scholarly journals Geographic-information-system-based topographic reconstruction and geomechanical modelling of the Köfels rockslide

2021 ◽  
Vol 21 (8) ◽  
pp. 2461-2483
Author(s):  
Christian Zangerl ◽  
Annemarie Schneeberger ◽  
Georg Steiner ◽  
Martin Mergili
Keyword(s):  
Information System ◽  
Shear Strength ◽  
Rock Mass ◽  
Groundwater Flow ◽  
Shear Zone ◽  
Failure Process ◽  
Friction Angle ◽  
Strength Properties ◽  
Low Friction ◽  
Basal Shear

Abstract. The Köfels rockslide in the Ötztal Valley (Tyrol, Austria) represents the largest known extremely rapid landslide in metamorphic rock masses in the Alps. Although many hypotheses for the trigger were discussed in the past, until now no scientifically proven trigger factor has been identified. This study provides new data about the (i) pre-failure and failure topography, (ii) failure volume and porosity of the sliding mass, and (iii) numerical models on initial deformation and failure mechanism, as well as shear strength properties of the basal shear zone obtained by back-calculations. Geographic information system (GIS) methods were used to reconstruct the slope topographies before, during and after the event. Comparing the resulting digital terrain models leads to volume estimates of the failure and deposition masses of 3100 and 4000 million m3, respectively, and a sliding mass porosity of 26 %. For the 2D numerical investigation the distinct element method was applied to study the geomechanical characteristics of the initial failure process (i.e. model runs without a basal shear zone) and to determine the shear strength properties of the reconstructed basal shear zone. Based on numerous model runs by varying the block and joint input parameters, the failure process of the rock slope could be plausibly reconstructed; however, the exact geometry of the rockslide, especially in view of thickness, could not be fully reproduced. Our results suggest that both failure of rock blocks and shearing along dipping joints moderately to the east were responsible for the formation or the rockslide. The progressive failure process may have taken place by fracturing and loosening of the rock mass, advancing from shallow to deep-seated zones, especially by the development of internal shear zones, as well as localized domains of increased block failure. The simulations further highlighted the importance of considering the dominant structural features of the rock mass. Considering back-calculations of the strength properties, i.e. the friction angle of the basal shear zone, the results indicated that under no groundwater flow conditions, an exceptionally low friction angle of 21 to 24∘ or below is required to promote failure, depending on how much internal shearing of the sliding mass is allowed. Model runs considering groundwater flow resulted in approximately 6∘ higher back-calculated critical friction angles ranging from 27 to 30∘. Such low friction angles of the basal failure zone are unexpected from a rock mechanical perspective for this strong rock, and groundwater flow, even if high water pressures are assumed, may not be able to trigger this rockslide. In addition, the rock mass properties needed to induce failure in the model runs if no basal shear zone was implemented are significantly lower than those which would be obtained by classical rock mechanical considerations. Additional conditioning and triggering factors such as the impact of earthquakes acting as precursors for progressive rock mass weakening may have been involved in causing this gigantic rockslide.

scholarly journals GIS-based topographic reconstruction and geomechanical modelling of the Köfels Rock Slide

2020 ◽  
Author(s):  
Christian Zangerl ◽  
Annemarie Schneeberger ◽  
Georg Steiner ◽  
Martin Mergili
Keyword(s):  
Shear Strength ◽  
Groundwater Flow ◽  
Friction Angle ◽  
High Water ◽  
Strength Properties ◽  
Trigger Factor ◽  
Rock Slide ◽  
Low Friction ◽  
Volume Estimates ◽  
The Impact

Abstract. The Köfels Rock Slide in the Ötztal Valley (Tyrol, Austria) represents the largest known extremely rapid landslide in metamorphic rock masses in the Alps. Although many hypotheses for the trigger were discussed in the past, until now no scientifically proven trigger factor has been identified. This study provides new data about the i) pre-failure and failure topography, ii) failure volume and porosity of the sliding mass, and iii) shear strength properties of the gneissic rock mass obtained by back-calculations. Geographic information system methods were used to reconstruct the slope topographies before, during and after the event. Comparing the resulting digital terrain models leads to volume estimates of the failure and deposition masses of 3.1 km3 and 4.0 km3, respectively and a sliding mass porosity of 26 %. For the back-calculations the 2D discrete element method was applied to determine the shear strength properties of the reconstructed basal shear zone. Results indicated that under no groundwater flow conditions, a very low friction angle below 24° is required to promote failure, whilst, with groundwater flow, the critical value increase to 28°. Such a low friction angle is unexpected from a rock mechanical perspective for this strong rock and groundwater flow, even if high water pressures are assumed, may not be able to trigger this rock slide. Additional conditioning and triggering factors should be identified by further studies, for example focussing on the impact of dynamic loading.

