Evaluación Genotoxicológica de suelos expuestos a plaguicidas por el test de micronúcleos / Evaluation genotoxicológica de suelos expuestos to pesticides by the test of micronucleuses

En el presente estudio se evaluó la composición físicaquímica y la capacidad genotoxica de suelos contaminados de la comunidad de Huaraco, Dpto. deLa Paz por el test de Micronúcleos en Vicia faba. Los resultados muestran que el suelo de Huaraco expuesto hace 20 años a pesticidas no es genotóxico, mientras que el suelo expuesto recientemente muestra un incremento en su capacidad genotóxica.

Changes in forest biomass litter dynamics and soils following shifting cultivation in southern México: an overview

Se evaluó el impacto relativo de los condicionantes ambientales y los efectos del uso de la tierra a nivel de lotes, sobre procesos del ecosistema en un bosque tropical seco del sur de la Penísula de Yucatán, a través del muestreo a lo largo de gradientes naturales y hechos por el hombre. Los objetivos fueron 1)describir los gradientes ambientes naturales de precipitación y suelos en escala regional, 2)explorar la respuesta de propiedades clave y procesos del ecosistema a tales gradientes, y 3)comprender los efectos de la edad del bosque sobre lotes dentro de una región dada del gradiente. Se estudiaron la biomasa superficial (viva y detrítica), la producción y química de hojarasca, y los suelos. En cada uno de 3 sitios con un gradiente de lluvia estacional entre 900-1400 mm/año se muestraron 10 a 13 lotes, imcluyendo bosque secundario y maduro. La caída de hojarasca aumentó y su contenido de nutrientes bajó en el pico de la estación seca. En el bosque maduro los factores ambientales asociados al gradiente de precipitación limitaron la producción de hojarasca, biomasa y materia orgánica del suelo. La historia humana del área, incluyendo la tala y decisiones acerca de áreas no afectadas (p.e. vertientes altas), añadió información crítica para comprender diferencias en la biomasa superficial del bosque maduro. Todos los aspectos de estructura y función en bosques secundarios jóvenes (biomasa viva superficial, producción de hojarasca, masa en el piso y propiedades críticos del suelo) están fuertemente influenciadas por la edad del lote. La recuperación de los niveles de bosque maduro se estima conservadoramente en 55-95 años. P y/o N parecen limitar procesos esenciales del ecosistema como producción de hojarasca, descomposición y biomasa superficial. Se sugiere que una vez superada la limitación de agua, el P se hace limitante. La evidencia incluye mayor reabsorción de P de la hojarasca, una fuerte respuesta de la concentración de P, pero no de la de N, al gradiente de precipitación, y un aumento en la eficiencia de uso de P con el umento en la edad del lote. La presencia de humanos en el sur de Yucatán resulta en mayores cambios del ecosistema que aquellos inducidos por variación natural del ambiente en escala regional. Para comprender mejor estos paisajes y para llevar estudios puntuales a evaluaciones regionales y globales, resulta vital integrar los impactos humanos en los procesos del ecosistema

El tipo de labranza como agente modificador de la materia orgánica: un modelo para suelos de sabana de los llanos centrales venezolanos / Farming modality as modifying agent of organic matter: a model for savanna soils in the cenezuelan centre plains

Se presenta un modelo conceptual del funcionamiento de suelos de los Llanos Centrales Venezolanos, basado en las relaciones de estructura del suelo y de las fracciones activas y estabilizadas de la materia orgánica, que muestra como cambian los procesos del suelo según el manejo agronómico. se consideran dos tipos de labranzas constrastantes, la siembra directa sin labranza y con presencia de una cobertura vegetal, y la labranza convencional con fuerte mecanización para romper el suelo y enterrar cualquier tipo de cobertura o residuo. Se consideran variables externas (labranza y coberturas), variables de estado (fracciones de materia orgánica) y los procesos involucrados. Dada la acidez de los suelos, su baja fertilidad con limitaciones para el uso agrícola, y su uso cada vez mayor para producción de cereales, en especial maíz, se discuten los cambios en las fracciones de la materia orgánica por la intensidad de la labranza y la ubicación de los residuos vegetales, aspectos que influyen en la producción de CO² contribuyendo al efecto invernadero y que por otra parte, pueden intensificar los procesos de erosión y pérdida de nutrimientos, agravando los problemas de fertilidad y de degradación de los suelos. El sistema convencional de labranza aumenta la liberación de CO²e intensifica la degradación del suelo, disminuyendo la materia orgánica. Alternativamente, la siembra directa es conservacionista e incrementa los compartimientos activos y lentos que son fuente potencial de nutrimientos aumentando la fertilidad a mediano plazo, los procesos de descomposición microbiana son más lentos y las emisiones de CO² más bajas. El modelo de siembra directa es parecido al modelo de sabana virgen, tanto en las variables de estado relacionadas con la conservación como en los procesos de pérdida o conservación, siendo una alternativa de manejo que permite el uso más sostenible de los suelos de la sabana

