CN108008114A - A kind of decision method of coarse-grained soil inside soil body stability - Google Patents
A kind of decision method of coarse-grained soil inside soil body stability Download PDFInfo
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Abstract
A kind of decision method of coarse-grained soil inside soil body stability, its step are：(1) screen analysis test is carried out to coarse grained soil filler, obtains the Grading feature particle diameter d of filler3, and measure the moisture content and grain density of filler；(2) by the coarse-grained soil soil body is formed after coarse grained soil filler setting density compacting, the porosity n of the soil body is determined, by coefficient of permeability K of the constant head permeability test measure filler under porosity n；(3) according to the porosity n and coefficient of permeability K of the coarse-grained soil soil body, its equivalent infiltration pore mean diameters D is calculated,(4) by contrasting D and d3Size so that obtaining internal stability of the coarse-grained soil soil body under porosity n differentiates result.This method definite principle, operation and calculating are easy, can just judge the internal stability of the coarse-grained soil soil body exactly using conventional soil test equipment, and the evaluation for rock-soil material structural stability provides reliable basis.
Description
Technical Field
The present invention relates to a method for determining internal stability of soil.
Background
In geotechnical engineering, soil with the particle size d of 0.075 mm-60 mm and the mass more than 50% of the total mass of the particles is called coarse-grained soil. The coarse-grained soil has the characteristics of good compaction performance, strong water permeability, high filling dry density, high shear strength and bearing capacity, small settlement deformation and the like, and is widely applied to geotechnical engineering, such as filling of earth-rock dams and roadbed engineering and filling material replacement in soft soil foundation treatment. However, coarse soil has dispersed particle size composition, large interparticle pores and small interparticle binding force, and is accompanied by poor internal stability under seepage action, i.e. the problem of penetration and damage easily occurs under the seepage action of water, thus seriously affecting the engineering characteristics of coarse soil. To ensure the safety and stability of the earth structure, the internal stability of coarse earth must be analyzed at the time of engineering design.
Along with the difference of particle grading and soil body compactness, the damage of coarse-grained soil body under the seepage action is shown as two typical forms of flowing soil or piping. The flowing soil is a phenomenon that the surface of a local soil body is raised or particle groups are started simultaneously and run off under the action of rising seepage water flow, and the phenomenon frequently occurs in soil which is tightly combined among particles, has strong restriction force and has a stable internal structure; piping is that under the action of seepage, fine particles in soil move in pore channels and are carried out of soil, and is usually coarse-grained soil with small constraint and unstable internal structure.
Currently, the internal stability of coarse-grained soil bodies can be determined visually by the osmotic deformation test in the soil test protocol (SL 237-1999). It requires a special test facility and an experienced test operator to perform complicated operations and a long test process. Therefore, a theoretical judgment method without the penetration deformation test is more convenient and important.
The method for judging the internal stability of the coarse-grained soil body specified in the geological survey Specification of the water conservancy and hydropower engineering (GB 50487-2008) is a fine material content method: the internal instability is considered when the mass content P of the fine materials is less than 25 percent, piping damage is shown under the seepage effect, the internal stability is considered when the mass content P is more than or equal to 35 percent, and the flowing soil damage is shown under the seepage effect. However, for coarse-grained soil with P being more than or equal to 25% and less than 35%, the method cannot accurately distinguish the internal stability of the coarse-grained soil and cannot judge the damage type under the seepage effect.
