CN107894311B - Model Test Method for Earthquake Damage of Earth-rock Dam - Google Patents

Abstract

The invention relates to the technical field of dynamic model tests of geotechnical structures, and discloses a model test method for earthquake damage of earth-rock dams. The invention includes: carrying out model similarity design according to the similarity rate requirements of the earth-rock dam model test; making the test model; carrying out the white noise microseismic test on the model dam to determine the natural vibration frequency of the model dam; Design seismic waves to be compressed to obtain seismic waves with the same amplitude and different spectral characteristics under different time-similar scales; then conduct vibration tests, and select the time-similar scales of seismic waves in the earthquake damage test; then, under different acceleration amplitude conditions, model The seismic damage vibration test of the dam increases the seismic wave acceleration amplitude from small to large, and tests the acceleration response and displacement response of the dam until the dam is damaged by the earthquake. The invention provides a scientific and feasible model test method for the research on the earthquake collapse failure problem of the high earth-rock dam structure which cannot be realized originally.

Description

Model Test Method for Earthquake Damage of Earth-rock Dam

technical field

The invention relates to the technical field of dynamic model tests of geotechnical structures, in particular to a model test method for earthquake damage of earth-rock dams.

Background technique

Due to its strong adaptability to terrain, high earth-rock dam is the main type of dam in hydropower development. More than 80% of the country's hydropower resources are concentrated in the western region of my country. Among the 13 major hydropower bases planned by the state, 7 major hydropower bases are located in the western region. A number of 200m high earth-rock dams and even 300m high earth-rock dams are under construction or will soon start construction building.

However, due to the frequent, high intensity and high intensity of seismic activity in the western region, it has a great impact on the safety of high earth-rockfill dams, and the seismic load often becomes the controlling condition for the feasibility of dam construction. Dam failures due to earthquakes will have disastrous consequences and secondary disasters.

Therefore, it is very necessary to strengthen the research on the mechanism of earthquake damage of high earth-rockfill dams, the research on the effectiveness of anti-seismic measures of high earth-rockfill dams and the research on the earthquake damage mode. Shaking table model tests of earth-rock dams can study the basic laws of earth-rock dam seismic response properties, failure mechanism, and the influence of each main parameter on the seismic dynamic response of the dam body under certain control conditions, and evaluate the overall seismic capacity of the structure. The attention of earthquake research workers. But the problem is that due to the huge geometric size of the high earth-rock dam, the section of the dam body exceeds 1000m, and the length reaches several kilometers. Due to the limitations, it is difficult to carry out earthquake damage tests, it is impossible to reproduce the earthquake damage of earth-rockfill dams, and it is difficult to conduct research on earthquake damage modes.

Contents of the invention

The invention provides a model test method for earthquake damage of an earth-rock dam by adopting a shaking table model test to simulate extreme earthquakes and realize complete model destruction.

The technical problem to be solved is: the geometric size of the high earth-rock dam is huge, and the 1g shaking table and the ng centrifuge shaking table have limited bearing capacity and maximum acceleration due to the limitation of the equipment itself, so it is impossible to accurately reproduce the earthquake collapse of the earth-rock dam Due to the severe earthquake damage situation, the current model design method for high earth-rock dams above 200m is immature, and there is a large deviation from the actual situation, making it difficult to study the earthquake damage model.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

2, the model test method of earth-rock dam earthquake damage of the present invention, comprises the following steps:

Step 1. Carry out model similarity design according to the similarity ratio requirements of the earth-rock dam model test;

Step 2. Make a test model according to the design requirements of the model similarity;

Step 3, carry out the white noise microseismic test to the model dam to determine the natural frequency of the model dam;

Step 4. According to the natural frequency of the model dam and the site-designed seismic wave spectrum characteristics of the prototype earth-rockfill dam, select a group of time-similar scales to compress the design seismic waves of the site to obtain the same amplitude and different spectral characteristics under different time-similar scales seismic waves;

Step 5. According to the seismic waves under the same amplitude and similar scale conditions at different times, carry out vibration tests to determine the acceleration response and dam surface displacement response of the model dam under the action of seismic waves of similar scales at different times. Combine the acceleration response and The time similarity scale of the seismic wave in the earthquake damage test is selected for the surface displacement response of the dam body;

Step 6. According to the determined time similar scale, under different acceleration amplitude conditions, carry out the earthquake damage vibration test of the model dam, start from the design peak earthquake acceleration, increase the seismic wave acceleration amplitude from small to large, and test the dam acceleration Response and displacement response until dam seismic failure.

The model test method of earth-rock dam earthquake damage of the present invention, further, model similarity design in step 1 specifically comprises the following steps:

B. Determine the geometric similarity constant C _l of the model;

Determine the geometric similarity constant C _l of the model according to formula (1),

In the formula: C _l is the geometric similarity constant of the model;

H _p is the height of the prototype dam, m;

H _m is the height of the model dam, m;

B. Determine the density similarity constant C _ρ of the model;

Through the triaxial compression test, the effective internal friction angles of the soil-rock materials of the prototype dam and the soil-rock materials of the model dam are determined under a certain stress state and different dry densities, and then the dry filling density ρ _m of the model dam is determined according to the effective internal friction angles, and then Determine the density similarity constant C _ρ according to formula (3);

C _ρ = ρ _p /ρ _m (3)

In the formula: C _ρ is the density similarity constant;

ρ _p is the design dry density of prototype dam soil and rock, g/cm ³ ;

ρ _m is the filling dry density of the model dam soil and rock, g/cm ³ ;

C. Determine the modulus coefficient similarity constant C _c ;

According to the dynamic deformation characteristic test, the dynamic shear modulus coefficients of the prototype dam soil-rock material and the model dam soil-rock material are determined, and then

Determine the modulus coefficient similarity constant C _c according to formula (6);

C _C ＝C _p /C _m (6)

In the formula: C _c is the similar constant of the modulus coefficient;

C _p is the dynamic shear modulus coefficient related to the design dry density of prototype dam soil and rock;

C _m is the dynamic shear modulus coefficient related to the design dry density of the model dam soil and rock;

