TECHNICAL REPORT A COMPARISON OF ATTERBERG AND RIGIDENSE TESTS FOR THE MEASURE OF PLASTICITY GILBERT JAFFE and FRANK W. GAETANO Oceanographic Survey Branch Division of Oceanography MAY 1955 Wie © U. S. NAVY HYDROGRAPHIC OFFICE patie i| WASHINGTON, D. C. ABSTRACT A brief discussion is given of the Atterberg liquid and plastic limit test as compared to the Rigidense method of deter- mining strength of bottom sediments. The relative merits of both methods are discussed. The U.S. Navy Hydrographic Office has adopted the Rigidense test as standard laboratory procedure. FOREWORD Plasticity is one of the properties of bottom sediments having an important bearing upon resistance to penetration. The measurement of plasticity is not a well-standardized proceduree Although both Atter=- berg and Rigidense tests are methods of quantitative measurement, the Rigidense method provides the more rapid analysise This report describes both methods and compares the relative merits of each. Je B. COCHRAN Captain, U. S. Navy Hydrographer ——— — == ———— —e CO — —— OO —— -0 {4-4 — ——— Ss — — es @ 2 atakal Oo 0301 0040 IMA DISTRIBUTION LIST ONR (Codes 16, 118, 166) BUSHIPS (Code 87)(2 copies) NRL (3 copies) NEL (Codes 550, 552) NOL BUDOCKS USNUSL AIR FORCE CAMBRIDGE RESEARCH LAB USCG USC&GS BEACH EROSION BD RADL DEF LAB HUNTERS PT DIR ASTIA (2 copies) USF&WS (Galveston, Texas) USF&WS (Hawaii) USF&WS (Brunswick, Georgia) US ARMY TRANSPORTATION TRAINING COMMAND US ARMY TRANSPORTATION RESEARCH AND DEVELOPMENT COMMAND CBI UNIV OF RHODE ISLAND TEXAS A&M UNIV OF TEXAS, INSTITUTE OF MARINE RESEARCH (Port Aransas, Texas ) UNIV OF CALIF UNIV OF WASH WHOL LAMONT GEOLOGICAL OBSERVATORY SIO UNIV OF MIAMT FLA STATE UNIV YALE UNIV CORNELL UNIV UNIV OF HAWAIT RUTGERS UNIV JOHN HOPKINS UNIV, APPLIED PHYSICS LABORATORY NATIONAL INSTITUTE OF OCEANOGRAPHY iv I. II. III. IV. CONTENTS Tn LeOdUCcLONeiellel el Kolrelieliel lelloilel lellcitonicnleltenie)(c) ohio Instrument Descriptious and Operations « «© e « © ce « e Results. o eo@e#enwoeeweeeeeaeewee eG @ © © ee Oe Conclusicns. Ce a | FIGURES Schematic diagram indicating liquid and plastic limits Liquid limit device and grooving toole « 6 e 0 © e © o Schematic diagram illustrating the sediment arrangement in cup prior to grooving. «« eseceecee eo ce oe eo e Schematic diagram illustrating the conditions of a sample before and after the liquid limit test . . . e « « eo 0 e Flow curve to determine liquid limit . 2. 2 .oeecvxee eo Schematic diagram illustrating a 15egram sediment sample above and below the plastic limit. « e«ecesecevece Rigidense instrument ¢ . « « 6 « « « 6 6 0 6 « « « se 6 ° Page “Nn UL A COMPARISON OF ATTERBERG AND RIGIDENSE TESTS FOR THE MEASURE OF PLASTICITY I. Introduction Plasticity is one of the properties of bottom sediments having an © important bearing upon resistance to penetration. However, the meas- urement of plasticity is not a well-standardized procedure. It is usually reported qualitatively as high, medium, or low, and quantita- tively as Atterbsrg limits (liquid and piastia), Recently the Chesa= peake Bay Institute suggested a device (the Rigidense instrument) that indirectly wowld measure plasticity much more rapidly than the Atterberg test. The purpose of this investigation is to determine the relative merits of both tests. II. Instrument Descriptions and Operations The Atterberg liquid limit (LL) is a measure of the water content of a sediment at the boundary between the plastic state and the semi- liquid state, whereas the Atterberg plastic limit (PL) is a measure of the water content of a sediment at the boundary between the plastic state and the semisolid state (fig. 1). The liquid and plastic limits INCREASING MOISTURE CONTENT ES) Y ] , PLASTIC CONSISTENCY SEMISOLID |-___-____+| SEMILIQUID CONSISTENCY “PLASTIC WQUID 7! CONSISTENCY LORAIT (PL) LIMIT (LL) Figure 1. Schematic diagram indicating Liquid and plastic limits (Atterberg) are determined from that portion of the sediment fraction passing through the No. 0 (20 micron) sieve. The water content or moisture content is expressed as a percentage of the oven-dried weight Wt. of water Gene sediment (WEF of oven-dried sediment * 100). He Mi <€§ § LOCK SCREW ae eer SS SSS TUACOON ~- ADJUSTING SCREW CAM AND -————— CRANK MECHANISM LIQUID LIMIT DEVICE ee cae GROOVING TOOL FIGURE 2. LIQUID LIMIT DEVICE AND GROOVING TOOL In the comparison of Atterberg and Rigidense tests the Atterberg Liquid limit? was determined by using a liquid limit device. This instrument consists essentially of a b-ass cup, crank and cam mecha=- nism, and carriage mounted on a hard rubber base (fig. 2). A standard grooving tool, made of 1/16 inch steel and having a cylindrical portion on the handle end, is also an essential part of the instrument, The cylindrical portion which serves to adjust the drop of the cup, has a diameter of 1 cm. A sediment sample of approximately 100 grams is placed in the brass cup and spread to form a smooth cake about 1/2 inch deep in the lower half of the cup (fig. 3). The sediment is then Figure 3. Schematic diagram illustrating the sediment arrangement in cup prior to grooving grooved and the instrument adjusted to permit a lecm. drop of the cup. The crank is turned, alternately lifting and allowing the cup to drop at the rate of 2 drops per second. A "flow curve" representing the relation between the moisture contents and corresponding number of shocks required to make the two sides of the sample flow together for 1/2 inch along the bottom of the groove (fig. h) are plotted on semilogarithmic paper (fig. 5). 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