Method for determining dynamic strength of loess through average particle size and macropore proportion

Abstract

A method for determining dynamic strength of loess through average particle size and macropore ratio comprises the following steps: sampling and determining basic physical properties of a soil sample, preparing an artificial structural loess sample, determining loess n, # imgabs0 # under a microstructure, and determining the dynamic strength of the loess according to the average particle size and the macropore ratio. The method comprises the following steps: establishing a three-dimensional model of dynamic characteristics and a microstructure of loess under the action of a dynamic load by utilizing a particle analysis test and a mercury injection test, and fitting a loess sample n, # imgabs1 # formula; fitting a relation formula, establishing a model, and fitting a dynamic internal friction angle, dynamic cohesion, average particle size and macropore proportion formula through data; and finally, measuring the dynamic strength of the loess, and performing simple qualitative verification on the dynamic strength index of the loess by using the neural network according to the given data in the step 4 and adopting the Moire-Coulomb strength theory. The test precision and efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering foundation soil evaluation, and specifically relates to a method for determining the dynamic strength of loess by average particle size and large pore proportion. Background Art

[0002] Loess is a special type of aeolian sediment with strong dry-wet change characteristics. Due to its complex pore structure, differences in water content and soil particle composition, the dynamic strength of loess shows great instability and is affected by various factors. Dynamic strength refers to the mechanical properties such as compressive resistance and shear resistance of soil under vibration, shock or load, which directly affects the stability and seismic performance of loess in construction projects. Therefore, how to evaluate the dynamic strength of loess by simple and effective means is of great significance for engineering construction and disaster prevention in loess areas. Traditionally, the evaluation of the dynamic strength of loess mostly relies on in-situ tests and laboratory tests, such as dynamic triaxial tests, liquefaction tests, etc. These methods are usually complex to operate, costly and time-consuming. Therefore, it has important practical application value to establish a simple and efficient prediction model based on the basic physical properties of loess (such as particle size distribution, porosity, etc.). Summary of the Invention

[0003] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a method for determining the dynamic strength of loess by average particle size and large pore proportion, so as to improve the test accuracy and efficiency.

[0004] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for determining the dynamic strength of loess by average particle size and large pore proportion, comprising the following steps:

[0006] Step 1: Sampling and determining the basic physical properties of the soil sample;

[0007] Step 2: Preparation of artificial structured loess soil samples;

[0008] Step 3: Determination of n of loess under microscopic structure Determination;

[0009] Step 4: Fitting the relationship formula and establishing a model;

[0010] Step 5: Determination of the dynamic strength of loess.

[0011] The specific content of the said Step 1 is: Taking soil at the target site, wrapping it with multiple layers of black plastic bags, and marking the top and bottom surfaces of the soil blocks; Making ring knife specimens, crushing the retrieved soil and drying it in an oven, placing the dried soil at room temperature, stirring it evenly, and putting it into a plastic bag for later use; Determining the basic physical properties of the soil sample, including soil particle specific gravity Gs, natural water content w(%), natural density ρ(g / cm3 ), dry density ρ d (g / cm 3 ), porosity ratio e.

[0012] The step 2 is specifically as follows: obtaining the original soil material, crushing and screening it after drying, and selecting particles with a particle size of less than 2 mm as the matrix material; dry-mixing the treated matrix material with cement and salt in a predetermined ratio, wherein the cement addition amount is 1.0-4.0% of the mass of the matrix material, and the salt addition amount is 4.0-8.0% of the mass of the matrix material; quantitatively injecting water into the mixture and fully stirring it to form a homogeneous mixture; loading the mixture into a standard molding mold in layers for compaction molding, and demolding the molded sample after sealing and curing to obtain a composite material with predetermined structural characteristics; the molding operation is strictly carried out in accordance with the requirements of GB / T50123-2019.

[0013] The step three is specifically as follows: using particle analysis test and mercury injection test to establish a three-dimensional model of the dynamic characteristics and microstructure of loess under dynamic load, and fitting the loess sample n, formula.

[0014] The step four is specifically: fitting the dynamic internal friction angle, dynamic cohesion, average particle size, and macropore ratio formula through data.

