Hasil untuk "Geology"

Xue Wu, Yueming Liang, Wenwu Zhao et al.

Abstract Background Nutrient limitation is a universal phenomenon in terrestrial ecosystems. Root and mycorrhizal are critical to plant nutrient absorption in nutrient-limited ecosystems. However, how they are modified by N and P limitations with advancing vegetation successions in karst forests remains poorly understood. The present study compared the diversity indices, composition, and co-occurrence network of arbuscular mycorrhizal fungi (AMF) between grassland, shrubland, shrub-tree forest, and tree forest in subtropical karst forests, as well as soil nutrients and fine root functional traits (e.g., specific root length (SRL), specific root area (SRA), diameter, biomass, and N and P contents). Results The fine roots diameter, biomass, and N and P contents increased with advancing succession, whereas SRL and SRA decreased. Network complexity and Richness and Chao1 indices of AMF increased from grassland to shrub-tree forest but decreased in tree forest. The fine roots N and P contents were positively related to their diameter and biomass, soil nutrients, and AMF composition but were negatively correlated with SRL and SRA. Moreover, these two parameters increased with the increase of soil nutrients. The variations in fine roots N and P contents were mainly explained by soil nutrients and fine root functional traits in grassland and by the interactions of soil nutrients, fine root functional traits, and AMF in the other three stages. Additionally, the interactive explanation with AMF increased from shrubland to shrub-tree forest but decreased in tree forest. Conclusions Our results indicated that mycorrhizal strategy might be the main nutrient acquisition strategy under N and P co-limitation. In contrast, the root strategy is the main one when an individual is subject to limitations in N or P in karst ecosystems. Root and mycorrhizal nutrient acquisition strategies are generally mutualistic, mycorrhizal strategy enhances plant nutrient acquisition under N and P co-limitation.

Ekrem Bektašević, Satko Filipović, Kemal Gutić et al.

Testing the integrity of piles is a key aspect of geotechnical analysis, and the application of non-destructive methods allows for a reliable assessment of the condition of piles without causing physical damage to the structure. This paper focuses on the application of the Pile Echo Test (PET) method for verifying the mechanical properties and quality of piles that serve as supports for portal structures. The testing showed that the measured velocities ranged from 4000 to 5000 m/s, with amplifications between 25% and 35%, indicating that the piles do not have serious structural issues and that no material degradation has occurred that would affect the load-bearing capacity or stability of the piles. By using the PET method, the integrity of the piles can be precisely determined, thereby enhancing the safety and long-term stability of portal structures. The results of this study confirm the importance of applying this method in geotechnical analyses as a reliable technique for verifying the quality of piles.

Hang LONG, Haifei LIN, Dongmin MA et al.

The study on the evolution characteristics of coal permeability is of great significance for rationally determining gas extraction parameters and increasing gas extraction efficiency. In order to study the effects of different coal stresses and gas pressures on coal permeability, the experiment on the deformation of stress-loaded coal and gas adsorption-diffusion was conducted, the segmented dynamic model of coal permeability was established, and the rationality of the established model was verified by the experimental results. The results shown that the gas adsorption amount and coal deformation both shown a Langmuir-type with the increasing gas pressure, and the dynamic diffusion coefficient of gas decreased exponentially with time. As the gas pressure decreased, the expansion deformation of the stress-loaded coal decreased, and the permeability increased gradually. The permeability and expansion deformation of stress-loaded coal gradually decreased with the increasing stress. The coal permeability shown a “V” shape with continuous stress loading, and it reached the smallest at the stress peak. The coupling between matrix and fracture deformation caused by gas adsorption, the dynamic diffusion of gas in matrix, and the mass exchange between matrix and fracture were all considered in the established permeability model of coal. The rationality of established segmented model of coal permeability was verified by the experimental results. The permeability model of coal based on elastic deformation can reflect the permeability evolution at the stage of elastic deformation. Within the experimental range, the absolute error between the experimental test and numerical simulation results of coal permeability was −0.135×10−15～0.296×10−15 m2, and the absolute error of volumetric strain of the coal due to gas seepage was −0.327×10−5～2.026×10−5. The permeability model considering plastic deformation can also reflect the permeability after stress peak. The error between experimental and numerical results was −0.435×10−15～0.997×10−15 m2.

