Soil Abrasion Research Articles

Development of soil abrasivity testing for soft ground tunneling using shield machines

Primary and secondary wear in soft ground tunneling using various types of shields has a major impact on machine operation, utilization, and tunneling costs. Wear occurs due to interaction between abrasive soils and cutters, as well as other components of the machine which come to contact with the muck. However, lack of a standard or universally accepted test for soil abrasivity in the geotechnical investigations has made the prediction of tool wear a difficult task. This paper introduces a new test device, designed to measure soil abrasion and the result of initial testing at the Pennsylvania State University. The testing system is configured to simulate the working condition of the cutting tools in excavation chamber of pressurized face shields. This includes the high contact stresses between the tool and the soil, maintaining the original soil size distribution, field moisture conditions, and possibility of applying high ambient pressures as well as soil conditioners. The preliminary results of testing on several soil types, moisture conditions, and various tool hardness is presented. The test set up is discussed to provide more detailed information on the testing conditions and potential implications in practical applications.

Variables físicas que explican la variabilidad de suelo aluvial y su comportamiento espacial

El objetivo de este trabajo fue utilizar el análisis de componentes principales y de semivarianza para seleccionar variables físicas que explicaran la variabilidad de un suelo aluvial, y establecer el comportamiento espacial de las variables seleccionadas, con el fin de definir técnicamente la localización de parcelas experimentales para estudiar los efectos de la abrasividad del suelo sobre el desgaste de herramientas agrícolas. Las pruebas de campo se realizaron en 2008, en un lote plano de 6.000 m² con suelos de textura media a pesada (Vertic Haplustepts). Se hizo un muestreo intensivo en cuadrícula de 10x14 m. Las variables que mayor peso tuvieron en los tres primeros componentes principales fueron los contenidos de limo, arena fina y media, gravilla media, la humedad a capacidad de campo y el coeficiente higroscópico. A excepción de la arena media y la capacidad de campo, las demás propiedades presentaron alta dependencia espacial y su distribución mostró que en el lote experimental se encuentran tres sectores de acumulación diferencial de limo y de arena fina. La combinación de los análisis de componentes principales y geoestadística permitió definir las propiedades del suelo involucradas en el desgaste de herramientas, su patrón espacial y la manera más adecuada de distribuir parcelas experimentales, para estudiar la abrasividad del suelo.

New soil abrasion testing method for soft ground tunneling applications

Prediction of the tool wear and life, as well as secondary wear on machine components, in soft ground tunneling using shielded machines with a pressurized face has been a difficult task due to the lack of a universally accepted measurement system for soil abrasion. While some existing abrasion tests have been adopted in recent years to measure soil abrasion, these systems have inherent mismatches with the actual working conditions at the tunnel face. This paper reviews some of the background studies in this area and introduces the initial steps towards the development of a new soil abrasion testing system. The design and operational parameters for a proposed device that is under development for measuring a soil abrasion index are discussed and the preliminary results of testing on various soil samples are presented.

Study of the energy abrasion rates of five soil types subject to oblique impacts

To measure the energy abrasion rates in inter-particle collisions, we bombarded 12 soil samples from five textural classes (sandy loam, silty loam, loam, silty clay loam, and silty clay) with 350 μm diameter glass beads falling freely from heights of 5 to 100 cm. The results indicated that brittle cracking plays a major role in the erosion of brittle soil surfaces during bombardment with impacting particles. The occurrence of such brittle cracking would be likely to chip off large pieces of irregular, sharp-edged fragments and aggregates, and would also give rise to a wide range of abrasion rates and dust production rates under the same impact velocity and by the same impacting particles. The soil abrasion rate is approximately proportional to the impact energy, and inversely proportional to the PM 2 content of the soil raised to the power 2.56 and the PM 10 content of the soil raised to the power 3. The sandy loam, loam, silty loam, silty clay loam, and silty clay had averaged energy abrasion rates of 0.791, 0.300, 0.033, 0.024, and 0.008 g J − 1 , respectively.

