CN114002409A - Rapid determination method for soil-water characteristic curve of unsaturated compacted soil transition region - Google Patents
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Abstract
The invention relates to a rapid determination method of a soil-water characteristic curve of an unsaturated compacted soil transition region, which comprises the following steps: s1, measuring the initial pore ratio e of the soil sample0And specific gravity GsThen measuring a relation curve of the accumulated mercury intrusion volume and the aperture by a mercury intrusion test; s2, converting the relation between the substrate suction force and the aperture according to a Young-Laplace equation; and S3, according to the basic definition of soil mechanics, the saturation or the water content corresponding to each suction force of the sample is represented by the accumulated mercury intrusion volume measured by the mercury intrusion test. The invention has the beneficial effects that: the method is simple and easy to implement, and the soil-water characteristic curve of the unsaturated compacted soil transition region with different pore ratios can be quickly determined by performing mercury intrusion experiments on soil samples with certain initial pore ratios to obtain a relation curve of accumulated mercury intrusion volume and pore diameter and combining the Young-Laplace equation and the basic definition of soil mechanics, wherein the whole experiment process only needs 1-2 hours, and the method is simple and easy to implement, and is simple and easy to implementThe accuracy of the measurement result is higher.
Description
Technical Field
The invention relates to research on unsaturated soil and water characteristics in geotechnical subgrade engineering, in particular to a rapid determination method of soil and water characteristic curves of unsaturated compacted soil transition regions based on mercury intrusion tests.
Background
The study on the soil-water characteristics of unsaturated compacted soil is the basis of analysis on the stability of unsaturated slopes. The method is characterized in that a shaft translation technology is usually adopted for acquiring the soil-water characteristic curve of unsaturated soil in a laboratory, and the balancing time under each stage of suction needs 4-5 days, if the time is clay, the time is even longer. If a soil-water characteristic curve is obtained, one or two months or more may be needed.
The distribution of the internal microscopic pores of the soil body is closely related to the soil-water characteristics, the relationship between the microscopic pores and the soil-water characteristics is indirectly established, a rapid determination method for indirectly measuring the soil-water characteristic curve is provided, only the pore size distribution data of the soil body needs to be measured through a mercury intrusion experiment, so that the soil-water characteristic curve of the soil body is indirectly obtained, the time is consumed for 1-2 hours, and the method has the advantages of simplicity, high efficiency, higher precision and the like, and can provide basic data for deformation analysis of unsaturated soil filling subgrade engineering.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a method for rapidly measuring a soil-water characteristic curve of an unsaturated compacted soil transition area.
The rapid determination method for the soil-water characteristic curve of the unsaturated compacted soil transition region provides a rapid determination method for indirectly acquiring the soil-water characteristic curve of unsaturated soil based on a pore distribution result measured by a mercury intrusion test, and comprises the following steps:
s1, measuring the initial pore ratio e of the soil sample0And specific gravity GsThen measuring a relation curve of the accumulated mercury intrusion volume and the aperture by a mercury intrusion test;
s2, converting the relation between the substrate suction force and the aperture according to a Young-Laplace equation;
and S3, according to the basic definition of soil mechanics, the saturation or the water content corresponding to each suction force of the sample is represented by the accumulated mercury intrusion volume measured by the mercury intrusion test.
According to the three steps, reasonable mercury intrusion data are selected, so that the relation curve of the saturation or the water content of the sample and the substrate suction can be determined, and the purpose of rapidly measuring the unsaturated soil-water characteristic curve is achieved.
Preferably, the method comprises the following steps: in step S1, the sample subjected to the mercury intrusion test should conform to the soil sample in the actual process of the soil-water characteristic test, and should conform to the pore size distribution corresponding to the sample during the main dehumidification, that is, the sample obtained after the unsaturated compacted soil is saturated.
Preferably, the method comprises the following steps: in step S1, assuming that the internal pores of the soil sample are cylindrical, a soil sample with a known initial pore ratio is subjected to a mercury intrusion test, and a relationship curve between the cumulative mercury intrusion volume of the sample and the pore diameter is measured.
Preferably, the method comprises the following steps: in step S2, the relationship between the substrate suction force and the aperture is calculated by the Young-Laplace equation as follows:
in the formula: s is suction, kPa; t issSurface tension of the liquid, N/m; thetawIs the contact angle of a liquid-solid surface; d is the pore diameter. In the calculation, the surface tension TsDependent on the ambient temperature, the surface tension T is at 25 ℃ for the ambient temperaturesTake 0.072N/m, thetawTake 0.
