CN112986071A - Loess structural potential strength determination method based on macro-micro correlation - Google Patents

Loess structural potential strength determination method based on macro-micro correlation Download PDF

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CN112986071A
CN112986071A CN202110154080.6A CN202110154080A CN112986071A CN 112986071 A CN112986071 A CN 112986071A CN 202110154080 A CN202110154080 A CN 202110154080A CN 112986071 A CN112986071 A CN 112986071A
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soil
loess
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CN112986071B (en
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张耀
李宁
傅少君
李祖锋
李阳
汪奇
陈树峰
习羽
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Xijing University
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Abstract

The invention discloses a loess structural potential strength judging method based on macro-micro correlation, which comprises the following steps of; the method comprises the following steps: calculating and judging the particle grade potential; step two: calculating and judging the pore potential; step three: calculating and judging the connection potential; step four: and comprehensively judging the loess structural potential of the in-situ site. The method has the characteristics of macro-micro correlation, simplicity, strong operability and high accuracy.

Description

Loess structural potential strength determination method based on macro-micro correlation
Technical Field
The invention relates to the technical field of geotechnical engineering foundation soil evaluation, in particular to a loess structural potential strength judgment method based on macro-micro correlation.
Background
Modern soil mechanics have developed rapidly since the last century. Geotechnical workers carry out intensive research on important theories and methods, so that the geotechnical workers can accurately and reliably solve a plurality of geotechnical engineering problems in reality. However, the conventional theory and method of modern soil mechanics have certain defects in describing and solving the problems of large deformation, discontinuity, progressive damage and the like of soil bodies. For example, when the stability of the landslide is calculated by using a traditional calculation method, such as swedish striping method, bischeimpfia method and finite element method, although the slide body is subdivided into a plurality of soil strips or unit points, the fall of the burial depth of the slide surface and the great difference of the structural property and the mechanical property of soil bodies with different depths are not considered, and c and phi are regarded as fixed values. This necessarily affects the accuracy of a bulky, thick landslide when calculating its stability. In addition, with the development of geotechnical engineering under different environmental conditions, a multi-element coupling stress mechanism of a geotechnical body under complex environmental conditions such as strong chemical action, strong radiation, high ground stress, ultrahigh/low temperature, high water pressure and the like becomes a new problem which needs to be overcome by geotechnical researchers and engineering technicians, and the geotechnical engineering problem under the environmental conditions cannot be explained and solved by using the traditional soil mechanics theory and method.
Loess, a typical structural soil, also faces the above-mentioned difficult problem, and the problem is further complicated because of its characteristic structural property. The loess has a structure mainly characterized by a large pore ratio, a low density, and a high content of soluble salts (fig. 8). Due to the structural characteristics, the composite material has a larger compression space, and can collapse or liquefy under the action of special external force, such as water immersion, earthquake or high load, so that serious resistance is brought to engineering construction. Taking city Yan' an of alpine of northern Shaanxi as an example, along with the construction of heavy projects such as flat mountain city building, fixed ditch tableland maintaining and ditch land building, catastrophe phenomena such as ground subsidence, side slope slippage, foundation failure and the like occur. The local government and the related technical departments adopt a plurality of engineering measures, and although the apparent mechanical index of the loess backfilled in the Yanan new area reaches the standard, the loess backfilled in the Yanan new area sinks continuously at the maximum rate of 45 mm/a. The final reason is that the specific structure of loess has no deep knowledge, and the root cause and deep mechanism of the catastrophe are not found. Collapsible loess has stronger structurality, has higher intensity under the normal moisture content condition, can not destroy its pore structure under the general pressure condition, makes its abundant compression. Even if the soil is soaked in water, if the soaking time is insufficient, the soluble salt can not be dissolved sufficiently, salt crystal colloidal crystals and an overhead pore structure in the soil can not be damaged completely, and the soil is difficult to collapse completely at one time. These phenomena cannot be reasonably explained and effectively solved only by means of research theories and methods of macroscopic soil mechanics, and can be verified and explained only by means of microscopic research methods.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a loess structural potential strength determination method based on macro-micro correlation, which has the characteristics of macro-micro correlation, simplicity, strong operability and high accuracy.
