Geometrical evolution of interlocked rough slip surfaces: The role of normal stress

International audienceWe study the evolution of slip surface topography using direct shear tests of perfectly mating surfaces. The tests are performed under imposed constant normal stress and constant slip rate conditions, to a sliding distance comparable to the roughness scale of the studied surfaces. Prismatic limestone blocks are fractured in tension using four-point bending and the generated surface topographies are measured using a laser profilometer. The initially rough fracture interfaces are tested in direct shear while ensuring a perfectly mating configuration at the beginning of each test. The predetermined sliding distance in all tests is 10 mm and the sliding velocity is 0.05mm/s. A constant normal stress is maintained throughout the tests using closed loop servo control. The range of normal stresses applied is between 2MPa and 15MPa. After shearing, the surface topographies are re-scanned and the geometrical evolution is analyzed. We find that surface roughness increases with increasing normal stress: under normal stresses below 5MPa the surfaces become smoother compared to the original geometry, whereas under normal stresses between 7.5 MPa and 15 MPa the surfaces clearly become rougher following shear. Statistical spectral analyses of the roughness profiles indicate that roughness increases with length-scale. Power spectral density values parallel to the slip orientation are fitted by power-law with typical power value of 2.6, corresponding to a Hurst exponent of 0.8, assuming self-affine roughness. This power value is consistent for the post-sheared surfaces and is obtained even when the original surface roughness does not follow initially a power-law form. The value of the scaling-law prefactor however increases with increasing normal stress. We find that the deformation associated with shearing initially rough interlocked surfaces extends beyond the immediate tested surface, further into the intact rock material. The intensity of the damage and its spatial distribution clearly increase with increasing normal stress. Wear loss is measured by subtracting the post-shear surface from the pre-shear surface matrices using known reference points. Our measurements indicate that wear loss and roughness evolution are both positively correlated with the mechanical shear work applied during the experiments. We argue, therefore, that normal stress plays a significant role in the evolution of interlocked surfaces, such as geological faults, and strongly affects the energy partitioning during slip

A Criterion for Brittle Failure of Rocks Using the Theory of Critical Distances

This paper presents a new analytical criterion for brittle failure of rocks and heavily overconsolidated soils. Griffith’s model of a randomly oriented defect under a biaxial stress state is used to keep the criterion simple. The Griffith’s criterion is improved because the maximum tensile strength is not evaluated at the boundary of the defect but at a certain distance from the boundary, known as the critical distance. This fracture criterion is known as the Point Method, and is part of the Theory of Critical Distances, which is utilized in fracture mechanics. The proposed failure criterion has two parameters: the inherent tensile strength, ó0, and the ratio of the half-length of the initial crack/flaw to the critical distance, a/L. These parameters are difficult to measure but they may be correlated with the uniaxial compressive and tensile strengths, óc and ót. The proposed criterion is able to reproduce the common range of strength ratios for rocks and heavily overconsolidated soils (óc/ót=3-50) and the influence of several microstructural rock properties, such as texture and porosity. Good agreement with laboratory tests reported in the literature is found for tensile and low confining stresses.The work presented was initiated during a research project on “Structural integrity assessments of notch-type defects", for the Spanish Ministry of Science and Innovation (Ref.: MAT2010-15721)

The relationship among children\u27s conceptualization of death, parental communication about death, and parental death anxiety

This study investigated the relationship between parents\u27 communications about death with their children and children\u27s conceptualization of death. The relationship between parental death anxiety and parents\u27, communications about death was also examined. Other variables examined were: parents\u27 belief in an afterlife, parents\u27 religion, children\u27s experiences with loss, children\u27s gender, and children\u27s age with children\u27s conceptualization of death, parents\u27 communications about death, and parental death anxiety. All 68 children, mainly second graders (37 females and 31 males), between the ages of 6 and 9 years, and their parents (mainly mothers) were of a higher socioeconomic level and were well educated. The Development of Death Concept Questionnaire was used to measure death conceptualization in children. It included five death concept scales: Irreversibility, Finality, Causality, Inevitability, and Old Age. The Communication on Death and Dying Questionnaire was used to measure parents\u27 communications about death. This questionnaire was specifically developed for this study. The Revised Death Anxiety Scale was used to measure death anxiety in parents. A significant positive relationship was found between parents\u27 communications about death and children\u27s death conceptualization, and a significant negative relationship was found between parental death anxiety and parents\u27 communications about death. No relationship was found between parental death anxiety and children\u27s death conceptualization. Significant positive relationships were found between parents\u27 communications about death and the death concepts of Causality, Inevitability, and Old Age, but not Irreversibility and Finality. Significant relationships were also revealed between children\u27s experiences with death, children\u27s age, children\u27s gender, and parents\u27 communications about death; between children\u27s experiences with losses, parents\u27 religion (Jewish or not Jewish), parental belief in an afterlife, and parental death anxiety, and children\u27s death conceptualization. Multiple regression analyses indicated that the best predictor of death conceptualization was parents\u27 afterlife beliefs, and that the best predictor of parents\u27 communications about death was child\u27s age, followed by child\u27s gender, and parental death anxiety. Although a significant relationship was found between parents\u27 religion and parents\u27 belief in an afterlife, indicating that Jewish parents were more death anxious than non-Jewish parents, partial correlations revealed that this relationship was not accounted for by belief in an afterlife. The results of this study suggested that parents play an important role in their children\u27s death conceptualization. It also suggested that parents who are more death anxious are less effective in their communications to their children about death. This suggests that educators and psychologists working with children in schools incorporate parents into their death education programs. The program could address parents\u27 anxieties and their communications about death. Also, religious beliefs of life after death should be distinguished from factual information about death, both in children\u27s death education and in the operationalization of death conceptualization

Dynamic rock slope stability analysis at Masada National Monumument using Block Theory and DDA

Creator Y.H. Hatzor provides information concerning the stability of the historic Masada mountains based on regional tectonics. The mechanical behavior of the rock and the topography are explored to determine key block displacements and stability. Additionally, projected failure modes are predicted within the system