Data acquisition system for an experimental setup used for
Contents
1. s drainage S 01 gt a 0 01 0 001 0 0 1 0 2 0 3 0 4 0 5 Volumetric water content cm cm Fig 18 Hysteresis effect on the water retention curve To compute soil water fluxes in unsaturated soils a common approach is to numerically solve the Richards equation which INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS ENGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 usually requires the parameterization of the soil water retention curve There are two main approaches for obtaining the soil water retention parameters the first is to experimentally determine the soil water retention and fit a water retention function to the experimental data e g Brooks and Corey 1966 Campbell 1974 van Genuchten 1980 Vogel and Cislerova 1988 Durner 1994 Kosugi 1996 and the second is to derive the soil water retention parameters from knowledge of basic soil physical properties by using pedotransfer functions Rawls et al 1982 Leij et al 1996 Schaap et al 1999 2001 Acutis and Donatelli 2003 The parameters obtained from the fitting of water retention curves are listed in Table III Table IV and the corresponding water retention curves are shown in Fig 19 and Fig 20 Only the results for layer I from 20 to 60cm and III from 80 to 120cm are shown the results from other soil depths in the stand model were similar Fitting result are presented in Table III and Table IV Table III Parameters2. Silty soils are intermediate Actual soil weights also include water To determine in the laboratory the initial water content on the soil profile the gravimetric method was used Soil water content profile is illustrated in the following figure 0 0 00 5 00 10 00 15 00 20 00 25 00 10 21 z cm 16 73 130 Fig 4 Soil water content variation In the laboratory the water retention curves were measured with a pressure plate apparatus using the equipment from the Geotechnical laboratory of the Faculty of Civil Engineering whose schematic is shown in Fig 5 P Air pressure Soil sample Porous plate Out flow vs Fig 5 Pressure plate apparatus scheme To compare the automated measurements taken with the tensiometers estimations of soil water content were conducted first on the pressure plate by using the following methodology Soil samples were placed on a porous plate held in 2cm high rings Then samples and plate were saturated with water 24h Once the porous plate and the samples were completely saturated with water the plate was installed and air pressure was used to extract moisture from soil samples under controlled conditions As soon as air pressure was raised above atmospheric pressure the higher pressure inside the chamber forced excess water through the microscopic pores i
3. caused by physical conditions at the soil surface and at the drain peripheries Knowledge the soil hydraulic properties in order to understanding the behavior of water movement in soil are important for many application of drainage design The soil hydraulic properties can be characterized by the soil water retention curve O h and the hydraulic conductivity curve K h or K 0 13 18 These can be determined in situ or by laboratory methods 6 The traditionally laboratory methods to estimate the hydraulic conductivity including infiltration or permeameter tests using constant head or falling head configurations on core samples taken from the field site The pressure plate outflow method Gardner 1956 is utilized to Constantin Buta is with the Faculty of Civil Engineering Ovidius University of Constanta Romania corresponding author to provide phone 4 0728 040 942 e mail costi_buta yahoo com Carmen Maftei is with the Faculty of Civil Engineering Ovidius University of Constanta Romania e mail cmaftei univ ovidius ro Cornel Ciurea is with the Faculty of Civil Engineering Ovidius University of Constanta Romania e mail cturea_68 yahoo com 692 estimate the soil water potential during drainage of the soil core 12 Recent technological developments are demonstrated that the most effective and efficient means of measuring soil water potentials are the tensiometers 10 In order to reduce analysis time and improve