Preferably, the method comprises the following steps: in step S3, the method for representing the saturation or water content of each suction force of the sample by using the accumulated mercury intrusion volume measured by the mercury intrusion test includes the following steps:
s3-1, the expression of the characteristic curve of the saturated soil and water is as follows:
wherein w is the water content,%, of the sample; srIs the saturation of the sample,%.
S3-2, effective water content w according to unsaturated soil and water characteristic curveeAnd effective saturation SeIs expressed as follows:
in the formula, wreThe water content is corresponding to the volume amount of pores which cannot be measured in the mercury intrusion test; sreSaturation corresponding to the volume amount of pores which can not be measured in the mercury intrusion test; the unmeasured pores are mainly closed pores and unmeasured fine pores in the mercury pressure range.
S3-3, and assuming that pore water corresponding to pore diameter larger than pore diameter air inlet value is removed, the effective saturation S of the sample under the suction force ise(d) Expressed as:
in the formula, r is the pore size corresponding to any pore; r ismaxThe maximum value of the pore diameter corresponding to the pores in the soil sample; f (r) is a cumulative pore distribution function; f (r) is a pore size distribution function. Both the pore size distribution function and the cumulative pore distribution function were measured by mercury intrusion experiments.
S3-4, based on the accumulated pore distribution curve of the mercury intrusion test, the effective water content and the effective saturation of the soil sample are respectively expressed as:
in the formula, F (d)min) The accumulated volume corresponding to the minimum pore diameter in the accumulated pore distribution curve obtained by the mercury intrusion test; f (d) is the accumulated volume amount corresponding to any pore diameter in the accumulated pore distribution curve; rhowTaking the density of water as 1g/cm3。
S3-5, porosity ratio e if measured in mercury intrusion testmComprises the following steps:
in the formula, VvIs the pore volume, VsIs the volume of the soil particles.
Since the unit of the ordinate in the cumulative pore distribution curve measured in the mercury intrusion test is mL/g, the mass per gram of dry soil (i.e., the mass m of dry soil) iss1g) pore volume VvComprises the following steps:
Vv＝F(dmin) (7)
volume V of soil particles in per gram of soilsComprises the following steps:
substituting the formulae (7) and (8) into the formula (6) to obtain the porosity ratio e measured by mercury intrusion testmComprises the following steps:
em＝ρwF(dmin)Gs (9)
s3-6, based on the cumulative pore distribution curve, the residual water content w in each gram of dry soilreAnd residual saturation SreExpressed as:
in the formula, e0Is the initial void ratio.
S3-7, based on the relation curve of the accumulated mercury intrusion volume and the aperture obtained by mercury intrusion test, and according to the formulas (1), (2), (3), (5), (9) and (10), the saturation S can be obtainedrAnd the relation between the substrate suction force s and the water content w and the substrate suction force s, namely, the soil-water characteristic curve of the compacted soil body can be rapidly determined through the data of the mercury intrusion test.
The invention has the beneficial effects that: the method designed by the invention can realize the rapid determination of the soil-water characteristic curve of the unsaturated compacted soil transition region, and effectively overcomes the difficulty of time and labor consumption in measuring the unsaturated soil-water characteristic curve. The method is simple and easy to implement, and the measurement result precision is high, and the rapid measurement of the soil-water characteristic curve of the unsaturated compacted soil transition region with different pore ratios can be realized by carrying out mercury intrusion experiments on soil samples with certain initial pore ratios to obtain the relation curve of the accumulated mercury intrusion volume and the pore diameter and combining the Young-Laplace equation and the basic definition of soil mechanics.
Drawings
FIG. 1 is a graph showing a relationship between a cumulative mercury intrusion volume and a pore diameter of silty clay obtained by a mercury intrusion test;
FIG. 2 is a graph showing a comparison of soil-water characteristics (water content) of silty clay measured by the method of the present invention and a conventional laboratory method;
FIG. 3 is a comparison graph of the soil-water characteristic curves (saturation) of silty clay measured by the method of the present invention and a conventional laboratory method;
FIG. 4 is a graph showing the relationship between the cumulative mercury intrusion volume and pore diameter of red clay obtained by mercury intrusion experiments;
FIG. 5 is a graph comparing the soil-water characteristic curves (water content) of the red clay measured by the method of the present invention and the conventional laboratory method;
FIG. 6 is a comparison graph of the soil-water characteristic curves (saturation) of the red clay measured by the method of the present invention and the conventional laboratory method.
