ÉCOLE POLY TECHNI QUE FÉDÉRALE DE LA USANNE. Fragmental rock fall paths:

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1 ÉCOLE POLY TECHNI QUE FÉDÉRALE DE LA USANNE Frametal rock fall paths: Compariso of simulatios o Alpie sites Experimetal ivestiatio of boulder impacts V. Labiouse Moutai Risks Itesive Course LMR LABORATOIRE DE MÉCANIQUE DES ROCHES September 1st, 2008

2 Frametal rock fall paths Itroductio Framework Basic features of computer codes observed depositio zoe Back-aalyses of rockfalls evets i the Alps Iterre project cliff istabilities Sait-Marcel (F) ad Les Crétaux (CH) case histories Experimetal ivestiatio of boulder impacts Restrictios of commo reboud models Small-scale experimets Results Coclusios ad Recommedatios

3 Frametal rock fall paths Itroductio Framework Basic features of computer codes observed depositio zoe Back-aalyses of rockfalls evets i the Alps Iterre project cliff istabilities Sait-Marcel (F) ad Les Crétaux (CH) case histories Experimetal ivestiatio of boulder impacts Restrictios of commo reboud models Small-scale experimets Results Coclusios ad Recommedatios

4 Steps for Rock Fall Risk Maaemet Idetificatio ad characterisatio of the departure zoe Evaluatio of rock fall propaatio Risk aalysis ad evaluatio Mitiatio measures Hazard mappi ad lad-use plai 4

Departure zoe Trasit zoe Deposit zoe Data from : Reister of evets Diital terrai models

5 Idetificatio ad characterisatio of rock fall paths Where does it start? What miht be its path? How fast is the propaatio? Where does it come to rest? Departure zoe Trasit zoe Deposit zoe Data from : Reister of evets Diital terrai models Vector maps (GIS) Ortho-photos Field observatios Rockfall pheomea map Rockfall pheomea map (Geotest) + trajectory modelli 5

6 Aims of rockfall trajectory aalyses 2. Locatio of protectio measures ad choice of their mai features 1. Delieatio of areas at risk (daer maps)? Velocity Heiht of bouce Bouce leth Eery? Maximum path leth (ruout) Propaatio path

7 4 kids of motio alo the path v 0 Fliht ω=0 v 1 Rolli v(t) ω(t) β β v 0 Bouci Slidi β v=0

8 Classificatio of trajectory codes Two cateories of prorams Riorous models cosider: 4 body with its ow shape ad volume 4 all the motio, icludi rotatio Lumped-mass models cosider: 4 block with o mass or with a mass cocetrated i oe poit 4 the traslatio oly (ot the rotatio)

9 Classificatio of trajectory codes 2 D 3 D Les Crétaux Groud profile selected i a vertical plae or alo the lie of deepest slope [Azzoi & al, 1995] 3D iteresti for complex toporaphy

10 Classificatio of trajectory codes Determiistic aalysis e.. the maximum rockfall reach Probabilistic aalysis parameters sampled radomly i a expected rae probabilistic distributio departure zoe 1.1 observed depositio zoe CETE ADRGT LMR [m] Percetae of passi blocks

11 Bad uderstadi ad predictio of the bouci pheomeo The bouci behaviour is overed by the eometry ad the mechaical characteristics of the slope the block? But it depeds as well o the kiematics at impact (velocity, collisio ale )

12 Several formulatios to express the reboud of a block ad the coefficiet(s) of restitutio + + = = t t t V V K V V K + K = V V ( ) ( ) ( ) ( ) ( ) ( ) + + ω + + ω = t t V V I m V V I m K ( ) ( ) ( ) ( ) ( ) ( ) t 2 2 t 2 V V V V V V K = + + = I terms of velocities : I terms of eeries :

13 Alterative defiitios of the restitutio coefficiets EBOUL-LMR code δ F t F The ormal coefficiet of restitutio K is a measure of the time-iterated actio of the cotact force perpedicular to the cotact plae F K + I = I = t t t t F F (t) dt (t) dt

