CN106812119A - Gasbag-type automatic safety device and its method for designing that face-plate of rockfill dam comes to nothing - Google Patents

Abstract

The gasbag-type automatic safety device that Face Slab of Concrete-faced Rockfill is come to nothing, is arranged in the extrusion side wall under Face Slab of Concrete-faced Rockfill, it is characterised in that automatic safety device is made up of three parts：Protection air bag, gas generator and automatic initiating device, protection air bag therein are installed in the precast concrete extrusion side wall for closing on dam crest position；Described gas generator is by breather pipe and the protection airbags；The amount of coming to nothing detector electric ignition mechanism is provided with described automatic initiating device, the electric ignition mechanism and the hair gas generator are connected, and control the startup of the hair gas generator.The present invention compensate for the blank of prior art; come to nothing between panel and bedding material and the amount of coming to nothing reach harm concrete slab safety value when; automatic gasbag-type protection device; make air bag support panel; so as to improve the stress of concrete slab, the secondary disease such as surface crack and faulting of slab ends is prevented.

Description

Air bag type automatic protection device and its design method for rockfill dam face plate

technical field

The invention relates to a protection device for a dam face, in particular to an airbag-type automatic protection device for the face of a concrete face rockfill dam to be hollowed out, and also relates to a design method of the airbag-type automatic protection device.

Background technique

Concrete face rockfill dams are favored by the dam industry at home and abroad because of their adaptability to topographic and geological conditions, the economy of local materials, and the convenience of construction and operation and maintenance [1,2]. Since my country built the first concrete face rockfill dam in 1982, its design, construction and monitoring technology have made great progress, and now it has become the country with the largest number of concrete face rockfill dams that have been built, are under construction and are planned to be built [3]. Among them, the Qingjiang Shuibuya face rockfill dam, which has been completed and put into operation, has a maximum dam height of 233m, ranking first among similar dam types in the world [1,3]; the maximum dam height of the proposed Ciha Gorge and Dashixia concrete face rockfill dams Even breaking through 250m [4,5]. Once such high dam projects have hidden dangers or dangers, they will pose a major threat to the lives and property of downstream residents, the safety of industrial and agricultural production, and the ecological environment. Therefore, it is of great significance to ensure their long-term, safe and stable operation.

Under the action of load and environmental factors, the coarse-grained materials of face rockfill dams are prone to particle edge breakage and exhibit significant rheological properties, so the dam will undergo considerable late deformation after completion [6], making the stiffness The gap between the larger concrete slab and the cushion material will deteriorate the stress state of the concrete slab, and horizontal cracks along the dam axis will appear [7,8]. Under the action of earthquake load, the rockfill material also shrinks due to particle breakage, and the dam as a whole sinks and makes the concrete face plate and cushion material void[5,9]. Numerical simulation studies on the earthquake failure mechanism of the Zipingpu face rockfill dam show that the shear failure of the horizontal construction joints between the slabs in the second and third phases of the Wenchuan earthquake was also caused by the voiding of the slabs[10,11]. It can be seen that the void between the face plate and the cushion material is an important disease affecting the long-term safety of concrete face rockfill dams. Once it occurs, it will pose a serious threat to the safety of the anti-seepage system.

The panel void caused by the rheology of the rockfill material lasts for a long time and is difficult to detect; while the panel void caused by the subsidence of the rockfill body occurs instantaneously during the earthquake, which cannot be prevented in time. Therefore, it is usually only possible to repair after secondary damage such as cracks on the surface of the panel. The conventional method is to use non-destructive testing methods such as infrared thermal imaging, ground penetrating radar, and acoustic imaging, supplemented by appropriate drilling to check the range and depth of the void, and then fill and grout the void area[12,13] .

At present, in the prior art at home and abroad, there is no device that automatically protects the panel immediately after it is empty, and prevents further damage to the anti-seepage system.

references

[1]Ma H Q, Cao K M.Key technical problems of extra-high concrete facedrock-fill dam.Science China Technological Sciences,2007,50(SM1):20-33.

[2] International Committee on Large Dams. Design and Construction Concept of Concrete Faced Rockfill Dam. Beijing: China Water Resources and Hydropower Press, 2010.

[3] Cao Keming, Wang Yisen, Xu Jianjun, Liu Sihong. Concrete face rockfill dam. Beijing: China Water Resources and Hydropower Press, 2008.

