f Reconstruction of complex sections of the underground pipelines

The great number of gas- and oil trunk lines in Russia are under operation more than 20 years. The results of the diagnostics of the pipelines technical state show the necessity of their repair and reconstruction. The pipelines reconstruction includes the analysis of design and technological specification, operational conditions as well as calculation of a stressed-deformed state in order to define the most loaded sections of a pipeline. As practice shows, sections of the pipelines running in the complicated engineeringgeological conditions need the reconstruction in the first turn. In soft ground, in swampy or flooded areas the filling fails and the full loss of the longitudinal stability of a pipeline takes place which provokes deflection and crushing of pipes. In order to diminish a pipeline displacement, different anchoring and strengthening devices are used. One of the means of a pipeline strengthening at the design marks is its ballasting with a mineral soil, reinforced with the geosynthetical material. The geosynthetical material is laid onto a pipeline at the trench bottom (at the design marks) and on a trench slopes, it is secured at the trench berms and is filled with the mineral soil. A soil layer is built above a trench and a width of the geosynthetics. The suggested method of calculation of a pipeline stressed-deformed state and soil holding capacity allows to determine the optimum distance between the reinforcing strips of the geosynthetics. The geosynthetical material parameters (mesh size, relative elongation, breaking load, etc.) are chosen on the basis of data of the experimental investigations of combined behaviour of the geosynthetics and the filling soil.