Experimental seismic shear force amplification in scaled RC cantilever shear walls with base irregularities

RC structural slender walls under large seismic excitation are expected to reach base moment capacity mainly affected by the first vibration mode. However, the base shear could be affected by higher modes once yielding in flexure has occurred, which might result in base shear underestimation in linear design. In this work, an experimental program is carried out on five RC rectangular walls 1:10 scaled. All five specimens considered irregularities at base, common in construction and one specimen did not consider shear reinforcement or boundary detailing. Tests are carried on a unidirectional shaking table and excitation is based on two Chile earthquake records with different intensities. Damage is concentrated at the wall base for all specimens; primary due to flexure with some participation of shear. For one of the records an average amplification of 1.3 is obtained, and a decrease in height of the resultant equivalent lateral force closes to 0.4 h_w. By increasing the intensity of the input record, amplification grows to an average of 1.7, while it decreases drastically when subjected to input records with low frequency content. No significant difference is observed in shear amplification in specimens with a base central opening, nor with setback, even though the cracking and failure mode was different for such specimens. Ductility demand shows no correlation when two different earthquakes are considered, whereas the frequency content and Arias intensity (I_a) of the input record directly affected the shear amplification.     

Heat Transport Processes in the Earth’s Crust

The heat of the Earth derives from internal and external sources. A heat balance shows that most of the heat provided by external sources is re-emitted by long-wavelength heat radiation and that the dominant internal sources are original heat and heat generated by decay of unstable radioactive isotopes. Understanding of the thermal regime of the Earth requires appreciation of properties and mechanisms for heat generation, storage, and transport. Both experimental and indirect methods are available for inferring the corresponding rock properties. Heat conduction is the dominant transport process in the Earth’s crust, except for settings where appreciable fluid flow provides a mechanism for heat advection. For most crustal and mantle rocks, heat radiation becomes significant only at temperatures above 1200°C.

Citizens as sensors: the world of volunteered geography

In recent months there has been an explosion of interest in using the Web to create, assemble, and disseminate geographic information provided voluntarily by individuals. Sites such as Wikimapia and OpenStreetMap are empowering citizens to create a global patchwork of geographic information, while Google Earth and other virtual globes are encouraging volunteers to develop interesting applications using their own data. I review this phenomenon, and examine associated issues: what drives people to do this, how accurate are the results, will they threaten individual privacy, and how can they augment more conventional sources? I compare this new phenomenon to more traditional citizen science and the role of the amateur in geographic observation.     

A case study to verify methods for estimating transmissivity distributions along boreholes

Two methods, both using data from fixed-interval-length hydraulic tests and geological mapping on different scales, have been utilised to estimate transmissivity distributions of individual fractures. Individual fracture properties are of importance in estimating transport of water and solutes; they influence the spreading of grout when sealing tunnels. One of the methods is non-parametric, while the other is based on combinatorics and the multiplication principle. The study verified the usefulness of both methods for estimating the probability of conductive and non-conductive fractures, and the transmissivity distributions. Data for estimating transmissivity distributions originate from flow logging of a borehole in Sweden. Fracture frequency data are from core logging and images using a borehole image processing system (BIPS). Estimated transmissivity distributions, based on flow log data from 3-m sections (test scale length, L: 3 m, and step length, dL: 3 m), were compared with transmissivities obtained directly from detailed, overlapping flow logging which identify individual conductive fractures (test scale, L: 0.5 m, step length, dL: 0.1 m). The latter data are considered to be an acceptable approximation of the individual fracture transmissivities; the agreement, compared with the calculated transmissivity distributions based on 3-m section data, is good for both methods.