In order to achieve the purpose, the invention adopts the technical scheme that:
a loess structural potential intensity judging method based on macro-microcosmic association comprises the following steps;
the method comprises the following steps: calculating and judging the particle grade potential;
step two: calculating and judging the pore potential;
step three: calculating and judging the connection potential;
step four: and comprehensively judging the loess structural potential of the in-situ site.
The first step is specifically as follows:
firstly, the method comprises the following steps: testing the particle size of the soil sample by using a laser particle sizer or an experiment, and drawing a particle size distribution curve of soil, wherein the abscissa is the particle size r, and the ordinate is the volume percentage N of the accumulated particles; wherein, the volume percentage is dimensionless, and the unit of r is mm;
II, secondly: the particle size potential of the soil is represented by the distribution characteristic of the cumulative volume ratio (N) of particles with a particle size larger than a certain particle size, namely the distribution characteristic of an r-N curve, and r and N have a corresponding relation of a power function, as shown in formula (1):
N∝r—Dps (1)Dpsthe granularity of the soil sample is divided into dimensions to reflect the size of the granular potential of the soil; wherein D ispsIs dimensionless;
thirdly, the method comprises the following steps: to DpsPerforming correlation calculation, defining the abscissa of a log-log coordinate system as the particle diameter r, defining the ordinate as the proportion N of the number of particles larger than the particle diameter, and determining the slope of the straight line of the fitted linear function as DpsConverting formula (1) to formula (2); k is a constant term obtained by taking logarithm of the formula (1), and is dimensionless;
lnN＝-Dps·lnr+k (2)
fourthly, the method comprises the following steps: to DpsAnd carrying out grading.
Said DpsThe grading basis is as follows:
size dimension value D of soil particlespsAnd coefficient of non-uniformity CuAnd also the coefficient of curvature CcHave similar meanings, will be for CuAnd also CcIs converted into a logarithmic form and applied to DpsIn the classification of (1), wherein CuNot less than 5 and Cc1-3 of soil is well graded soil;
of finely graded soils
Figure BDA0002933865860000031
Calculating the slope of the curve in logarithmic coordinates
Figure BDA0002933865860000032
Let DpsK, then DpsLess than or equal to 1.11, in the same way, composed of
Figure BDA0002933865860000033
Can calculate Dps≥0.37；
D of the well-graded soilpsIn [0.37, 1.11 ]]The particle grade potential in this interval is low grade, and the middle grade and high grade increase or decrease by 0.37, and the high grade is more than 1.85.
The second step is specifically as follows:
firstly, the method comprises the following steps: testing the pore information of different soil samples by using a mercury porosimeter or a CT (computed tomography), wherein the abscissa R is the equivalent pore diameter, and the ordinate is the percentage of the pores with the pore diameter R in the total pore volume, namely the pore size distribution, wherein the percentage of the pores with the pore diameter R in the total pore volume is dimensionless, and the unit of R is mum;
II, secondly: the pore potential of the soil is represented by the ratio of the large pore to the medium pore of the soil, the sum of the pores with different equivalent pore diameters is extracted, or the sum is directly read by a test instrument, and the ratio of the large pore to the medium pore can be expressed by the following formula (3):
Figure BDA0002933865860000041
in the formula, e0Is the void ratio of the soil sample, RmaxIs the measurable maximum pore diameter of the soil sample, upsilon is the volume percentage of large and medium pores,
Figure BDA0002933865860000042
is the volume of large and medium pores in the soil sample,
Figure BDA0002933865860000043
the total volume of pores in the soil sample; wherein e is0，υ，
Figure BDA0002933865860000044
And
Figure BDA0002933865860000045
is dimensionless, RmaxUnit of (d) is μm;
thirdly, the method comprises the following steps: and classifying upsilon.
