A method for judging the degree of loess damage using basic physical parameters

Abstract

The invention discloses a method for judging the damage degree of loess by using basic physical parameters, including: obtaining the basic physical parameters of the loess sample: saturation Sr, density ρ, particle size d; giving the test parameters of the triaxial shear test: confining pressure p, loading rate v; obtaining the initial structural parameter E0 of the loess sample according to the calculation formula of the structural parameter E; performing the triaxial shear test under the given confining pressure p and loading rate v; obtaining the saturation Sr, density ρ, particle size d of the soil sample after the test; obtaining the structural parameter E1 of the soil sample after the test according to the calculation formula of the structural parameter E; comparing the changes of the structural parameters of the soil sample before and after the test to judge the damage degree of the sample. The invention is used to scientifically judge the damage degree of loess after being subjected to external influences, solves the existing problem of being difficult to accurately judge the damage degree of loess, and can be widely used in geotechnical engineering, traffic engineering, single geological disaster evaluation and other aspects.

Description

Technical Field

[0001] The invention relates to the application field of loess damage degree analysis and testing in geotechnical engineering, and specifically designs a method for characterizing loess structural parameters using basic physical property parameters, which is used for quickly determining the damage degree of loess after the loess is damaged by external factors. Background Art

[0002] During the deposition process, loess forms a unique structure, which, like density, porosity and other properties, is a basic property of loess. Loess material has become a building material due to its unique structure. For example, the loess slopes and cave dwellings that exist in large areas in the loess region all rely on the unique structure of loess, especially the obvious vertical structure.

[0003] However, due to the large number of pores inside loess, its structure is rapidly destroyed after being subjected to external factors such as heavy rainfall and strong loading, resulting in a rapid decrease in loess strength, such as the large number of loess landslides, loess sinkholes, and foundation settlement in loess areas. For example, the loess landslide in Zhongyang County, Shanxi Province in November 2009 and the large-scale loess landslide in Zizhou County, Shaanxi Province in March 2010 both caused serious damage to houses and casualties among the people.

[0004] Existing advanced monitoring technologies can predict the occurrence of loess landslides, such as the "Real-time Monitoring and Early Warning System for Geological Disasters" developed by Chengdu University of Technology and the "High-precision Beidou Geological Disaster Monitoring and Early Warning Platform" developed by Chang'an University. Both have achieved good results in geological disaster monitoring. On January 27, 2021, Chang'an University successfully warned of a sudden loess landslide with a volume of nearly 100,000 cubic meters at Heifangtai.

[0005] Although the existing advanced monitoring technology can predict the occurrence of geological disasters, the monitoring and early warning system is expensive and difficult to popularize on a large scale. Therefore, it is very important to predict the occurrence of geological disasters efficiently and at a lower cost. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method for characterizing the structural parameters of loess in a triaxial shear test using basic physical property parameters, wherein the saturation Sr, density ρ, and particle size d of loess are measured by indoor geotechnical tests, and the structural parameters of loess in the triaxial shear test are calculated based on a self-developed formula, and then the structural parameters of the loess samples before and after the test are compared to determine the degree of damage to the loess according to the changes before and after. The method of the present invention is simple, has strong scalability, and is widely used.

[0007] The present invention is achieved in that:

[0008] The present invention provides a method for judging the damage degree of loess by using basic physical property parameters, comprising the following steps:

[0009] Step 10, measuring the basic physical parameters of the loess sample: saturation Sr, density ρ, particle size d;

[0010] Step 20, given the test parameters of the triaxial shear test: confining pressure p, loading rate v;

[0011] Step 30: Calculate the initial structural parameters E of the loess sample based on the basic physical parameters and test parameters of the loess sample. 0 ;

[0012] Step 40, performing a triaxial shear test on the loess sample under given confining pressure p and loading rate v, and performing humidification loading on the sample;

[0013] Step 50: After the test, obtain the saturation Sr, density ρ, and particle size d of the loess sample after the test;

[0014] Step 60: Calculate again the structural parameter E of the loess sample after humidification loading 1 ;

[0015] Step 70: Compare the changes in the structural parameters of the loess samples before and after the test, and determine the degree of damage to the loess based on the changes in the structural parameters.