The judgment of the internal stability of the coarse-grained soil filler and the determination of the damage form of piping or flowing soil can be realized by analyzing whether fine particles in the soil can run off along seepage pore channels or not. If the average diameter of seepage pores in the soil is smaller than the particle size of the lost fine particles, the soil is subjected to integral soil flowing damage, otherwise, piping damage is caused. In order to calculate the average diameter of the seepage pores in the soil with different particle compositions and porosities, currently, a seepage pore channel is generally abstracted into a cluster of parallel equal-diameter capillary circular tubes, and a capillary model discrimination method of a pore volume-surface area equivalent capillary model is established based on the principle that the pore volume and the wall surface area of the capillary model are respectively equal to the pore volume and the particle surface area of a soil body: the average pore diameter of the soil body is represented by the capillary diameter. However, the size of the pores in the soil is related to the permeability of the soil, and only the capillary model with the same permeability coefficient as the soil can truly reflect the geometrical characteristics of the pores in the soil. The pore volume-surface area equivalent capillary model does not consider the influence of the actual curved seepage path in the soil on the permeability of the soil body, the average pore diameter obtained by calculation is larger, and the model permeability coefficient is larger than the measured value of the soil body. Meanwhile, the higher the bending degree of the actual seepage path in the soil is, the more easily fine particles lost along with seepage encounter a larger bending section to cause silting, so that the further loss of the particles is prevented, and finally, the stability of the interior of the soil body is enhanced. It can be seen that the pore volume-surface area equivalent capillary model ignores the actual curved seepage path, and the determination result of the internal stability of the coarse-grained soil filler has a large error.
Disclosure of Invention
The invention aims to provide a method for judging the internal stability of a coarse-grained soil body, which has clear principle and simple and convenient operation, can accurately judge the internal stability of the coarse-grained soil body by utilizing conventional geotechnical test equipment, and has more accurate and reliable judgment result.
The technical scheme adopted by the invention for realizing the aim is that the method for judging the internal stability of the coarse-grained soil body comprises the following steps:
(1) Coarse-grained soil filler particle size d 3 Determination of water content and particle density
The grain grading characteristic grain diameter d of the coarse-grained soil filler is obtained by a grain analysis test 3 I.e. the particle size in the soil is less than d 3 The mass of the particles accounts for 3 percent of the total mass of the soil particles; measuring the water content and the particle density of the coarse-grained soil filler;
(2) Determination of permeability coefficient of coarse-grained soil body
Pressing the coarse-grained soil filler to a coarse-grained soil body with a set density, and calculating the porosity n of the coarse-grained soil body to be detected according to the water content and the particle density of the coarse-grained soil filler; then, determining the permeability coefficient K of the coarse-grained soil body by adopting a normal water head method;
(3) Calculation of average diameter D of equivalent infiltration pores of coarse-grained soil body
According to the porosity n and the permeability coefficient K of the coarse-grained soil body, calculating the equivalent osmotic pore average diameter D according to the following formula:
in the formula: k is a radical of 0 The pore shape correction coefficient is 2.5; eta is dynamic viscous coefficient of water, and its value is 1.003 × 10 -2 cm 2 /s；ρ w The density of water is 1.0g/cm 3 (ii) a G is gravity acceleration with the value of 980cm/s 2 ；
(4) Determination of internal stability of coarse-grained soil body
If the mean equivalent osmotic pore diameter D is less than or equal to the particle grading characteristic particle diameter D 3 Judging that the coarse-grained soil body is a soil body with stable interior, and showing flowing soil damage under the seepage action; otherwise, the coarse-grained soil body is judged to be an unstable soil body inside, and piping damage is shown under the seepage action.
The principle of the method of the invention is as follows:
the coarse-grained soil equivalent infiltration capillary model is shown in the attached figure 1: the rock-soil material is used as a porous permeable medium, and the flow of water in pore seepage channels in soil can be approximate to laminar flow. The theory of seepage in soil can refer to Poiseuille law of laminar flow theory of uniform capillary round tubes, namely:
in the formula: v' is the actual flow rate of the capillary; r is the radius of the capillary circular tube; i' is the actual hydraulic gradient of the water flow in the capillary; g is gravity acceleration; rho w Is the density of water; eta is the dynamic viscosity of water.
Because the formation and size composition of pore channels in soil are complex, the formula (1) cannot be directly used for describing the flow state of water, so that a seepage channel in soil is supposed to be composed of a cluster of parallel capillaries with irregular cross section shapes and constant total cross section area nA, wherein n is the porosity of the soil, and A is the cross section area of a macroscopic seepage flow normal soil body. The concept of introducing hydraulic radius to a single capillary makes it equivalent to capillary tube radius R in equation (1):
in the formula: m is the hydraulic radius of the capillary; v v Is the capillary channel volume; f is the capillary wetted area.
