A kind of accelerated test method for rheology of rockfill material based on small amplitude cyclic stress disturbance

Abstract

A kind of rockfill material rheological acceleration test method based on small amplitude cyclic stress disturbance belongs to geotechnical engineering technical field.It includes: preparing rockfill material sample and carrying out initial state adjustment;Loading to target confining pressure and target deviatoric stress state;On the basis of target deviatoric stress state, small amplitude axial cyclic stress is applied to promote rockfill material particle contact adjustment, skeleton structure rearrangement and cumulative deformation development;Axial deformation, volume deformation and plastic strain accumulation direction under cyclic loading condition are collected and arranged;Then, the development direction of the volume change-axial deformation obtained by the acceleration test is compared and verified by traditional pure static load rheological test.The invention introduces small amplitude cyclic stress as an acceleration disturbance means, which can quickly obtain the rheological deformation value of rockfill material under the premise that the development direction of volume change and axial change remains reasonable and consistent, shorten the duration of traditional rockfill material rheological test, reduce the long-term stable operation requirements of large test equipment, and improve the efficiency of obtaining rheological deformation value of rockfill material under multiple working conditions.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering technology and relates to an accelerated rheological test method for rockfill based on small-amplitude cyclic stress disturbance. Background Technology

[0002] With the continuous development of high earth-rock dams, especially high face rockfill dams and high core rockfill dams, the dam height, filling scale, and operating head have been continuously increasing. The rheological deformation of the rockfill material under long-term loads has become one of the important factors affecting the long-term service safety of the dam. Rheological deformation generally refers to the phenomenon that deformation of a material continues over time under conditions where the stress state remains basically constant or changes slowly. In rockfill dam projects, it mainly manifests as long-term settlement and lateral deformation of the dam body, and the resulting adjustments in the stress state of the face panels, joints, seepage barriers, or local areas of the dam body. For high dam projects, failure to reasonably understand and predict the long-term rheological characteristics of the rockfill material may affect dam deformation control, structural safety evaluation, and the interpretation of safety monitoring during long-term operation.

[0003] Rockfill material is a typical coarse-grained soil material, characterized by large particle size, wide gradation range, and significant particle breakage and rearrangement. Its stress-strain relationship and long-term deformation characteristics differ significantly from ordinary fine-grained soils. To obtain the rheological parameters of rockfill material, existing technologies typically employ indoor testing methods such as large-scale triaxial rheological tests or large-scale compressive rheological tests. These tests generally require maintaining relatively stable conditions such as confining pressure, axial stress, or stress ratio after sample preparation and consolidation loading to reach the target stress state, and continuously collecting axial deformation, volumetric deformation, or lateral deformation data over a relatively long period to establish the law governing the rheological deformation of rockfill material over time. For example, Chinese invention patent application (application number 201210076326.3) discloses a test method for simulating the long-term deformation of rockfill bodies. This method calculates the long-term deformation curve of rockfill body rheology by establishing a strength degradation model and a three-dimensional random model of rockfill particles. This method primarily focuses on the numerical simulation of long-term deformation of riprap, without addressing the issues of long testing cycles and the need for long-term stable operation of equipment in indoor riprap rheological tests. This makes it difficult to shorten the time required to obtain deformation values ​​in actual rheological tests. Chinese invention patent (application number 201911284567.5) discloses a riprap testing device and method, which can be used to study the wetting characteristics and long-term immersion softening characteristics of riprap, and to obtain the wetting constitutive model parameters and uniaxial rheological model parameters under uniaxial stress. However, this method still requires waiting for the sample to reach a stable rheological deformation state under various levels of compressive stress, and does not involve technical means to accelerate the acquisition of riprap rheological deformation values ​​through small-amplitude cyclic stress.

[0004] However, traditional rheological tests on rockfill materials suffer from long testing cycles. Because rheological deformation itself is significantly time-dependent, tests often require several days or even longer to obtain a complete deformation development process. For high dam rockfill materials, the sample size is typically large, and the loading system, confining pressure system, measurement system, and data acquisition system all need to maintain stable operation over extended periods. This places high demands on the rigidity, sealing performance, loading stability, long-term sensor stability, and environmental control conditions of the testing equipment.