[0016] Preferably, in step 10, sampling is performed on-site, and the moisture content, density, and particle size of the loess sample are measured according to geotechnical tests, and the saturation is calculated by the moisture content and density.

[0017] Preferably, in step 10, the sample is an original loess sample.

[0018] Preferably, in step 10, the saturation is calculated by the following formula using the water content and density:

[0019]

[0020] In the formula, Sr is the saturation, e is the porosity, ds is the relative density of soil particles, ρ is the density of loess, and ρ w is the density of water.

[0021] Preferably, in step 20, the values ​​of the confining pressure p and the loading rate v are set according to commonly used laboratory values. The confining pressure p can be set to 50 kPa, 100 kPa, 200 kPa, 300 kPa, and the loading rate v can be set to 0.125% / s, 0.25% / s, 1.25% / s, 2.5% / s.

[0022] Preferably, in step 30, the initial structural parameter E of the loess sample is calculated according to the calculation formula of the structural parameter E 0 :

[0023]

[0024] Where, saturation Sr, density ρ, particle size d, confining pressure p, loading rate v, A and B are fitting parameters obtained through triaxial shear test.

[0025] Preferably, in step 30, the fitting parameters A and B are determined as follows:

[0026] Step 31, using strain energy E to define structural parameters;

[0027] Step 32: Perform a triaxial shear test to obtain a stress-strain curve of load and deformation, and use the stress-strain curve to integrate the strain energy E using the following formula:

[0028] E=Sh∫σdε

[0029] Where, E is strain energy, S is the bottom area of ​​loess specimen, h is the specimen height, σ is stress, and ε is strain;

[0030] Step 33: According to the structural parameter formula Combining the basic physical properties of loess, saturation Sr, density ρ, particle size d, and mechanical parameters of confining pressure p and loading rate v, substitute them into the formula to solve the parameters A and B.

[0031] Preferably, in steps 50 and 60, the state of the loess sample after the test is kept unchanged during the process of obtaining the saturation Sr, density ρ, and particle size d.

[0032] Preferably, the method further comprises the following steps:

[0033] Step 80: For soil samples with the same loading method, according to the same confining pressure p and loading rate v, the structural properties of loess under another saturation Sr, density ρ, and particle size d are predicted from the known saturation Sr, density ρ, and particle size d.

[0034] The beneficial effects of the present invention relative to the prior art are as follows: the present invention provides a method suitable for evaluating the structural parameters of loess, which is based on the physical parameters of loess, according to the structural changes of loess under the influence of external factors, and quantitatively evaluates the degree of damage of loess by quantifying the structural parameters of loess, and is used to scientifically judge the degree of damage of loess after being subjected to external influences, solves the existing problem of difficulty in accurately judging the degree of damage of loess, and can be used in geotechnical engineering, transportation engineering, and geological disaster prevention and control fields such as rapid prediction of loess geological disasters and accurate evaluation of loess collapsibility. The present invention takes less samples and has an efficient method. Compared with traditional monitoring and evaluation technologies, the present invention is simple to operate, has strong feasibility, and is widely used. It can be widely used in geotechnical engineering, transportation engineering, and single geological disaster evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0036] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment in size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0037] Figure 1 is an implementation flow chart of an embodiment of the present invention;

[0038] Figure 2 It is the stress-strain curve of triaxial shear test;

[0039] Figure 3 It is a surface diagram of the relationship between structural parameters and saturation and density;

[0040] Figure 4 It is a diagram of the evolution of structure with saturation;

[0041] Figure 5 It is the structural evolution diagram during triaxial shear loading. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0043] In the description of the present invention, the terms "include / comprise", "consist of..." or any other variations thereof are intended to cover non-exclusive inclusion, so that a product, device, process or method including a series of elements includes not only those elements, but also other elements not explicitly listed when necessary, or also includes elements inherent to such product, device, process or method. In the absence of further restrictions, the elements defined by the sentences "include / comprise...", "consist of..." do not exclude the presence of other identical elements in the product, device, process or method including the elements.

