Underground pipeline stresses caused by damage near anchor mounting

The article considers the issues of underground pipeline strength, which are operated in geological or technogenic complication conditions (movements of indigenous soil in the tectonic fault zone, mutual displacements and rotations of rock blocks, etc.). The work aims at studying of a mobility limitation effect of a pipeline anchorage imposed on the stress state in the pipe wall in the site of a local damage foundation. The pipeline static was investigated in a geometrically linear formulation, modeling it with a tubular cross-section, and with a momentless cylindrical shell for straight issues. The interaction of the pipe with a dense base through soil backfill was described by the hypothesis of Winkler's elastic layer. The deformation of the anchored pipe caused by base local continuity disturbances was studied, which was modeled by the given jumps of longitudinal displacement and the block angle of rotation. This approach makes it possible to evaluate the strength of long underground communications not on the external load from the ground, which is usually unknown, but according to the observed parameters of riverside movements. The limiting state of the pipeline under the internal pressure of the transported product and under additional loading from kinematic perturbation was investigated by the energy theory of strength. The authors formulated boundary value problems for differential tensile-compression equations and torsion of a straight bar with discontinuous right-hand sides. On the basis of analytical solutions to the problems, the effect of normal separation crack damage, foundation blocks convergence and their turn around the axis of the pipe on the stress-strain state of the pipeline was studied. Plots of displacement distribution, angles of rotation and equivalent stresses of von Mises are constructed depending on the magnitude and direction of the mutual displacement and reversal of the riverside at different distances from the anchor to the base defect. It has been found that overlapping anchors in the form of anchorage leads to a significant increase in the equivalent stresses in the pipe. It has also been found that for pipes under internal pressure, the approximation of the base blocks is more dangerous than their divergence.

The mechanism of block collapse formation upon activizing the deep landslide in terms of dissipative structures

The paper considers the collapse mechanism in the back part of a new landslide block upon its separation from the bedrock massif. It is shown that in the course of failure preparation, two blocks participate, i.e., the elements of dissipative structures that appear in the stress field of the bedrock landslide-prone massif. The study reviews the conditions of failure formation, stress distribution (in accordance with the Laplace solutions for axisymmetric thin-walled shells) inside the block and along its boundary surfaces (shells) when the massif limit state forms. The mechanism of block separation (discontinuity of the massif) along the shell and specifics of soil deformation are also analyzed. The equilibrium in the head scarp massif is usually disturbed due to soil discontinuity forming along the earlier virtual circular-cylindrical shell of the first block, adjacent to the slope edge. In this case, the landslide block moves according to the detrusive mechanism. In addition to the ordinary process, the delapsive movement is also possible, with activating massif displacements in the lower part (washing-out, sliding, underworking of the lower part of the slope). This landslide activation favors to more intensely decreasing stresses in the back block shell in the head scarp massif, and consequently, to widening of the separation crack. At that moment, the influence of the subsequent block becomes evident, as displacements take place along the frontal block shell and a failure massif forms between the specified boundaries. The examples of failure-blocks formation when the landslide process activates on the natural slopes and quarry slopes are given.