[4] Fu Z Z, Chen S S, Wang T B. Predicting the earthquake-induced permanent deformation of concrete face rockfill dams using a strain potential concept in the finite element method. International Journal of Geomechanics, 2017.

[5] Chen Shengshui. Research on Earthquake Safety of Earth-rock Dams. Beijing: Science Press, 2015.

[6] Fu Z Z, Wang T B, Chen S S. Field observations made on four concrete facerockfill dams. In: Proceedings of the 4th International Conference on Civil Engineering and Urban Planning, Beijing, China. 25-27 July, 2015.pp.589- 595.

[7] Zhang Bingyin, Shi Ruifeng. Analysis of the effect of rheological deformation on face void of high face rockfill dam. Rock and Soil Mechanics. 2004,25(8):1179-1184.

[8] Zhang B Y, Wang J G, Shi R F. Time-dependent deformation in high concrete-faced rockfill dam and separation between concrete face slab and cushion layer. Computers and Geotechnics, 2004, 31(7): 559-573.

[9] Chen Shengshui, Huo Jiaping, Zhang Weimin. "5.12" Wenchuan Earthquake Impact on Zipingpu Concrete Face Dam and Analysis of Causes. Chinese Journal of Geotechnical Engineering, 2008, 30(6): 795-801.

[10] Chen S S, Fu Z Z, Wei K M, Han H Q. Seismic responses of high concreteface rockfill dams: A case study. Water Science and Engineering, 2016, 9(3): 195-204.

[11] Kong X J, Liu J M, Zou D G. Numerical simulation of the separation between concrete face slabs and cushion layer of Zipingpu dam during the Wenchuan earthquake. Science China Technological Sciences, 2016, 59(4): 531-539.

[12] Lu Chao, Liu Jie, Fu Yunxiang. Comprehensive geophysical prospecting method and application in face void detection of concrete face rockfill dam. Proceedings of the second academic exchange meeting of Geology and Exploration Professional Committee of China Hydropower Engineering Society. 2010 October.

[13] Niu Xinqiang, Tan Jiexiong, Tian Jinzhang. Disease characteristics of concrete face rockfill dams and their reinforcement. People's Yangtze River, 2016, 47(13): 1-5.

[14] He Wen, Zhong Zhihua, Yang Jikang. The New Development of Automobile Airbag Technology. Automobile Safety, 2000, 4:33-37.

[15] Zhong Zhihua, Yang Jikuang. Automobile airbag technology and its application. China Mechanical Engineering, 2000,11(1-2):234-237.

[16] Zhou Kuijun. Research on Gas Generator for Automobile Airbag. Doctoral Dissertation, Nanjing University of Science and Technology, Nanjing, 2007.

[17] Qu Yanbin, Xiao Zhongliang. Gas generating agent for automobile airbags. Journal of North China Institute of Technology, 2003, 24(6): 428-431.

[18] Ministry of Water Resources of the People's Republic of China. Code for Design of Concrete Faced Rockfill Dams. SL228-2013, released on 2013-01-22, implemented on 2013-04-22.

Contents of the invention

In order to make up for the above gaps in the prior art, the present invention provides an airbag-type automatic protection device and design method for concrete face rockfill dam face voiding, the purpose of which is to cause voiding between the face plate and the cushion material, and the voiding When the amount reaches a value that endangers the safety of the concrete panel, the airbag type protection device is automatically activated to make the inflatable airbag support the panel, thereby improving the stress state of the concrete panel and preventing secondary damage such as surface cracks and misplacement.

The technical solution for accomplishing the task of the above invention is an airbag-type automatic protection device for the emptying of the face of a concrete face rockfill dam, which is arranged in the extruded side wall under the face of the concrete face rockfill dam. It is characterized in that the automatic protection device consists of It consists of three parts: a protective airbag, a gas generator and an automatic trigger device, wherein the protective airbag is installed in the prefabricated concrete extruded side wall near the top of the dam; the gas generator is connected to the protective airbag through a vent pipe; The automatic triggering device is provided with an electric ignition mechanism of a void detector, which is connected with the gas generator to control the start of the gas generator.