scholarly journals Mineralogical and Geotechnical Characterization of the Clay Layers within the Basal Shear Zone of the 1963 Vajont Landslide

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 360
Author(s):  
Alberto Bolla ◽  
Paolo Paronuzzi ◽  
Daniela Pinto ◽  
Davide Lenaz ◽  
Marco Del Fabbro
Keyword(s):  
Shear Strength ◽  
Shear Zone ◽  
Friction Angle ◽  
Upper Jurassic ◽  
Rupture Zone ◽  
Rock Masses ◽  
Clay Layers ◽  
Basal Shear ◽  
Clay Lenses ◽  
Vajont Landslide

The 1963 Vajont landslide is a reference example of large rockslides involving clay interbeds emplaced in sedimentary rock masses in correspondence with the basal rupture zone (thinly stratified cherty limestone of the Fonzaso Formation dated to Middle–Upper Jurassic). The basal shear zone of the 1963 Vajont landslide was made up of a chaotic assemblage of displaced rock masses, limestone angular gravel, and spread clay lenses. The mineralogical investigations showed that the clays are characterized by complex assemblages of illite/smectite mixed layers (36–96%) admixed with variable amounts of calcite (4–64%) and quartz (0–6%). The clay layers show highly variable plasticity properties and shear strength characteristics. The samples with a large prevalence of clay mineral content (CM) (CM > 79%) are characterized by low values of the residual friction angle (6.7–14.9°), whereas clay materials characterized by a higher content of granular minerals (calcite and quartz) clearly show greater friction angle values (19.5–26.7°). The high permeability of the limestone angular gravel, which caused a rapid reservoir-induced inflow (1960–1963), together with the low friction angle of the clay layers were responsible for the overall shear strength reduction in correspondence with the basal rupture zone, thus favoring the huge sliding on 9 October 1963.

General concept of determining the parameters of non-mining walls of ultra-deep diamond deposits development open pits

2021 ◽  
pp. 48-53
Author(s):  
I. V. Zyryanov ◽  
A. N. Akishev ◽  
I. B. Bokiy ◽  
N. M. Sherstyuk
Keyword(s):  
Rock Mass ◽  
Structural Relaxation ◽  
Slope Angle ◽  
Field Tests ◽  
Friction Angle ◽  
Strength Properties ◽  
Strength Characteristics ◽  
Open Pit ◽  
Open Pit Mining ◽  
Relaxation Coefficient

A specific feature of open pit mining of diamond deposits in Western Yakutia is the construction of the open pits in the zone of negative ambient temperatures, which includes thick permafrost rock mass, and which is at the same time complicated by the influence of cryogenic processes on deformation of pit wall benches. The paper presents the comparative analysis of strength characteristics in frozen and thawed rocks, stability of benches during mining, the general geomechanical approach to the determination of parameters of non-mining walls of the ultra-deep open pit diamond mines, and the parameters of nonmining walls and benches. Optimization of open pit wall configuration should primarily be based on the maximum utilization of the strength properties of frozen rocks in combination with the development of new approaches, calculation schemes and methods for assessing stability of open pit walls and benches of unconventional design, including the non-mining vertical benches. The main design characteristic that determines the parameters of open pit walls is the structural tectonic relaxation coefficient, which specifies the calculated value of cohesion in rock mass. For the diamond deposits, the values of the structural relaxation coefficient were obtained in a series of field tests and back calculations. Full-scale tests were carried out both during exploration operations in underground mines and in open pits. The accuracy of determining the values of the structural relaxation coefficient in the range of 0.085–0.11 is confirmed by the parameters of non-mining walls in an open pit mine 385–640 m deep, with overall slope angles of 38–55° and a steeper H 0.35–0.5 lower part having the slope angle of up to 70° with average strength characteristics of 7.85–11.84 MPa and the internal friction angle of 28.1–37.4°. Using the natural load-bearing capacity of rock mass to the full advantage, which the values of the structural relaxation coefficient of deposits show, allows optimization of open pit wall slope design and minimization of stripping operations.

