CN110516322A - It is a kind of difference hydraulic gradient under clay saturation nonlinearity infiltration coefficient prediction technique - Google Patents
It is a kind of difference hydraulic gradient under clay saturation nonlinearity infiltration coefficient prediction technique Download PDFInfo
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- 238000001764 infiltration Methods 0.000 title claims abstract description 76
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Abstract
The invention belongs to geotechnical engineering fields, it is related to a kind of clay saturation nonlinearity predicting coefficient of permeability method under different hydraulic gradient, matric suction is regarded as to the index of pore channel size distribution based on capillary theory, by pressure plate apparatus and GDS permeability test, correction factor c existing for the soil―structure interaction and saturation permeability coefficient and matric suction and starting head of test clay is obtained；The initial hydraulic gradient that every grade of pore channel is calculated based on c value calculates comprehensive infiltration proportionality constant k using TK saturation permeability coefficient modelc；Under the conditions of known practical hydraulic gradient, differentiate to whether different size of pore channel occurs seepage flow, all pore channel infiltration coefficients that seepage flow has occurred are added to obtain the soil body saturation permeability coefficient under corresponding practical hydraulic gradient, so that it is determined that saturation nonlinearity infiltration coefficient under soil difference hydraulic gradient.The present invention is of great significance to soil counterforce seepage flow and starting head research, while can play the role of scientific guidance for dyke seepage control engineering.
Description
Technical field
The invention belongs to geotechnical engineering fields, are related to a kind of prediction technique of clay saturation nonlinearity infiltration coefficient, especially
It is related to a kind of prediction technique of clay saturation nonlinearity infiltration coefficient under different hydraulic gradient.
Background technique
Soil―structure interaction (Soil-Water Characteristic Curve, abbreviation SWCC) is description unsaturation
The curve of relationship between native mesostroma suction and volumetric(al) moisture content or quality moisture content, and soil―structure interaction is able to reflect
The size and the regularity of distribution of hole in the soil body.Osmotic coefficient k is also known as hydraulic conductivity (hydraulic conductivity),
It is an index of concentrated expression soil body penetration ability, the accurate determination of numerical value has very important meaning to infiltration calculation
Justice.Due in the very strong fine and close clay of stickiness, many scholars the study found that the v-i relation curve of clay before steady seepage
Non-linear growth is presented, and does not pass through origin.This is because the hygroscopic water of fine and close clay has a biggish viscous resistance, only when
Hydraulic gradient has been more than initial hydraulic gradient, after overcoming the viscous resistance in the soil body, could be permeated.And for existing
The determination of the clay saturation nonlinearity infiltration coefficient of initial hydraulic gradient, currently without the prediction side that can establish more system
Method.
Accordingly, it is considered to which the prediction technique for originating the cohesive soil saturation nonlinearity infiltration coefficient of head is badly in need of research, but at present
The research of this aspect can not obtain greater advance.Such as Tao Gaoliang, Kong Lingwei propose T-K saturation by microcosmic angle
Infiltration coefficient model, although the model can Accurate Prediction go out the saturation permeability coefficient of the soil body, do not account in clay
Existing initial hydraulic gradient can not accurately describe the percolation law in cohesive soil.For another example Xie Kang passes through a large amount of Xiaoshans with equal
The clay experimental study relationship of infiltration coefficient and soil body hole, approximately thinks that the infiltration coefficient under different hydraulic gradients is one
A constant.Although it is recognized that it is non-linearly increasing trend that saturation cohesive soil, which is v-i relation curve under different hydraulic gradients, but
But the prediction technique that accurate quantitative analysis can not be provided, the starting head considered are also only the starting corresponding to maximum pore channel
Head, it is at this moment far from being enough, because the aperture dimensions distribution of pore channel is very extensive.Since the soil body is by the continuous of magnanimity
Pore channel composition, and pore channel is not of uniform size, the sequence that seepage flow occurs is not also identical: seepage flow needs occur for macrovoid channel
Hydraulic gradient it is smaller, with the increase of hydraulic gradient, fine pore channel is also slowly added in seepage flow.The present invention passes through hair
It is thin theoretical, using matric suction as the index of reflection pore channel size, i.e., it will reflect volumetric water content in script unsaturated soil
The indirect indexes of reflection saturated soil pore channel size are regarded as with the soil―structure interaction of matric suction relationship.By T-K model,
The infiltration coefficient that the pore channel of seepage flow occurs under practical hydraulic gradient is overlapped, to obtain the infiltration of its saturation nonlinearity
Coefficient.