Basic working principle of the present invention:

The automatic protection device for panel hollowing should be installed in the central part of the valley where the rockfill material is relatively deep, the panel is prone to voiding and the amount of voiding may be large, and it extends to both bank slopes for a certain distance. The empty range is determined after calculation and analysis, as shown in Figure 1. The installation elevation of the void protection device can be determined by the structural mechanics analysis method through the tensile or cracking conditions of the cantilever panel, see below.

During the long-term operation of the face rockfill dam or when it is subjected to an earthquake, the rockfill body will settle and separate from the face plate, and the face face will be in a cantilever working state. There will be cracks or even breakage. The airbag-type automatic protection device involved in this patent will automatically trigger the gas generator when the panel void reaches a certain value. After the gas generator is ignited, a large amount of gas will be generated quickly, and the airbag will be quickly inflated to make the expanded airbag support empty. panel, thereby improving the working condition of the panel, as shown in Figure 2.

Structural design of the automatic protection device for empty concrete panels:

Figure 3 is a schematic diagram of the structure of the automatic protection device for the concrete panel. The device is installed in the precast concrete extrusion side wall near the top of the dam. The device is mainly composed of three parts, namely the protective airbag, the gas generator and the automatic trigger device.

(1) Protective airbag: it is the core component of the automatic protection device. When the panel void volume does not reach the ignition threshold, the protective airbag is folded in the airbag box and protected by an aluminum cover; when the panel void volume reaches the predetermined threshold , the airbag quickly inflates and bulges outward to support the panel. The protective airbag can refer to the production method in the automobile industry [14,15]. It is sewn from polyamide (nylon) fabric with high mechanical strength, good wear resistance and corrosion resistance, and is coated with neoprene or silicone Material. The number of protective airbags under a single panel and the tensile strength in the radial and weft directions can be determined through calculation and analysis, see below.

(2) Gas generator: it is the core component of the automatic protection device, which is connected with the protective airbag through the ventilation pipe. When the void volume of the panel reaches the predetermined threshold, it will automatically ignite and ignite the gas-generating agent in it, releasing a large amount of gas. After filtering, the gas will be filled into the protective airbag through the vent tube. Its working principle is similar to that of the car airbag[16,17 ]. The gas generating agent in the gas generator can be sodium azide (NaN ₃ ) as the main body, and the oxidant can be ferric oxide (Fe ₂ O ₃ ) or copper oxide (C _u O). This series of agents has the advantages of stable performance, relatively low gas temperature, and low cost[16]; however, sodium azide is highly toxic, and the content of nitrogen oxides (NO and NO ₂ ) in the gas generated after the reaction High, special attention should be paid when recovering the airbag.

(3) Automatic triggering device: it is the core component of the automatic protection device, which has dual functions of void detection and automatic power-on triggering of the gas generator, as shown in Figure 3(b). In the triggering device, a group of batteries for powering the gas generator electric igniter is connected to the concrete panel through high-strength steel wires. The cathode of the battery pack is connected to the cathode cable of the gas generator; its anode is facing a set of copper sheets, and the copper sheets are connected to the anode cable of the gas generator. When the panel is closely attached to the cushion material, the battery anode and the anode copper sheet are disconnected, and the automatic protection device does not work. With the increase of the void depth between the panel and the cushion material, the high-strength steel wire traction battery pack moves upward along its slope track and approaches the anode copper sheet. When the emptying volume reaches a predetermined threshold, the anode of the battery pack is in contact with the anode copper sheet, and the electric igniter is energized to trigger the gas generator to work. At the same time, the alarm placed on the crest of the dam and connected in parallel with the electric igniter started to work, reminding the inspectors that the void volume at this place had reached the set threshold and should be disposed of as soon as possible. The allowable void volume in the device can be realized by adjusting the distance between the anode of the battery pack and the anode copper sheet, which is convenient and reliable.

The technical solution for completing the second invention task of the present application is the design method of the airbag type automatic protective device for the empty face of the concrete face rockfill dam above, characterized in that the steps are as follows:

(1). One of the determination of the installation position of the automatic protection device: determine the critical void depth of the panel according to the load conditions, the strength of the panel concrete material, the size of the panel and its reinforcement method;

(2). The second determination of the installation position of the automatic protection device: determine the installation position according to the pressure condition at the escape point and consider the structural requirements;

(3). One of the determination of the strength parameters of the airbag: determine the internal pressure of the airbag when it is working according to the depth of the panel void, the size of the airbag, the installation location and the number of the airbags (referring to the total number of airbags under a single panel);

(4). The second determination of the strength parameters of the airbag: determine the warp and weft tensile strength of the airbag according to the internal pressure of the airbag, the size of the end of the airbag and its equilibrium condition.

