ARCHIVED REPORTS_2007_14 - Laserfiche WebLink

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n C� n [i 'J i I f] 1. SCOPE This report describes the calibration of six thermal dissipation sensors (TDS) for use in monitoring suctions in the final cover at the Forward Landfill. The TDS were provided by the requestor and were manufactured by Campbell Scientific, Inc. F1111111104400=1 400 Each TDS was calibrated in four steps: The temperature differential at saturation (ATS,,) was determined by placing the TDS in a saturation chamber containing de -aired and deionized water. Vacuum was applied to the head space in the chamber for 24 hr to extract all air retained in the TDS. 2. The temperature differential under completely dry conditions (ATO was determined by embedding. the sensor in a sealed vessel filled with desiccant. The TDS was air- dried before being placed in the vessel. The TDS was allowed to equilibrate in the vessel for 24 hr prior to measurement. 3. The temperature differential for suctions between 0 and 311 kPa was determined in a pressure plate extractor. The TDS was embedded in a 50-50 mixture of sand and non -plastic silt. Suctions were applied to the soil mixture and TDS in the pressure plate extractor following the methods described in ASTM D 6836. The soil mixture was saturated before calibration in the pressure plate extractor was initiated. 4. The temperature differential for suctions exceeding 311 kPa was determined by embedment in soil having known suction. Sand -silt mixtures having different water contents were prepared and packed into sealed vessels along with the TDS. The TDS was monitored to determine when equilibrium was established, and then the suction in the soil was measured using a chilled mirror hygrometer following the methods described in ASTM D 6836. 3. RESULTS All calibration data were normalized in terms of the dimensionless temperature, T*: T* ATd — AT ( ) AT, — AT 1 The suction (W) and T* data for each TDS were then fit to the following expression: W=Wo for T*=1; 1 1 w = wo(T * M —1)" for T* < 1; (2)