[0005] Meanwhile, the large particle size of riprap results in a significant size effect. To ensure that laboratory test results accurately reflect the mechanical behavior of the prototype material, experiments often require larger specimens or scaling down to a certain proportion, further increasing the demands on testing equipment and conditions. Due to limitations in equipment scale, long-term stable loading capacity, testing costs, and personnel maintenance capabilities, relatively few research institutions and universities are capable of conducting long-term riprap rheological tests. This results in insufficient accumulation of relevant experimental data and restricts the acquisition and engineering application of riprap rheological model parameters.

[0006] Furthermore, traditional static rheological tests rely primarily on natural time processes to gradually adjust the internal particle skeleton of rockfill, resulting in a slow deformation development rate and low testing efficiency. In engineering research and model parameter calibration, employing long-duration pure rheological tests for each stress state significantly increases the testing cycle and cost, and hinders comparative studies involving multiple confining pressures, stress levels, gradations, or different dam construction materials. Therefore, existing rockfill rheological testing techniques urgently require a method that can improve rheological deformation development efficiency, shorten testing duration, and reduce dependence on the stable operation of long-term testing equipment while maintaining interpretable main stress states and deformation patterns. Summary of the Invention

[0007] To address the problems of long testing cycles, low efficiency, and high requirements for the long-term stable operation of large-scale testing equipment in existing rheological tests of rockfill materials, this invention, based on the needs of long-term deformation analysis of high earth-rock dams and testing of the rheological properties of rockfill materials, proposes a test method to shorten the duration of rheological tests of rockfill materials. This method is primarily designed to solve the problems of slow deformation development, long test time, high equipment maintenance costs, and difficulty in efficiently conducting repeated tests under multiple conditions in traditional pure static load rheological tests. The innovation of this invention lies in introducing small-amplitude cyclic stress as an accelerating disturbance after the rockfill material reaches the target deviatoric stress state, to promote particle contact adjustment, skeletal structure rearrangement, and cumulative deformation development, thereby accelerating the acquisition of rheological deformation values.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An accelerated rheological testing method for riprap based on small-amplitude cyclic stress perturbation, the accelerated rheological testing method for riprap includes the following steps: Step S1: Preparation of rockfill sample.

[0009] Based on the gradation, maximum particle size, dry density, and moisture content of the rockfill at the engineering site, prepare rockfill samples that meet the requirements of large-scale triaxial tests or large-scale rheological tests. During sample preparation, basic physical parameters such as sample height, diameter, dry density, porosity, moisture content, and gradation composition should be recorded to ensure comparability between different test groups.

[0010] Step S2: Sample placement and initial state adjustment.

[0011] The prepared rockfill specimen 1 was placed in the testing equipment, and the axial loading system, confining pressure control system, deformation measurement system, and data acquisition system were connected. A predetermined confining pressure was then applied to bring the specimen to a set consolidation state. The purpose of this stage is to establish stable initial stress conditions and reduce the impact of specimen installation disturbances on subsequent rheological deformation test results.

[0012] Step S3: Apply axial stress to the target deviatoric stress state.

[0013] After isobaric loading to the target confining pressure, axial stress is increased to reach the target deviatoric stress state, so that the rockfill sample 1 reaches the rheological deviatoric stress state to be studied. After loading is completed, the stress state is kept unchanged, and axial strain and volumetric strain data are collected. It is observed whether the cumulative rate of axial deformation is ≤0.01% / 0.5h. After meeting the standard, the next step is carried out.

[0014] Step S4: Set small-amplitude cyclic stress conditions.

[0015] Based on the target deviatoric stress state, a small-amplitude axial cyclic stress is introduced. The magnitude of this axial cyclic stress is based on the target confining pressure, and the amplitude of the axial cyclic stress should be controlled within a range that will not cause significant strength failure or non-target large deformation of the specimen. Generally, the ratio of cyclic stress to confining pressure is taken as a reference of 0.1-0.3, so that its main function is to promote the adjustment of contact between riprap particles, local interlocking and rearrangement, and the development of cumulative deformation.

