CN114324103A - Method for measuring permeability coefficient of saturated clay body - Google Patents
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- 239000004927 clay Substances 0.000 title claims abstract description 245
- 229920006395 saturated elastomer Polymers 0.000 title claims abstract description 234
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- 239000002689 soil Substances 0.000 claims abstract description 118
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- 238000000326 densiometry Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
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Abstract
The invention provides a method for measuring the permeability coefficient of a saturated clay body, which is characterized by comprising the following steps: a, measuring clay body relevant soil mechanical parameters; step B, obtaining the effective pore ratio e of the clay bodye(ii) a Step C, obtaining the effective specific surface area S of the saturated clay bodye(ii) a D, measuring the total water flow of the cross section of the saturated clay body in unit time; and E, obtaining the permeability coefficient k of the saturated clay body. The saturated glutinous soil equivalent capillary duct permeability coefficient is obtained by removing ineffective pores and pore areas which have no influence on the seepage in the saturated glutinous soil on the basis of deeply analyzing and researching the seepage mechanism of the saturated glutinous soil, splitting and integrating a KC constant into parameters such as the seepage channel curvature, the effective specific surface area, the effective pore ratio and the like, and the series of parameters are easily measured by indoor tests, so that the measuring precision of the saturated glutinous soil equivalent capillary duct permeability coefficient established by the invention is greatly improved.
Description
Technical Field
The invention belongs to a method for measuring the permeability coefficient of saturated clay in the field of geotechnical engineering.
Background
The permeability coefficient is also called hydraulic conductivity coefficient. In isotropic media, it is defined as the unit flow rate per unit hydraulic gradient, representing the ease with which a fluid passes through a pore framework. The permeability coefficient is one of basic parameters in the engineering field, and the accurate determination of the permeability coefficient of the saturated sticky soil body is beneficial to calculating and determining the permeability, water pressure and seepage flow of the soil body. The accurate saturated clay permeability coefficient can accurately calculate the seepage water amount of earth-rock dams and channels, the water inflow amount during foundation pit excavation and the water supply amount of wells, and the accuracy of the permeability coefficient directly relates to the economic benefit of engineering. In slope engineering, seepage water pressure is a main cause of slope instability damage, and an accurate saturated clay permeability coefficient is directly related to stability evaluation and anti-slip engineering design of the slope engineering. The permeability coefficient is also a key parameter for evaluating the permeability deformation geological problem in the engineering foundation, not only directly influences the stability and safety of engineering projects, but also relates to the loss and benefit of engineering benefits, and the reasonable determination of the permeability coefficient of the saturated clay body is important in the engineering field.
The permeability of the saturated clay body is far less than that of the sandstone soil, the saturated clay body is often treated as a waterproof layer in early engineering application, but along with the frequent occurrence of a series of engineering safety problems such as ground subsidence deformation, slope sliding instability of a soft clay interlayer, leakage of a clay core earth-rock dam, foundation pit tunnel inrush and the like, the seepage research of the saturated clay body draws wide attention of the engineering and academic circles. The quantity and the scale of the internal pores of the cohesionless soil such as sand and stone are relatively large, and the influence of the electric field force on the surface of soil particles on the seepage water body is small, so the cohesionless soil seepage highly conforms to the macroscopic seepage principle of water, and research results such as Darcy seepage law, Dupuit seepage principle and the like are subjected to practical engineering tests for many years, and have been highly recognized by mass engineers and experts. However, the size of the pores inside the saturated clay body is far smaller than that of the non-cohesive soil, the coulomb force, the van der waals force and the like on the surface of the soil particles seriously affect the seepage inside the soil body, and cause that strong bound water and partial weak bound water on the surface of the soil particles cannot participate in the seepage activity inside the soil body, and a large number of ineffective disconnected pores such as blind holes, end holes and isolated holes exist inside the saturated clay body, thereby further causing the complex and various seepage mechanisms of the water body inside the saturated clay body. So far, a saturated cohesive soil body seepage model which is similar to the Darcy seepage law of non-cohesive soil and meets the high recognition of a large number of engineers and experts and scholars is not established. In recent years, many scholars at home and abroad establish a plurality of correction seepage models on the basis of Darcy law, K-C equation and the like according to factors such as porosity, saturated water content, effective specific surface area, initial hydraulic gradient, fluid type, soil structure and the like of a saturated clay body. However, the existing theoretical calculation model has the common defects that basic parameters are difficult to accurately determine, so that the calculation result has larger error, and the statistical model is influenced by data and soil body properties and has larger limitation.
