NUMERICAL STRENGTH CALCULATIONS OF UNDERGROUND GAS PIPELINES IN UNDERMINING AREAS

Abstract

Introduction . Various calculation methods, including empirical, analytical, and numerical ones, are used to assess the effect of undermining on base deformations and force variations in the structures of existing and projected pipelines. Empirical methods are typically developed using an experimental analysis of numerous results obtained during the engineering and geodetic observations of settlements and surface terrain shifts in undermining areas. However, such methods fail to take into account all the factors affecting settlements and shifts during underground excavations, including the vertical heterogeneity and physicomechanical properties of soils, etc. Aim . To determine the advantages of numerical methods and to develop a methodology for using numerical calculations in the Plaxis and Midas GTS NX geotechnical software applications. Compared to empirical and analytical methods, numerical approaches have the advantage of simulating the bedding heterogeneity of geological engineering elements and their physicomechanical properties, ensuring joint calculations of the “underground excavation – soil massif – existing structure” system, considering the gradual character and undermining technology, as well as providing the possibility to search through a large quantity of variants over a short period of time. The principles of numerical calculations of the strength of underground main gas pipelines during the arrangement of closed underground excavations for mineral mining are considered. Methods . The developed methodology is based on the degree and nature of effects produced by various factors on numerical modeling results, including the presence of a pipeline in the design model, width of the model calculated area, finite element mesh sizes, parameters of the soil geomechanical model, width, bedding depth, dip angle, thickness, and number of mineral mined formations, as well as the problem statement type (2D or 3D). Results . The results of the study are presented in the form of a methodological verification, performed on the basis of a comparison between the calculated and actual parameters of rock shifts. Conclusions . The presented methodology reliably predicts base deformations and force variations in the structures of existing and projected pipelines during the excavation of a coal seam at one of the mines of the Moscow lignite basin.