阅读说明：本技术 降低边界反射效应对应力波传播试验数据影响的方法 (Method for reducing influence of boundary reflection effect on stress wave propagation test data ) 是由 吴坚 张晓平 刘泉声 周垂一 任金明 王永明 于 2021-09-03 设计创作，主要内容包括：本发明涉及一种降低边界反射效应对应力波传播试验数据影响的方法。适用于应力波传播室内试验技术领域。本发明所采用的技术方案是：一种降低边界反射效应对应力波传播试验数据影响的方法,其特征在于：在试样和应力波传播试验的加载端之间设置边界材料,并在边界材料和加载端之间设置垫块；所述边界材料的波阻抗值为最优波阻抗Z-(b)。通过本发明中最优波阻抗的计算公式计算得到应力波传播室内试验中边界材料(吸波材料)的最优波阻抗,从而根据此选择合适的边界材料用于应力波传播室内试验中,对反射波进行吸收,从而切实改善应力波传播室内试验中的边界反射效应,最大化地减弱应力波在边界处的边界反射效应。(The invention relates to a method for reducing influence of a boundary reflection effect on stress wave propagation test data. The method is suitable for the technical field of stress wave propagation indoor tests. The technical scheme adopted by the invention is as follows: a method for reducing influence of boundary reflection effect on stress wave propagation test data is characterized in that: arranging a boundary material between the sample and a loading end of the stress wave propagation test, and arranging a cushion block between the boundary material and the loading end; the wave impedance value of the boundary material is the optimal wave impedance Z b . The optimal wave impedance of the boundary material (wave-absorbing material) in the stress wave propagation indoor test is calculated by the calculation formula of the optimal wave impedance, so that the proper boundary material is selected to be used in the stress wave propagation indoor test according to the optimal wave impedance, reflected waves are absorbed, and the stress is practically improvedThe boundary reflection effect in the wave propagation indoor test maximally weakens the boundary reflection effect of the stress wave at the boundary.)

1. A method for reducing influence of boundary reflection effect on stress wave propagation test data is characterized in that:

arranging a boundary material between the sample and a loading end of the stress wave propagation test, and arranging a cushion block between the boundary material and the loading end;

the wave impedance value of the boundary material is the optimal wave impedance Z_b；

The most importantWave impedance Z_bCalculated using the following equation:

-Z_b ⁵+Z_b ⁴(7Z_a-2Z_c)+Z_b ³(Z_a ²-10Z_aZ_c-_c ²)+Z_aZ_b ²(Z_a ²+10Z_aZ_c-Z_c ²)+Z_a ²Z_bZ_c(2Z_a-7Z_c)+Z_a ³Z_c ²＝0

wherein Z is_aIs the wave impedance value, Z, of the sample_cIs the wave impedance value of the pad.

2. The method of reducing the effect of edge reflection on stress wave propagation test data of claim 1, wherein: the thickness of the boundary material is 1/12-1/8 of the length of the sample.

3. The method of reducing the effect of edge reflection on stress wave propagation test data of claim 1, wherein: the boundary material has a thickness of 1/10 times the specimen length.

4. A method of reducing the effect of boundary reflection effects on stress wave propagation test data according to claim 1, 2 or 3, wherein: the thickness of the cushion block is 1/4-1/2 of the thickness of the boundary material.

5. The method of reducing the effect of edge reflection on stress wave propagation test data of claim 1, wherein: the cushion block is a steel cushion block.

6. The method of reducing the effect of edge reflection on stress wave propagation test data of claim 4, wherein: the cushion block is a steel cushion block.

7. The method of reducing the effect of edge reflection on stress wave propagation test data of claim 1, wherein: the cross-sectional areas of the block, boundary material and sample were the same.

Technical Field

The invention relates to a method for reducing influence of a boundary reflection effect on stress wave propagation test data. The method is suitable for the technical field of stress wave propagation indoor tests.

Background

Deep engineering rock bodies contain a large number of discontinuous structural surfaces, such as faults, joints, cracks and the like, and the existence of the discontinuous surfaces can cause rapid dissipation of stress wave energy. In addition, the deep rock body usually has higher ground stress, and excavation unloading disturbs the properties of surrounding rocks and a ground stress field, so that the physical and mechanical characteristics (porosity, permeability, joint stiffness and the like) of rocks and joints are changed, and the propagation attenuation rule of stress waves in the jointed rock body is influenced, so that the propagation attenuation mechanism of the stress waves in the deep engineering rock body is very complex, and the influence factors are numerous, so that the propagation attenuation rule of the stress waves in the jointed rock body is difficult to accurately analyze and predict theoretically. The indoor test is an effective means for researching the propagation attenuation law of the stress wave, can be mutually verified with theoretical research results, and can provide certain reference and reference for field engineering application.

