https://researchrepository.ucd.ie/bitstream/10197/3027/1/Schopfer_et_al_IRMMS_2009_repository.pdf

The impact of porosity and crack density on the elasticity, strength and friction of cohesive granular materials : insights from DEM modelling

Surface-parallel slabbing is a failure mode often observed in highly stressed hard rocks in underground excavations. This paper presents the results of experimental studies on slabbing failure of hard rock with different sample height-to-width ratios. The main purpose of this study was to find out the condition to create slabbing failure under uniaxial compression and to determine the slabbing strength of hard rock in the laboratory. Uniaxial compression tests were carried out using five groups of granite specimens. The mechanical parameters of the sample rock, Iddefjord granite from Norway, were measured on the cylindrical and Brazilian disc specimens. The transition of the failure mode was studied using rectangular prism specimens. The initiation and the propagation of slabbing fractures in specimens were identified by examining the relationship among the applied stress, strain and the acoustic emission. The stress thresholds identified were compared to those reported by other authors for crack initiation and brittle failure. It is observed that the macro failure mode will be transformed from shear to slabbing when the height/width ratio is reduced to 0.5 in the prism specimens under uniaxial compression. Micro σ
 1-parallel fractures initiate when the lateral strain departs from its linearity. Slabbing fractures are approximately parallel to the loading direction. Labotatory tests show that the slabbing strength (σ
 sl) of hard rock is about 60% of its uniaxial compression strength. It means that if the maximum tangential stress surrounding an underground excavation reaches about the slabbing threshold, slabbing fractures may take place on the boundary of the excavation. Therefore, the best way to stop or eliminate slabbing failure is to control the excavation boundary to avoid the big stress concentration, so that the maximum tangential stress could be under the slabbing threshold.

https://link.springer.com/content/pdf/10.1007%2Fs00603-010-0127-0.pdf

Influence of Sample Height-to-Width Ratios on Failure Mode for Rectangular Prism Samples of Hard Rock Loaded In Uniaxial Compression

Unrest at large calderas rarely ends in eruption, encouraging vulnerable communities to perceive emergency warnings of volcanic activity as false alarms A classic example is the Campi Flegrei caldera in southern Italy, where three episodes of major uplift since 1950 have raised its central district by about 3 m without an eruption Individual episodes have conventionally been treated as independent events, so that only data from an ongoing episode are considered pertinent to evaluating eruptive potential An implicit assumption is that the crust relaxes accumulated stress after each episode Here we apply a new model of elastic-brittle failure to test the alternative view that successive episodes promote a long-term accumulation of stress in the crust The results provide the first quantitative evidence that Campi Flegrei is evolving towards conditions more favourable to eruption and identify field tests for predictions on how the caldera will behave during future unrest

/pdf/progressive-approach-to-eruption-at-campi-flegrei-caldera-in-4zk00gu9i8.pdf

Progressive approach to eruption at Campi Flegrei caldera in southern Italy.

Correspondence Ronaldo I. Borja, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA. Email: borja@stanford.edu Summary Accurate prediction of strength in rocks with distinct bedding planes requires knowledge of the bedding plane orientation relative to the load direction. Thermal softening adds complexity to the problem since it is known to have significant influence on the strength and strain localization properties of rocks. In this paper, we use a recently proposed thermoplastic constitutive model appropriate for rocks exhibiting transverse isotropy in both the elastic and plastic responses to predict their strength and strain localization properties. Recognizing that laboratory-derived strengths can be influenced by material and geometric inhomogeneities of the rock samples, we consider both stress-point and boundary-value problem simulations of rock strength behavior. Both plane strain and 3D loading conditions are considered. Results of the simulations of the strength of a natural Tournemire shale and a synthetic transversely isotropic rock suggest that the mechanical model can reproduce the general U-shaped variation of rock strength with bedding plane orientation quite well. We show that this variation could depend on many factors, including the stress loading condition (plane strain versus 3D), degree of anisotropy, temperature, shear-induced dilation versus shear-induced compaction, specimen imperfections, and boundary restraints.

On the strength of transversely isotropic rocks

Magmatic intrusions and volcanic eruptions are intimately related phenomena. Shallow magma intrusion builds subsurface reservoirs that are drained by volcanic eruptions. Thus, the long-held view is that intrusions must precede and feed eruptions. Here we show that explosive eruptions can also cause magma intrusion. We provide an account of a rapidly emplaced laccolith during the 2011 rhyolite eruption of Cordon Caulle, Chile. Remote sensing indicates that an intrusion began after eruption onset and caused severe (>200 m) uplift over 1 month. Digital terrain models resolve a laccolith-shaped body ∼0.8 km3. Deformation and conduit flow models indicate laccolith depths of only ∼20-200 m and overpressures (∼1-10 MPa) that likely stemmed from conduit blockage. Our results show that explosive eruptions may rapidly force significant quantities of magma in the crust to build laccoliths. These iconic intrusions can thus be interpreted as eruptive features that pose unique and previously unrecognized volcanic hazards.

/pdf/rapid-laccolith-intrusion-driven-by-explosive-volcanic-4tz2pkn1am.pdf

Rapid laccolith intrusion driven by explosive volcanic eruption.

Part 1: Deformation and Fracture of Rocks 1. Precise Measurements of Fracture Strength of Rocks under Uniform Compressive Stress 2. Deformation and Failure or Rocks under Confining Pressure 3. Deformation and Fracture of Rocks under Triaxal Compression: The Effect of the Intermediate Principle Part 2: Acoustic Emission 4. Acoustic Emission Activity 5. Source Location of Acoustic Emission 6. Magnitude-Frequency Relation of Acoustic Emission Events 7. Acoustic Emission under Cyclic Loading Part 3: Rock Friction 8. Design of a New Apparatus for Friction Experiments 9. Laboratory Experimental Results 10. Stick-Slip Events in the Natural Field and Some Features in the Occurrence of Recent Great Earthquakes

清夫茂木

Papers

Experimental rock mechanics

東北日本西岸沖-フォッサ・マグナ-東海・伊豆の活動帯と近年の伊豆地方における地震活動について

清夫 茂木

Papers

Experimental rock mechanics

東北日本西岸沖-フォッサ・マグナ-東海・伊豆の活動帯と近年の伊豆地方における地震活動について

清夫茂木