CN109001810A - Gravity dam crack in dam body advanced early warning method based on micro seismic monitoring - Google Patents

Abstract

The invention provides a method for early warning of gravity dam body cracks based on microseismic monitoring, which is characterized in that the steps are as follows: 1. Delineate the monitoring area, arrange sensors and blast holes; 2. Blast in each blast hole at different time points, Record the take-off time of the elastic wave generated by each blasting, and calculate the average equivalent wave velocity of the rock mass; ③ Monitor the monitoring area through the microseismic monitoring system, measure the source position and occurrence time of the microseismic events generated in the monitoring area, and make a space for the source position Distribution map, when the source locations of microseismic events gather in one or some local areas of the monitoring area and present a strip or planar distribution, an early warning signal for gravity dam cracks is issued. The method of the invention can identify the risk of cracks in the gravity dam body in advance, and is beneficial to better guarantee the safe construction and safe operation of the hydropower station.

Description

Early warning method for gravity dam cracks based on microseismic monitoring

technical field

The invention belongs to the field of geotechnical engineering, and relates to a method for early warning of gravity dam cracks based on microseismic monitoring.

Background technique

A hydropower station is a comprehensive engineering facility that converts water energy into electrical energy. The hub of a hydropower station includes water-retaining structures, water-discharging structures, water-intake structures, water-diversion structures, water-leveling structures, and plant hub buildings, among which water-retaining structures And the hub of the plant is an important part of the hydropower station. According to statistics, most of the hydropower station accidents at home and abroad are accidents of water-blocking structures, that is, there are problems in the water-blocking dam system. The types of water blocking dams include concrete gravity dams, arch dams, earth-rock dams, rockfill dams, and river gates. Gravity dam, as a dam with good economy and safety, has been widely used at home and abroad, for example, domestic Liujiaxia gravity dam, foreign Grand Dixence gravity dam and so on.

With the continuous development of dam-building technology, the number of high dams is increasing, which puts forward higher requirements for the stability of dam bodies. Since the 1980s, roller compacted concrete technology has been applied to the construction of gravity dams, and the proportion of gravity dams has continued to increase. The safety of the gravity dam faces multiple challenges. For example, the safety of the gravity dam will be affected by the uncertainty of bedrock and dam material parameters, as well as random factors such as earthquakes. The dynamic response of high roller compacted concrete gravity dams on complex foundations under strong earthquakes has great uncertainty, and the analysis of the failure probability and system reliability of the dam body under earthquakes is currently a difficult point. The stability of the dam body is related to the safety of people's lives and property, as well as the national economic benefits. Any hydraulic structure cannot be guaranteed to be infallible, so advance forecasting and early warning are very necessary. Early forecasting and early warning of dam damage will help reduce unnecessary losses as much as possible.

The existing technology mainly uses vertical lines, tension lines, line of sight, laser alignment and conventional measurement to monitor the deformation of the dam body, and also uses multi-point displacement meters and anchor stress gauges to judge whether the dam body is damaged or not. There is deformation. Although the operation of these methods is relatively simple, they can only observe the deformation information after the dam body has been damaged, and can only show whether the dam itself is damaged with macroscopic data, and cannot identify the potential micro-cracks of the dam itself information, and it is impossible to give early warning to the hydropower station construction and operation and maintenance personnel before the dam is damaged.

For the gravity dam, there are grouting corridors and traffic inspection corridors in the center of the dam body. As an early warning signal of gravity dam failure, if an early warning method for gravity dam cracks can be developed based on this, it will have important significance for the safe construction and operation of hydropower stations using gravity dams as water blocking structures.

Contents of the invention

The purpose of the present invention is to address the deficiencies of the prior art, and provide a method for early warning of gravity dam cracks based on microseismic monitoring, so as to identify the risk of cracks in the gravity dam in advance, so as to better ensure the safe construction of hydropower stations and safe operation.