[0016] Step S5: Initiate the small-amplitude cyclic loading phase.

[0017] The cyclic process begins with the target deviatoric stress and ends with the difference between the target deviatoric stress and the axial cyclic stress. Within this range, small-amplitude axial cyclic stress is applied. Following the set cyclic loading method, a certain number of cycles (n cycles) of small-amplitude cyclic stress are applied to the rockfill sample 1. During this stage, axial strain and volumetric strain data are continuously collected under small-amplitude cyclic conditions. The core objective of this stage is to accelerate the adjustment process of the internal particle skeleton of the rockfill using small-amplitude cyclic disturbances, enabling the sample to produce observable cumulative rheological deformation in a relatively short time.

[0018] Furthermore, the small-amplitude cyclic stress refers to a cyclic stress-to-containing pressure ratio ranging from 0.1 to 0.3, and a cycle count ranging from 1000 to 3000.

[0019] Step S6: Organize the deformation data.

[0020] After the small-amplitude cyclic loading in step S5 reaches the predetermined condition, the cyclic disturbance is stopped, and the axial cyclic stress is restored to the target deviatoric stress. Based on the axial strain and volumetric strain data collected in step S5 under the small-amplitude cyclic conditions, the axial deformation of the specimen in the consolidation stage and the small-amplitude cyclic loading stage under the small-amplitude cyclic conditions is analyzed. e aa , e ac ) and volume deformation ( e va , e vc The direction of final plastic strain accumulation in the specimen during the consolidation and small-amplitude cyclic loading stages under the given magnitude and small-amplitude cyclic conditions. k a , k c The calculations are shown in equations (1) and (2): k a = e va / e aa (1) k c = e vc / e ac (2) In the formula, k a This represents the direction of plastic strain accumulation during the consolidation stage; k c This represents the direction of plastic strain accumulation during the small-amplitude cyclic loading stage; e va This refers to the volumetric deformation during the consolidation stage; evc This refers to the volume deformation during the small-amplitude cyclic loading phase. e aa This refers to the axial deformation during the consolidation stage; e ac This refers to the axial deformation during the small-amplitude cyclic loading stage; i.e., strain. e In the subscript, the first letter 'a' represents axial deformation and 'v' represents volumetric deformation; the second letter 'a' represents the consolidation stage; and the second letter 'c' represents the small-amplitude cyclic loading stage. k a , k a The subscript 'c' refers to the consolidation stage and the small-amplitude cyclic loading stage.

[0021] Step S7: Conduct rheological tests on the remaining targets under deviatoric stress states. Repeat steps S1-S6 to obtain the axial deformation and volumetric deformation values ​​of the riprap.

[0022] Compared with the prior art, the beneficial effects of the present invention are: (1) Improve the efficiency of obtaining the rheological deformation value of riprap. The present invention applies small-amplitude cyclic stress on the basis of the target deviatoric stress state, and uses cyclic disturbance to promote the contact adjustment, local interlocking rearrangement and cumulative deformation development of riprap particles, thereby reducing the dependence of traditional pure static load rheological tests on the long-term constant load holding process.

[0023] (2) Ensure the comparability of accelerated test results with engineering applications. By controlling the amplitude of cyclic stress, this invention ensures that the development direction of volumetric and axial deformation of the rockfill material during the accelerated test is consistent with or basically consistent with that of the traditional static load rheological test. This ensures that the obtained deformation values ​​can reflect the rheological deformation characteristics of the rockfill material under the corresponding stress state, and improves the rationality of the accelerated test results for engineering analysis and parameter comparison.

[0024] (3) Reduce the equipment operation requirements and test costs of long-term rheological tests. This invention shortens the test duration required to obtain rheological deformation values, reduces the stability requirements caused by the long-term continuous operation of the loading system, confining pressure system, measurement system and data acquisition system, reduces the risk of data error caused by factors such as loading fluctuation, confining pressure fluctuation and measurement drift, and reduces equipment occupation time and test maintenance costs.

