5. METHODS AND MEANS OF DIAGNOSTICS OF THE ROADBED
Abstract
Abstract: In this article, the concept of a diagnostic system using geophysical methods for specific railway track conditions, the elements of the diagnostic system are: the object of research; methods and technical means of diagnosis; classification of diagnostic signs (criteria for identifying deformations); trained technical personnel interacting with the object of research according to the rules established by the relevant regulatory and methodological documentation; expert opinion on the technical condition of the roadbed with an indication of the location, type and cause of deformations.
Keywords: Diagnostics, roadbed, soil properties, georadar, diagnostics of the main site, deformation, deep ground reference points, inclinometers, strain gauges, stresses.
МЕТОДЫ И СРЕДСТВА ДИАГНОСТИКИ ЗЕМЛЯНОГО ПОЛОТНА
Умаралиев Шохжахон Мухаммадрузи угли
Ташкентский государственный университет транспорта, ассистент.
Мирханова Мавжуда Михайиловна
Ташкентский государственный университет транспорта, старший преподаватель.
Ембергенов Авезмурат Бекмуратович
Ташкентский государственный университет транспорта, ассистент.
Абдуалиев Элёрбек Бегалиевич
Ташкентский государственный университет транспорта, доктарант.
Аннотация: Данной статье понятие систему диагностики с использованием геофизических методов для специфических условий железнодорожного пути элементами системы диагностики являются: объект исследования; методы и технические средства диагностирования; классификация диагностических признаков (критерии опознавания деформаций); подготовленный технический персонал, взаимодействующий с объектом исследования по правилам, установленным соответствующей нормативно-методической документацией; экспертное заключение о техническом состоянии земляного полотна с указанием места, вида и причины деформаций.
Ключевые слова: Диагностика, земляного полотна, свойств грунтов, георадар, диагностика основной площадки, деформация, глубинные грунтовые репера, инклинометры, тензодатчики, напряжения.
Introduction. The roadbed diagnostics system is based on the use of both traditional and new geophysical methods, modern measuring equipment and computer technologies. The diagnostic system also uses specially designed mobile diagnostic laboratories. The basis of the diagnostic system of the roadbed is made up of geophysical methods, which are based on the study of anomalies of physical fields caused by changes in the lithological structure of the roadbed, the difference in physical and mechanical
Physical fields in the roadbed arise from impacts:
- — direct or alternating electric current through electrodes driven into the ground (electrometric method and electrocontact dynamic sensing method);
- — emission of electromagnetic high-frequency signals (radar method);
- — hammer-type impact loads on the ground (seismic method);
- — moving rolling stock (vibration method).
A brief description of the geophysical methods is given below.
Electrometric method. It is based on the study of the resistance of various soils to the electric current passing through them. As a diagnostic feature, the electrical resistivity p, Ohm m is accepted. The dependence of p on the composition, properties and condition of various soils serves as the physical basis for the application of the electrometric method. The most widely used observation schemes are vertical electrical sounding (VEZ) and electrical profiling (EP)[1,2,3,4,5,6,7,8,9].
The method of electrocontact dynamic sensing (EDS). Combines two methods of simultaneous soil investigation: dynamic probing and current logging. For research, an EMF installation is used, with the help of which the depth of various layers of soil is determined by changing the magnitude of the current, and their strength characteristics are determined based on the results of dynamic probing.
Radar method. It is based on the study of the parameters of electromagnetic waves (propagation velocity and absorption coefficient) arising in soils from the pulsed action of a high-frequency generator.
The radar method does not require antenna contact with the ground surface, as in other geophysical methods, so it can be performed from mobile units (Fig.1), which provides high-speed diagnostics of extended sections of the roadbed. Georadar can diagnose the structure of the main site of the roadbed (the presence of ballast depressions), study the structure of the slope parts of the embankments (determining the size and location of ballast loops.
Fig. 1. Radar of the ground of the roadbed: a — the placement of the ground radar on the track trolley; b — the radar image of the fov), the determination of the boundaries of peat soils in the foundations of embankments in swamps, as well as the boundaries of the location of frozen soils. Diagnostics of the main site of the roadbed with the allocation of ballast depressions by georadar is shown in Fig. 2, b.
Seismic method. The physical prerequisite for the application of this method is the difference in the propagation velocities of longitudinal Vp and transverse Vs elastic waves associated with the presence of lithological boundaries in the earth bed and the difference in the properties and condition of the soil. Two observation methods are used: longitudinal seismic profiling and transverse seismic transmission. The seismic method is the most informative among other geophysical methods in terms of its capabilities and the range of diagnostic tasks to be solved. Vibration method. It is based on the use of soil vibrations of embankments arising from the impact of rolling stock. A group of diagnostic signs of a dynamic process corresponds to a certain condition of the operated embankments, which is a prerequisite for the use of the vibration method[10,11].