3-=Tres Dimensional istinct element simulation of liquefaction phenoma

The mechanism of liquefaction pehnomenon at microscopic level is studied using 3-Dimensional Distinct Element Model (3D-DEM) in which the effects of pore-water are directly considered using a simple algorithm. In this method, the region of DE simulation model, which is composed of many particle elements, is considered as an assembly of cubic shaped blocks having virtual boundary. Behavoir of pore-water is calculated usign each block as a unit volume in order to make the calculation algorithm simple. We applied the method to the hollow cylindrical torsion test and san boiling due to liquefaction. The simulation results obtained showed that the proposed 3-Dimensional Distinct Element Method can simulate the mechanism of liquefaction and its associated phenomena. (AU)

Down - hole measurements of seismic wave velocities in deep soil deposits beneath the Tokyo metropolitan area

From both seismological and earthquake engineering points of view, deep seismic P and S wave velocities were directly and systematically measured down to the depth of 2 to 3 km at the three deep borehole observatories of Iwatsuki, Shimosha, and Fuchu which were constructed for geophysical observations in the Tokyo metropolitan area (AU)

Uso de biofertilizantes en praderas: alternativa sostenible para producción animal / The use of bio-fertilizers in Colombian meadows: sustainable alternatives for the animal production

La utilización de caldos microbiales es un ejemplo de tecnologías posibles de usar, ofreciendo grandes ventajas que difícilmente pueden lograrse con los fertilizantes inorgánicos. Los biofertilizantes, o caldos microbiales, son cultivos de microorganismos, elaborados con base en estiércol de origen animal, disueltos en agua y enriquecidos con leches, sueros, fermentación, anaeróbico o aeróbico durante varios días. Los abonos orgánicos (biofertilizantes) son recomendados en suelos degradados ya que facilitan la disponibilidad de nutrientes. Se realizó la evaluación del efecto de la aplicación de tres caldos microbiales preparados con base en avestruzaza, humus y bovinaza en la producción y calidad nutricional del forraje del pasto India guinea (Panicum máximum), comparado con los efectos del manejo tradicional (sin fertilización) y convencional (fertilización química), en la finca la primavera del municipio de Nilo (Cund), y se compararon sus costos. Los resultados mostraron mejoría en el porcentaje de proteína obtenida de forrajes trabajados con urea. Respecto a la producción de forraje verde, los mejores resultados se obtuvieron con avestruzaza, bovinaza y urea respectivamente, aunque no hubo diferencias significativas entre ellos. Loa costos de fertilización con biopreparados son inferiores en menos del 50 por ciento y los rendimientos en producción y calidad del forraje son mayores comparados con la fertilización convencional...

Relationship between geomorphological land classification and soil amplification ratio based on JMA strong motion records

The relarionship between the soil amplification ratio and ground conditions was examined using strong motion records measured at 77 Japan Meteorological Agency (JMA) stations over a period of more than 8 years. The amplification ratios for the instrumental JMA intensity, as well as for the peak ground acceleration and velocity, were obtained from the station coefficients of the attenuation relationships. A combined use of geomorphological land classification and subsurface geology was found to yield the best estimate of the amplification ratio. This result suggests that the Digital National Land Information may be conveniently used for the estimation of strong motion distribution over large areas in Japan.(AU)

Liquefaction tests of toyoura sand measuring change of quasi-elastic deformation properties

Undrained cyclic torsional and triaxial shear tests were perfomed on hollow cylindrical specimens of dense Toyoura sand, which were consolidated isotropically after preparation by airpluviation. At several stress states, quasi-elastic deformation properties were measured by applying very small amplitude cyclic torsional and vertical loads. Some of the results could be explained by considering inhewrent and stress state-induced anisotropy in modeling of elastic deformation characteristics and by correcting for the effects of membrane penetration. Degradation in the values of elastic shear modulus and Young's modulus was observed during liquefaction when compared to those measured during isotropic consolidation.(AU)

