Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tFigure 2. South Bay south foundation thermal test section sensorlocations.number of sensors were also installed under all the buildingfoundation systems to help characterize the heat loss fromthe building.Soil temperature is monitored at various points usingsensors fabricated with triplicate YSI thermistors or stringsof 12 YSI thermistors at a predetermined spacing. Thecalibration for each sensor was verified. Figure 1 showsthe location of two of the thermistor strings: CCHTH1 andCCHTH3.Soil-water content was monitored with CampbellScientific, Inc. CS616 TDR-type sensors. These sensorsindicate the volumetric amount of unfrozen water content,based on changes in soil bulk dielectric properties.Water levels in observation wells are manually recordedat selected observation intervals. The groundwater wells arelocated near the four property corners, as shown on the mapin Figure 1.Sensor readings at each station were controlled andrecorded with a Campbell Scientific, Inc. CR1000 datalogger.Data are transmitted hourly to a central processing serverthough an Internet connection.Figure 2 shows sensor locations near one of the foundationjacking pad test sections. CCHTH## sensors are temperaturesensors consisting of triplicate thermistors. CCHSM##sensors are soil-moisture sensors.Results and DiscussionThe south foundation thermal test section is taken asrepresentative. Figure 3 shows soil temperatures sinceSeptember 1, 2006, for the sensors in the gravel fill andnatural silt to 2.26 m below the top of the jacking pad. Thesoil temperature did not fall below freezing here.Figure 4 shows soil-water content since September 1,2006, for the sensors in the gravel fill and natural silt to 2.26m below the top of the jacking pad. The sensors in the naturalsilt, below the gravel fill, show the soil to be very moist, nearsaturation. The gravel fill is very dry, between about 5 to 7percent by volume. The graph shows seasonal variability insoil-water content in the silt. The driest time is in the spring.Fall 2007 shows higher soil-water content than the sameperiod in 2006. The monitoring needs to continue in orderto ascertain if this is simply seasonal variability, if the soilFigure 3. South foundation thermal test section: soil temperature inthe gravel fill and in the natural silt.Figure 4. South foundation thermal test section: soil-water contentin the gravel fill and in the natural silt.is getting wetter, or if the soil was dried during constructionand is returning to a stable state.SummaryThe CCHRC RTF is a state-of-the-art facility located onshallow permafrost. The building foundation is designed toallow compensation for any differential settlement resultingfrom permafrost degradation. The building and surroundingarea is heavily instrumented to allow soil-temperatureand soil-moisture monitoring. The monitoring system isdesigned for long-term use. Preliminary results are given,but it is too soon to tell if the ground beneath the buildinghas reached equilibrium after the disturbance resulting fromthe construction.ReferencesMurton, J.B. & French, H.M. 1994. Cryostruc tures in permafrost,Tuktoyaktuk coastlands, western Arctic Canada.Canadian Journal of Earth Sciences 31: 737-747.188