In order to research the propagation attenuation rule of the stress wave in the jointed rock mass, a plurality of scholars at home and abroad develop a propagation test of the one-dimensional stress wave in the rock mass. When the stress wave reaches the boundary of the rock sample, the stress wave can generate a transflectance phenomenon among different media. Part of reflected waves generated at the boundary can be reflected back to the rock sample along the original path, and will generate superposition interference with the original waveform within the duration time of the stress wave, so that the collected stress wave signals are difficult to truly reflect the propagation attenuation law of the stress wave in the rock medium.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: in view of the above-mentioned problems, a method for reducing the influence of the boundary reflection effect on the stress wave propagation test data is provided.

The technical scheme adopted by the invention is as follows: a method for reducing influence of boundary reflection effect on stress wave propagation test data is characterized in that:

arranging a boundary material between the sample and a loading end of the stress wave propagation test, and arranging a cushion block between the boundary material and the loading end;

the wave impedance value of the boundary material is the optimal wave impedance Z_b；

The optimum wave impedance Z_bCalculated using the following equation:

-Z_b ⁵+Z_b ⁴(7Z_a-2Z_c)+Z_b ³(Z_a ²-10Z_aZ_c-Z_c ²)+Z_aZ_b ²(Z_a ²+10Z_aZ_c-Z_c ²)+Z_a ²Z_bZ_c(2Z_a-7Z_c)+Z_a ³Z_c ²＝0

wherein Z is_aIs the wave impedance value, Z, of the sample_cIs the wave impedance value of the pad.

The thickness of the boundary material is 1/12-1/8 of the length of the sample.

The boundary material has a thickness of 1/10 times the specimen length.

The thickness of the cushion block is 1/4-1/2 of the thickness of the boundary material.

The cushion block is a steel cushion block.

The cross-sectional areas of the block, boundary material and sample were the same.

The invention has the beneficial effects that: the optimal wave impedance of the boundary material (wave-absorbing material) in the stress wave propagation indoor test is calculated through the calculation formula of the optimal wave impedance, so that the proper boundary material is selected to be used in the stress wave propagation indoor test according to the optimal wave impedance, reflected waves are absorbed, the boundary reflection effect in the stress wave propagation indoor test is practically improved, the boundary reflection effect of the stress wave at the boundary is weakened to the maximum extent, the influence of the boundary reflection effect on stress wave propagation test data is avoided, and the authenticity and the effectiveness of the test data are ensured.

Drawings

Fig. 1 is a schematic structural diagram of a stress wave propagation test device in the embodiment.

FIG. 2 is a schematic diagram of a transflective model of a stress wave between three media in an embodiment.

FIG. 3 shows example V_L/V_IThe ratio is along the wave impedance curve of the wave absorbing material.

FIG. 4 is a graph showing the variation of the magnitude of a stress wave with the propagation distance when rubber is used as a boundary material in the example.

FIG. 5 is a graph showing the variation of the magnitude of a stress wave with the propagation distance when a steel block is used as a boundary material in the example.

FIG. 6 is a graph showing the variation of the magnitude of the stress wave with the propagation distance when pine is used as a boundary material in the example.

1. Sandstone samples; 2. a boundary material; 3. cushion blocks; 4. a sample and boundary material interface; 5. a boundary material and pad interface; 6. a pendulum system; 7. an acceleration sensor; 8. a rigid frame; 9. loading an oil cylinder; 10. a hydraulic jack; 11. a data acquisition instrument; 12. and a data transmission line.

Detailed Description

The method is characterized in that a boundary material is arranged between a sample and a loading end of a stress wave propagation test, and a cushion block is arranged between the boundary material and the loading end.