14 EBOUL-LMR code - The soil is modelled with a liear-elastic perfectly plastic behaviour Oly the part of eery related to elastic deformatios U + ca be restored to the block, the other part bei dissipated i the roud : U K + = = I I t t F (t) δ(t) K F dt yield m V U yield = 1 2 F 2 yield K The actio of the taetial compoet of the cotact force F t is accouted for by Coulomb s law of frictio : I t t3 t = F t t (t) dt t µ F (t) dt = µ I

15 Frametal rock fall paths Itroductio Framework Basic features of computer codes observed depositio zoe Back-aalyses of rockfalls evets i the Alps Iterre project cliff istabilities Sait-Marcel (F) ad Les Crétaux (CH) case histories Experimetal ivestiatio of boulder impacts Restrictios of commo reboud models Small-scale experimets Results Coclusios ad Recommedatios

16 Report published by the ed of 2001 Iterre Project Cliff istabilities Compariso of methodoloies for the detectio of potetial rock istabilities. Compariso of computer codes of sile block trajectories. 3 parters : CETE Lyo, ADRGT, LMR - EPFL Cotet : 4 Descriptio of the mathematical models 4 Applicatio ad compariso o 6 rockfall sites Sait-Marcel, Barjac, Comboire, Champrod, Bieudro, Crêtaux 4 Coclusios, recommedatios ad prospects

17 Cotet of this presetatio Brief overview of the three rockfall simulatio codes CETE Lyo ADRGT LMR Compariso of the prorams o 2 rockfall sites site of Sait-Marcel (Frace) documeted by CETE Lyo site of Les Crétaux (Switzerlad) documeted by LMR Coclusios ad recommedatios

18 CETE Lyo CETE Lyo ADRGT LMR - EPFL 2D lumped mass method three very differet mathematical models «black box» model, with parameters calibrated o may rockfall evets determiistic aalyses determiatio of the maximum rockfall reach results fuctio of the boulder aspect ratio The aspect ratio of a block is a dimesioless parameter defied as the ratio of major to mior axis

19 CETE Lyo ADRGT LMR - EPFL 2D lumped mass method three very differet mathematical models model close to the physical pheomea, thouh ot riorous radom parameters probabilistic aalyses

20 CETE Lyo ADRGT LMR - EPFL 3D three very differet mathematical models riorous method (ellipsoidal, parallelepiped or polyoal blocks) iteratio of the fudametal equatios of dyamics 4 free falli 4 bouci 4 rolli 4 slidi radom parameters probabilistic aalyses Polyoal block impacti a three-dimesioal roud surface

21 observed depositio zoe Methodoloy of compariso Data provided by a parter slope toporaphy outcroppi materials ad veetatio data o the experieced rockfall evet 4 size (or mass) ad shape of the boulders 4 starti zoe 4 depositio zoe ad extreme edpoits 4 locatio of a few impact poits 2. Calculatio by each parter of the trajectories ad edpoits 4 maximum reach for CETE Lyo 4 probability distributios for ADRGT ad LMR (usually 300 blocks) 3. Calculatio of the mai trajectory characteristics (heiht, velocity ad eery) at locatios where protectio structures are istalled 4. Collectio ad compariso of the results

22 Toporaphical profile Outcroppi materials Rockfall evet slidi of 10 m 3 alo a plae hard bedrock coarse debris, without veetatio earth ad small rock framets, uderwood observed depositio zoe coarse debris covered by veetatio, sparse forest debris covered by veetatio, medium dese forest forest road loam sparse rock framets dese beech-rove, φ 50 cm Sait-Marcel local roads mai road RN 90 boulder of 1.2 m 3 boulder of 1 m [m]

23 Locatio of block edpoits departure zoe 1.1 observed depositio zoe Sait-Marcel CETE ADRGT LMR Percetae of passi blocks [m]

1.1 1.5 observed depositio zoe 1.2 1.3 1.4 Site of Les Crétaux (Cato of Vallis, CH) 1.1 1.2 1.3 Departure zoe 1000 m above the Rhoe river Forest Avatché corridor (schist debris) Châtelet hill Blocks of 0.