At present, the most widely applied saturated clay permeability coefficient in the field of geotechnical engineering is to modify the Kozeny-Carman equation, but the modified Kozeny-Carman equation determines the permeability coefficient based on the pore ratio and specific surface area of the saturated clay mass, and a comprehensive constant is adopted for the factors of the shape of soil particles of the saturated clay body, the actual seepage direction, the path length and the like, i.e. the KC constant, originally proposed by Kozeny in 1927, which later Carman was corrected by introducing tortuosity in the percolation channel, but the KC constant was only a comprehensive empirical constant without practical physical significance, although the accuracy of the KC constant is continuously improved through the continuous efforts of a large number of experts and scholars, and a novel theoretical formula of the KC constant is established according to a fractal theory, however, the value of the comprehensive empirical constant still depends on experience to a great extent, and the seepage mechanism of the saturated clay body cannot be accurately described.
Disclosure of Invention
In order to solve the defects and defects of the existing saturated clay body permeability coefficient determination, the invention provides a permeability coefficient determination method based on an effective pore ratio and an effective specific surface area, and the technical scheme is as follows:
step A: determination of clay-related soil mechanical parameters
During geotechnical engineering investigation, geotechnical sampling is carried out according to the technical rules of geological exploration and sampling in constructional engineering (JGJ/T87-2012), particle analysis is carried out by adopting a densitometry method test according to the standard of geotechnical test methods (GB/T50123-2019), a particle grading curve is drawn according to test results, and a group of soil particle diameters d in the saturated clay body particle grading curve are respectively obtained1、d2Particle diameter of less than d1、d2Cumulative mass percentage m (d) of particles of1)、m(d2) The maximum soil particle diameter d in the saturated clay bodymaxAnd the minimum earth particle size dminAnd effective seepage limiting the particle size d of soil particlesreAccording to the theory of equivalent spherical pores of clay particles, suggest dre＝2.42×10-5And m is selected. Determining the specific gravity G of saturated clay particles by a specific gravity test according to geotechnical test method standard (GB/T50123-2019) by using a pycnometer methodsDetermining the dry density rho of the clay body by adopting a ring cutter method to carry out a density testdThe water temperature inside the saturated sticky soil body is measured by a water temperature meter, which is reported in geotechnical test method Standard
And (GB/T50123-2019) determining the dynamic viscosity coefficient eta of the water by a table look-up.
And B: obtaining effective pore ratio parameter of clay body
1. Obtaining the total pore ratio e of the saturated cohesive soil body
Determining the specific gravity G of clay particles based on the step A by three-phase conversion of soil mechanicssClay dry density rhodAnd (3) calculating and determining the total porosity e of the clay body according to the formula (1):
in the formula: rhowIs the natural density of water, pw＝1g/cm3。
2. Obtaining the effective pore ratio e of the saturated clay bodye
According to the invention, through researching the proportional relation between the volumes of flowing water and non-flowing water in a large amount of saturated clay bodies, the relation is found to be a function related to the porosity of a saturated cohesive soil body, but the effective porosity of the saturated cohesive soil body is influenced by the combined action of water and the soil body due to the volume ratio of water to soil body, the volume of water in the seepage process is continuously changed, so that the error of a calculation result is larger, the effective porosity is determined by using the total pore ratio of the saturated cohesive soil body according to the three-phase conversion principle and the hydraulics principle of the soil body, the volume of soil particles in the seepage process is constant because the total pore ratio and the effective pore ratio of the saturated cohesive soil body are the volume ratio of water to soil particles, and the theoretical formula of the effective pore ratio of the saturated cohesive soil body is established based on the proportional relation between the volumes of flowing water and non-flowing water in the saturated clay bodies, so that the calculation precision is greatly improved.
The main body of participation of the seepage of the saturated clay body is flowing water (containing free water and partial weak bound water), the volume of the flowing water is the effective pore volume related to the seepage in the saturated clay body, and the effective pore ratio of the saturated clay body is obtained according to the formula (2):
in the formula: and m is a constant related to the soil property, and the suggested value range is 1-2.
