Clayey Silty Sand Research Articles

Enhanced reductive dechlorination of trichloroethene in an acidic DNAPL impacted aquifer

A field pilot test was conducted using an emulsified vegetable oil (EVO) and colloidal magnesium hydroxide [Mg(OH)2] formulation to enhance reductive dechlorination of dense non-aqueous phase liquid (DNAPL) trichloroethene (TCE) in an acidic (pH < 4), heterogeneous aquifer. The field test consisted of i) a single well injection test to evaluate Mg(OH)2 distribution and ii) installation of two EVO-Mg(OH)2 permeable reactive barriers (PRBs; PRB-1 & PRB-2) at varying distances downgradient of the DNAPL source area. Distribution of Mg(OH)2 was observed up to 2.3 m away from the injection point within a permeable coarse sand layer; however, Mg(OH)2 transport in the overlying clayey-silty sand was minimal. Downgradient of the PRBs, colloidal Mg(OH)2 increased the pH of the coarse sand to levels appropriate for biological reductive dechlorination (pH >∼5); however, some settling of Mg(OH)2 in the injection wells generated persistent high pH (∼9–10) within the PRBs. A redesigned suspension of colloidal Mg(OH)2 was tested and proved to be more effective at raising aquifer pH without an excessive rise in pH within the PRBs. At PRB-1 (located closest to the DNAPL source area), limited TCE biodegradation was observed due to the influx of high TCE concentrations (up to 400 mg/L) and inhibition of dechlorinating bacteria. At PRB-2 (located 25 m downgradient of the DNAPL source area), TCE concentrations were much lower (13–26 mg/L) and production of cis-1,2-dichloroethene (cDCE) and some vinyl chloride (VC) was observed. Subsequent bioaugmentation with a commercial dechlorinating culture at PRB-2 improved conversion of cDCE to VC and ethene at downgradient monitoring wells over the duration of the study. These results emphasize the importance of PRB location (relative to the DNAPL source), base selection for pH adjustment, source strength, and local heterogeneities for the design and long-term performance of ERD in acidic DNAPL-impacted aquifers.

Seismically induced settlement of ground experiencing undrained shaking and laterally constrained compression

A method is proposed for estimating seismically induced settlement of saturated sands experiencing undrained shaking and laterally constrained compression. An empirical relationship is developed between the seismic coefficient of vertical compression, mvs, and standard penetration test blow count, N60, as a function of factor of safety against liquefaction, Fℓ, based on data interpreted from 18 sets of laboratory cyclic direct simple shear tests and 23 cases of field observations of seismic liquefaction. The proposed method is compared with seismic settlement observed at 78 sites subjected to 7.1–8.0 magnitude earthquakes, and with predictions by the previous well-known methods of settlement analysis for undrained shaking. For silty–clayey sands, the significant effect of the plasticity of fines on seismic settlement is illustrated. The use of pre- or post-earthquake penetration resistance for back-analyses of field seismic settlement observations is examined. A tentative correction factor is suggested for seismic settlement estimated based on the assumption of undrained shaking and laterally constrained compression for liquefied saturated sublayers at small distances from drainage boundaries or under buildings with small breadths, which may experience volumetric compression during ground shaking.

