Method for preparing and testing glacier debris flow mechanical property sample

Abstract

The invention provides a glacier debris flow mechanical property sample preparation and test method, which comprises the following steps: preparing test moraine soil with similar particle content and proper particle size proportion through a parallel grading method, and fully mixing ice particles with the test moraine soil to prepare an ice-soil mixture of which the volume ice content accords with test setting; a series of monotonic triaxial tests are carried out on ice-soil mixtures with different volume ice contents and different environment temperatures under different confining pressures, and the influences of the ice contents and the environment temperatures on the stress-strain relation, the shear strength, the Young modulus, the secant modulus, the Poisson's ratio, the dilatancy angle, the friction angle and the cohesive force are determined. The obtained mechanical behavior results of the ice-soil mixture at different temperatures are helpful for explaining the interaction between ice and soil particles, and have important significance on disaster prevention and control of existing Sichuan and Tibet railways and future infrastructures.

Description

Technical Field

[0001] This invention utilizes the determination of the physical properties of materials to test or analyze them, specifically relating to a method for preparing and testing samples of the mechanical properties of glacial debris flows. Background Technology

[0002] Due to global warming, Himalayan glaciers are experiencing significant glacial retreat. This retreat triggers frequent periglacial debris flows, with large amounts of loose glacial moraine eventually accumulating on the slopes of nearby valleys and in riverbeds. These deposits, typically composed of debris and ice, are unstable and extremely sensitive to temperature changes. Once temperatures rise, they are prone to collapse, moving along the mountainside and transforming into highly viscous glacial debris flows. These flows can temporarily block valley rivers, forming ice-soil mixed landslide dams. These dams have short lifespans, and sudden breaches often trigger catastrophic floods.

[0003] The initiation and evolution of glacial debris flows have been studied through field surveys and numerical simulations. Based on satellite imagery interpretation and field investigations, glacial debris flows are primarily triggered by rainfall and glacial melt. Once initiated, the moving ice-debris mixture carries loose glacial till along its path, rapidly transforming into a large-scale debris flow. A physics-based two-phase mechanical ice-debris avalanche model investigated the erosion and entrainment processes, finding that frictional heat at the sliding surface leads to additional ice melting, reducing base friction and significantly enhancing fluidity and amplifying the debris flow surge. Although the interaction between ice and soil particles has been qualitatively considered in the simulation of glacial debris flow initiation and evolution, the actual role of ice particles has not yet been fully characterized.

[0004] In addition to field and numerical studies, researchers have also investigated the mechanical behavior of glacial till sediments through large-scale field or laboratory experiments. Over the past few decades, most research has focused on tillites, i.e., soil particles dispersed within a matrix formed by ice lenses. For tillites at low temperatures, ice cementation significantly improves their mechanical properties. As temperatures rise near the freezing point, ice gradually melts, reducing shear strength and stiffness. Furthermore, the higher the ice content, the greater the decrease in shear strength and deformation rate of the tillite during the melting period. In contrast, most loose tillites are completely broken up by glaciers during transport and deposition, mixing with soil particles. In this case, the interaction between ice and soil particles may differ significantly from that of ice-soil tillites. In recent years, flume models have been used to study the fluidity of ice-soil mixtures, indicating that due to the lubricating effect of meltwater films, the transport distance and stopping distance of ice-soil mixtures increase with increasing ice content. The influence of ice morphology on the mechanical behavior of ice-soil mixtures containing 8% ice was investigated using triaxial isotropic strain tests at -3℃. The results showed that glacial till containing block ice exhibited higher peak strength, similar internal friction angle, and significantly greater cohesion than glacial till containing crushed ice. Particle sorting is inevitable during clastic transport and deposition, resulting in typically uneven distribution of ice particles in sediments. Furthermore, the mechanical behavior of ice-soil mixtures is affected by ambient temperature. However, there are currently no studies investigating the influence of ice content and temperature on the mechanical behavior of ice-soil mixtures in loose glacial till sediments. Summary of the Invention