D. Determine other similar constants, including stress similar constants, shear modulus similar constants, strain similar constants, velocity similar constants, time similar constants, frequency similar constants, soil damping ratio similar constants, soil effective cohesion similar constants, soil body effective friction coefficient similarity constant and acceleration similarity constant;

E. Determine the key control section of the model dam for real-time acceleration test and displacement test.

The model test method of earth-rock dam earthquake damage of the present invention, further, the determination method of the filling dry density ρ _m of model dam earth-rock material in the step B, specifically comprises the following steps:

a) For the prototype dam soil and stone material, carry out the triaxial compression test under the condition of prototype dam stress state and design dry density, and determine the effective internal friction angle φ' _p of the prototype dam soil and stone material under the condition of design dry density;

b) Carry out triaxial compression tests under low stress state and different dry density conditions for model dam soil and stone materials, and determine the effective internal friction angle φ' _m of model dam soil and stone materials under different filling dry densities;

c) Let the friction angle similarity constant C _φ' be 1, and select the corresponding model dam filling dry density ρ _m according to formula (2);

C _φ' = φ' _p / φ' _m (2)

In the formula: C _φ' is the similar constant of friction angle;

φ' _p is the effective internal friction angle of the prototype dam soil and rock;

φ' _m is the effective internal friction angle of the model dam soil and rock.

The model test method of earth-rock dam earthquake damage of the present invention, further, the determination method of the dynamic shear modulus coefficient of prototype dam earth-rock material and model dam earth-rock material in step C, specifically comprises the following steps:

③ For prototype dam soil and rock, carry out prototype dam stress state and dynamic deformation test under design dry density conditions, obtain the modulus and damping parameters of prototype dam soil and rock under design dry density conditions, and determine the prototype dam soil and rock based on this The functional relationship between the maximum shear modulus and the average effective stress is formula (4), from which the dynamic shear modulus C _p of the prototype dam soil and stone is obtained;

In the formula: G _max is the maximum shear modulus, that is, the shear modulus of the soil unit at small strain;

C _p is the dynamic shear modulus coefficient related to the design dry density of prototype dam soil and rock;

_Pa is the atmospheric pressure, which is 98kPa;

σ ₀ ′ is the mean effective stress;

n _p is a dimensionless exponent;

④ For the model dam soil and stone material, carry out the dynamic deformation characteristic test under the condition of low stress state and model dam filling dry density, obtain the modulus and damping parameters of the model dam soil and stone material under the condition of model dam filling dry density, and determine accordingly The functional relationship between the maximum shear modulus of the model dam soil and rock and the average effective stress is formula (5), from which the dynamic shear modulus C _m of the model dam soil and rock is obtained;

In the formula: G _max is the maximum shear modulus, that is, the shear modulus of the soil unit at small strain;

C _m is the dynamic shear modulus coefficient related to the design dry density of the model dam soil and rock;

_Pa is atmospheric pressure, 98kPa;

σ ₀ ′ is the mean effective stress;

n _m is a dimensionless exponent.

The model test method of earth-rock dam earthquake damage of the present invention, further, the determination method of the critical control section of model dam in the step E, specifically comprises the following steps:

Firstly, according to the terrain and the size of the prototype dam, select the key control section of the prototype dam, then scale it down according to the geometric similarity ratio _C1 , and the section after scale down is the key control section of the model dam; the key control section includes measurement The main control section and the auxiliary measurement control section, the measurement main control section is the largest section passing through the dam bottom or the center of the river bed, and the auxiliary measurement control section is the section near the river bed and the bank slope where the change is severe; the auxiliary measurement The number of control sections is 2-5.

The model test method of earth-rock dam earthquake damage of the present invention, further, the manufacturing method of test model in step 2 specifically comprises the following steps:

Ⅰ. Make a model box; select the key control section according to the size of the prototype dam, shrink the key control section according to the geometric scale C _l , and determine the shape and size of the model box; the box body of the model box is composed of steel plate welding, and the side wall of the steel plate There is a steel frame body fixed on it;

Ⅱ, pouring bedrock; supporting bedrock formwork, pouring concrete; said bedrock formwork is made according to the bedrock shape of the key control section of the prototype dam, and is made according to the _geometric scale C1;

Ⅲ. Filling the dam body;

First draw the filling height markings of each layer in the model box; then carry out formwork support along the dam slope, and then fill the dam body layer by layer, and carry out soil and stone filling of this layer along the formwork supported on the dam slope , the flatness of each layer of filling material is controlled from two directions: the horizontal direction of the dam crest axis and the horizontal direction along the river;

Ⅳ. Filling the dam slope;

The upstream template and the downstream template are supported, and the dam slope is filled, and the dam slope is consistent with the prototype dam.

The model test method of earth-rock dam earthquake damage of the present invention, further, step three methods for determining the natural vibration frequency of the model dam specifically include the following steps:

(1) Carry out white noise microseismic test;

Input white noise with a small amplitude to the model, and conduct a white noise microseismic test. The amplitude of the white noise is 0.03-0.05g. The acceleration excitation X(t) and The acceleration response Y(t) of different parts of the dam body;

(2), determine the acceleration frequency response function H(ω) of the model dam;

According to the self-power spectrum of platform acceleration excitation X(t) and the cross-power spectrum of acceleration responses Y(t) and X(t) at different parts of the dam body, the acceleration frequency response function H(ω );

In the formula: G _XX (ω) is the self-power spectrum of table acceleration excitation X(t);

G _XY (ω) is the cross-power spectrum of the acceleration response Y(t) at a certain point of the dam body and the acceleration excitation X(t) of the response platform;

(3), determine the natural frequency of the model dam;

The modal analysis of the acceleration frequency response function H(ω) is carried out using the modal parameter identification technology to determine the natural frequency f _m of the model dam.