Summary of the invention
In order to solve the above technical problems in background technology, the present invention provides a kind of for the non-linear of the soil body
The prediction of clay saturation nonlinearity infiltration coefficient under the different hydraulic gradients that seepage flow and the research for originating head are of great significance
Method.
In order to achieve the above object, using following scheme:
It is a kind of difference hydraulic gradient under clay saturation nonlinearity infiltration coefficient prediction technique, it is characterised in that: it is described not
With clay saturation nonlinearity infiltration coefficient under hydraulic gradient prediction technique the following steps are included:
1) it is tested by pressure plate apparatus, measures the soil―structure interaction of soil sample, soil―structure interaction is pressed into volume of aqueous
Rate is divided into n equal part, and every equal part corresponds to the pore channel of different pore size rank；
2) flowing based on Free water in Young-Laplace equation and soil body hole will overcome the viscous of stickiness soil pores
Resistance feature obtains the relationship of starting head and air-entry value, and the starting head of soil sample is measured by GDS experiment, obtains air inlet
The correction factor of value and infiltration hydraulic pressure；
3) it is tested by GDS, measures saturation permeability coefficient k of the soil sample used under maximum head pressures, according to step 1)
Relationship between the volumetric water content that the soil-water characteristic curve measured obtains and the starting head after step 2) modification just,
In conjunction with T-K saturation permeability coefficient model, inverse goes out comprehensive infiltration proportionality constant kc；The comprehensive infiltration ratio of the same type soil sample
Example constant kcFor a definite value；
4) the comprehensive infiltration proportionality constant k obtained using step 3)cCalculate the infiltration coefficient of every grade of pore channel.
Preferably, the specific implementation of step 1) of the present invention is: the data measured by pressure plate apparatus
Point acquires fitting parameter by VG three parameter model using Matlab software, fitting parameter is brought into origin and is fitted
To complete soil―structure interaction；It is on the basis of known specific dry density soil―structure interaction measured value, soil-water is special
Curve is levied from actual measurement minimum volume moisture content θminTo actual measurement maximum volume moisture content θmax, soil―structure interaction is divided into n etc.
Point；Wherein volumetric(al) moisture content knots modification is Δ θi=θi+1-θi；Its corresponding equivalent matric suction is Ψi=(Ψx+Ψy)/2,
Middle Ψx、ΨyFor the boundary matric suction up and down of certain grade matrix suction；θiIt is the volumetric water content under i-stage hydraulic gradient；θi+1
It is the volumetric water content under i+1 grade hydraulic gradient.
Wherein, VG three parameter model are as follows:
In formula:
Θ is standardized moisture level；
SeFor effective saturation degree；
A, n, m are fitting parameter；
Ψ is matric suction.
Preferably, the specific implementation of step 2) of the present invention is: hole in the soil body is considered as cylindrical body,
Then originating head is exactly the shearing strength τ that water overcomes viscosity resistance to be formed in holes, the Free water in the hole of cylindrical body wants
Compared with the power caused by the cylinder circumference shearing strength that flowing is exactly cylindrical body top and the bottom pressure, it may be assumed that
τs× 2 π rl=(P1-P2)×πr2 (a)
(a) formula deforms:
In formula:
τsFor the shearing strength for overcoming viscosity resistance to be formed；
L is aperture height；
R is pore radius；
Δ P is starting head；
P1、P2Respectively hole top and the bottom pressure；
And Young-Laplace equation is pointed out:
In formula:
Ψ is matric suction；
TSFor surface tension；
α is contact angle；
R is pore radius；
In conjunction with (b) formula and (c) formula, originates head and be inversely proportional with aperture, there are a proportional relations with air-entry value；
P=c × ψa (1)
In formula:
P is starting head；
ΨaFor the air-entry value of corresponding dry density；
C is correction factor；WhereinIt is identical to identical soil sample c value.