[0044] The implementation of the present invention is described in detail below in conjunction with preferred embodiments.

[0045] like Figure 1 A method for characterizing loess structural parameters using basic physical property parameters comprises the following steps:

[0046] Step 10: Measure the basic physical properties of the loess sample: saturation Sr, density ρ, and particle size d;

[0047] In some embodiments, the moisture content, density, and particle size of the loess sample are measured by field sampling according to geotechnical tests, and the saturation is calculated by the moisture content and density. The moisture content, density, and particle size can be measured according to the determination method given in the geotechnical test specification, and the present invention will not be elaborated in detail here.

[0048] In the present invention, the saturation is calculated by the following formula through the water content and density:

[0049]

[0050] In the formula, Sr is the saturation, e is the porosity, ds is the relative density of soil particles, ρ is the density of loess, and ρ w is the density of water.

[0051] In the present invention, the samples selected include original loess samples.

[0052] Step 20: Given the test parameters of the triaxial shear test: confining pressure p, loading rate v;

[0053] In some embodiments, the values ​​of the confining pressure p and the loading rate v are set according to commonly used laboratory values. For example, the confining pressure p can be set to 50 kPa, 100 kPa, 200 kPa, 300 kPa, etc., and the loading rate v can be set to 0.125% / s, 0.25% / s, 1.25% / s, 2.5% / s.

[0054] Step 30: Calculate the initial structural parameters E of the loess sample based on the basic physical parameters and test parameters of the loess sample. 0 ;

[0055] In some embodiments, the initial structural parameter E of the loess sample is calculated according to the calculation formula of the structural parameter E: 0 :

[0056]

[0057] Where, saturation Sr, density ρ, particle size d, confining pressure p, loading rate v, A and B are fitting parameters obtained through triaxial shear test.

[0058] The present invention has created a calculation formula for the structural parameter E. Compared with the traditional structural parameter expression, the formula embeds the basic physical parameters of loess, and directly characterizes the relationship between the physical parameters and the structure of loess. It can be seen from the calculation formula of the structural parameter E that the present invention can directly characterize the strength of the loess structure from the basic physical parameters (including saturation Sr, density ρ, and particle size d), and can also directly characterize the strength of the loess structure from the mechanical parameters (including confining pressure and loading rate).

[0059] In some embodiments, the fitting parameters A and B are determined as follows:

[0060] Step 31: Define structural parameters using strain energy E;

[0061] The structural parameter is a parameter that characterizes the structural properties of loess. Currently, there is no clear parameter to characterize the structural properties. Strain energy is a clear mechanical parameter of loess that can characterize the mechanical properties of loess, including structural properties. Therefore, the present invention uses strain energy to characterize structural properties.

[0062] Step 32: Perform a triaxial shear test. During the loading process, obtain a stress-strain curve of load and deformation (such as Figure 2 As shown in Figure 2, using the stress-strain curve, the strain energy E is obtained by integrating the following formula:

[0063] E=Sh∫σdε

[0064] Where, E is strain energy, S is the bottom area of ​​loess specimen, h is the specimen height, σ is stress, and ε is strain;

[0065] Step 33: The strain energy E obtained according to step 32 is the structural parameters of loess. Combined with the basic physical and mechanical parameters of loess, including saturation Sr, density ρ, particle size d, as well as confining pressure p and loading rate v, the structural parameter formula is obtained. In the above example, the parameters A and B are obtained by fitting.

[0066] It should be noted that the fitting parameters A and B in the structural parameter formula E are fitting parameters under the same confining pressure and the same loading rate. For different confining pressures and loading rates, tests need to be carried out separately to determine the parameters.

[0067] According to step 33, the values ​​of A and B under different experimental conditions are obtained as shown in Table 1.