Detailed Description
The present invention will be further described with reference to the following examples. The following examples are set forth merely to aid in the understanding of the invention. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Example one
The embodiment of the application provides a rapid determination method for a soil-water characteristic curve of an unsaturated compacted soil transition region, wherein a representative soil sample is selected to be subjected to an indoor mercury pressing test, the sample can be subjected to a freeze-drying method, the original pore structure is kept as much as possible, and a relation curve of accumulated mercury pressing volume and pore diameter is obtained through the mercury pressing test; converting a Young-Laplace equation to obtain the relation between the suction force of the matrix and the aperture; according to the basic definition of soil mechanics, the saturation or the water content of the sample is represented by the accumulated mercury intrusion volume obtained by a mercury intrusion test; and finally, calculating to obtain a relation curve of the matrix suction force and the saturation or the water content of the sample, and realizing the rapid determination of the soil-water characteristic curve of the unsaturated compacted soil transition region. The method comprises the following steps:
s1, firstly measuring the initial pore ratio e of the soil sample0And specific gravity GsAnd measuring a relation curve of the accumulated mercury intrusion volume and the aperture by a mercury intrusion test. The sample for mercury-pressing test should conform to the soil sample in the actual process of soil-water characteristic test, and should conform to the pore size distribution corresponding to the sample in the main dehumidification process, i.e. the sample after saturation of unsaturated compacted soil.
And S2, converting the relation between the substrate suction force and the aperture according to the Young-Laplace equation.
And S3, according to the basic definition of soil mechanics, the saturation or the water content corresponding to each suction force of the sample is represented by the accumulated mercury intrusion volume measured by the mercury intrusion test.
According to the three steps, reasonable mercury intrusion data are selected, so that the relation curve of the saturation or the water content of the sample and the substrate suction can be determined, and the purpose of rapidly measuring the unsaturated soil-water characteristic curve is achieved.
Example two
On the basis of the first embodiment, the second embodiment of the present application provides a more specific method for rapidly determining a soil-water characteristic curve of a non-saturated compacted soil transition region, which comprises the following specific steps:
1) assuming that the internal pores of the soil sample are cylindrical, performing mercury intrusion test on the soil sample with known initial pore ratio to obtain a relation curve between the accumulated mercury intrusion volume of the sample and the pore diameter;
2) the relationship between the matrix suction force and the pore diameter is calculated by a Young-Laplace equation as follows:
in the formula: s is suction, kPa; t issSurface tension of the liquid, N/m; thetawIs the contact angle of a liquid-solid surface. In the calculation, the surface tension TsDependent on the ambient temperature, the surface tension T is at 25 ℃ for the ambient temperaturesTake 0.072N/m, thetawTake 0.
3) The expression of the unsaturated soil-water characteristic curve is as follows:
wherein w is the water content,%, of the sample; srIs the saturation of the sample,%.
4) The unsaturated soil-water characteristic curve can be expressed as follows in terms of effective water content and effective saturation:
in the formula, wreThe water content corresponding to the volume of the pores which can not be measured in the mercury intrusion test, SreSaturation corresponding to the volume amount of pores which can not be measured in the mercury intrusion test; the unmeasured pores are mainly closed pores and unmeasured fine pores in the mercury pressure range.
5) Assuming that pore water corresponding to pore diameters larger than the pore diameter air inlet value is removed, the effective saturation S of the sample under the suction force ise(d) Can be expressed as:
in the formula, r is the pore size corresponding to any pore; r ismaxThe maximum value of the pore diameter corresponding to the pores in the soil sample; f (r) is a cumulative pore distribution function; f (r) is a pore size distribution function. Both the pore size distribution function and the cumulative pore distribution function were measured by mercury intrusion experiments.
6) Based on the pore accumulative distribution curve of the mercury intrusion test, the effective water content and the effective saturation of the soil sample can be respectively expressed as:
in the formula, F (d)min) The accumulated volume corresponding to the minimum aperture in the pore accumulated distribution curve obtained by the mercury intrusion test; f (d) is the accumulated volume amount corresponding to any pore diameter in the pore accumulated distribution curve; rhowTaking the density of water as 1g/cm3。
7) Porosity ratio e measured by mercury intrusion testmComprises the following steps:
in the formula, VvIs the pore volume, VsIs the volume of the soil particles.