Soil abrasion and eolian dust production: Implications for iron partitioning and solubility

Eolian dust is a source of iron for phytoplankton in many ocean areas, and there are complex pathways of atmospheric processing from soil to ocean. Overlooked parts of the pathways are the impact of large (>10 μm) grains (including a role as proxies for the behavior of smaller grains) and the effect of multiple cycles of uplift and abrasion in the dust source region. Partitioning (readily released, acid‐leachable and refractory) and dissolution rates of iron were determined for an artificial dust (produced by abrading an Australian soil), untreated soil, abraded soil (after production of the artificial dust), and a natural Australian eolian dust sample taken during a dust storm. Readily released iron is not created during abrasion, and therefore the amount of readily released iron in a dust or dust‐derived soil depends on processing events since the dust or soil last experienced an abrasion event. Our study develops a method for the partitioning of iron within airborne dusts and appears to be the first to consider the effect of multiple uplift events on iron partitioning.

Retardation Coefficients of Nonionic Organic Compounds Determined by Batch and Column Techniques

AbstractBatch and column techniques were utilized to determine retardation coefficients of two nonionic organic compounds: benzene and dimethylphthalate. Three sandy soil materials with medium to high organic C content were used as sorbents. Batch data consistently overestimated retardation coefficients of the two compounds. Several previously reported factors that may cause discrepancy between the two techniques were experimentally investigated. Sorption nonsingularity, sorption nonequilibrium, presence of immobile water regions in the column, and reduction in particle spacing in the column were eliminated as the cause of this discrepancy. Loss of sorbent from the column is unlikely to be the cause of the discrepancy. Although rapidly mixed batch tubes are subjected to soil abrasion, it causes no apparent impact on the value of sorption distribution coefficients. Batch isotherms at two solids concentrations were identical, indicating that differences in solids concentration between batch and column setup is not a significant factor. This was also confirmed by a column study. Sorption nonlinearity was found to have a minor impact. Column residence time had a major impact on one of the cases studied, but no effect on the other cases. When column residence time was accounted for, some differences in sorption distribution coefficients, which seemed to be independent of the organic C content, were noticed. In this study, all previously suggested causes for the discrepancy between batch‐ and column‐determined retardation coefficients were investigated and rejected. It remains unclear why the values determined by the two techniques were different.

Patterns of tree stem decline along a snow-drift gradient at treeline: a case study using stem analysis

Current hypotheses on conifer tree stem degradation at treeline indicate the influence of frost desiccation caused by dehydration of wind-exposed needles above the snowpack because of frozen soil or wind abrasion. Here, we examine, in an exploratory study, the potential of detailed stem analysis to identify other causal factors at a subarctic treeline site using black spruce (Picea mariana (Mill.) BSP.) trees distributed along a wind-exposure gradient and showing various degrees of stem damage, from the normal, conical growth form to the mat growth form. Temporal patterns of stem development revealed a relatively integrated growth system within the tree as long as the normal arborescent form was maintained. With the gradual loss of the normal form owing to defoliation, the growth system of the damaged trees became fragmented into a wind-exposed (west–ast), horizontal component and a vertical (below–bove snowpack) component outlined by the asymmetric development of stem and foliage. Although cool growing seasons reduce tree-ring growth, frost events in July appear also influential, possibly when killing frosts occur during bud break. The impact of such abrupt events may have a long-enduring influence on radial growth, a factor much neglected in dendroclimatological studies of boreal and subarctic environments. Stem degradation may be initiated by the changing position of the snowpack line associated with variable snow precipitation during several consecutive years, thus inducing a shifting erosional zone along the stem most effective when temperatures are below average, i.e., likely the result of mechanical defoliation caused by the synergistic influence of snow and ice abrasion during blizzards and severe windchill conditions on the brittle, cold-exposed needles. Our results suggest that sustained winter defoliation at treeline has an overwhelming influence on subsequent radial growth. More dendroecological studies and experimental field work are needed to test our conclusions. Keywords: stem analysis, treeline, black spruce, winter defoliation, tree rings, subarctic.