[0068] Table 1 A and B values ​​under different test conditions

[0069]

[0070] Step 30: Calculate the initial structural parameter E of the loess sample0 The structural potential surface of loess is as follows Figure 3 As shown in the figure, it can be seen that the structure shows a monotonically decreasing trend with the increase of saturation and density. Figure 3 The structural potential surface shown can form an intuitive analysis of the impact of physical properties on structural properties. Through comparative analysis of physical properties, the size of structural properties under different physical properties can be compared.

[0071] Step 40: performing a triaxial shear test on the loess sample under given confining pressure p and loading rate v, and humidifying and loading the sample;

[0072] Step 50: After the test, the saturation Sr, density ρ, and particle size d of the loess sample after the test are obtained;

[0073] Repeat steps 40 and 50 times under different test conditions to obtain Figure 4 , Figure 5 . Figure 4 , Figure 5 The characteristic points in the figure are test results, and the curves in the figure are calculated using the structural parameter expression.

[0074] Figure 4 shows the evolution of structure with saturation, Figure 4 It can be seen that the structure shows a monotonically decreasing trend with the increase of saturation. The greater the saturation, the weaker the structure. This shows that under the same strain conditions, the greater the saturation, the lower the required stress level, the smaller the strain energy generated, and the weaker the ability of loess to resist deformation.

[0075] During the loading process, the structural degradation process is not only related to the density and saturation, but also to the initial structure of the soil under its own properties. The difference in structural degradation of soil samples under different loading rates lies in the difference in initial structure, and the difference in initial structure is affected by the physical properties of the soil and the loading method. Figure 5 The structural evolution process under triaxial shear loading is shown. (a), (b), and (c) respectively show the structural evolution process under confining pressure P = 100, 200, 300, and Sr = 53.96%. It can be seen from the figure that the structural degradation process is related to the structural parameters and physical parameters. The magnitude of the decline depends on the initial structure, and the speed of the decline depends on the physical parameters of the loess.

[0076] Combining the definitions of structural parameters and Table 1 and Figure 5It can be seen that the structural degradation process is the reverse process of deformation. During the loading process, the strain increases with the loading process. When the stress is small, the strain energy increment is small; as the stress increases, the strain energy increment increases. The strain energy increases with the increase of deformation, showing a process of first slow and then fast. In the structural degradation process, when the strain is small, the stress is small, and the strain energy generated is small. As the strain increases, the stress increases, and the strain energy increases. The increment in the structural degradation process also shows a trend of first slow and then fast with the increase of deformation.

[0077] It can be seen from the test results and the calculation results that the test results are in good agreement with the calculation results. On the one hand, it verifies that there is a certain relationship between the physical parameters and mechanical parameters and the structural properties. On the other hand, it also verifies the rationality of the structural parameters in the present invention.

[0078] Step 60: Calculate the structural parameter E of the loess sample after humidification loading again 1 .

[0079] It should be understood that the structural parameter E of the loess sample after humidification loading is calculated again here. 1 The calculation is also performed according to the formula given in step 30.

[0080] In steps 50 and 60, the state of the loess sample after the test should be kept unchanged during the process of obtaining the saturation Sr, density ρ, and particle size d.

[0081] Step 70: Compare the changes in the structural parameters of the soil samples before and after the test to determine the degree of damage to the loess. The degree of structural degradation of the loess shown by the changes in the structural parameters indicates the degree of damage to the soil. Take Lanzhou loess as an example. Through the test results of the sample with a saturation of 18%, it can be obtained that when p=300kPa, E=8762.19, A=-1.26, B=3.86. Furthermore, through the calculation formula of the invention, it can be obtained that when the saturation is 36%, the structural parameter is 6413.66. It can be concluded that when the saturation increases from 18% to 36%, the structure degrades by 26.8%.

[0082] The method of the present invention can further predict the structural properties of loess through the physical properties of loess. For soil samples with the same loading method, that is, the same confining pressure p and loading rate v, the values ​​of A and B can be obtained through the test results at a certain saturation and density, and the structural properties of loess at other saturations and densities can be predicted, thereby judging or predicting the degree of damage to the loess after loading.