And C: obtaining the effective specific surface area parameter of the saturated clay body
1. Obtaining the fractal dimension D of saturated clay particles
A group of soil particle diameters d in the cohesive soil particle grading curve determined based on the step A1、d2And particle diameter less than d1、d2Cumulative mass percentage m (d) of particles of1)、m(d2) Substituting the formula (3) to obtain the fractal dimension D of the clay particles:
in view of the fact that the effective specific surface area of the saturated clay body and the result error measured by the mercury intrusion test calculated by the traditional theoretical formula are too large, the analysis reason finds that (1) the self precision of the porosity of the saturated clay body used in the formula is poor, and the effective porosity of the saturated clay body is adopted to improve the calculation precision; (2) the ratio of the total pore surface area of the saturated clay body to the effective pore volume is used as the effective specific surface area in the formula, so that the result is larger. Based on the maximum soil particle size, the minimum soil particle size and the effective seepage limit soil particle size d in the saturated clay body in the step Amax、dmin、dreEqual parameters, the total pore ratio e of the saturated cohesive soil body in the step B and the effective pore ratio e of the saturated cohesive soil bodyeAnd obtaining the effective specific surface area S of the saturated clay body according to the formula (4) by the fractal dimension D of the clay particles in the formula (3)e：
Step D: obtaining the total water flow of the saturated clay body passing through the cross section of the saturated clay body in unit time
1. Assumption of conditions
1) The saturated clay body is supposed to be formed by combining ideal spheres which are distributed continuously and have uniform particles;
2) supposing that pores communicated with the inside of the saturated clay body form a seepage channel, generalizing the seepage channel into a seepage system consisting of a large number of independent capillary pipelines with the same length and diameter and certain tortuosity;
3) the equivalent seepage capillary channels in the saturated clay body are assumed to have the same hydraulic radius, specific surface area and channel internal volume.
4) The equivalent seepage capillary channels in the saturated clay body are assumed to be independent and not influenced mutually.
2. Obtaining the actual bending length of the equivalent seepage capillary channel of the saturated viscous soil body
The seepage network in the actual saturated clay body is constructed by pore channels which are complicated in tortuosity and are mutually communicated, and the completely straight clay body pore seepage channel has a very small proportion in the clay body, so that the clay body pore seepage channel is generalized into a capillary with a certain tortuosity, the tortuosity of the equivalent seepage capillary channel of the saturated clay body is quantitatively parameterized by adopting the curvature according to the concept of the curvature of the channel, and the actual bending length of the equivalent seepage capillary channel in the saturated clay body is obtained according to a formula (5-7), and the concrete steps are as follows:
determining the effective porosity n of the saturated clay body according to the conversion of the three-phase index of the soile：
In the formula: e.g. of the typeeThe effective pore ratio of the saturated clay body; and e is the total porosity of the saturated clay body.
Because the saturated clay particles are assumed to be ideal spherical particles, the cluster is structured to form a clay body, and the micro-test research result of a large amount of saturated clay bodies is researched, the porosity in the traditional curvature calculation formula is deduced and applied through the effective pore ratio, the curvature of the equivalent seepage capillary pipeline of the saturated clay body is determined according to the effective pore ratio of the saturated clay body, and the application of the curvature to the effective pores in the saturated clay body is well matched.
In the formula: n iseIs the effective porosity of the saturated clay body.
Obtaining the actual bending length of the equivalent seepage capillary pipeline of the saturated clay body according to a formula (7):
Le＝τL (7)
in the formula: tau is the curvature of the equivalent seepage capillary channel in the saturated clay body; and L is the straight length (cm) of the equivalent seepage capillary pipeline in the saturated clay body along the water flow direction, namely the height of the saturated clay body in the seepage direction.
3. Obtaining the equivalent radius r of the seepage capillary channel of the saturated clay bodye
Because the seepage channels in the saturated viscous soil body have different cross-sectional shapes and sizes, the invention optimizes the sizes of the seepage channels with different shapes and sizes in the viscous soil body according to the basic concept of hydraulic radius, and carries out average conversion treatment by adopting the actual bending length, the effective pore ratio and the effective specific surface area of the equivalent seepage capillary pipeline of the saturated viscous soil body to obtain the equivalent radius r of the single equivalent seepage capillary pipeline filled with water in the saturated viscous soil bodyeThe result is more accurate, and the error is reduced for the later osmotic coefficient:
in the formula:
the effective flow area of a flow groove in the saturated clay body is shown;
the effective wet period of a saturated clay fluid launder; seThe effective specific surface area of soil particles in the saturated clay body.
4. Obtaining the total number N of equivalent capillaries in a saturated clay capillary model
According to the invention, the total number N of the equivalent capillaries in the saturated clay body capillary model is obtained by adopting a saturated clay body effective pore ratio establishing formula (11) according to the condition that the effective cross section area of a saturated clay body sample is equal to the total cross section area of N equivalent capillary pipelines because the total number N of the equivalent capillaries in the traditional saturated clay body adopts the total porosity, so that the N value is generally larger:
in the formula: a is the cross-sectional area of the saturated clay sample.
