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Tests of a Suggested Piezometric Method for Determining Hydraulic Conductivity of Saturated Soils

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Tests of a Suggested Piezometric Method for Determining Hydraulic Conductivity of Saturated Soils Utah State University DigitalCommons@USU All Graduate Plan B and other Reports Graduate Studies 5-1965 Tests of a Suggested Piezometric Method for Determining Hydraulic Conductivity of Saturated Soils K. R. Channarasappa Follow this and additional works at: https://digitalcommons.usu.edu/gradreports Part of the Hydraulic Engineering Commons Recommended Citation Channarasappa, K. R., "Tests of a Suggested Piezometric Method for Determining Hydraulic Conductivity of Saturated Soils" (1965). All Graduate Plan B and other Reports. 1136. https://digitalcommons.usu.edu/gradreports/1136 This Report is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Plan B and other Reports by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. TESTS OF A SUGGESTED PIE ZOMETRIC METHOD FOR DETERMINING HYDRAULlC CONDUCTIVITY OF SATURATED SOILS by K. R. Channarasappa Report submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Civil and Irrigation Engineering Plan B UTAH STATE UNIVERSITY Logan, Utah 1965 ACKNOWLEDGEMENTS The writer greatly appreciates the counsel and critical review of his report by his thesis director, Professor J. E. Christiansen. He also expresses his gratitude to Dr. A. Alvin Bishop for providing the funds for equipment and other facilities. Sincere thanks are extended to Professor Joel Fletcher, Professor Lyman S. Willardson and Professor Jack Keller for their advice and review of the thesis. K. R. Channarasappa TABLE OF CONTENTS Page INTRODUCTION ....... 1 REVIEW OF LITERATURE 2 Methods of measuring hydraulic conductivity 3 Laboratory methods 3 Field methods ... 3 EQUIPMENT AND PROCEDURE 8 Equipment 8 Piezometers . 8 Auger rod ... 8 Semiflexible tubing . 8 Electrical sounder . 8 Other equipment 9 Procedure . .. 9 Piezometer installation 9 Formation of cavity . 9 Flushing technique .. 9 Measurements .......... 10 Relative hydraulic conductivity 12 RESULTS .............. 13 Specimen calculations 13 Tables ........ 14 Discussion of results 25 Location A. 600 West 1400 North 25 Location B. Opposite to Logana Plunge 26 Location C. U.S.U. drainage farm. East of quonset shed ............... 26 Near the ditch. North of quonset shed .... 27 TABLE OF CONTENTS CONTINUED Page CONCLUSIONS AND RECOMMENDATIONS . 2 8 Conclusions . 28 Recommendations . 28 LITERATURE CITED . 30 LIST OF TABLES Table Page 1. Results of tests at locatjon A, 600 West 1400 North . 14 2. Results of tests at location B, opposite Logana Plunge, 1400 North . 19 3. Results of tests at location C, U.S. U. drainage farm . 23 4. Summary of results . 24 LIST OF FIGURES Figure Page 1. Diagram showing the use of a single piezometer to determine relative hydraulic conductivity of soils 11 INTRODUCTION A major factor in the design of drainage systems is the hydraulic conductivity of the soil strata to be drained. Various methods for measuring the hydraulic conductivity of soils in both the field and the laboratory have been devised. In many cases, however, laboratory methods fail to give reliable data since the natural field conditions under which flow actually takes place cannot be duplicated in the laboratory. Hence a need exists for a field method for measuring hydraulic conductivity of soils in situ. When a large number of tests are to be performed in a given location, a simple, quick, accurate, and inexpensive method would be very desirable. After making studies of Lagunda de La Nava Project in Spain for the purpose of analyzing irrigation, drainage, and salinity problems, Professor J. E. Christiansen (1964) Consultant for the Hydrotechnic Corporation, suggested a simple piezometer method for determining the relative hydraulic conductivity of the soils. Using this method and the formula suggested by Professor Christiansen, several tests were performed in various locations. The object of this report is to describe this piezometer method for determining the relative hydraulic conductivity of the soil strata and to present the results obtained in a limited field study, together with conclusions and recommendations. REVIBW OF LITERATURE Henry Darcy (1856), the French hydraulic engineer, studied the move­ ment of water through sand. He developed and published an empirical law, now w 1 knon as Darcy s law, which states that the groundwater flow is directly proportional to the hydraulic gradient. It can be expressed as V ·- Ki in which V is the flow velocity i is the h drauHc gradient K ls a proportionality constant The constant of proportionality, K depends on the properties of both porous media and the fluid and is known as the "hydraulic onducti.vity." It has the dimensions of