Modelling cyclic elastic behaviour of sands

The cyclic stress-strain behaviour of cohesionless soils is considered to be composed of elastic and inelastic components, and the cyclic elastic stress-strain relationships for one type of uniform sand are investigated by conducting isotropic and laterally constrained compression tests under low frequency cyclic loads. The effects of relative density, stress history, and stress state on the cyclic elastic behaviour are studied. Simple and practically applicable elastic stress-strain models are developed based on Hertzian contact theory. It was observed in both types of tests that elastic strains can accurately be modelled by a power function of stresses.     

Petrogenesis of the Neogene alkaline volcanics with implications for post-collisional lithospheric thinning of the Eastern Pontides, NE Turkey

Whole-rock geochemistry, Sr–Nd–Pb isotopes and K–Ar data are reported for alkaline samples collected from the Neogene alkaline volcanics (NAVs) in the Eastern Pontides, northeastern Turkey, in order to investigate their source and petrogenesis and geodynamic evaluation of the region. The NAVs were made of three groups that comprise of basanite–tephrite (feldspar-free; Group A), tephrite–tephriphonolite (feldspar and feldspathoid-bearing; Group B) and alkaline basalt–rhyolite (feldspathoid-free; Group C) series. These rocks cover a broad compositional range from silica-undersaturated to silica-oversaturated types, almost all of which are potassic in character. They show enrichment of LREE and LILE and depletion of HFSE, without a Eu anomaly in most of the mafic samples. Textural features and calculated pressures based on the Cpx-barometer in each series indicate that the alkaline magma equilibrated at shallow crustal depths under a pressure of about 3–4.5 kbar and approximating a crystallization depth of 9–14 km. The NAVs are slightly depleted in isotopic composition, with respect to ⁸⁷Sr/⁸⁶Sr (ranging from 0.705018 to 0.705643) and ¹⁴³Nd/¹⁴⁴Nd (ranging from 0.512662 to 0.512714) that indicate young Nd model ages (0.51–059 Ga). This may indicate that the parent melts tapped a homogeneous and young lithospheric mantle source which was metasomatized by subduction-derived sediments during the Late Mesozoic. Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb = 18.85–18.95; ²⁰⁷Pb/²⁰⁴Pb = 15.60–15.74; ²⁰⁸Pb/²⁰⁴Pb = 38.82–39.25) may also be consistent with a model for an enriched subcontinental lithospheric mantle source. Lithospheric thinning and resultant upwelling of asthenosphere induced by lithospheric delamination may have favoured partial melting of chemically enriched, young lithospheric mantle beneath the Eastern Pontides. Then, the melt subsequently underwent a fractional crystallization process along with or without minor amounts of crustal assimilation, generating a wide variety of rock types in a post-collision extensional regime in the Eastern Pontides during the Neogene.     

Probabilistic evaluation of observed earthquake damage data in Turkey

Empirical, theoretical or hybrid methods can be used for the vulnerability analysis of structures to evaluate the seismic damage data and to obtain probability damage matrices. The information on observed structural damage after earthquakes has critical importance to drive empirical vulnerability methods. The purpose of this paper is to evaluate the damage distributions based on the data observed in Erzincan-1992, Dinar-1995 and Kocaeli-1999 earthquakes in Turkey utilizing two probability models—Modified Binomial Distribution (MBiD) and Modified Beta Distribution (MBeD). Based on these analyses, it was possible (a) to compare the advantages and limitations of the two probability models with respect to their capabilities in modelling the observed damage distributions; (b) to evaluate the damage assessment for reinforced concrete and masonry buildings in Turkey based on these models; (c) to model the damage distribution of different sub-groups such as buildings with different number of storeys or soil conditions according to the both models. The results indicate that (a) MBeD is more suitable than the MBiD to model the observed damage data for both reinforced concrete and masonry buildings in Turkey; (b) the sub-groups with lower number of stories are located in the lower intensity levels, while the sub-groups with higher number of stories depending on local site condition are concentrated in the higher intensity levels, thus site conditions should also be considered in the assessment of the intensity levels; (c) the detailed local models decrease the uncertainties of loss estimation since the damage distribution of sub-groups can be more accurately modelled compared to the general damage distribution models.     

Recycling of abrasives in abrasive water jet cutting with different types of granite

The cost of abrasives has restricted usage of abrasive water jet (AWJ) technology in natural stone cutting applications. However, recycling of the abrasives makes the technology more economical, effective, and environmentally friendly. In this study, significant rock properties affecting the recycling of abrasives in AWJ cutting of granites are investigated. Abrasive mass percentage above 106 μm (AMP_106μm) is considered as a performance criterion in terms of recycling of abrasives since these abrasives can be effectively reused in the rock cutting applications. The study reveals that a considerable amount of used abrasives is in a reusable form. Among the rock properties, the microhardness is statistically determined as the most significant rock property affecting the AMP_106μm. It is also concluded that theAMP_106μm can be explained with high accuracy by the proposed model including the microhardness, the quartz content, and the plagioclase content.     