The model test method of earth-rock dam earthquake damage of the present invention, further, the determination method of time similar scale in step 4, specifically comprises the following steps:

(Ⅹ) According to the seismic wave preeminent frequency f _e and the determined model dam natural frequency f _m , determine the frequency compression scale that can make the compressed seismic wave preeminent frequency the same as the model dam natural frequency according to formula (8);

In the formula: C _fr is the frequency compression scale;

f _m is the natural frequency of the model dam;

f _e is the seismic wave preeminent frequency;

(Ⅺ) According to the maximum seismic wave frequency compression scale C _fr in the x, y, and z directions, determine its corresponding time compression scale C _tr according to formula (9), and thus determine a set of time similarity scales C _t ;

In the formula: C _tr is the time compression scale of seismic wave;

C _fr is the frequency compression scale;

(Ⅻ) Compress the design seismic waves according to a set of time similarity scales determined to obtain seismic waves with the same amplitude and different spectral characteristics under different time similarity scales.

The model test method of earth-rock dam earthquake damage of the present invention, further, the selection method of the time similarity scale of seismic wave in the earthquake damage test in the step 5 specifically comprises the following steps;

(5-1) Statistically analyze the acceleration of the dam crest measuring point under similar scale conditions at different times, divide the distribution area of the acceleration according to the level of the acceleration, and select a group of higher accelerations from it;

(5-2) determine the sample standard deviation of selecting a group of accelerations;

(5-3) When the sample standard deviation of the acceleration is not greater than 0.01, it means that the acceleration responses of this group are close; compare the displacement responses of the crest surface at different times corresponding to the acceleration responses at similar scales, and determine that the displacement of the crest surface is the largest The time similarity scale of is used as the time compression scale of seismic wave in earthquake damage test;

(5-4) When the selected acceleration sample standard deviation is greater than 0.01, repeat step (5-1), according to the level of acceleration, re-divide the distribution area of acceleration, select a group of accelerations with higher response, and then repeat step (5 -2) to (5-3), until the standard deviation of the selected acceleration samples is not greater than 0.01, determine the time compression scale of seismic waves in the earthquake damage test.

In the model test method of earth-rock dam earthquake damage of the present invention, further, the seismic wave acceleration amplitude value input in the earthquake damage vibration test in step 6 is determined according to the following method:

(6-1) Determine the initial acceleration amplitude a _d ;

Determine the initial acceleration amplitude a _d according to the peak ground acceleration of the dam site at a probability level of exceeding 2% in 100 years;

(6-2) Determine the seismic wave acceleration target value a _imax input in the earthquake damage vibration test,

a _imax =a _d +(i-1)×Δa (10)

In the formula, a _imax is the i-th input acceleration target value of the earthquake damage test;

i is the serial number of the earthquake damage test condition;

Δa is the acceleration increment, generally 0.05~0.2;

a _d is the initial acceleration amplitude in the earthquake damage vibration test.

Compared with the prior art, the model test method for earth-rock dam earthquake damage of the present invention has the following beneficial effects:

The model test method for earthquake damage of an earth-rock dam in the present invention starts with the model dam, the structural dynamic characteristics and the frequency spectrum characteristics of the input seismic wave, adopts the seismic wave with suitable frequency spectrum characteristics, simulates the extreme earthquake through the shaking table model test, and realizes the complete destruction of the model dam , to study the earthquake failure mechanism and failure mode of high earth-rockfill dams under extreme earthquakes and the verification of the effectiveness of seismic measures under extreme earthquakes.

The model test method for earth-rock dam earthquake damage of the present invention carries out model similarity design according to the requirement of model test similarity rate, determines foundation similarity constant through triaxial compression test and dynamic deformation characteristic test, and then determines other similarity constants, carries out model design and manufacture, model design It is more reasonable, and the simulation accuracy is high. The natural vibration frequency of the model dam can adapt to the selected seismic wave, and the complete destruction of the model dam can be realized.

The model test method of earthquake damage of earth-rock dams of the present invention is not only applicable to the earthquake damage model tests of general earth-rock dams, but also applicable to the earthquake damage model tests of high earth-rock dams with a height of more than 200m and superhigh earth-rock dams with a height of more than 300m, which can realize high The complete collapse of the earth-rock dam model avoids the situation that the limit test conditions that the shaking table can achieve due to its own performance limitations cannot meet the complete collapse of the model dam, and provides a scientific basis for the seismic design and performance evaluation of high earth-rock dams.

Below in conjunction with accompanying drawing, the model test method of earth-rock dam earthquake damage of the present invention will be further described.

Description of drawings

Fig. 1 is the control section distribution schematic diagram of high earth-rock dam in the embodiment;

Fig. 2 is the example of the acceleration time history of measuring the central line measuring point of the main control section in the embodiment;

Fig. 3 is the self-power spectrum example of the acceleration excitation of measuring the main control section center line measuring point in the embodiment;

Fig. 4 is an example of the acceleration frequency response function of the centerline measuring point of the main control section measured in the embodiment.

Detailed ways

Now take the model failure test of a high earth-rock dam of a certain hydropower station as an example to illustrate the model test method of the present invention.

The basic seismic intensity of the dam site area of a certain hydropower station is Ⅶ degree, and the key water retaining structure is a 211m high face rockfill dam.

The specific model test method for earth-rock dam earthquake damage includes the following steps:

Step 1. Carry out model similarity design according to the similarity ratio requirements of the earth-rock dam model test;

The vibration table used in the simulation test can be a 1g vibration table or a ng centrifuge vibration table; a 6m×6m 1g vibration table is used in the test of this embodiment.

C. Determine the geometric similarity constant C _l of the model;

According to the performance parameters of the shaking table, the dam height of the model is determined to be 1.50m; according to the data records, the prototype dam height is 211m, and the geometric similarity constant C _l of the model is determined to be 140.7 by formula (1);

In the formula: C _l is the geometric similarity constant of the model;

H _p is the height of the prototype dam, m;

H _m is the height of the model dam, in m.

