Slope state evolution and mechanical deterioration analysis method under rainfall-earthquake coupling effect

Abstract

The application discloses a kind of slope material state evolution and mechanical deterioration analysis method under rainfall-earthquake coupling, which relies on shaking table test, first constructs accumulation body slope model and lays out monitoring component, collects acceleration and pore pressure time history data under multistage seismic loading;Subsequently, shear stress-shear strain time history is calculated and hysteresis loop is disassembled, and the evolution process of four types of material state, shear shrinkage, shear dilation, unloading body shrinkage and unloading body expansion, is identified;Further, calculate the hysteresis dissipation energy to establish the material state-energy mapping, and construct the damage index standard to quantify the mechanical deterioration degree based on stiffness degradation;Finally, combined with the analysis of unsaturated soil shear strength and stress state, the dynamic failure mechanism is determined.The application realizes the accurate characterization of material state evolution and quantitative evaluation of deterioration degree, systematically clarifies the tensile-shear coupling failure mechanism, can effectively improve the accuracy of dynamic stability analysis of unsaturated accumulation body slope, and is suitable for seismic research and disaster prevention and control of various mountain accumulation body slopes.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering earthquake resistance and slope dynamic response analysis technology, specifically involving a method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling. Background Technology

[0002] Accumulated slopes are a widely distributed slope type in mountainous areas. They are highly susceptible to instability and failure under the combined effects of rainfall and earthquakes, making them a key target for geological disaster prevention and control. Shaking table model tests are a core method for studying the dynamic response and failure mechanism of slopes. They can visually reproduce the deformation and failure process of slopes under seismic loading and obtain real-time monitoring data of multiphysics fields.

[0003] Existing technologies for studying the dynamic response of embankment slopes often focus on the evolution of single mechanical indicators, such as the spatiotemporal distribution of dynamic pore water pressure and the decay trend of dynamic shear modulus. While such studies can reflect certain aspects of the soil's dynamic characteristics, they fail to reveal the intrinsic mechanism of soil stiffness degradation from the perspective of continuous evolution of the physical state, and it is difficult to establish a quantitative correlation between microscopic volume changes and macroscopic mechanical property degradation. Furthermore, existing technologies lack a unified energy-damage quantification system, failing to incorporate seismic energy input, soil strain accumulation, and mechanical property degradation into the same analytical framework. This results in a lack of systematic explanation of the dynamic failure mechanism of unsaturated embankments under rainfall-seismic coupling, ultimately affecting the accuracy and reliability of slope dynamic stability assessments.

[0004] It should be noted that the analysis of the above technical information is the result of creative labor. The detailed description of it in the background section is only intended to deepen the understanding of the non-obviousness of the overall background of this application by those skilled in the art, and should not be regarded as an admission or in any form an implication that the above technical information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling. The technical problem to be solved is: how to accurately characterize the continuous physical evolution of unsaturated sedimentary slopes and quantitatively assess the degree of mechanical deterioration under rainfall-earthquake coupling, systematically elucidate their dynamic failure mechanism, and improve the accuracy and systematicness of slope dynamic stability analysis.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupled action includes the following steps:

[0008] A shaking table test model of a slab slope under rainfall-seismic coupled action was constructed, and acceleration monitoring components and pore water pressure monitoring components were deployed. A graded and progressive seismic loading scheme was designed, and multiple levels of seismic loads were applied after rainfall infiltration and settling, while time history data of each monitoring point were collected simultaneously. Based on the acceleration data of adjacent elevations, the shear stress-shear strain time history curve of the target depth was calculated, and the hysteresis loop was decomposed into time-series segments according to time windows. Based on the combination relationship between shear strain increment and shear stress loading direction, the soil physical evolution process was identified time-by-time. The hysteretic dissipation energy and cumulative dissipation energy of each monitoring point were calculated to establish the mapping relationship between physical evolution and energy dissipation. A damage index was constructed based on dynamic shear modulus decay to quantify the degree of soil mechanical deterioration. Combined with the shear strength law of unsaturated soil and stress state analysis, the dynamic failure mechanism of the slope was determined.

[0009] Furthermore, the hysteresis loops in the shear stress-shear strain curve are decomposed into time segments according to continuous time windows. The closed loop time period is selected as an independent window, the cross-interference time period is eliminated, and the loading segment and unloading segment are divided according to the shear stress direction.

[0010] Furthermore, based on the combined relationship between the increase and decrease of shear stress and the increase and decrease of shear strain, the physical state of soil is divided into four categories: shear contraction, shear dilatation, unloaded contraction, and unloaded dilatation.

[0011] Furthermore, the dynamic shear modulus is calculated by the ratio of the shear stress amplitude to the shear strain amplitude under a single load level, and the soil stiffness value under that load level is obtained for each hysteresis loop.

[0012] Furthermore, the dynamic shear modulus is calculated for each physical phase, and the mapping law between the soil volume expansion and contraction process and stiffness attenuation and stiffness recovery is established.

