Long-term analysis of soil water regime and nitrate dynamics at agricultural experimental site : field-scale monitoring and numerical modeling using HYDRUS-1D
Description:
•Compaction improves splitting resistance of vertically cast specimens.•Top-cast specimens have a lower splitting resistance than bottom-cast specimens.•Higher splitting stress is generated orthogonal to the plane of the textile.•The main cause of splitting failure is the fiber strand’s varying cross-section.•Bond distribution depends on the cross-section variation along the fiber strand. Textile-reinforced concrete is an innovative combination of high-performance fine-grained concrete and textile reinforcements. This combination allows the production of thin, efficient, and durable structural elements. Impregnation is commonly used to improve the textile's mechanical performance. When stiff impregnation materials are used, a fiber strand with high transverse stiffness is formed. Textile-reinforced concrete structures with such fiber strands are prone to splitting failures. This paper investigates splitting failure in textile reinforced concrete experimentally and numerically. In the experimental part, the effect of concrete compaction, casting method, and position are studied as parameters. Finite element analysis is performed to investigate failure mode, tensile and bond stress distributions, and the effect of the varying cross-section of the fiber strand. Compaction improved the splitting resistance for the vertically cast specimens. The compacted vertically cast specimens showed a higher splitting resistance than their horizontally cast equivalents. The finite element model indicated that the main cause of splitting failure is the textile reinforcement's varying cross-section coupled with its flat elliptical shape. The model also showed that the bond stress distribution depends on the fiber strand's geometric configuration.
Description:
The present trend of inserting increasingly more solar photovoltaic (PV) sources into the electricity grid leads to a significant reduction in mechanical inertia. Inertia represents energy reserve in the grid, that inherently and instantaneously supports frequency stability. Therefore, recent studies have re-examined the frequency stability of the grid. Most of these consider scenarios where the participation from grid-following inverters remains relatively low. More importantly, these studies include an infinite bus in their analyses. The infinite bus acts as a very stiff voltage source which has a significantly stabilising influence, the more so as all control refers back to the infinite bus. Here, the frequency stability of a grid with significant generation from grid-tied PV inverters is considered without reference to an infinite bus. In the proposed simplified grid model, all the synchronous generators (SGs) are lumped as one large SG complete with classically operating controls. Similarly, all the PV generators are lumped as one large, quasi-instantaneous, non-linear power source. In this simplified network, the feasible operating region is identified using bifurcation techniques. It transpires that the stable operating region is bounded by a locus of Hopf bifurcations linked (inter-alia) to the fraction of power generated by grid-tied PV inverters.
Description:
Cohesive strength or intrinsic tensile strength as well as cohesive length are two important unknowns for cohesive modelling of fracture and failure analysis of quasi-brittle materials including rocks. There is no direct method for measuring these parameters and their quantification is always challenging and controversial. In this study, a novel multifractal framework is employed to quantify the cohesive length of four different rock types including sandstone, marble, fine-grained granite and coarse-grained granite by analysing the roughness of their fracture surfaces in a wide range of length scales. On the one hand, microstructural heterogeneities of rock material at small enough length scales will cause multifractality of the roughness of its fractured surface. On the other hand, this intrinsic heterogeneity together with extrinsic features including loading and environmental conditions as well as geometrical features including shape and size of a quasi-brittle specimen or structure are forming a fracture process zone (FPZ) in front of any stress concentrators before crack propagation. Therefore, it is proposed that locating the transition from multifractality to mono-fractality of a rough rock fractured surface using the employed statistical mechanics method leads to quantifying the effective length of FPZ of a sharp crack or the cohesive length. This length is quantified for the studied rocks ranging from 0.4 to 1.1 mm. Moreover, by employing the theory of critical distances, the cohesive strength
Description:
Cohesive strength or intrinsic tensile strength as well as cohesive length are two important unknowns for cohesive modelling of fracture and failure analysis of quasi-brittle materials including rocks. There is no direct method for measuring these parameters and their quantification is always challenging and controversial. In this study, a novel multifractal framework is employed to quantify the cohesive length of four different rock types including sandstone, marble, fine-grained granite and coarse-grained granite by analysing the roughness of their fracture surfaces in a wide range of length scales. On the one hand, microstructural heterogeneities of rock material at small enough length scales will cause multifractality of the roughness of its fractured surface. On the other hand, this intrinsic heterogeneity together with extrinsic features including loading and environmental conditions as well as geometrical features including shape and size of a quasi-brittle specimen or structure are forming a fracture process zone (FPZ) in front of any stress concentrators before crack propagation. Therefore, it is proposed that locating the transition from multifractality to mono-fractality of a rough rock fractured surface using the employed statistical mechanics method leads to quantifying the effective length of FPZ of a sharp crack or the cohesive length. This length is quantified for the studied rocks ranging from 0.4 to 1.1 mm. Moreover, by employing the theory of critical distances, the cohesive strength