Characterization and engineering properties of AMU Morasko soft clay

AMU Morasko soft clay is the normally consolidated, postglacial clayey silty sand to sandy clay, deposited during the last glaciation (Weichselian) within the marginal zone of end moraine of Posnanian Phase. These soils are characterized by low plasticity, high porosity and are fully saturated, therefore, from a geotechnical point of view they can be defined as soft clays. The over 10 meter thick complex of clayey glacial sediments is covered with fine and medium sands with single grains of gravel of the so-called first sandur level from the youngest glaciation. This kind of sediments are very common in the area of north-western Poland and, due to high compressibility, become a problematic subsoil for the shallow foundations. The high porosity and saturation also causes significant problems in obtaining high quality samples for laboratory tests. This means that in situ tests are very often the only possible and economically justifiable test methods. Extended investigations carried out on these clays, which provide reliable correlations between in situ and laboratory test results, will be very useful. For the purpose of this research paper, a wide variety of in situ (CPTU, DMT, FVT) and laboratory (physical properties, direct shear, oedometer) tests have been carried out on the material found at the depth of up to 16 m, in the area of 8 ha, within the campus of Adam Mickiewicz University (AMU) in Poznan, Poland. Preliminary investigations (performed four years ago) showed high uniformity of the test site. The current laboratory tests were carried out on both high quality natural samples and reconstructed samples. The rate effect on the results of some of the tests was also investigated. The obtained results allowed to present a wide geological and engineering characterization of these interesting glacial deposits.

ESR Dating Ungulate Teeth and Molluscs from the Paleolithic Site Marathousa 1, Megalopolis Basin, Greece

At 37°24′ N 22°8′ E, the Megalopolis Basin lies in the central Peloponnese Peninsula, southwestern Greece. In the Megalopolis Basin at ~350 m amsl, the Paleolithic site, Marathousa 1, sits within a palustrine/lacustrine clastic package between Lignite Seams III and II, that both likely correlate with interglacial periods. At Marathousa 1, immediately below Lignite Seam III, lies a clayey-silty sand layer with a horizon rich in molluscs ranging from ~20–40 cm thick. About 0.8–1.3 m below the shell-rich horizon (SRH), lacustrine silty to muddy sands rich in organic matter yielded Paleolithic lithic artefacts associated with Middle Pleistocene fauna, some with cut marks and possible bone knapping, found within palustrine/lacustrine clastic deposits. Since ESR (electron spin resonance) can date teeth and molluscs aged &gt;2 Ma, two bivalve samples, AM66 and AM65, five subsamples from a cervid molar, AT39, and one subsample from another cervid molar, AT68, were independently dated by ESR from Marathousa 1. To calculate the ages, time-averaged cosmic and time- and volumetrically-averaged sedimentary dose rates were calculated using past water depths and sedimentation rates as determined from paleontological and geological criteria. Found in the SRH in Layer UA2, AM66 and AM65 averaged 488 ± 37 ka, which correlates with MIS 13a. Because the bivalves sat stratigraphically above the artefacts and mammalian fossils, their ages constrain the ESR ages for the teeth deposited below. Lying on the unconformity at the base of Layer UA3c with UA4, and its correlative unconformity at the Layer UB4c/UB5 boundary, sat the dated teeth from large mammals. Because the bones in the Palaeoloxodon antiquus skeleton lay in quasi-anatomical association, the likelihood for fossil reworking on the Layer UB3c/UB4 surface is low. Isochron analysis suggests that using a U uptake model with p = 2 provides the most accurate ages for AT39. With p = 2, AT39 dates to 503 ± 13 ka, while AT68 dates to 512 ± 34 ka. Nonetheless, two to three more teeth and molluscs should be dated to confirm these ages, when more samples suitable for ESR dating are found. Both tooth ages correlate well with early MIS 13, an interglacial period with cooler mean global temperatures compared to MIS 11 or 9. Assuming that the archaeological site formed in one event, rather than as a palimpsest, the data suggest that hominins processed elephant and other faunal carcasses along the shores of a shallow lake or marsh in the Megalopolis Basin at 503 ± 12 ka. Between the two horizons dated here, their sedimentation rate averaged 4.8 ± 1.8 to 7.8 ± 2.9 cm/ka.

