Papers by Keyword: Hydraulic Conductivity

Abstract: Pervious concrete is considered an advanced pavement material in terms of environmental benefits resulting from its basic feature - high water permeability. While natural aggregate is a standard component for permeable concrete production, the paper presents the potential of air-cooled blast furnace slag aggregate. The aggregate is specific for its open internal structure and at the same time high hardness and strength, which was assumed to be advantageous for this type of concrete. As permeable concrete is characterized by a specific structure and low amount of binder, it needs for optimization of kind and composition of aggregate, as well as the quantity and quality of the binder. In the experiment, following variables of composition were applied: a ratio of binder to aggregate b/a (0.28 and 0.36), a ratio of fine to coarse aggregate f/c (0.1, 0.2 and 0.3), and a set of blended cements. Experimental results point to the specific benefit of slag aggregate for permeable concrete production. The values of total porosity (30-38%) and permeability (4.6-17.5 mm/s) are higher than those recommended by most publications, as well as than those of concretes with natural aggregates. The compressive strength runs from 7.5 MPa to 15.0 MPa depending on the variables, while the effect of fine aggregate portion on both compressive strength and hydraulic conductivity is found to be much greater than that of the amount of binder. An important aspect is that, due to the nature of the aggregate, sufficient permeability is maintained even with higher proportion of fines. The range and variance values of the individual properties indicate that a change in the quality of the binder causes less variation in the results than a change in the composition of the mixtures.

Abstract: This study investigates the use of wadi sediments as a potential source for the core of rock-fill dams. The current practice utilizes clay and silty materials for the core of the rock-fill dam. In Oman, clay is not abundantly available, so there is a need to propose a local alternative material as a potential source for the core of the rock-fill dam. Dredged sediment is believed to have properties like clay but is a waste material deposited in reservoirs. The samples of wadi sediments were grouped from the reservoir of Wadi Jizzi Dam, located a few kilometers away from the city of Sohar. A detailed laboratory-testing program investigates the physical characteristics, grain size distribution, liquid and plastic limits, specific gravity, compaction, hydraulic conductivity (permeability), swelling potential, and unconfined compressive strength. All the tests were performed following the British Standard. The pure dredged sediment has a hydraulic conductivity of 7.11x10^-6 cm/s, which is comparable to the requirements of the core of the dam. To improve the other properties of the dredged sediment, it is mixed in different proportions with dune sand collected from the Al-Sharqia Desert of Oman. The test results suggest that a mixture ratio of 50% of sediment to the dune sand gives optimal strength, durability, and permeability. On the other hand, for the comparison purposes, bentonite was mixed with sand by various percentage. The microscopic investigation and X-ray diffraction (XRD) analysis tests on dredged sediments suggest that the material can be utilized without causing any environmental concerns. The outcomes of this study is expected to assist the practitioners in achieving cost-effectiveness and sustainability in the design.

Abstract: This study introduces the experiment based on following parameters: kind of aggregate (natural river gravel and air-cooled blast furnace slag), the aggregate gradation and content of binder. Main properties such as compressive strength, void content and hydraulic conductivity of pervious concrete were investigated in the experiment. The experiment showed satisfactory results in the case of pervious concrete made of natural aggregate. Results of pervious concrete made of air-cooled blast furnace slag aggregates are perspective, however needs for some optimizations. Results confirmed the opposite relationship between compressive strength and void content/hydraulic activity. ACBFS performs worse than NA as for compressive strength, while it performs better in the case of hydraulic conductivity and void content.

Abstract: This paper intends to evaluate changes in permeability of a soil sample from Formação Barreiras, in Natal, the capital city of Rio Grande do Norte State, related to the degree of compaction and the adding of clay to the soil sample. In field works, samples were collected and permeability and density tests were performed. In laboratory, grain size distribution, Attemberg limits and particle density tests were conducted. Afterwards, compaction and permeability tests fulfilled the set of laboratory tests, with changes in compactive energy and sample clay content. The results from field and laboratory tests were compared and the relationship between compaction energy and sample clay content were portrayed. The soil was classified as silty sand. Field and laboratory test results were quite similar. As expected, the tests indicated that permeability is inversely proportional to both compaction energy and sample clay content in the soil tested.

Abstract: Bioretention media composition plays an important role in maintaining hydraulic conductivity within appropriate range and treating stormwater runoff to reduce pollution to receiving water bodies. This study investigated 4 types of bioretention media, 2 of which different types of compost and another 2 using shredded newspaper and crushed cockle shell as additives to modify the bioretention media. The objective of the study was to provide insight on hydraulic performance and media characteristics that control bioretention stormwater treatment performance. Results showed that organic matter content has no effect on hydraulic conductivity and nutrient removal performance of the media. Comparison of hydraulic conductivity and nutrient removal showed that reduced hydraulic conductivity (from 250mm/hr to 159mm/hr) increased total suspended solids (TSS) removal of the media (up to 98.5%) but has no effect on total nitrogen (TN) and total phosphorus (TP). The preliminary pollutant test using natural runoff showed that bioretention media enhanced with 10% shredded newspaper performed the best in TN removal (up to 85.3%) and bioretention media enhanced with 10% crushed cockle shell removed the most TP (up to 95.6%).