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Resumen Se han utilizado dos métodos, ambos procesando datos de pruebas hidráulicas de longitud e intervalo fijo y mapas geológicos en distintas escalas, para estimar las distribuciones de transmisividad de fracturas individuales. Las propiedades de fracturas individuales son de importancia para estimar el transporte de agua y solutos; las propiedades influyen en la propagación de lechada al sellar túneles. Uno de los métodos es no paramétrico mientras que el otro se basa en el principio de multiplicación y combinatorio. El estudio verifica la utilidad de ambos métodos para estimar la probabilidad de fracturas conductivas y no conductivas y las distribuciones de transmisividad. Los datos para estimar las distribuciones de transmisividad se originan del registro de flujo de un pozo en Suecia. Los datos de frecuencia de fracturas provienen de registros de núcleo e imágenes usando un Sistema de Procesamiento de Imágenes de Pozo (BIPS). Se compararon las distribuciones estimadas de transmisividad basadas en datos del registro de flujo en secciones de 3 m (longitud de escala de la prueba L: 3 m, y escalón de longitud dL: 3 m), con transmisividades obtenidas directamente de registros detallados de flujo superpuesto el cual identifica fracturas conductivas individuales (escala de la prueba, L: 0.5 m, escalón de longitud, dL: 0.1 m). Los últimos datos se consideran una aproximación aceptable de las transmisividades de fracturas individuales; la consistencia, comparada con las distribuciones de transmisividad calculada basadas en datos de sección de 3 m, es buena para ambos métodos.

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Résumé Deux méthodes ont été testées afin d’estimer la distribution des transmissivités de fractures unitaires; toutes deux utilisent des données issues de tests hydrauliques effectués à intervalles réguliers et de cartographies géologiques à plusieurs échelles. La connaissance des propriétés des fractures unitaires est importante pour estimer le transport d’eau et de solutés; elles influencent en outre l’étalement du coulis lors du scellement des tunnels. La première méthode est non-paramétrique, et la seconde repose sur l’analyse combinatoire et le principe de multiplication. Cette étude a vérifié l’utilité des deux méthodes pour estimer la probabilité d’occurrence de fractures conductrices et non-conductrices, et la distribution des transmissivités. Les distributions des transmissivités ont été estimées à partir de diagraphies effectuées sur un forage situé en Suède. Les densités de fracturation proviennent de carottages et d’imagerie BIPS (Borehole Image Processing System). Les distributions estimées des transmissivités, basées sur des diagraphies de flux effectuées sur des sections de 3 m (échelle du test L:3 m; pas dL:3 m), ont été comparées aux transmissivités obtenues sur des diagraphies de flux détaillées et se chevauchant, identifiant les fractures conductrices unitaires (échelle du test L: 0.5 m ; pas dL: 0.1 m). Il est admis que ces dernières données représentent une approximation satisfaisante des transmissivités des fractures unitaires; les deux méthodes sont en accord avec les distributions des transmissivités calculées à partir des données acquises sur des sections de 3 m.

     

Vertical migration of municipal wastewater in deep injection well systems,South Florida,USA

Deep well injection is widely used in South Florida, USA for wastewater disposal largely because of the presence of an injection zone (“boulder zone” of Floridan Aquifer System) that is capable of accepting very large quantities of fluids, in some wells over 75,000 m³/day. The greatest potential risk to public health associated with deep injection wells in South Florida is vertical migration of wastewater, containing pathogenic microorganisms and pollutants, into brackish-water aquifer zones that are being used for alternative water-supply projects such as aquifer storage and recovery. Upwards migration of municipal wastewater has occurred in a minority of South Florida injection systems. The results of solute-transport modeling using the SEAWAT program indicate that the measured vertical hydraulic conductivities of the rock matrix would allow for only minimal vertical migration. Fracturing at some sites increased the equivalent average vertical hydraulic conductivity of confining zone strata by approximately four orders of magnitude and allowed for vertical migration rates of up 80 m/year. Even where vertical migration was rapid, the documented transit times are likely long enough for the inactivation of pathogenic microorganisms.     

Performance of surface footing on geocell-reinforced soft clay beds

This paper presents the results of laboratory model tests carried out to develop an understanding of the behaviour of geocell-reinforced soft clay foundations under circular loading. Natural silty clay was used in this study. The geocells were prepared using biaxial polymer grid. The performance of the reinforced bed is quantified using non-dimensional factors i.e., Bearing capacity improvement factor (I_f) and Percentage reduction in footing settlement (PRS). The test results demonstrate that the geocell mattress redistributes the footing load over a wider area thereby improving the performance of the footing. The load carrying capacity of the clay bed is increased by a factor of up to about 4.5 times that of unreinforced bed. From the pressure-settlement responses, it is observed that the geocell-reinforced foundation bed behaves as a much stiffer system compared to the unreinforced case indicating that a substantial reduction in footing settlement can be achieved by providing geocell reinforcement in the soft clay bed. The maximum reduction in footing settlement obtained with the provision of geocell mattress of optimum size placed close to the footing is around 90%. Further improvement in performance is obtained with provision of an additional planar geogrid layer at the base of the geocell mattress.     