The third step is specifically as follows:
testing the content of soluble salt in the loess by using an X-ray fluorescence spectrometer and an X-ray diffractometer, and testing the content of calcium carbonate in the loess by using the following experimental method to approximately represent the content of soluble salt in the loess under the condition that the X-ray fluorescence spectrometer and the X-ray diffractometer are not used for testing;
the specific operation steps are as follows:
firstly, the method comprises the following steps: accurately weighing 1-8g (calcium carbonate content is not more than 0.25g) of air-dried soil sample passing through a 0.15mm sieve pore by using an analytical balance, placing the air-dried soil sample into a wide-mouth bottle, adding 5ml of potassium hydroxide solution with the concentration of 2mol/L into a plastic cup, tightly plugging a bottle stopper to prevent air leakage, connecting a 50ml medical injector to the upper end of a latex tube, pinching off a glass bead switch, and pumping 50ml of air out of the wide-mouth bottle;
II, secondly: injecting 20ml of hydrochloric acid solution with the concentration of 2mol/L into the wide-mouth bottle through the latex tube by using an injector, clamping the upper end of the latex tube by using a water stop clamp, slightly rotating the wide-mouth bottle to ensure that the sample is fully and uniformly contacted with the hydrochloric acid, and standing at room temperature for 16-24 hours;
thirdly, the method comprises the following steps: opening a bottle stopper, carefully taking out a plastic cup, using 50ml of pure water without carbon dioxide, washing a potassium hydroxide solution in the plastic cup into a 200ml triangular bottle, adding 20 drops of thymol-orcinol mixed indicator, titrating with 1mol/L hydrochloric acid solution until the solution is changed from purple to light red, titrating with 0.1mol of hydrochloric acid standard solution until the solution just appears yellow and the red does not completely disappear (pH is 8.3) (not counting amount), then adding 16 drops of bromokaliophenol green indicator, titrating with 0.1mol/L hydrochloric acid standard solution until the solution is changed from blue to bright yellow (pH is 3.9), and counting the titration amount;
fourthly, the method comprises the following steps: performing a blank test again according to the method;
fifthly: calculating the calcium carbonate content according to formula (4);
Figure BDA0002933865860000051
wherein C is the concentration of the hydrochloric acid standard solution; v1Using potassium bromophenol green as an indicator to titrate the dosage of a hydrochloric acid standard solution; v2For blank comparison test, using potassium bromophenol green as indicator to titrate the dosage of hydrochloric acid standard solution; m isdThe mass of the dried soil is shown in the specification, wherein the unit of C is mol/L, V1、V2Has the unit of L, mdThe unit of (a) is g;
sixthly, the method comprises the following steps: the soluble salt content was graded.
The fourth step is specifically as follows:
firstly, the macroscopic (comprehensive) structural potential of a single soil sample is mainly determined by the three microscopic structural potentials together, so the strength of the structural potential of the single soil sample needs to be calculated and judged from the 3 microscopic structural potentials respectively;
and secondly, in the in-situ site, at least 3 representative sites are taken on the site ground level for structural potential evaluation and grade judgment of the loess site, when the soil body of the site is uneven, the number of the representative sites is properly increased, one point is taken every 3-5 meters from the top to the bottom of the loess layer for each selected representative site, and the connection potential, the pore potential and the connection potential of each soil sample are calculated and judged according to the first step, the second step and the third step.
The invention has the beneficial effects that:
(1) compared with the research of the mechanical property and comprehensive structure potential of the loess from a macroscopic view angle, the research method can more deeply disclose the intrinsic mechanism and the essential reason of deformation and damage of the loess.
(2) Compared with observing and testing the properties of a certain point of the soil sample at a microscopic visual angle, the research method can control the overall properties of the soil body, can directly or indirectly evaluate the structural potential and the engineering properties of the undisturbed or disturbed loess, and provides theoretical basis and guidance for actual engineering.
(3) Compared with the method for evaluating the engineering properties of the loess by macroscopic physical or mechanical properties, the evaluation method considers the microstructure factors causing deformation and damage of the loess, and can make up for the defect that the existing loess evaluation and judgment method cannot accurately reflect the large deformation of the loess in the outdoor field.