Traditional methods can be used, if necessary, at various stages of diagnosing the roadbed. Mobile diagnostic complexes (PNCs) in the form of reference load laboratories, track-measuring laboratory wagons (VP), including with radar complexes, are used for preliminary diagnostics and routine observations. Diagnostic studies of the listed complexes are carried out from the rail track and cover only the working area of the roadbed to a depth of no more than 3-4 m. Geophysical methods are usually used for detailed diagnostics, when it is necessary to obtain the most complete and specific information about the condition of the roadbed, indicating the type and size of existing deformations. Diagnostics of the main site. By the seismic method and in separate areas for a more detailed separation of soil layers by the method of electrocontact dynamic sounding, the following are determined: depressions in the main site in the form of ballast troughs, beds, bags, and also water-saturated and weakened soil zones are isolated[12].
Diagnostics of mounds of clay soils. By seismic and electrometric methods, the power of ballast plumes is established on the slopes of embankments; by the method of electrocontact dynamic sounding, separate layers of soil weakened in strength are isolated on the slopes, along which deformations of the embankment are possible. Seismic and electrometric methods and, in some cases, the method of electrocontact dynamic sounding separate the soils of the body of the embankment according to their appearance and condition, identify and outline the zones weakened in strength in the body of the embankments. The vibration method makes it possible to assess the dynamic state of embankments and predict the appearance of their sudden deformations under trains.
Diagnostics of the foundation of the roadbed. As the main methods, it is recommended to use seismic and electrometric methods; additionally, radar and the method of electrocontact dynamic sensing. When diagnosing embankments erected in swamps, using the electrometric method, the amount of immersion of the embankment into the thickness of silty sediments is determined and the sections of the path where the embankment has settled on the mineral bottom are identified.
On the landslide slopes on which the roadbed is constructed, using the seismic method, the boundaries between the landslide (or prone to landslide) and stable rocks are determined; the morphology of the landslide bed is established; the geometry of the landslide blocks in the plan and sometimes the number of floors of the landslide are clarified; the nature of the fracturing of the landslide massif and the predominant direction of landslide cracks are estimated. In areas of rock recesses, the seismic method can be used: to establish the thickness of loose cover deposits of rock massifs; the thickness of the weathered zone of bedrock; identification and delineation of vertical weakened zones in rocks; determination of azimuths of vertical and steeply falling cracks or layers of vertically layered strata; determination of the coefficient of volumetric fracture voidness.
In areas where karst processes are spreading, karst cavities may be located under the roadbed or in the immediate vicinity of its bases, which, under certain conditions, pose a real threat to the safety of train traffic. The use of seismic and electrometric methods makes it possible to identify the location, depth of occurrence and thickness of the karst rocks. In areas of permafrost, where the roadbed is exploited, electrometric and seismic methods are used to determine: the depth of the upper and lower boundaries of frozen rocks; the thickness of loose deposits; thawed and talic zones in the frozen rock massif; physical and mechanical properties of frozen soils in their natural occurrence.
Thus, geophysical methods have great opportunities for detailed diagnostics of the roadbed and its base. The choice of a single geophysical method or a rational set of methods depends on the effectiveness and accuracy of the methods in specific geoseismic and geoelectric conditions of the object and their technical and economic feasibility. For the successful application of geophysical methods, a small volume (10-15% of the total amount of work) of reference drilling wells is required for a more reliable interpretation of the obtained geophysical data.
Routine observations consist in measuring the time-varying parameters of the roadbed. First of all, various deformations of the roadbed are subject to measurement at the initial stage, until they have reached large values. In addition, the parameters of the humidity and temperature regimes of the roadbed are effective for regime observations. Methods and means of regime observations should promptly provide information on changes in the main parameters of the roadbed with sufficient regularity. Methods and means of regime observations can be divided into two large groups: stationary and mobile. The first include various sensors and control and notification systems installed at the facility, the removal of information from which can be carried out on portable devices or obtained by transmitting a signal in automatic mode. These methods and means are used to measure: deformations (deep ground reference points, inclinometers, strain gauges); stresses (messdoses, strain gauges and pore pressure sensors); temperature (thermal pumps and electric thermometers, thermal imagers); humidity (strain gauges, sorption sensors); groundwater level (hydrometric wells, etc.).
Mobile vehicles include: track measuring wagons; loading devices; georadar complexes. The stability of the track gauge geometry determined by track measuring cars depends on the condition of the track elements, including the roadbed. The transition of the roadbed to an unstable state causes increased disorders of the geometry of the rail track.
Another diagnostic mobile means for identifying areas with increased deformability of the sleeper base are load complexes. These complexes perform continuous measurement along the length of the track of the elastic precipitation of the rail and sleeper under the reference load when the complex is moving at a speed of 5-10 km / h. It is desirable to carry out the passages of the complex during the unfavorable period of spring thawing of the soil of the roadbed or prolonged rains. The complex consists of a load unit mounted on a special wagon, which provides a given reference load on the track and a measuring and computing complex that fixes and processes elastic deformations (precipitation) of the track that occur during load tests.
Conclusion. With a high degree of probability of exogenous geological hazards such as landslide, karst, landslide, scree and mudslide in areas adjacent to the roadbed, alarm systems or control and notification systems should be arranged. As such alarms, separate sensors can be used (for example, such as GPS, Glonas), allowing in real time to provide information about the movements of specially installed deformation reference points, or a barrier whose sensors are triggered when the barrier is deformed or destroyed, which in their magnitude exceed the systems established by the project.
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