The method of determining the installation position of the automatic protection device:

The installation position of the automatic protection device in the present invention refers to the elevation of the centerline of the airbag, as shown by the horizontal dotted line in FIG. 1 . Its determination can be implemented in two steps: (1) Determine the critical void depth of the face plate according to the loading conditions, strength of the face concrete material, face size and reinforcement method; (2) According to the compression conditions at the point of void and considering the structural requirements Determine the installation location. For ease of exposition, the following notations are introduced:

h _s = elevation of the top of the panel; h _w = normal water storage level; h _g = elevation of the panel void (the boundary between the void area and the non-evacuation area); ρ _w = density of reservoir water; ρ _s = density of panel concrete ; w = width of the panel; h = thickness of the panel; g = acceleration of gravity, positive downward; a _x = horizontal seismic acceleration, positive downward; a _y = vertical seismic acceleration, positive downward ; θ = angle between panel and horizontal plane; f _c = compressive strength of concrete; f _t = tensile strength of concrete; z = thickness of equivalent compression zone of panel; f _y = tensile strength of steel bar; A _s = Area of reinforcement in a single-width panel.

Figure 4 is a schematic diagram of the force analysis of the cantilever panel after the panel and the cushion material are voided. The boundary between the voided area of the panel and the non-evacuated area is the part that bears the largest bending moment and is most likely to crack or break. The slope axial force is

Where: a _t is the downward acceleration along the slope of the panel, that is

a _t ＝(g+a _y )sinθ-a _x cosθ (2)

The bending moment at this point is

Where: a _n is the inward acceleration along the normal direction of the panel, namely

a _n ＝(g+a _y )cosθ+a _x sinθ (4)

In formula (3), if the void height of the panel is above the water storage level, the bending moment contributed by the water pressure in the second term on the right end should not be included.

Most of the concrete slabs in face rockfill dams use single-layer bidirectional reinforcement and are arranged in the middle of the slab thickness [3,18], as shown in Fig. 5(a). The critical void depth of the panel should be determined according to the anti-crack analysis or fracture analysis. For the void caused by rheology, it is not easy to detect due to the slow process. , should be determined by resistance analysis.

The anti-crack analysis assumes that both the steel bar and the concrete are in a state of elastic deformation, and the stress of the concrete can be superimposed by the contributions of the axial force and the bending moment, as shown in Figure 5(b). Since the steel bar is located in the center of the plate thickness, it does not bear the bending moment, and the reinforcement ratio is low (0.3-0.4%) [18], the axial force it bears can be ignored, so the panel under the joint action of the axial load N and the bending moment M The crack resistance condition of the upper surface can be expressed as:

Substituting Equation (1) and Equation (3) into Equation (5) can get a quadratic equation with void depth h _g as unknown quantity, and the critical void depth based on crack resistance analysis can be obtained by numerical method or graphical method .

For the panel fracture analysis, the effect of concrete in the tension zone is ignored, and the stress state of the concrete in the compression zone is simplified as shown in Figure 5(c), that is, it is assumed that the concrete in the compression zone has reached its compressive strength, and the steel bars have also reached their maximum strength at the same time. Tensile strength, the following two formulas can be listed according to the axial force balance and moment balance:

f _c · w · zf _y · w · A _s = N (6)

Substituting equations (1) and (3) into equations (6) and (7) can obtain an equation system containing two unknown quantities, that is, the void depth h _g and the thickness z of the equivalent compression zone of the panel, which can also be obtained by The critical void depth based on fracture analysis is obtained numerically or graphically.

The invention makes up for the gaps in the prior art. When a void occurs between the panel and the cushion material and the void amount reaches a value that endangers the safety of the concrete panel, the airbag type protection device is automatically activated to make the inflatable airbag support the panel, thereby improving The stressed state of the concrete slab prevents secondary damage such as surface cracks and misalignment.

The present invention aims to automatically start the airbag type protection device when the face plate of the concrete face rockfill dam and its cushion material are voided, and the voided amount reaches a certain value, so as to prevent the secondary damage of the water stop system. The main innovation points are :

(1) The idea of using airbag protection device with air bag, gas generator and automatic trigger device as the core components to protect the panel after voiding is proposed. At present, there is no automatic protection device for panel voiding at home and abroad.