Jared M. Kodero, Benjamin S. Felzer, Yuning Shi

Abstract Climate change is expected to impact vegetation in the western United States, leading to shifts in dominant Plant Functional Types and carbon storage. Here, we used a biogeographic model integrated with a biogeochemical model to predict changes in dominant Plant Functional Type by 2070−2100. Results show that under the Representative Concentration Pathway 4.5 scenario, 40% of the originally forested areas will transition to shrubland (7%) or grassland (32%), while under the Representative Concentration Pathway 8.5 scenario, 58% of forested areas shift to shrubland (18%) or grassland (40%). These shifts in Plant Functional Types result in a net overall loss in carbon storage equal to −60 gigagram of carbon and −82 gigagram of carbon under Representative Concentration Pathway 4.5 and 8.5, respectively. Our findings highlight the need for urgent action to mitigate the effects of climate change on vegetation and carbon storage in the region.

Yubo Lan, Ping Guo, Yong Liu et al.

This paper delivers an examination of relative permeability hysteresis in porous media in the field of petroleum engineering, encompassing mathematical modeling, experimental studies, and their practical implications. It explores two-phase and three-phase models, elucidating the generation of scanning curves and their applications in various porous materials. Building on the research of traditional relative permeability hysteresis models, we have incorporated literature on forward calculations of relative permeability based on digital rock core models. This offers a new perspective for studying the hysteresis effect in relative permeability. Additionally, it compiles insights from direct relative permeability and flow-through experiments, accentuating the methodologies and key findings. With a focus on enhanced oil recovery (EOR), carbon capture, utilization and sequestration (CCUS), and hydrogen storage applications, the paper identifies existing research voids and proposes avenues for future inquiry, laying the groundwork for advancing recovery techniques in oil and gas sectors.

H.C. Nguyen, L. Nguyen-Son

A numerical procedure using a stable cell-based smoothed finite element method (CS-FEM) is presented for estimation of stability of a square tunnel in the soil where the shear strength increases linearly with depth. The kinematically admissible displacement fields are approximated by uniform quadrilateral elements in conjunction with the strain smoothing technique, eliminating volumetric locking issues and the singularity associated with the Mohr–Coulomb model. First, a rich set of simulations was performed to compute the static stability of a square tunnel with different geometries and soil conditions. The presented results are in excellent agreement with the upper and lower bound solutions using the standard finite element method (FEM). The stability charts and tables are given for practical use in the tunnel design, along with a newly proposed formulation for predicting the undrained stability of a single square tunnel. Second, the seismic stability number was computed using the present numerical approach. Numerical results reveal that the seismic stability number reduces with an increasing value of the horizontal seismic acceleration (αh), for both cases of the weightless soil and the soil with unit weight. Third, the link between the static and seismic stability numbers is described using corrective factors that represent reductions in the tunnel stability due to seismic loadings. It is shown from the numerical results that the corrective factor becomes larger as the unit weight of soil mass increases; however, the degree of the reduction in seismic stability number tends to reduce for the case of the homogeneous soil. Furthermore, this advanced numerical procedure is straightforward to extend to three-dimensional (3D) limit analysis and is readily applicable for the calculation of the stability of tunnels in highly anisotropic and heterogeneous soils which are often encountered in practice.

