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Agronomski in okoljski vidiki prekrivnih posevkov v ekološki pridelavi zelenjadnic
Martina Robačer, 2019, doktorsko delo/naloga

Opis: Cover crops can reduce the use of external inputs such as pesticides and fertilisers and can at the same time suppress weeds as well as improve or maintain soil fertility. Cover crops can also modify the microclimate which affects pest populations and diseases. Determining cover crop species and management practices is based on the needs and goals of production. The effects of introducing living mulch (LM) and management strategies on cash crop yield, product quality and energy use were studied in certain European countries (Slovenia, Italy, Germany and Denmark) in different climatic and soil conditions. In Slovenia, in organic production of cauliflower and leek, the effects of two terms of sowing white clover with additive design were compared with a production with black foil and with the usual agricultural practice by hoeing. In the field experiments the effect of LM on arthropod dynamics and activity density was investigated. The results demonstrated that the LM systems with a substitutive design, can be effectively implemented in vegetable production if the value of the ecological services (positive externalities) delivered by LM can counterbalance the yield loss due to the cash crop density reduction. If an additive design is used, the LM should be sown several weeks after the cash crop planting. Different cash crop genotypes (i.e., open pollinated/local cultivars in comparison with the hybrids) performed similarly. Use of human labor (HL) and fossil fuel (FF) energy slightly increased in LM systems (7%). The farmers’ acceptance of the LM techniques was quite high (75% of the interviewed sample). The LM technique did not affect the infestation of cabbage caterpillar Pieris spp., showing no detrimental effect of this technique on this key pest of cabbage. In Denmark, aphid populations were higher in the sole crop system than in the LM system. In Italy, a level of larval parasitization was detected and in the first year the percentage of parasitization was higher in LM (88%) than in sole crop (63%). Overall, the LM positively affected the activity density of Carabid beetles, also increasing the diversity and evenness of species (Slovenia and Italy) or activity density of some taxa (Slovenia and Denmark). Due to numerous agroecological services of cover crops, growing simultaneously with vegetables as LM, this could be promising technique for organic and others production systems in the future.
Ključne besede: organic vegetable production, cover crops, agroecological service, living mulch, energy consumption, biodiversity, soil arthropod
Objavljeno: 01.02.2019; Ogledov: 939; Prenosov: 126
.pdf Celotno besedilo (1,43 MB)

A general analytical solution to the one-dimensional consolidation problem for unsaturated soil under various loading conditions
Jiwei Li, Changfu Wei, Yanlin Zhao, 2018, izvirni znanstveni članek

Opis: A general analytical solution is developed for the onedimensional consolidation problem of unsaturated soil under various time-dependent loading conditions based on a differential transformation method (DTM). In particular, analytical solutions are obtained for different relationships between the coefficients in the governing equations for unsaturated soil consolidation. The Fourier series expansion technique is adopted to account for both the continuous differentiable loading and the periodic piecewise loading. A comparison between the results of the current solution and the existing theoretical solution indicates that the proposed solution yields excellent results, while it is straightforward to obtain the analytical solution of the unsaturated consolidation problems. It was also found that the variations in the coefficients in the governing equations can significantly influence the dissipation of both the excess pore-air pressure and the excess pore-water pressure, though the magnitudes of their variations are different.
Ključne besede: one-dimensional consolidation problem, unsaturated soil, analytical solution, time-dependent loading
Objavljeno: 11.10.2018; Ogledov: 548; Prenosov: 308
.pdf Celotno besedilo (814,44 KB)
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A simplified approach to estimating the soil stress distribution due to a single pile
Ping Li, Tao Yu, Dongdong Zhang, 2017, izvirni znanstveni članek

Opis: This paper reports a simplified analytical solution for estimating the soil stress distribution due to pile dependence on the pile dimensions. The exponentially increasing ultimate skin friction along the pile shaft is derived by means of an equilibrium analysis of the soil element around the pile. The soil stress distribution due to the exponentially increasing skin friction and uniformly distributed end bearing of the piles is proposed. The estimated soil stresses are compared using the original Geddes solution, which validates the derivation and formulae obtained.
Ključne besede: analytical solution, soil stress distribution, skin friction, end bearing
Objavljeno: 18.06.2018; Ogledov: 605; Prenosov: 42
.pdf Celotno besedilo (877,24 KB)
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Engineering properties of tropical clay and bentonite modified with sawdust
Isaac I. Akinwumi, Oluwapelumi O. Ojuri, Adebanji S. Ogbiye, Colin A. Booth, 2017, izvirni znanstveni članek