[0015] The step five is specifically as follows: using a neural network, according to the data given in step four, and using the Mohr-Coulomb strength theory to perform a simple qualitative verification on the dynamic strength index of loess.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the particle size distribution and pore characteristics of the soil directly affect the dynamic strength of the soil. By measuring the particle size and the proportion of macropores, the microstructural characteristics of the soil can be obtained relatively simply. The dynamic strength of loess under different stress conditions can be predicted more quickly and accurately through the microstructural characteristics. The traditional method requires a large number of mechanical tests, and the external stress conditions are relatively fixed. Unlike the traditional method that relies on a large amount of soil sample data, the method based on particle size and macropore proportion can provide a more unified evaluation model under different loess soil qualities, water contents and other conditions, and obtain more accurate calculation results. This method makes the prediction of dynamic strength faster and more reliable, and is suitable for geotechnical engineering projects with various complex geological conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a flow chart of an embodiment of the present invention.

[0018] Figure 2 This is the loess particle size gradation curve of Xi'an City in the embodiment of the present invention.

[0019] Figure 3 This is the three-petal molding sample process of an embodiment of the present invention.

[0020] Figure 4 For the τ d -N f relationship curve with a cement content of 1% in the embodiment of the present invention.

[0021] Figure 5 For the τ d -N f relationship curve with a cement content of 2% in the embodiment of the present invention.

[0022] Figure 6 For the τ d -N f relationship curve with a cement content of 4% in the embodiment of the present invention.

[0023] Figure 7 Relationship diagram of the dynamic strength index and the cement content in the embodiment of the present invention.

[0024] Figure 8 Particle size distribution curve of artificially structured loess under different cement contents in the embodiment of the present invention.

[0025] Figure 9 Mercury intrusion curve of artificially structured loess under different conditions in the embodiment of the present invention.

[0026] Figure 10 Scattered points and three-dimensional model of dynamic deformation of artificially structured loess under different conditions in the embodiment of the present invention.

[0027] Figure 11 Relationship between the large pore ratio and the dynamic strength parameters in the embodiment of the present invention.

[0028] Figure 12 Three-dimensional model of the average particle size - large pore ratio - dynamic cohesion of artificially structured loess in the embodiment of the present invention.

[0029] Figure 13 Three-dimensional model of the average particle size - large pore ratio - dynamic internal friction angle in the embodiment of the present invention.

[0030] Figure 14 Dynamic strength failure envelope in the embodiment of the present invention. Detailed implementation manners

[0031] The present invention will be further described in detail below with reference to the embodiments and the drawings.

[0032] As Figure 1 shown, a method for determining the dynamic strength of loess by the average particle size and the large pore ratio includes the following steps:

[0033] Step 1: Sampling and measuring the basic physical properties of the soil sample;

[0034] Specifically: soil is taken from the target site with a depth of 2.0m-3.0m, and a suitable cubic soil sample is chiseled out on the side wall of the foundation pit. It is wrapped in multiple layers of black plastic bags, and the soil block is tightly sealed with transparent tape in all directions to ensure that moisture is not lost as much as possible, and the top and bottom surfaces of the soil block are marked; after crushing, the soil sample that has passed the 2mm sieve is placed in a well-sealed self-sealing bag for subsequent tests; a ring knife sample with a height of 20mm and a diameter of 79.8mm is made, and the retrieved soil is crushed and placed in an oven for drying for no less than 8 hours, and the dried soil is placed at room temperature, fully stirred, and placed in a plastic bag for standby use;

[0035] Determine the basic physical properties of soil samples, including soil particle specific gravity Gs, natural moisture content w (%), natural density ρ (g / cm 3 ), dry density ρ d (g / cm 3 ), porosity e; specify the basic indicators of the standard sample, and determine the initial porosity (e0) of the soil sample according to formula (1), where the soil density (ρ0), soil particle specific gravity (Gs), and natural water content (w0) are determined in accordance with GB / T 50123-2019 "Standard for Geotechnical Test Methods";

[0036]

[0037] Where: e0: initial porosity of soil sample (l); ρ w : Density of water, taken as (1.0g / cm3); Gs: specific gravity of soil particles (unitless); ρ0: natural density of soil (g / cm3); w0: natural moisture content of soil (%); The basic physical indicators of loess taken in this embodiment are shown in Table 1.

[0038] Table 1 Basic physical properties of loess

[0039]

[0040] The particle size distribution of the loess selected in this paper was determined by sieving method (particle size 0.075mm-0.5mm) and densimeter method (particle size less than 0.075mm). Figure 2 As shown, the particle analysis results are shown in Table 2, and the gradation is good.