D. Rickenmann, L. Ammann, T. Nicollier et al.

<p>The Swiss plate geophone (SPG) system has been installed and tested in more than 20 steep gravel-bed streams and rivers, and related studies generally resulted in rather robust calibration relations between signal impulse counts and transported bedload mass. Here, we compare this system with three alternative surrogate measuring systems. A variant of the SPG system uses the same frame (housing) set-up but with an accelerometer instead of a geophone sensor to measure the vibrations of the plate (GP-Acc, for geophone plate accelerometer). The miniplate accelerometer (MPA) system has a smaller dimension of the impact plate and is embedded in more elastomer material than the SPG system. The Japanese pipe microphone (JPM) is a 1 m long version of the system that has been installed in many streams in Japan. To compare the performance of the four systems, we used calibration measurements with direct bedload samples from three field sites and an outdoor flume facility with controlled sediment feed. At our field sites, the systems with an accelerometer and a microphone showed partly large temporal variations in the background noise level, which may have impaired the calibration measurements obtained during certain time periods. Excluding these periods, the SPG, GP-Acc, and JPM all resulted in robust calibration relations, whereas the calibration of the MPA system showed a poorer performance at all sites.</p>

Riyadh F. Halawani, Myra E. Wilson, Kenneth M. Hamilton et al.

Red Sea coastal development has rapidly accelerated in recent decades that has led to a rise in the anthropogenic heavy metal levels in sediments. A total of 80 surficial sediment samples were collected from the shallow waters along the eastern Red Sea coast near Jeddah, Saudi Arabia. These samples were collected from three locations, designated as North, Middle and South of Jeddah, to assess the concentrations of six heavy metals: chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), and lead (Pb). The results showed that the concentrations (mg/kg) of these metals in the studied sediments follow this order: Pb (77.34 ± 150.59) > Mn (36.52 ± 37.72) > Zn (18.02 ± 23.94) > Cr (9.56 ± 5.81) > Cu (9.18 ± 13.67) > Ni (3.68 ± 4.54). The majority of the polluted sediments were recorded in the Middle and South locations. Pollution and enrichment indices such as Geo-accumulation indices (Igeo), Enrichment Factors (E_f), Contamination Factors (C_f), Pollution Load Indices (PLI), Potential Ecological Risk Indices (PERI) and Potential Toxicity Response Indices (RI) were calculated from the measured metals to establish baselines for the region and assess specific metal enrichments by location along the Jeddah coastline. The Igeo values showed that 30% of the Southern location stations are considered moderately to highly polluted. The Ef for all the studied sediments followed this order: Pb (extremely severe enrichment) > Zn > Cu > Cd > Cr (severe enrichment) > Ni (moderate enrichment).

Shrijan Bahadur Malla, Ranjan Kumar Dahal, Shuichi Hasegawa

Abstract Local authorities i.e. government officials working at the district level and below and elected representatives of municipalities are the steering body of local-level disaster response mechanism in Nepal. The effectiveness of response operation moreover depends on their competency. This paper investigates their disaster response knowledge, preparedness, and perception, and to identify gaps and suggest recommendations. The prevailing competency of Nepalese local authorities doesn’t warrant an effective response during the time of disaster. They lack awareness and preparedness. Amidst their positive perception towards the need of disaster response capacity building, in the void of an effective mechanism, the government has failed to enhance their competency. The national investment for disaster response competency building is meager in Nepal. The country heavily relies on foreign aid. The present capacity-building mechanism should be redressed from the newer dynamic.

JOACHIM T. HAUG, PAULA G. PAZINATO, GIDEON T. HAUG et al.