Windbreaks: An Important Component in a Plasticulture System

Windbreaks reduce wind speed and modify the microclimate in sheltered areas. Many producers use wind barriers in their production systems, but few producers recognize all of the benefits available or understand the principles involved in windbreak function and design. Wind has direct and indirect effects on plant growth and development. Direct effects include soil abrasion, increased transpiration, and lodging. Indirect effects are based on changes in the crop microclimate, which influence plant growth and yield. Windbreaks increase soil and air temperatures and can extend the growing season in sheltered areas, resulting in increased crop development, earlier crop maturity, and market advantage. Plant-water relations and irrigation efficiency are improved by shelter. Overall, modifications to the microclimate in sheltered areas contribute to 5% to 50% higher crop yields. Winds in excess of about 5 m·s−1 (1.0 m·s−1 = 2.25 miles/h; miles/h × 0.447 = m·s−1) result in wind erosion and soil abrasion and may cause a loss of crop stand. Wind speeds below 5 m·s−1 may have an equally adverse impact on crop quality and marketable yield. In both cases, wind-breaks can reduce damage effectively in sheltered areas. Wind protection reduces certain problems associated with plasticulture under windy conditions.

Increasing the length of hyphae in a sandy soil increases the amount of water-stable aggregates

The contribution from increased lengths of saprophytic and mycorrhizal hyphae to the aggregation of a sandy soil was assessed in a glasshouse experiment. Increased length of mycorrhizal hyphae was encouraged by inoculation of Lolium rigidum with Scutellospora calospora and the effects of the roots on aggregation were restricted by containment within 38 μm mesh bags. The hyphae of saprophytic fungi were increased by the addition of glucose or straw substrates at 2.3 mg g −1. After incubation of the soils for five weeks, changes in > 2 mm water-stable aggregates were assessed in the root-free soil before and after drysieving through 8 mm mesh, to test the resistance of the aggregates to soil abrasion. Hyphal lengths and hot-water extractable carbohydrate C contents were measured in the > 2 mm water-stable fraction and non-aggregate ( < 2 mm) soil of the soils that were not dry-sieved. The treatments increased hyphal lengths from 3.2 m g −1 to 4–6.2 m g −1, but the hyphal lengths were not different between the treated soils ( P < 0.05) because much of the hyphal growth occurred only in the soil that was aggregated. The lengths of hyphae in the > 2 mm aggregates from the soils amended with straw and glucose were 2–5.7 m g −1 greater ( P < 0.05) than the lengths in non-aggregate soil (4–6 m g −1). Inoculation of non-amended soil increased the proportion of mycorrhizal roots by 340% ( P < 0.05) but had little effect on hyphal length in the non-amended soils. Water-stable aggregation was increased from 7–16 g kg −1 in the non-amended soils to 84–143 g kg −1 in the straw- and glucose-amended soils ( P < 0.05). Under a Scanning Electron Microscope, sand grains in the aggregates appeared to be linked together only by hyphae. In addition, the hot-water-extractable carbohydrate C contents of water-stable aggregates and non-aggregate soil were not different, indicating little involvement of microbial polysaccharides in stabilising the aggregates. Despite the strong evidence for hyphal involvement in stabilising aggregates, only the hyphal lengths in the whole soil of the non-amended soil and > 2 mm aggregate fraction of the soil amended with glucose were significantly correlated with aggregation ( P < 0.05). The amounts of dry-stable aggregates in 8 mm sieved soil were generally increased by 63–147% in the amended soils compared to non-amended soils and 27 to 33% of these aggregates were water-stable aggregates indicating that hyphae also contributed to the stabilisation of dry aggregates. Increases in aggregate stability could be largely attributed to the increased growth of hyphae in the sandy soil. Hyphae were able to contribute greatly to the stability of the sand aggregates because much of the soil was > 250 μm sand which favoured cross-linking of the sand grains by short lengths of hyphae.

