Organic Clay Layers Research Articles

In-field performance of continuous flight auger (CFA) energy piles with different configurations

In order to face the national energy crisis in Brazil, the use of geothermal energy piles (GEP) integrated with heat pumps is an attractive and cost-effective solution for the building cooling demand. On the other hand, there are very few field studies on the thermal performance of GEP systems in Brazilian soils and climate conditions, and for this reason, the implementation of this technology is still a challenge. Motivated by this need, continuous flight auger (CFA) energy piles were constructed to support a building in São Paulo city, and an experimental study, described in this paper, was carried out to provide useful data for the design of these GEPs. This work examined two key aspects of the design of GEP systems: (1) the influence of the heat exchange pipe configuration, and (2) the thermal response of GEPs and their effect on nearby piles installed in multi-layered ground. For this study, thermal response tests (TRTs) were conducted on four GEPs constructed with different pipe configurations, installed in a saturated sandy deposit intercalated by soft organic clay layers. The results obtained showed that: (i) the influence of pipe configuration on the GEP heat transfer is more significant during the first hours of pile heating process, and decreases with time due to the thermal interference between the pipe loops; (ii) the GEP temperature profile is impacted by the presence of soil layers of highly different thermal conductivities and groundwater flow velocities; and (iii) the temperature variation of nearby piles was also affected by the thermal characteristics of the soil layers, and therefore it should be considered for the structural design of GEPs.

Disentangling and Parameterizing Shallow Sources of Subsidence: Application to a Reclaimed Coastal Area, Flevoland, the Netherlands

AbstractThe natural surface area of many coastal and delta plains has been increased by land reclamation in response to growing populations. These reclaimed lands are often experiencing subsidence. The reclaimed South Flevopolder in the coastal plain of the Netherlands has experienced severe subsidence after its reclamation in 1968. The subsidence is caused by phreatic groundwater level lowering and the associated aeration of the former subaqueous shallow subsurface and increased effective stresses. In this study, surface elevation measurements that quantify the subsidence, conducted annually between 1968 and 1993, and in 2009 and 2012, have been used to constrain and estimate the parameters in models that describe subsidence. For the estimation an Ensemble Smoother with Multiple Data Assimilation was employed. For the forward models, we employed correlations for compression (primary consolidation and creep), oxidation, and shrinkage of coastal deposits. Shrinkage of the aerated clay and organic clay layers was found to be the main contributor to subsidence, and the measurements could be represented well. The quantification of the model parameters allows for better subsidence forecasts. The stochastic method that was employed further facilitates to define a quality measure for forecasts in terms of a covariance matrix or a confidence range.

Neotectonics, flooding patterns and landscape evolution in southern Amazonia

Abstract. The paper examines the role of neotectonic activity in the evolution of the landscape in southern Amazonia during the Holocene. It uses both new and published data based on the analysis of remote sensing imagery and extensive field work in the Llanos de Moxos, Bolivian Amazon. The study of the region's modern and palaeorivers, ria lakes, palaeosols and topography provides a strong case in favour of the thesis that the northern part of the Llanos de Moxos constitutes the southern margin of the Fitzcarrald Arch and that it has experienced uplift during the Holocene. The paper assesses the extent and timing of the neotectonic activity in light of the new data and reconstructs the evolution of the landscape since the late Pleistocene. The evidence suggests that at least two uplift events took place: a first uplift in the late Pleistocene, which caused the formation of Lake Oceano, and a second uplift during the mid-Holocene, which formed Lake Rogaguado. These two uplifts appear to be linked to the knickpoints observed close to the towns of Guayaramerín and Puerto Siles respectively. The backwater effect due to these uplifts transformed the region's major rivers in seasonal ria lakes, causing the deposition of thick organic clay layers along the Beni, Mamoré and Madre de Dios river banks. I argue that neotectonic episodes could have dramatically changed the drainage of the Llanos de Moxos, determining its flooding regime, soil properties and forest–savannah ecotone. These results stress the need for geomorphologists, palaeo-ecologists and archaeologists to take into account neotectonics when reconstructing the region's past.

Toughening of ethylene-propylene random copolymer/clay nanocomposites: Comparison of different compatibilizers

Ethylene/propylene-random-copolymer (PPR)/clay nanocomposites were prepared by two-stage melt blending. Four types of compatibilizers, including an ethylene-octene copolymer grafted maleic anhydride (POE-g-MA) and three maleic-anhydride-grafted polypropylenes (PP-g-MA) with different melt flow indexes (MFI), were used to improve the dispersion of organic clay in matrix. On the other hand, the effects of organic montmorillonite (OMMT) content on the nanocomposite structure in terms of clay dispersion in PPR matrix, thermal behavior and tensile properties were also studied. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the organic clay layers are mainly intercalated and partially exfoliated in the nanocomposites. Moreover, a PP-g-MA compatibilizer (compatibilizer B) having high MFI can greatly increase the interlayer spacing of the clay as compared with other compatibilizers. With the introduction of compatibilizer D (POE-g-MA), most of the clays are dispersed into the POE phase, and the shape of the dispersed OMMT appears elliptic, which differs from the strip of PP-g-MA. Compared with virgin PPR, the Young’s modulus of the nanocomposite evidently increases when a compatibilizer C (PP-g-MA) with medium MFI is used. For the nanocomposites with compatibilizer B and C, their crystallinities (X c) increase as compared with that of the virgin PPR. Furthermore, the increase of OMMT loadings presents little effect on the melt temperature (T m) of the PPR/OMMT nanocomposites, and slight effect on their crystallization temperature (T c). Only compatibilizer B can lead to a marked increases in crystallinity and T c of the nanocomposite when the OMMT content is 2 wt%.

