The report gives a brief summary of the activities carried out by the Japanese - Norwegian collaboration on snow avalanche reasearch during the winter of 1990/19991. The research was mainly carried out in the Ryggfonn experiment site and at NGI research station in Grasdalen in Ryggfonn. The installation in Ryggfonn were extended by a wind sensor, a seismometer, an air pressure sensor and two video-cameras. One artifically released wet snow avalanche was recorded. The avalanche had a volume of approximately 20.000m3 and a velocity of 25 m/s in the steep part of the path. Snow cover studies were carried out to investigate if there were differencies in the potential sliding layers of the snow pack in Japan and Norway. In addition, theories of the dynamics of granular materials developed in Norway and Japan were compared.K Nishimur

Norem, Harald

English

The report gives a brief summary of the activities carried out by the Japanese - Norwegian collaboration on snow avalanche reasearch during the winter of 1990/19991. The research was mainly carried out in the Ryggfonn experiment site and at NGI research station in Grasdalen in Ryggfonn. The installation in Ryggfonn were extended by a wind sensor, a seismometer, an air pressure sensor and two video-cameras. One artifically released wet snow avalanche was recorded. The avalanche had a volume of approximately 20.000m3 and a velocity of 25 m/s in the steep part of the path. Snow cover studies were carried out to investigate if there were differencies in the potential sliding layers of the snow pack in Japan and Norway. In addition, theories of the dynamics of granular materials developed in Norway and Japan were compared