Drawings
FIG. 1 is a schematic flow chart of the present invention.
FIG. 2 is an exemplary plot of soil size grading.
FIG. 3 is an exemplary graph of a soil particle size dimension curve.
FIG. 4 is an exemplary graph of pore size distribution curves.
Fig. 5 is a 3D structural view of loess particles and granules.
FIG. 6 is a schematic diagram of sampling points.
FIG. 7 is an exemplary diagram of sampling points in loess strata of yellow canal.
FIG. 8 is an SEM image of a microscopic cross-section of loess.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1: a loess structural potential intensity judging method based on macro-microcosmic association comprises the following steps;
the method comprises the following steps: calculating and judging the particle grade potential;
step two: calculating and judging the pore potential;
step three: calculating and judging the connection potential;
step four: and comprehensively judging the loess structural potential of the in-situ site.
The first step is specifically as follows:
firstly, the method comprises the following steps: testing the particle size of the soil sample by using a laser particle sizer or an experiment, and drawing a particle size distribution curve of soil, wherein the abscissa is the particle size r, and the ordinate is the volume percentage N (shown in figure 2) of the accumulated particles; wherein, the volume percentage is dimensionless, and the unit of r is mm;
II, secondly: the particle size potential of the soil is represented by the distribution characteristic of the cumulative volume ratio (N) of particles with a particle size larger than a certain particle size, namely the distribution characteristic of an r-N curve, and r and N have a corresponding relation of a power function, as shown in formula (1):
N∝r—Dps (1)Dpsthe granularity of the soil sample is divided into dimensions to reflect the size of the granular potential of the soil; wherein D ispsIs dimensionless.
Thirdly, the method comprises the following steps: to DpsPerforming correlation calculation, defining the abscissa of a log-log coordinate system as the particle diameter r, defining the ordinate as the proportion N of the number of particles larger than the particle diameter, and determining the slope of the straight line of the fitted linear function as Dps(FIG. 3), converting formula (1) into formula (2); k is a constant term obtained by taking the logarithm of the formula (1) and is dimensionless.
lnN＝-Dps·lnr+k (2)
Fourthly, the method comprises the following steps: to DpsThe ranking was done according to table 1.
D of Table 1psScientific basis of grading:
size dimension value D of soil particlespsAnd coefficient of non-uniformity CuAnd also the coefficient of curvature CcHave similar meanings, will be for CuAnd also CcIs converted into a logarithmic form and applied to DpsIn the classification of (1), wherein CuNot less than 5 and Cc1-3 of soil is well graded soil;
of finely graded soils
Figure BDA0002933865860000071
Calculating the slope of the curve in logarithmic coordinates
Figure BDA0002933865860000072
Let DpsK, then DpsLess than or equal to 1.11, in the same way, composed of
Figure BDA0002933865860000073
Can calculate Dps≥0.37；
Therefore, D of well-graded soilpsIn [0.37, 1.11 ]]The particle grade potential in this interval is low grade, and the middle grade and high grade increase or decrease by 0.37, and the high grade is more than 1.85.
The second step is specifically as follows:
firstly, the method comprises the following steps: the pore information of different soil samples is tested by a mercury porosimeter or a CT (computed tomography), the abscissa R is the equivalent pore diameter, and the ordinate is the percentage of the pores with the pore diameter R in the total pore volume, namely the pore size distribution (figure 4), wherein the percentage of the pores with the pore diameter R in the volume is dimensionless, and the unit of the R is mum.
II, secondly: the pore potential of the soil is represented by the ratio of the large pore to the medium pore of the soil, the sum of the pores with different equivalent pore diameters is extracted, or the sum is directly read by a test instrument, and the ratio of the large pore to the medium pore can be expressed by the following formula (3):
Figure BDA0002933865860000081
in the formula, e0Is the void ratio of the soil sample, RmaxIs the measurable maximum pore diameter of the soil sample, upsilon is the volume percentage of large and medium pores,
Figure BDA0002933865860000082
is a soil sampleThe volume of the medium-large and medium-pore spaces,
Figure BDA0002933865860000083
the total volume of pores in the soil sample; wherein e is0，υ，
Figure BDA0002933865860000084
And
Figure BDA0002933865860000085
is dimensionless, RmaxIn μm.