[0013] Furthermore, based on the characteristics of modulus time history variation, stiffness evolution is divided into three characteristic stages: initial decay stage, local recovery stage, and rapid decay stage.

[0014] Furthermore, the hysteretic dissipation energy under a single load is calculated using the area enclosed by the hysteresis loop, and the cumulative dissipation energy is obtained by accumulating the energy level step by step. This energy is then matched with the temporal state characteristics to obtain the energy dissipation level under different states of matter.

[0015] Furthermore, based on the initial dynamic shear modulus, a damage index is constructed based on the attenuation range of the current dynamic shear modulus, and the mechanical degradation level is divided according to the numerical range.

[0016] Furthermore, the static and dynamic stress combination states of the slope crest and slope surface units are analyzed separately to identify the tension-shear coupling effect. Combined with the shear strength loss law of the bedrock surface, the overall failure mode of the slope is determined.

[0017] This invention represents a significant technological advancement over existing technologies and is applicable to the dynamic characteristic analysis and failure mechanism study of unsaturated aggregate slopes under multi-field coupling. Its beneficial effects are mainly reflected in the following aspects:

[0018] This invention achieves accurate characterization of the continuous evolution of soil state under seismic load by decomposing the shear stress-strain hysteresis loop and classifying its state of matter. It establishes the intrinsic relationship between volume expansion and contraction and stiffness change, and reveals the evolution mechanism of soil mechanical deterioration from the perspective of microscopic state of matter, thus making up for the limitations of single index analysis in existing technologies.

[0019] This invention constructs a dual quantitative system of hysteretic dissipation energy and stiffness damage index, and incorporates seismic energy input, strain accumulation and mechanical deterioration into a unified analysis framework, realizing a quantitative assessment of the degree of degradation of soil mechanical properties, and providing standardized parameters for slope dynamic damage evaluation.

[0020] This invention combines the theory of unsaturated soil shear strength with multi-location stress state analysis to systematically elucidate the dynamic failure mechanism of slopes under tension-shear coupling, demonstrates the differentiated failure modes of embankments with different densities, and shows that the analysis results are in high agreement with the experimental phenomena. It can effectively improve the accuracy and engineering applicability of embankment slope dynamic stability assessment.

[0021] The method of this invention can realize the whole process analysis based on conventional shaking table test data, without the need for additional monitoring equipment. It can be widely used in the study of dynamic characteristics of various unsaturated accumulation slopes and has strong versatility and engineering promotion value. Attached Figure Description

[0022] To more clearly illustrate the embodiments of this technical solution, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this technical solution. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the planar layout of the accelerometer and the pore water pressure sensor in an embodiment of the present invention. The units of dimensioning are cm.

[0024] Figure 2 This is the shear stress-strain hysteresis loop evolution diagram of the loose aggregate A6-7 measuring point in this embodiment of the invention;

[0025] Figure 3 This is a segmented breakdown diagram of the hysteretic shear stress and shear strain at measuring point A6-7 in this embodiment of the invention;

[0026] Figure 4 This is a graph showing the variation of cumulative dissipated energy under seismic waves of different amplitudes in an embodiment of the present invention;

[0027] Figure 5 This is a graph showing the changes in soil damage indicators in a medium-dense packing structure according to an embodiment of the present invention.

[0028] Figure 6 This is a graph showing the changes in soil damage indicators in a loosely packed body according to an embodiment of the present invention.

[0029] Figure 7 This is a schematic diagram of the stress state of soil and rock elements under natural and seismic loads in an embodiment of the present invention;

[0030] Figure 8 This is a schematic diagram of the stress state of a slope rock and soil unit under seismic load in an embodiment of the present invention.

[0031] Explanation of reference numerals in the attached figures:

[0032] A0 - Platform acceleration sensor; A1-A14 - Slope acceleration sensor;

[0033] K1-K12 - Pore water pressure sensor. Detailed Implementation

[0034] The technical solutions of this technical solution will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this technical solution. Obviously, the described embodiments are only a preferred embodiment of this technical solution, and not all embodiments. Based on the core concept of this technical solution and the following embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this technical solution.

[0035] It should be noted that these embodiments are provided to make the application thorough and complete, and to fully express the scope of the application to those skilled in the art. It should be observed that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​described in these embodiments should be interpreted as merely exemplary and not as limiting.

[0036] In the description of this technical solution, it should be understood that the terms axial, radial, left, right, top, inner, and outer, indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings. They are used solely for the convenience of describing the technical solution and for simplification, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this technical solution. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this technical solution, "several" means one or more, unless otherwise explicitly specified.

[0037] In this technical solution, unless otherwise explicitly specified and limited, the terms installation, connection, linking, fixing, etc., should be interpreted broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to mechanical connection or electrical connection; they can refer to direct connection or indirect connection through an intermediate medium; and they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this technical solution can be understood according to the specific circumstances.