Experimental Study on Sedimentation Removal of Pervious Concrete

Abstract Pervious concrete is a unique and effective material used to tackle important environmental problems, to maintain green, sustainable growth, and to reduce storm water runoff and pollutants. Clogging of pervious concrete is an important potential issue in serviceability, considered one of the primary limitations of pervious concrete systems. The sediment deposition pattern of pervious concrete was determined using three clogging materials: clay, sand, and clayey silty sand. The clogged specimens were cleaned by pressure washing, vacuuming, and a combined method. In total, ten clogging and cleaning cycles were carried out on each sample to evaluate the draining capacity of the pervious concrete. The clogging test was assessed by measuring the infiltration rate during clogging and after cleaning, for each cycle. The experiment results showed that a reduction in permeability due to different types of sedimentation material as well as recovery in permeability was achieved after applying various cleaning methods.

Physical Characterization of a Deep Weathering Profile Over Rhyolite in Humid Tropical Peninsular Malaysia

The weathering profile, exposed at 38.2 km of the Kuala Lumpur—Karak Highway, can be differentiated into three broad zones; the topmost Zone I (pedological soil) comprising A, B and C soil horizons and made up of clayey silty sand with indistinct relict bedrock textures. The intermediate Zone II (saprock) consists of gravelly silty sand with distinct relict bedrock texture and structures, and can be sub-divided based on differences in volumes of litho-relicts. The bottom Zone III (bedrock) is a continuous outcrop of rhyolite with alteration along discontinuity planes; its upper surface marked by an unconfined groundwater table. The weathering zones thin towards valley sides and can be assigned rock mass weathering grades; Zones I and II defining the residual soil over bedrock. Constant volume samples in Zone II show an upward decrease in dry unit weights, porosities and silt contents, but a corresponding increase in clay contents. Constant volume samples in Zone I show it to be distinct from Zone II with large clay contents but low porosities and silt contents. Decreasing fine clay contents with depth and stained quartz grains show pedological processes to have given rise to Zone I. As the silt-sized (sericite) particles mainly originate from alteration of bedrock feldspars and later break-down to clay-sized (illite and kaolinite) particles, a textural weathering index (Iw) based on the ratio of clay to silt and clay contents, is proposed to describe the progress of weathering within the profile. It is concluded that the saprock results from in situ alteration of the rhyolite rock mass due to lowering of an unconfined groundwater table whilst the A, B and C soil horizons have formed by pedological processes acting on saprock.

Kaolin soil and its stabilization potentials as nanostructured cementitious admixture for geotechnics purposes

The use of nanostructured kaolin as an additive in the stabilization of lateritic soils and its effect at different percentages on the natural soil were investigated. A UV–vis spectrophotometric characterization was conducted to determine the absorbance and average particle size of the nanostructured kaolin. The preliminary tests on the soil showed that it was a poorly graded (GP) soil on USCS. The soil sample was also observed to be silty clayey sand. The consistency limits result showed a liquid limit (LL) of 47% and plastic limit (PL) of 25.15%. The soil was observed to be highly plastic, of high swelling potential and medium expansion properties. Further, the effect of the addition of Nanostructured kaolin (NK) in the proportions of 3%, 6%, 9%, 12% and 15% by weight of the treated lateritic soil recorded the following results; the consistency limits results showed that the addition of variable proportions of nanostructured kaolin (NK) improved the plasticity index of the stabilized soil and gave 11.77%-a medium plastic material at 15% NK by weight addition compared to the preliminary result at 0% by weight additive which gave 21.85%-a highly plastic material. The strength properties test also showed significant improvements with the addition of NK; CBR test results recorded 23% at 15% by weight proportion of NK, which satisfies the material condition for use as a sub-base material and the UCS test results similarly improved consistently and recorded a maximum of 340.18 kN/m2 at 15% by weight proportion of NK addition, which satisfies “very stiff” material consistency for use as a sub-base material. With the foregoing, NK has shown to be a good admixture material for soil stabilization towards solving the myriad pavement and environmental failures and problems with our road pavements.