Generacion de un modelo digital del terreno con la utilizacion de tres herramientas (ILWIS,DIGEM, MICRODEM) / sss

Solo mediante la utilizacion del programa ILWIS es que pudimos estratificar el paisaje, ya que esto nos permite realizar operaciones entre mapas, dominios, tablas de una o dos dimenciones y un sin fin de operaciones mas. En las otras dos herramientas DIGEM y el MICRODEM, trabajan apartir de DEMs y mapas (Microdem) ya realizados y es por esto que estos dos programa tienen una gran cantidad de extenciones compatibles. Podemos concluir que el programa ILWIS es el de mas amplia adaptacion a las caracteristicas de nuestro medio principlamente por su gran amplitud con el usuario ya que atraves de un scripst, uno puede adecuar las funciones a sus objetivos. Siendo la unica desventaja de este programa el grado de capacitacion que se necesita para menejarlo...

Behavior of sand after liquefaction

Behavior of sand after liquefaction is discussed and formuled. Material properties that are usually assumed constant, such as internal friction angle, is ahown to change due to cyclic loading causing liquefaction. It is also shown that regions with very small stiffness appears by the cyclic loading. They may expand several ten percents, which causes liquefaction-induced large permanent displacement. A simlified model is introduced and improved so as to be able to take into new features such as change of material property and appearance of low stiffness region. The agreement of the numerical calculation and test are very good. Future research needs for evaluating the amount of liquefaction-induced permanent displacement more precisely are also pointed out.(AU)

Ground remediation : Aspects of the theory and approach to compaction grouting

In this paper , selected compaction grouting case histories are first briefly reviewed to illustrate the application of the technique. The technique has seen limited use for liquefaction mitigation of dams, building foundations and bridge foundations, and is particularly suited for liquefaction mitigation of existing foundation soils. However, more widespread use has possibly been prevented due to the lack of a unified design approach.(AU)

Failure criterion for buried pipe subject to longitudinal PGD : Benchmark case history

The effects of longitudinal Permanent Ground Deformation (PGD) on a buried continuous steel pipeline is considered. Longitudinal PGD, (ground movement parallel to the pipe's axis) is characterized by the amount of movement, & and its spatial extent, L. Local compressional buckling of the pipe wall and tensile failure of pipeline are taken as the failure modes of interest. Critical values for the amount of ground movement and the spatial extent, which lead to compressive failure, &cr and Lcr, are determined for five grades od steel, various R/t ratios and burial conditions. Three buried pipelines which were subject to longitudinal PGD during the 1994 Northridge California event are used to benchmark the proposed failure criterion. The proposed analytical procedure suggest that two of the three pipes, the Los Angeles Dept of Water and Power Granada Trunk Line and the So. Cal. Gas (SCG) Line 120; both located along Balboa Blvd. at the Northern and of the San Fernando Valley would suffer damage. The observed behavior matches the predicted behavior. The third line, the newer SCG line along McLennan Ave., is also considered. For the third line, we postulate as to why it was not damaged. There are two other lines along Balboa which were undamaged by the PGD. These two lines are excluded from consideration because of a lack of information on certain parameters. Finally the effects of an expansion joint which was installed in the LADWP line after the 1971 San Fernando earthquake are discussed in detail.(AU)

Soil stability, soil structure interaction and foundation

This volume includes information about the following topics: Dynamic properties and liquefaction behavior of soils, Embankment dams, natural slopes, and retaining walls, Deep foundations and underground structures, Soil structure interaction

Stable fault sliding and earthquake nucleation

The process of earthquake nucleation is studied assuming that faults are rupture surfaces on which sliding is controlled by friction. Earthquakes are assumed to arise through an instability of frictional sliding. Empirical slip laws indicate that, under constant ambient conditions, friction depends on time, slip rate and slip history. Regular stick-slip behaviour is induced by velocity weakening, a negative dependence of friction on slip rate. Velocity weakening is introduced into a model for a propagating Somigliana dislocation under slowly increasing ambient shear stress. The instability occurs when the rate at which friction decreases becomes greater than the rate at which the applied stress must increase to produce an advance of fault slip. The possibility that this condition is fullfilled depends on the velocity dependence and on the spatial distribution of friction on the fault. A critical nucleation width of the dislocation is associated with the instability and is controlled by the friction distribution, which determines the size of the initial slipping patch. Depending on the stress drop and the characteristics slip distance, the critical nucleation width may be greater for small earthquakes than for large earthquakes, with respect to the initial slipping patch