D. Determine the density similarity constant C _ρ of the model;

Through the triaxial compression test, determine the effective internal friction angle of the prototype dam soil-rock material and the model dam soil-rock material under a certain stress state and different dry density conditions, and then determine the density similarity constant C _ρ according to the effective internal friction angle, which specifically includes the following steps:

a), carry out prototype dam stress state, the triaxial compression test under the condition of design dry density to prototype dam soil-rock material, determine the effective internal friction angle φ ' _p of prototype dam soil-rock material under design dry density ρ _p condition;

Among them, the design dry density ρ _p of the prototype dam soil and rock is 2.15g/cm ³ ; in the actual dam body, the dynamic characteristics of the dam body are mainly determined by the soil under relatively high confining pressure. , carry out a triaxial compression test under the stress state of 98kPa, and determine that the effective internal friction angle φ' _p of the prototype dam soil and rock is 47°;

b) Carry out triaxial compression tests under low stress state and different dry density conditions for model dam soil and stone materials, and determine the effective internal friction angle φ' _m of model dam soil and stone materials under different filling dry densities;

In the model dam, the soil stress in the dam body is relatively low. For the 1.5m high model dam in this embodiment, the confining pressure at the centroid position of the section is about 20kPa; Triaxial compression tests under low stress state and different dry densities determine the effective internal friction angle φ' _m of model dam soil and stone materials under different filled dry densities under 20kPa confining pressure, as shown in Table 1;

Table 1 Triaxial compression test results of model dam soil and rock materials

Model dam soil and rock Dry density (g/cm³) φ'_m(°) Group 1 1.79 44.4 2 teams 1.89 47.0 3 groups 1.99 50.1 4 groups 2.09 54.4

c), the friction angle similarity constant C _φ' is 1, according to the formula (2), select the corresponding model dam filling dry density ρ _m ;

C _φ' = φ' _p / φ' _m (2)

In the formula: C _φ' is the similar constant of friction angle;

φ' _p is the effective internal friction angle of the prototype dam soil and rock;

φ' _m is the effective internal friction angle of the model dam soil and rock;

Let the friction angle similarity constant C _φ' = 1 to ensure that the average effective internal friction angle of the prototype dam and the model dam are equal, that is, determine φ' _m = φ' _p = 47°, according to the triaxial compression test results in step b), determine When φ' _m = 47°, the corresponding model dam filling dry density ρ _m is 1.89g/cm ³ ;

D), according to formula (3), determine that density similarity constant C _ρ is 1.14;

C _ρ = ρ _p /ρ _m (3)

In the formula: C _ρ is the density similarity constant;

ρ _p is the design dry density of prototype dam soil and rock, g/cm ³ ;

ρ _m is the filling dry density of the model dam soil and rock, g/cm ³ .

C. Determine the modulus coefficient similarity constant C _c ;

According to the dynamic deformation characteristic test, the modulus coefficient similarity constant C _c is determined, which specifically includes the following steps:

① For the prototype dam soil and rock, carry out the prototype dam stress state and the dynamic deformation characteristics test under the condition of design dry density, obtain the modulus and damping parameters of the prototype dam soil and rock under the design dry density condition, and determine the prototype dam soil and rock accordingly. The functional relationship between the maximum shear modulus and the average effective stress is formula (4);

In the formula: G _max is the maximum shear modulus, that is, the shear modulus of the soil unit at small strain;

C _p is the dynamic shear modulus coefficient related to the design dry density of prototype dam soil and rock;

_Pa is the atmospheric pressure, which is 98kPa;

σ ₀ ′ is the mean effective stress;

n _p is a dimensionless exponent;

The relevant modulus coefficients of the prototype dam soil and stone materials determined from this are shown in Table 2.

Table 2 Correlation modulus coefficients of prototype dam soil and rock

Dry density g/cm³ n_p C_p Prototype dam soil and rock 2.15 0.32 2400

② For the model dam soil and stone material, carry out the dynamic deformation characteristic test under the condition of low stress state and model dam filling dry density, obtain the modulus and damping parameters of the model dam soil and stone material under the condition of model dam filling dry density, and determine accordingly The functional relationship between the maximum shear modulus of the model dam soil and rock and the average effective stress is formula (5);

In the formula: G _max is the maximum shear modulus, that is, the shear modulus of the soil unit at small strain;

C _m is the dynamic shear modulus coefficient related to the design dry density of the model dam soil and rock;

_Pa is atmospheric pressure, 98kPa;

σ ₀ ′ is the mean effective stress;

n _m is a dimensionless exponent;

The relevant modulus coefficients of the model dam soil and rock materials thus determined are shown in Table 3.

Table 3 Correlation modulus coefficients of model dam soil and rock materials

Dry density g/cm³ n_m C_m Model dam soil and rock 1.89 0.573 1375

③ According to the formula (6), it is determined that the modulus coefficient similarity constant C _c is 1.745;

C _C ＝C _p /C _m (6)

In the formula: C _c is the similar constant of the modulus coefficient;

C _p is the dynamic shear modulus coefficient related to the design dry density of prototype dam soil and rock;

C _m is the dynamic shear modulus coefficient related to the design dry density of model dam soil and rock.

D. Determine other similar constants, including stress similar constants, shear modulus similar constants, strain similar constants, velocity similar constants, time similar constants, frequency similar constants, soil damping ratio similar constants, soil effective cohesion similar constants, soil body effective friction coefficient similarity constant and acceleration similarity constant;

According to the similarity constants that have been obtained above, the geometric similarity constant C _l is 140.7, the density similarity constant C _ρ is 1.04, the modulus coefficient similarity constant C _c is 1.745, and the friction angle similarity constant C _φ' is 1. According to Table 4 The formula determines the remaining similar constants.

Table 4 Other similar constants

E. Determine the key control section of the model dam for real-time acceleration testing and displacement testing;

First, select the key control section of the prototype dam according to the terrain and the size of the prototype dam, and then scale it down according to the geometric similarity ratio of 140.7. The scaled section is the key control section of the model dam; arrange test instruments on the key control section; The main measurement control section selected is the largest section passing through the dam bottom or the center of the river bed, and then 2-5 auxiliary measurement control sections are selected, and the auxiliary measurement control sections are selected near the river valley and the section where the bank slope changes sharply;

The dam site area of the high earth-rock dam described in this embodiment is an asymmetric V-shaped valley with narrow valley and steep bank slope, and the vertical 9 section passing through the bottom of the valley is the largest section, so the vertical 9 section corresponding to the prototype dam is selected as the quantity Measure the main control section, and at the same time select the left side of the main control section (close to the left bank) corresponding to the vertical 7 and vertical 5 sections of the prototype dam, and the right side of the main control section (close to the right bank) corresponding to the longitudinal section of the prototype dam. Section 11 is the auxiliary measurement control section, and the specific section distribution is shown in Figure 1.