Quasi‐static analysis of elastic behavior for some systems having higher fracture densities

Elastic behavior of geomechanical systems with interacting (but not intersecting) fractures is treated using generalizations of the Backus and the Schoenberg–Muir methods for analyzing layered systems whose layers are intrinsically anisotropic due to locally aligned fractures. By permitting the axis of symmetry of the locally anisotropic compliance matrix for individual layers to differ from that of the layering direction, we derive analytical formulas for interacting fractured regions with arbitrary orientations to each other. This procedure provides a systematic tool for studying how contiguous, but not yet intersecting, fractured domains interact, and provides a direct (though approximate) means of predicting when and how such interactions lead to more dramatic weakening effects and ultimately to failure of these complicated systems. The method permits decomposition of the system elastic behavior into specific eigenmodes that can all be analyzed, and provides a better understanding about which of these specific modes are expected to be most important to the evolving failure process. Copyright © 2009 John Wiley & Sons, Ltd.     

A precise gravimetric geoid model in a mountainous area with scarce gravity data: a case study in central Turkey

In mountainous regions with scarce gravity data, gravimetric geoid determination is a difficult task that needs special attention to obtain reliable results satisfying the demands, e.g., of engineering applications. The present study investigates a procedure for combining a suitable global geopotential model and available terrestrial data in order to obtain a precise regional geoid model for Konya Closed Basin (KCB). The KCB is located in the central part of Turkey, where a very limited amount of terrestrial gravity data is available. Various data sources, such as the Turkish digital elevation model with 3 ?? × 3?? resolution, a recently published satellite-only global geopotential model from the Gravity Recovery and Climate Experiment satellite (GRACE) and the ground gravity observations, are combined in the least-squares sense by the modified Stokes?? formula. The new gravimetric geoid model is compared with Global Positioning System (GPS)/levelling at the control points, resulting in the Root Mean Square Error (RMS) differences of ±6.4 cm and 1.7 ppm in the absolute and relative senses, respectively. This regional geoid model appears to be more accurate than the Earth Gravitational Model 2008, which is the best global model over the target area, with the RMS differences of ±8.6 cm and 1.8 ppm in the absolute and relative senses, respectively. These results show that the accuracy of a regional gravimetric model can be augmented by the combination of a global geopotential model and local terrestrial data in mountainous areas even though the quality and resolution of the primary terrestrial data are not satisfactory to the geoid modelling procedure.     

Use of joint-growth directions and rock textures to infer thermal regimes during solidification of basaltic lava flows

Thermal contraction joints form in the upper and lower solidifying crusts of basaltic lava flows and grow toward the interior as the crusts thicken. Lava flows are thus divided by vertical joints that, by changes in joint spacing and form, define horizontal intraflow layers known as tiers. Entablatures are tiers with joint spacings less than about 40 cm, whereas colonnades have larger joint spacings. We use structural and petrographic methods to infer heat-transfer processes and to constrain environmental conditions that produce these contrasting tiers. Joint-surface morphology indicates overall joint-growth direction and thus identifies the level in a flow where the upper and lower crusts met. Rock texture provides information on relative cooling rates in the tiers of a flow. Lava flows without entablature have textures that develop by relatively slow cooling, and two joint sets that usually meet near their middles, which indicate mostly conductive cooling. Entablature-bearing flows have two main joint sets that meet well below their middles, and textures that indicate fast cooling of entablatures and slow cooling of colonnades. Entablatures always occur in the upper joint sets and sometimes alternate several times with colonnades. Solidification times of entablature-bearing flows, constrained by lower joint-set thicknesses, are much less than those predicted by a purely conductive cooling model. These results are best explained by a cooling model based on conductive heat transfer near a flow base and water-steam convection in the upper part of an entablature-bearing flow. Calculated solidification rates in the upper parts of such flows exceed that of the upper crust of Kilauea Iki lava lake, where water-steam convection is documented. Use of the solidification rates in an available model of water-steam convection yields permeability values that agree with measured values for fractured crystalline rock. We conclude, therefore, that an entablature forms when part of a flow cools very rapidly by water-steam convection. Flooding of the flow top by surface drainage most likely induces the convection. Colonnades form under conditions of slower cooling by conductive heat transfer in the absence of water.     

Distribution of rare earth elements and oxyhydroxide phases within a weathered felsic igneous profile in Hong Kong

Variation in type and abundance of oxyhydroxide phases and the fractionation of rare earth elements (REE) within a weathered felsic pyroclastic profile in Hong Kong were investigated in order to assess the key factors and micro-environmental conditions controlling their distribution during weathering at rock and mineral scales. Three types of oxyhydroxide phases (Fe-, Mn- and Ce-rich) were recognized based on their most abundant elements. The Fe-rich types appeared in all samples at different stages of weathering. The Mn-rich types, however, were limited to samples at advanced stages of weathering, while the Ce-rich types were found solely in samples from oxyhydroxide-rich zones. Fractionation of REE likely started at the early stages of weathering, but became evident only at the advanced stages. Characteristics of REE patterns, especially the direction (negative or positive) and extent of Ce-anomalies, correlated very well with the appearance and abundance of Mn-oxyhydroxides, and were attributed to the co-existence of distinct micro-environmental conditions within the profile. These conditions resulted from two major competing processes, “leaching and fixation” and “oxidation (precipitation) and reduction (dissolution)”, which operated simultaneously within the profile at any given stage of weathering.