The Luco dei Marsi deep-seated gravitational deformation: first evidence of a basal shear zone in the central Apennine mountain belt (Italy) 

2021 ◽  
Author(s):  
Emiliano Di Luzio ◽  
Marco Emanuele Discenza ◽  
Maria Luisa Putignano ◽  
Mariacarmela Minnillo ◽  
Diego Di Martire ◽  
...  
Keyword(s):  
Rock Mass ◽  
Shear Zone ◽  
Engineering Geology ◽  
Slope Deformation ◽  
European Alps ◽  
Structural Constraints ◽  
Normal Faulting ◽  
Central Apennines ◽  
Gravity Driven ◽  
Basal Shear

<p>The nature of the boundary between deforming rock masses and stable bedrock is a significant issue in the scientific debate on Deep-Seated Gravitational Slope Deformations (DSGSDs). In many DSGSDs the deforming masses move on a continuous sliding surface or thick basal shear zone (BSZ) [1-3]. This last feature is due to viscous and plastic deformations and was observed (or inferred) in many worldwide sites [4]. However, no clear evidence has been documented in the geological context of the Apennine belt, despite the several cases of DSGSDs documented in this region [5-6].</p><p>This work describes a peculiar case of a BSZ found in the central part of the Apennine belt and observed at the bottom of a DSGSD which affects the Meso-Cenozoic carbonate ridge overhanging the Luco dei Marsi village (Abruzzi region). The NNW-SSE oriented mountain range is a thrust-related Miocene anticline, edged on the east by an intramountain tectonic depression originated by Plio-Quaternary normal faulting. The BSZ appears on the field as a several meters-thick cataclastic breccia with fine matrix developed into Upper Cretaceous, biodetritic limestone and featuring diffuse rock damage.</p><p>The gravity-driven process was investigated through field survey, aerial photo interpretation and remote sensing (SAR interferometry) and framed into a geological model which was reconstructed also basing on geophysical evidence from the CROP 11 deep seismic profile. The effects on slope deformation determined by progressive displacements along normal faults and consequent unconfinement at the toe of the slope was analysed by a multiple-step numerical modelling constrained to physical and mechanical properties of rock mass.</p><p>The model results outline the tectonic control on DSGSD development at the anticline axial zone and confirm the gravitational origin of the rock mass damage within the BSZ. Gravity-driven deformations were coexistent with Quaternary tectonic processes and the westward (backward) migration of normal faulting from the basin margin to the inner zone of the deforming slope.</p><p><strong>References</strong></p><p>[1] Agliardi F., Crosta G.B., Zanchi A., (2001). Structural constraints on deep-seated slope deformation kinematics. Engineering Geology 59(1-2), 83-102. https://doi.org/10.1016/S0013-7952(00)00066-1.</p><p>[2] Madritsch H., Millen B.M.J., (2007). Hydrogeologic evidence for a continuous basal shear zone within a deep-seated gravitational slope deformation (Eastern Alps, Tyrol, Austria). Landslides 4(2), 149-162. https://doi.org/10.1007/s10346-006-0072-x.</p><p>[3] Zangerl C., Eberhardt E., Perzlmaier S., (2010). Kinematic behavior and velocity characteristics of a complex deep-seated crystalline rockslide system in relation to its interaction with a dam reservoir. Engineering Geology 112(1-4), 53-67. https://doi.org/10.1016/j.enggeo.2010.01.001.</p><p>[4] Crosta G.B., Frattini P., Agliardi F., (2013). Deep seated gravitational slope deformations in the European Alps. Tectonophysics 605, 13-33. https://doi.org/10.1016/j.tecto.2013.04.028.</p><p>[5] Discenza M.E., Esposito C., Martino S., Petitta M., Prestininzi A., Scarascia-Mugnozza G., (2011). The gravitational slope deformation of Mt. Rocchetta ridge (central Apennines, Italy): Geological-evolutionary model and numerical analysis. Bulletin of Engineering Geology and the Environment,70(4), 559-575. https://doi.org/10.1007/s10064-010-0342-7.</p><p>[6] Esposito C., Di Luzio E., Scarascia-Mugnozza G., Bianchi Fasani G., (2014). Mutual interactions between slope-scale gravitational processes and morpho-structural evolution of central Apennines (Italy): review of some selected case histories. Rendiconti Lincei. Scienze Fisiche e Naturali 25, 161-155. https://doi.org/10.1007/s12210-014-0348-3.</p>

scholarly journals Determining the Shear Strength and Permeability of Soils for Engineering of New Paddy Field Construction in a Hilly Mountainous Region of Southwestern China