Chemical and geotechnical assessment of low organic foundation soils across the coastal area of Southwestern Nigeria

Pressure on land use has caused great site development along the coastal area of south western Nigeria. However, research works for the purpose of evaluating appropriate depths of foundations in the area were without cognizance of engineering challenges that may ensue as a result of the organic content, and associated factors of the soils. This paper evaluates the compositional effects of the soils on foundation materials, and a phenomenological model of compressibility of fines during design and construction of problem-free foundations in the area. Thirty (30) disturbed soils were analysed for moisture content, grain size distribution, consistency limits, chloride, pH and sulphate, while the oedometer consolidation test was carried out on another 30 undisturbed soils. The stratigraphic sequence in the profile comprises medium dense to coarse grained silty clayey sand to 16.80 m depth, below loose grey organic silty clayey sand from the surface. Results show in most cases, that the foundation soils contain insignificant percentages (0.95–5.8%) of organic solids. Moisture content (44–70%), chloride (74.9 ppm), sulphate (420 ppm) ions concentration and pH (8.96) could enhance the corrosive potential of the soils. It is recommended that Portland cement concrete will be suitable in the environment. Foundation settlement with respect to surface area (0.028≤ mv ≤ 0.434m2MN−1 at 200 kNm−2; 0.038mv ≤ 0.776m2MN−1 at 400 kNm−2; 0.038≤ mv ≤ 0.879m2MN−1 at 800 kNm−2) ranges from low to medium compressibility with respect to consolidation pressure. Therefore, footings load need be spread over the soils, and foundation design need be based on site-specific soil information.

Geotechnical Study on the Use of Sanitized Sewage Sludge in Cover Layers of Solid Waste Landfills

Giving the current trend of recycling and reutilization residues, sludge reuse has become an environmental, social and economic necessity. A possible destination would be the utilization of sludge as part of cover layer in solid waste landfills. This paper aimed at investigating the geotechnical implications of the addition of domestic sanitized sewage sludge on clayey-silty sand. The sludge was sanitized with hydrated lime, in the proportion of 25% lime and 75% sludge, and held for 90 days in an agricultural greenhouse for its total stabilization. Then, geotechnical tests were conducted using pure soil, pure sanitized sewage sludge and mixtures of these two materials. Three mixtures were tested: 50% soil and 50% sludge, 66% soil and 33% sludge and 90% soil and 10% sludge. The results showed that the sanitized sludge is a coarse-grained material and, its Atterberg’s limits showed the lack of plasticity. Generally, the greater the sludge percentage in the mixture, the bigger the decrease on the shear strength parameters, it also leaves them lighter and more permeable. At the end, the conclusions were that the 10% sludge and 90% soil mixture has shown geotechnical characteristics that allow its utilization as daily and intermediate cover layers. The sludge and the 50% sludge mixture have shown geotechnical properties adequate for their utilization as component in draining sub-layer in final cover layer.

Earthquake induced liquefaction hazard, probability and risk assessment in the city of Kolkata, India: its historical perspective and deterministic scenario

