Iskanje po katalogu digitalne knjižnice

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 v DKUM: 01.02.2019; Ogledov: 1666; Prenosov: 228
Celotno besedilo (1,43 MB)

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 v DKUM: 18.06.2018; Ogledov: 1238; Prenosov: 70
Celotno besedilo (877,24 KB)
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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 v DKUM: 18.06.2018; Ogledov: 922; Prenosov: 92
Celotno besedilo (1,53 MB)
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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 v DKUM: 18.06.2018; Ogledov: 649; Prenosov: 91
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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 v DKUM: 18.06.2018; Ogledov: 704; Prenosov: 75
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