5. Obtaining the water flow Q of the cross section of a single equivalent seepage capillary pipeline in the saturated clay body in unit time
According to the practical engineering experience, the water seepage speed in the saturated clay body is not more than 10-6cm/s, therefore, the water seepage form in the saturated clay body is laminar flow, and the water flow Q of the cross section of a single equivalent seepage capillary pipeline in the saturated clay body in unit time is obtained according to the formula (12):
in the formula: r iseThe equivalent radius (m) of the capillary seepage pipeline of the saturated clay body; eta is the kinetic viscosity coefficient (kPa · s) of water; l iseIs equivalent permeation of saturated clay bodyThe actual bending length (m) of the flow capillary channel; Δ p is the head difference (m), γ, at the two ends of the capillarywIs the water gravity (kN/m)3)。
6. Obtaining the total water flow Q of the saturated clay body passing through the cross section of the saturated clay body in unit timez
The macroscopic hydraulic gradient i of the saturated clay body is as follows:
according to the assumed conditions of the model, the internal seepage channel of the saturated clay body consists of equivalent seepage capillaries which are independent from each other, the total seepage flow of the saturated clay body in unit time is the sum of the water flow of the saturated clay body in unit time of the N equivalent seepage capillary channels in unit time, and the sum is the product of the total number of the equivalent seepage capillary channels in the saturated clay body and the flow of the clay body single equivalent seepage capillary. The model established by the invention is based on effective pores actually participating in seepage, the effective pore ratio and the effective specific surface area parameters are extracted, and the formula (14) is established for obtaining the total water flow Q of the cohesive soil body passing through the cross section of the cohesive soil body in unit timezThe result is more in line with the actual seepage process.
Step E: obtaining the permeability coefficient of the saturated clay body
The Darcy law shows that the total water flow of the saturated clay per unit time in the cross section is as follows:
Qz＝kiA (15)
in the formula: k is the permeability coefficient of the saturated clay body.
The effective pore ratio and the effective specific surface area parameters determined in the steps are adopted, a calculation formula of the permeability coefficient of the saturated clay body is deduced and established according to the Darcy law, and the scientificity and the advancement of the method are proved through an indoor seepage test of the saturated clay body and a traditional theoretical formula.
In the simultaneous steps D, the permeability coefficient of the saturated clay body can be calculated by the formula (14) and the formula (15):
the invention achieves the following beneficial effects:
the saturated clay equivalent capillary duct permeability coefficient is obtained by removing ineffective pores and pore areas which have no influence on the seepage in the saturated clay on the basis of in-depth analysis and research of the seepage mechanism of the saturated clay, splitting and integrating a KC constant into parameters such as the seepage channel curvature, the effective specific surface area, the effective pore ratio and the like, and the series of parameters are easily measured by indoor tests, so that the measurement accuracy of the saturated clay equivalent capillary duct permeability coefficient established by the method is greatly improved and is superior to the conventional correction Kozeny-Carman equation.
Drawings
FIG. 1 is a grading curve of soil particles of a yellow clay sample.
Detailed Description
Embodiments of the present invention are described in detail below with reference to the accompanying drawings.
This embodiment provides a method for determining permeability coefficient of a saturated clay body, including the following steps:
the method comprises the following steps: obtaining clay body related soil mechanical parameters
The method selects 5 cylindrical saturated remolded yellow clay soil samples with different total pore ratios, the cross section diameter of the clay samples is 3.91cm, the height of the clay samples is 8cm for explanation, particle analysis is carried out by adopting a densitometry test according to geotechnical test method standard (GB/T50123-2019), a particle grading curve (as shown in figure 1) is drawn according to test results, and a group of soil particle diameters d in the saturated clay soil particle grading curve are respectively obtained1＝0.0075cm、d20.001cm, particle diameter less than d1、d2Cumulative mass percentage m (d) of particles of1)＝94.2％、m(d1) 45.6 percent of the maximum soil particle size and the minimum soil particle size in the saturated clay body and effective seepage limiting soil particlesParticle diameter dmax＝0.025cm、dmin＝1×10-5cm、dre＝2.42×10-5And m is selected. According to the standard of soil test methods (GB/T50123-2019), a specific gravity test is carried out by adopting a pycnometer method to obtain the specific gravity G of the saturated clay particless2.71, determining the dynamic viscosity coefficient eta of water according to a table look-up of water temperature in geotechnical test method standard (GB/T50123-2019), and determining that the water temperature is 20 ℃, so that the dynamic viscosity coefficient of the water is 1.01 multiplied by 10-6kPa · s. Density test is carried out by adopting a ring cutter method to determine dry density rho of claydSee table 1 for details.