(2) The automatic trigger device designed according to the panel void problem is controlled by a battery pack placed on the sliding track, and the allowable void volume can be realized by adjusting the distance between the anode of the battery pack and the anode copper sheet. This idea is original .

(3) The method of determining the critical void depth of the inclined panel according to the crack resistance criterion and the fracture resistance criterion is proposed, and a method for determining the installation height of the protective airbag is suggested considering the structural requirements comprehensively.

(4) A method for determining the longitudinal and latitudinal tensile strength of the airbag is proposed considering factors such as the panel void depth, airbag size, installation location, and the number of airbags (referring to the total number of airbags under a single panel).

Special Note: This device is a temporary protection device, which is designed to buy time for the use of engineering methods to deal with the panel voiding disease. Once the automatic trigger device works and the alarm on the dam crest sends out the alarm message of voiding, permanent protective measures such as filling and grouting should be used as soon as possible. Disposal measures.

Description of drawings

Figure 1 is the installation range and elevation (upstream view) of the airbag type automatic protection device;

In Figure 1, the installation range of the airbag automatic protection device is 1-1, the automatic protection device is 1-2, the concrete plinth is 1-3, and the concrete panel is 1-4;

Fig. 2 is the basic working principle of inflatable air bag protection concrete panel;

In Fig. 2, the inflatable air bag 2-1, the initial outline 2-2, the rockfill material 2-3, the deformed outline 2-4, the cushion material layer 2-5, the main rockfill area 2-6, and the secondary rockfill area 2- 7. Upstream cover weight 2-8, transition material 2-9;

Figure 3-a, Figure 3-b, and Figure 3-c are structural schematic diagrams of the automatic protection device for emptying of concrete panels;

In Fig. 3-a, Fig. 3-b, Fig. 3-c, protective airbag 3-1, gas generator 3-2, electric ignition device 3-3, cathode cable 3-4, anode cable 3-5, Ring cable (connected to the cathode of the power supply) 3-6; battery pack 3-7; high-strength steel wire 3-8, copper sheet (connected to the anode cable) 3-9, ventilation pipe 3-10, fixed pulley 3-11, concrete Panel 3-12, aluminum cover 3-13, battery pack rail 3-14, air bag box 3-15, siren 3-16;

Figure 4-a and Figure 4-b are schematic diagrams of the force analysis of the cantilever panel;

In Figure 4-a and Figure 4-b, the easily cracked surface 4-1;

Figure 5-a, Figure 5-b, and Figure 5-c are schematic diagrams of the reinforcement form of the concrete slab and the analysis of crack resistance and fracture resistance;

In Fig. 5-a, Fig. 5-b, and Fig. 5-c, the reinforcement along the slope is 5-1, the reinforcement is 5-2 horizontally, the stress caused by the axial force is 5-3, the stress caused by the bending moment is 5-4, and cracks 5-5;

Figure 6-a and Figure 6-b are the drawing determination method of the critical void depth;

Fig. 7 is a schematic diagram of the force when the airbag supports the panel;

In Fig. 7, the airbag installation position 7-1, the emptying point 7-2;

Figure 8-a to Figure 8-e are schematic diagrams of internal force analysis when the airbag supports the panel;

Figure 9 is a graph showing the relationship between the tensile strength of the airbag and its number.

detailed description

Example 1: The parameters of a concrete face rockfill dam are listed in Table 1, and the critical void depth of the face plate is determined according to the crack resistance criterion and the fracture resistance criterion respectively.

Table 1 Calculation parameters of critical voiding of a concrete face rockfill dam

Referring to Figure 6-a, Figure 6-b:

Figure 6-a plots the relationship between the tensile stress on the surface of the panel and the depth of the void at the void point calculated according to the elastic assumption in the process of voiding the panel. According to the tensile strength of the concrete of the panel, the elevation at the critical void point can be calculated as approximately 98.5m, that is, the void depth of the panel determined by the crack resistance analysis is about 1.5m. Figure 6-b plots the relationship between the void depth determined according to formula (6) and formula (7) and the height of the equivalent compression zone during the process of panel voiding. (z/h) must be less than 0.5, here the height of the relative compression zone is set to 0.3, and the elevation of the void point of the panel at the moment of fracture is about 98.0m, that is, the void depth of the panel determined by the fracture resistance analysis is about 2.0m.