Nishimura, Koichi

Bakkehøi, Steinar

Norwegian Geotechnical Institute (NGI) Digital Archive

INTERNAL REPORTACTIVITIES OF THEJAPANESE-NORWEGIAN COLLABORATIONON SNOW AVALANCHE RESEARCH,MARCH 1991byHarald NoremKoichi NishimuraSteinar Bakkehøi581200-23 August, 1991~NGIINTERNAL REPORTACTIVITIES OF THEJAPANESE-NORWEGIAN COLLABORATIONON SNOW AVALANCHE RESEARCH,MARCH 1991by Harald NoremKoichi NishimuraSteinar Bakkehøi581200-23 AUGUST, 1991S U M M A R YNorgesGeotekniskeInstituttNorwegianGeotechnicalInstituteThe report gives a brief summary of the activities carried out by theJapanese - Norwegian collaboration on snow avalanche reasearch during thewinter of 1990/19991. The research was mainly carried out in theRyggfonn experiment site and at NGI research station in Grasdalen inRyggfonn.The installation in Ryggfonn were extended by a wind sensor, aseismometer, an air pressure sensor and two video-cameras. Oneartifically released wet snow avalanche was recorded. The avalanche hada volume of approximately 20.000m3 and a velocity of 25 m/s in the steeppart of the path.Snow cover studies were carried out to investigate if there weredifferencies in the potential sliding layers of the snow pack in Japanand Norway. In addition, theories of the dynamics of granular materialsdeveloped in Norway and Japan were compared.f\brukere\wut\581200\rap\23Street Address:Sognsveien 72OsloTelephone:National(02) 23 03 88International+472230388Telefax: Telex:National 19787ngi n(02) 230448International+472230448Postal GiroAccount No.:08145160643Postal Address:P.O.Box 40 TåsenN-0801 Oslo 8NorwayBankers:Den norske BankAccount No.:5095.05.01281581200-23 2l. INTRODUCTIONThis report gives a brief summary of the activities carried out by theJapanese-Norwegian collaboration on snow avalanche research during thewinter 1990/1991.The collaboration was initiated during the International Symposium onGlacier and Avalanche Research organized by the InternationalGlaciological Society in Lom, Norway, 1988. In February 1990, theJapanese scientist, K. Fujisawa from Public Works Institute, TsukubaCity, visited NGI, and in March 1990 J.O. Larsen, NGI, visited severalresearch institutes in Japan.The Institute of Low Temperature Science, Hokkaido University, Sapporo,presented in February 1990 a project proposal to collaborate on researchin snow avalanche dynamics. The project included participating in thefull-scale project in Ryggfonn, Grasdalen, run by NGI, participating inmodel experiments at the Institute in Sapporo, and exchange of theories.Prof. N. Maeno and Dr. K. Nishimura visited Norway in October to plan forthe activities in the winter 90/91.During the period March 3-25, four scientists from Japan visited Norway.They took part in the Ryggfonn project and carried out separate studiesof the snow cover and the snow crystals in the region of the NGI researchstation Fonnbu. The participants of the collaborative research groupwere:K. NishimuraM. NakagaweY. NohguchiT. FukuzawaK. LiedH. NoremS. BakkehøiK. Kristensen- Inst. of Low Temp. ScienceFaculty of Eng. Tohoku Univ.- Nat. Res. Cen. for Disaster Prevention,- Inst. of Low Temp. Science- NGI- NGI- NGI- NGINagaokaf:\brukere\wut\581200\rap\23~NG.581200-23 32. THE RYGGFONN PROJECTInstallations and instrumentationThe Ryggfonn project is a full scale experiment carried out toinvestigate impact forces of avalanches on structures and the effects ofa retaining dam in the avalanche path. The experimental site is close toNGI's research station, Fonnbu, in Grasdalen, Western Norway.The avalanche in Ryggfonn starts at 1530 a.s.l. and the vertical drop is910 m. The volume and maximum speed of the avalanches vary within10.000 - 100.000 m3 and 30-60 m/s respectively.The experimental set-up consists of (fig. l):A 15 m high and 75 m wide retaining dam in the avalancherunout zone. On top of the dam is one 6.5 m high steel mastwhich is instrumented with strain gauges, and one 1.0 m highmast which has a load cell.230 m upslope from the dam, a 4.5 m high concrete structurewith three load cells, each 0.72 m2 in area, has beenconstructed.320 m upslope from the dam a 10 m tubaler tower has beenerected. The tower is instrumented with strain gauges torecord shear forces and moments in three sections.Mechanical pressure indicators are also mounted on front ofthe tower for every 0.5 m.50 and 100 m upslope from the dam, two vertical geophones aresensing the vibrations from the passing avalanche.The analogue signals are digitized and recorded on a magnetictape recorder in Pulse-Code-Modulation (PCM) format.f:\brukere\wut\581200\rap\23~NG.581200-23 43. INSTRUMENTS SUPPLIED BY INSTITUTE OF lOW TEMPERATURE SCIENCEWind sensorA wind sensor was mounted on top of the mast on top of the dam, Fig. 2.The wind sensor has no moving parts and record the wind speed in threedirections. The main characteristics of the sensor is given inAppendix l.The main scope of the sensor is to study the wind condition within thesnow cloud, and especially if there exists internal velocities well abovethe frontal speed of the avalanche. The output signal of the wind sensormakes it also possible to evaluate the turbulence within the snow cloud.The analysed data may be important to estimate the impact pressure onconstructions and to evaluate the capacity of the snow cloud to transportsnow particles in suspension.SeismometerA seismometer was installed in a tube located into the top of the dam.The seismometer data will give the magnitude of ground vibrations, andthus detect the time of the avalanche and the influence of the avalancheflow to the ground.Air pressure sensorAn air pressure sensor was installed on the top of the dam. The sensorrecords the air pressure variations when the avalanche passes the dam.Both the increase in the air pressure and especially if there is asubstantial reduction in the air pressure, are important to evaluate thehazard of being caught by the snow cloud.f:\brukere\wut\581200\rap\23~NG.581200-23 5Video-camerasTwo video-cameras were installed to film the movement of the slides. Onecamera has a fixed position in front of the avalanche path, and thesignals of the camera are transmitted by a 500 m cable to the instrumenthut.The other camera is used close to the instrument hut and is operatedmanually.4. ARTIFICIAL RELEASE OF AVALANCHESAll instruments were installed in the Ryggfonn area in the period ofMarch 7-ll.The first attempt to release an avalanche was made on March 15. The last3 days in advance, there had been approx. 30 mm of precipitation. Thetemperature at Fonnbu was below DoC, and the snow was dry in the wholeavalanche path.Detonation of 100 kg dynamite released a small avalanche. The avalancheentrained, however, very little snow in the avalanche path, and died outat the 1100 m level, and never arrived to the construction area.On March 20 a new attempt to release an avalanche was made. Since thefirst attempt, there had been 15 mm of precipitation and very hightemperatures, 12°C in maximum at the Research station. The snow in thestarting zone had thus changed from dry snow to wet snow within less thanone week.The detonation of 100 kg explosives released an avalanche with thegliding layer within the remaining snow from the winter 89/90. Thereleased avalanche was a moderate sized avalanche, approx. 