A COMPARISON OF ATTERBERG AND HIGIDENSE 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 Atterberg limits (liquid and plastic). Recently the Chesa- 

 peake Bay Institute suggested a device (the Rigidense instrument) that 

 indirectly would 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 «■▲ 



SEMISOLID 



CONSISTENCY 



PLASTIC 

 LIMIT (PL) 



LIQUID 

 LIMIT «LL) 



SEMILIQUID 

 CONSISTENCY 



Figure 1» Schematic diagram indicating liquid and plastic limits 



(Atterberg) are determined from that portion of the sediment fraction 

 passing through the No. 1*0 (U20 micron) sieve. The water content or 

 moisture content is expressed as a percentage of the oven-dried weight 



Wi* of W3.i*©y* 



of the sediment (iftToT^gn- dried aedimen C X 100) ' 



