Numerical Study on the Deformation of a Twin-Track Tunnel Subjected to Adjacent Excavation of Foundation Pit

As well known, foundation pit excavation influences the stress and deformation of adjacent soil, and thus existing tunnel. However, the behavior on the deformation of a twin-track tunnel subjected to adjacent excavation is not clear. In order to investigate this behavior, a series of numerical simulations using PLAXIS are conducted in this study. The result shows that the displacement and internal forces near the foundation pit is almost double those far away. Moreover, as the depth of excavation reaches the burial depth of tunnel, the value of displacement of tunnel begins to increase markedly.

Effects of Soil and Water Conservation at Different Landscape Positions on Soil Properties and Farmers’ Perception in Hobicheka Sub-Watershed, Southern Ethiopia

This study aimed to evaluate the effects of soil and water conservation (soil bund with desho grass and soil bund only) at different landscape positions on selected soil properties and farmers’ perception in the Hobicheka sub-watershed (with an area of 400 ha) of Kechabira District. Composite soil samples were taken from soil bunds with desho grass and soil bunds only at three landscape positions with three replications, whereas 117 respondents were identified using simple random sampling. The result revealed that the clay, soil moisture content, soil pH, OC, TN, Av.P, and CEC were higher in soil bund with desho grass as compared to adjacent soil bund only, whereas, bulk density, silt, and sand contents were higher in adjacent soil bund only compared to soil bund with desho grass. About 83.5% of the respondents were users of soil and water conservation measures and among them, 40.19% perceived that soil bund with desho grass has an effect on soil properties, while 25.35% perceived that soil bund only had better soil and water conservation practices. Respondents’ years of experience, education level, and access to soil and water conservation extension services significantly ( p ≤ 0.1 ) affected their perception of the use of soil bunds with desho grass. Therefore, soil bund with desho grass at appropriate landscape positions by considering farmer perception improves the soil’s physicochemical properties.

Carbon dioxide levels in initial nests of the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae)

Claustral foundation of nests by Atta sexdens Forel (Hymenoptera: Formicidae) involves great effort by its queens, solely responsible for the cultivation of the fungus and care for her offspring at this stage. The minimum workers, after 4 months, open access to the external environment to foraging plants to cultivate the symbiotic fungus, which decomposes the plant fragments and produces gongilidea nodules as food for the individuals in the colony. Colony gas exchange and decomposition of organic matter in underground ant nests generate carbon dioxide (CO2) emitted into the atmosphere. We described the carbon dioxide concentration in colonies in the field. The objective was to evaluate the carbon dioxide concentration in initial A. sexdens colonies, in the field, and their development. The CO2 level was also measured in 4-month-old colonies in the field, using an open respirometric system fitted with an atmospheric air inlet. The CO2 level of the respirometric container was read by introducing a tube into the nest inlet hole and the air sucked by a peristaltic pump into the CO2 meter box. The CO2 concentration in the initial colony was also measured after 4 months of age, when the offspring production (number of eggs, larvae, pupae and adult workers) stabilized. Ten perforations (15 cm deep) was carried out in the adjacent soil, without a nest of ants nearby, to determine the concentration of CO2. The composition of the nests in the field was evaluated after excavating them using a gardening shovel and they were stored in 250 ml pots with 1 cm of moistened plaster at the bottom. The CO2 concentration was higher in field nest than in adjacent soil. The concentration of carbon dioxide in A. sexdens nests in the field is higher than in those in the soil, due to the production of CO2 by the fungus garden and colony.

Invertebrates in Fruitbodies of Heterobasidion spp., Infected Picea abies Logs and Adjacent Soil

Heterobasidion spp. pathogenic fungi produce conspicuous fruitbodies on infected wood, which may represent a habitat for a range of organisms, including invertebrates. The aim was to: (i) assess and compare invertebrate diversity in Heterobasidion spp. fruitbodies, infected Picea abies wood and adjacent soil; (ii) test methods for collecting invertebrates from Heterobasidion spp. fruitbodies. A total of 69 Heterobasidion fruitbody samples, 46 wood samples and 19 soil samples were collected at two forest sites in Latvia. In total, 7311 invertebrate individuals were collected representing 62 different taxa, among which 55 were in fruitbodies, 47 in wood and 36 in soil. The dominant invertebrates in fruitbodies were Acari (82.4%), Collembola (6.2%), Coleoptera (4.7%); in wood were Acari (78.6%), Collembola (9.6%), Diplopoda (3.1%); in soil were Acari (90.6%), Collembola (3.4%) and Coleoptera (1.4%). Among all taxa, 17.7% were found exclusively in fruitbodies, 3.2% in wood, 4.8% in soil, while 48.4% were shared among different substrates. Although many invertebrate taxa were shared, their relative abundance differed substantially among different substrates. The sampling methods used provided valuable information on invertebrate communities. Further development of these methods may be needed to obtain more detailed and specific information about invertebrates inhabiting different habitats.

Test study on thickness of soil layer at top of plate affecting uplift failure of the NT-CEPP

This paper studies the influence of the thickness of the soil layer on the head of the plate on the carrying capacity of the new type concrete plates-expanded pile (NT-CEPP) under vertical tension, and innovatively uses the half-section pile test method to measure undisturbed soil and ANSYS is used for comparative analysis. Due to the small-scale test based on the half-section pile and disturbed soil, not only can the overall invalidation mechanism of the soil around the pile be seen more clearly, but the undisturbed soil can also be used to better ensure the stability of the soil. At the same time, in the test, depending on the real station under construction, the authenticity and economy of the test should be ensured. The results of test reveal that the invalidation behaviour of the on the top of plate of the NT-CEPP has little effect on the adjacent soil layer when the soil thickness of embedded slab is more than 3 times the length of the cantilever of the slab, and the characteristics of adjacent soil-layer had no influence on the carrying capacity of the plate.