[0038] This invention utilizes a shaking table testing system. The test model is a single-slope structure of an unsaturated deposit overlying bedrock, with the bedrock surface divided into upper and lower sections. The upper section has a greater dip angle than the lower section, forming a concave bedrock-overlying interface. The deposit consists of well-graded coarse-grained soil, layered according to the designed density, with a straight slope. Before the test, constant-intensity rainfall is applied, and after allowing the seepage to stabilize, multiple levels of seismic loads are applied, simultaneously collecting acceleration and dynamic pore water pressure data. The core of this invention lies in the in-depth processing and multi-dimensional analysis of the monitoring data, which will be described in detail below through several embodiments.

[0039] Basic Implementation

[0040] This embodiment takes the soil near the bedrock inflection point of a loose deposit slope as the analysis object, and fully implements the complete analysis method of this invention. The specific steps are as follows:

[0041] S1. Construction of the shaking table test model: A rigid model box was used, with brick masonry bedrock inside. The bedrock surface was designed as a concave folded surface with an upper section inclination angle of 60° and a lower section inclination angle of 40°. The bedrock surface was roughened to simulate the roughness of a real interface. A loose stockpile was filled on top of the bedrock. The soil was prepared using a similar gradation scale-down method, compacted in layers to the designed dry density, and the slope was trimmed into a straight surface with an inclination angle of 50°. Slope acceleration sensors (A1-A14) and pore water pressure sensors (K1-K12) were deployed along the bedrock surface and slope surface, respectively. All sensors were positioned at the mid-surface of the model. The slope acceleration sensors were used to collect the horizontal acceleration time history, and the pore water pressure sensors were used to monitor the dynamic changes in dynamic pore water pressure. A table acceleration sensor A0 was set on the shaking table surface as an input reference. The sensor's planar layout is as follows... Figure 1 As shown. Foam padding layers 5 are used to line the front and rear walls of the model box to reduce boundary reflection effects.

[0042] S2-level seismic loading and data acquisition: First, a constant-intensity rainfall was applied for 1 hour, followed by a 2-hour settling period to allow the seepage field to stabilize. Then, multiple levels of seismic loads were applied in sequence, first natural waves and then artificial waves, with amplitudes increasing from low to high. Seismic wave types included Kobe waves, EL waves, and sine waves, with peak ground accelerations ranging from 0.06g to 0.9g. During loading, acceleration and dynamic pore water pressure time history data were simultaneously acquired at 0.01s sampling intervals at all measuring points. After each loading level, slope deformation and failure phenomena were recorded.

[0043] S3 Shear Stress-Shear Strain Calculation and Hysteresis Loop Decomposition: Slope acceleration sensors at two adjacent elevations near the bedrock inflection point are selected. Based on the acceleration time history data of the two points, the displacement time history is obtained through quadratic integration. The average shear strain time history is calculated by combining the vertical distance between the two points. At the same time, the shear stress time history at the corresponding depth is obtained by integrating the acceleration along the depth. Finally, the shear stress-shear strain time history curve at the target location is obtained.

[0044] The formula for calculating the mean shear strain is as follows:

[0045] ;

[0046] In the formula: The average shear strain between the two acceleration measurement points; The difference in horizontal displacement between the two measuring points is obtained by the second integral of the acceleration time history. The vertical distance between the two measuring points is denoted as .

[0047] The formula for calculating shear stress is as follows:

[0048]

[0049] In the formula: The shear stress at the target depth; This refers to the soil density. It is horizontal acceleration; For target depth; This represents the total height of the slope.

[0050] After baseline correction and bandpass filtering of the time history curve, continuous closed time intervals were selected as time windows. The hysteresis loops in the curve were then segmented, and interfering time intervals with path intersections were eliminated. Each hysteresis loop was divided into a loading half-loop and an unloading half-loop according to the direction of shear stress increase or decrease. The evolution process of the shear stress-strain hysteresis loop at the inflection point of the bedrock in the loose deposit is as follows: Figure 2 As shown.

[0051] S4 Temporal Soil Evolution Identification: For each decomposed hysteresis loop time period, the changing trends of shear stress and shear strain are extracted. Based on four combinations of shear stress increase or decrease, and shear strain increase or decrease, the soil state for the corresponding time period is determined: increased shear stress and decreased shear strain correspond to contraction; increased shear stress and increased shear strain correspond to dilatation; decreased shear stress and decreased shear strain correspond to unloading contraction; decreased shear stress and increased shear strain correspond to unloading dilatation. After continuous identification time periods, the soil state evolution sequence throughout the entire seismic loading process is obtained.

[0052] S5 Establishment of the state-energy mapping relationship: The hysteretic dissipation energy under a single-stage load is calculated, and the cumulative dissipation energy time history curve is obtained by accumulating the energy dissipation energy step by step. The time series nodes of energy dissipation are mapped one-to-one with the time periods of state evolution, and the energy dissipation increment within each state period is statistically analyzed to obtain the energy dissipation level per unit time corresponding to different state types, thus establishing a quantitative mapping relationship between the state evolution process and energy dissipation.