TABLE 1 Dry Density of yellow clay samples
Step two: obtaining effective pore ratio parameter of clay body
1. Obtaining the total pore ratio e of the saturated cohesive soil body
Adopting a three-phase conversion formula of soil mechanics, and determining the clay particle specific gravity G based on the step onesClay dry density rhodAnd (3) calculating and determining the total porosity e of the clay body according to the formula (1), and details of the result are shown in a table 2.
In the formula: rhowIs the natural density of water, pw＝1g/cm3。
TABLE 2 porosity ratio of yellow clay samples
2. Obtaining the effective pore ratio e of the saturated clay bodye
According to the invention, through researching the proportional relation between the volumes of flowing water and non-flowing water in a large amount of saturated clay bodies, the relation is found to be a function related to the porosity of a saturated cohesive soil body, but the effective porosity of the saturated cohesive soil body is influenced by the combined action of water and the soil body due to the volume ratio of water to soil body, the volume of water in the seepage process is continuously changed, so that the error of a calculation result is larger, the effective porosity is determined by using the total pore ratio of the saturated cohesive soil body according to the three-phase conversion principle and the hydraulics principle of the soil body, the volume of soil particles in the seepage process is constant because the total pore ratio and the effective pore ratio of the saturated cohesive soil body are the volume ratio of water to soil particles, and the theoretical formula of the effective pore ratio of the saturated cohesive soil body is established based on the proportional relation between the volumes of flowing water and non-flowing water in the saturated clay bodies, so that the calculation precision is greatly improved.
The main body of the saturated clay body seepage is flowing water (including free water and part of weakly bound water), and the volume of the flowing water is the effective pore volume related to seepage in the saturated clay body, the effective pore ratio of the saturated clay body is obtained by using a formula (2) (m in the formula is 1), and the result is detailed in a table 3.
In the formula: and m is a constant related to the soil property, and the suggested value range is 1-2.
TABLE 3 effective void ratio of yellow clay samples
Step three: obtaining the effective specific surface area parameter of the saturated clay body
1. Obtaining the fractal dimension D of saturated clay particles
The particle size determined in the step one is less than d1、d2Cumulative mass m (d) of particles of1)、m(d2) Particle size d of a group of soil particles in a grading curve of cohesive soil particles1、d2Substituting the formula (3) to obtain the fractal dimension D of the clay particles:
in view of the fact that the effective specific surface area of the saturated clay body and the result error measured by the mercury intrusion test calculated by the traditional theoretical formula are too large, the analysis reason finds that (1) the self precision of the porosity of the saturated clay body used in the formula is poor, and the effective porosity of the saturated clay body is adopted to improve the calculation precision; (2) the ratio of the total pore surface area of the saturated clay body to the effective pore volume is used as the effective specific surface area in the formula, so that the result is larger. Representing the maximum soil particle size, the minimum soil particle size and the effective seepage limiting soil particle size d in the saturated clay body determined based on the step onemax、dmin、dreThe total pore ratio e of the saturated clay body and the effective pore ratio e of the saturated clay body determined in the second step are equal in parameterseDetermining the fractal dimension D of the clay particles determined by the formula (3), and calculating and determining the effective specific surface area S of the saturated clay body according to the formula (4)eThe results are detailed in Table 4.
TABLE 4 effective specific surface area of yellow cohesive soil samples
Step four: determination of total water flow of saturated clay body through cross section in unit time
1. Assumption of conditions
1) The saturated clay body is supposed to be formed by combining ideal spheres which are distributed continuously and have uniform particles;
2) supposing that pores communicated with the inside of the saturated clay body form a seepage channel, the saturated clay body is generalized into a seepage system formed by a large number of independent capillary pipelines with the same length and diameter and certain tortuosity;
3) the equivalent seepage capillary channels in the saturated clay body are assumed to have the same hydraulic radius, specific surface area and channel internal volume.
4) The equivalent seepage capillary channels in the saturated clay body are assumed to be independent and not influenced mutually.
2. Obtaining the actual bending length of the equivalent seepage capillary channel of the saturated viscous soil body
The seepage network in the actual saturated clay body is constructed by pore channels which are complicated in tortuosity and are mutually communicated, and the completely straight clay body pore seepage channel occupies a very small proportion in the clay body, so that the clay body pore seepage channel is generalized into a capillary with a certain tortuosity, the tortuosity of the equivalent seepage capillary channel of the saturated clay body is quantitatively parameterized by adopting the curvature according to the concept of the curvature of the channel, and the actual bending length of the equivalent seepage capillary channel in the saturated clay body is obtained according to a formula (5-7), and the result is detailed in a table 5.