Effects of Rock Outcrops On Adjacent Soil Patches And Plants In A Karst Ecosystem In Southwest China

Purpose Rock outcrops (ROCs) are common structures in terrestrial ecosystems, especially in karst regions. However, their effects on adjacent soil patches and plants are rarely studied. In this study, the effects of ROCs on surrounding soils and plants were investigated. Methods Thirty isolated ROCs were randomly selected in a typical semi-humid karst grassland in Southwest China. Rainfall and ROC runoff were collected for chemical analyses. Soil physical and chemical properties and herb above- and belowground biomass were determined at 0 to 30, 31 to 60, 61 to 90, 91 to 190, and 191 to 290 cm from the ROC rock–soil interface. Results The pH and total organic carbon and Ca2+ contents were higher in ROC runoff than in rainfall. Some soil physical and chemical properties were significantly higher in samples at 0 to 30 cm, and above- and belowground plant biomass were both significantly higher from 0 to 30 cm and from 31 to 60 cm than at greater distances. The ROC effect zone, as estimated by logistic equation, was approximately 75 cm. When the area covered by an ROC was between 0.7 and 1.3 m2, herb biomass increased sharply from 0 to 30 cm and from 31 to 60 cm. Conclusions Karst ROCs affected soils and plants close to their bases, and the effects increased sharply when the area covered by an ROC was of intermediate size.

Some physiochemical properties of termite mound soil and its effect on yield and yield components of maize (Zea mays L.) Under Greenhouse condition at Nekemte, western Ethiopia

Termite mound soil amends soil fertility and utilized as an alternative to npk fertilizers by smallholder farmers in Africa. Experiment was conducted in western Ethiopia to compare selected physical and chemical properties of mound soil (ms), Adjacent soil (as) and non-mound soil (nms) and the effect of these soils on maize plant growth and yield in the Greenhouse. In Limu district, Fitbako kebele, cultivated land was purposively selected for sampling. In the cultivated land, a plot of 100m x100m was delineated and three mounds within the plot were also purposively selected to collect composite soil sample for soil analysis and Greenhouse pot experiment. From each mound, 10kg soil each from bottom, middle and top (total= 30 kg) were collected and mixed to obtain working sample of 10 kg. About 30kg of adjacent soil 5m away from mound soils and Non-mound soil at the distance of 20 m away from mound soil at the depth of 0-30cm were collected and thoroughly mixed to make working sample of 10kg from each soil type. Three kilograms of mound soil, adjacent soil and non-mound soil each was put in separate plastic bucket for greenhouse pot experiment. About 100 gm of each soil type was used for selected physical and chemical properties analyses. The result obtained demonstrated that termite mound soil was significantly (P<0.05) high in bulk density (bd), moisture contents (mc), porosity (P), Soil pH, percent organic carbon (% oc) and percent organic matter (% om). Total Nitrogen (tn), average (av.) P, av. K, Exch. Ca and Exch. Mg were also significantly (P<0.05) higher in mound soil in comparison with adjacent soil and non-mound soil. Maize plant growth traits and yield were significantly (P<0.05) high in mound soil. From the current study, it can be concluded that the use of npk fertilizer on plots having termite mound is not recommended. However, further research is needed on how to use mound soil on large plot of land

Indirect Effects of Microplastic-Contaminated Soils on Adjacent Soil Layers: Vertical Changes in Soil Physical Structure and Water Flow

Previous microplastic research under laboratory conditions has focused on microplastics that are homogeneously mixed into test media, in order to maximize test reproducibility and uniform bio-accessibility. Here we specifically focused on testing the idea that microplastics in soil could affect adjacent soil layers not containing microplastic themselves. We included two different microplastics (low-density polyethylene films and polyacrylonitrile fibers) and carried out a soil column test consisting of three different vertical layers (0–3 cm, top, control soil; 3–6 cm, middle, microplastic-containing soil; 6–9 cm, bottom, control soil). Our study shows that microplastic-containing soil layers can act as an anthropogenic barrier in the soil column, interrupting the vertical water flow. These changes directly affected the water content of adjacent layers, and changes in the proportion of soil aggregate sizes occurred for each depth of the soil columns. We also observed that these physical changes trigger changes in soil respiration, but do not translate to effects on enzyme activities. These results imply that the soil environment in non-contaminated parts of the soil can be altered by microplastic contamination in adjacent layers, as might occur for example during ploughing on agricultural fields. More generally, our results highlight the need to further examine effects of microplastic in experiments that do not treat this kind of pollution as uniformly distributed.

Performance Evaluation of Buried Concrete Pipe Considering Soil Pressure and Crack Propagation Using 3D Finite Element Analysis

Numerous factors affect the soil pressure distributions around buried pipes, including the shape, size, and stiffness of the pipe, burial depth, and the stiffness of the surrounding soil. Additionally, to some extent, a pipe can benefit from the soil arching effect, where the overburden and surcharge pressure at the crown can be supported by the adjacent soil. As a result, a buried pipe only needs to support the portion of the load that is not transferred to the adjacent soil. This paper presents numerical investigations of the soil pressure distributions around buried concrete pipes and crack propagation under different environmental conditions, such as loading, saturation level, and the presence of voids. To this end, a nonlinear elastoplastic model for backfill materials was implemented using finite element software and a user-defined subroutine. Three different backfill materials and two different native soils were selected to examine the material-specific behaviors of concrete pipes, including soil pressure distributions and crack propagation. For each backfill material, the effects of the loading type, groundwater, and voids were investigated. These simulation results provide helpful information regarding pressure redistribution and buried concrete pipe behavior under various environmental conditions.