4. to 950 hPa 697 Senzor 8571133 y 908 61x 54 802 R 0 9985 Presiune hPa Tensiune mV Presiune Tensiune Linear Presiune Tensiune Fig 13 Calibration equation for tensiometer D Experimental protocol We have taken account of the following methodologies to establish a functioning drainage in the physical model 11 1 The dry soil will be crushed in particle with the size of diameter of O lt 10mm Placing and compacting soil samples in the drainage model are made in layers of about 20 30cm thickness For mixing and plugging between the layers the compacted soil surface is furrowed before introducing a new layer We avoid placing a filter layer of sand or graveling on the drainage box bottom because this will modify the conditions of the water flow to the drains Regarding the experimental protocol will do so l at the beginning the model will operate as a constant head permeameter the soil from the model is saturated by applying a constant volume of water the piezometric tubes are checked for removing the air from the tubes with a vacuum pump the volume of water which percolate the soil profile is colected and measured at fixed time steps and when we get the same volume of water than the piezometric tubes are connected to the piezometric tableau will wait until the water level in the piezometric tubes is establish and after that it is made the first m
5. Took B H BEI a0aornas 13pt Application Font w ofie indow Help BRI 11 2 hale 13pt Application Font fidae Continuous Samples Sample Rate 13 P ial Nhan Samp S pA r ustom Voltage with Excitation s Sample Clock B i Fig 14 LabVIEW block diagram The front panel Fig 15 is the user interface which has controls for selecting test parameters that depend on the test method selected Four commonly used MSO testing regimes are supported by the LabVIEW control code for each the following data are displayed on the computer screen and written to a spreadsheet file tensiometer reading water volume in the burette elapsed time and laboratory room temperature Fig 15 Front panel for Labview platform program Pressure head measurement First the system will automatically read soil tensiometers Each tensiometer uses a vacuum transducer whose output voltage varies linearly with the amount of tension in the tensiometer All the eight tensiometers SKT 850T SDEC 698 France with pressure transducers 0 100mV are introduced by the back side of the drainage box Fig 16 and arranged in three vertical sections of the model a
6. data consistency an automatic tool to acquisition tensiometer data and their analyses have been developed We also present a physical model to examine water flow to a subsurface drain and to acquire experimental data 4 The main purpose of the study was to validate a fast and accurate method for measuring soil drainage s parameters in which the LabVIEW program from National Instrument is used for the computer management of tensiometers from a physical model II PROBLEM FORMULATION A Theory Before water flow to a subsurface drain through unsaturated soil is discussed one must first understand the basics of saturated flow Darcy s law for one dimensional steady state laminar flow of a fluid through a saturated homogeneous isotropic porous media is dH ey ee as q Sk 1 where q LT is volumetric discharge rate per unit cross sectional area flux g LT is the saturated hydraulic conductivity and S dH dz difference between two points in the direction of flow divided by the distance between them where H is the hydraulic head equal to the pressure head h and elevation head z In unsaturated soils Darcy s law for steady state flow becomes q K h is the hydraulic gradient defined as the hydraulic head dH dz where the unsaturated hydraulic conductivity K is a function of pressure head K h or volumetric water content K 0 2 INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS E
7. soil texture classes Soil texture is quantified by the relative percentages by mass of sand silt and clay after removal of salts and organic matter frac iuni Fig 4 Particle size distribution on soil profile N sand P silt A clay Both texture and structure determine the soil water characteristic curve which quantifies the relationship between soil water content and soil water potential which is the strength with which the soil holds water and are important in drainage system design This relationship differs largely according to texture but can be strongly affected by organic matter and salt contents Soil bulk density is the oven dry weight of soil divided by the soil volume Units are g cm Fig 3 gt Da p gicm P 1 00 1 20 1 40 1 60 1 80 2 00 2 20 2 40 2 60 0 z cm Fig 3 Soil density p and dry bulk density pa on soil profile INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS ENGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 The bulk density of a soil is related to a textural class and organic matter content Bulk densities typically range from less than 1 g cm to nearly 2 g cm Bulk densities less than 1 g cm are often soils that contain large amounts of organic matter Clayey soils tend to have the smallest bulk densities of mineral soils while sandy soils have the highest bulk densities