Description:
he paper under discussion (Díaz et al., 2021) investigated the application of machine learning techniques to relate the Casagrande percussion-cup liquid limit (LLCUP) with the fall-cone liquid limit (LLCONE) determined using the 30°–80 g British Standard (BS) fall-cone device (BSI, 2018) for low–medium plasticity fine-grained soils (having plasticity index values of <30% and which mostly classify as CL–ML and CL) sampled from a specific site in SE Spain. As reported in their paper, the experimental LLCUP data were obtained in accordance with the UNE 103103:94 standard (AENOR, 1994), which employs a percussion-cup device having ‘hard’ base material satisfying the same hardness and resilience specification ranges as those of the ASTM percussion-cup device (ASTM, 2017). The clay mineralogy of the investigated fine-grained soils was not reported in Díaz et al. (2021); however, as explained in Haigh (2012) and O'Kelly et al. (2020a), clay mineralogy does not majorly account for dissimilarities in LLCUP and LLCONE measurements for a given fine-grained soil; rather they largely arise due to the different mechanics of the percussion-cup and fall-cone test devices (O'Kelly et al., 2018; O'Kelly, 2021; O’Kelly et al., 2022), and also due to variations in the hardness/resilience of the cup base-material (being ‘soft’ or ‘hard’) (Haigh, 2012, Haigh, 2016). The LLCUP water content is associated with the soil's specific strength (i.e., ratio of remolded undrained shear strength su to saturated bulk density
Description:
•Glasshouse experiments on Sprayable Biodegradable Polymer Membrane (SBPM) Technology.•Water conservation using SBPM increased with increasing application rate.•Crop emergence decreased with increasing application rate.•The 150 mm width and 0.5 kg m-2 SBPM rate was most effective in reducing weeds.•SBPM band application had positive effects on soil water potential. With a rapidly growing global population, increased agricultural productivity is required to achieve future food security. Efficient use of water and other agricultural inputs such as nutrients and pesticides must underpin agronomic practices to improve crop establishment and increase crop yields. A glasshouse study was conducted to explore the potential of a newly developed sprayable biodegradable polymer membrane (SBPM) applied in bands to reduce soil evaporation and increase soil temperature, thus improving germination, emergence and crop establishment. The aims were two-fold: (i) to evaluate the effectiveness of the SBPM in reducing seedbed water loss and its effect on seedling emergence and (ii) to determine an effective band width (100 vs 150 mm) and application rate of SBPM to conserve seedbed water. Our study demonstrated that a high application rate (1 kg m-2) is effective at reducing soil water loss, but it reduces crop emergence (cotton, sunflower, sorghum, mung bean, carrot, capsicum and rockmelon). All three SBPM application rates (1, 0.5 and 0.25 kg m-2) showed increased soil water content compared to the control plot (bare soil surface). The applied bands, 100 and 150 mm width, limit evaporation and increased soil water potential and temperature compared to the control, however with no significant differences between the two treatments. Crop emergence was proportional to the application rate and decreased with increasing application rate (i.e., control < 0.25 kg m-2 < 0.5 kg m-2 < 1 kg m-2). The SBPM suppressed weed growth similar to conventional mulch film and was most effective at 0.5 kg m-2 and 150 mm width. Future research should focus on the field SBPM application management with an emphasis on crop emergence zones, biodegradability and comparing its effectiveness with other conventional mulches.
Description:
AbstractBond behavior is an important subject in the design and performance of reinforced concrete structures. In this research, the bond property between sand-coated glass fiber–reinforced polymer (GFRP) bars, a corrosion-resistant substitute to steel bars, and fly ash–based geopolymer cement (GPC) concrete, a more environmental friendly alternative to ordinary portland cement (OPC) concrete, is investigated. Pullout test specimens containing GFRP bars embedded in GPC and OPC concrete cylinders with 100-mm diameter and 170-mm height were prepared. Three different embedment lengths were tested: three, six, and nine times the bar diameter. Average concrete compressive strengths of approximately 25 and 45 MPa and GFRP bar diameters of 12.7 and 15.9 mm were the other test parameters. For each specimen, the test results include the bond failure mode, the average bond strength, the slip at the loaded and free end, and the bond-slip relationship curves. The test results showed that GFRP-reinforced GPC concrete has similar bond strength as that of GFRP-reinforced OPC concrete. The increase in embedment length resulted in the decrease of the bond strength as well as a change in the failure mode of the specimens. Furthermore, the experimental results were used to generate a constitutive bond-slip law. Finally, finite-element modeling is performed by using the constitutive bond-slip law to investigate strain and bond distribution along the embedment length of the bar.