Hassan Rahimi

Non-Darcy Flow of Water Through a Packed Column Test

As the flow velocity and Reynolds number increase in rockfilled porous media, the flow deviates from Darcy conditions and enters into a new phase known as non-Darcy conditions. Due to a linear relationship between hydraulic gradient and the flow velocity in Darcy formula, the flow can be analyzed with no difficulty. However, as the velocity increases the Darcy law is violated, the flow becomes turbulent, making the analysis more challenging. In this paper a laboratory packed column was built to study high-velocity flow through granular materials and new experimental data have been obtained. The laboratory experiments include application of for six different sizes of rounded aggregates and using different hydraulic gradients to assess the flow behavior. Using new experimental data, the validity of four widely-used head-loss equations were evaluated. The results indicated that the Sidiropoulou et al. (Hydrol Process 21:534–554, 2007) and Ergun’s head-loss equations yield satisfactory results comparing to other available relationships.

Distribution and tensile strength of Hornbeam (Carpinus betulus) roots growing on slopes of Caspian Forests, Iran

Biomechanical characteristics of the root system of hornbeam (Carpinus betulus) were assessed by measuring Root Area Ratio (RAR) values and tensile strength of root specimens of eight hornbeam trees growing on hilly terrain of Northern Iran. RAR values of the roots were obtained using profile trenching method at soil depth of the top 0.1 m. In total 123 root specimens were analyzed for tensile strength. Results indicate that in general, RAR decreases with depth, following a power function. The RAR values in up and down slopes have no significant statistical differences. In most cases, the maximum RAR values were located in soil depth of the top 0.1 m, with maximum rooting depth at about 0.75 m. The minimum and maximum RAR values along the profiles were 0.004% and 6.431% for down slope and 0.004% and 3.995% for up slope, respectively. The number of roots in the up and down slope trenches was not significantly different. In the same manner as for RAR, number of roots distributing with depth was satisfactorily approximated a power function. The penetration depths of above 90 percent of the roots were at soil depths of 50 cm and 60 cm for up and down slopes, respectively. Results of Spearman’s bivariate correlation showed no significant correlation between the RAR value with tree diameter and gradient of slope and number of roots. The mean value of root tensile strength was 31.51 ± 1.05 MPa and root tensile strength decreased with the increase in root diameter, following a power law equation. Using ANCOVA, we found intraspecies variation of tensile strength.

Adoption of Manning's equation to 1D non-Darcy flow problems

In this paper, the concept of Darcy–Weisbachs friction loss in pipe flows is employed and combined with Mannings widely used formula in open-channel flow problems to obtain a new relation for flow in porous rockfill media. A new formula to determine Mannings roughness coefficient of rockfill materials is presented based on the flow and grain characteristics and validated using new experimental data. The results confirm the applicability of Mannings formula for the hydraulically rough regime.

Laboratory Investigation of the Seepage Control Measures under Coastal Dikes

In the present study, the effects of seepage control measures under coastal dikes have been experimentally investigated. For the purpose of the study a laboratory model hydraulic flume 8.65 m long, 1 m deep, and 1 m wide was employed. The coastal dike was assumed as impermeable and made of a stainless-steel sheet of trapezoidal shape. The experiments were carried out employing five upstream and one downstream water levels. Besides, four different depths of sheet piles and four different lengths of impermeable blanket were used as seepage control measures. Results of the experiments were recorded at various points at the downstream foundation of the dike. The results indicated that the integrated application of two of the seepage control measures had more significant effect on reduction of uplift pressure. The results of the current study and two old empirical methods, that is Bligh and Lane, indicated that the Lane method underestimates the magnitude of uplift pressure and risk of piping in comparison with the Bligh’s method. Finally, the optimal values for impermeable blanket length and cut-off depth for minimizing the uplift pressure were determined.

An Analytical Solution for 1-D Non-Darcy Flow Through Slanting Coarse Deposits

In this paper, an analytical solution to solve 1-D partial differential equation is presented for fully developed turbulent flow through highly permeable sloping deposited porous medium. The present solution will be applicable for a wide range of slopes varying from zero to relatively steep slopes. To confirm the solution, the analytical results have been validated using two sets of experimental data including rounded and crushed material. To see the compatibility of solution, a Darcy-based form of the solution is derived and compared with proposed solution and experimental data. The results showed a satisfactory agreement with experimental records from water surface profiles through rock cavities for both rounded and crushed rock materials. Finally, it may be concluded that the proposed solution could be used to analyze water surface profiles and normal depth in such slanting permeable porous media. This solution provides a reliable realization of the flow profiles in porous materials which are widely used in open-channel flow concepts.

One-Dimensional Fully Developed Turbulent Flow through Coarse Porous Medium

A fully developed turbulent regime is considered as a specific case of non-Darcy flow, and an analytical approach has been developed to determine normal depth, water surface profile, and seepage discharge of the flow through coarse porous medium in steady condition. The results of a laboratory rock drain with length, height, and width of 6.4, 0.8, and 0.8 m, respectively, and longitudinal slope of 0.04 were compared with the analytical solution developed in this study, and the results showed a good agreement between analytical and experimental data. To see the compatibility of the solution, a Darcy-based form of the solution (Pavlovskys method) and a flow analysis of buried streams (FABS) model are compared with the proposed solution and experimental data. Compared with Pavlovskys solution and FABS model, the results showed a satisfactory agreement with experimental records from water surface profiles through rock drain. DOI: 10.1061/(ASCE)HE.1943-5584.0000937.