In order to acquire parameter c, the parallel sample of the identical dry density of preparation multiple groups is arranged under different pressures difference after being saturated
Carry out GDS permeability test；The pressure difference that infiltration coefficient is increased suddenly is considered as initial pressure head；The starting head is corresponding at this time
In the air-entry value of the dry density soil sample, i.e. the soil body takes place draining, permeates the pressure value of generation:
Preferably, the specific implementation of step 3) of the present invention is: by the soil of certain dry density of preparation
Sample after being saturated by vacuum pump, measures saturation permeability coefficient k of the sample under maximum head pressure by GDS experiments；It will lead to
It crosses VG three parameter model and is fitted the soil―structure interaction obtained, in the identical situation of aliquot volume moisture content, by fitting
Curvilinear equation inverse find out the Ψ of the corresponding matric suction of each volumetric water contentx、Ψy。。。, then by the upper of every grade matrix suction
Lower Limits matric suction Ψx、ΨyFind out its Ψi；Different Ψ each of is acquired by T-K modeliAs corresponding in the soil body
The theoretical equivalent starting head of hole seepage flow, is repaired the starting head of pore channel seepage flow corresponding in the soil body by (1) formula
It is just the starting head of the saturation soil body；Due to ΨaFor the air-entry value of the soil body, air-entry value starts the finger drained as the soil body
Mark, and originate the index that seepage flow takes place as hole for head.By (c) formula it is found that different aperture r corresponds to different matrix
Suction Ψ, therefore, soil―structure interaction can also be used as the index of reflection soil body pore channel distribution, i.e. matric suction size
It is considered as the indirect indexes of soil body pore channel size, pore channel is bigger, and matric suction is smaller, and pore channel is smaller, then matrix
Suction is bigger.Know that starting head is directly proportional to air-entry value by (1), so the starting head for different pore channels is different.
(1) formula becomes at this time；
Pi=c × ψi (2)
In formula: PiFor the starting head relative to i grades of pore channels；
By T-K saturation permeability coefficient model, the comprehensive infiltration proportionality constant k of this kind of soil sample is acquiredc:
In formula:
kcProportionality constant is permeated to be comprehensive；
ksFor saturation permeability coefficient；
ΔθiFor the volumetric(al) moisture content knots modification under i-stage hydraulic gradient；
ΨiFor the equivalent starting head under i-stage hydraulic gradient；
J is j-th stage gap；j≤n.
Preferably, the specific implementation of step 4) of the present invention is:
Matric suction is modified to hydraulic pressure, the soil body is made to start what seepage flow in the air-entry value GDS permeability test of draining occurred
Originate head；
By hydraulic pressure formula:
P=ρ gh (4)
In formula:
P is hydraulic pressure；
ρ is the density 1 × 10 of water3kg/m3；
G is acceleration of gravity 9.8N/kg；
H is pressure point to liquid level, and the pressure point to liquid level is head value；
It is provided in Darcy's law:
In formula:
I is hydraulic gradient；
Δ h is head loss；
L is specimen length；
By (c) formula it is found that different matric suctions corresponds to different pore sizes, i.e., using matric suction as reflection
The index of pore-size.It is obtained by formula (2) (4) (5):
The initial hydraulic gradient of i-stage pore channel is acquired by (6) formula；
When actual hydraulic gradient I reaches the hydraulic gradient I of i-stage (i > 1) pore channeliWhen, i-stage hole starts
Seepage flow occurs.The infiltration of all pore channels of seepage flow will be actually occurred by the formula (3) of T-K saturation permeability coefficient model at this time
Saturating coefficient is overlapped, and when actual hydraulic gradient is bigger, the infiltration coefficient of superposition is also bigger；
When
Have
In formula:
I is actual hydraulic gradient；
IiFor the initial hydraulic gradient of i-stage pore channel；
ksiThe saturation permeability coefficient of 1-i grades of hole superposition when for hydraulic gradient being i；
kcIt is comprehensive infiltration proportionality constant；
ΨiIt is the equivalent starting head under i-stage hydraulic gradient；
ΔθiIt is the volumetric(al) moisture content knots modification under i-stage hydraulic gradient；
Differentiate whether different size pore channel occurs seepage flow according to (6) formula, i.e., when practical hydraulic gradient is more than this grade of hole
Seepage flow just occurs for this grade of pore channel when the initial hydraulic gradient in gap channel, obtains under different hydraulic gradients in conjunction with (7) formula
Saturation nonlinearity infiltration coefficient.