8. soil water pressure head L and 0 0 A n m are the parameters to be estimated To reduce the number of parameters and to facilitate the calculation of hydraulic conductivity the restriction m 1 1 was adopted n The Kosugi model 7 is given by h za iva 4 e O where Q x is the complementary cumulative normal distribution function defined by Q x 1 x in which x is a normalized form of the cumulative normal distribution function h 7 is an empirical parameter whose inverse is often referred to as the air entry value L Determination of unsaturated hydraulic conductivity by laboratory experiment is time consuming and therefore researchers have attempted to relate the soil water retention function with the unsaturated hydraulic conductivity Fig 1 0 0 Az k z l Darcy s law in z 7 0 hlo 0 0 Fig 1 Algorithm to relate the soil water retention function with the unsaturated hydraulic conductivity INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS ENGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 Hydraulic conductivity can be described by the Mualem van Genuchten equation van Genuchten 1980 2 2 m L i_l1 s e K S K S 5 where 0 7 0 g r_ is the effective saturation se 7 an g is the saturated hydraulic conductivity LT and S L is the parameter of tortuosity B Soil data analyses Tests on undisturbed soil samples were used to
9. test we have used a constant head permeameter without suction Fig 7 Fig 7 Constant head permeameter without suction 695 INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS ENGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 Once the saturated hydraulic conductivity was measured we used the algorithm to relate the soil water retention function with the unsaturated hydraulic conductivity from Fig 1 Thus we determined the hydraulic conductivity curve Fig 8 Curba conductivitate hidraulica umiditate volumica K 6 Orizont sol lut argilo prafos 0 0006 Ks 0s K cm s 0 1 0 2 0 3 cm cm 0 4 0 6 Curba conductivitate hidraulica umiditate volumica K Orizont III sol praf lutos Klo K 4 83 107 9 0 41 0 1 0 2 0 3 0 4 0 5 cm cm Fig 8 Hydraulic conductivity curve for soil layer I up and soil layer HI down All the experimental laboratory results are summarized in Table II Table II Physical and Hydraulic properties of the experimental soil Soil properties Lava depth cm I io ee 80 Particle pia density g cm Bulk cen ees g cm a 8 44 5 Sand elas A 9 content Saturated water content Qs Residual water content Or Saturated hydraulic conductivity Ks 10 cm s 9 5 6 32 4 12 120 19 9 5 29 696 C E
10. INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS ENGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 Data acquisition system for an experimental setup used for measuring the soil drainage s parameters Constantin Buta Carmen Maftei and Cornel Ciurea Abstract An automated data acquisition system was developed using National Instruments Austin TX hardware and LabVIEW software to understand the behavior of water movement in the unsaturated zone that lies between ground surface and the saturated zone below which is important for designing soil drainage Thus a drainage experiment with a physical model was conducted in laboratory to examine water flow to a subsurface drain and to acquire experimental data about the water flow characteristics of layered soils to serve as a base for numerical analyses In order to reduce analysis time and improve data consistency an automatic tool National Instruments LabVIEW software to acquisition data and their analyses have been developed Keywords data acquisition system drainage physical model LabVIEW software soil hydraulic properties I INTRODUCTION HE purpose of installing subsurface drains in soils is to remove water in order to improve soil physical conditions for environmental protection for agricultural production and for engineering operations The problem facing the drainage engineering is therefore one of the physics of water flow through both saturated and unsaturated soils
11. NGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 Thus to compute the flux one must know the value of K h which varies with soil water content and consequently pressure head Due to the increasing capacity of computers more and more numerical models for the simulation of both saturated and unsaturated soil water flow are being developed and applied 14 15 20 Most of these models are based upon the Richards equation ee 2 Kan Ko 3 Ot OZ OZ where h is the soil water pressure head the negative of matric potential h lt 0 t is time z is soil depth or the vertical coordinate axis positive upward K is the unsaturated hydraulic conductivity and O is the volumetric water content Richards equation is derived from Darcy s law for unsaturated soils and the continuity equation Note that h is a function of z and t and 0 is a function of h z and t The functional relationships between K and h and 0 and h must be known to solve Eq 3 Equation 3 is a partial differential equation which requires the knowledge of two soil physical relationships the soil water retention curve the relationship between water content and pressure head and the hydraulic conductivity curve the relationship between hydraulic conductivity and pressure head These relationships are strongly non linear and different for each soil layer They are very important for obtaining an accurate description of unsaturated wa
12. Texas U S A April 2003 Edition National Instruments Corp LabVIEW Development Guidelines Austin Texas U S A April 2003 Edition A Paris Etude du transfert d eau et de solutes dans un sol a nappe superficielle drainee artificiellement These pou obtenir le grade de docteur ENGREF Paris 2004 E Nitescu Contributii la studiul drenajului in scop de desalinizare si de prevenire a salinizarii secundare in masivele irigate IP Iasi 1980 2 A Musy and M Soutter Physique du sol Press polytehnique et universitaires romandes Lausanne pp1 335 1991 Vogel and M Cislerova On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve Transp Porous Media 1 15 2001 K Seki SWRC fit a nonlinear fitting program with a water retention curve for soils having unimodal and bimodal pore structure Hydrology and Earth System Sciences 4 407 437 2007 M G Schaap F J Leij and M T van Genuchten Rosetta A computer program for estimating soil hydraulic parameters with hierarchical pedotransfer functions Journal of Hydrology 163 176 2001 C Maftei A Barbulescu C Buta C Serban Change points detection on variability analysis of some precipitation series Recent Researches in Computational Techniques Non Linear Systems amp Control pp 232 237 2011 M Carmen C Buta Evaluation of the Mathematical Models for Quantifying the Unsaturated Hydr
13. ased testing time and reduced the amount of operator interruption LabVIEW also eliminated the need for separate data acquisition spreadsheet and mathematical software packages With its numerous features LabVIEW made implementing this new test and measurement method easy Regarding the parameters obtained from the fitting of water retention curve from the figure and table we get the impression that VG and LN models give better fitting than BC model on average while VG and LN models are not so different in precision of the fitting The h K functions had been established with accuracy and the results are global INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS ENGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 satisfactory In this work a user friendly easily assembled automated data acquisition system was designed and built using National Instruments Austin TX hardware and National Instruments LabView software and validated via comparisons with manual laboratory outflow test results The resulting device eliminates several problems related to manual testing and allows for several undisturbed or reconstituted soil samples to be tested The system is capable of saturating draining and re wetting samples so that drainage and wetting soil characteristic curves can be developed in its current configuration Future work should include more experiments to confirm the applicability of the data acquisition system and LabVIEW a
14. aulic Conductivity Lucr ri Stiintifice anul XLIX Vol 1 49 seria Horticultura ed I I Brad pp 951 957 2007 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 700 18 M Th Van Genuchten F J Leij and S R Yates The RETC Code for Quantifying the Hydraulic Functions of Unsaturated Soils Robert S Kerr Environmental Research Laboratory U S EPA pp92 1991 A B rbulescu E Pelican On the Sulina Precipitation Data Analysis Using the ARMA models and a Neural Network Technique Recent Advances in Mathematical and Computational Methods in Science and Engineering Proceedings of the 10th WSEAS International Conference on Mathematical and Computational Methods in Science and Engineering MACMESE 08 Part II Bucharest 2008 pp 508 511 A Barbulescu C Gherghina Mathematical modeling of the water retention in different soil textural type Bull For Applied amp Computer Mathematics XCVI C Technical University of Budapest 2001 pp 23 30 Schaap M G F J Leij and M T van Genuchten A bootstrap neural network approach to predict soil hydraulic parameters In Characterization and measurement of the hydraulic properties of unsaturated porous media Part 1 Ed M Th van Genuchten et al Univ of California Riverside 1999 A Barbulescu E Bautu Meteorological Time Series Modelling Based on Gene Expression Programming Recent Advan