In this example, the boundary material has a wave impedance value closest to the optimal wave impedance Z_bMaterial of (2), optimum wave impedance Z_bCalculated using the following equation:

-Z_b ⁵+Z_b ⁴(7Z_a-2Z_c)+Z_b ³(Z_a ²-10Z_aZ_c-Z_c ²)+Z_aZ_b ²(Z_a ²+10Z_aZ_c-Z_c ²)+Z_a ²Z_bZ_c(2Z_a-7Z_c)+Z_a ³Z_c ²＝0(1)

wherein Z is_aIs the wave impedance value, Z, of the sample_cThe wave impedance value of the pad.

In this example, the thickness of the boundary material is 1/12-1/8, preferably 1/10, of the length of the sample. The thickness of the cushion block in the embodiment is 1/4-1/2, preferably 1/4 of the thickness of the boundary material.

In the following, whether the influence of the boundary reflection effect on the data can be reduced in this embodiment is verified through a stress wave propagation test, taking an indoor propagation test of a stress wave in a sandstone medium as an example:

step 1, as shown in fig. 1, the stress wave propagation test device mainly comprises a pendulum bob system, an acceleration sensor, a rigid frame, a loading end (a loading oil cylinder and a jack), a data acquisition instrument, a data transmission line and the like, wherein the length, width and height of a sandstone sample are 1500mm multiplied by 120mm respectively, and the sandstone sample is horizontally placed in the rigid frame; the loading oil cylinder and the hydraulic jack are positioned at the right end of the sandstone sample, and axial load is applied to the sandstone sample through the counter force provided by the rigid frame; placing a boundary material between the sandstone sample and the loading oil cylinder for improving the reflection effect of the stress wave at the boundary; as the cross-sectional area of the loading oil cylinder is smaller than that of the boundary material, in order to avoid deformation damage caused by uneven stress of the boundary material due to axial loading, a cushion block (steel cushion block) is arranged between the loading oil cylinder and the boundary material, and the cushion block, the boundary material and the sandstone sample have the same cross-sectional area.

And 2, knocking the sandstone sample by using a pendulum bob system positioned at the left end to excite stress waves, collecting stress wave signal amplitudes at different propagation distances by using each acceleration sensor when the stress waves are propagated in the sandstone sample, and evaluating the inhibition effect of different boundary materials on the boundary reflection effect by analyzing the attenuation rules of the stress wave signal amplitudes at the different propagation distances.

And 3, simplifying a calculation model of the optimal wave impedance of the boundary material on the basis of the stress wave propagation indoor test, and only considering the transflective effect of the stress wave among the sandstone sample, the boundary material and the cushion block. As shown in figure 2, a transflectance calculation model of stress waves in the three media is established, and the wave impedance value of the sandstone sample is Z_a＝6.96×10⁶kg/m²S, wave impedance value of boundary material Z_bWave impedance value of the steel pad is Z_c＝41.08×10⁶kg/m²·s。

Step 4, when the excited stress wave is transmitted to the boundary material from the sandstone sample, a first transflect phenomenon occurs at the interface of the sample and the boundary material, and reflected waves V are respectively generated_R1And a transmitted wave V_T1The expression is shown in the following formula 2, wherein the reflected wave V_R1Returning to sandstone sample along original path, and transmitting wave V_T1Into the boundary material.

In the formula: v_IIs the initial incident wave.

Step 5, when the transmitted wave V_T1When the light beam continuously propagates from the boundary material to the cushion block, a second transflective phenomenon occurs at the interface between the boundary material and the cushion block to respectively generate reflected waves V_R2And a transmitted wave V_T2The expression is shown in the following formula 3, wherein the reflected wave V_R2Returning to the boundary material along the original path, transmitting the wave V_T2And enters the cushion block.

Step 6, only considering the transflective effect of the stress wave among the sandstone sample, the boundary material and the cushion block, only reflecting wave V returning into the boundary material is reflected_R2And (6) carrying out analysis. When the reflected wave V is reflected_R2When the sandstone sample is continuously transmitted from the boundary material, a third transflectance phenomenon occurs at the interface of the sample and the boundary material, and reflected waves V are respectively generated_R3And a transmitted wave V_T3The expression is shown in formula 4, wherein the reflected wave V is_R3Returning to the boundary material along the original path, transmitting the wave V_T3Into a sandstone sample.

Step 7, and so on, the reflected wave V_R3Continuously generating multiple transflections between the interface of the sample and the boundary material and between the interface of the boundary material and the cushion block, and repeatedly adopting the methods of the step 5 and the step 6 to obtain V_T5、V_T7Etc.

