases, namely, soil skeleton phase, movable fine particle phase, and water phase. For a multiphase fluid system, the mass conservation equation of the α phase:

为产生α相的质量速率。左边第一项表示α相的分密度变化率，第二项表示α相在单元体dV内的净积累量，右边项

是在单位体积dV中由于侵蚀作用产生的α相的质量速率。式(1)的物理意义为：dV内α相的质量增长率与α相的净积累质量速率之和等于dV内产生α相的质量速率。In the formula, ρ ^α is the partial density of α phase, v ^α is the true velocity of α phase, t is time,

is the mass rate at which α-phase is produced. The first item on the left indicates the fractional density change rate of the α phase, the second item indicates the net accumulation of the α phase in the dV of the unit body, and the right item

is the mass rate of α-phase produced by erosion in unit volume dV. The physical meaning of formula (1) is: the sum of the mass growth rate of α phase in dV and the net accumulation mass rate of α phase is equal to the mass rate of α phase in dV.

In the formula, dm ^α is the mass of α phase, ρ ^sR is the density of soil particles, and n ^α is the volume fraction of α phase. Substituting formula (2) into formula (1), we get:

For the soil skeleton phase, its mass conservation equation is:

φ为孔隙率，v^s为土骨架的运动速度。

表示dV内产生土骨架相的质量速率，负号表示土骨架相受水流侵蚀产生了可动细颗粒相，质量损失。因此，式(4)可以简化为：where n ^s is the volume fraction of soil framework phase,

φ is the porosity, and v ^s is the movement velocity of the soil skeleton.

Indicates the mass rate of the soil skeleton phase produced in dV, and the negative sign indicates that the soil skeleton phase is eroded by water flow and produces a mobile fine particle phase, resulting in mass loss. Therefore, formula (4) can be simplified as:

Further expand the formula (5), we get

In the formula, the first item on the left end is the local derivative item of the field, which reflects the unsteady nature of the field change; the second item is the spatial derivative item of the field, which is essentially the convection item caused by the displacement of the solid skeleton, reflecting the unsteady nature of the field change. Uniformity. In the small deformation theory of solid mechanics, it can be ignored; the third item is the change item caused by the deformation of the solid skeleton, using the relationship between velocity and displacement:

From the small deformation geometric relationship, we get

In the formula, ε _v is the volume strain, u(u _x , u _y , u _z ) is the displacement vector of the soil skeleton. Substituting formulas (7)-(8) into formula (6), we get:

During the time period t ₀ ~ t ₁ , the above formula is integrated to get:

分别为t₀，t₁时刻的孔隙率，

分别为t₀，t₁时刻的体积应变，

分别为t₀，t₁时刻的细颗粒流失量。In the formula:

are the porosity at time t ₀ and t ₁ , respectively,

are the volumetric strains at t ₀ and t ₁ , respectively,

Respectively t ₀ , t ₁ the loss of fine particles.

Therefore, the method of utilizing the above-mentioned seepage-erosion stress-coupled piping test device to measure the porosity in the piping development process includes the following steps:

为0；确定试验初始时刻细颗粒流失量为0；(1) Determine the initial porosity φ ₀ of the filling sample according to the filling dry density of the sample and the saturated water demand; determine the volume strain at the initial moment of the sample test

is 0; determine the loss of fine particles at the initial moment of the test is 0;

确定t₀时刻试样的体积应变

(2) During the period from 0 to t ₀ , the axial strain ε ₁ is obtained by dividing the settlement monitored by the displacement sensor by the sample height; the hoop strain ε ₂ is obtained by collecting the resistance strain gauge pasted in the middle of the sample; The relationship between volume strain ε _v , axial strain ε ₁ and hoop strain ε ₂ in the test:

Determine the volumetric strain of the sample at time t ₀

(3) During the period from 0 to t ₀ , collect the loss of fine particles at time t ₀

(4) According to the following formula, calculate the porosity at time t ₀ in the period from 0 to t ₀

In the formula, ρ ^sR represents the density of soil particles.

确定t₁时刻试样的体积应变

(6) During the period from t ₀ to t ₁ , the axial strain ε ₁ is obtained by dividing the settlement monitored by the displacement sensor by the sample height; the hoop strain ε ₂ is obtained by collecting the resistance strain gauge pasted in the middle of the sample; The relationship between volume strain ε _v , axial strain ε ₁ and hoop strain ε ₂ in the axial test:

Determine the volumetric strain of the sample at time t ₁

(7) During the period from t ₀ to t ₁ , test the loss of fine particles at time t ₁

(8) According to the following formula, calculate the porosity at time t ₁ in the period from t ₀ to t ₁

In the formula, ρ ^sR represents the density of soil particles.

As stated above, while the invention has been shown and described with reference to certain preferred embodiments, this should not be construed as limiting the invention itself. Various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (1)

1. A method for measuring porosity in the piping development process, characterized in that it comprises the steps: (1) Determine the initial porosity φ ₀ of the filling sample according to the filling dry density of the sample and the saturated water demand; determine the volume strain at the initial moment of the sample test

is 0; determine the loss of fine particles at the initial moment of the test

is 0; (2) During the period from 0 to t ₀ , the axial strain ε ₁ is obtained by dividing the settlement monitored by the displacement sensor by the sample height; the hoop strain ε ₂ is obtained by collecting the resistance strain gauge pasted in the middle of the sample; The relationship between volume strain ε _v , axial strain ε ₁ and hoop strain ε ₂ in the test: ε _v = ε ₁ + 2ε ₂ , determine the volume strain of the sample at time t ₀

(3) During the period from 0 to t ₀ , collect the loss of fine particles at time t ₀

(4) According to the following formula, calculate the porosity at time t ₀ in the period from 0 to t ₀ ${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</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">\; \&epsiv;</span>}}_{{\mathrm{<span\; class="notranslate">\; v</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{{\mathrm{<span\; class="notranslate">\; v</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}}}<span\; class="notranslate">\; )</span>$ In the formula, ρ ^sR represents the density of soil particles; (5) During the period from t ₀ to t ₁ , the axial strain ε ₁ is obtained by dividing the settlement monitored by the displacement sensor by the sample height; the hoop strain ε ₂ is obtained by collecting the resistance strain gauge pasted in the middle of the sample; The relationship between volume strain ε _v , axial strain ε ₁ and hoop strain ε ₂ in the axial test: ε _v = ε ₁ + 2ε ₂ , determine the volume strain of the sample at time t ₁

(6) During the period from t ₀ to t ₁ , test the loss of fine particles at time t ₁

(7) According to the following formula, calculate the porosity at time t ₁ in the period from t ₀ to t ₁

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</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">\; \&epsiv;</span>}}_{{\mathrm{<span\; class="notranslate">\; v</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{{\mathrm{<span\; class="notranslate">\; v</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; m</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}^{\mathrm{<span\; class="notranslate">\; R</span>}}}<span\; class="notranslate">\; )</span>$ In the formula, ρ ^sR represents the density of soil particles.

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