15. ces in Evolutionary Computing Proceedings of the 10th WSEAS Int Conf on Evolutionary Computing EC 09 Prague Czech Republic March 23 25 2009 pp 17 23 19 20 21 22
16. easurement of water depth in soil the pressure head data in soil are measured with the tensiometers SDEC and soil moisture data is obtained with soil moisture meter Watermark it is measured the wetting time of each layers determining the volume of water drained through the PVC corrugated tube in steady and unsteady state it is measured the time from when the rain begin to the moment when the drain start to function it is measured the drain discharge at different time period 5min 15 30min it is read the piezometers at each measurements of drain discharge 2 INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS ENGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 e it is also read the tension indicated by the tensiometers II PROBLEM SOLUTION Using LabVIEW graphical system design software 8 9 we built an application that consists of a customized user interface a display interface for the follow up and a recording The data we had to acquire includes a variety of soil hydraulic parameters National Instruments LabVIEW software is used for instrument control and automation A single programming code or virtual instrument in LabVIEW includes a block diagram Fig 14 and a front panel The block diagram contains graphical representations of functions to read from or write to an instrument e g pressure transducer or valves File Edt Operate Tools Browse Wi Edit Operate Tools Browse Window Help Fle Ec
17. ig 11 Data acquisition system DAQ with two SCXI modules For the computer management of tensiometers we have used the LabVIEW program 8 whose front panel is presented in Fig 12 File Edit Operate Tools Browse Window Help AE a n 13pt Application Font ARo mdee For instructions select File gt gt I Properties gt gt Documentation Channel Parameters Measur SCiModi ai0 Zax Physical Channel 980 0 970 0 SaN i Vee witt E 960 0 SC1Modi ai 3 5C1Mod2 ai0 3 Minimum Value Maximum Value 950 0 Yo 008 Sa Tess 12 0 005 940 0 3 fa86 14 a 930 0 1886 45 920 0 Timing Parameters Tas5 98 865 98 Sample Rate Hz A A 910 0 11 00 900 0 Samples to Read f 890 0 canali canalS 880 0 885 819 Tes6 12 o i Time s canal 2 canal 6 Be he fs85 819 fss6 135 135 file path dialog if empty Documents and Settings user Desktop test txt canal 3 canal 7 4 fe85 341 1886 45 canal 8 885 977 v i i Sls Bh a 2 47PM E LabVIEW Fig 12 Front panel for Labview platform program I Achizitie vi Front Panel IB Achizitie vi Block Diag EN Output voltage of the tensiometers is automatically converted into units of pressure head hPa using the calibration equations experimentally determined Fig 13 based on the certificate issued by the manufacturer The measurement range of this sensor is 0 hPa mbar
18. n the ceramic plate and through the outflow tube towards the outlet of the pressure plate During an extraction run at any given air pressure established in the apparatus soil moisture flowed from around each of the soil particles and out through the plate until the curvature of the water film throughout the soil was the same as the pores in the plate When this occurred equilibrium was reached and the water flow ceased Wet samples were weighed after removal from the plate and oven was dried at 105 C during 24h Samples were weighed again and water content was obtained For illustration the result of water retention curves for soil layer I and soil layer III are shown in Fig 6 Curba caracteristic a umidit ii h Orizont sol lut argilo prafos 1 2 1 y 16 003x 15 345x 5 4148x 0 9258 oa R 0 929 amp 0 6 0 4 0 2 0 0 0 1 0 2 0 3 0 4 0 5 0 6 cm cm Curba caracteristic a umiditatii 6 h Orizont III sol praf lutos 1 2 4 y 97 456x 49 652x 2 8151x 0 351x 0 9974 R 0 9999 0 8 0 6 0 4 0 2 0 T T T T 0 0 1 0 2 0 3 0 4 0 5 cm cm Fig 6 Soil water characteristic curve for soil layer I up and soil layer III down The saturated hydraulic conductivity was measured for every type of soil layer horizon using undisturbed cylindrical samples with 2 cm high and 5 6cm in diameter For this