2020 ◽  
Vol 17 (5) ◽  
pp. 1555
Author(s):  
Zhen Han ◽  
Jiangwen Li ◽  
Pengfei Gao ◽  
Bangwei Huang ◽  
Jiupai Ni ◽  
...  
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Water Content ◽  
Engineering Design ◽  
Soil Water ◽  
Soil Water Content ◽  
Paddy Field ◽  
Friction Angle ◽  
Strength Properties ◽  
Mountainous Region

As a constructed wetland ecosystem, paddy field plays an irreplaceable role in flood storage and detention, groundwater replenishment, environmental protection, and ecological balance maintenance. New paddy field construction can give full play to the production and ecological functions of paddy field and can adjust the development structure of the agricultural industry effectively. The soil properties of shear strength and permeability, which provide a theoretical basis for engineering design, construction, and post-operation, are important indexes in the site selection of new paddy field. The shear strength and permeability properties of soils from different land use types (vegetable field, gentle slope dryland, corn field, grapery, and abandoned dryland) for engineering new paddy field construction were investigated in this study. The results showed that the soil water content had a significant effect on the soil shear strength, internal friction angle, and cohesion. The total pressure required for soil destruction decreased with increasing water content under the same vertical pressure, resulting in easier destruction of soils. The internal friction angle decreased with increasing soil water content, and the soil cohesion first increased and then decreased with increasing soil water content. Considering that paddy fields were flooded for a long time, the soil strength properties had certain water sensitivity. Effective measures must be taken to reduce the change in soil water content, so as to ensure the stability of the embankment foundation, roadside ditch foundation, and cutting slope. In addition, the influence of changing soil water content on the strength properties of paddy soils should be fully considered in engineering design and construction, and the soil bulk density at the plough pan should reach at least 1.5 g cm−3 or more to ensure better water retention and the anti-seepage function of paddy field. The study can provide construction technology for engineering new paddy field construction in a hilly mountainous region of southwestern China.

Model Testing and Analysis Study on Shear Strength of Rock Mass Containing Multiple Cracks under Compression-Shearing Loading

2008 ◽  
Vol 33-37 ◽  
pp. 617-622
Author(s):  
Wei Shen Zhu ◽  
Bin Sui ◽  
Wen Tao Wang ◽  
Shu Cai Li
Keyword(s):  
Shear Strength ◽  
Rock Mass ◽  
Rock Sample ◽  
Failure Process ◽  
Jointed Rock ◽  
Multiple Cracks ◽  
Test Results ◽  
Failure Model ◽  
Two Phase ◽  
Bridge Failure

Two-phase modelling testing was performed to study the shear strength of rock bridges of jointed rock mass in this paper. The failure process of rock sample containing multiple collinear cracks was observed. Based on theory of fracture mechanics and analytical method, a rock-bridge failure model was proposed and the expression of shear strength was derived. Comparison of calculated shear strength and the model test results was made and they agree well.

scholarly journals Shape or friction? Which of these characteristics drives the shear strength in granular systems?

2021 ◽  
Vol 249 ◽  
pp. 06008
Author(s):  
Theechalit Binaree ◽  
Emilien Azéma ◽  
Nicolas Estrada ◽  
Mathieu Renouf ◽  
Itthichai Preechawuttipong
Keyword(s):  
Shear Strength ◽  
Sliding Friction ◽  
Strength Properties ◽  
Contact Dynamics ◽  
Granular Systems ◽  
Combined Effects ◽  
Low Friction ◽  
Systematic Analysis ◽  
Dynamics Simulations ◽  
Two Parameters

The shape of the particles and local friction, separately, are known to strongly affect the macroscopic properties of an assembly of grains. But the combined effects of these two parameters still remain poorly described. By means of extensive two dimensional contact dynamics simulations, we perform a systematic analysis of the interplay between friction and shape on strength properties of granular systems. The shape of the particles is varied from disks to triangles, while the friction is varied from 0 to 0.7. We find that the macroscopic friction first increases with angularity, but it may decline (for low friction values), saturate (for intermediates friction values), or continue to increase (for large friction values) for the most angular shapes. In other words, the effect of the particle’s angularity on the shear strength depends on the level of sliding friction. In contrast, the effect of local friction on the shear strength does not depend on the specific properties of shape. The results presented here highlight the subtle coupling existing between shape and friction effects.