Abstract: New theoretical justification for the function of soil differential moisture capacity (dependence of the relative water volume content on the capillary pressure) and its antiderivative is presented. New method is based on the concept of capillarity and the lognormal distribution of the effective radii of pores. Relative hydraulic conductivity of soil is calculated with usage of these functions and Mualem's approach. Hydrophysical parameters have been interpreted and evaluated on the base of some physical and statistical soil characteristics. Also the approximation for functions of water-retention capacity and relative hydraulic conductivity of soil has been proposed.

Abstract: The hydraulic conductivity and correlated factors of undisturbed soil profile (0-20cm、20-40cm、40-60cm) are researched, by taking different forest types (cyclobalanopsis chungii, phyllostachys pubescens, bambusa multiplex var.nana, eucalyptus forests) in typical small watershed of Moufengshan area in Guangzhou of China as study objects. In conclusion, generally, the hydraulic conductivity is decreasing with an increase in profile depth. The variation ranges of hydraulic conductivity are 13.64-4.91, 8.16-2.96, 7.92-3.71, and 10.4-3.63m/d for phyllostachys pubescens, cyclobalanopsis chungii, bambusa multiplex var.nana, and eucalyptus forests respectively. In general, coefficients of permeability are found to be positively related to porosity and root density, and negatively related to dry density, whilst the correlation with root diameter remains uncertain. However, the degrees of correlation with dry density, root density, and root diameter vary substantially for different types of forest land, whereas an overall well correlation with porosity is presented.

Abstract: Runoff and soil loss affect both farmland productivity and environmental quality. This study tested the interaction effects among polyacrylamide (PAM) application rate, PAM molecular weight, and slope gradient on runoff and soil loss under simulated sprinkler irrigation in laboratory. Experimental treatments consisted of four PAM application rates of 0 (control), 0.5, 1.0, and 2.0 g m^-2, two PAM molecular weights of 12 and 18 Mg mol^-1, and three slope gradients of 5^o, 15^o, and 25^o. Results indicated that compared with the control treatment, PAM application generally decreased total runoff volume but increased soil loss. Total runoff volume and soil loss increased with the increased PAM application rate. Under control treatment, total runoff volume increased with the increased slope gradient. However, total runoff volume was similar for different slope gradients when PAM application rates were 0.5 and 1.0 g m^-2, but it decreased with the increased slope gradient when PAM application rate was 2.0 g m^-2. Total soil loss increased with the increase of slope gradient under experimental conditions. Polyacrylamide molecular weight did not affect total runoff volume but did soil loss significantly at P < 0.001, and a high PAM molecular weight resulted in less soil loss than a low one did. Statistical analysis demonstrated that there existed a significant interaction effect at P < 0.001 between PAM application rate and soil slope gradient on runoff volume and soil loss. The interaction effects between PAM molecular weight and slope gradient or among PAM application rate, PAM molecular weight, and slope gradient on soil loss were also significant at P < 0.01. A PAM application rate less than 2 g m^-2 is suggested to control water and soil loss on sloped lands under sprinkler irrigation.

Abstract: Fractured rock aquifers provide the most extensive groundwater resources in Northeast Thailand. The hydraulic conductivity (K) of these aquifers controls the flow of water and is therefore, an essential parameter for groundwater modeling and management. K values may be directly determined by conducting pumping tests at the aquifer or by performing fracture analysis using data acquired from outcrops. The K value at outcrop should be greater than that at aquifer of deeper position due to the effect of aperture reduction by overburden compression. The goal of this study was therefor to find the correlation between K values determined from outcrop with those directly measured at an aquifer. This study was conducted on the Phu Phan sandstone aquifer at the Huay Luang watershed, Udon Thani Province of Northeast Thailand. The orientation, aperture, and spacing of fractures were measured at four outcrops and used for determining the K values by fracture analysis. Single well pump test data from 17 wells in the Phu Phan aquifer (30-120 m depth) were analyzed to obtain transmissivity (T) and K. Both sets of the K values, from outcrop and aquifer, were correlated using the plotting position of Weibull. Both plots were linear on a semi-log scale but the outcrop curve was steeper. Lognormal distributions fitted both plotting positions quite well. These results show that for the same probability value, K values found from the pumping test to be about an order of magnitude smaller than K values determined from outcrop data.

Abstract: Hydraulic conductivity (HC) is deduced indirectly from soil water retention curves (SWRC) by Mualem model, but the mathematical calculation in the Mualem model is sensitive to integration interval near saturation. After the van Genuchten model fit actual SWRC, the van Genuchten-Mualem (VGM) HC is integrated simply by an analytical function for unsaturated soils. However the analytical solution on VGM HC results in the rapid change of HC near saturation. For unsaturated soils sampled in Korea, SWRCs and unsaturated HCs were obtained by experiments. The HC experiments were compared with the HC models from the SWRCs. As a result, VGM models of HC function underestimate the unsaturated HC and show rapid reduction near saturation. It is found that a modification in VGM model should be required to predict accurate HC functions.