The method for early warning of gravity dam body cracks based on microseismic monitoring provided by the present invention has the following steps:

① Delineate the surrounding rock of the traffic inspection corridor in the center of the gravity dam body as the monitoring area, and install the sensors of the microseismic monitoring system on the rock mass in the monitoring area. There are at least 4 sensors. Link to the acquisition instrument of the microseismic monitoring system, then connect the acquisition instrument with the host part of the microseismic monitoring system; establish a three-dimensional rectangular coordinate system, measure the coordinates of each sensor, and mark the coordinates of the i sensor as ( _xi , y _i , z _i ); set at least one blast hole on the rock mass in the tunnel, measure the coordinates at the center of the bottom of each blast hole, and mark the coordinate at the center of the bottom of the jth blast hole as (X _j , Y _j , Z _j );

②Install explosives at the bottom of each blast hole, carry out a blast in each blast hole at different time points, record the take-off time of the elastic wave generated by each blast through the sensor, and record the blasting time of the jth blast hole as t _j , the take-off time when the i-th sensor receives the elastic wave generated by the blasting after the j-th blasting hole is blasted is recorded as t _ji ;

According to the distance between the jth blast hole and each sensor, and the relationship between speed and time, corresponding to each blast hole, the following equations (1-1)~(1-i) are listed according to the two-point distance formula. The i in 1-i refers to the total number of sensors:

…

Substitute the values of the coordinates of the 1st, 2nd,...,j blastholes, the blasting time of the corresponding blasthole blasting, and the take-off time when the i-th sensor receives the elastic wave generated by the blasting after the corresponding blasthole blasting into the formula One of (1-1)～(1-i), the equivalent wave velocity of the rock mass can be solved respectively, denoted as v ₁ ,v ₂ ,…,v _j , and then the average equivalent wave velocity v of the rock mass can be calculated,

③Monitor the monitoring area through the microseismic monitoring system, determine the source location and time of the microseismic events in the monitoring area, and make real-time statistics on the source location of the microseismic events in the monitoring area and mark the source location in the three-dimensional Cartesian coordinate system. The spatial distribution map of the source position. When the source positions of the microseismic events gather in one or some local areas of the monitoring area and present a strip or planar distribution, it indicates that the micro-cracks in the corresponding local area are densely gathered, and the micro-cracks are densely packed Aggregation will lead to the instability of the center of the gravity dam, and the instability of the center of the gravity dam will lead to cracks in the gravity dam body. When distributed, the gravity dam body crack warning signal is issued;

The method of determining the source location and the moment of occurrence of microseismic events in the monitoring area is as follows:

Assuming that the coordinates of the source of the microseismic event are (X _k , Y _k , Z _k ), and the moment when the microseismic event occurs is t _k , define t _ki as the take-off time when the i-th sensor receives the elastic wave generated by the microseismic event. According to the microseismic event The distance between the source of the earthquake and each sensor, and the relationship between speed and time, the following equations (2-1)~(2-i) are listed according to the two-point distance formula, where i in 2-i refers to the sensor’s total:

…

At least 4 equations in the simultaneous equations (2-1)~(2-i) are substituted into the average equivalent wave velocity v of the rock mass, the coordinates of each sensor, and the take-off time when each sensor receives the elastic wave generated by the microseismic event value, the coordinates (X _k , Y _k , Z _k ) of the source of the microseismic event and the moment t _k of the microseismic event can be obtained.

In the technical scheme of the above-mentioned microseismic monitoring-based advanced warning method for gravity dam body cracks, the microseismic monitoring system may adopt the ESG microseismic monitoring system or other microseismic monitoring systems.

In the above-mentioned technical scheme of the advanced warning method for gravity dam cracks based on microseismic monitoring, the equivalent wave velocity of the rock mass can be measured and calculated by setting one blast hole and performing one blast. In order to increase the accuracy of the calculation of the equivalent wave velocity of the rock mass , preferably using more than one blast hole, more preferably, the number of blast holes is 2-5.

In the above-mentioned technical scheme of the advanced warning method for gravity dam cracks based on microseismic monitoring, the construction is stopped during blasting to avoid interfering with the acquisition of the elastic wave signals generated by the blasting sensor. After the acquisition of the elastic wave signals generated by the blasting is completed, the normal construction.