[0083] The main purpose of the present invention is to characterize the structure of loess by using basic physical parameters. After completing the characterization of the structure, the present invention further applies the structural parameters to engineering applications, that is, by comparing the degree of degradation of the loess structure shown by the changes in the structural parameters, the degree of soil damage is indicated, thereby illustrating the rationality and practicality of the characterization method of the structural parameters of the present invention.

[0084] The method of the present invention can quantitatively evaluate the degree of damage to loess, and is used to scientifically determine the degree of damage to loess after being subjected to external influences. The method is applicable to loess samples in all regions. For example, after the samples are immersed in water, they can simulate the common deformation of soil bodies in engineering due to water contact, which causes the subsidence of roadbeds and foundations. If soil samples of the proposed site can be obtained in advance, the deformation of the site soil after damage can be predicted, providing data and theoretical guidance for engineering design.

[0085] It is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for judging the degree of loess damage using basic physical property parameters, characterized in that: The steps include: Step 10, measuring the basic physical parameters of the loess sample: saturation Sr, density ρ, particle size d; Step 20, given the test parameters of the triaxial shear test: confining pressure p, loading rate v; Step 30, calculating the initial structural parameter E0 of the loess sample based on the basic physical property parameters and test parameters of the loess sample; Step 40, performing a triaxial shear test on the loess sample under given confining pressure p and loading rate v, and performing humidification loading on the sample; Step 50: After the test, obtain the saturation Sr, density ρ, and particle size d of the loess sample after the test; Step 60, recalculate the structural parameter E1 of the loess sample after humidification loading; Step 70, comparing the changes in the structural parameters of the loess sample before and after the test, and judging the degree of damage of the loess according to the changes in the structural parameters; in In step 30, the initial structural parameter E0 of the loess sample is calculated according to the calculation formula of the structural parameter E: Where, saturation Sr, density ρ, particle size d, confining pressure p, loading rate v, A and B are fitting parameters obtained through triaxial shear test; and In step 30, the fitting parameters A and B are determined as follows: Step 31, using strain energy E to define structural parameters; Step 32: Perform a triaxial shear test to obtain a stress-strain curve of load and deformation, and use the stress-strain curve to integrate the strain energy E using the following formula: E=Sh∫σdε Where, E is strain energy, also known as structural parameter, S is the bottom area of ​​the loess specimen, h is the specimen height, σ is stress, and ε is strain; Step 33: According to the structural parameter formula Combining the basic physical properties of loess, saturation Sr, density ρ, particle size d, and mechanical parameters of confining pressure p and loading rate v, substitute them into the formula to solve the parameters A and B.

2. The method according to claim 1, characterized in that In step 10, sampling is performed on site, and the moisture content, density, and particle size of the loess sample are measured according to geotechnical tests, and the saturation is calculated using the moisture content and density.

3. The method according to claim 1, characterized in that In step 10, the sample is an original loess sample.

4. The method according to claim 1, characterized in that: In step 10, the saturation is calculated using the water content and density using the following formula: In the formula, Sr is the saturation, e is the porosity, ds is the relative density of soil particles, ρ is the density of loess, and ρ w is the density of water.

5. The method according to claim 1, characterized in that In step 20, the values ​​of the confining pressure p and the loading rate v are set according to the commonly used values ​​in the laboratory. The confining pressure p can be set to 50 kPa, 100 kPa, 200 kPa, and 300 kPa, and the loading rate v can be set to 0.125% / s, 0.25% / s, 1.25% / s, and 2.5% / s.

6. The method according to claim 1, characterized in that In steps 50 and 60, the state of the loess sample after the test is kept unchanged during the process of obtaining the saturation Sr, density ρ, and particle size d.

7. The method according to claim 1, characterized in that The following steps are also included: Step 80: For soil samples with the same loading method, according to the same confining pressure p and loading rate v, the structural properties of loess under another saturation Sr, density ρ, and particle size d are predicted from the known saturation Sr, density ρ, and particle size d.

Images