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

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Abstract

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.

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G. P. Postoev

Sergeev Institute of Environmental Geoscience, Russian Academy of Sciences

Author for correspondence.
Email: opolzen@geoenv.ru
Russian Federation, Ulanskii per., 13, str. 2, Moscow, 101000

References

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2. Fig. 1. Schematic section along the central section of the landslide source with the designation of blocks - dissipative structures in the bedrock. A thin solid line shows the boundaries of the blocks and arrows indicate the pressure Pi inside the block on the shell. AB is the day surface of the block in the landslide massif at the Acr level.

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3. Fig. 2. Scheme of simultaneous imbalance of two block-elements of dissipative structures. 1, 2 - respectively, the root and landslide massifs; 3 - a deepened crack of a pin with offset Δ; 4 - part of the new landslide block I being formed (with the center O1), combined with the neighboring block II (with the center O2).

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4. Fig. 3. Schematic engineering-geological section along the axis of the center of activation of the landslide process in 1990 (Rybnaya Sloboda section, Republic of Tatarstan): 1 - root massif; 2 - landslide massif; 3 - the profile of the earth's surface and the edge of the slope in 1975 (before the occurrence of landslide deformations); 4, 5 - exploration wells; 6 - the fence of the tank farm; 7 - landslide cracks and secant sliding surfaces; 8 - the main sliding surface of the landslide.

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5. Fig. 4. Schematic geological section along the axis of the landslide of 1968 on the Sokolovaya Hill in the city of Saratov [7]. A - the bottom strip of the upper part of the slope; B - site sagging surface of the earth in the head of the landslide; B - the main part of the landslide massif, approaching the lower landslide step: D - the lower landslide step. 1 - Jurassic (Oxfordian) clays (J3ox); 2 - Barrem sands (K1b1); 3 - Barremian (K1b2) and Aptian (K1ap2) clays; 4 - lower pack of apta: weak sandstones and sands (K1ap1); 5-6 - horizontally displaced array of Lower Cretaceous rocks: 5 - Barrem clay, 6 - rocks of the Lower Aptian pack; 7 - landslides displaced by Lower Cretaceous clays; 8 - crushed landslide clays and loams; 9 - sands of modern alluvium; 10 - groundwater level; 11-12 - slope profile: before (11) and after (12) landslide movements; 13 - the landslide sole (including the sole of the massif, which has advanced on the lower landslide step); 14 - displacement vectors when the landslide moves and their scale.

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6. Fig. 5. Scheme of a landslide in the East Maritsky coal deposit: 1 - loam; Pliocene clays: 2 - greenish-gray; 3 - black; 4 - coal seam; angular clay: 5 - layered; 6 - with sand lenses containing pressure water (Pliocene); working board profiles: 7 - before and 8 - after deformation; 9 - sliding surface.

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7. Fig. 6. Scheme of the organization of internal dumps in the area of the "Northern Pocket" (based on the materials of A. Demin).

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8. Fig. 7. Schematic section of the northwestern side with a prism of active pressure (based on the materials of AM Demin).

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