24 observed depositio zoe Site of Les Crétaux (Cato of Vallis, CH) Departure zoe 1000 m above the Rhoe river Forest Avatché corridor (schist debris) Châtelet hill Blocks of 0.3 to 32 m 3 P3 Vieyards (o a alluvial coe) P2 P1 Difficult trajectory modelli due to a complex toporaphy 3D (LMR) alo three 2D profiles (CETE & ADRGT)

25 0 250 Zoe de départ Site of Les Crétaux P Débris de schistes P P1 Collie de Châtelet Modelli of the 1987 evet LMR CETE ADRGT

26 Spatial distributio of the deposit zoe CETE ADRGT P Blocks observed i the vieyards P LMR P1 Lateral dispersio the profiles chose for the 2D computatios aree with the observed rock fall paths, but their relative importace ca ot be determied. the 3D computatio allows to reproduce the lateral dispersio of the blocks deposited i the vieyards. Ruout The extreme ruouts predicted by the CETE are shorter tha the observed deposited boulders o P1 ad P2, but coicide for a shape ratio of 1.5 o P3. The abscissas computed by the ADRGT for probabilities of reach of 10-2 ad 10-3 boud the extreme blocks o P1 ad P2, but are too far o P3. 20% of the blocks computed by the LMR come to rest further tha the extreme observed blocks o P1 ad P2, but the areemet is very ood o P3.

27 Coclusios of the compariso 1. The mathematical models i the CETE, ADRGT ad LMR prorams are very differet (2D 3D; lumped mass riorous model; determiistic probabilistic;...) 2. After some adjustmet of the model parameters, each simulatio proram is able to reproduce the deposit zoe observed i the field 4 the results of the CETE software for aspect ratios betwee 1.1 ad 1.5 eerally mark the pricipal zoes of arrest of the blocks. 4 the probability distributios calculated by ADRGT ad LMR are rather close, with the same preferetial depositio zoes. However, i eeral, the LMR distributio is more spread out tha the ADRGT oe. 3. O the Bieudro site, althouh the 3 prorams predict rather similar depositio zoes, their estimatio of velocities (ad eeries) are very diveret. I the absece of i situ observatios, it is ufortuately difficult to appreciate these results

28 Frametal rock fall paths Itroductio Framework Basic features of computer codes observed depositio zoe Back-aalyses of rockfalls evets i the Alps Iterre project cliff istabilities Sait-Marcel (F) ad Les Crétaux (CH) case histories Experimetal ivestiatio of boulder impacts Restrictios of commo reboud models Small-scale experimets Results Coclusios ad Recommedatios

29 May factors ca affect the motio of a block after impact Slope characteristics Block characteristics Kiematics streth stiffess rouhess icliatio streth stiffess weiht size shape traslatioal velocity rotatioal velocity collisio ale cofiuratio of the block at impact

30 Restrictios of commo reboud models A umber of rockfall prorams model the bouci of boulders by (overall) restitutio coefficiets. R V = V + R t = V V + t t R TE = E E +? Those restitutio coefficiets are i eeral estimated based o a rouh descriptio of the outcroppi material ad veetatio. Coefficiets of restitutio ca o loer be cosidered as costat parameters oly fuctio of the slope material (as assumed by may computer codes)

31 Small-scale experimetal campai (PhD thesis of Barbara Heidereich, EPFL-LMR, 2004) Aim better uderstadi of the bouci mechaism ad determiatio of the most siificat impact parameters. Testi procedure vertical ad iclied impacts of spheres (φ 7.5 cm) o iclied ad horizotal roud cosisti of bulked or compacted raular materials. Iclied impact o horizotal soil Vertical impact o iclied soil

film by meas of a imae processi software Cetre of

32 Data processi Reistratio of the impact by a diital hih-speed camera (250 frames/sec) Aalysis of the film by meas of a imae processi software Cetre of the bowl v tras, E tras Marks fixed o the bowl ω, E rot

deree Impact ale θ Slope icliatio β Block weiht Kiematics Block

33 Parametrical study based o 210 small-scale tests Depedecy of the coefficiets of restitutio o Frictio ale ϕ Slope Compactio deree Impact ale θ Slope icliatio β Block weiht Kiematics Block Small-scale modelli of rockfall impacts o raular slopes. i RIG 2004

34 Ifluece of the compactio deree of the soil bulked SF I sad compacted SF I sad Siificat ifluece of the compactio : R, R t, R TE

Ifluece of the impact ale θ Impact of a cocrete bowl o the SF I+G soil (ϕ = 32 ) Rt, R, RTE 1.0 0.9 0.6 0.5 0.4 0.3 0.