The specific arrangement is as follows:

x, y, z represent the horizontal direction along the river, the horizontal direction along the dam axis and the vertical direction respectively;

The measuring instruments used in the acceleration measurement points are the accelerometers on the table and the accelerometers on the control section and the accelerometer on the crest; The horizontal direction along the river is the main direction, and the accelerometers pointing to the horizontal and vertical directions of the dam crest axis are properly arranged; in this embodiment, 22 acceleration measuring points are arranged on the main control section of the measurement, including 16 in the x direction and 3 in the y direction. 3 in the z direction, 2 acceleration measuring points in the x direction on the auxiliary vertical 7 section, 3 acceleration measuring points in the x direction on the vertical 5 section, and 3 acceleration measuring points in the x direction on the vertical 11 section point;

The measuring instruments used at the strain and stress measuring points are strain gauges, which are arranged on each measurement control section, mainly on the main control section, and appropriately arranged on the auxiliary measurement control section;

The measuring instrument used in the displacement measurement point is the optical fiber grating displacement sensor. The optical fiber grating displacement sensor is arranged along the surface of the dam crest and dam slope, buried at different depths, and marked. After the vibration test is completed, the excavation inspection is carried out to monitor the depth of the landslide .

Step 2. Make the test model according to the design requirements of the model similarity, which specifically includes the following steps:

Ⅰ. Make model box;

Select the key control section according to the size of the prototype dam, shrink the key control section according to the geometric scale 140.7, and determine the shape and size of the model box; the model box is composed of steel plates welded and fixed on the side walls of the steel plates; In the embodiment, according to the distribution of the control section shown in Figure 1, the reduction is performed successively to make the model box;

Ⅱ. Pouring bedrock;

The bedrock formwork is supported, and concrete is poured on site to form the bedrock of the reinforced concrete structure, so as to ensure that the natural frequency of the bedrock structure is higher than twice the first-order natural frequency of the model, and the natural frequency of the model adopts a shear wedge Preliminary estimation of the method; the bedrock formwork is made according to the geometric scale reduction according to the bedrock shape of the key control section of the prototype dam;

In order to ensure the accuracy of the formwork, the 3D geometric modeling of the scaled bedrock was carried out with AUTOcad and ANSYS, and it was used to assist in the production of the bedrock pouring formwork;

Ⅲ. Filling the dam body;

First, draw the filling height marking lines of each layer in the model box to ensure that the filling height of each layer does not exceed 20cm. At the same time, determine the weight of the filling soil and stone materials in each layer according to the design density of the rockfill area upstream and downstream of the prototype dam. In order to strictly control the design compaction density, the geometric modeling of each layer of the 3D overall model was carried out to obtain the volume of the filled soil and stone materials in each layer, and then the design density of each layer of the model dam was determined to determine the density of each layer. The weight of the filled soil and stone material; then formwork support is carried out along the dam slope, and then the dam body is filled in layers. In this embodiment, the dam body is filled in 10 layers. The dry density ρ _m is 1.89g/cm ³ , and the earth-rock filling of this layer is carried out along the formwork supported on the slope of the dam. to control;

Ⅳ. Filling the dam slope;

First make the upstream formwork and downstream formwork, the upstream formwork and downstream formwork are designed and manufactured through actual lofting, the formwork is made of wood, and the formwork support is welded with angle steel; then the upstream formwork and downstream formwork are supported, and then the dam slope is filled, and the dam slope and the prototype The dam agrees.

Step 3, the model dam is subjected to a white noise microseismic test to determine the natural frequency of the model dam, which specifically includes the following steps:

(1) Carry out white noise microseismic test;

Input white noise with a small amplitude to the model, and conduct a white noise microseismic test. The white noise amplitude is 0.03-0.05g. In this embodiment, the predetermined input white noise amplitude is 0.05g. The accelerometer on the top of the dam can obtain the table acceleration excitation X(t) and the acceleration response Y(t) of different parts of the dam body;

In the present embodiment, the center line measuring points of the vertical 9 section of the main control section are measured, and the acceleration time history and the self-power spectrum of the acceleration excitation are shown in Figure 2 and Figure 3 respectively;

(2), determine the acceleration frequency response function H(ω) of the model dam;

According to the self-power spectrum of platform acceleration excitation X(t) and the cross-power spectrum of acceleration responses Y(t) and X(t) at different parts of the dam body, the acceleration frequency response function H(ω );

In the formula: G _XX (ω) is the self-power spectrum of table acceleration excitation X(t);

G _XY (ω) is the cross-power spectrum of the acceleration response Y(t) at a certain point of the dam body and the acceleration excitation X(t) of the response platform;

For example, one example of the acceleration frequency response function in the x-direction is shown in Figure 4 for the centerline measurement point of the vertical 9-section of the main control section measured in this embodiment;

(3), determine the natural frequency of the model dam;

The modal analysis of the acceleration frequency response function H(ω) is carried out using the modal parameter identification technology, and the natural frequency f _m of the model dam is determined. The average value of the natural frequency in the x direction is 33.6 Hz, and the natural frequency in the y direction is about 38.0 Hz, and the z-direction natural frequency is about 43.4Hz.