The invention has the advantages that
The present invention provides a kind of prediction technique of clay saturation nonlinearity infiltration coefficient under different hydraulic gradients, the present invention
By capillary theory, the index as reflection soil body pore channel size of matric suction will be used as anti-in unsaturated soil
Reflect indirect indexes of the soil―structure interaction of volumetric water content and matric suction as reflection saturated soil pore channel size, benefit
With pressure plate apparatus test and GDS permeability test, the soil―structure interaction for testing clay and saturation permeability coefficient and base are obtained
The relationship of matter suction and starting head；Comprehensive infiltration proportionality constant k is calculated using TK saturation permeability coefficient modelc；According to survey
Try the k of claycAnd soil―structure interaction obtains the saturation permeability coefficient of such soil using correlation model inverse and is overlapped
Obtain the saturation permeability coefficient for overcoming starting head.The present invention considers the different startings that diverse microcosmic pore channel permeates
Head, pore channel aperture is smaller, it is bigger that starting starting head needed for seepage flow occurs, and only when hydraulic gradient is more than the grade
When the initial hydraulic gradient of hole, this grade of pore channel just participates in seepage flow and contributes to infiltration coefficient.Due to being deposited in the soil body
In the pore channel not of uniform size of magnanimity, therefore head pressure is bigger, and the pore channel quantity for pushing it to participate in seepage flow is got over
More, saturation permeability coefficient is bigger.Again by the proportional relation of the starting head and air-entry value derived, starting starting is being considered
Under the action of head, clay saturation nonlinearity infiltration coefficient is predicted using T-K model.This method is considering to originate head
Angle set out, non linear fluid flow through porous medium for the soil body and the research for originating head are of great significance.Test is descended certain by this method
The volume of stage pressure discharge water regards the seepage discharge of seepage through soil mass as, using soil―structure interaction as reflection soil body pore size
Indirect indexes, this method consider the starting head of clay seepage flow, and the clay saturation predicted under different hydraulic gradients is non-
Linear infiltration coefficient more completely reflects the percolation law of the soil body, for studying saturation permeability coefficient and the starting of clay
Head has initiative meaning, while can play the role of scientific guidance for seepage control projects such as dykes and dams, and this method can be applied to rock
In terms of geotechnological journey, clay can be effectively predicted and exist on the basis of measuring soil―structure interaction (SWCC) and saturation permeability coefficient
Saturation nonlinearity infiltration coefficient under different hydraulic gradients.
Detailed description of the invention
Fig. 1 is the pore channel schematic diagram that seepage flow occurs under different starting heads.
Fig. 2 is the Hunan clay percolation curve figure of the method for the present invention prediction.
Specific embodiment
The invention discloses a kind of prediction technique of clay saturation nonlinearity infiltration coefficient under different hydraulic gradients, this method
Its reasonability is verified by experimental data, specifically includes the following steps:
1) it is tested by pressure plate apparatus, measures the soil―structure interaction of soil sample, soil―structure interaction is pressed into volume of aqueous
Rate is divided into n equal part, and every equal part corresponds to the pore channel of different pore size rank:
The data point measured by pressure plate apparatus acquires fitting parameter using Matlab software, fitting parameter is brought into
Fitting obtains complete soil―structure interaction in origin.On the basis of known specific dry density soil―structure interaction measured value
On, by soil―structure interaction from actual measurement minimum volume moisture content θminTo actual measurement maximum volume moisture content θmax, soil-water is special
Sign curve is divided into n equal part.Wherein volumetric(al) moisture content knots modification, Δ θi=θi+1-θi；Its corresponding equivalent matric suction is Ψi
=(Ψx+Ψy)/2, wherein Ψx、ΨyFor the boundary matric suction up and down of certain grade matrix suction.Step 1) proposes soil-water is special
Sign curve is divided into n equal part, therefore refers to moisture content knots modification Δ θ1=Δ θ2=...=Δ θn。
2) the starting head of soil sample is measured by GDS experiment, and obtains air-entry value and permeates the correction factor of hydraulic pressure:
The parallel sample for preparing the identical dry density of multiple groups is arranged under different pressures difference after being saturated and carries out GDS infiltration examination
It tests.The pressure difference that infiltration coefficient is increased suddenly is considered as initial pressure head (originating head at this time).The starting head at this time
Corresponding to the air-entry value of the dry density soil sample, i.e. the soil body takes place draining, permeates the pressure value of generation:
P=c × ψa (1)
In formula: P is starting head；ΨaFor the air-entry value of corresponding dry density；C is correction factor.
3) it is tested by GDS, measures saturation permeability coefficient k of the soil sample used under maximum head pressures, according to step
1), in conjunction with T-K saturation permeability coefficient model, inverse goes out comprehensive infiltration proportionality constant kc(the comprehensive of the same type soil sample is seeped
Saturating proportionality constant kcFor a definite value):
By the soil sample of certain dry density of preparation, after being saturated by vacuum pump, sample is measured by varying head GDS experiment and is existed
Saturation permeability coefficient k under maximum head pressures.By the Δ θ obtained in step 1) by equal partiAnd Ψi, it is saturated and is seeped by T-K
Saturating Modulus Model, i.e. (3) formula acquire the comprehensive infiltration proportionality constant k of this kind of soil samplec:
In formula: kcTo permeate proportionality constant；ksFor saturation permeability coefficient；ΔθiFor volumetric water content knots modification；ΨiFor etc.