Since the unit of the ordinate in the cumulative mercury intrusion curve of the pore volume measured by the mercury intrusion test is mL/g, the unit of the ordinate is in per gram of dry soil (namely the mass m of the dry soil)s1g) pore volume VvComprises the following steps:
Vv＝F(dmin) (7)
the volume of soil particles in each gram of soil is VsComprises the following steps:
by substituting the formulae (7) and (8) into the formula (6), the pore ratio e determined in the mercury intrusion test can be obtainedmComprises the following steps:
em＝ρwF(dmin)Gs (9)
8) based on the pore cumulative distribution curve, the residual water content w in the dry soil per gramreAnd residual saturation SreCan be expressed as
In the formula, e0Is the initial void ratio.
9) Based on the relation curve of the accumulated mercury intrusion volume and the aperture obtained by mercury intrusion test, and according to the formulas (1), (2), (3), (5), (9) and (10), the saturation S can be obtainedrAnd the relation between the substrate suction force s and the water content w and the substrate suction force s, namely, the soil-water characteristic curve of the unsaturated compacted soil transition region can be rapidly determined through data of mercury intrusion tests.
EXAMPLE III
Measuring the soil-water characteristic curve of silty clay with specific gravity of GsAt 2.7, initial void ratio e0Is 1.01. Measuring the soil-water characteristic curve of the soil transition region by adopting two methods:
the method comprises the following steps: a laboratory pressure plate instrument test and a saturated salt solution method are adopted to measure the soil-water characteristic curve of the powdery clay within a wider suction force range. And (3) testing by a pressure plate instrument: the suction path is 6 → 1280kPa, each stage of suction is balanced for about three days for 1 more months; suction was obtained at 3290 and 7480kPa by saturated salt solution steam equilibrium, which required about two months. The method takes about two months in total to measure the soil-water characteristic curve.
The method 2 comprises the following steps: the soil-water characteristic curve of the silty clay is rapidly determined by adopting the method designed by the invention. Firstly, taking a representative soil sample to carry out mercury intrusion test, and then calculating according to the formulas (1), (2), (3), (5), (9) and (10) to obtain a soil-water characteristic curve required to be measured. This process takes a total of about two hours.
Fig. 1 is a graph showing the relationship between the cumulative mercury intrusion volume and pore diameter of the powdered clay obtained by mercury intrusion experiments.
FIGS. 2 and 3 are graphs comparing soil-water characteristic curves of the silty clay measured by the method of the present invention and a conventional laboratory method. As can be seen from fig. 2 and 3, the soil-water characteristic curve measured by the method of the present invention has high accuracy and consumes little time.
Example four
Measuring the soil-water characteristic curve of red clay with specific gravity of GsAt 2.74, initial void ratio e0Is 1.04. Measuring the soil-water characteristic curve of the soil transition region by adopting two methods:
the method comprises the following steps: and measuring the soil-water characteristic curve of the red clay within the wide suction range by adopting a laboratory pressure plate instrument test, a filter paper method and a saturated salt solution method. And (3) testing by a pressure plate instrument: suction path 0 → 1280kPa, balanced for about four days per stage for 1 to 2 months; a filter paper method: suction force is 0.6 → 23.6MPa, and suction force balance needs about half a month; saturated salt solution steam equilibrium method: suction force is 3.29 → 367.5MPa, and suction force balance needs about two months. The method takes about 2 months for measuring the soil-water characteristic curve totally, and three experiments are needed.
The second method comprises the following steps: the method designed by the invention is adopted to rapidly determine the soil-water characteristic curve of the red clay. Firstly, taking a representative soil sample to carry out mercury intrusion test, and then calculating according to the formulas (1), (2), (3), (5), (9) and (10) to obtain a soil-water characteristic curve required to be measured. This process takes a total of about two hours.
Fig. 4 is a graph showing the relationship between the cumulative mercury intrusion volume and pore diameter of red clay obtained by mercury intrusion experiments.
FIGS. 5 and 6 are graphs comparing soil-water characteristic curves of red clay measured by the method of the present invention and a conventional laboratory method. As can be seen from fig. 5 and 6, the soil-water characteristic curve measured by the method of the present invention has high accuracy and consumes little time.
In conclusion, the rapid determination method for the unsaturated compacted soil-water characteristic curve based on the mercury intrusion test can accurately measure the soil-water characteristic curves of different types of compacted soil transition areas, effectively solves the problem that the laboratory measurement of the soil-water characteristic curve wastes time and labor, can rapidly acquire more accurate soil-water characteristic data, and can provide basic data for subsequent unsaturated filling embankment filling deformation calculation and the like.
