PSI - Issue 32

V. Epin et al. / Procedia Structural Integrity 32 (2021) 64–70 V. Epin/ Structural Integrity Procedia 00 (2021) 000–000

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3. Method and approaches To measure the vertical movements of an object, you can use the hydrostatic leveling method. Based on Pascal's law, the levels of the liquid columns at the measurement points will determine the surface of an equal level relative to the earth's surface. Deviations in height from this surface will determine the elevation or subsidence of individual parts of the building foundations. The basic principles of constructing measuring systems based on the hydrostatic leveling method were described in the middle of the XX century in the work of Pellissier (1965). This method is often used in geotechnical applications, Yin (2013) or Jacob at al. (2010). The advantage of this method of measuring vertical movements over others is that there is no need for a line of sight between the individual parts of the system. The error of the hydrostatic leveling system depends on the installation method and its quality, which imposes certain requirements on the installation of the system. The term “hydrostatic leveling” assumes that the liquid level in the measuring vessels is stable. However, it is influenced by various factors:  Inhomogeneity of the density (temperature) of the liquid in the hydrostatic level  Inhomogeneity of the air pressure above the measuring vessels The structural features of real structures usually do not allow the use of ideal schemes (with a minimum difference in height and temperature), which are achieved in the laboratory and allow you to get a micron error. Under the combined influence of external factors, the fluid level in the communicating vessels is not at one constant level, but changes over time. The greatest problems are caused by the temperature expansion of the liquid, which can occur not only in the measuring vessel, but also in the connecting tubes. To solve it, complex compensation schemes of several liquids are used. It reduces the height difference or equalize the temperature along the length of the level. These errors occur for all measuring systems based on the hydrostatic leveling method. In addition to the noted hardware errors, it is necessary to consider the measurement error. There are several methods for measuring the liquid level:  Using pressure sensors placed in the liquid.  Vibration effects  Surface tension  Air bubbles in the tube and other factors

 Using force sensors that measure the weight of a body partially submerged in liquid.  Using a displacement sensor that determines the distance from the sensor to the liquid.  Visually using the eyes or the camera

To register changes in the values of the vertical component of the settlement of foundations interacting with the soil, an original and maintainable monitoring system was developed based on a set of hydrostatic leveling sensors, which provides measurement of settlement values from 0 to 60 mm with a resolution of ~ 0.1 mm. IP cameras were used to record vertical displacements of the liquid level in the measuring module. The processing of video images from the entire set of sensors using specially developed software allows it possible to determine the digital numerical values of the vertical settlements of the supporting columns of the structure. A typical photo obtained from a video camera of the hydro-leveling sensor is shown in Fig. 2.