The matric suction of effect.
4) k obtained using step 3)cCalculate the infiltration coefficient of every grade of pore channel.Reflected by soil―structure interaction
Ψ-θ relationship, calculate different pore size rank pore channel starting head, when practical hydraulic gradient be more than the starting head value
When, this grade of pore channel just participates in seepage flow and contributes to the infiltration coefficient of the soil body, i.e., the prediction soil body total infiltration coefficient when only
Can infiltration coefficient to the pore channel for having occurred and that seepage flow under practical hydraulic gradient be superimposed through row.But in unsaturated soil, soil
Also contain air in body opening gap, causes to form meniscus there are the water-gas interface i.e. presence of surface tension in hole.And satisfy
Due to only having hydraulic pressure to have an effect so there is no this meniscus formed by surface tension, therefore need when seepage flow occurs with soil
The correction factor obtained according to step 2) is modified the starting head that saturated soil infiltration is translated into this to matric suction.
Accordingly, in conjunction with the prediction technique of clay saturation nonlinearity infiltration coefficient under T-K model foundation difference hydraulic gradient.And it utilizes and is somebody's turn to do
Model, which calculates, obtains saturation nonlinearity infiltration coefficient under different hydraulic gradients, specifically:
4.1) surface tension is made it have due to there is the presence of air to form shrink film in soil body hole in unsaturated soil
To make hole liquid level form concave meniscus, there is hole air pressure and pore water pressure and shrink film subjects greater than hole in hole
The air pressure of gap hydraulic pressure, this pressure difference are matric suction.But hole air pressure is not present in saturated soil, therefore does not have concave meniscus and matrix
The presence of suction.Therefore it to matric suction is equivalent to hydraulic pressure, then needs to be modified.The knot obtained according to step 2)
By at this point, the air-entry value for making the soil body start to drain is the starting head that seepage flow occurs in GDS permeability test.
By hydraulic pressure formula:
P=ρ gh (4)
In formula: P is hydraulic pressure；ρ is the density 1 × 10 of water3kg/m3；G is acceleration of gravity 9.8N/kg；H is pressure point to liquid
Face height (is used as head value) in text.
It is provided in Darcy's law:
In formula: I is hydraulic gradient；Δ h is head loss；L is specimen length.
It is obtained by formula (2) (4) (5):
4.2) soil―structure interaction that is fitted by eyeball and (c) formula are it is found that each matric suction corresponds to level-one hole
Gap, i.e., under i-stage matric suction, the 1st to i-stage hole can occur seepage flow, and i+1 grades of seepage flow will not occur, and only work as base
When matter suction is more than i, the soil body has seepage flow (such as Fig. 1) can occur.Therefore, the starting of different pore size rank can be acquired by (6) formula
Hydraulic gradient.
4.3) can obtaining i-stage hole by analysis 4.2) when seepage flow, the 1st to i-1 grade has occurred and that seepage flow, that is, is counting
When calculating the infiltration coefficient of i-stage pore channel, pore channel (macrovoid channel) before is already engaged in infiltration, because
This will obtain the saturation permeability coefficient under complete i-stage hydraulic gradient, it is necessary to will be already engaged in the pore channel of seepage flow before
Infiltration coefficient be overlapped.The saturation nonlinearity under different hydraulic gradients is just obtained by T-K model (3) formula and (6) formula to seep
Saturating coefficient.
In formula: ksiThe saturation permeability coefficient of 1-i grades of hole superposition when for hydraulic gradient being i.