Archaeoseismological investigation of the ancient Ayla site in the city of Aqaba,Jordan

Many tens of severe earthquake damage patterns were revealed at the ancient city of Ayla. The seismic deformation patterns are of various types, including systematic tilting of walls, systematic shifting and rotation of wall fragments and individual stones, arch deformations and joints crossing two or more stones. Features of later repair, supporting walls and secondary use of building stones suggest that the damage patterns can be explained by two historical devastating earthquakes: (I) revealed in the constructions built during the late Rashidun period (644–656 A.D.); (II) revealed in the structures restored and/or built during the Fatimid period (1050–1116 A.D.). The maximum observed intensity of both earthquakes at the studied site was not less than IX (EMS98 scale). The sources of the seismic events were probably the Dead Sea Transform and Wadi Araba Faults that cross the site obliquely. The last 1995 Nuweiba earthquake with maximum observed intensity VIII has also left its clear traces in the excavated ancient Ayla buildings. The severity of the destruction was significantly increased because of site effects.     

Pervasive melt percolation reactions in ultra-depleted refractory harzburgites at the Mid-Atlantic Ridge, 15° 20′N: ODP Hole 1274A

ODP Leg 209 Site 1274 mantle peridotites are highly refractory in terms of lack of residual clinopyroxene, olivine Mg# (up to 0.92) and spinel Cr# (∼0.5), suggesting high degree of partial melting (>20%). Detailed studies of their microstructures show that they have extensively reacted with a pervading intergranular melt prior to cooling in the lithosphere, leading to crystallization of olivine, clinopyroxene and spinel at the expense of orthopyroxene. The least reacted harzburgites are too rich in orthopyroxene to be simple residues of low-pressure (spinel field) partial melting. Cu-rich sulfides that precipitated with the clinopyroxenes indicate that the intergranular melt was generated by no more than 12% melting of a MORB mantle or by more extensive melting of a clinopyroxene-rich lithology. Rare olivine-rich lherzolitic domains, characterized by relics of coarse clinopyroxenes intergrown with magmatic sulfides, support the second interpretation. Further, coarse and intergranular clinopyroxenes are highly depleted in REE, Zr and Ti. A two-stage partial melting/melt–rock reaction history is proposed, in which initial mantle underwent depletion and refertilization after an earlier high pressure (garnet field) melting event before upwelling and remelting beneath the present-day ridge. The ultra-depleted compositions were acquired through melt re-equilibration with residual harzburgites. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Properties of the aftershocks sequences of the 2000 and 2002 earthquakes in Aksehir-Afyon graben,west-central Anatolia,Turkey

The b-value of the Gutenberg–Richter’s frequency–magnitude relation and the p-value of the modified Omori law, which describes the decay rate of aftershock activity, were investigated for more than 500 aftershocks in the Aksehir-Afyon graben (AAG) following the 15 December 2000 Sultandagi–Aksehir and the 3 February 2002 Çay–Eber and Çobanlar earthquakes. We used the Kandilli Observatory’s catalog, which contains records of aftershocks with magnitudes ≥2.5. For the Çobanlar earthquake, the estimated b-values for three aftershock sequences are in the range 0.34 ≤  b ≤ 2.85, with the exception of the one that occurred during the first hour (4.77), while the obtained p-values are in the range 0.44 ≤ p ≤ 1.77. The aftershocks of the Sultandagi earthquake have a high p-value, indicating fast decay of the aftershock activity. A regular increase of b can be observed, with b < 1.0 after 0.208 days for the Çay–Eber earthquake. A systematic and similar increase and decrease pattern exists for the b- and p-values of the Çobanlar earthquakes during the first 5 days.