Le＝τL (7)
In the formula: e.g. of the typeeThe effective pore ratio of the saturated clay body; e is the total pore ratio of the saturated clay body; n iseEffective porosity of saturated clay body; tau is the curvature of the equivalent seepage capillary channel in the saturated clay body; l is the straight length (cm) of the equivalent seepage capillary pipeline in the saturated clay body along the water flow direction, namely the height of the cylindrical saturated remolded yellow clay soil sample.
TABLE 5 effective porosity, curvature, equivalent capillary equivalent bending length of the equivalent seepage capillary
3. Obtaining the equivalent radius r of the seepage capillary channel of the saturated clay bodye
Because the seepage channels in the saturated viscous soil body have different cross-sectional shapes and sizes, the invention optimizes the sizes of the seepage channels with different shapes and sizes in the viscous soil body according to the basic concept of hydraulic radius, and adopts the actual bending length, the effective pore ratio and the effective specific surface area of the equivalent seepage capillary pipeline of the saturated viscous soil body to carry out the averaging conversion treatment, thereby determining the equivalent radius r of the equivalent seepage capillary pipeline of a single equivalent seepage capillary pipeline filled with water in the saturated viscous soil bodyeThe theoretical result has higher precision, and the error is reduced for the later osmotic coefficient. Calculating and determining the equivalent radius r of a single equivalent seepage capillary channel filled with water in the saturated viscous soil body according to the formula (8-10)eThe results are detailed in Table 6.
In the formula:
the effective flow area of a flow groove in the saturated clay body is shown;
the effective wet period of a saturated clay fluid launder; seThe effective specific surface area of soil particles in the saturated clay body.
TABLE 6 equivalent radius of single equivalent seepage capillary channel of yellow cohesive soil sample
4. Obtaining the total number N of equivalent capillaries in a saturated clay capillary model
According to the invention, the total number N of the equivalent capillaries in the saturated clay body capillary model is obtained by adopting a formula (11) according to the condition that the effective cross section area of a saturated clay body sample is equal to the total cross section area of the N equivalent capillary channels, and the result is detailed in the result
Table 7.
In the formula: a is the cross-sectional area of the saturated clay sample.
TABLE 7 Total equivalent capillary count of yellow clay samples
5. Obtaining the water flow Q of the cross section of a single equivalent seepage capillary pipeline in the saturated clay body in unit time
According to the practical engineering experience, the water seepage speed in the saturated clay body is not more than 10-6cm/s, therefore, the water seepage form in the saturated clay body is laminar flow, and the water flow Q of the cross section of a single equivalent seepage capillary pipeline in the saturated clay body in unit time is obtained according to the formula (12):
in the formula: r iseThe equivalent radius (m) of the capillary seepage pipeline of the saturated clay body; eta is the kinetic viscosity coefficient (kPa · s) of water; l iseThe equivalent bending length (m) of a seepage capillary in a saturated clay body; Δ p is the head difference (m), γ, at the two ends of the capillarywIs the water gravity (kN/m)3)。
6. Obtaining the total water flow Q of the saturated clay body passing through the cross section of the saturated clay body in unit timez
The water head difference at the two ends of the capillary tube is delta p which is 200cm, and the macroscopic hydraulic gradient i of the saturated clay body is as follows:
in summary, according to the assumed conditions of the model, the internal percolation channel of the saturated clay body is composed of mutually independent equivalent percolation capillaries, and the total percolation rate per unit time of the cross section of the saturated clay body is the sum of the water flows per unit time of the cross sections of the N equivalent percolation capillaries of the saturated clay body, i.e. the product of the total number of the equivalent percolation capillaries in the saturated clay body and the flow rate of a single equivalent percolation capillary of the clay body. The model established by the invention is based on the effective pores actually participating in seepage, the effective pore ratio and the effective specific surface area parameters are extracted, and the formula (14) is established for calculating and determining the total water flow Q of the cohesive soil body passing through the cross section of the cohesive soil body in unit timezThe result is more in line with the actual seepage process. Calculating and determining the total water flow Q of the cohesive soil body passing through the cross section of the cohesive soil body in unit time according to the formula (14)zThe results are detailed in Table 8.