Specific implementation of the invention is:
Firstly, clay saturation nonlinearity infiltration coefficient theory under the different hydraulic gradients of consideration starting head of the invention
Be: for being saturated the soil body, since the hole of the soil body is filled with water, at this time, the drainage procedure in the soil body is understood that
The process of seepage flow occurs for the soil body.Since there are magnanimity pore channel not of uniform size, the holes of different pore size rank in the soil body
Channel occur to permeate hydraulic gradient to be achieved it is different, should and when hydraulic gradient only therein is more than initial hydraulic gradient
Grade hole just permeates.Therefore soil―structure interaction can be considered as to the index of reflection soil body pore size indirectly.But due to full
There is no concave meniscus and matric suction in the hole of soil, to using soil―structure interaction as between reflection soil body pore size
Index is connect, then needs for matric suction to be modified, is translated into the starting head (pressure corresponding to matric suction on SWCC
Head):
Wherein: c is correction factor ΨiFor equivalent matric suction, L is specimen height, IiFor the starting of i-stage pore channel
Hydraulic gradient；ρ is the density 1 × 10 of water3kg/m3；G is acceleration of gravity 9.8N/kg
Under this theory, calculating can be significantly facilitated using TK saturation permeability coefficient:
In formula: ksFor saturation permeability coefficient；kcProportionality constant is permeated to be comprehensive；ΨiFor equivalent matric suction；θiFor phase
It should be in starting head ΨiVolumetric water content；Wherein, Δ θi=θi+1-θi；
Here is to be predicted in conjunction with specific embodiments using this method: used soil sample is Hunan Shaoyang red clay, is surveyed
Obtain its basic index.
Here by taking the clay of Hunan as an example, Hunan clay 1.5g/cm is measured by GDS experiment3Dry density 35kPa at 15 DEG C
Saturation permeability coefficient correction value under pressure is 0.0000588612cm/s；
It is tested by pressure plate apparatus, measures 1.5g/cm3Soil―structure interaction under dry density.By 1.5g/cm3Dry density
Soil―structure interaction fitting parameter is acquired by Matlab by measured value.Here it is calculated for convenience by the 1.5g/ after fitting
cm3The volume of aqueous that dry density soil―structure interaction is acquired by actual measurement maximum volume moisture content and actual measurement minimum volume moisture content
Rate knots modification is divided into 10 equal parts.It is obtained using formula (3):
In formula: Δ θ=θ2-θ1=0.00988, Ψi=57kPa similarly obtains Δ θ2、Δθ3...Δθ9, under 35kPa pressure
KsFor 0.0000588612cm/s, k is calculatedcIt is 0.008890543.
It then, is 10 equal portions by its natural division by measured value by soil―structure interaction, by required obtained Δ θiWith
Ψi, bring into formula (3) by superposition obtain every grade permeate when corresponding hole saturation permeability coefficient ks:
In order to preferably reflect the percolation law of water in soil, preparation dry density is respectively 1.5g/cm3The Hunan of dry density is viscous
Sample is placed in back-pressure in GDS permeameter and is saturated 48 hours by soil sample.Measurement 2,4,6,8,10kPa pressure respectively after the completion of saturation
The infiltration coefficient (such as table 2) of clay is saturated under power difference.It can be seen that by 2 data of table for different dry density soil samples, in 2-
Infiltration coefficient is minimum in 4kPa and 8-10kPa pressure range, and increases suddenly in 4-6kPa pressure range, therefore taking 6kPa is the lake
The starting head of southern clay.The present embodiment 1.5g/cm3Dry density sample is advised also for the seepage flow of the better reflection soil body
Rule.Therefore, the correction factor c of the soil body is determined according to (1) formula by the air-entry value of existing different initial dry densities:
P=c × ψa (1)
In formula: P=6kPa, Ψa=9.77kPa, is calculated c=0.6141.
Saturation permeability coefficient corresponding to every grade of starting head and corresponding hydraulic gradient are as shown in table 1:
The saturation permeability coefficient and initial hydraulic gradient (dry density 1.5g/cm of 1 this method of table prediction3)
1.5g/cm under GDS permeability test3Infiltration coefficient such as table 2 of the dry density sample under different pressures difference:
2 GDS of table seeps 1.5g/cm under test different pressures difference3The infiltration coefficient (× 10 of dry density-6cm/s)
The 6kPa starting head that the minimum initial hydraulic gradient of sample is obtained by GDS is acquired according to (6) formula as I=3.061；
Sample hydraulic gradient, percolation flow velocity and seepage flow the situation such as table 3 obtained according to the method for the present invention:
Hydraulic gradient, percolation flow velocity and the seepage flow situation that table 3 obtains according to the method for the present invention
Based on above-mentioned data, when hydraulic gradient is smaller, seepage flow does not occur for clay known to analysis, once more than after certain value
Seepage flow takes place in the soil body, but nonlinear change is presented in seepage flow, and with the increase of hydraulic gradient, seepage flow, which tends towards stability, to be presented linearly
Increase, k in table 1sThe as slope of v-I relation curve equally can reflect the percolation law of the soil body by the variation of slope, i.e.,
Seepage flow phase change of the slope after overcoming starting head is larger, and seepage through soil mass is unstable to which non-linear increasing is presented in infiltration coefficient
Add, with the gradually progress of seepage flow, slope variation is smaller and smaller, and seepage flow tends towards stability substantially, and infiltration coefficient presents linearly increasing.