Study on the Shear Strength Properties of the Silt in Hangzhou, China

2013 ◽  
Vol 405-408 ◽  
pp. 349-352
Author(s):  
Zhen Ying Zhang ◽  
Da Zhi Wu ◽  
Cha Wang
Keyword(s):  
Shear Strength ◽  
Soil Mechanics ◽  
Friction Angle ◽  
Strength Properties ◽  
Soil Samples ◽  
Uniformity Coefficient ◽  
Cohesion Force ◽  
Natural Density ◽  
Hardening Curve ◽  
The Relationship

To investigate the shear strength properties of the silt, three soil samples are collected from Xiasha zone, Hangzhou, Zhejiang Province, China. The geotechnical engineering parameters of the silt soil are measured in the soil mechanics laboratory. Tests results show that the uniformity coefficient of the silt is 13.6, the natural density is 1.96t/m3, the moisture content is 17.0%, the plasticity index is 9.4, the cohesion force varies from 20.8 to 28.3kPa, and the internal friction angle varies from 12.3 to 31.8degree. Finally, the properties of the shear strength are studied, and find that the relationship between the shear stress and the shear strain is conformity with the strain hardening curve, and the relationship between the shear strength and the vertical pressure applied on the soil samples is linear, and agrees with the Coulombs law.

Numerical Experimental Research on Shear Strength of Rock Mass Discontinuity Concerning Roughness

2014 ◽  
Vol 707 ◽  
pp. 289-293
Author(s):  
Ji Hong Wei ◽  
Yuan Yuan Yang ◽  
Xiao Bing Gao
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Rock Mass ◽  
Numerical Experiment ◽  
Inclination Angle ◽  
Friction Angle ◽  
Direct Shear ◽  
Asperity Height ◽  
Complex Process ◽  
Inclination Angles

The discontinuity’s surface topography is often assumed as smooth and straight. To overcome non-considering roughness of discontinuity, direct shear numerical experiment is proposed to research influences of discontinuous roughness on its strength. Firstly, based on researched mechanical properties of discontinuity, the laws how asperity inclination angles and asperity heights of discontinuity and the mechanical behavior of discontinuity are studied. The results show that the failure of discontinuity considering roughness is not instantaneous. It is a complex process which goes through energy accumulation. The cohesive force increases with asperity inclination angle and asperity height increasing. The inner friction angle also goes through the same changes. However, when the normal stress reaches 500kPa for asperity inclination angle and 700kPa for asperity height, the shear strength experiences a decreasing process.

scholarly journals Direct Shear Behavior of Nanometer Magnesia Reinforced Cement Soil with 28d Age

2014 ◽  
Vol 8 (1) ◽  
pp. 509-513
Author(s):  
Shuai Zhang ◽  
Wei Wang ◽  
Xinjiang Song ◽  
Xuchao Chi ◽  
Tinghao Lu
Keyword(s):  
Shear Strength ◽  
Shear Failure ◽  
Mechanical Performance ◽  
Failure Process ◽  
Particle Interaction ◽  
Friction Angle ◽  
Mixing Ratio ◽  
Convex Shape ◽  
Mixing Ratios ◽  
Cement Soil

In order to properly understand the modification effects of nanometer magnesia additive on cement soil’s mechanical performance, a consolidated quick shear laboratory test on nano-magnesium-modified cement-soil (NmCS) sample with different mixing ratio at 28-day age was conducted. Eight kinds’ of nanometer magnesia additives with mixing ratios ranging from 0% to 3% were designed to be used in the test. The result shows that: (1) shear stressdisplacement curves of all samples consisted of three distinct stages with brittle failure. Moreover, (2) as the nanometer magnesia mixing ratio increased, the NmCS shear strength also showed an increase at first, followed by a decrease, and the shear strength reached the maximum with the mixing ratio of 1%. (3)In addition, both the friction angle and cohesive force were fluctuating and had a concave and convex shape respectively and (4) with greater deformation resistance, the shear displacement of NmCS was significantly less than the ordinary cement soil in the shear failure process. Finally, according to the test results, the micro-mechanism of NmCS mechanical performance was analyzed from the perspective of cement hydration and particle interaction.

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