Liquefaction-induced ground failure is one amongst the leading causes of infrastructure damage due to the impact of large earthquakes in unconsolidated, non-cohesive, water saturated alluvial terrains. The city of Kolkata is located on the potentially liquefiable alluvial fan deposits of Ganga-Bramhaputra-Meghna Delta system with subsurface litho-stratigraphic sequence comprising of varying percentages of clay, cohesionless silt, sand, and gravel interbedded with decomposed wood and peat. Additionally, the region has moderately shallow groundwater condition especially in the post-monsoon seasons. In view of burgeoning population, there had been unplanned expansion of settlements in the hazardous geological, geomorphological, and hydrological conditions exposing the city to severe liquefaction hazard. The 1897 Shillong and 1934 Bihar-Nepal earthquakes both of M w 8.1 reportedly induced Modified Mercalli Intensity of IV–V and VI–VII respectively in the city reportedly triggering widespread to sporadic liquefaction condition with surface manifestation of sand boils, lateral spreading, ground subsidence, etc., thus posing a strong case for liquefaction potential analysis in the terrain. With the motivation of assessing seismic hazard, vulnerability, and risk of the city of Kolkata through a consorted federal funding stipulated for all the metros and upstart urban centers in India located in BIS seismic zones III, IV, and V with population more than one million, an attempt has been made here to understand the liquefaction susceptibility condition of Kolkata under the impact of earthquake loading employing modern multivariate techniques and also to predict deterministic liquefaction scenario of the city in the event of a probabilistic seismic hazard condition with 10% probability of exceedance in 50 years and a return period of 475 years. We conducted in-depth geophysical and geotechnical investigations in the city encompassing 435 km2 area. The stochastically synthesized bedrock ground motion for both the 1897 and 1934 earthquakes on non-linear analysis of local site conditions through DEEPSOIL Geotechnical analysis package present surface level peak ground acceleration of the order of 0.05–0.14 g for the 1934 Bihar-Nepal earthquake while for the 1897 Shillong earthquake it is found to be in the range of 0.03–0.11 g. The factor of safety (FOS) against liquefaction, the probability of liquefaction (P L), the liquefaction potential index (LPI), and the liquefaction risk index are estimated under the influence of these two earthquakes wherein the city is classified into severe (LPI > 15), high (5 < LPI ≤ 15), moderate (0 < LPI ≤ 5), and non-liquefiable (LPI = 0) susceptibility zones. While the 1934 Bihar-Nepal earthquake induced moderate to severe liquefaction hazard condition in the city in mostly the deltaic plain and interdistributary marsh geomorphologic units with 13.5% sites exhibiting moderate hazard with a median LPI of 1.8, 8.5% sites depicting high with a median LPI of 9.1 and 4% sites with a median LPI of 18.9 exhibiting severe hazard condition, 1897 Shillong earthquake induced mostly non-liquefaction condition with very few sites depicting moderate and high liquefaction hazard. A conservative liquefaction hazard scenario of the city on the other hand estimated through deterministic approach for 10% probability of exceedance in 50 years predicts a high hazard zone in the 3.5–19 m depth region with FOS < 1 and P L > 65% comprising of coarse-grained sediments of sand, silty sand, and clayey silty sand in mostly the deltaic plain geomorphologic unit with 39.1% sites depicting severe liquefaction hazard with a median LPI of 28.3. A non-linear regression analysis on both the historical and deterministic liquefaction scenarios in P L versus LPI domain with ± 1 standard deviation confidence bound generated a cubic polynomial relationship between the two liquefaction hazard proxies. This study considered a bench mark for other cities in the country and elsewhere forms an integral part of the mega-seismic microzonation endeavors undertaken in all the earthquake-prone counties in the world.

Chemical potential of a two-component liquid in porous media: The case of unsaturated soil

The aim of this paper is to propose a method to determine the chemical potential of two miscible components of a solution in porous media, particularly in the case of an unsaturated soil. It is limited to the capillary state; the equilibrium of the liquid phase in the soil is determined by gas–liquid interfaces whose geometry obeys Laplace’s law. Deduction of the chemical potential of the two components from the chemical potential of pure water is based on the assumption that, for the same volume occupied by the fluid phase in the porous medium, the geometry of the fluid phase is independent of the composition of the solution.The expressions of the chemical potentials of the two components were established. They show the superposition of two effects: the effect of interfacial forces and the effect of the presence of the other component. A study of the water–alcohol solution in a clayey silty sand soil was then conducted to alcohol mole fractions between 0 and 0.15 and water content in the 5%–15% range. In this field, the chemical potential of the water was seen to be affected by the capillary effects below a water content of 10%. Above that, its variation as a function of the mole fraction of alcohol differed little from that of the potential of the water in a free solution. The chemical potential of the alcohol was little affected by the capillary effects.