Claims (4)
1. A rapid determination method for soil-water characteristic curves of unsaturated compacted soil transition regions is characterized by comprising the following steps:
s1, measuring the initial pore ratio e of the soil sample0And specific gravity GsThen measuring a relation curve of the accumulated mercury intrusion volume and the aperture by a mercury intrusion test;
s2, converting the relation between the substrate suction force and the aperture according to a Young-Laplace equation;
and S3, the cumulative mercury intrusion volume measured by the mercury intrusion test represents the saturation or water content corresponding to each suction force of the sample.
2. The method for rapidly determining the soil-water characteristic curve of the unsaturated compacted soil transition region according to claim 1, wherein the method comprises the following steps: in step S1, the internal pores of the soil sample are cylindrical, and a soil sample with a known initial pore ratio is subjected to a mercury intrusion test to obtain a relationship curve between the cumulative mercury intrusion volume of the sample and the pore diameter.
3. The method for rapidly determining the soil-water characteristic curve of the unsaturated compacted soil transition region according to claim 1, wherein the method comprises the following steps: in step S2, the relationship between the substrate suction force and the aperture is calculated by the Young-Laplace equation as follows:
in the formula: s is suction, kPa; t issSurface tension of the liquid, N/m; thetawIs the contact angle of a liquid-solid surface; d is the pore diameter.
4. The method for rapidly determining the soil-water characteristic curve of the unsaturated compacted soil transition region according to claim 1, wherein the method comprises the following steps: in step S3, the method for representing the saturation or water content of each suction force of the sample by using the accumulated mercury intrusion volume measured by the mercury intrusion test includes the following steps:
s3-1, the expression of the characteristic curve of the saturated soil and water is as follows:
wherein w is the water content,%, of the sample; srIs the saturation of the sample,%;
s3-2, effective water content w according to unsaturated soil and water characteristic curveeAnd effective saturation SeIs expressed as follows:
in the formula, wreThe water content is corresponding to the volume amount of pores which cannot be measured in the mercury intrusion test; sreSaturation corresponding to the volume amount of pores which can not be measured in the mercury intrusion test;
s3-3, and the pore water corresponding to the pore diameter larger than the pore diameter air inlet value is removed, so the effective saturation S of the sample under the suction forcee(d) Expressed as:
in the formula, r is the pore size corresponding to any pore; r ismaxThe maximum value of the pore diameter corresponding to the pores in the soil sample; f (r) is a cumulative pore distribution function; (r) is a pore size distribution function;
s3-4, based on the accumulated pore distribution curve of the mercury intrusion test, the effective water content and the effective saturation of the soil sample are respectively expressed as:
in the formula, F (d)min) The accumulated volume corresponding to the minimum pore diameter in the accumulated pore distribution curve obtained by the mercury intrusion test; f (d) is the accumulated volume amount corresponding to any pore diameter in the accumulated pore distribution curve; rhowIs the density of water;
s3-5, porosity ratio e if measured in mercury intrusion testmComprises the following steps:
in the formula, VvIs the pore volume, VsIs the volume of the soil particles;
since the unit of the ordinate in the cumulative pore distribution curve measured in the mercury intrusion test is mL/g, the volume of pores per gram of dry soil is VvComprises the following steps:
Vv＝F(dmin) (7)
volume V of soil particles in per gram of soilsComprises the following steps:
substituting the formulae (7) and (8) into the formula (6) to obtain the porosity ratio e measured by mercury intrusion testmComprises the following steps:
em＝ρwF(dmin)Gs (9)
s3-6, based on the cumulative pore distribution curve, the residual water content w in each gram of dry soilreAnd residual saturation SreExpressed as:
in the formula, e0Is the initial void ratio;
s3-7, obtaining the saturation S based on the relation curve of the accumulated mercury intrusion volume and the aperture obtained by mercury intrusion test and the formulas (1), (2), (3), (5), (9) and (10)rThe substrate suction force s and the relationship between the water content w and the substrate suction force s.
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| 王雪;谭晓慧;李;辛志宇;汪贤恩;: "加湿条件下膨胀土土水特征曲线的试验研究", 工业建筑, no. 05, pages 81 - 85 * |
| 邹静蓉;李志勇;: "考虑体积变化修正的红黏土土水特征曲线试验研究", 水资源与水工程学报, no. 01, pages 183 - 189 * |
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