[0005] This invention provides a method for preparing and testing specimens of the mechanical properties of glacial debris flows. The method involves conducting a series of monotonic triaxial tests on ice-soil mixtures with different volumes of ice and different ambient temperatures under varying confining pressures. The results determine the effects of ice content and ambient temperature on stress-strain relationships, shear strength, Young's modulus, secant modulus, Poisson's ratio, dilatation angle, friction angle, and cohesion. The obtained results on the mechanical behavior of ice-soil mixtures at different temperatures help explain the interaction between ice and soil particles.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing and testing samples of the mechanical properties of glacial debris flows includes the following steps:

[0008] Step 1: On-site sampling, and obtaining particle size distribution curves through sieving tests and data processing;

[0009] Step 2: Prepare experimental moraine soil with similar particle content and appropriate particle size ratio using the parallel gradation method;

[0010] Step 3: Freeze deionized water to make freshwater ice blocks, then use an ice crusher to crush the ice blocks and screen out ice particles with a particle size that meets the set requirements.

[0011] Step 4: Thoroughly mix the ice particles with the experimental moraine to prepare an ice-soil mixture with a volume ice content that meets the experimental requirements;

[0012] Step 5: Press the ice-soil mixture into the sample preparation mold in multiple layers to prepare the ice-soil mixture sample;

[0013] Step 6: Quickly transfer the sample to a temperature-controlled triaxial apparatus. Then, install a temperature sensor on the sample surface to continuously monitor the sample temperature and conduct a triaxial compression test at the set temperature. Specifically, at each temperature, set up multiple identical samples, apply different confining pressures, and then compress them at a constant axial strain rate. When the axial strain reaches the predetermined value, the triaxial compression test ends.

[0014] The triaxial compression test determined the following:

[0015] (1) Determine the deviatoric stress q of the ice-soil mixture sample as a function of axial strain ε a The changing pattern;

[0016] (2) Determine the relationship between the shear strength of the ice-soil mixture and the volumetric ice content;

[0017] (3) Determine the peak friction angle according to the peak stress state using the following formula. and peak cohesion :

[0018] ; ;

[0019] Where M and S are the slope and intercept of the peak stress state line in the pq coordinate system, respectively; p is the average total stress.

[0020] (4) Determine the relationship between cohesion and friction angle with volume ice content under different temperature conditions.

[0021] Furthermore, in the aforementioned method for preparing and testing samples of the mechanical properties of glacial debris flows, the maximum particle size of the glacial till soil prepared in step two and the ice particles prepared in step three is less than 1 / 5 of the diameter of the ice-soil mixture sample prepared in step five.

[0022] Furthermore, in the aforementioned method for preparing and testing samples of mechanical properties of glacial debris flows, in step two, the ice particles obtained have a particle size range of 2-5 mm.

[0023] Furthermore, in the aforementioned method for preparing and testing samples of the mechanical properties of glacial debris flows, step four involves preparing samples with a volumetric ice content θ. i The ice-soil mixtures were 0%, 10%, 30%, and 50% respectively.

[0024] Furthermore, in the aforementioned method for preparing and testing samples of mechanical properties of glacial debris flows, in step five, the mixture is pressed into a split sample preparation mold with an inner diameter of 50 mm in three layers to prepare an ice-soil mixture sample; the prepared ice-soil mixture sample has a diameter of 50 mm and a height of 100 mm.

[0025] Furthermore, in the aforementioned method for preparing and testing samples of the mechanical properties of glacial debris flows, in step five, when preparing the ice-soil mixture sample, the mold is placed entirely in an insulated container filled with ethylene glycol solution.

[0026] Furthermore, in the aforementioned method for preparing and testing samples of mechanical properties of glacial debris flows, in step five, when preparing the ice-soil mixture sample, a cooling copper tube is wrapped around the outer wall of the mold, and the cooling copper tube is connected to a temperature-controlled circulating bath.

[0027] Furthermore, in the aforementioned method for preparing and testing samples of the mechanical properties of glacial debris flows, in step six, the ice-soil mixture is tested at two representative temperatures: -2.0℃ and -8.0℃.