TABLE 8 Total Water flow through the yellow cohesive soil sample per unit time
Step five: obtaining the permeability coefficient of the saturated clay body
The Darcy law shows that the total water flow of the saturated clay per unit time in the cross section is as follows:
Qz＝kiA (15)
in the formula: k is the permeability coefficient of the saturated clay body.
In conclusion, the effective pore ratio and the effective specific surface area parameters determined in the steps are adopted, a calculation formula of the permeability coefficient of the saturated clay body is deduced and established according to the Darcy law, and the scientificity and the advancement of the method are proved through an indoor seepage test of the saturated clay body and a traditional theoretical formula.
The simultaneous steps of equations (14) and (15) result in the permeability coefficient k of the saturated clay mass, the results are detailed in table 9.
TABLE 9 permeability coefficient of yellow clay test specimens
The invention mainly aims to establish a saturated clay body permeability coefficient determination method which is convenient for engineering application and has definite physical and mechanical significance by combining parameters which are easy to obtain in a laboratory with a saturated clay body equivalent seepage capillary bundle theory and a Poiseiulle law according to an indoor clay particle test and a pore ratio test, and lays a foundation for support design and stability evaluation of foundation pits and side slopes.
The rationality and the advancement of the saturated clay infiltration system determined by the method are verified by a comparative test and a theoretical formula as follows:
(1) a piece of filter paper and a piece of permeable stone were placed on each of the two ends of the 5 test soil samples of the above example, and labels were accurately recorded. According to the water permeability and the structure of the test soil sample, a vacuum saturation method is selected as a test soil sample saturation treatment method, the clay sample after saturation treatment is loaded into a permeameter, and the clay sample continues to be saturated for 12 hours after air is exhausted. Setting an initial water head difference to be 2m to carry out a variable water head permeation test, measuring the water temperature and reading and recording after the seepage is stable, wherein the specific test steps refer to the 16.3 specification in the geotechnical test method standard (GB/T50123-2019).
According to the recorded data of the variable head permeability test of each clay sample, the permeability coefficients of 5 clay samples under different pore ratio conditions are obtained through calculation and analysis, and the details are shown in table 10.
TABLE 10 Permeability coefficients for various pore ratios of cohesive soil samples
(2) Theoretical calculation formula of saturated clay permeability coefficient without effective pore theory correction
When the parameters of the saturated clay pore ratio and the total pore specific surface area are adopted, the theoretical calculation formula of the saturated clay equivalent capillary permeability coefficient is as follows:
(3) modified Kozeny-Carman permeability equation
The modified Kozeny-Carman permeability equation is one of the most widely applied permeability coefficient theoretical calculation formulas in the field of porous medium seepage.
In the formula: c is a coefficient related to the shape of cohesive soil particles and the actual seepage direction, and the value is generally 0.125; rhowIs the density of water (g/cm)3) (ii) a Eta is dynamic viscosity coefficient of water (g.s/cm)2)。
In conclusion, theoretical permeability coefficients of all clay samples are respectively determined by utilizing the parameters and a theoretical calculation formula of the permeability coefficient of the saturated clay equivalent capillary pipeline and a corrected Kozeny-Carman equation, and are compared and analyzed with a variable water head permeability test result, and the result is detailed in a table 11.
TABLE 11 Permeability coefficients for various pore ratios of cohesive soil samples
The results of research and analysis on the experimental permeability coefficient and the theoretical permeability coefficient show that the clay permeability coefficient determined according to the uncorrected theoretical formula of the saturated clay permeability coefficient is 159-336 times of the experimental permeability coefficient, the error is overlarge, the reference value is extremely low, the corrected theoretical calculation formula of the clay equivalent capillary permeability coefficient and the corrected Kozeny-Carman equation have smaller errors with the experimental permeability coefficient, and the method has great engineering application and theoretical research values.
According to the results of the experimental permeability coefficient and the theoretical permeability coefficient of the saturated clay sample in the table 11, error analysis is carried out by taking the experimental permeability coefficient as a reference term and two theoretical permeability coefficients as a comparison term, and the result error of correcting the Kozeny-Carman equation is less than 3 multiplied by 10-nm/s, the error of the calculation result of the correction model established by the invention is less than 2 multiplied by 10-nm/s, the error of the correction model established by the method is smaller, the required index data such as the particle size, the mass percentage, the pore ratio, the water gravity, the dynamic viscosity coefficient and the like of clay particles are easier to obtain through indoor tests, the precision of basic parameters is high, and the method has guiding significance for seepage analysis and seepage-proofing design of civil, geotechnical and hydraulic engineering and research on seepage consolidation settlement theory of saturated clay.