The percolation law of Darcy's law in clay is also coincide with this conclusion.Fig. 2 is the percolation curve figure that the present invention predicts.
Claims (5)
1. the prediction technique of clay saturation nonlinearity infiltration coefficient under a kind of difference hydraulic gradient, it is characterised in that: the difference
Under hydraulic gradient clay saturation nonlinearity infiltration coefficient prediction technique the following steps are included:
1) it is tested by pressure plate apparatus, measures the soil―structure interaction of soil sample, soil―structure interaction is drawn by volumetric water content
It is divided into n equal part, every equal part corresponds to the pore channel of different pore size rank；
2) flowing based on Free water in Young-Laplace equation and soil body hole will overcome the viscosity resistance of stickiness soil pores
Feature obtains the relationship of starting head and air-entry value, and measures the starting head of soil sample by GDS experiment, obtain air-entry value and
Permeate the correction factor of hydraulic pressure；
3) it is tested by GDS, measures saturation permeability coefficient k of the soil sample used under maximum head pressures, measured according to step 1)
The volumetric water content that obtains of soil-water characteristic curve and starting head after step 2) modification just between relationship, in conjunction with
T-K saturation permeability coefficient model, inverse go out comprehensive infiltration proportionality constant kc；The synthesis infiltration ratio of the same type soil sample is normal
Number kcFor a definite value；
4) the comprehensive infiltration proportionality constant k obtained using step 3)cCalculate the infiltration coefficient of every grade of pore channel.
2. the prediction technique of clay saturation nonlinearity infiltration coefficient, special under difference hydraulic gradient according to claim 1
Sign is: the specific implementation of the step 1) is: the data point measured by pressure plate apparatus is passed through using Matlab software
VG three parameter model acquires fitting parameter, and fitting parameter is brought into fitting in origin and obtains complete soil―structure interaction；
On the basis of known specific dry density soil―structure interaction measured value, soil―structure interaction is contained from actual measurement minimum volume
Water rate θminTo actual measurement maximum volume moisture content θmax, soil―structure interaction is divided into n equal part；Wherein volumetric(al) moisture content changes
Amount is Δ θi=θi+1-θi；Its corresponding equivalent matric suction is Ψi=(Ψx+Ψy)/2, wherein Ψx、ΨyFor the suction of certain grade matrix
The boundary matric suction up and down of power；θiIt is the volumetric water content under i-stage hydraulic gradient；θi+1It is under i+1 grade hydraulic gradient
Volumetric water content；
Wherein, VG three parameter model are as follows:
In formula:
Θ is standardized moisture level；
SeFor effective saturation degree；
A, n, m are fitting parameter；
Ψ is matric suction.
3. the prediction technique of clay saturation nonlinearity infiltration coefficient, special under difference hydraulic gradient according to claim 2
Sign is: the specific implementation of the step 2) is: hole in the soil body being considered as cylindrical body, then originating head is exactly water in hole
The shearing strength τ for overcoming viscosity resistance to be formed in gaps, it is exactly cylindrical body or more that the Free water in the hole of cylindrical body, which will flow,
Compared with portion's pressure power caused by the cylinder circumference shearing strength, it may be assumed that
τs× 2 π rl=(P1-P2)×πr2 (a)
(a) formula deforms:
In formula:
τsFor the shearing strength for overcoming viscosity resistance to be formed；
L is aperture height；
R is pore radius；
Δ P is starting head；
P1、P2Respectively hole top and the bottom pressure；
And Young-Laplace equation is pointed out:
In formula:
Ψ is matric suction；
TSFor surface tension；
α is contact angle；
R is pore radius；
In conjunction with (b) formula and (c) formula, originates head and be inversely proportional with aperture, there are a proportional relations with air-entry value；
P=c × ψa (1)
In formula:
P is starting head；
ΨaFor the air-entry value of corresponding dry density；
C is correction factor；WhereinIt is identical to identical soil sample c value；
In order to acquire this parameter c, the parallel sample of the identical dry density of preparation multiple groups, be arranged under different pressures difference after being saturated into
Row GDS permeability test；The pressure difference that infiltration coefficient is increased suddenly is considered as initial pressure head；The starting head corresponds at this time
Draining takes place in the air-entry value of the dry density soil sample, the i.e. soil body, permeates the pressure value of generation.