Meanwhile, the combined soil particles are impermeable and have actual seepage length L e The factors of the path bending caused by the macro seepage length L are larger than the factors, and the average flow velocity v on the unit soil body cross section and the average hydraulic slope drop i on the macro seepage length respectively have the following relations with v 'and i':
substituting equations (2) to (4) into equation (1), and considering the irregular pore shape of the soil body, the following expressions can be obtained:
in the formula: k is a radical of 0 For the coefficient of the section shape of the irregular pore, the pore channel k with different section shapes 0 Are all close to 2.5; t represents the bending degree of an actual seepage path in soil, is called seepage bending rate, and T = L e /L。
The wetting area of the seepage in the soil is the particle surface area, the hydraulic radius m is actually equal to the ratio of the pore volume of a unit soil body to the particle surface area, and the expression of the soil body permeability coefficient K can be obtained by combining the Darcy law:
in the formula: s 0 The specific surface area of the particles is the surface area corresponding to the volume of the particles in the soil.
The curvature and specific surface area are defined as a particle equivalent specific surface area parameter S 'in formula (6)' 0 Is, namely S' 0 ＝S 0 T, equation (6) can be changed to:
for soil with a definite particle size composition, the specific surface area of the particles reflects the physical properties specific to the particles themselves, and should be a fixed value. S 'of formula (7)' 0 The seepage bending rate is considered, and the value of the seepage bending rate changes along with the difference of the actual seepage length in the soil.
Formula (6) shows that the main factors determining the permeability of the soil are porosity, particle surface area and tortuosity. If the capillary die porosity and specific surface area are equal to n and S 'in formula (7), respectively' 0 That is, it can be ensured that the permeability coefficient of the model is equal to that of the soil body, the established model is called an equivalent permeability capillary model, and the model diameters D, n and S 'are respectively shown in formula (8) and formula (9)' 0 The establishment relationship between the two components:
(1-n)S' 0 ＝NπD×1 (9)
in the formula: n is the number of capillaries per unit area.
The expressions of D can be obtained by the joint equations (7) to (9):
in the formula: d is the equivalent infiltration pore average diameter of the soil, and simultaneously characterizes the infiltration pore volume and the path bending degree in the soil.
Engineering practice has recognized that the loss of internally unstable soil structure particles is typically in excess of 3%. Therefore, during infiltration of coarse-grained soilIt is considered that when D.ltoreq.d 3 In the meantime, the interior of the soil is stably damaged, D>d 3 Internal unstable piping failure occurs.
Compared with the prior art, the invention has the beneficial effects that:
1. equivalent specific surface area S' 0 Is a function S 'of porosity n and permeability coefficient K' 0 (n, K), calculating different equivalent specific surface areas S 'based on actual porosity n and permeability coefficient K under different physical states of soil body' 0 Including the actual percolation path curvature T in the soil. The capillary model comprehensively considers the conditions of porosity, particle surface area and curvature of the soil body, compared with the existing method without considering the seepage curvature, the permeability of the capillary model is closer to the actual permeability of the soil body, the obtained equivalent seepage pore average diameter D can better represent the permeability of the soil body, and the judgment result of the internal stability of the coarse-grained soil body is more accurate and more reliable.
2. The method has simple operation and convenient calculation, and can obtain the discrimination result of the internal stability of the coarse-grained soil body superior to the prior method by utilizing the conventional geotechnical test.
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Drawings
FIG. 1 is a schematic diagram of a capillary model for determining the average diameter of equivalent infiltration pores of coarse-grained soil according to the method of the present invention.
