Permafrost in Marine Deposits at Ilulissat Airport in Greenland, Revisited

Transcription

1 NICOP IX International Conference on Permafrost University of Alaska Fairbanks 2008 Session 28: Cold Regions Infrastructures and Transportation Permafrost in Marine Deposits at Ilulissat Airport in Greenland, Revisited Niels Foged Director of Research, PhD,,. Thomas Ingeman-Nielsen PhD in Arctic Geophysics, Ass. Professor at ARTEK,, Technical University of Denmark. Polar Earth Science Program, (ARC ) Collaboration: UAF GI Permafrost Laboratory Danish Meteorological Institute ASIAQ, Greenland Survey

2 Ilulissat Airport Soil investigations Project invest.& Design 1981 Construction Control and MSc-study 1993 Revisited 2007 A single local depression with repair in pavement due to settling caused by thawing of an ice-segregated clay layer, which was not replaced during construction between rock fill layer and gneiss bed rock.

3 Humlum & Christiansen, 2000 Ilulissat Nuuk

4 Highest marine levels West Greenland Altitude (metres) above recent sea level Weidick, A.; 1976: Glaciation and the Quaternary of Greenland. GGU: Geology of Greenland.

5 Ilulissat Airport Geotechnical investigations using resistivity profiling and boreholes with field and laboratory testing and soil temperature data collection. Test fill on a bassin filled with more or less saline marine clays. Foged,N. & Bæk-Madsen C. (1980): Jacobshavn Airport Thermal Stability in Marine deposits, Proc. 2nd. Int. Symp. on Ground freezing, Trondheim, Norway.

6 Cross section in basin SW of Runway

7 Cl -(g/l) Ilulissat Airport Typical Boring Profile Active layer: 0.4m (Tf 0 degc) Permafrozen low salinity clay: 3,8m (Tf 1degC) Unfrozen (partially frozen) high salinity clay: 3,0m (Tf 2 to-3 degc)

8 Oedometer testing Depth 3.2 m Silty clay with thin icelayers giving rise to a fissured blocky structure after thawing. Water content 31.5%(dry weight) σ 0 = 55 kpa σ pc = 210 kpa Cl - -content 13 Theoretical Tf ~ -1.4 C Controlled thawing caused 7.8% deformation Main deformation occurs between -3 and -1 C Drainage occurs also under partially frozen conditions

9 Soil temperature measurement station in Ilulissat town Ole B. Olesen (GEUS)

10 ILULISSAT WEST GREENLAND Yearly mean air temperature MAAT (degc) from ASIAQ and DMI Files 0,00-1,00-2,00-3,00-4,00-5,00-6,00 ASIAQ KLIMA INFO Ilulissat DMI files -7,00-8,00-9,00-10, Construction of airport

11 Test fill at Ilulissat Airport

12 Section a-a in Test Fill

13 Soil temperature at(jakobshavn) test fill Soil temperatures measurements at Test Fill in Airport of Ilulissat B82007 Borehole Boreholes 82006B82006 andand Temperature (degc) CH2: B m b.g.s. CH3: B m b.g.s. 5 CH7: B m b.g.s. CH8: B m b.g.s. CH9: B m b.g.s. CH10: B m b.g.s. 0 CH11: B m b.g.s. CH12: B m b.g.s Day-Month-Year BYG DTU

14 Settlement of top of Test Fill and at top of settlement gauges set in permafrozen layer Levels at Test Fill Site compared to and : A = 0.17m / <0.124m B missed C = 0.0 m / 0.0 m D = 0.25m / 0.138m E = 0.24m / 0.173m Levels of top of settlement gauges placed in the middle of the test fill: No distinct settlement of previous surface and top and bottom of frozen clay layer Note: Measurements are wrong (fix point was not correct)

15 Test fill at Ilulissat Airport

16 Cross sections 1, 2, 3 and 4 in Test Fill based on survey Level (m) 30,0 29,5 29,0 28,5 28,0 27,5 27,0 26,5 26,0 Levelling point C 0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 Section 1 Section 2 Section 3 Section 4 St. (m) from Safety Area Boundary Levelling and visual inspection revealed a block failure from approx St. 17 in the eastern part of the fill combined with a horizontal displacement of the topsoil and active layer and tilting piles of the airport fence.

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18 Ilulissat Airport Conclusions The airport was designed and constructed in an area with permafrost in saline marine clays based on detailed geophysical and geotechnical studies in field and laboratory. Variable permafrost conditions with organic solifluction soils on icerich low salinity frozen clay underlain by partially frozen to unfrozen saline permafrost caused a conservative approach with removal of these layers and substitution with rock fill. Control investigations show in general fine operational conditions and very limited maintenance costs during the period from 1984 to A test fill revealed good thermal control due to convection in a 2m thick coarse grained rock fill topped with coarse gravel on the clay basin. However, minor settlements and missing side stability especially after 1993 have been observed. Revisiting the area in 2007 it was selected as a type locality in the present NSF funded ARC project: Recent and future permafrost variability, retreat and degradation in Greenland and Alaska : An integrated approach carried out by UAF, DMI, ASIAQ and ARTEK.

19 Figure 2. Test sites proposed and their relation to the permafrost zones of Greenland and Alaska. For Greenland, estimated and compiled by Humlum and Christiansen (Jakobsen et al., 2000); Alaska, modified from Brown et al. (1997, 1998).