The sum of the left-going stress waves reflected back to the sandstone sample is recorded as V_LWhich comprises V_R1、V_T3、V_T5…. As the number of transflects increases, the magnitude of the left-going stress wave reflected back into the rock sample decreases gradually. Therefore, to simplify the calculation, only V is taken_LThe first three items in the expression are calculated, the size of the subsequent left traveling wave can be ignored, and then V is obtained_LThe expression of (b) is shown in formula 5;

V_L＝V_R1+V_T3+V_T5 (5)

step 8, mixing V_R1、V_T3、V_T5Substituting the calculation formula of (2) into the formula 4, then V_LThe expression of (b) is shown in formula 6.

Wherein the wave impedance value Z of the sandstone sample_a＝6.96×10⁶kg/m²S wave impedance value of the pad is Z_c＝41.08×10⁶kg/m²S, can obtain V_L/V_IRatio and boundary material wave impedance (Z)_b) The variation curve of (2) is shown in fig. 3.

As can be seen from FIG. 3, the wave impedance value Z increases from the point O to the point A_bIncrease from 0 to 1.12X 10⁶kg/m²·s，V_L/V_IThe ratio curve of (A) shows a steep falling trend; current wave impedance value Z_b＝1.12×10⁶kg/m²S, the amplitude of the left traveling wave is zero, and theoretically, the point A in FIG. 3 represents the optimal wave impedance value of the boundary material under the working condition; increasing from point A to point B, the wave impedance value Z_bFrom 1.12X 10⁶kg/m²S increases to 6.82X 10⁶kg/m²·s，V_L/V_IThe ratio of (A) is increased from zero to-0.71, namely the amplitude of the left traveling wave is gradually increased; after point B, with the wave impedance value Z_bContinued increase of V_L/V_IThe ratio of (a) gradually tends to be stable.

In conclusion, when V is_L/V_IWhen the ratio of the wave impedance values is zero, the amplitude values of all left-going stress waves reflected back to the sandstone sample are minimum, and the corresponding wave impedance value is the optimal wave impedance value Z of the boundary material_b＝1.12×10⁶kg/m²S. When V is_L/V_IWhen the ratio of (d) is zero, equation 6 can be transformed into equation 1.

And 9, calculating by adopting the formula 1 based on the calculation model of the optimal wave impedance of the boundary material to obtain the optimal wave impedance value of the boundary material under the test working condition of 1.12 multiplied by 10⁶kg/m²·s。

By replacing boundary materials with different wave impedance values, multiple stress wave propagation indoor tests are respectively carried out, so that the optimal wave impedance calculation method related to the embodiment is verified. Three mediums with different wave impedance values are mainly selected as boundary materials, the medium a is rubber, and the wave impedance value is 0.35 multiplied by 10⁶kg/m²S; medium b is steel block, wave impedance value is 41.08 x 10⁶kg/m²S; medium c is pine, and wave impedance value is 1.89 x 10⁶kg/m²S (nearest).

And step 10, respectively taking the three media as boundary materials, and exciting a stress wave signal by using pendulum bob knocking under each working condition. Five repetitive strokes were performed for each condition in order to obtain a stable waveform signal. Stress wave signal amplitude data at different propagation distances are collected through acceleration sensors uniformly distributed on a sandstone sample, and the inhibition effect of three media serving as boundary materials on the boundary reflection effect is analyzed. Fig. 4, 5 and 6 are curves of the amplitude of the stress wave signal with the propagation distance when rubber, a steel block and pine are used as boundary materials respectively.

Step 11, according to V in FIG. 3_L/V_IAccording to a curve of the ratio value along with the change of the wave impedance value of the boundary material, when rubber and a steel block are used as the boundary material, the generated left-going reflected waves are respectively 0.75 time and 0.7 time of the incident wave, and it can be seen from fig. 4 and 5 that along with the increase of the propagation distance, the signal amplitudes received by two sensors close to the boundary of the rock sample are increased, because the reflected wave generated by the stress wave at the end part of the rock sample and the original wave form have a superposition amplification effect, the inhibition effect of the rubber and the steel block on the boundary reflection effect is poor.

When pine is used as the boundary material, the left-hand reflected wave is 0.21 times of the incident wave, and it can be seen from fig. 6 that the signal amplitudes of the stress waves are gradually decreased along with the increase of the propagation distance without abnormal increase.