[0053] S6 Mechanical Deterioration Quantification: Based on the initial dynamic shear modulus, a damage index is constructed based on the attenuation range of the dynamic shear modulus under various load levels. The magnitude of this index is used to quantify the degree of mechanical deterioration of the soil under seismic load. The larger the index value, the more significant the decrease in soil stiffness and the more severe the deterioration of mechanical properties.

[0054] S7 Dynamic Failure Mechanism Determination: Based on the formula for calculating the shear strength of unsaturated soil, the shear strength loss caused by changes in dynamic pore water pressure is analyzed. Simultaneously, stress state models of soil and rock elements are established at the slope crest and slope surface to analyze the tension-shear coupling effect under reciprocating horizontal seismic stress. Combining the strength loss at the bedrock surface, the stress state of the slope, and the laws governing physical evolution and stiffness degradation, the dynamic failure mode and intrinsic mechanism of the accumulated slope are systematically determined.

[0055] Preferred Implementation Example 1: Dynamic Shear Modulus Calculation and Stiffness Evolution Stage Identification

[0056] This embodiment, based on the basic embodiment, further refines the calculation of dynamic shear modulus and the identification of stiffness evolution stages. The specific details of all calculation methods and formulas are as follows:

[0057] The dynamic shear modulus is a core parameter characterizing the dynamic stiffness of soil. It is calculated by the ratio of shear stress amplitude to shear strain amplitude and can accurately reflect the average stiffness level of soil under a single load.

[0058] The formula for calculating the dynamic shear modulus is as follows:

[0059]

[0060] In the formula: The dynamic shear modulus under a single-stage load; This represents the shear stress amplitude under this load level. This represents the corresponding shear strain amplitude.

[0061] Taking two typical measuring points in a loose deposit as examples—the measuring point between A6 and A7 near the bedrock inflection point and the measuring point between A8 and A9 near the upper bedrock surface—the stiffness evolution at both measuring points exhibits a clear three-stage characteristic under 0.6gEL wave loading. The corresponding hysteresis loop morphology changes are as follows: Figure 2 As shown:

[0062] The first stage is the initial attenuation stage. The soil stiffness is relatively high at the beginning of loading. As the seismic energy is input, the dynamic shear modulus decreases rapidly. The initial modulus of measuring point A6-7 is about 49.60 kPa, which drops to about 27.42 kPa after the first attenuation period. The initial modulus of measuring point A8-9 is about 38.69 kPa, which drops to about 31.51 kPa after attenuation.

[0063] The second stage is the local recovery stage. During the loading process, the soil becomes denser or the effective stress increases under a specific strain direction, and the dynamic shear modulus rebounds locally. The modulus at measuring point A6-7 rebounds to about 41.38 kPa, and the modulus at measuring point A8-9 rebounds even more significantly. This is directly related to the dissipation of pore water pressure and the increase in effective stress caused by volume expansion.

[0064] The third stage is the rapid decay stage. As the seismic energy continues to be input, the soil damage continues to accumulate, and the stiffness enters an irreversible rapid decay stage. In the later stage of loading, the modulus of measuring point A6-7 drops to about 5.43 kPa, and the modulus of measuring point A8-9 drops to about 4.35 kPa, both less than 15% of the initial value.

[0065] Through the modulus calculation and stage division in this embodiment, the dynamic evolution law of soil stiffness under random seismic load can be accurately captured, the critical turning point of stiffness deterioration can be accurately identified, and reliable stiffness parameters can be provided for mechanical deterioration analysis.

[0066] Preferred Example 2: Mapping Analysis of Matter Evolution and Stiffness Change

[0067] This embodiment, based on the basic embodiment, further refines the segment-by-segment identification of the time-domain state evolution and establishes a mapping relationship between state changes and stiffness evolution. The specific content is as follows:

[0068] The loading and unloading process of the hysteresis loop is further decomposed into multiple sub-time periods. Within each sub-time period, the shear stress and shear strain maintain a single increasing or decreasing trend, corresponding to a specific state of matter. Taking a typical hysteresis loop at measuring point A6-7 of a loose aggregate under 0.6gEL wave loading as an example, the segmented decomposition results of the shear stress and shear strain corresponding to the state of matter identification in each time period are as follows: Figure 3 As shown, the specific recognition results are as follows:

[0069] During the 0.72-1.04s period, the shear strain is generally positive. In the early stage of loading, the shear stress increases and the shear strain accumulates, exhibiting shear contraction characteristics. After the shear stress reaches its peak, it decreases, and the shear strain decreases simultaneously, exhibiting unloading shrinkage characteristics. In the reverse loading stage, the unloading expansion and shear dilatation processes occur sequentially. Overall, this period is characterized by volume reduction, corresponding to relatively high soil stiffness.