Lacewing larvae are mostly predatory, highly mobile larval forms of Insecta. The modern fauna yields several morphotypes of lacewing larvae, each closely associated with a distinct evolutionary lineage within the group of lacewings, Neuroptera. Back in the Cretaceous, about 100 million years ago, many of these larval forms had already evolved. Additionally, many larval forms seem to have been present that are now extinct. We report here a new form, which appears to be extinct now. This new larva has a prominent forward projecting labrum like larval forms of Nevrorthidae and Psychopsidae. It furthermore has (again similar to the latter two) curved venom-injecting stylets formed by mandibles and maxillae. We used quantitative outline analysis to compare the new larva to those of Nevrorthidae and Psychopsidae. The results of this analysis demonstrate that the new larva differs in all aspects of head capsule shape from all known larvae of Nevrorthidae. Its head shape is more similar to that of many larvae of Psychopsidae, yet also here the new larva differs recognisably in one principal component. Also qualitative differences clearly differentiate the new larva from already known ones. Hence, the new larva represents a new, so far unknown morphotype of lacewing larva. This finding adds to the growing 'zoo' of unusual lacewing larvae back in the Cretaceous, indicating that form diversity and ecological diversity of lacewings were much higher 100 million years ago.

Y. Zhou, Y. Zhou, Y. Zhang et al.

<p>Targeting a long-term effort towards a variable-resolution (VR) global weather and climate model, this study systematically configures and evaluates an unstructured mesh atmospheric model based on the multiresolution approach. The model performance is examined from dry dynamics to simple physics and full physics scenarios. In the dry baroclinic wave test, the VR model reproduces comparable fine-scale structures in the refined regions as a fine-resolution quasi-uniform (QU) mesh model. The mesh transition zone does not adversely affect the wave pattern. Regional kinetic energy spectra show that the fine-scale resolving ability improves as the fine resolution increases. Compared to a QU counterpart that has equivalent degrees of freedom, the VR model tends to increase the global errors, but the errors can be reduced when the resolution of the coarse region is increased. The performance over the coarse region is generally close to that of a low-resolution QU counterpart. Two multi-region refinement approaches, the hierarchical and polycentric refinement modes, further validate the model performance under the multiresolution refinement. Activating hyperdiffusion for horizontal velocity is helpful with respect to VR modeling. An idealized tropical cyclone test is further used to examine its ability to resolve fine-scale structures. In the simple physics environment, the VR model can have the tropical cyclone stably pass the transition zone in various configurations. A series of sensitivity tests examines the model performance in a hierarchical refinement mode. The simulations exhibit consistency even when the VR mesh is slightly perturbed by one of the three parameters that control the density function. The tropical cyclone, starting from the second refinement region and passing through the inner transition zone, gets intensified and covers a smaller area in the refined regions. Such variations are consistent with the behavior that one may observe when uniformly refining the QU mesh. In the full physics environment with a highly variable mesh that reaches sub-10 km resolution, the VR model also produces a reasonable evolution for the tropical cyclone. The explicit diffusion shows its usefulness in terms of suppressing some unrealistic isolated-scale structures that are far away from the initial vortex and does not adversely affect the physically important object. The fine-scale structure is determined mainly by the fine-resolution area, although the systems may have larger differences before they move into the fine-resolution area. Altogether, this work demonstrates that the multiresolution configuration is a reliable and economic alternative to high-resolution global modeling. The adverse impact due to mesh transition and the coarse region can be controlled well.</p>