Critical loads of acidity to surface waters in the Vosges massif (north-east of France)

Acid clearwater fishless streams have been identified in the Vosges mountains. In order to evaluate the relatipnships between acidifying factors (such as atmospheric deposition), buffering factors (such as bedrock and soil type), and surface water acidity, an exhaustive survey of streamwater acidity in the Vosges mountains (N-E France) was performed. A network of 11 measurement stations of atmospheric deposition was used to estimate and map deposition over the whole massif (total area ≠ 5000 km2). Data on bedrock, soil, superficial deposits, and vegetation were collected from published studies. Sensitive areas as well as acidifying environment factors were derived from the corresponding maps. Over the whole massif, 19% of streams showed baseflow alkalinity below 30 μeq.r1 and 7.5 % were identified as acid (pH < 5.4). Acid streams occur on the north-western side of the massif on quartzrich sandstone and acid granites. In each of these areas, we could clearly point out on one hand, the negative influence of conifer vegetation and glacial soil abrasion or induration, and on the other hand the buffering effect of moraine deposits. A corresponding range of critical loads (< 0.2 to 2.0 Keq. ha1 yr1) for surface water was calculated using the Steady State Water, Chemistry method (SSWC).

Demonstration of an X-ray Fluorescence Sensor for the Cone Penetrometer

A feasibility test at the Naval Research Laboratory has shown that a miniature X-ray Fluorescence (XRF) sensor can be constructed for the cone penetrometer. Such a sensor would have detection limits for heavy metal contaminants in soils of a few parts per million. The next step is to demonstrate the capabilities of such a sensor in the cone penetrometer. A sensor for this purpose is being constructed and will be tested both in the laboratory and in the field. The XRF sensor will be capable of evaluating the in-situ detection limits and field screening (semi-quantitative) capabilities of x-ray fluorescence and can be transitioned to field activities for further evaluation and feedback. The sensor will consist of a miniature x-ray tube and an x-ray detector, together with appropriate apertures and x-ray filters, in a custom fabricated section of penetrometer pipe. The sensor will use commercially available components. High voltage and signal cables will couple the sensor to electronics in the truck. Boron carbide will be used for the x-ray windows which protect the sensor components from soil abrasion.

An evaluation of the wear behaviour of metallic materials subjected to soil abrasion

A wear-test rig has been developed which is suitable for the evaluation of materials for tillage tools in actual field working conditions. The reproducibility of the test has been shown to be good when steels were subjected to the harsh soil conditions of the Western Cape region in South Africa. The relative wear resistance of medium-carbon and high-carbon heat-treated steels has been determined, and compared with the results from laboratory abrasion testing. The surface and sub-surface layers on steels subjected to abrasion in the soil have been examined, using optical and scanning electron microscopy. The nature and mechanism of wear occurring during field trials of materials for tillage tools is described. It has been found that the extent of surface deformation can be considerable, giving rise to the appearance of extremely hard non-etching (white) surface layers.

Soil Aggregate Abrasion by Impacting Sand and Soil Particles

ABSTRACT DURING wind erosion, erodible particles (< 0.85 mm diameter) are removed continually in saltation and suspension, but the supply of particles is rarely exhausted because new erodible-size particles are created constantly by abrasion. Little is known about the physics of soil abrasion, however. This study was undertaken to determine the effects of particle speed, size, impact angle, and stability on the abrasive erosion (W) of soil aggregates of various stabilities. A calibrated sandblasting device was used to abrade individual aggregates with weighed amounts of abrader in an enclosed chamber and the weight of soil abraded from the aggregates was determined. Regression equations relating aggregate abrasion to the experimental variables were then developed. Sand abrader produced higher values of W than soil abrader. W also increased as a power of particle velocity. The power was near 2.0 for fragile aggregates and ranged from 1.5 to 2.3 for the most stable aggregates tested. The W of all aggregates decreased nonlinearly as aggregate stability increased. The largest W occurred at impact angles of 20 to 30 deg, and a small increase in W occurred as average particle diameter increased from 125 to 715 /um..

Abrasive Action of Windblown Soil on Plant Seedlings1

SynopsisSeedlings of El Reno sideoats grama were found to be more tolerant to windblown soil than Blackwell switchgrass, sand lovegrass, and Indiangrass. Buffalo alfalfa seedlings were not as resistant to soil abrasion as the range grasses studied.