Detailed Description
Examples
In a specific embodiment of the present invention, a method for determining the internal stability of a coarse-grained soil body includes the steps of:
(1) Coarse-grained soil filler particle diameter d 3 Determination of water content and particle density
The grain grading characteristic grain diameter d of the coarse-grained soil filler is obtained by a grain analysis test 3 I.e. the particle size in the soil is less than d 3 The mass of the particles accounts for 3 percent of the total mass of the soil particles; measuring the water content and the particle density of the coarse-grained soil filler;
(2) Determination of permeability coefficient of coarse-grained soil body
Pressing the coarse-grained soil filler to a coarse-grained soil body with a set density, and calculating the porosity n of the coarse-grained soil body to be detected according to the water content and the particle density of the coarse-grained soil filler; then, determining the permeability coefficient K of the coarse-grained soil body by adopting a normal water head method;
(3) Calculation of average diameter D of equivalent infiltration pores of coarse-grained soil body
According to the porosity n and the permeability coefficient K of the coarse-grained soil body, calculating the equivalent osmotic pore average diameter D according to the following formula:
in the formula: k is a radical of formula 0 The pore shape correction coefficient is 2.5; eta is dynamic viscous coefficient of water, and its value is 1.003 × 10 -2 cm 2 /s；ρ w The density of water is 1.0g/cm 3 (ii) a G is gravity acceleration with the value of 980cm/s 2 ；
(4) Determination of internal stability of coarse-grained soil body
If the mean diameter D of equivalent penetration pores is less than or equal to the particle grading characteristic particle diameter D 3 Judging that the coarse-grained soil body is a soil body with stable interior, and showing flowing soil damage under the seepage action; otherwise, the coarse-grained soil body is judged to be an unstable soil body inside, and piping damage is shown under the action of seepage.
Test verification:
the result of judging the internal stability of the good-gradation soil-containing fine-grit coarse-grained soil filler commonly used in a certain railway roadbed by adopting the method is given below.
(1) Coarse-grained soil filler particle size d 3 Determination of water content and particle density
The particle size distribution of the filler sample obtained by the particle analysis test is shown in Table 1, and the mass of the particles with the particle size of less than 0.01mm, which is 3 percent of the total mass of the particles in the soil, is obtained by linear interpolation, namely the particle size distribution characteristic particle size d 3 ＝0.01mm。
TABLE 1 Filler particle size distribution
The water content of the filler is w =3.4% measured by a drying method, and the density rho of the filler particles is measured by combining a floating weighing method and a volumetric flask method s ＝1.91g/cm 3 。
(2) Determination of permeability coefficient of coarse-grained soil body
Pressing the coarse-grained soil filler to a set density rho =1.53g/cm 3 And 1.31g/cm 3 The porosity n of the coarse-grained soil body to be measured is calculated to be 0.23 and 0.34 respectively by combining the water content and the particle density of the filler; according to the operation specification of the soil engineering test, the permeability coefficients K of the coarse-grained soil are respectively 1.18 multiplied by 10 under the conditions that the porosity n is equal to 0.23 and 0.34 by adopting a normal water head method -4 cm/s、1.23×10 -2 cm/s。
(3) Calculation of average diameter D of equivalent infiltration pores of coarse-grained soil body
Get k 0 ＝2.5、η＝1.003×10 -2 cm 2 /s、ρ w ＝1.0g/cm 3 、G＝980cm/s 2 Then, the equivalent average diameter D of the infiltration pores corresponding to the soil body with the known porosity n and permeability coefficient K is calculated by the following formula:
when n =0.23, the corresponding equivalent mean diameter D of the infiltration pores 1 Is composed of
When n =0.34, the corresponding equivalent mean diameter D of the infiltration pores 2 Is composed of
(4) Determination of internal stability of coarse-grained soil body
By comparing D with D 3 The results of the internal stability determinations at porosities n equal to 0.23 and 0.34 are respectively the internal stable fluid soil failure and the internal unstable piping failure, as shown in table 2.
Meanwhile, table 2 shows the results of the osmotic deformation test of the above two soil bodies and the results of the internal stability discrimination of the other existing methods.
