Figure 13-7.—Nuclear moisture-density meter.moisture-density meter, such as the one illustrated inand receive certification through the Navalfigure 13-7.The meter contains sealed radioactive materials,typically cesium and a combination of americium mixedwith beryllium powder. The cesium emits gammaradiation that the detector in the meter can count whenit is passed through the soil. This count can be translatedto density. The americium, interacting with theberyllium, emits neutrons following collision withhydrogen that are moderated and detected by the meter.The moisture content can be determined by measuringthe hydrogen concentration in the soil.When you are using the moisture-density meter,counts or readings are obtained and used with acalibration chart to determine the wet density andmoisture content. The dry density is computed from thewet density.CAUTIONBefore using the nuclear moisture-densitymeter, you must complete specialized trainingConstruction Training Center at either Gulfport,Mississippi, or Port Hueneme, California.BEARING TESTSThe bearing capacity of a soil is expressed in termsof shear resistance, which means the capacity of theload-bearing portion of a material or member to resistdisplacement in the direction of the force exerted by theload.There are various types of load-bearing tests. Fordescription purposes we will briefly discuss theCalifornia bearing ratio (CBR) test.The California bearing ratio is a measure of theshearing resistance of a soil under carefully controlledconditions of density and moisture. The CBR isdetermined by a penetration shear test and is used withempirical curves for designing flexible pavements.The test procedure used to determine the CBRconsists of two principal steps. First, the soil test13-10
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