Step 4. According to the natural frequency of the model dam and the seismic wave spectrum characteristics of the prototype earth-rockfill dam site design, select a group of time-similar scales to compress the design seismic waves of the site, and obtain the same amplitude and different spectral characteristics under different compression scales. Seismic waves; specifically include the following steps:

(Ⅹ) According to the seismic wave preeminent frequency f _e and the determined model dam natural frequency f _m , determine the frequency compression scale that can make the compressed seismic wave preeminent frequency the same as the model dam natural frequency according to formula (8). In this embodiment The seismic wave excellent frequency f _e of the dam site is 4.8Hz, and the site design seismic wave vibration duration is 26s. From this, it is determined that the frequency compression scale of the x-direction seismic wave is 0.143, the frequency compression scale of the y-direction seismic wave is 0.126, and the z-direction seismic wave The frequency compression scale is 0.111.

In the formula: C _fr is the frequency compression scale;

f _m is the natural frequency of the model dam;

f _e is the seismic wave preeminent frequency;

(Ⅺ) According to the maximum seismic wave frequency compression scale C _fr in the x, y, and z directions, the corresponding time compression scale C _tr is determined to be 7 according to the formula (9), and thus a set of time similarity scales C _t is determined is 7, 6, 5, 4, 3;

In the formula: C _tr is the time compression scale of seismic wave;

C _fr is the frequency compression scale;

(Ⅻ) Compress the design seismic waves according to a set of time similarity scales determined to obtain seismic waves with the same amplitude and different spectral characteristics under different time similarity scales.

Step 5. According to the seismic waves under the same amplitude and similar scale conditions at different times, carry out vibration tests to determine the acceleration response and dam surface displacement response of the model dam under the action of seismic waves of similar scales at different times. Combine the acceleration response and The time compression scale of seismic wave in the earthquake damage test is selected for the surface displacement response of the dam body;

The selection method of the time similarity scale of seismic waves in the earthquake damage test is as follows:

(5-1) Statistically analyze the acceleration of the dam crest measuring point under similar scale conditions at different times, divide the distribution area of the acceleration according to the level of the acceleration, and select a group of higher accelerations from it;

(5-2) determine the sample standard deviation of selecting a group of accelerations;

(5-3) When the sample standard deviation of the acceleration is not greater than 0.01, it means that the acceleration responses of this group are close; compare the displacement responses of the crest surface at different times corresponding to the acceleration responses at similar scales, and determine that the displacement of the crest surface is the largest The time similarity scale of is used as the time compression scale of seismic wave in earthquake damage test;

Among them, the surface displacement response of the dam body can be judged in combination with the duration of the seismic wave, and the duration of the seismic wave is positively correlated with the accumulation of deformation caused by it;

(5-4) When the standard deviation of the selected acceleration sample is greater than 0.01, repeat step (5-1), according to the height of the acceleration, re-divide the distribution area of the acceleration more densely, and reselect a group of accelerations with a higher response, Then repeat steps (5-2) to (5-3), until the selected acceleration sample standard deviation is not greater than 0.01, determine the time compression scale of the seismic wave in the earthquake damage test;

The vibration test in this example shows that when the time similarity scale C _t = 4-7, the acceleration response of the model dam has little difference, and the standard deviation of the sample data is 0.078, but it is significantly higher than that of the model dam when C _t = 3 The acceleration response of the dam; the duration of the seismic wave and the amount of dam crest collapse caused by each time compression scale are shown in Table 5.

Table 5 Seismic wave duration and its crest collapse

Time similarity scale C_t 7 6 5 4 3 Seismic wave duration/s 3.7 4.3 5.2 6.5 8.7 Average seismic subsidence of the dam crest/mm 1.2 1.8 2.5 3.2 2.6

It can be seen from Table 5 that, for the time similarity scale C _{t = 4-7 when the acceleration response of the model dam is not much different, when the time similarity scale C t =} 4, the duration of the seismic wave is 6.5s, and the average subsidence of the dam crest is The largest amount is 3.2mm, so combining the acceleration response and the displacement response of the dam crest surface, C _t = 4 is selected as the time similarity scale of seismic waves in the earthquake damage test.

Step 6. According to the determined time similar scale, under different acceleration amplitude conditions, carry out the earthquake damage vibration test of the model dam, start from the design peak earthquake acceleration, increase the seismic wave acceleration amplitude from small to large, and test the dam acceleration Response and displacement response until dam earthquake failure;

The seismic wave acceleration amplitude input in the earthquake damage vibration test is determined according to the following method:

(6-1) Determine the initial acceleration amplitude a _d ;

According to the peak ground acceleration of the 100-year probability level of the dam site exceeding the probability of 2%, determine the initial acceleration amplitude a _d , and determine the initial acceleration amplitude a _d to be 0.299 in this embodiment;

(6-2) Determine the seismic wave acceleration target value a _imax input in the earthquake damage vibration test,

a _imax =a _d +(i-1)×Δa (10)

In the formula, a _imax is the i-th input acceleration target value of the earthquake damage test;

i is the serial number of the earthquake damage test condition;

Δa is the acceleration increment, generally 0.05 to 0.2, and the value of Δa in this embodiment is 0.072;

a _d is the initial acceleration amplitude in the earthquake damage vibration test;

In the earthquake destructive vibration test in this embodiment, the amplitude of the input seismic wave acceleration is shown in Table 5, and gradually increases from small to large.

Table 5 The seismic wave acceleration amplitude input in the earthquake damage vibration test

Working condition serial number seismic wave acceleration amplitude 1 0.299g 2 0.371g 3 0.443g 4 0.515g 5 0.587g 6 0.659g 7 0.731g 8 0.803g 9 0.875g

The test process shows that under the vibration of the seismic wave acceleration amplitude of 0.299g, the deformation of the model dam is very small; with the increase of the seismic wave acceleration amplitude, under the vibration of 0.371g, it is equivalent to checking the ground rock Peak acceleration, which is equivalent to the 100-year probability level earthquake situation of 1% probability of exceeding, the range of rolling stones or shallow sliding of the model dam gradually expands; in the process of gradually increasing the acceleration amplitude of 0.443g ~ 0.731g, the vibration effect gradually becomes stronger , the damage scope and degree of the dam gradually increased. Under the action of a strong earthquake with a peak acceleration of 0.515g, the downstream slope of the dam body will slide as a whole, and there is a possibility of a large landslide, and the dam crest and the dam body will suffer severe earthquake damage; During the severe vibration of 0.875g, the downstream dam slope collapsed and damaged as a whole, and the entire model dam suffered irreparable and complete earthquake damage.