The above description is only a preferred embodiment of the present invention, and not intended to limit the present invention in other forms, and any person skilled in the art may apply the above modifications or changes to the equivalent embodiments with equivalent changes, without departing from the technical spirit of the present invention, and any simple modification, equivalent change and change made to the above embodiments according to the technical spirit of the present invention still belong to the protection scope of the technical spirit of the present invention.
Claims (6)
1. A method for measuring the permeability coefficient of a saturated clay body is characterized by comprising the following steps:
step A, clay body relevant soil mechanical parameter determination
Carrying out particle analysis on the sampled rock soil by adopting a densimeter test, and respectively determining a group of soil particle diameters d in a saturated clay body particle grading curve1、d2Particle diameter of less than d1、d2Cumulative mass percentage m (d) of particles of1)、m(d2) The maximum soil particle diameter d in the saturated clay bodymaxAnd the minimum earth particle size dminAnd effective seepage limiting the particle size d of soil particlesre(ii) a Specific gravity test is adopted to determine the specific gravity G of saturated clay particlessDetermining the dry density rho of the clay body by adopting a ring cutter method to carry out a density testdMeasuring the water temperature inside the saturated clay body by using a water temperature meter, and further determining the dynamic viscosity coefficient eta of the water;
step B, obtaining the effective pore ratio e of the clay bodye
Determining effective pore ratio through the total pore ratio of the saturated clay body, and obtaining the effective pore ratio e of the saturated clay body based on the proportional relation between the volumes of flowing water and non-flowing water in the saturated clay bodye；
Step C, obtaining the effective specific surface area S of the saturated clay bodye
Obtaining the fractal dimension D of clay particles, and determining the maximum soil particle size, the minimum soil particle size and the effective seepage limiting soil particle size D in the saturated clay body based on the step Amax、dmin、dreParameters, the total pore ratio e of the saturated cohesive soil body measured in the step B and the effective pore ratio e of the saturated cohesive soil bodyeObtaining saturated clayEffective specific surface area S of the bodye：
Step D, measuring total water flow of the saturated clay body in unit time through the cross section
Step D1, generalizing the seepage network in the saturated clay body into a capillary with a certain tortuosity through a formula Le＝τL、
Obtaining the actual bending length of the equivalent seepage capillary channel of the saturated clay body, wherein L is the straight length of the equivalent seepage capillary channel in the saturated clay body along the water flow direction, neIs the effective porosity of the saturated clay body, eeThe effective pore ratio of the saturated clay body; e is the total pore ratio of the saturated clay body;
step D2, carrying out average conversion on the actual bending length, the effective pore ratio and the effective specific surface area of the saturated clay equivalent seepage capillary pipeline to obtain the equivalent radius r of the single equivalent seepage capillary pipeline filled with water in the saturated clay bodye；
Step D3, obtaining the total number N of equivalent capillaries in the saturated clay capillary model
Step D4, obtaining the water flow Q of the cross section of a single equivalent seepage capillary pipeline in the saturated clay body in unit time
In the formula: r iseIs equivalent radius of capillary seepage pipeline of saturated clay body, eta is dynamic viscosity coefficient of water, LeThe actual bending length of the capillary pipeline is equivalent to that of a saturated clay body seepage flow, the delta p is the water head difference (m) at the two ends of the capillary, and the gamma iswIs the water gravity (kN/m)3)；
Step D5, obtaining total water flow Q of the saturated clay body passing through the cross section of the saturated clay body in unit timez
step E, obtaining the permeability coefficient k of the saturated clay body
By the formula QzA saturated cohesive mass permeability coefficient k was obtained kiA,
2. the method for determining the permeability coefficient of a saturated cohesive soil body according to claim 1, wherein: in the step B, the effective pore ratio of the saturated clay body
Wherein the total pore ratio of the clay body
ρwIs the natural density of water, m is a constant and has a value range of 1-2.
3. The method for determining the permeability coefficient of a saturated cohesive soil body according to claim 1, wherein: in the step C, the fractal dimension of saturated clay particles
4. The method according to claim 3, wherein the permeability coefficient of the saturated cohesive soil mass is determined by: in the step C, the effective specific surface area of the saturated clay body
5. The method for determining the permeability coefficient of a saturated cohesive soil body according to claim 1, wherein: in the step D2, in the step D,
6. the method for determining the permeability coefficient of a saturated cohesive soil body according to claim 1, wherein: in the step D3, in the step D,
in the formula: a is the cross-sectional area of the saturated clay sample.
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