[0041] Table 2 Analysis of loess particles in Xi'an

[0042]

[0043] Step 2: Preparation of artificial structural loess soil samples;

[0044] Specifically: In this embodiment, artificial structured loess was added for comparison. In order to detect the structural characteristics of the artificial structured loess, the preparation of specimens was carried out. In this experiment, in order to eliminate the influence of dry density on the effect of loess, all the prepared soil samples were uniformly set to 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 . Before the test; at the same time, in order to simulate the structural characteristics of undisturbed soil, different contents of cement (1.0%, 2.0%, 4.0%) and edible salt (4%, 6%, 8%) were added; during the preparation process, indoor sample preparation was carried out strictly in accordance with the "Standard for Geotechnical Test Methods" GB / T50123-2019, and specimens with a diameter of 39.1 mm and a height of 80 mm were made. After sprinkler curing, the required artificial structured loess specimens were obtained; the specific operation steps are as follows:

[0045] First, obtain soil samples from the construction site. After air-drying and grinding, sieve them with a 2 mm sieve and dry them. Then weigh a certain mass of dry soil, mix it with pure water, and place the prepared soil sample in a plastic-sealed bag for 24 hours; during the preparation process, pour the soil material into the ring knife until both ends are leveled, and weigh its mass; to ensure the stability of the specimen, seal it with plastic wrap and let it stand for 3 days; the process of preparing artificial structured loess is mainly divided into the following steps: 1) weighing soil; 2) uniformly mixing cement, salt particles and loess; 3) spraying water; 4) standing still; 5) loading; 6) sample preparation; 7) demolding; (as Figure 3 shown).

[0046] Step 3: Determination of loess n under microscopic structure ;

[0047] Establish a three-dimensional model of the dynamic characteristics and microscopic structure of loess under dynamic load by using particle analysis test and mercury intrusion test, and fit the formula of loess specimen n ;

[0048]

[0049] In the formula: Average particle size (μm); D: Cement content (%); ρ d : Dry density (g / cm 3 );

[0050] n = 55.3917 - 3.0295D - 16.7083ρ d (3)

[0051] In the formula: n: Proportion of large pores (%); D: Cement content (%); ρ d : Dry density (g / cm 3 );

[0052] It can be seen from Figures 4 - 6 that the laws exhibited by artificial structured loess are similar. The dynamic strength curves of undisturbed loess and artificial structured loess corresponding to different confining pressures are basically arranged from top to bottom in the coordinate diagram according to the magnitude of the confining pressure. That is, under the action of the consolidation confining pressure, the dynamic strength of artificial structured loess decreases with the increase of the number of vibrations. When the dry density of the soil is 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 respectively, when the confining pressure is 100 kPa, the dynamic strength of artificial structured loess is in the range of 45 kPa - 65 kPa; when the confining pressure is 200 kPa, the dynamic strength of artificial structured loess is in the range of 65 kPa - 90 kPa; when the confining pressure is 150 kPa, the dynamic strength curve is between the two curves.

[0053] It can be clearly seen from Figure 4 that the magnitude of the consolidation confining pressure has an obvious influence on the dynamic strength of artificial structured loess. At the same number of vibrations, the dynamic strength of artificial structured loess increases with the increase of the confining pressure. The greater the consolidation confining pressure, the more tightly the soil sample is consolidated, the smaller the distance between soil particles, the greater the friction force between soil particles, the more compact the structure of the soil sample is, and more energy is required for external actions to break the connection of soil particles. Therefore, the anti-vibration ability of artificial structured loess is stronger, and its dynamic strength is also stronger.

[0054] It can be seen from Figures 4 - 6 that the dry density has an influence on the dynamic strength of artificial structured loess. It can be seen from Figures 4 - 6 that when the densities of artificial structured loess are 1.2 g / cm 3 , 1.4 g / cm 3 , 1.6 g / cm 3 respectively, the dynamic strength curves of artificial structured loess are arranged from top to bottom in the coordinate diagram, that is, the smaller the dry density, the lower the position of the dynamic strength curve of artificial structured loess in the coordinate diagram. Under the action of a confining pressure of 100 kPa, when the dry density is 1.2 g / cm 3 , the dynamic strength of artificial structured loess is in the range of 45 kPa - 55 kPa; when the dry density is 1.4 g / cm 3 , the dynamic strength of artificial structured loess is in the range of 50 kPa - 70 kPa, and above the dynamic strength curve under the same confining pressure at a dry density of 1.2 g / cm 3 ; when the dry density is 1.6 g / cm 3 , the dynamic strength is in the range of 55 kPa - 80 kPa, and above the dynamic strength curve under the same confining pressure at a dry density of 1.4 g / cm 3 .