[0028] Furthermore, in the aforementioned method for preparing and testing mechanical properties of glacial debris flows, in step six, three identical specimens are set up at each test temperature, and different confining pressures of 50, 100, and 200 kPa are applied respectively, followed by compression at a constant axial strain rate of 0.5 mm / min.

[0029] Furthermore, in the aforementioned method for preparing and testing samples of the mechanical properties of glacial debris flows, in step six, the triaxial compression test ends when the axial strain reaches 20%.

[0030] Compared with existing technologies, the present invention's method for preparing and testing samples of the mechanical properties of glacial debris flows has achieved the following significant advancements: Test glacial till with similar particle content and appropriate particle size ratios is prepared using a parallel gradation method. Ice particles are thoroughly mixed with the test glacial till to prepare an ice-soil mixture with a volumetric ice content conforming to the experimental settings. A series of monotonic triaxial tests were conducted on the ice-soil mixtures with four volumetric ice contents (0, 10%, 30%, and 50%) and two ambient temperatures (-2℃ and -8℃) under different confining pressures. The tests determined the effects of ice content and ambient temperature on stress-strain relationships, shear strength, Young's modulus, secant modulus, Poisson's ratio, dilatation angle, friction angle, and cohesion. The obtained results of the mechanical behavior of the ice-soil mixture at different temperatures help explain the interaction between ice and soil particles, which is of great significance for disaster prevention and mitigation of existing highways and future infrastructure. Attached Figure Description

[0031] Figure 1 The particle size distribution curves of the field-grown glacial till and the experimental glacial till are shown.

[0032] Figure 2 This is a diagram of a triaxial compression test model;

[0033] Figure 3 The deviatoric stress (q) of the ice-soil mixture specimen as a function of axial strain (ε) is shown at different temperatures of -2.0℃ and -8.0℃. a The changing pattern of )

[0034] Figure 4 The relationship between the shear strength of ice-soil mixtures and volumetric ice content under different ambient temperatures is shown.

[0035] Figure 5 The relationship between cohesion and friction angle with volumetric ice content under different temperature conditions is shown.

[0036] The attached diagram is labeled as follows: 1-Ice-soil mixture sample; 2-Cooling copper tube; 3-Temperature-controlled triaxial apparatus. Detailed Implementation

[0037] The present application will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present application. Contents not described in detail in the following embodiments are all common knowledge in the art.

[0038] Example (see) Figure 1-5 ):

[0039] The experimental material was a mixture of glacial till and ice particles. Due to the difficulty in obtaining a large quantity of undisturbed glacial till mixture samples, the test samples were prepared in the laboratory. The glacial till was collected from the Zelongnong Gully in the Yarlung Tsangpo River basin in southeastern Tibet, an area that experienced three large-scale debris flows in the summer of 2020 due to rising temperatures. The natural moisture content of the collected glacial till was 5.5%. The particle size distribution curve of the field glacial till is shown below. Figure 1 As shown, this glacial till soil has poor gradation and sorting, with gravel accounting for 57.3% and sand accounting for 42.7%. Its coefficient of uniformity (Cu) is 81.25 and its coefficient of curvature (Cc) is 0.14.

[0040] The triaxial pressure chamber used in this embodiment allows for a sample diameter of 50 mm, while the maximum particle size of the undisturbed glacial till in the field reaches 60 mm. To minimize the sample size effect, the maximum particle size should be less than 1 / 5 of the sample diameter. Therefore, based on the parallel gradation method, model glacial till with a maximum particle size of 5.0 mm was used to replace the undisturbed glacial till in the field. The model glacial till prepared by the parallel gradation method, with similar particle content and appropriate particle size ratio, can better represent the mechanical behavior of the undisturbed glacial till in the field.

[0041] Under the same sieving percentage, the particle size relationship between model glacial till and on-site glacial till is established using the following formula:

[0042] ;

[0043] Where Dmax, Dmin, and D represent the maximum particle size, minimum particle size, and a given particle size, respectively; the superscripts s and t represent the field-grown glacial till and the test soil, respectively; A is the scaling factor. Based on this method, the particle size distribution curve of the test glacial till was obtained ( Figure 1 Subsequently, based on the mass ratio of each particle size group, the on-site glacial till was mixed into different groups to prepare experimental glacial till. The basic physical properties of the experimental glacial till were also determined. The specific gravity of the experimental glacial till was 2.68 Mg / m³, and the maximum and minimum void ratios were 0.710 and 0.332, respectively.