In the earthquake damage vibration test, the data recorded at each measuring point can be used as the basic data for analyzing and studying the earthquake damage mechanism and failure mode of high earth-rock dams under the action of extreme earthquakes. Provide an effective research key support means and scientific basis.

The above-mentioned embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the scope of the present invention. Variations and improvements should fall within the scope of protection defined by the claims of the present invention.

Claims (10)

1. The model test method of earth-rock dam earthquake damage is characterized in that: comprise the following steps: Step 1. Carry out model similarity design according to the similarity ratio requirements of the earth-rock dam model test; Step 2. Make a test model according to the design requirements of the model similarity; Step 3, carry out the white noise microseismic test to the model dam to determine the natural frequency of the model dam; Step 4. According to the natural frequency of the model dam and the site-designed seismic wave spectrum characteristics of the prototype earth-rockfill dam, select a group of time-similar scales to compress the design seismic waves of the site to obtain the same amplitude and different spectral characteristics under different time-similar scales seismic waves; Step 5. According to the seismic waves under the same amplitude and similar scale conditions at different times, carry out vibration tests to determine the acceleration response and dam surface displacement response of the model dam under the action of seismic waves of similar scales at different times. Combine the acceleration response and For the surface displacement response of the dam body, the time similarity scale of the seismic wave in the earthquake damage vibration test is selected; Step 6. According to the determined time similar scale, under different acceleration amplitude conditions, carry out the earthquake damage vibration test of the model dam, starting from the design peak ground acceleration, increase the seismic wave acceleration amplitude from small to large, and test the model dam Acceleration response and displacement response until the earthquake failure of the model dam. 2. the model test method of earth-rock dam earthquake damage according to claim 1, is characterized in that: in step one, model similarity design specifically comprises the following steps: A. Determine the geometric similarity constant C _l of the model; Determine the geometric similarity constant C _l of the model according to formula (1), In the formula: C _l is the geometric similarity constant of the model; H _p is the height of the prototype dam, m; H _m is the height of the model dam, m; B. Determine the density similarity constant C _ρ of the model; Through the triaxial compression test, the effective internal friction angles of the soil-rock materials of the prototype dam and the soil-rock materials of the model dam are determined under a certain stress state and different dry densities, and then the dry filling density ρ _m of the model dam is determined according to the effective internal friction angles, and then Determine the density similarity constant C _ρ according to formula (3); C _ρ = ρ _p /ρ _m (3) In the formula: C _ρ is the density similarity constant; ρ _p is the design dry density of prototype dam soil and rock, g/cm ³ ; _ρm is the filling dry density of the model dam soil and rock, g/cm ³ ; C. Determine the modulus coefficient similarity constant C _c ; Determine the dynamic shear modulus coefficients of the prototype dam soil-rock material and the model dam soil-rock material respectively according to the dynamic deformation characteristic test, and then determine the similarity constant C _c of the modulus coefficient according to formula (6); C _C ＝C _p /C _m (6) In the formula: C _c is the similar constant of the modulus coefficient; C _p is the dynamic shear modulus coefficient related to the design dry density of prototype dam soil and rock; C _m is the dynamic shear modulus coefficient related to the design dry density of the model dam soil and rock; D. Determine other similar constants, including stress similar constants, shear modulus similar constants, strain similar constants, velocity similar constants, time similar constants, frequency similar constants, soil damping ratio similar constants, soil effective cohesion similar constants, soil body effective friction coefficient similarity constant and acceleration similarity constant; E. Determine the key control section of the model dam for real-time acceleration test and displacement test. 3. the model test method of earth-rock dam earthquake damage according to claim 2 is characterized in that: the determination method of the dry density _p of model dam earth-stone material in step B, specifically comprises the following steps: a) For the prototype dam soil and stone material, carry out the triaxial compression test under the condition of prototype dam stress state and design dry density, and determine the effective internal friction angle φ' _p of the prototype dam soil and stone material under the condition of design dry density; b) Carry out triaxial compression tests under low stress state and different dry density conditions for model dam soil and stone materials, and determine the effective internal friction angle φ' _m of model dam soil and stone materials under different filling dry densities; c) Let the friction angle similarity constant C _φ' be 1, and select the corresponding model dam filling dry density ρ _m according to the formula (2); C _φ' = φ' _p / φ' _m (2) In the formula: C _φ' is the similar constant of friction angle; φ' _p is the effective internal friction angle of the prototype dam soil and rock; φ' _m is the effective internal friction angle of the model dam soil and rock. 4. the model test method of earth-rock dam earthquake failure according to claim 2 is characterized in that: the determination method of the dynamic shear modulus coefficient of prototype dam earth-rock material and model dam earth-rock material in step C, specifically comprises the following steps: ① For the prototype dam soil and rock, carry out the prototype dam stress state and the dynamic deformation characteristics test under the condition of design dry density, obtain the modulus and damping parameters of the prototype dam soil and rock under the design dry density condition, and determine the prototype dam soil and rock accordingly. The functional relationship between the maximum shear modulus and the average effective stress is formula (4), from which the dynamic shear modulus C _p of the prototype dam soil and rock is obtained; In the formula: G _max is the maximum shear modulus, that is, the shear modulus of the soil unit at small strain; C _p is the dynamic shear modulus coefficient related to the design dry density of prototype dam soil and rock; _Pa is the atmospheric pressure, which is 98kPa; σ ₀ ′ is the mean effective stress; n _p is a dimensionless exponent; ② For the model dam soil and stone material, carry out the dynamic deformation characteristic test under the condition of low stress state and model dam filling dry density, obtain the modulus and damping parameters of the model dam soil and stone material under the condition of model dam filling dry density, and determine accordingly The functional relationship between the maximum shear modulus of the model dam soil and rock and the average effective stress is formula (5), from which the dynamic shear modulus C _m of the model dam soil and rock is obtained; In the formula: G _max is the maximum shear modulus, that is, the shear modulus of the soil unit at small strain; C _m is the dynamic shear modulus coefficient related to the design dry density of the model dam soil and rock; _Pa is atmospheric pressure, 98kPa; σ ₀ ′ is the mean effective stress; n _m is a dimensionless exponent. 