Thirdly, the method comprises the following steps: the v is graded according to table 4.
Scientific basis for the large and medium pore fraction rating of table 5:
the deformation of loess mainly comprises compression deformation before soaking and collapsible deformation after soaking, and the compression coefficient a of loess is used to distinguish soil compressibility and the collapse coefficient delta is usedsDifferentiate the size of the collapsible deflection of loess after pressurized soaking, and the sum of the two is the maximum deflection of loess soil sample under this load, therefore, refer to the division of the compressibility of standard soil (table 2) and the division of the collapsible deflection of loess (table 3), carry out classification to its big-to-middle pore ratio, if the compression grade of this soil sample is high, and the collapsible grade is strong, then the pore structure potential that the soil sample corresponds is high, if the compression grade of this soil sample is low compressibility, and the collapsible grade is slight, then the pore structure potential that the corresponding of soil sample is low.
Since the external force mainly compresses the large and medium pores in the soil and has little effect on the small and medium pores, it is assumed that the two deformations are both from the compression of the large and medium pores in the soil. According to the relevant specifications, it is assumed that the compression deformation at 100-. When the soil has high compressibility and strong collapsibility, the ratio of large to medium pores is large, and the pore potential is high. When the compressibility of the soil is low and there is no wet-fall, the ratio of large to medium pores is small and the pore potential is low. The macropores and mesopores were divided as shown in Table 4 according to tables 2 and 3.
The third step is specifically as follows:
the soluble salt content of the loess is tested by an X-ray fluorescence spectrometer and an X-ray diffractometer, and under the condition of no test by the X-ray fluorescence spectrometer and the X-ray diffractometer, the content of calcium carbonate in the soil can be tested by the following experimental method to approximately represent the soluble salt content in the loess.
The specific operation steps are as follows:
firstly, the method comprises the following steps: accurately weighing 1-8g (calcium carbonate content is not more than 0.25g) of air-dried soil sample passing through a 0.15mm sieve pore by using an analytical balance, placing the air-dried soil sample into a wide-mouth bottle, adding 5ml of potassium hydroxide solution with the concentration of 2mol/L into a plastic cup, tightly plugging a bottle stopper to prevent air leakage, connecting a 50ml medical injector to the upper end of a latex tube, pinching off a glass bead switch, and pumping 50ml of air out of the wide-mouth bottle;
II, secondly: injecting 20ml of hydrochloric acid solution with the concentration of 2mol/L into the wide-mouth bottle through the latex tube by using an injector, clamping the upper end of the latex tube by using a water stop clamp, slightly rotating the wide-mouth bottle to ensure that the sample is fully and uniformly contacted with the hydrochloric acid, and standing at room temperature for 16-24 hours;
thirdly, the method comprises the following steps: opening a bottle stopper, carefully taking out a plastic cup, using 50ml of pure water without carbon dioxide, washing a potassium hydroxide solution in the plastic cup into a 200ml triangular bottle, adding 20 drops of thymol-orcinol mixed indicator, titrating with 1mol/L hydrochloric acid solution until the solution is changed from purple to light red, titrating with 0.1mol of hydrochloric acid standard solution until the solution just appears yellow and the red does not completely disappear (pH is 8.3) (not counting amount), then adding 16 drops of bromokaliophenol green indicator, titrating with 0.1mol/L hydrochloric acid standard solution until the solution is changed from blue to bright yellow (pH is 3.9), and counting the titration amount;
fourthly, the method comprises the following steps: performing a blank test again according to the method;
fifthly: calculating the calcium carbonate content according to formula (4);
Figure BDA0002933865860000091
wherein C is the concentration of the hydrochloric acid standard solution; v1Using potassium bromophenol green as an indicator to titrate the dosage of a hydrochloric acid standard solution;V2for blank comparison test, using potassium bromophenol green as indicator to titrate the dosage of hydrochloric acid standard solution; m isdThe quality of the drying soil is shown. Wherein the unit of C is mol/L, V1、V2Has the unit of L, mdThe unit of (b) is g.