[0055] When the dry density is relatively large, the degree of soil compaction increases, the spacing between soil particles is smaller, and the connection relationship between soil particles becomes closer. At this time, the friction force between soil particles becomes larger, so it takes more effort to overcome the friction force between soil particles, increasing the dynamic strength of the soil sample. At the same number of vibration cycles, the dynamic strength of artificially structured loess increases with the increase of dry density. At this time, there is less water in the voids between the particles in the soil, and the connection degree between the soil particles is relatively stable, with good overall structure. Therefore, the soil has a stronger ability to resist vibration, that is, the dynamic strength of artificially structured loess is stronger.

[0056] The dynamic strength curves of artificially structured loess corresponding to different consolidation confining pressures, different dry densities, and different cement contents are plotted in the same coordinate system. From this, the dynamic strength curves of artificially structured loess with dry densities of 1.2, 1.4, and 1.6 g / cm 3 and under the conditions of consolidation confining pressures of 100 kPa, 150 kPa, and 200 kPa, the influence and law of cement content on the dynamic strength of artificially structured loess can be obtained. From Figures 4 - 6 it can be seen that the cement content has an impact on the dynamic strength of artificially structured loess. As can be seen from the figure, when the cement contents are 1%, 2%, and 4% respectively, the dynamic strength curves of artificially structured loess are arranged from bottom to top in the coordinate diagram, that is, the greater the cement content, the higher the position of the dynamic strength curve in the coordinate diagram. When the cement content is 1% and the consolidation confining pressure is 100 kPa, the dynamic strength of artificially structured loess is in the range of 45 kPa - 55 kPa. When the cement content is 4% and the consolidation confining pressure is 100 kPa, the dynamic strength of artificially structured loess is in the range of 65 kPa - 80 kPa. And the dynamic strength curve with a cement content of 2% is between the two curves, indicating that the dynamic strength value is also between the two. From Figure 6 it can be clearly seen that under the same test conditions, when the confining pressure and dry density are constant, the greater the cement content, the greater the dynamic strength, and the greater the number of vibration cycles required for the artificial structured loess to be damaged. This is because for specimens with a larger cement content, the internal structure is arranged more closely. During the loading process, the ability to resist deformation is correspondingly enhanced, and the corresponding failure strength is also increased, and the number of vibration cycles required to reach failure is also larger. For specimens with a lower cement content, there are more pores in the internal structure. During the vibration process, the internal structure is easily affected by the load, the structure is more unstable, the dynamic strength at failure is correspondingly reduced, and the required number of vibration cycles is also correspondingly less. After the cement content is increased, when cement is added to the loess to form artificially structured loess, under the condition of a certain dry density, oxides such as calcium silicate or calcium aluminate in the cement react with water to generate a cementitious substance, which is exactly this cementitious substance that enhances the strength of the artificially structured loess.

[0057] Plot the calculation results in Table 3 in Figure 6In the relationship curve between the dynamic strength parameters and the cement content, the influence of each factor on the dynamic strength parameters of artificially structured loess can be observed more intuitively. Figure 7 (a) is the relationship curve between the dynamic cohesion (c d ) of artificially structured loess and the cement content, Figure 7 (b) is the relationship curve between the dynamic internal friction angle (φ d ) of loess and the cement content. Figure 7 It shows that: The variation laws of the dynamic cohesion and the dynamic internal friction angle with the dry density are basically the same, both increasing with the increase of the dry density. Only the decreasing trend of the dynamic internal friction angle with the increase of the water content is relatively gentle, not as obvious as the decreasing trend of the dynamic cohesion with the increase of the water content. This is because, the smaller the dry density, the looser the soil mass, the less closely the soil particles contact each other, so the dynamic cohesion and the dynamic internal friction angle are smaller. And the larger the dry density, the more compact the soil mass is extruded, the more closely the soil particles contact each other, so the dynamic cohesion and the dynamic internal friction angle are larger.

[0058] Table 3 Dynamic strength indexes of artificially structured loess

[0059]

[0060]

[0061] When measuring the influence of the cement content on the dynamic strength indexes, it can be found that their dynamic cohesion and dynamic friction angle increase with the increase of the cement content. With the increase of the cement content, the dynamic cohesion c d of the soil mass increases, and the dynamic internal friction angle φ d increases less than the dynamic cohesion, indicating that the improvement of the dynamic strength of the soil mass by cement mainly plays a role by increasing the dynamic cohesion. This is because a large number of silicate particles adhere to the surface of the powdery cement dispersed in the loess, forming a certain bonding and frictional effect between the cement and the soil particles, making the discrete cement form many cementitious bodies inside the loess, restricting the displacement of the soil particles and the deformation of the soil mass, and sharing a certain compressive stress, thereby improving the cohesion of the artificially structured loess and increasing the dynamic strength of the soil mass. The relatively slow increase in the dynamic internal friction angle is mainly due to the smooth surface of the cement.

