Modeling the rock landslides process using the Rocscience program suite

Modeling the rock landslides process using the Rocscience program suite

Transcript

1. Modeling the rock landslides process using the Rocscience program suite Saint Petersburg, 2018 Российский государственный геологоразведочный университет имени Серго Орджоникидзе D.N. Gorobtsov, I.K. Fomenko, V.V. Pendin, M.E. Nikulina
2. The main objectives of the work are 1. to consider the main terms connected with sliding surface types in quantity stability assessment of rock slopes; 2. to pose the main slant on the modelling; 3. to show the examples and application instructions of Swedge, Slide and RS units in quantity stability assessment of rock slopes. Consideration of landslides that are formed in rock soils and quantity assessment of rock slopes stability using the Rocscience program suite. The main aim of the work
3. The types of rock slope’s idealization in quantity stability assessment with well-defined sliding plane which matches the spread direction of slope with two main sliding planes that fall towards and downslope; the displacement of the sliding block runs in a direction matches the line of their crossing (“wedge”- type) with circular cylindrical sliding plane
4. Rock landslides along well-defined sliding plane that matches the spread direction of slope •  mostly happened on existing continuous separation surfaces (bedding, fracturing, and schistosity) which fall aside a slope (the consequent landslides formation by F.P. Savarenski); •  the displacement block cutoff occurs on joints, lateral crevasse or subvertical tectonic fractures.
5. Rock landslides with two main glide planes that fall towards and downslope (“wedge” type) •  the formation and occurrence of such landslides depends on lithology and rock massifs structure; •  favorable conditions for such landslides are created in rock massifs with schistose and fine- stratified texture and in cleavage zones •  in the process of landslides with two main glide planes that fall towards, one sliding surface is influenced by bedding and inclined or vertical jointing zone
6. Rock landslides with circular cylindrical sliding plane •  form as in massifs with chaotic jointing as in stratified rock massifs (insequent landslides according to F.P. Savarenski)
7. Stability quantity assessment of rock landslides Following groups of methods were chosen to perform the stability assessment: 1. variants which solve the rock landslides stability assessment problem in case of circular cylindrical sliding plane (without existing surface of separation straight): - method of limit equilibrium group which includes Morgenstern- Price, simplified Bishop’s and Janby’s methods [5]; - finite elements method which represent numerical method class. 2. variants which assess the stability on the base of existing surface of separation: - method of limit equilibrium group which includes Morgenstern- Price, simplified Bishop’s and Janby’s methods; - finite elements method; - method of volume rock blocks assessment (for the “wedge” type landslides).
8. The results of stability modelling Design characteristics of soils strength properties in massif were corrected (with an allowance) based on rock soils classification GSI. Generalized criteria of Hoek-Brown was used as strength criteria (soil’s properties that were used during calculation are shown on figure 1.410 1.410 1.410 1.410 1.410 1.410 Method Name Min FS Bishop simplified 1.414 Janbu simplified 1.352 GLE / Morgenstern-Price 1.410 Material Name Color Unit Weight (kN/m3) Strength Type UCS (kPa) m s a Material 1 28 Generalized Hoek-Brown 50000 0.064921 1.90286e-005 0.531267 60 40 20 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
9. The results of stability modelling Geomechanical schemes with results of estimation by limit equilibrium and finite elements methods are shown on figure Critical SRF: 1.42 Total Displacement min (stage): 0.0000 m max (stage): 0.0278 m 0.0000 0.0028 0.0056 0.0084 0.0112 0.0140 0.0168 0.0196 0.0224 0.0252 0.0280 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
10. Rock landslides with clearly distinguished glide plane which matches the slope’s spread direction (dip angle is oriented along the slope) Linear anisotropic criteria was used as strength criteria (Snowden, 2007). Meanwhile as soil’s properties along fracture were chosen cohesion and friction angle (specified on the base of Barton-Bandis criteria [Barton 1990, Hoek E., 2002). In massif as soil’s properties were chosen equivalent cohesion and friction angle values that were calculated by conversion from Hoek-Brown criteria. Geomechanical schemes with results of estimation by limit equilibrium and finite elements methods are shown on next slides.
11. 0.965 1.044 0.965 0.965 0.965 1.044 0.965 0.965 55° Method Name Min FS Bishop simplified 0.965 Janbu simplified 0.913 GLE / Morgenstern-Price 1.018 Material Name Color Unit Weight (kN/m3) Strength Type Cohesion (kPa) Phi (deg) Cohesion 2 (kPa) Phi 2 (deg) Anisotropic Linear A (deg) Anisotropic Linear B (deg) Material 1 28 Anisotropic Linear 10 38 112 24 0 5 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
12. Critical SRF: 1.11 55° Total Displacement min (stage): 0.0000 m max (stage): 0.0481 m 0.0000 0.0049 0.0098 0.0147 0.0196 0.0245 0.0294 0.0343 0.0392 0.0441 0.0490 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
13. Rock landslides with two main glide planes, which fall towards, and downslope (“wedge” type) The sliding block of “wedge” type falling down analysis was organized for observed fracturing systems with the following slope parameters: - slope height 25 m; - dip angle/drop azimuth for slope’s surface - 65/245; - dip angle / drop azimuth for upper slope’s surface - 0/245; Strength properties along fractures: с = 10 kPa, φ = 38°.
14. Rock slope’s stability results The stability estimation result of considered slope: Кs= 1.009, volume 315 m3, weight – 8.2 МН Perspective Factor of Safety: 1.0089
15. Conclusion Rock slope’s collapse happens on the base of the other principles than sliding processes in dispersed soils. Calculation shows that on the considered territory may occur rock landslides of following types: 1. fracturing drop azimuth matches the slope’s drop azimuth (fracture falls «in slope»); 2. fracturing system drop azimuth does not match the slope’s drop azimuth. Formation of “wedge” type landslides requires confirmation by the results of kinematic analysis; 3. slope is broken by chaotic oriented fracturing system (the presence of oriented fractures fall «in slope» is allowed).
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