Sixthly, the method comprises the following steps: the soluble salt content was graded according to table 6.
Table 6 scientific basis for soluble salt partitioning:
the bonding force between loess particles mainly includes van der waals force, coulomb force, and adhesive force. The Van der Waals force and the Coulomb force are much smaller than the level of the adhesive force, so that the van der Waals force and the Coulomb force can be simplified for facilitating engineering application and popularization, the Van der Waals force and the Coulomb force are neglected, and the adhesive force is only used for representing the magnitude of the connecting potential.
The cementing substance in the soil mainly comprises salt crystal cementation and clay mineral, and the clay mineral has low content in the loess and can be neglected. Therefore, the division of the loess connection potential is simplified into the division of the salt crystal colloidal content in the soil. The soluble salt content of loess in China regularly changes from the northwest to the southeast, the soluble salt content in the northwest is high, the connection potential is strong, and the soluble salt content in the southeast is low, and the connection potential is weak. The soluble salt in loess mainly comprises CaCO3、MgSO4、Na2SO4、Na2CO3、NaCl、CaSO4The linking potential of the loess was classified into 4 grades according to the specific gravity of the loess (table 5) occupied by soluble salts in the loess (table 6).
The fourth step is specifically as follows:
the macroscopical (comprehensive) structural potential of a single soil sample is mainly determined by the three microcosmic structural potentials, so the strength of the single soil sample structural potential needs to be calculated and judged from the 3 microcosmic structural potentials respectively.
In the in-situ field, the geological conditions such as the buried depth of a soil layer, the landform and the like have great influence on the structural performance of the soil. Therefore, at least 3 representative places should be taken on the ground level of the loess field for structural potential evaluation and grade judgment, and the number of the places can be increased appropriately when the soil body of the field is uneven. Each selected representative place should be a point every 3-5 meters from the top to the bottom of the loess layer, and the sampling method can be seen in a schematic diagram of a sampling point selected in fig. 6. And calculating and judging the connection potential, the pore potential and the connection potential of each soil sample according to the first step, the second step and the third step.
TABLE 1 grading of granular potentials
Figure BDA0002933865860000111
TABLE 2 compressibility ratings of soils
Figure BDA0002933865860000112
TABLE 3 collapsible grading of loess
Figure BDA0002933865860000113
TABLE 4 grading of the pore potential
Figure BDA0002933865860000114
Table 5 soluble salt content (%) -in self-weight collapsible loess and non-self-weight collapsible loess
Figure BDA0002933865860000115
TABLE 6 ranking of connection potentials
Figure BDA0002933865860000116
TABLE 7 grading of loess stratum microstructure potential of yellow canal field
Figure BDA0002933865860000117
Figure BDA0002933865860000121
TABLE 8 loess collapsibility grade near yellow Trench
Figure BDA0002933865860000122
Example (b):
the determination and evaluation method is exemplified by a site where the excessive wet settlement occurs near the yellow canal in Dali county of Shaanxi province. As shown in FIG. 7, wells 1, 2 and 3 were selected from collapsible loess layers of 1.5 to 20.0m, and samples were taken every 3 m. The microstructural index was measured and calculated according to the above method, and the results are shown in table 7. The macroscopic mechanical index-coefficient of wet fall of each sample point was experimentally measured and the grade thereof was judged as shown in table 8. Comparing table 7 and table 8, it can be found that the porosity potential grade of the soil layer and the collapsibility grade goodness fit of the soil layer tested and divided according to the invention are better, which indicates that the physical index of the collapsibility coefficient of loess is mainly related to the large-medium porosity ratio of loess, and the determination method of the invention is accurate.