[0044] To prepare the ice-soil mixture, ice particles were used in the experiment. First, deionized water was frozen at -25°C for approximately 24 hours to create freshwater ice blocks. These blocks were then crushed using an ice crusher and sieved through a 2mm sieve. Because smaller ice particles melt more easily, ice particles with a diameter less than 2mm were not used in this embodiment to avoid rapid melting during sample preparation. Due to sample size limitations, the maximum particle size of the ice particles used was 5mm. Therefore, the final ice particle size range used in this work was 2-5mm.

[0045] Ice particles were thoroughly mixed with glacial till pre-cooled at -25°C. To investigate the effect of ice content, a volumetric ice content θ was prepared. i Ice-soil mixtures were prepared at concentrations of 0%, 10%, 30%, and 50%, respectively. Volumetric ice content was defined as the ratio of ice particle volume to the total volume of the ice-soil mixture. The mixture was then pressed into a split-type sample preparation mold with an inner diameter of 50 mm in three layers. Cooling copper tubing 2 was wrapped around the outer wall of the mold, and the entire mold was placed in an insulated container filled with ethylene glycol solution. Cooling copper tubing 2 was connected to a temperature-controlled circulating bath to prevent the ice particles from melting during sample preparation. The final ice-soil mixture sample 1 was 50 mm in diameter and 100 mm in height.

[0046] In the embodiment, the target void ratio of the compacted ice-soil mixture sample 1 was 0.523, and the relative density was 49.5%, corresponding to a medium-dense state. Including ice particles in the solid portion, the void ratio (e) was defined as: Where Va, Vs, and Vi are the volumes of soil particles, ice, and air in the sample, respectively.

[0047] After compaction, the sample was quickly transferred to a temperature-controlled triaxial apparatus 3. A temperature sensor was then installed on the sample surface to continuously monitor the sample temperature. To investigate the effect of temperature, this embodiment tested the ice-soil mixture sample 1 at two representative temperatures: -2.0℃ and -8.0℃. For each temperature condition, three identical samples were used, with confining pressures of 50, 100, and 200 kPa applied, followed by compression at a constant axial strain rate of 0.5 mm / min. It is important to note that no additional liquid water was added after installation to facilitate control of the sample condition. During the triaxial compression process, the drain valve remained open to allow air to escape. The triaxial compression test ended when the axial strain reached 20%.

[0048] Figure 3 The deviatoric stress (q) of ice-soil mixture sample 1 as a function of axial strain (ε) is shown at different temperatures of -2.0℃ and -8.0℃. a The variation law of ) . In a low-temperature environment of -2.0℃, the samples without ice and with a low volumetric ice content (10%) exhibit obvious strain softening characteristics: the deviatoric stress increases rapidly with the axial strain to a peak value and then gradually decreases, eventually tending to a stable value. This phenomenon is particularly significant under low confining pressure conditions. In general, the lower the volumetric ice content and the smaller the confining pressure, the more obvious the strain softening behavior of the sample. With the increase of ice content, the deviatoric stress-axial strain curves under different confining pressure conditions all show an overall downward trend. When the ice content is high (30% and 50%), the sample exhibits strain hardening characteristics, with the deviatoric stress continuously increasing and gradually tending to stabilize. Figure 3 ).

[0049] When the temperature drops to -8℃, the mechanical behavior of ice-free till remains essentially unchanged. However, a comparison reveals that, under -8℃ conditions, the deviatoric stress-axial strain curve of the high-ice-content sample is significantly higher than that of the low-ice-content sample. Figure 4 This indicates that the decrease in temperature significantly enhances the mechanical strength of the ice-soil mixture. Furthermore, the ice-soil mixture at -8°C exhibits a more significant strain softening behavior than that at -2°C.