[0062] The particle size distribution curves of artificially structured loess with different ratios are as Figure 7 shown. According to the particle size classification standard, the loess particles can be sequentially divided into 5 components from small to large particle size: clay particles (<4μm), fine silt ((4, 16)μm), medium silt ((16, 32)μm), coarse silt ((32, 63)μm), and sand particles (>63μm). Among them, d 10 , d 30 , d 50 and d60 They are the particle sizes corresponding to the cumulative mass fractions of the particles being 10%, 30%, 50% and 60% respectively. From Figure 8 (a)-(b), it can be seen that: Overall, the distribution laws of the particle differential mass distribution curves of the artificial structured loess specimens with a cement content of 1% are generally the same, and the interval percentages reach the peak points at the median particle sizes; the cumulative percentages show an ascending stage, significantly increase at the median particle sizes, and finally reach 100%; in addition, with the increase of the dry density, the interval percentages and cumulative percentages have no obvious changes, indicating that the dry density has little influence on the artificial structured loess with a cement content of 1%.

[0063] From Figure 8 (a) the cumulative distribution curve, it can be seen that there is a slow ascending stage within the clay particle range (<5μm), a rapid growth stage within the medium silt particle range (5 - 75μm), and a stable stage within the sand particle range (>75μm). From Figure 8 (b) the interval distribution curves, it can be seen that peak points appear within both the medium silt particle range (5 - 75μm) and the clay particle range (<5μm), the particle size frequency distribution curve shows an obvious "single peak" characteristic, and the peak is at the same position as that of the undisturbed loess.

[0064] From the interval distribution curves, it can be seen that peak points appear within both the medium silt particle range (5 - 75μm) and the clay particle range (<5μm). In summary, the distribution laws of the interval distribution curves of the artificial structured loess specimens with the same cement content are generally consistent, and the interval percentages reach the peak points at the medium silt particle range (5 - 75μm) and the clay particle range (<5μm); the cumulative percentages show an ascending stage, significantly increase at the median particle sizes, and finally reach 100%. From Figure 8 (c)-(d), it can be seen that: with the increase of the cement content, the changes in the interval percentages and cumulative percentages are more obvious than those with a cement content of 1%, indicating that the cement contents of 2% and 4% have greater influence on the artificial structured loess; under the same structured loess, with the increase of the dry density, the median particle sizes gradually increase. Within the medium silt particle range (5 - 75μm), under the same confining pressure, for the artificial structured loess with a cement content of 4%, the interval proportion is the largest, for the artificial structured loess with a cement content of 2%, the interval proportion is the second, and the interval proportion of the undisturbed loess is the last; while within the clay particle range (<5μm), the interval proportion is opposite to that within the medium silt particle range. From the cumulative distribution curve, the distribution curve shows an ascending stage. Compared with the undisturbed loess, the artificial structured loess with an increased cement content rises later and more slowly. With the increase of the cement, the stronger-structured loess has a relatively later rising trend.

[0065] Table 4 Particle size parameters and gradation parameters of artificial structured loess under different conditions

[0066]

[0067] Through the test results of the mercury intrusion method, the pore density distribution curve and the pore cumulative distribution curve can be used to describe the distribution of pores. The pore cumulative distribution curve describes the relationship between the cumulative amount of all pores larger than a certain pore size and the pore size. According to the test principle of the mercury intrusion instrument, the cumulative mercury injection volume obtained by the test represents the cumulative amount of all pores larger than a certain pore size. By deriving the pore cumulative distribution curve, the distribution density corresponding to a certain pore size can be obtained, and the pore density distribution curve can be obtained. The curve reflects the pore volume size corresponding to different pore sizes. Lei Xiangyi divided the loess structure pores into four categories based on the pore radius size in the loess: large pores (pore diameter d>16μm), medium pores (pore diameter d=4-16μm), small pores (pore diameter d=1-4μm), and micropores (pore diameter d<1μm). Figure 9 The mercury injection curves of original loess and artificial structured loess under different conditions. Figure 9 As shown in (a), (c), and (e), with the gradual increase of dry density, the change amplitude of the cumulative pore volume of the sample gradually shifts downward. When the cement content is 1%, the change trend of small pores and medium pores of artificial structural loess with different dry densities is particularly prominent; when the cement content is 2%, the cumulative pore volume distribution curve of artificial structural loess with different dry densities has no obvious change in the micropore (<0.25μm) stage; the pore changes in the medium pore (0.1μm~10.5μm) are significant. With the increase of dry density, large and medium pores are gradually compacted. The reason is that after the sample is destroyed, there is no significant local deformation feature. Inside the sample, the deformation is uniform and compressed as a whole, which leads to a significant decrease in the cumulative pore volume of the sample measured by the mercury injection test. When the dry density is 1.6g / cm 3 The cumulative mercury input curve of the original loess is similar to that of the original loess, and the change trend and change amount of large, medium and small pores are basically the same. When the cement content is 4%, the cumulative pore volume does not change significantly in the large pore stage, indicating that the pore volume does not change significantly under the condition of high cement content, and the large pores are filled with cement; under high cement content, the cumulative pore volume of artificial structural loess with different dry densities changes significantly at a pore size of 5μm; the large pores of both gradually decrease, while the micropores gradually increase.