According to the current engineering experience, the critical void depth of the panel is generally below the normal water storage level, so the effect of water pressure can be ignored when analyzing the stress on the panel supported by the airbag. In addition, the bending moment at the panel of the empty part can be zero by rationally designing the size of the airbag, so its stress situation can be simplified as shown in Figure 7. If it is assumed that the length of the panel along the slope is L in the critical void state, and the installation position of the airbag is x (counted from the top of the panel), the installation position of the airbag should meet the following conditions:

Among them: the reason why the second inequality constraint must be satisfied is that once the condition is not satisfied, the void point needs to bear the tension, and it is impossible for the cushion material to provide the tension. This means that if the protective airbag is installed below half of the critical void depth, it will cause a new void. Since a horizontal water stop needs to be installed between the top of the panel and the wave wall, in order to reduce construction difficulties, the airbag should not be installed on the top of the panel. Based on the above considerations, it is recommended to install the protective airbag at x=L/3.

With reference to Fig. 7: method for determining the strength parameter of safety airbag (airbag installation position 7-1 in Fig. 7, emptying point 7-2):

The airbag strength parameters are implemented according to the following steps: (1) Determine the internal pressure of the airbag when it is working according to the panel void depth, the size of the airbag, the installation location and the number of airbags (referring to the total number of airbags under a single panel); ( 2) Determine the warp and weft tensile strength of the airbag according to the internal pressure of the airbag, the size of the end of the airbag and its equilibrium condition. The internal stress situation when the airbag supports the panel is shown in Figure 8, and it is now recorded as follows:

L = clearance length of the panel along the dam slope; x = installation position of the airbag (Fig. 7); W = width of the airbag; H = height of the airbag (length along the dam slope); N = number of airbags under a single panel; p = internal pressure of the airbag; T, T' = longitudinal and latitudinal strength of the airbag; a, b, c = length of the semi-axis of the ellipse at the end of the airbag (Fig. 8).

The internal pressure of the airbag can be obtained according to the moment balance condition of the panel of the void section around the void point, namely

so

Assume that the shape of the end of the airbag is an ellipse under the action of internal pressure p, as shown in Figure 8(b) and Figure 8(c), and record the lengths of the two semi-axes of the ellipse as a and b respectively, then according to the shape of the end of the airbag The equilibrium condition can obtain the maximum tensile force T per unit length of the airbag, that is,

T=max{a·p,b·p} (11)

Equation (11) gives the maximum tension value of the airbag in the A-A section. The maximum tension value of the airbag along the other direction can be determined according to the same principle, as shown in Figures 8(d) and 8(e), namely

T'=max{a p,c p} (12)

The tensile strength of the airbag per unit width in the warp direction (A-A section) and weft direction (B-B section) shall not be lower than the value determined by formula (11) and formula (12).

Example 2: The critical void depth of a concrete face rockfill dam face determined according to the parameters described in Table 1 and the principle of failure resistance is 2m. Now, given the following supplementary conditions, try to determine the longitudinal and latitudinal tensile strength of the protective airbag strength.

Supplementary parameters of airbag strength determined in Table 2

Figure 9 plots the strength requirements for the installation of different numbers of protective airbags calculated according to formulas (9) to (12). It can be seen from this that the greater the number of airbags under a single panel, the greater the impact on the tensile strength of the airbags. The lower the requirement, in this case, when the number of protective airbags is 10, the tensile strength is T=T'=6.89kN/m. The material for making the airbag can be selected according to the strength requirement.

Claims (10)