Electrokinetic Remediation of Tropical Soils: Effect of the Electric Potential Difference

t. This paper addresses the influence of electric potential difference on the electroosmotic decontamination of two tropical soils from Brazil. The laboratory testing program encompassed: (i) two residual soils of gneiss, a C-horizon saprolite clayey silty sand (soil sample A) and a B-horizon sandy silty clay (soil sample B); (ii) mineralogical and chemical analysis of the soils; (iii) addition of an aqueous solution of cadmium nitrate in the concentration of 100 mg.L-1 to the soil samples; (iv) compaction of the mixtures specimens at the Standard AASHTO; (v) electroosmotic decontamination tests applying 5, 15 and 30 V; (vi) application of a modified sequential extraction analysis adapted to tropical soils. The results support that the PZC of soils influenced the direction of cadmium migration and that the increase in the applied electric potential difference led to the increase in the amount of extractable contaminant.

COMPACTAÇÃO DE SOLOS EM LABORATÓRIO: EFEITO DO DIÂMETRO E DO NÚMERO DE CAMADAS DO CORPO DE PROVA

RESUMONeste trabalho, estudou-se a influência do diâmetro e do número de camadas do corpo de prova nas curvas de compactação de laboratório e na resistência mecânica de dois solos residuais de gnaisse da Zona da Mata Norte de Minas Gerais, respectivamente, de texturas argilo-areno-siltosa (Solo 1) e areno-silto-argilosa (Solo 2), com vistas à construção de estradas florestais. Além dos resultados dos ensaios de compactação, determinou-se a resistência à compressão não confinada dos solos empregando corpos de prova compactados na umidade ótima (wot) e nos teores de umidade 3% abaixo e 2% acima, considerando como referência a energia de compactação do ensaio Proctor normal e empregando corpos de prova compactados em uma, duas e três camadas, bem como nos diâmetros de 35 mm, 73 mm e 100 mm, com nove repetições. Para fins práticos de engenharia e com base em análise estatística aplicada aos parâmetros massa específica aparente seca e resistência à compressão não confinada, pode-se concluir que: (i) há diferenças significativas entre as compactações realizadas em uma e em três camadas, não ocorrendo o mesmo nas compactações realizadas em duas e em três camadas, para ambos os solos; e (ii) há diferenças significativas entre a compactação de corpos de prova de diâmetro 100 mm e os demais de 73 mm e 35 mm, para o solo 1 (argiloso), bem como há também diferenças apenas no ramo seco da curva de compactação, para o solo 2 (arenoso).

Incorporation of reactive magnesia and quicklime in sustainable binders for soil stabilisation

The utilisation of reactive magnesia or quicklime as novel activators for slag offers a range of technical and environmental benefits over conventional caustic alkali activators and showed great potential in soil stabilisation. This paper investigates the mechanical and microstructural properties of two model soils, i.e., a clayey soil and a slightly silty clayey sand, stabilised by ground granulated blastfurnace slag (GGBS) using various techniques including unconfined compressive strength (UCS) test, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). A number of MgO and CaO mixtures with different MgO/CaO ratios were adopted for slag activation. The activator to GGBS ratio was 1:3 and the dosage of the binder (including MgO, CaO and GGBS) was 12% by weight of the dry soil. The result demonstrated that the increasing MgO/CaO ratio in the binder led to an increase in the UCS of the stabilised clayey soil up to 90days, due to the increased homogeneity of C–S–H gel structure, the decreased Ca/Si ratio of C–S–H gel and the increased amount of voluminous hydrotalcite-like phases. On the other hand, slag activated with MgO–CaO mixtures showed poorer mechanical performance than slag activated with either MgO or CaO alone for sand stabilisation. In addition, strength enhancement was observed for the stabilised clayey soil upon different soaking conditions up to 7days. After 28days, although binders with higher MgO/CaO ratios showed slight strength degradation upon soaking, they still exhibited higher strength than those with lower MgO/CaO ratios.

