GEODETIC SIGNS USED IN DETERMINING THE SEDIMENTION OF LARGE HYDROTECHNICAL STRUCTURES AND THEIR INSTALLATION

ABSTRACT

This article provides a detailed overview of the procedures and geodetic methods used to monitor deformation in large hydraulic engineering structures. Special emphasis is placed on the selection and installation of benchmarks and settlement markers based on the geological and hydrogeological conditions of the site. The study highlights the classification of benchmarks (deep, surface, and wall-mounted) and the organization of level networks (II and III class) for observing settlements. The Chimkurgan reservoir is presented as a case study, including analysis of benchmark layout, leveling routes, and the use of triangulation and polygonometry to detect vertical and horizontal displacements. Recommendations are provided for ensuring the precision and stability of geodetic control systems used in hydraulic construction.

АННОТАЦИЯ

В данной статье представлен подробный обзор методов и процедур геодезического контроля деформаций крупных гидротехнических сооружений. Особое внимание уделено выбору и установке реперов и осадочных марок с учетом геологических и гидрогеологических условий местности. Рассматривается классификация реперов (глубинные, грунтовые и настенные) и организация нивелирных сетей II и III классов для наблюдения за осадками. В качестве примера приведен Чимкурганский водохранилище, с анализом схемы расположения реперов, нивелирных ходов, а также использованием триангуляции и полигонометрии для определения вертикальных и горизонтальных смещений. Даны рекомендации по обеспечению точности и устойчивости геодезического контроля при строительстве гидротехнических объектов.

Keywords: geodetic monitoring, settlement markers, deep benchmark, hydraulic structure deformation, leveling network, Chimkurgan reservoir, triangulation, polygonometry.

Ключевые слова: геодезический мониторинг, осадочные марки, глубинный репер, деформация гидротехнических сооружений, нивелирная сеть, Чимкурганское водохранилище, триангуляция, полигонометрия.

Introduction. To ascertain the deformation of large hydraulic structures, the following geodetic marks may be installed, depending on the geological and hydrogeological conditions of the site.

1. Benchmarks: These are the initial marks used to establish the basis of absolute heights. These can be either deep, fundamental, soil or wall-mounted.

2. Settlement centers are marks used to monitor the settlement of industrial and hydraulic structures. These markers can be categorized into various types, including wall-mounted, scale-mounted, magnetic, pedestal, surface, temporary, and open-wall models.

These benchmarks are installed at depths ranging from 2 to 100 meters. In industrial facilities, deep benchmarks are placed at a distance of 50 to 100 meters, while in hydraulic structures, the distance is increased to 100 to 300 meters. The primary function of deep benchmarks is to measure subsidence through leveling class I, while ground and wall benchmarks are employed to measure subsidence through leveling classes II and III. In such instances, the number of ground benchmarks must not fall below three, while the number of wall benchmarks should not be less than four [1-8].

Materials and methods. The installation of elevation base marks is a fundamental step in the process of establishing a geodetic reference framework. The measurement work on the subsidence of hydraulic structures can be divided into three groups.

1. The installation of marks near the structure, with subsequent monitoring of subsidence through these marks, constitutes the primary method.

2. It is imperative that working benchmarks placed close to large hydraulic structures are leveled during deformation.

3. Initial benchmarks installed in the boundary zone are stable against deformation.

It is expected that the heights of these initial benchmarks will change over time.

The monitoring of subsidence, specifically that of the primary dam segment, is facilitated by the installation of five rows of subsidence marks on the upper and lower slopes. It is imperative to note that these marks must have been installed during the construction of the dam (this was not the case in our study). The number of marks on the upper slopes is 28, and on the lower slopes, there are 37.

Two-line leveling on the upper and lower slopes relies on a Class II leveling hydraulic leveling point.

The leveling points are connected to two main benchmarks located 500-550 metres outside the deformation zone. (Figure 1)

Conventional symbols

Figure 1. Geodetic markers installed at the Chimkurgan reservoir facility

Results and discussion. All leveling lines are formed of interconnected polygons. A class II leveling line is laid between the main benchmarks. The main benchmarks consist of two foundation main benchmarks (1-AP, 01-02-03, 2-AP, III-IV) fixed to a depth of 2 m. Each of these two fundamental main benchmarks consists of three fundamental benchmarks. These fundamental benchmarks are located at a distance of up to 30 metres from each other. The leveling method involves the placement of the leveler at the centre, with counts being taken forward and back from each fundamental benchmark. The result of this process is documented in the journal. After leveling, the most satisfactory non-sag, non-shifted fundamental benchmark between the 1st main benchmark is selected from the journal. The leveling line is then laid and connected to the selected fundamental benchmark from the 2nd main benchmark, and this process is repeated for each subsequent fundamental benchmark.

The distance between the first and second main benchmarks is 3 km, and there are 30 stations in total. When a class II level track is laid between them, the marginal error should not exceed 4.2 mm.

Conventional symbols

Figure 2. Planimetric-altitude geodetic bases located in the Chimkurgan Reservoir

Following the determination of the primary benchmarks' stability, these benchmarks are regarded as fundamental. Subsequently, leveling, polygonometry and triangulation routes are conducted from these benchmarks, as illustrated in Figure 2. The rationale behind undertaking the polygonometry route is that it facilitates the determination of the horizontal displacement of the structure. The triangulation route, on the other hand, facilitates the determination of vertical displacement.

A special leveling network of classes II and III is established at the experimental facility. The distinguishing factor between the aforementioned special leveling routes and the standard leveling routes of classes I and II is that the former are designated for the state geodetic leveling routes of classes I and II. The utilization of class I and II leveling routes within this hydraulic structure does not fully meet the requisite standards; consequently, special hydraulic leveling routes of classes II and III with high accuracy are carried out for this substantial hydraulic structure [2-5].

The depth of the marker is subject to variation, ranging from 2 metres to 10 metres or more, depending on the parameters of the structure. The placement of the marker within the designated zone is contingent upon the pressure exerted by the structure.

The utilisation of ground and wall markers is instrumental in the determination of the settlement of substantial hydraulic structures in class II-III leveling. The standard stipulates that the number of ground markers should be a minimum of two and that the number of wall markers should be a minimum of four (see instructions) [6-8].

Conclusion. Ideally, the settlement marks should be placed at the same level as possible. The longitudinal and transverse joints of the wall in the area of double-sided weight settlement should be at a distance of 10-15 m.

References:

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