Opis: Construction engineers typically avoid the use of expansive soils as construction materials because they are usually difficult to work on and can cause structural failure. This research work investigates how the application of sawdust to tropical clay and bentonite influences their geotechnical properties in order to determine their suitability for use as landfill-liner materials for the effective containment of toxic substances from landfills. X-ray diffractometry, X-ray fluorescence spectroscopy and scanning electron microscopy were used to determine the mineralogical composition, oxide composition and microstructure, respectively, of the clay and the bentonite. A series of laboratory tests were conducted to determine the specific gravity, Atterberg limits, compaction, unconfined compressive strength and permeability characteristics of the clay and the bentonite for varying proportions of sawdust application. Generally, increasing the percentage of sawdust caused a reduction in its specific gravity, maximum dry unit weight and unconfined compressive strength, while it caused an increase in the optimum moisture content and permeability of the modified clay and bentonite. The clay and bentonite both have a sufficiently low permeability that satisfies the hydraulic conductivity requirement for use as clay liners. Eight percent sawdust application to a clay having similar properties as that in this study is recommended as an economic way of modifying it – with the potential of improving its adsorbent property – for use in landfill-liner systems in order to prevent the toxic substances leaching from the landfills, thereby protecting the environment and public health.
Ključne besede: geotechnical properties, hydraulic barrier, landfill, construction, soil improvement, sustainability
Objavljeno: 18.06.2018; Ogledov: 346; Prenosov: 29
.pdf Celotno besedilo (766,16 KB)
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Critical setback distance for a footing resting on slopes
Rajesh Prashad Shukla, Ravi Sankar Jakka, 2017, izvirni znanstveni članek

Opis: Structures are often constructed on slopes in hilly regions, which results in a lack of soil support on the sloping side of the footings. This causes a reduction in the bearing capacity of the footings. Though there are number of studies about foundations on slopes, most of these studies are confined to surface footings only (i.e., without the depth of embedment). Furthermore, there is no consensus in the literature over the influence of the setback distance on bearing capacity. This paper presents the results of finite-element analyses on a strip footing resting on stable slopes. A very large number of possible soil slopes with different footing depths were analysed. From the results it is found that the critical setback distance increases with an increase in the internal friction angle of soil, the depth of the footing and the slope gradient. The critical setback distance is varying between 2 to 4 times the footing width for soils with a low internal friction angle, while it is more than 10 times the footing width for soils with a higher internal friction angle. A regression equation is also developed based on the outcomes of the study. The developed equation is able to predict the influence of various parameters affecting the bearing capacity of a footing resting over the slopes. The results are compared with earlier experimental and numerical studies.
Ključne besede: bearing capacity ratio, cohesionless soil, footing, setback distance, slopes
Objavljeno: 18.06.2018; Ogledov: 501; Prenosov: 52
.pdf Celotno besedilo (1,53 MB)
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Numerical study of the dynamic active lateral earth pressure coefficient of cohesive soils
Mehrab Jesmani, Hossein Alirezanejad, Hamed Faghihi Kashani, Mehrad Kamalzare, 2017, izvirni znanstveni članek

Opis: Retaining walls are proposed in many projects, such as bridges, coastal structures, road constructions and wherever lateral support is required for the vertical surface of an excavation. The active lateral pressure coefficient of soil, Ka , is an important parameter for studying the static and dynamic behaviors of these retaining walls. Many studies have evaluated this coefficient in static situations, but in most previous dynamic studies, researchers have worked on the behavior of cohesionless backfill soil or made simplifying assumptions (e.g., pseudo-static status) for cohesive soils as backfill soil. In this study, the size of the active lateral earth pressure coefficient (Ka) was studied in a full dynamic situation (Kae). A retaining wall with cohesive backfill soil is evaluated using the finite-difference method (FDM) and the effects of important soil and loading properties are assessed. The model is based on Mohr-Coulomb failure criteria under seismic loading. The results show that the value of Kae at the top of the wall, where it is highly sensitive to any variation in the soil and loading properties, is greater than one due to the high pressure value induced by the horizontal dynamic acceleration and the presence of tension cracks.
Ključne besede: dynamic active lateral earth pressure coefficient (Kae), cohesive backfill soil, finite difference method (FDM), tension cracks, retaining wall, seismic loading
Objavljeno: 18.06.2018; Ogledov: 644; Prenosov: 45
.pdf Celotno besedilo (3,26 MB)
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Evaluation of dynamic soil pressures acting on rigid culverts
Deniz Ulgen, Mehmet Yener Özkan, 2016, izvirni znanstveni članek