A. Hueter, S. Huck, S. Bodin et al.

<p>Short-term hypoxia in epeiric water masses is a common phenomenon of modern marine environments and causes mass mortality in coastal marine ecosystems. Here, we test the hypothesis that during the early Aptian, platform-top hypoxia temporarily established in some of the vast epeiric seas of the central Tethys and caused, combined with other stressors, significant changes in reefal ecosystems. Potentially interesting target examples include time intervals characterized by the demise of lower Aptian rudist–coral communities and the establishment of microencruster facies, as previously described from the central and southern Tethys and from the proto-North Atlantic domain. These considerations are relevant as previous work has predominantly focused on early Aptian basinal anoxia in the context of Oceanic Anoxic Event (OAE) 1a, whereas the potential expansion of the oxygen minimum zone (OMZ) in coeval shallow-water environments is underexplored. Well-known patterns in the <span class="inline-formula"><i>δ</i>¹³C</span> record during OAE 1a allow for a sufficiently time-resolved correlation with previously studied locations and assignment to chemostratigraphic segments. This paper presents and critically discusses the outcome of a multi-proxy study (e.g., rare earth elements (REEs), U isotopes, and redox-sensitive trace elements) applied to lower Aptian shallow-water carbonates today exposed in the Kanfanar quarry in Istria, Croatia. These rocks were deposited on an extensive, isolated high in the central Tethys surrounded by hemipelagic basins. Remarkably, during chemostratigraphic segment C2, the depletion of redox-sensitive trace elements As, V, Mo, and U in platform carbonates, deposited in normal marine oxic waters, record the first occurrence of basinal, organic-rich sediment deposition in which these elements are enriched. During the C3 segment, seawater oxygen depletion established on the platform top as indicated by the patterns in <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">Ce</mi><mo>/</mo><msup><mi mathvariant="normal">Ce</mi><mo>*</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="40pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="dd7522a8beb8d5f78db0d9a1e86f2aa5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-15-1327-2019-ie00001.svg" width="40pt" height="14pt" src="cp-15-1327-2019-ie00001.png"/></svg:svg></span></span> and U isotopes. Shifts in redox-sensitive proxies coincide with the expansion of microencruster facies. Segment C4 witnesses the return to normal marine reefal faunas on the platform top and is characterized by patterns in redox-sensitive proxies typical of normal marine dissolved oxygen levels. It remains unclear, however, if platform-top hypoxia resulted from the expansion and upwelling of basinal, oxygen-depleted water masses or if spatially isolated, shallow hypoxic water bodies formed on the platform. Data shown here are relevant as they shed light on the driving mechanisms that control poorly understood faunal patterns during OAE 1a in the neritic realm and provide evidence on the intricate relation between basinal and platform-top water masses.</p>

CHU Chen, ZHANG Ying, WANG Shang-xian et al.

With the widespread application of rare earth elements analysis, the development of rapid detection technology of rare earth elements has increasingly become a necessity within the industry. Microwave Plasma Torch (MPT) as the ion source and Quadrupole Mass Spectrometry (QMS) as the mass analyzer to develop a method for fast detection of rare earth elements (REEs) in water and ore samples has been developed and discussed in this paper. With the MPT-QMS method, for elements Y, La, Ce, Nd, Eu in water samples, the limits of detection (LODs) are 11.0-60.5 μg/L, and the linear ranges are 50-1000 μg/L. When analyzing ore samples, the samples were firstly digested by acid solution and the sample solution formed an aerosol, which was then cooled to keep it dry. The aerosol entered the plasma by the centre tube of the MPT and formed REE ions. These ions enter the QMS, and concentrations of REE elements can be quantitatively determined. Repeated analyses of the same sample by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) yield similar results, indicating that the semi-quantitative analyses of MPT-QMS are precise and reliable. Therefore, MPT coupled with QMS is suitable for portable, rapid analysis of metal elements in water and can be used in the field of in situ quality monitoring of environmental and drinking water.

S. Tessitore, S. Tessitore, S. Tessitore et al.

Subsidence is a hazard that may have natural or anthropogenic origin causing important economic losses. The area of Murcia city (SE Spain) has been affected by subsidence due to groundwater overexploitation since the year 1992. The main observed historical piezometric level declines occurred in the periods 1982–1984, 1992–1995 and 2004–2008 and showed a close correlation with the temporal evolution of ground displacements. Since 2008, the pressure recovery in the aquifer has led to an uplift of the ground surface that has been detected by the extensometers. In the present work an elastic hydro-mechanical finite element code has been used to compute the subsidence time series for 24 geotechnical boreholes, prescribing the measured groundwater table evolution. The achieved results have been compared with the displacements estimated through an advanced DInSAR technique and measured by the extensometers. These spatio-temporal comparisons have showed that, in spite of the limited geomechanical data available, the model has turned out to satisfactorily reproduce the subsidence phenomenon affecting Murcia City. The model will allow the prediction of future induced deformations and the consequences of any piezometric level variation in the study area.