TABLE 2 determination results of internal stability of coarse-grained soil
As can be seen from Table 2:
the determination result of the internal stability of the filler soil body by a fine material content method in the water conservancy and hydropower engineering geological survey specification (GB 50487-2008) is transition type, and the internal stability of the soil body formed by the filler under different porosities cannot be distinguished accurately.
In the existing capillary model method (namely, the equivalent capillary model method of pore volume-surface area), the judgment result obtained when n =0.23 is inconsistent with the result of the osmotic deformation test carried out according to geotechnical test regulation (SL 237-1999), and the piping is judged to be unstable internally, and the actual test result is stable flowing soil internally. The judgment result is not consistent with the actual result, and the judgment method is unreliable.
The method of the invention has the advantages that the internal stability discrimination results under the porosity n =0.23 and 0.34 are consistent with the penetration deformation test results according to geotechnical test regulation (SL 237-1999), and the discrimination results are accurate and reliable.
Claims (1)
1. A method for judging the internal stability of a coarse-grained soil body comprises the following steps:
(1) Coarse-grained soil filler particle diameter d 3 Determination of water content and particle density
The grain grading characteristic grain diameter d of the coarse-grained soil filler is obtained by a grain analysis test 3 I.e. the particle size in the soil is less than d 3 The mass of the particles accounts for 3 percent of the total mass of the soil particles; measuring the water content and the particle density of the coarse-grained soil filler;
(2) Determination of permeability coefficient of coarse-grained soil body
Pressing the coarse-grained soil filler to a coarse-grained soil body with a set density, and calculating the porosity n of the coarse-grained soil body to be measured according to the water content and the particle density of the coarse-grained soil filler; then, determining the permeability coefficient K of the coarse-grained soil body by adopting a normal water head method;
(3) Calculation of average diameter D of equivalent infiltration pores of coarse-grained soil body
According to the porosity n and the permeability coefficient K of the coarse-grained soil body, calculating the equivalent osmotic pore average diameter D according to the following formula:
in the formula: k is a radical of 0 The pore shape correction coefficient is 2.5; eta is dynamic viscous coefficient of water, and its value is 1.003 × 10 -2 cm 2 /s；ρ w The density of water is 1.0g/cm 3 (ii) a G is gravity acceleration with the value of 980cm/s 2 ；
(4) Determination of internal stability of coarse-grained soil body
If the mean diameter D of equivalent penetration pores is less than or equal to the particle grading characteristic particle diameter D 3 Judging that the coarse-grained soil body is a soil body with stable interior, and showing flowing soil damage under the seepage action; otherwise, the coarse-grained soil body is judged to be an unstable soil body inside, and piping damage is shown under the seepage action.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113075106A (en) * | 2021-03-26 | 2021-07-06 | 桂林理工大学 | Method for determining hydraulic parameters and water inflow amount of gravel soil in erosion stage |
| CN115343201A (en) * | 2022-05-31 | 2022-11-15 | 山东大学 | Method for testing gap rate of roadbed filled with road arches by irrigation |
| CN115598023A (en) * | 2022-11-08 | 2023-01-13 | 四川中德禄江装备科技有限公司（Cn） | Method for determining three-dimensional tortuosity of loose broken rock-soil mass |
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2017
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| 刘孟适: "铁路路基火山渣掺配土质砾砂混合土渗透稳定研究", 《中国优秀硕士学位论文全文数据库 工程科技Ⅱ辑》 * |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113075106A (en) * | 2021-03-26 | 2021-07-06 | 桂林理工大学 | Method for determining hydraulic parameters and water inflow amount of gravel soil in erosion stage |
| CN115343201A (en) * | 2022-05-31 | 2022-11-15 | 山东大学 | Method for testing gap rate of roadbed filled with road arches by irrigation |
| CN115598023A (en) * | 2022-11-08 | 2023-01-13 | 四川中德禄江装备科技有限公司（Cn） | Method for determining three-dimensional tortuosity of loose broken rock-soil mass |
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