velocity, LT-l, and may be defined as the rate of a fluid (water) through a unit c.;ross-sectional area under a unit hydraulic gradient during a unit period of time. A modified form of Darcy1 s law is expressed as V = Y- K'i /-""' in which Y is the density of the fluid 14-- is the dynamic viscosity K' is a constant of proportionality, known as the intrinsic permeability 3 The intrinsic permeability depends on the·v, properties r). of soil only and dces not include the effects of fluid properties { It has the dimensions 2 of L . Factors affecting hydraulic conductivity are: (1) shape and size of grain, (2) porosity, (3) structural arrangement, and (4) properties of fluid, such as denisty and viscosity. Methods of measuring hydraulic conductivity The methods and techniques for determining hydraulic conductivity fall into two classes, depending on whether representative soil samples are tested in the laboratory or whether the tests are made i!! sit-q_. Laboratory methods. Hydraulic conductivity tests may be made on undisturbed soil cores or on samples of disturbed soil. The two common methods y used for measuring permeabilit are the constant head permeameter, devised by Meinzer, as cited by Kadir (1951), and the variable head permeameter, developed by Theis, as cited by Kadir (1951). Since the laboratory tests are not conducted under natural flow conditions the results obtained are only approximate. Field methods. Various field methods have been developed for deter­ mining the hydraulic conductivity of soils. Two methods commonly used for measuring hydraulic conductivity of soils below the water table are: (1) the p'.ezometer method, and (2) the auger hole method. Kirkham (1946) proposed a piezometer method for measuring the hydraulic conductivity of soils. In this method, the piezometer tube is installed by angering out a hole 6 inches at a time and then driving a tube to within 1 inch 4 of the bottom of the hole. The diameter of the auger should be 1/16 inch less than the inside diameter of the tube. Upon reaching the desired depth, a cylindrical cavity of known iength is augered out below the tube. Water rising into the piezometer is removed several times by pumping or bailing in order to flush the soil pores along the cavity wall. After flushing, the water is left to rise to equilibrium with the water table. The water is then pumped out again and the rate of rise is noted by means of an appropriate water level indicator and a stop watch. The hydraulic conductivity, K, is then determined from the relation i.n which R is the radius of the cavity h1 and h2 are the water levels below the equilibrium level at times t1 and t2, A is a factor depending on the geometry of the flow system. In the auger hole method a hole is augered out to the desired depth below the water table and the water is allowed to rise in the hole until in equilibrium with the water table. The water level is then lowered by bailing or pumping, and the rate of rise of the water level in the hole is measured. Several different formulas have been developed by various investigators h for determining te hydraulic conductivity of the soil using the observed rate of rise of water in the auger hole. Hooghurdt and Ernst, as cited by Luthin (1957) 5 made improvements over t.he formula derived by Diserens, as cited by Luthin i h (1957). Kirkham and van Bavel, as cited by Lu th n (1957), reexamined te problem of flow into an auger hole, from a more rigorous vie-wpoint, and van Bavel and Kirkham, as cited by Luthin (1957), developed new field techniques for making the tests. The auger hole method and the hydraulic conductivity of soil is described in a report by the ASAE Drainage Research Committee (1959), revised 1961. One of the formulas presented is K - if R2 Ah dh dt in which K is the hydraulic conductivity R is the radius of the auger hole h is the hydraulic head at time, t A is a geometric factor The equation may also be written 2 K= 2 11'R (h1 - h2) A (t2 - t1) (h1 + h2) in which h1 and h2 are the head at times t1 and t2. 6 a Christiansen i1964. p. 10- ll suggested simpler method for measuring whfoh the relative hydraulic condu<'bvitv in t..iJ.!!. in the water enters the cavity below a piezome1er. He desr ribed the method as follows. A transparent tube is mounted on top of the piezometer. This tube may be of glass or plastic, and it should be about the same outside diameter as the piezometer pipe. The tube should be graduated in milliliters reading from the top down­ so wards, or a :.;;cale should be attached to the tube and its inside diameter measured that the actual rate of flow into the soil can be determined by timing the rate of drop of the water surface. The technique suggested is as follows: After installation, the pie:z:ometer should be flushed and the water level in the pie10met0rof allowed to reach its static level.
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