[0068] from Figure 9 From the pore cumulative distribution curves of artificial structural loess under different conditions, it can be seen that the overall trend of the pore size distribution density curve is relatively consistent. From the perspective of the boundary pore size division of the pores, the pore size distribution density of the medium pores varies relatively greatly and occupies a dominant position, followed by the pore size distribution density of the large pores, and the pore size distribution density of the micro and small pores is relatively small.

[0069] The pore sizes of artificial structured loess are mainly concentrated in large, medium, and small pores, that is, the pore distribution of artificial structured loess is a three-peak pore structure. When the cement content is 1%, artificial structured loess with different dry densities has the same obvious changes. Among them, in the range of medium pores, the pore size distribution has relatively significant differences. The artificial structured loess with a dry density of 1.2 g / cm 3 has more pore distribution than the artificial structured loess with a dry density of 1.4 g / cm 3 , and the former two have more pore distribution than the artificial structured loess with a dry density of 1.6 g / cm3. When the pore size is (10 μm - 100 μm), with the increase of dry density, the pores are gradually compressed and compacted, resulting in the gradual increase of micro-pores and the decrease of medium pores; secondly, in the range of large pores, there is also a situation where some large pores decrease, indicating that dry density is an important factor leading to the change of large and small pores. When the cement content is 2%, the distribution curves are roughly the same, and the change of large pores is more significant. It can be seen from this that the cement output also has a significant impact on it; with the increase of cement content, the medium pores gradually decrease, indicating that the loess reacts fully with water and cement to form clay minerals, resulting in increased strength and good cementation. When the cement content is 4%, the distribution curve is significantly lower than that under other cement contents. Thus, it can be known that the cement content has a close relationship with the pore size distribution curve.

[0070] Step Four: Fit the relationship formula and establish a model;

[0071] Specifically: By data fitting, the formula for the dynamic internal friction angle, dynamic cohesion, average particle size, and proportion of large pores is:

[0072]

[0073] In the formula: c d : Dynamic cohesion (kPa); n: Proportion of large pores (%); Average particle size (μm);

[0074]

[0075] In the formula: —Dynamic internal friction angle (°); —Average particle size (μm); n—Proportion of large pores (%);

[0076] Refer to Figure 10 , Figure 10 (a)-(b) is a non-linear surface model constructed with the average particle size, cement content, and dry density of artificial structured loess under different conditions as measurement indicators. The fitting factor R2 of the model is 0.9470; Figure 10(c)-(d) is a non-linear surface model constructed with the large pore proportion, cement content, and dry density of artificial structured loess under different conditions. The fitting factor R2 of the model is 0.9745,

[0077] It can be seen from this that: the three-dimensional surface model of the large pore proportion, cement content, and dry density of artificial structured loess presents a "slope" shape under different conditions; taking the Z-axis as the research object, with the increase of the cement content, the color changes significantly, from red to blue, and the large pore proportion gradually decreases. When the cement content of artificial structured loess is 2% and the dry density is 1.6 g / cm, the large pore proportion begins to decrease slowly. In the three-dimensional surface model, it can be clearly found that the corresponding "slope" surface begins to decrease slowly. When the cement content and dry density of artificial structured loess are the largest, the large pore proportion reaches the minimum value.

[0078] The large pore proportion is the percentage of the measured pore area in the total image area. The larger the porosity, the larger the pore volume in the slip zone soil, and the lower the dynamic strength of artificial structured loess. From Figure 11 it can be seen that there is also an obvious regularity between the porosity and mechanical parameters. It can be seen from the figure that there is a good linear relationship between the dynamic strength parameters of artificial structured loess and the porosity. With the decrease of the porosity, both the dynamic cohesion and the dynamic internal friction angle of artificial structured loess increase to a certain extent, and both show a negative correlation. This is because the coarse particles are continuously broken and decomposed during repeated shearing. As the shear displacement gradually increases, the pores between the soil particles become larger, the shape of the soil particles becomes long and narrow, and there is an obvious phenomenon of directional arrangement. Finally, the shear stress no longer changes with the increase of the shear displacement, and the soil strength reaches a stable strength.