[0070] During the period from 1.32 to 1.92 s, the shear strain is negative overall, and it undergoes phase transitions of unloading body expansion-shear expansion and unloading body contraction-shear contraction. Overall, it exhibits volume expansion, which corresponds to a significant decrease in soil stiffness and a reduction in modulus to about 55% of the initial value.

[0071] During the period of 2.20-2.81s, the shear strain returned to the positive range and underwent another complete physical cycle of shear contraction-unloading body contraction-unloading body expansion-shear dilatation. Overall, the volume decreased, the soil became denser to a certain extent, and the stiffness was partially restored.

[0072] In subsequent periods, as damage accumulates, the strain amplitude of the physical cycle continuously increases, the stiffness level continues to decrease, and eventually, a sharp decay occurs during the alternating process of volume expansion-shrinkage-expansion.

[0073] By identifying the state of matter segment by segment, it can be found that the attenuation and recovery of soil stiffness always correspond one-to-one with the state changes of volume expansion and contraction: periods of total volume contraction are usually accompanied by stiffness increase or recovery, while periods of total volume expansion are usually accompanied by stiffness attenuation; repeated cycles of volume expansion and contraction will continuously aggravate soil structural damage, eventually leading to irreversible stiffness degradation. The state-stiffness mapping relationship established in this embodiment reveals the intrinsic mechanism of stiffness degradation from the microscopic perspective of soil volume changes, making up for the shortcomings of existing technologies that only focus on changes in modulus values.

[0074] Preferred Example 3: Hysteresis Dissipation Energy Calculation and Differential Response Analysis

[0075] This embodiment, based on the basic embodiment, further refines the calculation of hysteretic dissipation energy and cumulative dissipation energy, and explains the differentiated nature of soil dynamic response under different waveforms and densities from an energy perspective. The specific content is as follows:

[0076] Hysteretic dissipation energy is the energy consumed by soil under cyclic loading. Numerically, it is equal to the area enclosed by a single hysteresis loop and is a core parameter characterizing the energy dissipation level of soil. The hysteretic dissipation energy under a single-stage load is calculated using the integral method, and the cumulative dissipation energy is obtained by summing the values ​​of each stage.

[0077] The formula for calculating the hysteretic energy dissipation per unit volume under a single-stage load is as follows:

[0078]

[0079] In the formula: The hysteretic energy dissipated per unit volume under a single-stage load; Shear stress; For shear strain.

[0080] The formula for calculating cumulative energy dissipation is as follows:

[0081]

[0082] In the formula: To accumulate dissipated energy; Let be the hysteretic dissipation energy under the i-th level load; For load levels.

[0083] The cumulative dissipated energy variation curves under seismic waves of different amplitudes are as follows: Figure 4 As shown, comparing the energy accumulation characteristics of Kobe waves and EL waves, two types of natural waves, reveals the following:

[0084] Under the action of Kobe wave, the energy accumulation of soil exhibits a two-stage characteristic of "rapid rise - tending to stabilize". The energy increases rapidly in the first 3 seconds of loading, and the subsequent increase narrows significantly, eventually stabilizing.

[0085] Under the action of EL waves, the energy accumulation of soil exhibits four stages: the energy rises sharply in the first second before loading, continues to increase but the rate of increase slows down in the first 1-3 seconds, increases slowly in the first 3-8 seconds, and basically stabilizes after 8 seconds. The total energy input is significantly higher than that of Kobe waves of the same amplitude.

[0086] The energy response of soils with different densities exhibits a significant time lag effect: soils with higher density begin energy accumulation earlier and acquire a larger total energy within the same time frame; soils with lower density show a significant lag in energy accumulation, ultimately acquiring a relatively smaller total energy. Spatially, the soil near the bedrock inflection point dissipates the most energy and is the region with the strongest dynamic response, perfectly aligning with the characteristics of most significant stiffness deterioration and most concentrated deformation at this location.

[0087] This embodiment demonstrates through energy-dimensional analysis that the differences in soil shear stress-strain response under different waveforms, locations, and densities are essentially caused by the differences in the total energy input and the energy dissipation rate. The greater the energy dissipation, the greater the amplitude of soil shear strain, the more intense the physical cycle, and the more significant the stiffness degradation. This conclusion provides energy-level theoretical support for the essential explanation of soil dynamic degradation.

[0088] Preferred Example 4: Construction of Damage Indicators and Classification of Deterioration Levels

[0089] This embodiment, based on the basic embodiment, further refines the construction and application of damage indicators and establishes a quantitative evaluation standard for mechanical deterioration. The specific content is as follows:

[0090] The damage index is defined based on stiffness degradation. Taking the initial dynamic shear modulus as the benchmark, the degree of soil damage is characterized by the attenuation of the current dynamic shear modulus. This index has a clear physical meaning and can directly reflect the deterioration level of the soil's mechanical properties.