Description of the drawings: point 1 is closest to the channel because the drill point has collapsed about 2m below due to channel water leakage. The point 2 is far away and can be divided into 2 layers, the collapse is generated below 9.5m due to water leakage, and the loess on the layer is not submerged by the leaked water due to shallow burial depth above 9.5 m. Point 3 is far from the channel and the leaked water does not affect the loess therein.

Claims (6)

1. A loess structural potential intensity determination method based on macro-microcosmic association is characterized by comprising the following steps;
the method comprises the following steps: calculating and judging the particle grade potential;
step two: calculating and judging the pore potential;
step three: calculating and judging the connection potential;
step four: and comprehensively judging the loess structural potential of the in-situ site.
2. The loess structural potential strength judging method based on macro-micro correlation as claimed in claim 1, wherein the first step is specifically as follows:
firstly, the method comprises the following steps: testing the particle size of the soil sample by using a laser particle sizer or an experiment, and drawing a particle size distribution curve of soil, wherein the abscissa is the particle size r, and the ordinate is the volume percentage N of the accumulated particles; wherein, the volume percentage is dimensionless, and the unit of r is mm;
II, secondly: the particle size potential of the soil is represented by the distribution characteristic of the cumulative volume ratio (N) of particles with a particle size larger than a certain particle size, namely the distribution characteristic of an r-N curve, and r and N have a corresponding relation of a power function, as shown in formula (1):
N∝r—Dps (1)
Dpsthe granularity of the soil sample is divided into dimensions to reflect the size of the granular potential of the soil; wherein D ispsIs dimensionless;
thirdly, the method comprises the following steps: to DpsPerforming correlation calculation, defining the abscissa of a log-log coordinate system as the particle diameter r, defining the ordinate as the proportion N of the number of particles larger than the particle diameter, and determining the slope of the straight line of the fitted linear function as DpsConverting formula (1) to formula (2); k is a constant term obtained by taking logarithm of the formula (1), and is dimensionless;
lnN＝-Dps·lnr+k
(2)
fourthly, the method comprises the following steps: to DpsAnd carrying out grading.
3. The method for determining loess structural potential strength based on macro-micro correlation as claimed in claim 2, wherein D ispsThe grading basis is as follows:
size dimension value D of soil particlespsAnd coefficient of non-uniformity CuAnd also the coefficient of curvature CcHave similar meanings, will be for CuAnd also CcIs converted into a logarithmic form and applied to DpsIn the classification of (1), itC inuNot less than 5 and Cc1-3 of soil is well graded soil;
of finely graded soils
Figure FDA0002933865850000021
Calculating the slope of the curve in logarithmic coordinates
Figure FDA0002933865850000022
Let DpsK, then DpsLess than or equal to 1.11, in the same way, composed of
Figure FDA0002933865850000023
Can calculate Dps≥0.37；
D of the well-graded soilpsIn [0.37, 1.11 ]]The particle grade potential in this interval is low grade, and the middle grade and high grade increase or decrease by 0.37, and the high grade is more than 1.85.
4. The loess structural potential strength judging method based on macro-micro correlation as claimed in claim 1, wherein the second step comprises:
firstly, the method comprises the following steps: testing the pore information of different soil samples by using a mercury porosimeter or a CT (computed tomography), wherein the abscissa R is the equivalent pore diameter, and the ordinate is the percentage of the pores with the pore diameter R in the total pore volume, namely the pore size distribution, wherein the percentage of the pores with the pore diameter R in the total pore volume is dimensionless, and the unit of R is mum;
II, secondly: the pore potential of the soil is represented by the ratio of the large pore to the medium pore of the soil, the sum of the pores with different equivalent pore diameters is extracted, or the sum is directly read by a test instrument, and the ratio of the large pore to the medium pore can be expressed by the following formula (3):
Figure FDA0002933865850000031
in the formula, e0Is the void ratio of the soil sample, RmaxIs the measurable maximum pore diameter of the soil sample, upsilon is the volume percentage of large and medium pores,
Figure FDA0002933865850000032
is the volume of large and medium pores in the soil sample,
Figure FDA0002933865850000033
the total volume of pores in the soil sample; wherein e is0，υ，
Figure FDA0002933865850000034
And
Figure FDA0002933865850000035
is dimensionless, RmaxUnit of (d) is μm;
thirdly, the method comprises the following steps: and classifying upsilon.