I. M. Howat, A. Negrete, B. E. Smith

As part of the Greenland Ice Mapping Project (GIMP) we have produced three geospatial data sets for the entire ice sheet and periphery. These are (1) a complete, 15 m resolution image mosaic, (2) ice-covered and ice-free terrain classification masks, also posted to 15 m resolution, and (3) a complete, altimeter-registered digital elevation model posted at 30 m. The image mosaic was created from a combination of Landsat-7 and RADARSAT-1 imagery acquired between 1999 and 2002. Each pixel in the image is stamped with the acquisition date and geo-registration error to facilitate change detection. This mosaic was then used to manually produce complete ice-covered and ice-free land classification masks. Finally, we used satellite altimetry and stereo-photogrammetric digital elevation models (DEMs) to enhance an existing DEM for Greenland, substantially improving resolution and accuracy over the ice margin and periphery.

T. Fischer, M. Veste, O. Bens et al.

Dew formation was investigated in three developmental stages of biological soil crusts (BSC), which were collected along a catena of an inland dune and in the initial substrate. The Penman equation, which was developed for saturated surfaces, was modified for unsaturated surfaces and used for prediction of dewfall rates. The levels of surface saturation required for this approach were predicted using the water retention functions and the thicknesses of the BSCs. During a first field campaign (2–3 August 2011), dewfall increased from 0.042 kg m&lt;sup&gt;−2&lt;/sup&gt; for the initial sandy substrate to 0.058, 0.143 and 0.178 kg m&lt;sup&gt;−2&lt;/sup&gt; for crusts 1 to 3, respectively. During a second field campaign (17–18 August 2011), where dew formation was recorded in 1.5 to 2.75-h intervals after installation at 21:30 CEST, dewfall increased from 0.011 kg m&lt;sup&gt;−2&lt;/sup&gt; for the initial sandy substrate to 0.013, 0.028 and 0.055 kg m&lt;sup&gt;−2&lt;/sup&gt; for crusts 1 to 3, respectively. Dewfall rates remained on low levels for the substrate and for crust 1, and decreased overnight for crusts 2 and 3 (with crust 3 &gt; crust 2 &gt; crust 1 throughout the campaign). Dew formation was well reflected by the model response. The suggested mechanism of dew formation involves a delay in water saturation in near-surface soil pores and extracellular polymeric substances (EPS) where the crusts were thicker and where the water capacity was high, resulting in elevated vapor flux towards the surface. The results also indicate that the amount of dewfall was too low to saturate the BSCs and to observe water flow into deeper soil. Analysis of the soil water retention curves revealed that, despite the sandy mineral matrix, moist crusts clogged by swollen EPS pores exhibited a clay-like behavior. It is hypothesized that BSCs gain double benefit from suppressing their competitors by runoff generation and from improving their water supply by dew collection. Despite higher amounts of dew, the water availability to the crust community decreases with crust development, which may be compensated by ecophysiological adaptation of crust organisms, and which may further suppress higher vegetation or mosses.

D. J. Nicolsky, E. N. Suleimani, R. A. Hansen

A numerical model of the wave dynamics in Passage Canal, Alaska during the &lt;i&gt;M&lt;/i&gt;&lt;sub&gt;w&lt;/sub&gt; 9.2 megathrust earthquake is presented. During the earthquake, several types of waves were identified at the city of Whittier, located at the head of Passage Canal. The first wave is thought to have been a seiche, while the other two waves were probably triggered by submarine landslides. We model the seiche wave, landslide-generated tsunami, and tectonic tsunami in Passage Canal and compute inundation by each type of wave during the 1964 event. Modeled results are compared with eyewitness reports and an observed inundation line. Results of the numerical experiments let us identify where the submarine landslides might have occurred during the 1964 event. We identify regions at the head and along the northern shore of Passage Canal, where landslides triggered a wave that caused most of the damage in Whittier. An explanation of the fact that the 1964 tectonic tsunami in Whittier was unnoticed is presented as well. The simulated inundation by the seiche, landslide-generated tsunami, and tectonic tsunami can help to mitigate tsunami hazards and prepare Whittier for a potential tsunami.