[0091] The formula for calculating the damage index is as follows:

[0092]

[0093] In the formula: D is the damage index, which ranges from 0 to 1. The larger the value, the more severe the damage. This is the dynamic shear modulus under the current load; This is the initial dynamic shear modulus.

[0094] The changes in damage indices of medium-dense and loose deposits are as follows: Figure 5 , Figure 6 As shown, comparing the two sets of calculation results reveals that:

[0095] The damage index growth rate of medium-dense soil is relatively slow. Under 0.8gEL wave loading, the damage index of measuring point A8-9 is about 0.89 and that of measuring point A6-7 is about 0.83, indicating that medium-dense soil experiences a larger shear strain amplitude and a higher stiffness decay.

[0096] The damage index of the loosely packed body increased at a faster rate, especially in the later stage of loading. Under the same working conditions, the damage index of the A6-7 measuring point was about 0.89, and that of the A8-9 measuring point was about 0.88, which was close to that of the medium-dense group, but the inflection point of growth appeared earlier.

[0097] However, the degree of damage is not directly positively correlated with slope stability: Although the medium-dense deposits have higher cumulative damage, their initial dynamic strength is greater, and the remaining strength after stiffness decay is still sufficient to maintain slope stability, eventually resulting in only shallow local landslides; Although the final damage index of the loose deposits is similar to that of the medium-dense deposits, their initial dynamic strength is small, their stiffness decay rate is fast, and their remaining strength is insufficient to resist the sliding force, eventually resulting in deep overall sliding.

[0098] Based on a large amount of experimental data, the damage index values ​​can be divided into three levels: mild deterioration (D<0.3), moderate deterioration (0.3≤D<0.7), and severe deterioration (D≥0.7). Different levels correspond to different stiffness attenuation and stability states, providing a standardized quantitative basis for slope dynamic damage evaluation.

[0099] Preferred Implementation

[0100] This embodiment simultaneously covers two groups of sediment tests, one medium-dense and one loose, and synchronously analyzes two typical locations: the bedrock inflection point and the upper bedrock surface. It fully implements the whole-process analysis method of this invention and combines it with the theory of unsaturated soil mechanics to derive the dynamic failure mechanism, forming a complete analysis and verification system.

[0101] I. Basic Parameters of the Experimental System

[0102] Both sets of experiments used identical model dimensions, sensor placement, and loading schemes, differing only in the initial density and moisture content of the packings: the medium-dense pack had a dry density of approximately 1.53 g / cm³ and an initial moisture content of approximately 9.06%; the loose pack had a dry density of approximately 1.38 g / cm³ and an initial moisture content of approximately 6.02%. Each set of experiments deployed 14 slope accelerometers (A1-A14) and 12 pore water pressure sensors (K1-K12), arranged in layers along the bedrock surface and slope. A platform accelerometer A0 was placed on the platform for input calibration. The deployment method is as follows: Figure 1 As shown. The seismic loading used a magnitude 35 load condition, which included white noise scanning, natural wave and sine wave loading, with the peak acceleration gradually increasing from 0.03g to 0.9g.

[0103] II. Full-process analysis

[0104] Shear stress-strain calculation and hysteresis loop decomposition

[0105] Shear stress and shear strain were calculated at measuring points A6-7 and A8-9 in both sets of experiments. Before calculation, the acceleration signals were bandpass filtered from 0.3 to 50 Hz and baseline corrected to eliminate the effects of noise and baseline drift. The calculation results show that under the same loading conditions, the shear stress amplitude and shear strain amplitude of the dense group are significantly greater than those of the loose group. For example, under a 0.6gEL wave loading, the shear strain amplitude at measuring point A6-7 in the dense group is approximately 6.83%, while that in the loose group is only approximately 1.32%, with the former being more than five times that of the latter.

[0106] Hysteresis loops were decomposed from the shear stress-strain curves according to the time window. Both groups exhibited irregular, intersecting hysteresis loop morphology. The hysteresis loop area in the denser group was larger, indicating stronger energy dissipation. The typical evolution morphology of the hysteresis loops is as follows: Figure 2 As shown.

[0107] Evolution of State and Stiffness Mapping Analysis

[0108] The material evolution process of two sets of measuring points was identified time-by-time, and the piecewise results of shear stress and shear strain for each time period are as follows: Figure 3 As shown, the results indicate that both groups of soils undergo cyclic changes in physical state, including shear contraction, shear dilatation, unloading contraction, and unloading dilatation, but the magnitude and rate of evolution differ significantly.

[0109] The strain amplitude of the medium-density group during the physical cycle is large, the stiffness decay rate is relatively slow, the stiffness recovery stage is more obvious, and the overall degradation process is smoother.

[0110] Loose soils exhibit smaller strain amplitudes during cyclic loading, but their stiffness decays at a faster rate, especially in the later stages of loading, where the inflection point of rapid stiffness decay occurs earlier, leading to more rapid soil deterioration.

