1. Sight line method.

Use the line of sight of the optical measuring instrument to establish a fixed vertical plane parallel to or passing through the dam axis as the reference plane, and regularly observe the deviation between the determined point and the reference plane, that is, the level of the point Displacement. This method is suitable for the observation of the lateral horizontal displacement of the top of concrete buildings and the lateral horizontal displacement of earth-rock buildings. The line-of-sight method requires that the displacement punctuation (measurement point), work base point and check base point be arranged on and near the hydraulic structure. Theodolite or collimator can be used for observation. There are two types of observation methods: the active standard method and the small angle method.

2. Tension line method.

Using the stainless steel wire tensioned between two working base points as the reference line, measure the relative displacement between the measuring point along the line and the steel wire to determine the horizontal displacement of this point. This method is suitable for linear concrete dams, which are generally set up in horizontal longitudinal corridors.

There are two observation methods:

①After aligning the measuring wire with naked eyes or optical instruments, read the scale installed on the measuring point, and calculate the horizontal displacement of this point.

②Install a telemetering tensioner on the measuring point, and use the receiving instrument or automatic detection device in the observation room to perform telemetering and recording, and then obtain the horizontal displacement.

3. The vertical line method.

Taking the vertical line of the dam body or dam foundation as the reference line, use a coordinate instrument to determine the relative displacement between the points and the vertical line at different elevations of the dam body along the line. The deflection curve of the dam body along the vertical line can be drawn from the horizontal displacement observation data at different elevation points on the vertical line. This method is also called deflection observation. It is suitable for various types of concrete dams. It has high observation accuracy and is easy to realize centralized telemetry and automation. It is the main item of automatic dam safety monitoring. A few high earth-rock dams also use the vertical line method to observe the horizontal displacement of the dam foundation.

4. Laser collimation method.

Using a laser beam instead of collimating through the sight of an optical measuring instrument. This method is suitable for linear concrete dams. According to different observation devices, it can be divided into three types: laser collimator, zone plate laser collimation system and vacuum pipe laser collimation system. Among them, the observation accuracy of the first two is slightly higher than that of the line of sight, but still cannot eliminate the influence of air refraction. The latter method eliminates the influence of air refraction, so that the observation accuracy can reach 2X10 units, and the vertical of the measuring point can be measured at the same time. Displacement, but high cost and difficult to maintain.