[0079] The pore shape ratio of artificial structured loess is used to describe the roundness of the pores. The larger the shape ratio, the better the roundness of the pore pair. From Figure 11 it can be seen that there is a certain linear relationship between the pore shape ratio of artificial structured loess and the mechanical strength parameters. The dynamic cohesion has a good negative correlation with the pore shape ratio, and the same is true for the dynamic internal friction angle. Both increase with the decrease of the pore shape ratio. The reason for this phenomenon may be that the increase of the fine particle content makes the pores smaller, and the small pores have better roundness than the large pores. At the same time, the increase of the fine particle content leads to an increase in the dynamic strength of artificial structured loess and an increase in the dynamic internal friction angle. The distribution fractal dimension of the pores reflects the distribution of the pores in the entire two-dimensional plane as a whole. The larger the fractal dimension of the pores, the more disordered the arrangement of the pores and the worse the orientation. From Figure 11It can be seen that the dynamic cohesive force and the dynamic internal friction angle both show a good negative correlation with the pore fractal dimension. As the pore fractal dimension increases, both of them decrease to a certain extent. This is because an increase in the fractal dimension means that the microscopic interface of the pores becomes rougher, the pore diameter gradually increases, the pore shape is continuously elongated, resulting in a decrease in the porosity, and the corresponding soil density is higher, and the dynamic strength will be enhanced to a certain extent.

[0080] Figure 12 (a) is the three-dimensional scatter plot and three-dimensional model diagram of the average particle size - large pore proportion - dynamic cohesive force of artificially structured loess. It can be seen from this: The three-dimensional surface model of the average particle size - large pore proportion - dynamic cohesive force of artificially structured loess presents a "triangular surface" type; taking the Z-axis as the research object, as the average particle size increases, the color depth changes significantly, from blue to red, and the dynamic cohesive force gradually increases. As the large pore proportion decreases, the dynamic cohesive force gradually increases. This is because an increase in the average particle diameter means that there are more large particles, and a decrease in the large pore proportion indicates that the pores between particles are filled with small particle size particles and cement hydrates. The combined effect leads to an increase in particle aggregates, thereby increasing the cohesive force inside the artificially structured loess.

[0081] Figure 12 (b) is the fitting diagram of the non-linear surface fitting model constructed with the dynamic cohesive force, large pore proportion, and average particle size of artificially structured loess as the measurement indexes. It is established by fitting with the non-linear surface equation PLANE. The fitting factor R2 of the model is 0.9819, and the quantification equation is shown in Equation (4):

[0082] Figure 13 (a) is the three-dimensional scatter plot and three-dimensional model diagram of the average particle size - large pore proportion - dynamic internal friction angle of artificially structured loess. It can be seen from this: The three-dimensional surface model of the average particle size - large pore proportion - dynamic internal friction angle of artificially structured loess presents a "triangular surface" type; taking the Z-axis as the research object, as the average particle size increases, the color depth changes significantly, from blue to red, and the dynamic internal friction angle gradually increases. As the large pore proportion decreases, the dynamic internal friction angle gradually increases. This is because an increase in the average particle diameter means that there are more large particles, and a decrease in the large pore proportion indicates that the contact between particles increases. The combined effect leads to an increase in the particle surface area, thereby increasing the cohesive force inside the particles.

[0083] Figure 13 (b) is the fitting diagram of the non-linear surface fitting model constructed with the dynamic internal friction angle, large pore proportion, and average particle size of artificially structured loess as the measurement indexes. It is established by fitting with the non-linear surface equation PLANE. The fitting factor R2 of the model is 0.9699, and the quantification equation is shown in Equation (5): Establish the dynamic strength failure envelope diagram, substitute the data to get (0, 21.490132), and the slope is 4.8435, asFigure 14 As shown: where c d As shown in formula (4), As shown in formula (5).

[0084] Step Five: Determine the dynamic strength of loess;

[0085] Specifically: Using a neural network, according to the data given in Step Four, the Mohr-Coulomb strength theory is used to simply and qualitatively verify the dynamic strength index of loess. The formula is as follows:

[0086]

[0087] Where: Τd: Dynamic shear strength (kPa); C d : Dynamic cohesive force (kPa); φ d : Dynamic internal friction angle (°); σ: Applied dynamic stress (kPa).