[0025] In summary, this invention introduces controllable small-amplitude cyclic stress under a target static stress state to promote particle contact adjustment, skeletal structure rearrangement, and cumulative deformation development in riprap. Under the premise of maintaining a reasonable consistency between the directions of volumetric and axial deformation, it rapidly obtains deformation values ​​that can characterize the rheological deformation level of riprap. This method reduces the dependence of traditional static load rheological tests on long-term constant load maintenance, lowers the requirements for long-term stable operation of large-scale testing equipment, and improves the efficiency of obtaining rheological deformation values ​​under multiple working conditions and conducting engineering comparative analysis of riprap. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the main process of the method of the present invention; Figure 2 It is a loading process for accelerated rheological testing of riprap based on small-amplitude cyclic stress disturbance; Figure 3 These are the test results from the consolidation stage and the small-amplitude cyclic loading stage; Figure 4 This is the loading process of a traditional static load current transformer test; Figure 5 These are results from traditional static current transformer tests; Figure 6 The results are a comparison between traditional static rheological tests and small-amplitude cyclic accelerated rheological tests. Detailed Implementation

[0027] The relevant design of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] Example 1 Taking the rheological test of rockfill material in a rockfill dam under construction as an example, this paper provides an accelerated rheological test method for rockfill material based on small-amplitude cyclic stress disturbance, such as... Figure 1 As shown, it includes the following steps: Step S1: Preparation of rockfill sample.

[0029] Based on the gradation, maximum particle size, dry density, and moisture content of the rockfill at the engineering site, prepare rockfill samples that meet the requirements of large-scale triaxial tests or large-scale rheological tests. During sample preparation, basic physical parameters such as sample height, diameter, dry density, porosity, moisture content, and gradation composition should be recorded to ensure comparability between different test groups.

[0030] Step S2: Sample placement and initial state adjustment.

[0031] The prepared rockfill specimen 1 was placed in the testing equipment, and the axial loading system, confining pressure control system, deformation measurement system, and data acquisition system were connected. A predetermined confining pressure was then applied to bring the specimen to a set consolidation state. The purpose of this stage is to establish stable initial stress conditions and reduce the impact of specimen installation disturbances on subsequent rheological deformation test results.

[0032] Step S3: Apply axial stress to the target deviatoric stress state.

[0033] After isobaric loading to the target confining pressure, axial stress is increased to reach the target deviatoric stress state, bringing the riparian deviatoric stress state of the rockfill sample 1 to be studied. After loading, the stress state is kept constant, and axial strain and volumetric strain data are collected. The cumulative rate of axial deformation is observed to be ≤0.01% / 0.5h. Once the standard is met, the next step is carried out. Figure 2 As shown.

[0034] Step S4: Set small-amplitude cyclic stress conditions.

[0035] Based on the target deviatoric stress state, a small-amplitude axial cyclic stress is introduced. The magnitude of this axial cyclic stress is based on the target confining pressure. In this embodiment, the amplitude of the axial cyclic stress is applied at a ratio of cyclic stress to confining pressure of 0.3, so that its main function is to promote the adjustment of contact between riprap particles, local interlocking and rearrangement, and the development of cumulative deformation.

[0036] Step S5: Initiate the small-amplitude cyclic loading phase.

[0037] The cyclic process begins with the target deviatoric stress and ends with the difference between the target deviatoric stress and the axial cyclic stress. Small-amplitude axial cyclic stress is applied within this range. Following the set cyclic loading method, 1500 cycles of small-amplitude cyclic stress are applied to the riprap sample 1. Figure 2 As shown. In this stage, axial strain and volumetric strain data are continuously collected under small-amplitude cyclic conditions. The core objective of this stage is to accelerate the adjustment process of the internal particle skeleton of the rockfill material using small-amplitude cyclic perturbation, so that the sample can produce observable cumulative rheological deformation in a short period of time.

[0038] Step S6: Organize the deformation data.