The microseismic monitoring based gravity dam crack early warning method provided by the present invention uses the microseismic monitoring technology to obtain the accumulation of the source positions of the moderate earthquake events in the micro monitoring area, and judges the monitoring area according to the accumulation of the source positions of the microseismic events Development of micro-cracks: If the source locations are gathered in one or some local areas of the monitoring area, it indicates that cracks are widely developed in these local areas; When it is distributed in a shape or planar shape, it indicates that the cracks in the corresponding local area are developed in a band or planar shape, indicating that the micro-fractures in the corresponding local area are densely aggregated, and the dense accumulation of micro-cracks will lead to the instability of the center of the gravity dam body. The instability of the center of the dam body will lead to cracks in the gravity dam body. Therefore, when the source locations of the microseismic events gather in one or some local areas of the monitoring area and are distributed in strips or planes, a gravity dam is issued. Body crack warning signal. The method of the present invention utilizes microseismic monitoring to determine whether there is potential instability in the center of the gravity dam body, utilizes the law that the center of the gravity dam body will cause cracks (i.e. cracks) in the gravity dam body, and realizes the stability of the gravity dam body. Early warning of cracks. Cracks in the gravity dam body can lead to the instability of the gravity dam, so the method of the present invention can give early warning to the hydropower station construction and operation and maintenance personnel before the gravity dam body damages, prompting them to take measures to protect the potential instability area, so as to Ensure the construction and operation safety of hydropower stations.

Compared with the prior art, the present invention has the following beneficial effects:

1. The gravity dam body crack early warning method based on the microseismic monitoring provided by the present invention, the method utilizes the microseismic monitoring technology to obtain the accumulation situation of the source position of the microseismic event, and judge the center of the gravity dam body according to the accumulation situation of the source position The development of micro-cracks in the surrounding rock in the region, and then judge whether there is a possibility of potential instability in the center of the gravity dam body. On this basis, using the rule that the center of the gravity dam body will cause cracks in the gravity dam body, Early warning of cracks in the gravity dam body can be realized. Compared with the existing dam deformation monitoring methods such as vertical line, tension line, line of sight, laser alignment and conventional measurement, the method of the present invention has advanced forecast and convenience, and can better and more effectively guide the use of Safe construction and operation of hydropower stations with gravity dams as water blocking structures.

2. The method provided by the present invention is a non-destructive monitoring method in a spatial range, especially capable of identifying microcracks caused by disturbing the center of the gravity dam body due to changes in water pressure during the water storage process of the gravity dam, and judging whether the microcracks are Aggregation sprouts and develops, and then identifies whether there is a potential instability in the gravity dam body and issues an early warning.

Description of drawings

Fig. 1 is the sectional view of the gravity dam in the embodiment, among the figure, 1-dam body drainage pipe, 2-grouting corridor, 3-traffic inspection corridor, 4-drain hole curtain, 5-seepage prevention curtain.

Figure 2 is a network topology diagram of the ESG microseismic monitoring system.

Fig. 3 is a layout diagram of sensors in a traffic inspection corridor.

Fig. 4 is a diagram of the spatial distribution of seismic source positions made in the embodiment.

Detailed ways

The method for early warning of gravity dam body cracks based on microseismic monitoring of the present invention will be further described below through specific embodiments and in conjunction with the accompanying drawings. It must be pointed out that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Those skilled in the art make some non-essential improvements and adjustments to the present invention based on the above-mentioned content of the invention. The specific implementation still belongs to the protection scope of the present invention.

Example 1

This embodiment takes a gravity dam of a large-scale hydropower station as an example to specifically describe the method for early warning of gravity dam cracks based on microseismic monitoring. The section view of the gravity dam is as shown in Figure 1. The center of the gravity dam body is provided with a traffic inspection corridor and a grouting corridor.

The microseismic monitoring system adopted in this embodiment is the ESG microseismic monitoring system (ESG Corporation of Canada). host part of the system). The network topology of the ESG microseismic monitoring system is shown in Figure 2. Each acceleration sensor is connected to the Paladin digital signal acquisition system through a cable. The Paladin digital signal acquisition system is connected to the Hyperion digital signal processing system through a network cable. The Hyperion digital signal processing system is connected through a network cable. After connecting to the server, connect to the computer in the camp center by means of wireless transmission. The sensitivity of the sensor is 30V/g, and the frequency response range is 50Hz～5kHz. The sampling frequency of the Paladin digital signal acquisition system is 20kHz. The sensor converts the received stress wave into an electrical signal, and converts it into a digital signal through the Paladin digital signal acquisition system. The signal is then stored in the Hyperion digital signal processing system. In this embodiment, the take-off times of the elastic waves collected by the sensor are all the take-off times of the P waves.