Opis: The seismic safety of underground structures (culvert, subway, natural-gas and water-sewage systems) plays a major role in sustainable public safety and urban development. Very few experimental data are currently available and there is no generally accepted procedure to estimate the dynamic pressures acting on these underground structures. This study aims to enhance the state of the prevalent information necessary to understand the dynamic behaviour of box culverts and the stresses acting under dynamic excitations through experimental analyses. For this purpose, a series of shaking-table tests were conducted on box-type culverts buried in dry sand. To simulate the free-field boundary conditions, a laminar box was designed and manufactured for use with a 1-g shake table. Two culvert models having different rigidities were tested under various harmonic motions in order to examine the effect of the flexibility ratio on dynamic lateral soil pressures. Based on the test results, a simplified dynamic pressure distribution acting on the sidewalls of the culvert model was suggested. Then, a dynamic lateral coefficient was defined for the proposed peak pressure value in the distribution. The values of this coefficient were obtained as a function of the shear strain by considering the relative stiffness between the soil and the underground structure.
Ključne besede: box culvert, dynamic earth pressure, shaking table, dynamic soil-structure interaction, laminar box, dynamic lateral coefficient
Objavljeno: 18.06.2018; Ogledov: 321; Prenosov: 36
.pdf Celotno besedilo (584,65 KB)
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A comparison of linear and nonlinear seismic tunnel-ground interaction analyses
Elefterija Zlatanović, Marina Trajković-Milenković, Dragan Lukić, Stanko Brčić, Vlatko Šešov, 2016, izvirni znanstveni članek

Opis: In order to study the effects of a seismically induced tunnel–ground interaction, two-dimensional numerical analyses are performed using the sofware ANSYS. The study employs a coupled beam–spring model subjected to earthquake loading that is simulated under pure shear conditions and determined by a free-field ground-response analysis using the code EERA. The properties of the soil material are considered as both linear and nonlinear. The results obtained by linear dynamic analyses are compared with state-of-practice analytical elastic solutions. A comparison of the results of both linear and nonlinear analyses is also performed, and significant differences, as well as important factors influencing the tunnel–ground interaction for both cases, are evaluated.
Ključne besede: circular tunnel, linear/nonlinear soil behaviour, beam–spring model, plane-strain conditions, simplified dynamic FE analysis, soil–structure interaction
Objavljeno: 18.06.2018; Ogledov: 454; Prenosov: 36
.pdf Celotno besedilo (1,57 MB)
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A method for predicting the deformation of swelling clay soils and designing shallow foundations that are subjected to uplifting
Baheddi Mohamed, Djafarov Mekhti, Charif Abdelhamid, 2016, izvirni znanstveni članek

Opis: Swelling soils can be found in many parts of the world. The state of practice in this area has been changing over recent decades. The design of foundations for expansive soils is an impo rtant challenge facing engineers. The excessive damage is, in part, due to the lack of proper design, resulting in the need for better tools for practitioners in order to assess the impact of swelling soils in typical design applications. A correct measurement of the swelling pressure is required for an accurate prediction of the heave. A theoretical model is proposed to describe the swelling potential of clay soils on the basis of their characteristics obtained from oedometer tests. This paper describes analysis of the behavior of swelling soils when moistened under buildings and structures. The methods and principles currently used for the design of structure foundations on swelling soils involve important problems due to the non-uniform deformations of these soils when subjected to structural loads. The current study was conducted to compute the uplifting of shallow foundations on swelling soils considering the water-content change as well as the contact-pressure distribution under the footing.
Ključne besede: swelling soil, swelling magnitude, swelling pressure, free-swell oedometer test, loaded-swell oedometer test, shallow foundations
Objavljeno: 18.06.2018; Ogledov: 341; Prenosov: 31
.pdf Celotno besedilo (465,96 KB)
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Performance of soilnailed and anchored walls based on fieldmonitoring data in different soil conditions in Istanbul
Dogan Çetin, 2016, izvirni znanstveni članek

Opis: In this study, data on the lateral wall displacements of 28 deep excavations in Istanbul soil from over 90 field monitors were collected and analysed. The most commonly used retaining walls for deep excavations in Istanbul are soil-nailed shotcrete walls (SNPWs) and contiguous pile walls (CPWs). Other types of retaining walls include anchored micropile walls (MPWs), diaphragm walls (DWs), concrete walls (CWs) and secantpile walls (SPWs). The analyses were performed under two main headings: analysis of soil-nailed walls’ data and analysis of anchored walls’ data. The data of δh,max generally range from 0.05%H to 0.35%H with an average value of 0.20%H in the soil-nailed projects. The data of δh,max generally range from 0.043%H to 0.32%H with an average value of 0.155%H in anchored pile wall projects. Some factors affecting the deformation of deep excavations, such as nail density, embedded wall ratio and wall stiffness, were studied based on field-monitoring data. Wall movements were also compared with observations in some case histories from around the world.
Ključne besede: deep excavation, wall displacement, soil formation, soilnailed wall, anchored wall
Objavljeno: 18.06.2018; Ogledov: 369; Prenosov: 59
.pdf Celotno besedilo (483,16 KB)
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