Inclinometer Sensors for Dam Health Monitoring And Dam Deformation Monitoring

I. Preface

A dam is a water retaining structure that intercepts the flow of river channels to raise the water level or regulate the flow. It can form reservoirs, raise water level, regulate runoff and concentrate heads for flood control, water supply, irrigation, hydropower generation, improving shipping conditions. Generally, the chosen location of dam is a narrow deep valley.

The preparation period of the dam is very complicated that there are many factors to consider, such as permeability, surrounding rocks or soil, the frequency of earthquakes, natural landslides, nearby residents and etc. In modern dam construction, the inclination sensor has been widely used, some are installed directly on the dam, some are installed in the dam or in the foundation structure to monitor the minor changes of the dam and the surrounding environment such as water seepage in the dam, severe corrosion of surrounding rocks, earthquakes or landslides, and the impact of landslides on nearby geological environments. Although sometimes the impact is very small, serious consequences may occur if small impacts are not processed in time. Many dam collapses are caused by small deformations that are not taken seriously.

The SST series inclinometer sensors, independently developed by Vigor Technology, can not only meet the needs of most structural health monitoring and structural deformation monitoring, but also can be used in special applications such as dam deformation. The Vigor SST series tilt sensors can record the angle change of the dam structure in real time, and can transmit the tilt angle value to the control system which can implement prompts and alarms, so that the dam maintenance personnel can get the alarm information in time and do the corresponding processing immediately.

II. Monitoring Content of Slope Detection System

The gravity of the dam foundation, dam body and water storage may cause uneven settlement and deformation of dam, rotational deformation of the foundation and the dam body. Additionally, the water storage pressure on the dam in the horizontal direction and the change of external temperature cause distortion and deformation of the dam body. If these deformations are too large, the stability and safety of the dam will be seriously affected. Therefore, it is exceedingly important to monitor the vertical displacement, horizontal displacement and inclination of the dam.

By monitoring the deformation size and regularity of the dam during construction and operation, engineers can predict and forecast the deformation trend of the dam according to the monitored data, so as to ensure the quality and safety of the dam in construction and operation period. The reservoir dam deformation monitoring contents mainly include horizontal displacement and vertical displacement in crest and bottom of dam, and detection of dam slope.

1. Tilt Detection of Vertical Activity

The vertical displacement of the monitoring point caused by the dam foundation, dam body and the upstream water weight force is transmitted to the in-place inclinometer through the installation conduit. When the sensor detects a tile change, the tilt angle of the horizontal node can be measured. The in-place inclinometer can be set as a measuring unit to work independently, and the tilting amount, or it can be set to measure the inclination of each segment of the measuring structure, so as to describe the deformation curve of the structure. If the in-place inclinometers are installed in the two-dimensional direction on the measured object, the two-dimensional deformation of the structure can be measured. The in-place inclinometer is recyclable and convenient to realize automation of tilt measurement.

2. Tilt Detection of Horizontal Activity

Under the condition of empty storage, the hydropower dam body may tilt toward the upstream under the effect of gravity; After impoundment, the dam body inclines downstream with the influence of reservoir water thrust. The magnitude of the inclination has a great influence on the stability of the dam. By connecting the horizontal displacement along the river to the elevation measurement points of the same vertical line into a line, the angle between the line and the vertical surface of the left and right banks is the vertical inclination of the dam. By connecting the vertical displacement of the dam foundation corridor along the river to the measurement points of the static level system into a line, the angle between the line and the horizontal plane is the horizontal inclination of the dam.

3. Slope Monitoring of Dam Body

Affected by the vertical settlement of the dam and displacement in the horizontal direction, the slope of the dam will generate a certain slope. Monitoring the slope will provide a reliable basis for analyzing the overall operation of the dam.

III. Establish a Dam Attitude Monitoring System Using Vigor SST Series Angle Sensors

The entire dam system monitoring includes the overall tilt attitude monitoring, horizontal displacement monitoring, vertical settlement monitoring, and slope (dam slope) monitoring.

Horizontal displacement is monitored via in-place inclinometer, and a sensor string is placed through a vertical conduit on the inclined dam body. Vertical settlement uses a in-place horizontal inclinometer, by placing a sensor string in the horizontal direction of the dam. The slope of dam body is monitored using the SST series inclination sensor and placed at the predicted slope point.

With a centralized data processing method, the sensor strings are connected to the data acquisition system. After a long period of data acquisition, alarms can be triggered based on a certain rate of change or other criteria. Through data analysis, you can know the horizontal displacement and vertical settlement of the dam in a certain period of time, and you can get a more detailed attitude state of the dam on the basis of slope analysis.

1. SST2200 Series In-Place Inclinometer for Horizontal Displacement Monitoring of Dam

A number of in-place inclinometer sensors are mounted in the sloping tube which provides access for subsurface measurements. The guide groove inside the sloping tube controls the direction of the sensor. Inclinometers are installed in vertical boreholes which pass through areas where displacement movement may occur. A set of guide grooves should be aligned in the expected displacement direction.

For example, in an excavated cave, the SST2200 in-place inclinometer is fixed in the sloping tube and spans the displacement active area. When the stratum displacement occurs, then the sloping tube also displaces, which causes the SST2200 inclinometer sensor installed in the tube to tilt. The displacement profile can be obtained by measuring the tilt of sensors. The displacement of each sensor is displayed in millimeters, and the cumulative displacement of the entire string of sensors is also displayed in millimeters.

2. SST2200 Fixed Inclinometer for Vertical Settlement Monitoring of Dam

A proper number of fixed inclinometer sensors are mounted in the sloping tube. The guide groove inside the tube controls the direction of the sensors. SST2200 in-place inclinometers are installed in horizontal boreholes which pass through areas where displacement movement may occur. A set of guide grooves should be aligned in the expected displacement direction.

3. SST Series Inclination Sensor for Slope Angle Monitoring of Dam

Relying solely on the horizontal inclinometer and vertical inclinometer, the influence of dam body movement on the overall slope of the dam cannot be comprehensively analyzed. By using the MEMS inclinometer such as SST300 or SST400, engineers can comprehensively estimate the impact of horizontal and vertical displacement on the slope of dam.

On the basis of objective monitoring to the vertical displacement, horizontal displacement and dam body inclination with Vigor inclinometer sensors, the precise dam deformation status can be monitored in time conveniently and provides reliable basis for dam health monitoring.