Rock Bedding Planes Research Articles

A Hybrid Anisotropic Elastoplastic Model for Layered Rock Mass and Numerical Implementation

An elastoplastic model that exhibits hybrid initial and stress-induced anisotropy is developed for layered rock masses. The formulation considers the thermodynamic aspect, and is consistent and rigorous. Both initial anisotropy and stress-induced deformation anisotropy are reflected by a hybrid anisotropic stiffness matrix influenced by the deterioration development degree (DDD) in different directions. By employing a combination of the strength criterion of rock material and rock bedding plane, an anisotropic failure formulation for layered rock mass has been established. The hybrid anisotropic model has been implemented in cellular automata software for the engineering rock mass fracturing process (CASRock). The performance of the anisotropic part is demonstrated by reproducing the deformation and failure characteristics of initial or stress-induced anisotropic behaviors for layered rocks under uniaxial, conventional triaxial, and true triaxial compression and Brazilian splitting conditions. Important features, such as the strength, mechanism, deformation, DDD, and fracturing process variation, can be captured by the proposed model. In addition, a numerical simulation of tunnel excavation in a layered rock mass is performed to study the anisotropic excavation-induced damage zone (EDZ) distribution in the field. The results indicate that the model is able to reproduce the observed failure mode satisfactorily.

Permeability and Effective Stress in Dipping Gas Shale Formation With Bedding—Experimental Study

Abstract Shale gas well deliverability and economics depend on extremely low permeability that is not only dependent on the rock bedding trend but also controlled by in situ stresses. The purpose of this study was to determine relative contributions of normal and tangential stresses with respect to the rock bedding plane on permeability evolution of shale. The study involved an analysis of the rock bedding structure, followed by triaxial testing of rock samples and theoretical modeling. Also simulated were the effects of stress-bedding and load cycling. The results showed shale permeability reduction during the stress loading process and its gradual recovery during the unloading process. Permeability change was more pronounced in response to normal stress but some effects of the tangential stresses were also observed. Moreover, a theoretical model was derived to describe permeability change with effective stress in the presence of normal and tangential stresses. The model was empirically matched with the experimental results. The assessment of relative contributions of normal and tangential stresses was quantified with the analysis of variance (ANOVA). The analysis revealed significance levels of normal stress, and two tangential stresses σt1 and σt2 on shale permeability as 81%, 5%, and 14%, respectively. An almost 20-percent contribution of tangential stress loading to permeability response indicates a need for the improvement in computing effective stress. Therefore, a new method was suggested to determine effective stress when predicting permeability evolution of shale.

Direct Tensile Behavior of Limestone and Sandstone with Bedding Planes at Different Strain Rates

To investigate the tensile behavior of rock bedding planes, a series of direct tensile tests were conducted on cylindrical limestone and sandstone specimens with a distinct bedding plane perpendicular to the axial direction. Different tensile strain rates of the bedding plane areas within the magnitude range from 10−6 to 10−2 s−1 were considered. The results indicate that the limestone fracture surfaces maintain the original roughness of bedding planes with few grain fractures. However, the sandstone fracture surfaces display many intergranular and transgranular fractures and are rough at the grain scale. The stress–strain curves of limestone specimens can be divided into elastic deformation stage and yield stage (the nonlinearity of yield stage is weaker with the increase of strain rate), while that of sandstone specimens develop in a nonlinear way accompanied by plastic deformation throughout the loading process. The strain rate significantly affects the tensile deformation and strength of the tested specimens (except the average deformation modulus of sandstone specimens). The elastic modulus, average deformation modulus, peak strain and tensile strength increase as strain rate goes up and have a linear relation with the logarithm of strain rate under the tested strain rate range (namely, under a relatively low strain rate range).

The early Famennian (Late Devonian) conodonts natural assemblages from Holy Cross Mountains (Poland)

ABSTRACT Two early Famennian natural assemblages of conodont elements were found in a marly shale bed within a limestone and shale sequence representing the Palmatolepis triangularis conodont zone at the Kowala quarry in the Holy Cross Mountains, Poland. The most complete of these assemblages, identified as Ctenopolygnathus brevilamina, contained nine skeletally preserved elements and four imprints on the rock bedding plane. A peculiar aspect of the apparatus was the disposition of S4 elements with respect to other S-array elements. Moreover, the denticles of S4 elements were unusually robust and slightly twisted towards the caudal side, which may have resulted from a mode of food processing different from those of other conodonts known from natural assemblages. Moreover, the location of S0 was not consistent with the hypothetical arrangements of similar apparatuses proposed by previous authors. The second assemblage, representing an unidentified palmatolepidid, contained scattered two fragmentary elements and four imprints.