Pasini G.

In the speleological literature three terms are utilized to designate the “ascending erosion”: paragenesis (= paragénésis, coined in1968), antigravitative erosion (= erosione antigravitativa, coined in 1966) and antigravitational erosion (wrong English translation ofthe Italian term erosione antigravitativa, utilized later on). The term paragenesis should be abandoned because of the priority of theterm erosione antigravitativa - on the ground of the “law of priority” – and because of its ambiguous etimology. On the other hand,the term antigravitational erosion should be forsaken in favour of the term antigravitative erosion, given the meaning that the termsgravitation and gravity have in Physics. Therefore, to designate the phenomenon of the “ascending erosion” there would be nothingleft but the term antigravitative erosion.The antigravitative erosion process and its recognizability are illustrated.Examples of caves with evident antigravitative erosion phenomena, developed in different karstifiable rocks and in several partsof the world, are given.It is recalled that the antigravitative erosion is a phenomenon well-known since 1942 and widely proven and supported, and that it isrelatively easy – in many cases - to recognize the antigravitative origin of karstic passages.It is stressed that the antigravitative erosion is an important phenomenon, exclusive of the karstic caves and unique in nature.

José Borges

Usando um modelo numérico baseado no método de elementos finitos, analisa-se o comporta mento duma escavação não suportada, em talude, num maciço argiloso sobreconsolidado. O modelo utiliza a teoria multidimensional de consolidação de Biot (formulação acoplada das equações de equilíbrio e escoamen to) com relações constitutivas modeladas pelo modelo de estados críticos p-q-θ . São postos em evidência, por um lado, os aspectos fundamentais do comportamento da obra, designadamente a evolução no tempo, durante e após o período construtivo, dos excessos de pressão neutra, das tensões efectivas, dos deslocamentos e dos níveis de tensão no maciço. Por outro lado, tendo em conta a influência da consolidação na resistência ao corte do maciço, avalia-se a variação no tempo da segurança, usando um programa de cálculo automático de análise da estabilidade global. O programa, formulado segundo pressupostos de equilíbrio limite, utiliza os resultados numéricos das aplicações pelo método de elementos finitos. Por fim, comparam-se os resultados obtidos no problema em estudo (problema-base) com os de outros dois problemas similares nos quais se alteram alguns dos parâmetros, designadamente a geometria da obra e o grau de sobreconsolidação do solo.

M. Lurdes Lopes, A. Vieira Monteiro

Neste trabalho estudar-se-á o papel de quatro agentes de degradação no comportamento ao punçoamento estático de dois tipos de geossintéticos. Para tal, seleccionaram-se três geotêxteis não tecidos agulhados de filamento longo em polipropileno da mesma marca mas com massas por unidade de área diferentes (I 50g/m2, 235g/m2 e 400g/m2) e três geomembranas lisas em polietileno de alta densidade da mesma marca mas com espessuras diferentes (1mm, 1,5mm e 2mm).  Os seis materiais foram submetidos por períodos de 5, 15 e 30 semanas à acção de quatro soluções: Jixiviado de um aterro de RSU e soluções ácida, alcalina e de cloreto de sódio. Para cada agente de degradação e para cada um dos materiais foi definida a resistência ao punçoamento estático no fim de cada período de exposição, tendo-se comparado os valores obtidos com os valores do mesmo parâmetro da amostra do material virgem. Neste trabalho descrever-se-ão os materiais utilizados e as metodologias de análise seguidas, analisar-se-ão os resultados obtidos e formular-se-ão as conclusões julgadas mais importantes face aos resultados obtidos.