[0111] From the perspective of the state-stiffness mapping relationship, both groups conform to the basic rule that "volume contraction corresponds to stiffness increase and volume expansion corresponds to stiffness decrease". The loose group has a greater stiffness decrease during the volume expansion stage, which is the core reason for its faster overall deterioration.

[0112] Energy dissipation and damage quantification

[0113] Calculate the hysteretic dissipation energy and cumulative dissipation energy at the two sets of measuring points. The change in cumulative dissipation energy under different amplitudes is as follows: Figure 4 As shown, the results indicate that the total energy dissipation of the medium-dense group under all working conditions is higher than that of the loose group, and the corresponding damage index is also greater; however, the energy-damage conversion efficiency of the loose group is higher, that is, the stiffness attenuation caused by unit energy input is more significant.

[0114] Spatially, both groups exhibit characteristics of concentrated energy and more severe damage near the bedrock inflection point. The changes in damage indices of the medium-dense and loose deposits are as follows: Figure 5 , Figure 6As shown, this is completely consistent with the experimental phenomenon that slope failure first starts from the middle and upper parts.

[0115] Derivation and Verification of Dynamic Destruction Mechanism

[0116] Based on the theory of unsaturated soil shear strength and combined with dynamic pore water pressure monitoring data, the shear strength loss at the bedrock surface and slope surface is calculated. The formula for calculating the shear strength of unsaturated soil is as follows:

[0117]

[0118] In the formula: This refers to the shear strength of unsaturated soil. For effective cohesion; This represents the total normal stress. Pore ​​gas pressure; The effective internal friction angle; Pore ​​water pressure; The internal friction angle is related to the matrix suction.

[0119] Calculation results show that: the dynamic pore water pressure amplitude is large at the bedrock surface of the loose group, resulting in significant shear strength loss, with the greatest strength loss at the bedrock shoulder; the pore water pressure amplitude is small at the bedrock surface of the medium-dense group, resulting in relatively limited strength loss.

[0120] Establish element stress state models for the slope crest and slope surface, and compare the element stress states of the soil and rock mass under natural conditions and seismic loads as follows: Figure 7 As shown, the stress state at the slope location is as follows: Figure 8 As shown. Analysis of stress transformation under horizontal reciprocating ground motion: Under dynamic tensile stress, the soil at the top of the slope is prone to tensile stress exceeding its tensile strength, resulting in tensile cracks; Under dynamic reciprocating ground motion, the soil on the slope experiences tensile-shear coupling, and the cracks continuously expand and deepen.

[0121] By combining strength loss, stress state, and stiffness degradation analysis, the differentiated failure mechanisms of the two sets of slopes can be systematically elucidated:

[0122] Loose deposits have low dynamic strength and large shear strength loss at the bedrock surface. In addition, the stiffness decay rate is fast, which eventually leads to a deep shear slip failure mode of "upper tensile cracking - sliding along the bedrock surface - lower soil layer shearing out", corresponding to the experimental phenomenon of overall collapse.

[0123] The medium-dense deposits have high dynamic strength and low strength loss on the bedrock surface. Although the cumulative strain damage is greater, the remaining strength is sufficient to maintain overall stability. Ultimately, only tensile-shear cracks form on the slope shoulder and in the upper middle part, resulting in shallow local landslides.

[0124] The above analytical conclusions are completely consistent with the deformation and failure phenomena observed in the model test, verifying the accuracy and reliability of the method of the present invention.

[0125] III. Shear Strength and Stress Principle of Unsaturated Soil

[0126] Rainfall infiltration increases soil saturation, raising the internal friction angle parameter related to matrix suction while simultaneously decreasing matrix suction; both factors work together to alter the soil's shear strength. The dynamic pore water pressure generated during earthquakes further alters the effective stress state, causing dynamic fluctuations in shear strength. For unsaturated deposits with high permeability and good drainage, dynamic pore water pressure exhibits alternating positive and negative fluctuations without continuous accumulation. However, near the bedrock surface, due to relatively poor drainage, the amplitude of dynamic pore water pressure is larger, resulting in more significant shear strength loss.

[0127] From a stress state perspective, the natural stress at the top of the slope is dominated by self-weight stress, with relatively small horizontal static earth pressure. The cyclic dynamic stress generated by horizontal seismic motion causes continuous changes in the soil stress state: when the dynamic stress is in the opposite direction to the static horizontal stress, the center of the Mohr's circle shifts to the left, and the radius increases; when the minimum principal stress drops below the tensile strength, tensile failure occurs in the soil. When the dynamic stress is in the same direction as the static horizontal stress, the center shifts to the right, and the soil tends towards shear failure. This cyclic tension-shear action gradually causes the soil at the top of the slope to crack and break apart, with the cracks continuously extending deeper.