Monitoring the Quarry Pit Development

Planning and maintaining intact pit slopes in a quarry/mine pit is an important aspect for a sustainable quarry development and operation. It is a main concern in ensuring the constructed pit slopes and benches are stable and safe during quarrying operation activities as well as after permanent closure of a quarry pit. An appraisal for slope instability and failures is conducted at the quarry pit of the Lafarge Rawang Sdn. Bhd. which is located in Rawang, Selangor. Determination of the failures level, integrity and governing geological parameters the contributed to the failures, stability and the hazards are done by field observation, geological mapping and geophysical surveys. The earth resistivity and seismic imaging surveys were conducted to image the subsurface condition such as extent and thickness of limestone bedrock and overburden, including suspicious features like the presence of underground seepage, sinkhole and soil/rock inferred strength indirectly. Occurrences of a few slope failures are considered minor, small scale and localized in nature. The rock slope failures mainly due to structural parameters of the in-situ rock which imposed a heavy jointing intersection and rock bedding plane that coincidently constructed parallel to pit slope face.

An Experimental Study on Destructive Nature of Seam Roof Strata with Horizontal Bedding

Subjected to external forces, the structure surface between rocks (ie, bedding planes) should be deformed under external force. If the two side walls of the rock bedding plane has perfectly flat smooth surface, after the composite layered rock subjected to force, bedding plane can be closed as surface contact manner. However, the rock bedding plane side walls generally showed local contact state in the nature, the rock layers of bedding planes will produce compressive deformation under stress. Through complete stress - strain triaxial loading experimental study on the effects of the presence of horizontal bedding on layered composite rock strength and deformation, and the elastic deformation of layered rocks are calculated using elastic mechanics, the result shows that due to the presence of irregular bedding plane, the presence of horizontal bedding formation will reduce the overall strength, and increase the overall rock deformation.

Timing and temperature of decollement on hydrocarbon source rock beds in cyclic lacustrine successions

The generation of hydrocarbons causes lubrication of source rock bedding planes which can enhance deformation during basin subsidence and subsequent tectonic events. Deformation includes decollement, i.e. gravitational sliding of rocks above the lubricated horizon. In cyclic sequences, such as occur in many lacustrine basins, decollement is generally restricted to the organic-rich beds of the cycle. Case studies in lacustrine successions in the Devonian Orcadian Basin, Scotland, and the Triassic–Jurassic Hartford–Deerfield Basin, USA, show that movement of material associated with the decollement surface occurred in the current down-dip direction. These extensional basins experienced rapid subsidence and a high heat flow such that hydrocarbon generation, and therefore decollement, occurred early in the basin histories. During extension, half-graben rotation ensured that the beds were dipping during hydrocarbon generation, facilitating decollement. Inversion of the Orcadian Basin reactivated decollement surfaces, involving thrust motion in some cases. Minerals precipitated in tension cavities associated with decollement yield fluid inclusion homogenization temperatures in the ranges 96–139°C and 85–96°C for the Orcadian and Hartford–Deerfield basins, respectively. These data are consistent with burial into the oil window at depths of between 1.5 and 2.0 km.

95/06165 Biomass production of sugarcane cultivars and early-generation hybrids

Planning and maintaining intact pit slopes in a quarry/mine pit is an important aspect for a sustainable quarry development and operation. It is a main concern in ensuring the constructed pit slopes and benches are stable and safe during quarrying operation activities as well as after permanent closure of a quarry pit. An appraisal for slope instability and failures is conducted at the quarry pit of the Lafarge Rawang Sdn. Bhd. which is located in Rawang, Selangor. Determination of the failures level, integrity and governing geological parameters the contributed to the failures, stability and the hazards are done by field observation, geological mapping and geophysical surveys. The earth resistivity and seismic imaging surveys were conducted to image the subsurface condition such as extent and thickness of limestone bedrock and overburden, including suspicious features like the presence of underground seepage, sinkhole and soil/rock inferred strength indirectly. Occurrences of a few slope failures are considered minor, small scale and localized in nature. The rock slope failures mainly due to structural parameters of the in-situ rock which imposed a heavy jointing intersection and rock bedding plane that coincidently constructed parallel to pit slope face.