scholarly journals Unsaturated flow through a fracture-matrix network: Dynamic preferential pathways in mesoscale laboratory experiments

2002 ◽  
Vol 38 (12) ◽  
pp. 17-1-17-17 ◽  
Author(s):  
R. J. Glass ◽  
M. J. Nicholl ◽  
S. E. Pringle ◽  
T. R. Wood
Keyword(s):  
Laboratory Experiments ◽  
Unsaturated Flow ◽  
Network Dynamic ◽  
Flow Through ◽  
Preferential Pathways

scholarly journals Experimental Study of Rainfall Infiltration in an Analog Fracture-matrix System

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Zhen Zhong ◽  
Huicai Gao ◽  
Yunjin Hu
Keyword(s):  
Unsaturated Flow ◽  
Rainfall Infiltration ◽  
Combination Method ◽  
Matrix System ◽  
Capillary Barrier ◽  
Hydraulic Behaviour ◽  
Experimental Apparatus ◽  
Matrix Interactions ◽  
The Matrix ◽  
Flow Through

In this study, an experimental apparatus was developed to investigate unsaturated infiltration in an analog fracture-matrix system. Fracture and adjacent matrix is simulated by sands with various particle sizes. Four rainfall infiltration experiments were performed on the analog fracture-matrix system at a constant rainfall rate of 100 mm/h. The process of rainfall infiltration is measured by a combination method of tensiometers and quick moisture apparatus. The measured results reveal that fracture-matrix interactions certainly exert influences on the hydraulic behaviour of unsaturated fractured matrix, and the fluid flow mainly infiltrates along the nonuniform paths within the matrix. Moreover, it is observed that the influences are greater when using a coarser sand to mimic the fracture. Specifically, the wetting phase in the matrix moves faster than that in the fracture; the fracture, therefore, acts as a vertical capillary barrier, but there exists lateral water exchange from the matrix to the fracture. Overall, this study has demonstrated the importance of fracture/matrix interactions, which should be considered when dealing with unsaturated flow through permeable matrices.

Permeability Modeling Considering Microstructure of Preform

2007 ◽  
Vol 334-335 ◽  
pp. 437-440 ◽  
Author(s):  
Do Hoon Lee ◽  
Joon Ho Lee ◽  
Woo I. Lee
Keyword(s):  
Porous Medium ◽  
Unsaturated Flow ◽  
Manufacturing Industries ◽  
Experimental Measurements ◽  
Resin Flow ◽  
Flow Conditions ◽  
Composite Manufacturing ◽  
Liquid Molding ◽  
Flow Through ◽  
Inhomogeneous Microstructure

Liquid molding processes are becoming more popular among the composite manufacturing industries due to their versatility and economy among other merits. In analyzing the flow during the process, permeability is the most important parameter. Permeability has been regarded as a property of the porous medium. However, in many practical cases, the value may vary depending on the flow conditions such as the flow rate. It is speculated that this deviation is caused by inhomogeneous microstructure of the medium. In this study, numerical simulations as well as experimental measurements have been done to investigate the cause of deviation. Microstructure of porous medium was modeled as an array of porous cylinders. Resin flow through the array was simulated numerically. Simulations were performed for two different flow conditions, namely saturated flow and unsaturated flow. Based upon the results, permeabilities were estimated and compared for the two flow conditions. In addition, a model was proposed to predict the permeability for different flow conditions. Results showed that experimental data were in agreement with the prediction by the model.

scholarly journals The Influence of Grain Size Distribution on the Hydraulic Gradient for Initiating Backward Erosion

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2644 ◽  
Author(s):  
Willem-Jan Dirkx ◽  
Rens Beek ◽  
Marc Bierkens
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Laboratory Experiments ◽  
Hydraulic Gradient ◽  
Concentrated Flow ◽  
Pipe Formation ◽  
Novel Method ◽  
Flow Through ◽  
The Stability

Backward erosion by piping is one of the processes that threaten the stability of river embankments in the Netherlands. During high river stages, groundwater flow velocities underneath the embankment increase as a result of the steepened hydraulic gradient. If a single outflow point exists or forms, the concentrated flow can entrain soil particles, leading to the formation of a subsurface pipe. The processes controlling this phenomenon are still relatively unknown due to their limited occurrence and because piping is a subsurface phenomenon. To study the initiation of piping, we performed laboratory experiments in which we induced water flow through a porous medium with a vertically orientated outflow point. In these experiments, we explicitly considered grain size variations, thus adding to the existing database of experiments. Our experiments showed that the vertical velocity needed for the initiation of particle transport can be described well by Stokes’ law using the median grain size. We combine this with a novel method to relate bulk hydraulic conductivity to the grain size distribution. This shows that knowledge of the grain size distribution and the location of the outflow point are sufficient to estimate the hydraulic gradient needed to initiate pipe formation in the experiment box.

Unsaturated Flow through a Small Fracture-Matrix Network: Part 1. Experimental Observations

2004 ◽  
Vol 3 (1) ◽  
pp. 90-100 ◽  
Author(s):  
T. R. Wood ◽  
R. J. Glass ◽  
T. R. McJunkin ◽  
R. K. Podgorney ◽  
R. A. Laviolette ◽  
...  
Keyword(s):  
Unsaturated Flow ◽  
Flow Through

Modelling chemical and biological reactions during unsaturated flow through sandy soils

Soil Research ◽  
2010 ◽  
Vol 48 (3) ◽  
pp. 221
Author(s):  
B. Ludwig ◽  
S. Herrmann ◽  
K. Michel
Keyword(s):  
Ion Transport ◽  
Unsaturated Flow ◽  
Sandy Soils ◽  
Cation Transport ◽  
Anion Transport ◽  
Calibration Model ◽  
Model Variant ◽  
Reliable Assessment ◽  
Model Predictions ◽  
Flow Through

Predicting chemical and biological reactions during unsaturated flow through soils is complex, and the accuracy of model predictions is open to question. Objectives were to test how accurately the transport of nutrients (Ca2+, Mg2+, K+, NH4+, and NO3–) in soils can be predicted when differing amounts of nutrients or acid are added. Undisturbed columns of 2 sandy surface soils from arable sites in Darmstadt, Germany, and Sohar, Oman, were irrigated for 360 and 376 days with 3 mm/day at 10°C. Three treatments were carried out: the columns were irrigated with differing fertilising solutions (Fert-1 or Fert-2 treatments) or with HCl. The model PHREEQC2 was used to calculate 1-dimensional transport, inorganic complexation, dissolution or precipitation of CaCO3, multiple cation exchange, and nitrification. We compared 3 model variants: one with no adjustable parameters, a second with optimised nitrification rates and pCO2, and a third with an additional optimisation of the exchange coefficients. In model variant v2 and v3, the Fert-1 treatment was used for calibration. Model variant v1 was of little use in predicting cation transport in soils. The second was more appropriate for both soils, but an optimisation of the exchange coefficients (model variant v3) was required for a more accurate description (Fert-1) and prediction (Fert-2 and HCl) of ion transport. The included proton buffering reactions resulted in a moderately accurate prediction of pH and release of ions. Nitrification in the Fert-1 and Fert-2 experiments considered in the model variants accounted for a range of 0.03–0.04 µmol N/(day.g soil). Overall, our results indicate that calibration experiments are required for a reliable assessment of ion transport in soils during unsaturated flow. The parameter optimisation program PEST in combination with PHREEQC2 best simulated cation and anion transport in sandy soils under unsaturated conditions.

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