[0050] Figure 4 This paper demonstrates the relationship between the shear strength of ice-soil mixtures and the volumetric ice content under different ambient temperatures. It should be noted that for specimens exhibiting strain softening behavior, the peak deviatoric stress is considered as the shear strength; while for strain hardening specimens, the deviatoric stress corresponding to 15% axial strain is taken as the shear strength (based on the People's Republic of China Industry Standard: Geotechnical Testing Procedures, 1999).

[0051] The experimental results show that under different ice contents and temperature conditions, increasing confining pressure leads to an increase in the shear strength of the samples. For ice-free till, temperature changes have little effect on its shear strength. In contrast, the shear strength of ice-soil mixtures exhibits a significant temperature dependence. Under the same confining pressure, the addition of ice particles reduces the shear strength of samples at -2℃, but increases it at -8℃. With increasing volumetric ice content, the shear strength of ice-soil mixtures at -2℃ gradually decreases, while the shear strength at -8℃ shows an increasing trend. Furthermore, the higher the confining pressure, the more significant the change in shear strength with ice content.

[0052] The peak friction angle is determined according to the peak stress state using the following formula. and peak cohesion :

[0053] ; ;

[0054] Where M and S are the slope and intercept of the peak stress state line in the pq coordinate system, respectively; p is the average total stress. Figure 5 The relationship between cohesion and friction angle with volumetric ice content under different temperature conditions is shown. For ice-soil mixtures at -2℃, both cohesion and friction angle decrease with increasing ice content; conversely, at -8℃, both increase with increasing ice content. Overall, temperature has a negligible effect on the cohesion and friction angle of ice-free moraine, but a significant impact on the mechanical behavior of ice-soil mixtures.

[0055] Taking a sample with 50% ice content as an example, the cohesion and friction angle at -8℃ were 43.9 kPa and 34.9°, respectively, while at -2℃ they were only 15.7 kPa and 24.5°. Clearly, the cohesion and friction angle of the ice-soil mixture at -2℃ were significantly lower than the corresponding values ​​at -8℃. The higher the ice content, the more significant the differences in cohesion and friction angle of the samples at different temperatures.

[0056] For ice-soil mixtures prepared at -2°C, even at ambient temperatures below zero, ice particles may still partially melt under pressure. Meltwater is adsorbed onto the particle surface, forming a water film that acts as a lubricant, reducing frictional resistance during shearing. This explains the decrease in friction angle and cohesion as ice content increases from 0% to 50%. Furthermore, with the addition of ice particles, some soil particles are replaced by softer ice particles, leading to a decrease in overall skeletal stiffness. Therefore, under the same confining pressure, Poisson's ratio increases with increasing ice content, while the dilatation angle decreases.

[0057] As the ice-soil mixture gradually cools, two or more soil particles agglomerate with at least one ice particle through a meltwater film upon refreezing. This thin water film acts as the binding agent for the ice-soil agglomerates. This phenomenon can be confirmed in images of the ice-soil mixture taken after a triaxial compression test. Particle agglomeration caused by meltwater refreezing results in larger agglomerates in the ice-soil mixture at -8°C. With increasing ice content, the refreezing-induced particle agglomeration becomes more significant, and the agglomerate size further increases. Therefore, during triaxial compression, the shear stress required to break the refreezing bond between particles is higher, resulting in higher cohesion in the ice-soil mixture at -8°C compared to ice-free moraine. On the other hand, the increased agglomerate size enhances interparticle friction. Simultaneously, ice particles become harder and stiffer at low temperatures, leading to greater interparticle frictional resistance at -8°C than at -2°C. This explains why the friction angle is larger in mixtures with high ice content at -8°C. Furthermore, the increased agglomerate size and ice particle stiffness at -8°C enhance the mixture's resistance to deformation. Therefore, for the same ice content, the Poisson's ratio of the -8℃ sample is lower than that of the -2℃ sample, while the shear dilatation angle is larger.