20.000 m3,having an average velocity of 25 m/s and a runout-distance to the frontof the dam.f:\brukere\wut\581200\rap\23~NG.581200-23 6The flow of the avalanche was both filmed by video-cameras andphotographed. There are recordings from all impact sensors. The snowcloud had, however, a run-out distance not far enough to reach thesensors on top of the dam.The recordings and the characteristics of the avalanche will be given ina separate year report of the Ryggfonn-project.5. SNOW COVER STUDIESNorway is mostly situated between 600 and 700 north while Japan issituated between 300 and 450 north. This causes great differences in thesunshine radiation in the winter season, in Grasdalen (62°N) at midwinter, the maximum sun elevation above horizon is 4,50 while at Sapporo(43°N) it is 23,50•The main topic with the snow cover investigation was to find out if therewere differences in the potential sliding layers of the snow pack inJapan and Norway. While Grasdalen has a maritime climate, a part of thestudy was also to compare the snow pack with a more continental snowpack. Grasdalen is very close to the water divide in Southern Norway,and it is easy access to areas with more continental climate at Grotlionly 20 km eastward.In the period of the investigation, the temperature were above DOC almostall the time at the research station. It was therefore necessary to takesnow samples 200 m above the station and bring them in an insulated boxback to the cold lab. The procedure was to dig a pit, classify the snowlayers and measure temperature and density each 10 centimeter.Thereafter snow samples with potential sliding layers were dug out andput into the insulated box. The temperature in the cold lab were approx.-20°C, and the samples were investigated in microscope under theseconditions.f:\brukere\wut\581200\rap\23~NG.581200-23 7Samples from Grotli were also brought over to the cold lab andinvestigated. A report of the investigations and the preliminary resultswill be presented, and the research will continue next winter.The Japanese group brought an automatic snow height sensor based onoptical fibres. The measurements were given on a digital display, and alinear voltage output made it possible to connect the sensor to theautomatic snow and weather registrating data equipment in Grasdalen.The sensor has been working excellent since it was installed, and theresolution is one centimeter in a range of three meter.6. STUDIES ON HORIZONTAL HETEROGENITY OF SNOW COVERAny snow cover, in general, suffers a lot of horizontally heterogeneousfluctuations; for example, accumulation and erosion of snow by wind,occurrence of water drainage channel due to snow melting or rain fall,and so on. As a result, the snow cover becomes horizontallyheterogeneous, even though snow falls homogeneously.The horizontally heterogeneity of snow cover in Norway was observed byusing ramsonde to compare it with that in Japan. A tube of ramsonde of aguide rod for hammer was penetrated into snow cover from its surface withsome blows of hammer at intervals of 10 or 2 cam along some measuringlines 10-100 m in total length, and then the variation of the penetraiondepth was obtained due to horizontal heterogeneity of snow cover. Theresults is now analyxzing from a viewpoint of Fractal.7. THEORETICAL COLLABORATION ON THE DYNAMICS OF GRANULAR MATERIALSBoth the Japanese and the Norwegian group has carried out theoreticalstudies on the flow of snow avalanches and on the dynamics of granularmaterials.f:\brukere\wut\581200\rap\23~NG.581200-23 8NGI has concentrated their studies on the flow of the dense part of theavalanche close to the ground. Their model assumes that the densitywithin the flowing mass is constant and that the particles are in closecontact to each other.An interesting feature of this model is that above a certain velocity andinclination of the avalanche path, the model indicates that the particlesno longer can be in close contact to each other. This physical processhas also been shown experimentally in chute experiments.The Nakagawa model is based on the assumption that there exists a freedistance between the flowing particles and the binary collisions are thedominating mechanism for momentum transfer. The developed equationsmakes it then possible to calculate the shear and normal stressesdependent on the volumetric density and the velocity gradient.A preliminary investigation indicate that it is possible to combine thesetwo models to cover a wider range of velocities and steepnesses. Thismay also explain the reduced density that some times has been observedfor certain types of avalanches.The Japanese-Norwegian group plans to make a publication on these ideas.The results of such a publication will have importance for estimatingavalanche impacts on constructions and how to combine the results of theNorwegian full-scale experiments and the Japanese model experiments.ACKNOWLEDGEMENTThis Norwegian - Japanes collaboration has been made possible byfinancial support from the Japan Ministery of Education, Science andCulture and by the Royal Norwegian Council for Scientific and IndustrialResearch. We thank for their support and for all help received by ourco 11egues.f:\brukere\wut\581200\rap\23~NG.581200-23 9A P P E N D I X 1ULTRASONIC ANEMOMETERSpecificationsMeasuring Mode: • Time-shearing sonic pulse method processing mode• Two horizontal and l vertical components to bevector-synthesized electricallyRange: • Wind velocity 0-60 mis• Wind direction 0-540 deg.(0-360 deg., 180-540 deg. automatic shifting)Accuracy: • Wind velocity: 4 % or 0.2 mis• Wind direction: 5 deg.Responding time: • 0.05 sec (both wind direction and velocity)f:\brukere\wut\581200\rap\23~NG.referanseside · documentation pageRapportnummer I Report No.581200-23~NG.,D RapportReport Il Intern rapportW Internal ReportDEJDSider I PagesRapporttittel I Report titleActivities of the Japanese-Norwegian collaborationon snow avalanche research, March 1991Oppdragsgiver I GlientProsjektleder I Project ManagerHara ld NoremUtarbeidet av I Prepared byH. Norem, K. Nishimura and S. BakkehøiEmneord I KeywordsSnow avalanches, snow cover, granular flowDistribusjon I DistributionFriUnlimitedBegrensetLimitedIngenNoneDatol DateAugust 1991Revisjon I RevisionGeografiske opplysninger / Geographlca/lnformatlonLandområder / OnshoreLand, fylke I Country, GountyKommune / MunicipalitySted I LocationKartblad I MapUTM-koordinater / UTM-coordinatesHavområder IOffshoreHavområde / Offshore areaFeltnavn I Field nameSted / LocationFelt, blokknr.! Field, Block No.

Activities of the Japanese-Norwegian collaboration on snow avalanche research, march 1991

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Activities of the Japanese-Norwegian collaboration on snow avalanche research, march 1991

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