[0128] At the slope surface, the direction of the principal stresses deflects, with the maximum principal stress parallel to the slope surface. Under dynamic compressive stress, the amplitude of the principal stresses increases, and the soil tends towards shear failure; under dynamic tensile stress, the minimum principal stress decreases, easily inducing tensile failure. The slope soil also experiences tensile-shear coupling under cyclic dynamic stress, which is the core driving force for crack propagation and slope deformation.

[0129] The above theoretical derivation and experimental analysis results corroborate each other, together forming a complete analytical system for the dynamic failure mechanism of accumulated body slopes.

[0130] All aspects not detailed in this invention are conventional technical means known to those skilled in the art.

[0131] The above content shows and describes the basic principles, main features, and beneficial effects of this technical solution. The above description is merely a preferred embodiment of this technical solution and is not intended to limit the scope of this technical solution. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this technical solution should be included within the protection scope of this technical solution.

Claims

1. A method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupled action, characterized in that, Includes the following steps: S1 constructs a shaking table test model of an accumulation slope under rainfall-earthquake coupling, and sets up acceleration monitoring components and pore water pressure monitoring components inside the model; The S2 design employs a graded and progressive seismic loading scheme, applying multiple levels of seismic loads after rainfall infiltration and settling, while simultaneously collecting acceleration time history data and dynamic pore water pressure time history data at each monitoring point. S3 uses time history data from acceleration monitoring points at adjacent elevations to calculate the shear stress-shear strain time history curve of the soil at the target depth through integration and interpolation, and then performs time-series segmentation of the hysteresis loops in the curve according to continuous time windows. S4 identifies the soil physical evolution process corresponding to each hysteresis loop in time period based on the combination of the positive and negative directions of the shear strain increment and the shear stress loading direction. S5 calculates the hysteresis dissipation energy and cumulative dissipation energy at each monitoring point, and performs time-series matching between the material evolution period and the energy dissipation period to establish a mapping relationship between the material evolution process and the energy dissipation level. S6 constructs a damage index based on the dynamic shear modulus attenuation law to quantify the degree of mechanical deterioration of soil under seismic load; S7 combines the variation law of unsaturated soil shear strength with the stress state analysis at different locations of the slope to systematically determine the dynamic failure mechanism of the accumulated slope.

2. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling as described in claim 1, characterized in that, In step S3, the specific rules for the time-series segmentation of the hysteresis loop are as follows: select the continuous time period in which shear stress and shear strain form a closed loop as an independent time window, eliminate the interference time period of path intersection, and divide the single hysteresis loop into loading segment and unloading segment according to the direction of increase and decrease of shear stress.

3. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling as described in claim 1, characterized in that, In step S4, the criterion for determining the state of soil is as follows: based on the combined relationship between the trends of shear stress increase and decrease and shear strain increase and decrease, the state of soil within a single time period is divided into four categories: shear contraction, shear dilatation, unloaded contraction, and unloaded dilatation.

4. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling as described in claim 2, characterized in that, Step S3 also includes dynamic shear modulus calculation: the dynamic shear modulus is calculated by the ratio of shear stress amplitude to shear strain amplitude under a single load level, and the soil stiffness value under that load level is obtained for each hysteresis loop.

5. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling as described in claim 3, characterized in that, Step S4 also includes establishing a mapping between the evolution of the state of matter and the change in stiffness: calculating the dynamic shear modulus for each state of matter period to obtain the corresponding laws of the expansion and contraction of soil volume and stiffness decay and stiffness recovery.

6. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling as described in claim 4, characterized in that, The rule for identifying the evolution stages of the dynamic shear modulus is as follows: based on the modulus time history change characteristics during the full loading process, the stiffness evolution is divided into three characteristic stages: the initial decay stage, the local recovery stage, and the rapid decay stage.

7. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling as described in claim 5, is characterized in that, In step S5, the method for calculating and mapping energy dissipation is as follows: calculate the hysteretic dissipation energy under a single load by using the area enclosed by the hysteresis loop, accumulate the cumulative dissipation energy step by step, match the energy dissipation time sequence with the material state evolution period one by one, and obtain the energy dissipation level corresponding to different material state types.

8. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling as described in claim 1, characterized in that, In step S6, the damage index is calculated as follows: based on the initial dynamic shear modulus, a damage index is constructed based on the attenuation range of the current dynamic shear modulus, and the soil mechanical deterioration level is divided according to the index value range.

9. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling as described in claim 1, characterized in that, In step S7, the determination of the dynamic failure mechanism is as follows: analyze the static and dynamic stress combination states of the soil and rock units at the top and bottom of the slope, identify the tension-shear coupling effect, and determine the overall failure mode of the accumulated slope by combining the shear strength loss law at the bedrock surface.

10. The method for analyzing the physical evolution and mechanical deterioration of slopes under rainfall-earthquake coupling according to any one of claims 1-9, characterized in that, This method is applied to the seismic dynamic stability assessment of unsaturated deposit slopes with a broken bedrock surface.

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