[0039] After the small-amplitude cyclic loading reaches the predetermined condition, the cyclic disturbance is stopped, and the axial stress is restored to the target deviatoric stress. Based on the collected axial strain and volumetric strain data under the small-amplitude cyclic conditions, the final axial deformation of the specimen during the consolidation stage and the small-amplitude cyclic loading stage under the small-amplitude cyclic conditions is summarized. e aa , e ac ) and volume deformation ( e va, e vc The direction of cumulative plastic strain in the specimen during the consolidation and small-amplitude cyclic loading stages under the given magnitude and small-amplitude cyclic conditions. k a , k c The calculations are shown in equations (1) and (2), and the experimental results are as follows. Figure 3 As shown, the directions of plastic strain accumulation in the consolidation stage and the small-amplitude cyclic loading stage are respectively... k a =0.99、 k c =1.01, the difference is only 2%, less than 5%, the cumulative plastic strain directions are close, and the test time is 3.5h and 4.2h.

[0040] k a = e va / e aa (1) k c = e vc / e ac (2) In the formula, the strain symbol e In the subscript, the first letter 'a' represents axial deformation and 'v' represents volumetric deformation; the second letter 'a' represents the consolidation stage; and the second letter 'c' represents the small-amplitude cyclic loading stage. k a , k a The subscript 'c' refers to the consolidation stage and the small-amplitude cyclic loading stage.

[0041] Comparative Example 1 A conventional pure static load rheological test was carried out in a comparative manner, and steps S1-S3 were the same as those in Example S1-S3.

[0042] Step S4: Maintain the target deviatoric stress state and continue loading.

[0043] The comparative model is operated without applying small amplitude cycles, maintaining the target deviatoric stress state unchanged, and then continuously acquiring axial strain and volumetric strain data, such as... Figure 4 As shown.

[0044] Step S5: Organize deformation data.

[0045] The final axial deformation of the traditional static load current test is summarized as follows ( e as ) and volumetric deformation value ( e vsThe direction of plastic strain accumulation in traditional static hydrodynamic tests is shown in the test results. Figure 5 As shown, the direction of plastic strain accumulation in traditional hydrostatic tests. k s =0.98, calculated as shown in equation (3), and the test took 58 hours.

[0046] k s = e vs / e as (3) In the formula, the strain symbol e In the subscript, the first letter 'a' represents axial deformation, 'v' represents volumetric deformation, and the second letter 's' represents conventional static current deformation testing. k s The subscript 's' refers to the traditional static load rheometry test.

[0047] Verification of the rheological acceleration test results of Example 1 and Comparative Example 1: Comparing the direction of plastic strain accumulation in specimens under small-amplitude cyclic conditions during the consolidation and small-amplitude cyclic loading stages with that in traditional static hydrodynamic tests. k s The comparison results are as follows Figure 6 As shown: 1. Comparative Example 1: Direction of plastic strain accumulation in conventional hydrostatic tests k s =0.98; 2. The direction of cumulative plastic strain during the consolidation stage in Example 1 k a =0.99; 3. The direction of cumulative plastic strain during the small-amplitude cyclic loading stage in this embodiment 1 k c =1.01; 4. Direction of plastic strain accumulation in traditional static hydrodynamic tests k s =0.98 and the direction of plastic strain accumulation during the consolidation stage k a The error of 0.99 is 1%, which is less than 5%. 5. Direction of plastic strain accumulation in traditional static hydrodynamic tests k s =0.98 and the direction of plastic strain accumulation during the small-amplitude cyclic loading stage k c The error of 1.01 is 3%, which is less than 5%. Therefore, the small-amplitude cyclic loading method of this embodiment accelerates the rheological test and meets the requirement that the plastic strain accumulation direction is consistent. The test time is shortened from 58h (Comparative Example 1) to 3.5+4.2h (Example 1), which greatly improves the rheological test speed and solves the problems of slow deformation development rate, low test efficiency and long test time in traditional pure static load rheological tests.