19. obtained from the fitting of water retention curve for layer I 0 911 0 981 1980 a 0 0043884 n 2 7678 s 0 39777 0 1 5789e 06 0 984 hm 279 80 o 0 75280 0 0 40328 Brooks 0 3 1021e and Corey 07 1964 hp 99 421 0 87780 0 0 38583 van 0 5 1546e Genuchten S 07 m 1 1 n measured Volumetric water content l 10 100 Pressure head cm 1000 Fig 19 Fitting of water retention curve soil layer I 699 Table IV Parameters obtained from the fitting of water retention curve for layer III 0 769 0 0 31875 Brooks and 0 1 0409e Corey 05 1964 hp 100 23 0 40396 s 0 29321 0 1 1759e van 05 Genuchten aes 0 861 1380 0 0024229 n 1 9154 0 0 31750 0 1 6772e 06 0 827 hm 722 71 c 1 8475 0 35 0 3 0 25 S 2 Nn N gt Volumetric water content cm3 cm3 0 05 l 10 100 Pressure head cm 1000 Fig 20 Fitting of water retention curve soil layer III IV CONCLUSION A fast and accurate method for measuring retention curves has been developed in which the LabVIEW program is used for the computer management of tensiometers from a physical model This LabVIEW based test system has been an effective development and checkout tool for our laboratory drainage box This type of testing would have been a difficult task without LabVIEW which simplified data collection and analysis decre
20. out 50 mm the other looks like a rigid spiral tube with diameter of 50mm Drains are set at 50 mm from the tank bottom and from the side wall to minimize the influence of the boundary conditions infiltration besides the tank walls These two drains will produce the pattern of distance between the drains of 6 m and 3 m respective and will function as a drain or two drains Drains are provided with valves to control the operating mode of the model To prevent clogging the drains are wrapped with geotextile The drainage box bottom is provided from 10 to 10 cm with piezometric outlets protected by a geotextile Piezometer capillary tubes made of PVC are caught on a piezometric table This resulted in a total of 54 piezometric tubes The model is equipped with a set of eight tensiometers SKT INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS ENGINEERING amp DEVELOPMENT Issue 6 Volume 5 2011 850T SDEC France Fig 10 with pressure transducers 0 100mV introduced by the back side of the tank and arranged in three vertical sections of the model at equal distances and at various depths 20 cm and 40 cm Pressure sanso Differential vallage SKI B50 T Fig 10 Tensiometer SKT 850T SDEC France These eight tensiometers fitted with pressure transducers will be attached to a central box of data acquisition data acquisition system with two SCXI modules from National Instruments which is connected to a computer Fig 11 F
21. pplications for subsurface drainage systems calculus REFERENCES 1 2 R H Brooks and A T Corey Hydraulic properties of porous media Hydrol Paper 3 Colorado State Univ Fort Collins CO USA 1964 C Buta C Maftei C Ciurea C Bucur L Balasa Using NI LabVIEW to automate analyses of water flow to a subsurface drain in a layered soil Computational Engineering in Systems Applications Vol ID Proceedings of International Conference on Energy Environment Economics Devices Systems Communications Computers IAASAT pp 125 130 Ia i iulie 2011 C Buta C Maftei Analysis of hydrodimamics properties of soils in a laboratory tank model Lucr ri stiintifice Anul XLIX Vol I Seria Horticultur Ed Ion Ionescu de la Brad Ia i 2008 C Buta Cercet ri privind tehnica si tehnologia drenajului superficial coroborat cu folosin a terenului amenajat teza de doctorat 2010 M Th van Genuchten A closed form equation for predicting the hydraulic conductivity of unsaturated soils Soil Sci Soc Am J 44 892 898 1980 C Kao Fonctionnement hydraulique des nappes superficielles de fonds de vall es en interaction avec le r seau hydrographique These pou obtenir le grade de docteur ENGREF Paris 2002 K Kosugi Lognormal distribution model for unsaturated soil hydraulic properties Water Resour Res 32 2697 2703 1996 National Instruments Corp LabVIEW User Manual Austin
22. t equal distances and at various depths 20 cm and 40 cm timp ore 4 08 201 0 02 24 h cm Fig 16 Tensiometers location on physical model and tensiometers record at time A data acquisition system DAQ is programmed to scan the transducers at selected intervals and record the information The information is then transferred to a computer for calculations and plotting of soil water potential with time see Fig 16 A Characterization and parameter estimation When the soil water potential measurement is combined with a soil water content measurement a soil water retention curve is obtained Soil water retention curve on physical model Horizon 5 30cm 1000 100 4 e Tensiometer 1 _ gt O gt Suction h cm 0 01 0 001 i i 0 0 1 0 2 0 3 0 4 0 5 Volumetric water content cm cm Fig 17 Soil water retention curve Soil from drainage model was also drained and re wetted with the automatically read of tensiometers to demonstrate the effects of hysteresis on soils Hysteresis effect Fig 18 is defined as the phenomena by which a soil s water content will be greater during drying rather than re wetting at a given soil water pressure head Water retention curve hysteresis effect 1000 100 10 4 S i e wetting 5