[0088] The known dynamic strength formula is (6), and the formulas for estimating the dynamic internal friction angle and dynamic cohesive force from the average particle size and the proportion of large pores are (4) and (5). Substitute the standard experimental data, and the normal stress σ = 100 kPa as shown in Table 5. Table 5 Standard experimental data

[0089]

[0090] Based on the derivation of the above data by a neural network, a multi-layer perceptron (MLP) model is used. With the average particle size (mm) and the proportion of large pores (%) as input features, and the internal friction angle (°), dynamic cohesive force (kPa), and dynamic strength (kPa) as multi-output targets, a regression task is constructed. The network structure contains 3 hidden layers (the number of neurons is 128, 64, and 32 respectively). The ReLU activation function is used to capture the non-linear relationship. The linear activation function is used in the output layer. The mean squared error (MSE) is selected as the loss function, and the Adam optimizer (initial learning rate 0.001) is used. And L2 regularization (λ = 0.01) is introduced to prevent overfitting. The original 10 groups of data are trained by 5-fold cross-validation (training set: validation set = 8:2). After 500 rounds of iteration, the model reaches an average relative error ≤ 5% on the validation set (the lowest dynamic strength error is 3.2%, and the highest large pore proportion error is 6.8%). The results show that the model can effectively characterize the complex mapping relationship between the particle size, the proportion of large pores, and the dynamic strength parameters: as the particle size increases, the model successfully reproduces the monotonically increasing trend of the proportion of large pores (gradient weight +0.73), the exponential decay law of the internal friction angle and the dynamic cohesive force (non-linear coefficient β = 1.8), and the logarithmic decline curve of the dynamic strength (R2 = 0.98). Further, through the SHAP value determination, the marginal contribution ratio of the particle size to the dynamic strength reaches 89%, verifying the internal physical consistency of the data. Further verify formulas (4), (5), and (6); the formulas are correct. Summarize the formulas to get:

[0091]

[0092] In the formula: Dynamic internal friction angle (°); c d : Dynamic cohesive force (kPa); Average particle size (μm); n: Proportion of large pores (%); τ: Dynamic shear strength (kPa); σ: Applied dynamic stress (kPa).

Claims

1. A method for determining the dynamic strength of loess by average particle size and macropore proportion, characterized in that: The following steps are involved: Step 1: Sampling and determination of basic physical properties of soil samples; Step 2: Preparation of artificial structural loess soil samples; Step 3: Loess n under microstructure, Determination; Step 4: Fit the relationship formula and establish the model; Step 5: Determine the dynamic strength of loess.

2. The method according to claim 1, characterized in that The step 1 specifically includes: taking soil from the target site, wrapping it with multiple layers of black plastic bags, and marking the top and bottom surfaces of the soil block; making a ring knife sample, crushing the retrieved soil and drying it in an oven, placing the dried soil at room temperature, stirring it evenly, and putting it into a plastic bag for later use; measuring the basic physical properties of the soil sample, including the specific gravity of the soil particles Gs, the natural moisture content w (%), and the natural density ρ (g / cm 3 ), dry density ρd(g / cm 3 ), porosity ratio e.

3. The method according to claim 1, characterized in that The step 2 is specifically as follows: obtaining the original soil material, crushing and screening it after drying, and selecting particles with a particle size of less than 2 mm as the matrix material; dry-mixing the treated matrix material with cement and salt in a predetermined ratio, wherein the cement addition amount is 1.0-4.0% of the mass of the matrix material, and the salt addition amount is 4.0-8.0% of the mass of the matrix material; quantitatively injecting water into the mixture and fully stirring it to form a homogeneous mixture; loading the mixture into a standard molding mold in layers for compaction molding, and demolding the molded sample after sealing and curing to obtain a composite material with predetermined structural characteristics; the molding operation is strictly carried out in accordance with the requirements of GB / T50123-2019.

4. The method according to claim 1, characterized in that The step three is specifically as follows: using particle analysis test and mercury injection test to establish a three-dimensional model of the dynamic characteristics and microstructure of loess under dynamic load, and fitting the loess sample n, formula.

5. The method according to claim 1, characterized in that The step four is specifically: fitting the dynamic internal friction angle, dynamic cohesion, average particle size, and macropore ratio formula through data.

6. The method according to claim 1, characterized in that The step five is specifically as follows: using a neural network, according to the data given in step four, and using the Mohr-Coulomb strength theory to perform a simple qualitative verification on the dynamic strength index of loess.

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