[0048] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for accelerated rheological testing of riprap based on small-amplitude cyclic stress disturbance, characterized in that, The accelerated rheological testing method for riprap includes the following steps: Step S1: Prepare rockfill samples; Based on the gradation, maximum particle size, dry density and moisture content of the rockfill material at the engineering site, prepare rockfill material samples that meet the requirements of large-scale triaxial tests or large-scale rheological tests. Step S2: Place the riprap sample and adjust its initial state to establish stable initial stress conditions; Step S3: Apply axial stress to the target deviatoric stress state; Step S4: Set small-amplitude cyclic stress conditions; Based on the target deviatoric stress state, a small-amplitude axial cyclic stress is introduced; the magnitude of the axial cyclic stress is based on the target confining pressure, and the amplitude of the axial cyclic stress should be controlled within a range that does not cause strength failure or non-target large deformation of the rockfill sample. Step S5: Initiate the small-amplitude cyclic loading phase; The cyclic process starts with the target deviatoric stress and ends with the difference between the target deviatoric stress and the axial cyclic stress. Within this range, small-amplitude axial cyclic stress is applied. Small-amplitude cyclic stress is applied to the rockfill sample according to the set cyclic loading method. Axial strain and volumetric strain data under small-amplitude cyclic conditions are continuously collected. Step S6: Obtain deformation data; After the small-amplitude cyclic loading in step S5 reaches the predetermined condition, the cyclic disturbance is stopped, and the axial cyclic stress is restored to the target deviatoric stress. Based on the axial strain and volumetric strain data collected in step S5 under the small-amplitude cyclic conditions, the magnitudes of axial deformation and volumetric deformation of the specimen in the consolidation stage and the small-amplitude cyclic loading stage under the small-amplitude cyclic conditions, as well as the final plastic strain accumulation direction of the specimen in the consolidation stage and the small-amplitude cyclic loading stage under the small-amplitude cyclic conditions, are obtained. Step S7: Conduct rheological tests on the remaining targets under deviatoric stress; repeat steps S1-S6 to obtain the axial deformation and volumetric deformation values ​​of the riprap material rheological test.

2. The accelerated rheological test method for riprap based on small-amplitude cyclic stress disturbance according to claim 1, characterized in that, In the process of preparing the rockfill sample in step S1, basic physical parameters are recorded, including sample height, diameter, dry density, porosity, moisture content, and gradation composition, to ensure comparability between different test groups.

3. The accelerated rheological test method for riprap based on small-amplitude cyclic stress disturbance according to claim 1, characterized in that, Specifically, step S2 involves placing the rockfill sample in the testing equipment and connecting the axial loading system, confining pressure control system, deformation measurement system, and data acquisition system; applying a predetermined confining pressure to bring the rockfill sample to a set consolidation state; and establishing stable initial stress conditions to reduce the impact of sample installation disturbances on subsequent rheological deformation test results.

4. The accelerated rheological test method for riprap based on small-amplitude cyclic stress disturbance according to claim 1, characterized in that, Step S3 specifically involves: after isobaric loading to the target confining pressure, increasing the axial stress to reach the target deviatoric stress state, so that the rockfill sample reaches the rheological deviatoric stress state; after loading is completed, keeping the stress state unchanged, starting to collect axial strain and volumetric strain data, observing whether the cumulative rate of axial deformation is ≤0.01% / 0.5h, and proceeding to the next step after meeting the standard.

5. The accelerated rheological test method for riprap based on small-amplitude cyclic stress disturbance according to claim 1, characterized in that, In step S4, the magnitude of the axial cyclic stress is determined according to the standard that the ratio of cyclic stress to confining pressure is not greater than 0.

3.

6. The accelerated rheological test method for riprap based on small-amplitude cyclic stress disturbance according to claim 1, characterized in that, In step S5, the small-amplitude cyclic stress refers to the ratio of cyclic stress to confining pressure ranging from 0.1 to 0.3, and the number of cycles ranging from 1000 to 3000.

7. The accelerated rheological test method for riprap based on small-amplitude cyclic stress disturbance according to claim 1, characterized in that, The calculation in step S6 is shown in equations (1) and (2): k a = ε va / ε aa （1） k c = ε vc / ε ac （2） In the formula, k a This represents the direction of plastic strain accumulation during the consolidation stage; k c This represents the direction of plastic strain accumulation during the small-amplitude cyclic loading stage; ε va This refers to the volumetric deformation during the consolidation stage; ε vc This refers to the volume deformation during the small-amplitude cyclic loading phase. e aa This refers to the axial deformation during the consolidation stage; e ac This refers to the axial deformation during the small-amplitude cyclic loading stage.

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