The concrete steps of this embodiment are as follows:

① Delineate the surrounding rock of the traffic inspection corridor in the center of the gravity dam body as the monitoring area, and install the sensors of the ESG microseismic monitoring system on the side wall of the traffic inspection corridor. There are 6 sensors, which are respectively installed at the entrance of the traffic inspection corridor In the surrounding rock drilling on three sections of 50m, 100m and 150m, two sensors are installed on each section. The elevations of the sensors are different and the spatial network structures are formed respectively. On a straight line, any four sensors are located on the same plane, as shown in Figure 3. Each sensor is connected with the acquisition instrument of the microseismic monitoring system, and then the acquisition instrument is connected with the host part of the microseismic monitoring system.

Select the coordinate origin of a point in the traffic inspection corridor, establish a three-dimensional rectangular coordinate system, measure the coordinates of each sensor, and denote the coordinates of the i-th sensor as ( _xi , y _i , z _i ), i=1,2 ,...,6; set two blast holes on the rock mass of the left bank abutment, measure the coordinates at the center of the bottom of each blast hole, and mark the coordinate at the bottom center of the jth blast hole as (X _j , Y _j , Z _j ), j=1,2. Measure the coordinates of each sensor and the center of the bottom of each blast hole, and record them in Table 1 and Table 2 respectively.

Table 1 Coordinates of each sensor

sensor x(m) y(m) z(m) 1 7.00 50.00 1.50 2 -7.20 50.00 1.20 3 6.90 100.00 1.70 4 -7.10 100.00 2.00 5 7.30 150.00 1.20 6 -740 150.00 1.50

Table 2 Coordinates at the bottom center of each blast hole

blast hole X(m) Y(m) Z(m) 1 7.00 70.00 1.00 2 -7.00 120.00 2.00

② Install emulsion explosives at the bottom of each blast hole, connect detonating wire and high-voltage electrostatic detonator, and seal the opening of each blast hole with loose soil particles on site to reduce energy loss during blasting. A blast is carried out in the first blast hole and the second blast hole in turn, with an interval of 5 hours between the two blasts, and the sensor records the take-off time of the elastic wave generated by each blast, and the blasting time of the jth blast hole Denote it as t _j , and denote the take-off time when the i-th sensor receives the elastic wave generated by blasting after the j-th blast hole is blasted as t _ji .

According to the distance between the jth blasthole and each sensor, and the relationship between speed and time, corresponding to each blasthole, formula (1-1) is listed according to the two-point distance formula:

Substitute the coordinates of the first blast hole and the second blast hole, the blasting time of the corresponding blast hole, and the take-off time when the i-th sensor receives the elastic wave generated by the blast after the corresponding blast hole is blasted into the formula (1-1), respectively solve the rock mass equivalent wave velocity v ₁ =4050m/s, v ₂ =4092m/s, and then calculate the rock mass average equivalent wave velocity v,

③ During the operation of the large-scale hydropower station, the ESG microseismic monitoring system is used to monitor the monitoring area, and the source location and occurrence time of the microseismic events generated in the monitoring area are determined. The method of determining the source location and the moment of occurrence of microseismic events in the monitoring area is as follows:

Assuming that the coordinates of the source of the microseismic event are (X _k , Y _k , Z _k ), and the moment when the microseismic event occurs is t _k , define t _ki as the take-off time when the i-th sensor receives the elastic wave generated by the microseismic event. According to the microseismic event The distance between the seismic source and each sensor, and the relationship between speed and time, according to the two-point distance formula, the following six equations are listed:

…

Combining the above six equations, substituting the average equivalent wave velocity v of the rock mass, the coordinates of each sensor, and the value of the take-off time when each sensor receives the elastic wave generated by the microseismic event, the coordinates of the source of the microseismic event (X _k , Y _k , Z _k ) and the moment t _k of microseismic occurrence.

During the microseismic monitoring period, the source locations of the microseismic events in the monitoring area are counted in real time, and the source locations are marked in the three-dimensional rectangular coordinate system in real time to obtain the spatial distribution map of the source locations, which is combined with the distribution of the source locations in the spatial distribution map of the source locations. Judgment: If the source position of the microseismic event is discretely distributed in one or some local areas of the monitoring area, and there is no aggregation phenomenon, it means that there is no risk of instability in the corresponding local area; when the source position of the microseismic event is in a certain local area of the monitoring area When one or some local areas are aggregated and distributed in a striped or planar manner, it indicates that the cracks in the corresponding local area are developed in a banded or planar form, indicating that the microcracks in the corresponding local area are densely gathered, and the microcracks are densely packed. Aggregation will lead to the instability of the center of the gravity dam body, and instability of the center of the gravity dam body will lead to cracks in the gravity dam body. When it is distributed in a shape or planar shape, an early warning signal for cracks in the gravity dam body will be issued.