Effects of Deicing Salts on the Clogging of Stormwater Filter Media and on the Media Chemistry

AbstractStormwater filter media (SFMs) play a vital role in decreasing flooding and preventing urban contaminants from polluting surface and ground waters. The infiltration rate of a SFM is a governing factor in the hydrological and environmental performance of the stormwater management systems. This paper describes the effect of a common deicing salt (sodium chloride) in reducing the infiltration capacity of two types of SFMs, which were prepared using a clayey silty sand, one with compost and another without compost. This paper also describes the effect of sodium chloride application in the release of zinc, calcium, nitrogen, magnesium, phosphorous, potassium, and sulfur from the SFM, and whether their release was accelerated or reduced from the SFM with compost. Laboratory constant-head infiltration tests were conducted using sodium chloride (as the deicing salt) at concentrations of 150 and 1,200 mg/L. After conducting the tests for comparable cumulative pore volumes of infiltration, soil only SFM ex...

Determination of migration rates of contaminants in a hydrocarbon-polluted site using non-reactive tracer test in the Niger Delta, Nigeria

A natural gradient tracer test with sodium chloride as the injectate was conducted using one injection well and eleven observation wells in an oil-contaminated site in the study area. The aim was to characterize the site and to determine migration rates of the contaminants to provide information on their fate in groundwater resources in the area. The migration of the tracer was constantly monitored by sampling all the observation wells spaced 5 m from each other at 15–30 min intervals for a period of 6 days. The test soil layer is a clayey silty sand consisting of 50 % sand, 30 % silt and 20 % clay. The average static water level at the site is about 2.5 m. Gas chromatography fingerprinting showed that kerosene and diesel are the dominant fractions within the soil matrix. The arrival times of the breakthrough moments of the migrating tracer plume from two observation piezometers situated 2.0 and 7.22 m away from the injection well showed that the mean velocity in the longitudinal direction in the aquifer is 1.403 × 10−3 ms−1 (121 m/day). The longitudinal and transverse dispersion coefficients of 2.45 × 10−3 m2s−1 and 2.3 × 10−3 m2s−1 were used to obtain longitudinal and transverse dispersivities of 1.78 and 1.64 m, respectively. High hydraulic conductivity denoted by the high migration rate of the tracer implies that contaminant at the site will migrate through the aquifer with relative ease. However, the significant clay fraction within the soil provides the medium for adsorption and partitioning of contaminants to the soil.

Clogging Mechanism of Stormwater Filter Media by NaCl as a Deicing Salt

The effect of NaCl deicing salt on compost-included stormwater filtration media (SFM) has not been studied so far. This article presents results of an experimental and analytical study conducted to understand the mechanism of permeability reduction in two SFM caused by the application of a common deicing salt (NaCl). The two SFM used were made up of clayey silty sand with and without added compost (15% by mass). Constant-head flow experiments were conducted applying NaCl at two different concentrations. Permeability of SFM without compost reduced by an average of 19.1%, while the permeability of SFM with compost reduced by an average of 93.7%. Mercury intrusion porosimetry (MIP) tests and chemical analyses were conducted on representative samples of the media, both before and after salt application. MIP results showed that median pore sizes enlarged, while permeability reduced. This is counterintuitive, as we usually expect that permeability reduction would be caused by pore-size reduction. MIP results (enlarged pore sizes) suggest that deicing salts caused flocculation of aggregates. Based on analysis of our experimental results and comparison with similar results in the literature, we conclude that permeability reduction of SFM was due to blocking of pore throats by dispersed particles and biofilms. Permeability reduction of the SFM with compost was larger, because compost-salt interactions were comparatively greater than the soil-salt interactions. Results of this study suggest that salt-laden snow should not be piled up near the bioretention facilities built with compost-included SFM.