5. The loess structural potential strength judging method based on macro-micro correlation as claimed in claim 1, wherein the third step is specifically:
testing the content of soluble salt in the loess by using an X-ray fluorescence spectrometer and an X-ray diffractometer, and testing the content of calcium carbonate in the loess by using the following experimental method to approximately represent the content of soluble salt in the loess under the condition that the X-ray fluorescence spectrometer and the X-ray diffractometer are not used for testing;
the specific operation steps are as follows:
firstly, the method comprises the following steps: accurately weighing 1-8g (calcium carbonate content is not more than 0.25g) of air-dried soil sample passing through a 0.15mm sieve pore by using an analytical balance, placing the air-dried soil sample into a wide-mouth bottle, adding 5ml of potassium hydroxide solution with the concentration of 2mol/L into a plastic cup, tightly plugging a bottle stopper to prevent air leakage, connecting a 50ml medical injector to the upper end of a latex tube, pinching off a glass bead switch, and pumping 50ml of air out of the wide-mouth bottle;
II, secondly: injecting 20ml of hydrochloric acid solution with the concentration of 2mol/L into the wide-mouth bottle through the latex tube by using an injector, clamping the upper end of the latex tube by using a water stop clamp, slightly rotating the wide-mouth bottle to ensure that the sample is fully and uniformly contacted with the hydrochloric acid, and standing at room temperature for 16-24 hours;
thirdly, the method comprises the following steps: opening a bottle stopper, carefully taking out a plastic cup, using 50ml of pure water without carbon dioxide, washing a potassium hydroxide solution in the plastic cup into a 200ml triangular bottle, adding 20 drops of thymol-orcinol mixed indicator, titrating with 1mol/L hydrochloric acid solution until the solution is changed from purple to light red, titrating with 0.1mol of hydrochloric acid standard solution until the solution just appears yellow and the red is not completely disappeared (pH is 8.3), then adding 16 drops of bromokaliophenol green indicator, titrating with 0.1mol/L hydrochloric acid standard solution until the solution is changed from blue to bright yellow (pH is 3.9), and recording the titration amount;
fourthly, the method comprises the following steps: performing a blank test again according to the method;
fifthly: calculating the calcium carbonate content according to formula (4);
Figure FDA0002933865850000041
wherein C is the concentration of the hydrochloric acid standard solution; v1Using potassium bromophenol green as an indicator to titrate the dosage of a hydrochloric acid standard solution; v2For blank comparison test, using potassium bromophenol green as indicator to titrate the dosage of hydrochloric acid standard solution; m isdThe mass of the dried soil is shown in the specification, wherein the unit of C is mol/L, V1、V2Has the unit of L, mdThe unit of (a) is g;
sixthly, the method comprises the following steps: the soluble salt content was graded.
6. The loess structural potential strength judging method based on macro-micro correlation as claimed in claim 1, wherein the fourth step is specifically:
firstly, the macrostructure potential of a single soil sample is mainly determined by the three microstructure potentials together, so the strength of the structure potential of the single soil sample needs to be calculated and judged from the 3 microstructure potentials respectively;
and secondly, in the in-situ site, at least 3 representative sites are taken on the site ground level for structural potential evaluation and grade judgment of the loess site, when the soil body of the site is uneven, the number of the representative sites is properly increased, one point is taken every 3-5 meters from the top to the bottom of the loess layer for each selected representative site, and the connection potential, the pore potential and the connection potential of each soil sample are calculated and judged according to the first step, the second step and the third step.
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CN109142168A (en) * 2018-07-05 2019-01-04 湖北工业大学 A kind of soil particle gradation evaluation method based on fractal dimension
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CN109142168A (en) * 2018-07-05 2019-01-04 湖北工业大学 A kind of soil particle gradation evaluation method based on fractal dimension
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