[0058] The foregoing general description of the invention and its specific embodiments should not be construed as a limitation on the technical solution of the invention. Those skilled in the art, based on the disclosure of this application, can add, reduce, or combine the disclosed technical features in the foregoing general description and / or specific embodiments (including examples) without departing from the constituent elements of the invention, to form other technical solutions within the scope of protection of this application.

Claims

1. A method for preparing and testing samples of mechanical properties of glacial debris flows, characterized in that, Includes the following steps: Step 1: On-site sampling, and obtaining particle size distribution curves through sieving tests and data processing; Step 2: Prepare experimental moraine soil with similar particle content and appropriate particle size ratio using the parallel gradation method; Step 3: Freeze deionized water to make freshwater ice blocks, then use an ice crusher to crush the ice blocks and screen out ice particles with a particle size that meets the set requirements. Step 4: Thoroughly mix the ice particles with the experimental moraine to prepare an ice-soil mixture with a volume ice content that meets the experimental requirements; Step 5: Press the ice-soil mixture into the sample preparation mold in multiple layers to prepare the ice-soil mixture sample; Step 6: Quickly transfer the sample to a temperature-controlled triaxial apparatus. Then, install a temperature sensor on the sample surface to continuously monitor the sample temperature and conduct a triaxial compression test at the set temperature. Specifically, at each temperature, multiple identical specimens are set up and different confining pressures are applied to them. Then, they are compressed at a constant axial strain rate. When the axial strain reaches a predetermined value, the triaxial compression test ends. The triaxial compression test determined the following: (1) Determine the deviatoric stress q of the ice-soil mixture sample as a function of axial strain ε a The changing pattern; (2) Determine the relationship between the shear strength of the ice-soil mixture and the volumetric ice content; (3) Determine the peak friction angle according to the peak stress state using the following formula. and peak cohesion : ； ； Where M and S are the slope and intercept of the peak stress state line in the pq coordinate system, respectively; p is the average total stress. (4) Determine the relationship between cohesion and friction angle with volume ice content under different temperature conditions.

2. The method for preparing and testing samples of mechanical properties of glacial debris flows according to claim 1, characterized in that: The maximum particle size of the test moraine prepared in step two and the ice particles prepared in step three is less than 1 / 5 of the diameter of the ice-soil mixture sample prepared in step five.

3. The method for preparing and testing samples of mechanical properties of glacial debris flows according to claim 1, characterized in that: In step two, the ice particles obtained have a particle size range of 2-5 mm.

4. The method for preparing and testing samples of mechanical properties of glacial debris flows according to claim 1, characterized in that: In step four, the volume ice content θ was prepared. i The ice-soil mixtures were 0%, 10%, 30%, and 50% respectively.

5. The method for preparing and testing samples of mechanical properties of glacial debris flows according to claim 1, characterized in that: In step five, the mixture is pressed into a split mold with an inner diameter of 50 mm in three layers to prepare an ice-soil mixture sample; the prepared ice-soil mixture sample has a diameter of 50 mm and a height of 100 mm.

6. The method for preparing and testing samples of mechanical properties of glacial debris flows according to claim 5, characterized in that: In step five, when preparing the ice-soil mixture sample, the mold is placed entirely inside an insulated container filled with ethylene glycol solution.

7. The method for preparing and testing samples of mechanical properties of glacial debris flows according to claim 6, characterized in that: In step five, when preparing the ice-soil mixture sample, a cooling copper tube is wrapped around the outer wall of the mold, and the cooling copper tube is connected to a temperature-controlled circulating bath.

8. The method for preparing and testing specimens of mechanical properties of glacial debris flows according to any one of claims 1-7, characterized in that: In step six, the ice-soil mixture was tested at two representative temperatures: -2.0℃ and -8.0℃.

9. The method for preparing and testing samples of mechanical properties of glacial debris flows according to claim 8, characterized in that: In step six, at each test temperature, three identical specimens were set up and subjected to different confining pressures of 50, 100 and 200 kPa, respectively, followed by compression at a constant axial strain rate of 0.5 mm / min.

10. The method for preparing and testing samples of mechanical properties of glacial debris flows according to claim 9, characterized in that: In step six, the triaxial compression test ends when the axial strain reaches 20%.

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