When technology joins symbolic behaviour: The Gravettian burials at Grotta Paglicci (Rignano Garganico – Foggia – Southern Italy)

In 1971, a complete burial of an adolescent male (Paglicci II) was found in the Evolved Gravettian layers at Grotta Paglicci (Rignano Garganico, Foggia, Southern Italy). Nearly 20 years after (1988–1989), the burial of a young woman belonging to the same cultural complex (Paglicci III) was brought to light.The re-examination of ochre and grave goods/parures from both burials provided new insights about the ritual behaviour and the technological know-how in raw material processing of the Gravettian groups. Analyses were carried out by means of 3D optical microscopy, polarized light microscopy in thin section, XRD, ICP-OES, SEM, TEM, HPLC and ToF-SIMS. Investigation was performed on a fragment of manganese oxides bearing deep incisions (discovered between the ankles of Paglicci II), which is nearly unique in the Upper Palaeolithic funerary contexts. Use-wear observations on this block suggested that it was used to obtain black pigment with different kinds of actions. Ochre materials were analysed in order to identify their nature and their processing techniques. This study was integrated with the study of a sample of natural local reddish soil and with experimental analyses carried out by grinding coarse hematites under various operative conditions. Results detected the characteristics of raw materials: a nanosized hematite-rich clayey natural material, likely technologically ready for use (Paglicci III ochre), and a mixture of a clayey–silty sand with a natural earthy-micaceous hematite (Paglicci II ochre). New inferences from the behavioural standpoint (such as the use/non-use of the grave goods, the connection between the parure shells and the sex of the dead and the hairstyling of the woman) as well as a range of possible raw material procurement sources are discussed.

Feasibility of a soft biological improvement of natural soils used in compacted linear earth construction

Increasing demand for infrastructures requires innovative, cheap and environmental sustainable practices in construction. The soils which are available on site for linear embankments often need to be improved to satisfy the necessary performance and strength requirements. A bio-improvement is evaluated here, for use in compacted earth construction. To the aim of sustainability and cost reduction, a soft technique was chosen by the industrial party, which consisted in adding bacteria to a superficial soil retrieved in situ, and letting them precipitate calcium carbonate with the aid of the nutrients available in the organic matter of the soil and in the compaction water. The effects of the soft biological treatment on silty clayey sand were studied systematically in a comprehensive laboratory investigation, focused on the properties mostly affecting the performance of earth constructions: compaction energy, water retention, hydraulic conductivity, small-strain shear stiffness, collapse potential and shear strength. Mercury intrusion porosimetry tests and scanning electron microscopy were performed to help in providing a comprehensive picture of the consequences of the soft biological treatment on the natural soil. Lack in artificial nutrients reduces the efficiency of the biological treatment with respect to other cases reported in the literature. Nonetheless, organogenic aggregates and bonds are created during mixing and ageing, as detected from small-stiffness measurement during the curing time lapse. The bio-cemented bonds are mostly broken during compaction, while the aggregated structure remains, and the fine fraction generated by broken bonds ends in acting as filler of some inter-grain and inter-aggregate porosity. Eventually, the effects of the adopted technique on the hydro-mechanical behaviour of the compacted soil can be described in a coherent picture as the result of bio-filling of an aggregated compacted soil fabric.

Residual shear strength of unsaturated soils via suction-controlled ring shear testing

Results from a comprehensive series of suction-controlled ring shear tests, conducted on statically compacted specimens of silty clayey sand and silty sand, are presented. The experiments were accomplished in a newly developed servo/suction-controlled ring shear apparatus suitable for testing unsaturated soils under large deformations and suction-controlled conditions via the axis-translation technique. The present work focuses primarily on two crucial aspects of compacted unsaturated soil behavior, namely, the behavior of silty clayey sand under suction-controlled ring shear testing, and the effects of pre-shearing and suction histories on unsaturated residual shear strength of compacted silty sand. Test results corroborate the important role played by matric suction on residual shear strength properties of unsaturated soils. For the range of net normal stresses and suction states investigated, the increase in residual shear strength with increasing suction was confirmed to be a linear trend for silty sand, but significantly nonlinear for silty clayey sand. Results from multi-stage ring shear tests confirmed that the residual shear strength of unsaturated soils is virtually independent of the pre-shearing and suction histories experienced by the soil.