23. ter flow and can be measured in the field or in the laboratory using different methods Hydraulic soil properties are described by functions A parameter optimization process estimates the parameters The unsaturated soil hydraulic properties 0 h and K h are in generally highly nonlinear functions of the pressure head Data from several soil tensiometers give sufficient information to estimate soil hydraulic parameters Different analytical models are used for the hydraulic properties 17 Brooks and Corey 1964 van Genuchten 1980 Vogel and Cislerova 1988 Durner 1994 Kosugi 1996 the most popular ones being those by Brooks and Corey BC model van Genuchten VG model and lognormal pore size distribution model of Kosugi LN model The Brooks and Corey model 1 is given by ae ees h gt h and 1 h lt h 2 e h b e b b where S ase is the effective saturation e 0 0 O and 0 are the saturated and residual volumetric water contents respectively 693 h L is an empirical parameter whose inverse is often referred to as the air entry value or bubbling pressure and is a pore size distribution parameter affecting the slope of the retention function In this study soil water retention was described by the van Genuchten model 5 one of the widely used models in the specific literature m l 3 1 ah S e where 0 is the volumetric water content L L h is the
24. verify the new data acquisition system capabilities Samples were collected from an experimental site located in Eforie Sud area Constanta The soil profile was limited to four layers In the drainage box we tried to keep the sequence of the natural soil layers and the ratio for soil depth Table I Table I Soil profile characteristics Soil texture Layer cm classes 0 Ame 0 20 10YR3 2 Siltloam loam Sa E a E loam _ loam In addition to soil layer thickness and orientation the water flow simulation requires information on the hydraulic properties of each layer First a number of attempts were made on the soil samples collected in order to determine its physical and hydraulic parameters The tests were made in the Physical Soil Laboratory of the Civil Engineering Faculty of Constanta and the results can be seen in the following paragraphs Measured data include particle size distributions particle density dry bulk density soil water content characteristics and saturated hydraulic conductivity The particle size analysis was done with the hydrometer analysis method To determine soil texture classes we used Texture AutoLookup TAL for Windows a program based on several major soil classification schemes including custom user defined schemes Using the user defined scheme Fig 2 we have determined the soil texture type for each layer Soil profile 694 Fig 2 User defined scheme for
25. xperimental setup In the experimental drainage model setup had been considered the following directions e Establishment of the artificial rain simulator e Drains installation Establish the physical properties of soil under natural conditions Establish the parameters of the artificial rain Procedures for verification and calibration of measuring instruments Management of the data acquisition and computer system The drainage physical model 4 7 consists of a metal box with the frontal wall from 10mm glass mounted on a metal substrate and having the following dimensions 3000 L x 1000 H x200 L mm Fig 9 Acquisition Alimentation g a systems for watermeter Rain simulatod drip system Acquisition systems for tensiometer oe Fig 9 Laboratory drainage box hela model The front side of the model is transparent to facilitate visual observations and photography The rain simulator is designed as a drip system Gardena micro irrigation system which consists of two lines with 10 dropping on the line one dropper has a capacity of 2I h Thus precipitation may be given an intensity of 70mm h which creates water excess 19 22 At the same time it can be given different volumes of water meaning that can manage an intensity of 35mm h At the bottom of the physical model there are two drains screwed in the front wall of the tank One drain is from corrugated PVC with diameter ab
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