4. the prediction technique of clay saturation nonlinearity infiltration coefficient, special under difference hydraulic gradient according to claim 3
Sign is: the specific implementation of the step 3) is: by the soil sample of certain dry density of preparation, after being saturated by vacuum pump,
The saturation permeability coefficient k under maximum head pressure is measured by GDS experiments；The soil-obtained will be fitted by VG three parameter model
Water characteristic curve finds out each volume by the curvilinear equation inverse fitted in the identical situation of aliquot volume moisture content
The Ψ of the corresponding matric suction of moisture contentx、Ψy。。。, then by the matric suction of the boundary up and down Ψ of every grade matrix suctionx、ΨyIt finds out
Its Ψi；Different Ψ each of is acquired by T-K modeliTheoretical equivalent starting water as hole seepage flow corresponding in the soil body
The starting head of hole seepage flow corresponding in the soil body is modified to the starting head of the saturation soil body by (1) formula by head；Due to Ψa
For the air-entry value of the soil body, air-entry value starts the index drained as the soil body, and originates head as hole and infiltration takes place
The index of stream；By (c) formula it is found that different aperture r corresponds to different matric suction Ψ, therefore, soil―structure interaction is as anti-
The index of soil body pore channel distribution, i.e. the matric suction size indirect indexes that are considered as soil body pore channel size are reflected, hole is logical
Road is bigger, and matric suction is smaller, and pore channel is smaller, then matric suction is bigger；Know starting head and air-entry value at just by (1)
Than so (1) formula becomes at this time for the starting head difference of different pore channels；
Pi=c × ψi (2)
By T-K saturation permeability coefficient model, the comprehensive infiltration proportionality constant k of this kind of soil sample is acquiredc:
In formula:
kcProportionality constant is permeated to be comprehensive；
ksFor saturation permeability coefficient；
ΔθiFor the volumetric(al) moisture content knots modification under i-stage hydraulic gradient；
ΨiFor the equivalent starting head under i-stage hydraulic gradient；
J is j-th stage gap；j≤n.
5. the prediction technique of clay saturation nonlinearity infiltration coefficient, special under difference hydraulic gradient according to claim 4
Sign is: the specific implementation of the step 4) is:
4.1) matric suction is modified to hydraulic pressure, the soil body is made to start what seepage flow in the air-entry value GDS permeability test of draining occurred
Originate head；
By hydraulic pressure formula:
P=ρ gh (4)
In formula:
P is hydraulic pressure；
ρ is the density 1 × 10 of water3kg/m3；
G is acceleration of gravity 9.8N/kg；
H is pressure point to liquid level, and the pressure point to liquid level is head value；
It is provided in Darcy's law:
In formula:
I is hydraulic gradient；
Δ h is head loss；
L is specimen length；
By (c) formula, different matric suctions corresponds to different size pore channels, i.e., using matric suction as reflection hole
The index of channel size；It is obtained by formula (2) (4) (5):
4.2) initial hydraulic gradient of i-stage pore channel is acquired by (6) formula；
4.3) when actual hydraulic gradient I reaches the hydraulic gradient I of i-stage (i > 1) pore channeliWhen, i-stage hole starts to send out
Raw seepage flow；The infiltration of all pore channels of seepage flow will be actually occurred by the formula (3) of T-K saturation permeability coefficient model at this time
Coefficient is overlapped, and when actual hydraulic gradient is bigger, the infiltration coefficient of superposition is also bigger；
When
Have
In formula:
I is actual hydraulic gradient；
ksi1-i grade pore channel infiltration coefficient accumulative the infiltration coefficient of seepage flow occurs when for hydraulic gradient being I；
kcIt is comprehensive infiltration proportionality constant；
ΨiIt is the equivalent starting head under i-stage hydraulic gradient；
ΔθiIt is the volumetric(al) moisture content knots modification under i-stage hydraulic gradient；
4.4) differentiate whether different size pore channel occurs seepage flow according to (6) formula, i.e., when practical hydraulic gradient is more than this grade of hole
Seepage flow just occurs for this grade of pore channel when the initial hydraulic gradient in gap channel, obtains under different hydraulic gradients in conjunction with (7) formula
Saturation nonlinearity infiltration coefficient.
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