Geological criteria for waste disposal site selection: a case study from Kanichadar, Dhangarhi, Far Western Nepal

Proper management of municipal solid waste in an environmentally friendly way needs first-hand knowledge of site geology. A clay layer (i.e. geological barrier) of sufficient thickness and extension beneath the surface is a suitable condition for a sanitary landfill site. The clay layer acts as a natural barrier against the migrating pollutants originating from leachate into the ground. The leachate generated at the landfill site can pollute the groundwater in absence of such geologic barrier.
 The Kanichadar area is underlain by about 3 m thick fine-grained soil. The topmost soil layer is 20-50 cm thick dark brown organic clay. There is a highly compact, dark brown and dry inorganic clayey silt layer of more than 1.5 m thickness below the organic clay layer. Soil samples collected from different Auger holes were subjected to laboratory analysis to determine their physical and chemical properties. The values thus obtained indicated that the soil belongs to 'CL' type, implying that the soil is inorganic clay of low to medium plasticity. However, the hydrometer analysis showed that the samples were of clayey silt.
 The cation exchange capacity (CEC) values obtained from the depth of 0.5-2.30 m revealed that the soil had moderate to high barrier potential for attenuation of the migrating pollutants. Therefore, the area close to these auger holes was found to be suitable for sanitary landfill.

Using microtremors to assess potential earthquake site response: A case study in Flushing Meadows, New York City

Abstract We have used portable 5-sec period seismometers to record ambient noise across a glacially cut valley filled with unconsolidated Holocene sediments. The valley, located in Flushing Meadows, New York City, is surrounded by a densely populated urban environment. Microtremors were recorded at several sites on and adjacent to the valley. While some raw spectra of valley site microtremors exhibit no predominant peaks, spectral ratios taken with respect to recordings made at a reference station outside the valley show a sharp peak near 0.8 Hz. A secondary peak near 2.4 Hz is also visible in some of the spectral ratios. The frequency of the predominant peak remains constant across the valley width, while the relative amplitude decreases systematically from a maximum at the valley center to background levels near the valley edge. Resonant frequencies predicted by one-dimensional modeling of the valley center site response show excellent agreement with observations. The 0.8-Hz spectral ratio peak is interpreted as the fundamental resonance mode, and the 2.4-Hz peak is interpreted as the first harmonic of the region above the base of an organic clay layer observed in borehole data. The amplification factors implied by the observed spectral ratios are unrealistically high (up to 100), which can be attributed to the close proximity of microtremor sources. An experiment involving the use of a pile-driver source located outside the valley was also performed. Signals obtained at valley sites during times when the pile-driver was in operation show a two-fold increase in the amplitude of a spectral peak when compared to signals obtained when the pile-driver was turned off. This observation gives additional evidence that observed spectral peaks represent soil layer resonances in the valley. Based on the results of this and other previous studies, we conclude that easily obtained microtremor measurements can contribute valuable microzonation and site response information to a study of regional earthquake hazard.

Palaeomangroves of Kanara coast, Karnataka, India and their implications on Late Pleistocene sea-level changes

Along the Kanara coast, some wells, show an organic clay layer, 1.5 to 7 m thick, between a layer of 2 to 6 m of coarse yellow sand above and white sand and pebbles below. The altitude of this intermediate organic clay formation is more or less at the present mean sea-level. Palynological analyses reveal that this sediment had been deposited within a mangrove environment i.e. at sea-level, while the 14 C datings give ages older than 40,000 years B. P. No proof of vertical movements after the deposit of the intermediate organic clay formation has been put forward up to now. Therefore, it can be accepted that the present elevation of this formation is more or less the same as its original altitude i.e., the present sea-level. Comparison of this altitude with the curves of global sea-level changes indicates that the period of deposition of these organic sediments should be around 125,000 years B.P., during the last Interglacial (Eemian) when the sea-level was ± the same that it is today. The main characteristics of “Eemian” flora were the same as the present. The climatic regime may have been slightly different with the less contrasting season.

Influence of cenozoic geology on mass movement and sediment yield response to forest removal, North Westland, New Zealand

Clear-felling of beech-podocarp-hardwood forests and their replacement withP. radiata plantations on steep, dissected hill country underlain by massive, late-Tertiary sandstone and siltstone has resulted in an increase in denudation rate from c. 100 m3/km2/a to c. 4000 m3/km2/a. Landslide densities increased from 1/km2 to 20/km2. Forest operations of this nature on topographically similar areas underlain by late-Pleistocene and early-Pleistocene gravels have been followed by less-severe increases in mass-movement. Analyses of slope stability using the infinite slope model indicate that slopes greater than 25° underlain by late-Tertiary sandstone are unstable when saturated, unless additional shear strength is provided by a network of tree roots. Principal causes of this instability are 1) the impermeable sandstone promotes regolith saturation during moderatesized rainstorms (1 – 2 yr return period), 2) the sandstone surface is smooth, planar, coated with an allophane-rich organic clay layer, and is rarely pentrated by tree roots; shear strength at the regolith-sandstone interface is low.