1. A kind of airbag type automatic protection device for concrete face rockfill dam face plate is empty, is arranged in the extruded side wall under the face plate of concrete face rockfill dam, it is characterized in that, automatic protection device is made up of three parts: protection air bag , a gas generator and an automatic trigger device, wherein the protective air bag is installed in the prefabricated concrete extruded side wall near the top of the dam; the gas generator is connected to the protective air bag through a vent pipe; in the automatic trigger device There is an electric ignition mechanism for the void detector, which is connected with the gas generator to control the start of the gas generator. 2. The air bag-type automatic protection device for concrete face rockfill dam face voiding according to claim 1, characterized in that the protective air bag is folded in the air bag box and protected by an aluminum cover plate. 3. The airbag-type automatic protection device for concrete face rockfill dam face stripping according to claim 1, characterized in that, said protective airbag is sewn by polyamide fabric, and is coated with neoprene or silicone layer material. 4. The airbag-type automatic protection device for concrete face rockfill dam face stripping according to claim 1, wherein said "protection airbag is installed in the prefabricated concrete extruded side wall near the dam crest" is Refers to: the above-mentioned protective airbag is installed in the central part of the valley where the rockfill material is relatively deep, the panel is prone to voiding, and the amount of voiding may be large, and it extends to both bank slopes for a certain distance. 5. The air bag-type automatic protection device for concrete face rockfill dam face stripping according to claim 1, characterized in that, in the gas generator, the gas-generating agent is mainly sodium azide, and its oxidant adopts dioxygen trioxide iron or copper oxide. 6. The air bag-type automatic protection device for concrete face rockfill dam face voiding according to claim 1, characterized in that, in the automatic trigger device, a group of batteries for the electric igniter of the gas generator pass through the high-strength steel wire It is connected to the concrete panel; the cathode of the battery pack is connected to the cathode cable of the gas generator; its anode is facing a set of copper sheets, which are connected to the anode cable of the gas generator; when the panel is closely attached to the cushion material, The anode of the battery is disconnected from the anode copper sheet, and the automatic protection device does not work; when the void volume reaches a predetermined threshold, the anode of the battery pack contacts the anode copper sheet, and the electric igniter is energized to trigger the gas generator to work. 7. The air bag type automatic protection device for concrete face rockfill dam face voiding according to any one of claims 1-6, characterized in that, the automatic trigger device is also provided with an alarm, which is placed in the dam The top is connected in parallel with the electric igniter. 8. The design method of the airbag type automatic protection device for the concrete face rockfill dam face plate of claim 1 is characterized in that, the steps are as follows: ⑴. One of the determination of the installation position of the automatic protection device: determine the critical void depth of the panel according to the load conditions, the strength of the panel concrete material, the panel size and its reinforcement method; ⑵. Determination of the installation position of the automatic protection device 2: determine the installation position according to the pressure conditions at the escape point and considering the structural requirements; ⑶. One of the determination of the strength parameters of the airbag: determine the internal pressure of the airbag when it is working according to the depth of the panel, the size of the airbag, the installation position and the number of the airbag; ⑷. The second determination of the strength parameters of the airbag: according to the internal pressure of the airbag, the size of the end of the airbag and its equilibrium conditions, determine the tensile strength of the airbag in the warp direction and weft direction. 9. The design method of the air bag-type automatic protection device for the concrete face rockfill dam face plate according to claim 8, characterized in that, the installation position of the automatic protection device described in steps (1) and (2) should meet the following conditions: $\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; <</span>\frac{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ;</span>$ Among them, it is assumed that the length of the panel along the slope direction is L and the installation position of the airbag is x when the critical void state is reached. 10. according to claim 8 or 9 described concrete face rockfill dam face design method of the air bag type automatic protection device that the face is empty, it is characterized in that, the intensity parameter of the safety air bag described in step (3), (4) should satisfy following condition : L = the clearance length of the panel along the dam slope; x = installation position of the airbag; W = width of the airbag; H = height of the airbag; N = number of airbags under a single panel; p = internal pressure of the airbag; T, T' = airbag Longitudinal and latitudinal strength; a, b, c = the length of the semi-axis of the ellipse at the end of the airbag; The internal pressure of the airbag can be obtained according to the moment balance condition of the panel of the void section around the void point, namely $\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$ so $\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&rho;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; w</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; L</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; W</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$ Assuming that the shape of the end of the airbag is an ellipse under the action of the internal pressure p, and recording the lengths of the two semi-axes of the ellipse as a and b respectively, then the maximum tensile force T per unit length of the airbag is obtained according to the equilibrium condition of the end of the airbag, namely T=max{a·p,b·p} (11) Equation (11) gives the maximum tension value of the airbag in the A-A section; the maximum tension value of the airbag along the other direction is determined according to the same principle, namely: T'=max{a p,c p} (12) The tensile strength of the airbag per unit width in the warp direction and weft direction shall not be lower than the value determined by formula (11) and formula (12).