Post - liquefaction ground flow in shaking table tests

The behavior of liquefied ground in lateral flow was studied in shaking table using a smaller and a larger container. Tests were conducted in a submerged model slope made with Toyoura sand. The dilatancy characteristics were considered to be very important. Since the shear deformation behavior of model ground at low confining pressure is dilative, the flow created in regular1-G shaking table tests is limited and cannot continue after shaking stops. However, this problem was solved by using a very loose model ground with contractive behavior. The model ground was prepared by moist placement and wet tamping methods. In order to trigger free flow an impact load was applied in the direction perpendicular to the slope (Transverse direction). Some tests were conducted with continuous shaking applied in the direction parallel to the slope (Longitudinal direction). In order to observe the soil deformation in detail, markers made from dyed sand were placed in contact with the transparent side wall of container. The displacement obtained from markers and a transducer placed in the center of the ground were compared. A relationship between the velocity of flow and the void ratio was obtained. Results of experiments with free flow triggered by an impact load and flow applied by continuous shaking were also examined.(AU)

Earthquake response analysis of the Higashi-Kobe bridge

This paper presents results of observation and analysis fo the response of onte of the longest cable-stayed bridges in the world to the Hygoken-nambu (Kobe) eathquake of January 17, 1995. It is determined that intercation of the foundations of the bridge towers with the supporting soil plays a decisive role in the overall structural behavior. The key factor governing the changes of the soil properties at this site is pore water pressure builup, which results in liquefaction of the saturated surface soil layers unde large dynamic loads. Models of the soil and structure are created and initially validated by accurately simulating the system response to a small eathquake. Soil parameters reflecting the pore-water pressure builup in the strong eathquake are determied by advanced nonlinear effective stress analysis, combining the Ramberg-Osgood model of stress-strain dependence with a pore pressure model based on shear work concept. They are utilized to investigate and simulate the interaction of the foundation and the supporting soil using the program SASSI with the flexible volume substructuring approach. The results show a good agreement with the observations and have useful implications to the scientific and engineering practice. (AU)

Retrofitting lifeline facilities on liquefied deposits

Liquefaction was widespread in Northern Luzon during the recent 16 July 1990 Philippine Earthquake which registered a magnitude of 7.7 on the Richter scale. Dagupan City, located approximately 200 kilometers north of Manila, suffered most of the liquefaction damages within the region. The lifeline facilities of Dagupan City were devastated but due to the combined efforts of the residents of the area and the goverment, remedial measures were done. Retrofitting the lifeline facilities of the city consisted mainly of 3 basic steps namely: 1- identifying the damage and assigning an order of priority; 2- providing a temporary facility to make the lifeline functionable; and, 3- constructing a facility which is properly designed to handle the effects pf liquefaction. This paper describes in detail the pre-earthquake and post-earthquake condition of the existing lifeline facilities of Dagupan City and discusses the various retrofitting procedures employed for the facilities lying on the liquefied deposits.(AU)

Recent lessons regarding seismic response analysis of soft and deep clay sites

The strong motion data obtained during the 1989 Loma Prieta Earthquake provides an unprecedented opportunity for study of the seismic response of "soft" and deep clay sites. The first phase of the studies described herein investigated the ability of contemporary response analysis techniques using both "equivalent linear" and fully nonlinear medelling to accurately predict observed response of soft day clay sites at the moderate levels of shaking experienced during the Loma Prieta event. The "predictive" capability of both types of analysis was found to be very good, but only coupled with thorough characterization of soil behavior and parameter evaluation, and suitable consideration of nonlinearity and potential soil "failure". As a second phase of these studies, additional analyses were perfomed at higher (and more typical "design") levels of shaking, and some of the important findings are noted. The results of these studies indicate a potential need to reconsider the fundamental basis and principles of current practice in this field, as well as an obvious need to re-assess widely-used current seismic building codes.(AU)