5. the model test method of earth-rock dam earthquake damage according to claim 2 is characterized in that: the determining method of the critical control section of model dam in the step E, specifically comprises the following steps: First, according to the topography and the size of the prototype dam, select the key control section of the prototype dam, and then scale it down according to the geometric similarity constant _C1 , the section after scale down is the key control section of the model dam; the key control section includes measurement The main control section and the auxiliary measurement control section, the measurement main control section is the largest section passing through the dam bottom or the center of the river bed, and the auxiliary measurement control section is the section near the river bed and the bank slope where the change is severe; the auxiliary measurement The number of control sections is 2-5. 6. the model test method of earth-rock dam earthquake damage according to claim 1, is characterized in that: the manufacturing method of test model in step 2, specifically comprises the following steps: Ⅰ. Make a model box; select the key control section according to the size of the prototype dam, shrink the key control section according to the geometric similarity constant C _l , and determine the shape and size of the model box; the box body of the model box is composed of steel plate welding, and the side wall of the steel plate There is a steel frame body fixed on it; Ⅱ. Pouring the bedrock; supporting the bedrock formwork and pouring concrete; the bedrock formwork is made according to the bedrock shape of the key control section of the prototype dam, and is made according to the _geometric similarity constant C1; Ⅲ. Filling the dam body; First draw the filling height markings of each layer in the model box; then carry out formwork support along the dam slope, and then fill the dam body layer by layer, and carry out soil and stone filling of this layer along the formwork supported on the dam slope , the flatness of each layer of filling material is controlled from two directions: the horizontal direction of the dam crest axis and the horizontal direction along the river; Ⅳ. Filling the dam slope; The upstream template and the downstream template are supported, and the dam slope is filled, and the dam slope is consistent with the prototype dam. 7. The model test method of earth-rock dam earthquake damage according to claim 1, is characterized in that: the determination method of step 3 model dam natural frequency, specifically comprises the following steps: (1) Carry out white noise microseismic test; Input white noise with a small amplitude to the model, and conduct a white noise microseismic test. The amplitude of the white noise is 0.03-0.05g. The acceleration excitation X(t) and The acceleration response Y(t) of different parts of the dam body; (2), determine the acceleration frequency response function H(ω) of the model dam; According to the self-power spectrum of platform acceleration excitation X(t) and the cross-power spectrum of acceleration responses Y(t) and X(t) at different parts of the dam body, the acceleration frequency response function H(ω ); In the formula: G _XX (ω) is the self-power spectrum of table acceleration excitation X(t); G _XY (ω) is the cross-power spectrum of the acceleration response Y(t) at a certain point of the dam body and the acceleration excitation X(t) of the platform; (3), determine the natural frequency of the model dam; The modal analysis of the acceleration frequency response function H(ω) is carried out using the modal parameter identification technology to determine the natural frequency f _m of the model dam. 8. the model test method of earth-rock dam earthquake damage according to claim 1 is characterized in that: the determination method of time similar scale in step 4, specifically comprises the following steps: (Ⅹ) According to the seismic wave preeminent frequency f _e and the determined model dam natural frequency f _m , determine the frequency compression scale that can make the compressed seismic wave preeminent frequency the same as the model dam natural frequency according to formula (8); In the formula: C _fr is the frequency compression scale; f _m is the natural frequency of the model dam; f _e is the seismic wave preeminent frequency; (Ⅺ) According to the maximum seismic wave frequency compression scale C _fr in the x, y, and z directions, determine its corresponding time compression scale C _tr according to formula (9), and thus determine a set of time similarity scales C _t ; In the formula: C _tr is the time compression scale of seismic wave; C _fr is the frequency compression scale; (Ⅻ) Compress the design seismic waves according to a set of time similarity scales determined to obtain seismic waves with the same amplitude and different spectral characteristics under different time similarity scales. 9. The model test method of earth-rock dam earthquake damage according to claim 1, is characterized in that: the selection method of the time similar scale of seismic wave in the earthquake damage vibration test in the step 5, specifically comprises the following steps; (5-1) Statistically analyze the acceleration of the dam crest measuring point under similar scale conditions at different times, divide the distribution area of the acceleration according to the level of the acceleration, and select a group of higher accelerations from it; (5-2) determine the sample standard deviation of selecting a group of accelerations; (5-3) When the sample standard deviation of the acceleration is not greater than 0.01, it means that the acceleration responses of this group are close; compare the displacement responses of the crest surface at different times corresponding to the acceleration responses at similar scales, and determine that the displacement of the crest surface is the largest The time similarity scale of is used as the time compression scale of seismic wave in earthquake damage vibration test; (5-4) When the selected acceleration sample standard deviation is greater than 0.01, repeat step (5-1), according to the level of acceleration, re-divide the distribution area of acceleration, select a group of accelerations with higher response, and then repeat step (5 -2) to (5-3), until the standard deviation of the selected acceleration samples is not greater than 0.01, determine the time compression scale of seismic waves in the earthquake damage vibration test. 10. the model test method of earth-rock dam earthquake damage according to claim 1 is characterized in that: the seismic wave acceleration amplitude value input in the earthquake damage vibration test in the step 6 is determined according to the following method: (6-1) Determine the initial acceleration amplitude a _d ; Determine the initial acceleration amplitude a _d according to the peak ground acceleration of the dam site at a probability level of exceeding 2% in 100 years; (6-2) Determine the seismic wave acceleration target value a _{i max} input in the earthquake damage vibration test, a _{i max} =a _d +(i-1)×Δa (10) In the formula, a _{i max} is the i-th input acceleration target value of the earthquake damage vibration test; i is the sequence number of the seismic damage vibration test; Δa is acceleration increment, take 0.05～0.2; a _d is the initial acceleration amplitude in the earthquake damage vibration test.