2 vertical impact o iclied soil Rt R RTE 0.1 0.1 0.0 90 85 80 75 70 65 60 55 0.

35 Ifluece of the impact ale θ Impact of a cocrete bowl o the SF I+G soil (ϕ = 32 ) Rt, R, RTE iclied impact o horizotal soil Rt R RTE Rt, R, RTE vertical impact o iclied soil Rt R RTE Impact ale d'impact ale θ [ ] icliaiso Slope icliatio de la pete β β [ ] If θ (impact more ormal to the slope), R, R TE, R t cst? Similar results for impacts o rock slopes (Wu, Chau)

36 Ifluece of block weiht Tests performed with spheres of same diameter but differet weiht Iclied impact o SF I sad θ = 58 If weiht (ad thus impact eery ) : R, R TE, R t Loical peetratio, plastic deformatios of the soil, eery loss

37 Experimetal ivestiatio of rockfall impacts o raular slopes The bouci pheomeo is poorly uderstood. It depeds o the slope characteristics but also o factors related to the kiematics ad the block itself. The modelli of impacts by meas of costat restitutio coefficiets oly fuctio of the slope material is ot satisfactory. A better kowlede ad quatificatio of bouci is still ecessary.

38 Half-scale experimetal campai (PhD thesis of Barbara Heidereich, EPFL-LMR, 2004) 174 impacts completed 500 k dropped from 5 m heiht Quatificatio of the bouci of blocks

39 Frametal rock fall paths Itroductio Framework Basic features of computer codes observed depositio zoe Back-aalyses of rockfalls evets i the Alps Iterre project cliff istabilities Sait-Marcel (F) ad Les Crétaux (CH) case histories Experimetal ivestiatio of boulder impacts Restrictios of commo reboud models Small-scale experimets Results Coclusios ad Recommedatios

The choice of appropriate restitutio coefficiets coditios ood trajectory predictios Calibratio by meas of : i situ tests back aalyses o the site of iterest Most

40 The choice of appropriate restitutio coefficiets coditios ood trajectory predictios Calibratio by meas of : i situ tests back aalyses o the site of iterest Most reliable ways Determiatio from : experieces o other slopes the literature o the basis of the slope material [Richards, Barbieri, Azzoi] Useful, but ca be very misleadi

41 Methodoloical recommedatios Importace of a comprehesive field data collectio to achieve a ood reliability of computer simulatio. I particular, ai iformatio o rockfall paths of recet evets : scars i the cliff impacts o the slope zoes of accumulatio The eoloists or eieers that perform the field data collectio should carry out by themselves the calculatios. Collected field observatios are proe to misiterpretatio by modellers.

Predictio capacity of rockfall prorams Reliable predictios of rockfall paths are coditioed by a thorouh calibratio of the proram parameters ad more tha 10 000

42 Predictio capacity of rockfall prorams Reliable predictios of rockfall paths are coditioed by a thorouh calibratio of the proram parameters ad more tha trajectory rus were performed to desi adequately the rockfall barriers Permaet cocer to check the simulatio results with field observatios o the site of iterest

43 Great cautio I the preset state of kowlede, the methodoloy of applicatio of rockfall simulatios to hazard mappi is still ot straihtforward The results of computer simulatios should be cosidered as a Decisio Aid Tool ad ot as a absolute criterio

LABORATOIRES DE MÉCANIQUE DES ROCHES ET DES SOLS

LABORATOIRES DE MÉCANIQUE DES ROCHES ET DES SOLS ÉCOLE POLY TECHNI QUE FÉDÉRALE DE LA USANNE Cotributio to the Moutai-Risks project of the Rock ad Soil Mechaics Laboratories of the Swiss Federal Istitute of Techoloy Lausae Dr. Vicet Labiouse Prof. Lyesse