In the monitoring process of this embodiment, after monitoring for 60 days, there were 237 microseismic events in total, and the spatial distribution map of the hypocenter position made is shown in Figure 4. If local areas are gathered and distributed in a planar manner, an early warning signal for cracks in the gravity dam body should be issued at this time. The gravity dam body crack warning signal indicates that during the operation of the hydropower station, protective measures should be taken in the local area, such as concrete grouting and other measures to ensure the safe operation of the arch dam.

Claims (3)

1. the gravity dam crack in dam body advanced early warning method based on micro seismic monitoring, it is characterised in that steps are as follows:

1. drawing a circle to approve gravity dam dam body central traffic inspection gallery country rock as monitoring region, the sensor of Microseismic monitoring system is pacified Mounted in monitoring region rock mass on, sensor is at least 4, and each sensor antarafacial is installed on different elevations, by each sensor with The Acquisition Instrument of Microseismic monitoring system is connected, and then connects the host machine part of the Acquisition Instrument and Microseismic monitoring system；Establish three Rectangular coordinate system is tieed up, the coordinate of each sensor is measured, the coordinate of i-th of sensor is denoted as (x_i,y_i,z_i)；Rock in tunnel At least one blast hole is set on body, the coordinate at each blast hole bottom hole center is measured, at j-th of blast hole bottom hole center Coordinate is denoted as (X_j,Y_j,Z_j)；

2. the bottom hole in each blast hole installs explosive, onepull is carried out in each blast hole respectively in different time points, is passed through Sensor records the take-off moment for the elastic wave that each separate explosion generates, and the blowing-up time of j-th of blast hole is denoted as t_j, by jth The take-off moment that i-th of sensor receives the elastic wave of explosion generation after a blast hole explosion is denoted as t_ji；

According to the distance between j-th of blast hole and each sensor and the relationship of speed and time, correspond to each explosion Hole following equation (1-1)~(1-i) is listed according to two o'clock range formula:

…

Respectively by the 1,2nd ..., the coordinate of j blast hole, the blowing-up time of corresponding blast hole explosion and corresponding explosion After the explosion of hole i-th of sensor receive explosion generation elastic wave the take-off moment value substitute into formula (1-1)~(1-i) it One, the equivalent velocity of wave of rock mass can be solved respectively, be denoted as v₁,v₂,…,v_j, rock mass average equivalent velocity of wave v is then calculated,

3. being monitored by Microseismic monitoring system to monitoring region, the hypocentral location for the microseismic event that measurement monitoring region generates And the moment occurs for microseism, hypocentral location is simultaneously shown in three-dimensional by the hypocentral location for the microseismic event that real-time statistics monitoring region occurs In rectangular coordinate system, obtain hypocentral location spatial distribution map, when the hypocentral location of microseismic event monitoring region a certain or certain When a little regional area aggregations and presentation ribbon or planar distribution, that is, issue gravity dam crack in dam body pre-warning signal；

It is as follows that the method at moment occurs for the hypocentral location for the microseismic event that measurement monitoring region generates and microseism:

Assuming that the coordinate of the focus of microseismic event is (X_k, Y_k, Z_k), it is t at the time of microseism occurs_k, define t_kiIt is sensed for i-th Device receives the take-off moment of the elastic wave of microseismic event generation, according between the focus of microseismic event and each sensor away from From and speed and time relationship, following equation (2-1)~(2-i) is listed according to two o'clock range formula:

…

At least four equation in joint type (2-1)~(2-i), substitute into rock mass average equivalent velocity of wave v, each sensor coordinate, with And each sensor receives the value at the take-off moment of the elastic wave of microseismic event generation, can solve the seat of the focus of microseismic event Mark (X_k, Y_k, Z_k) and microseism occur at the time of t_k。

2. the gravity dam crack in dam body advanced early warning method based on micro seismic monitoring according to claim 1, which is characterized in that institute Stating Microseismic monitoring system is ESG Microseismic monitoring system.

3. the gravity dam crack in dam body advanced early warning method according to claim 1 or claim 2 based on micro seismic monitoring, feature exist In the quantity of blast hole is 2~5.