Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />DAVID ROSSI<br />USE OF HOLLOW GRANULAR M...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />INTRODUCTION<br />In analogue modelling t...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />MATERIAL<br />Hollow aluminium hydroxid m...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />DENSITY DETERMINATION<br />Plot of data d...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />SHEAR TEST DATA<br />Shear tests were car...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />COHESION<br />The variability range of th...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENTAL SETUP <br />The efficacy of ...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-12 <br />sand = 100%<br />...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-06<br />sand = 66%<br />mi...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-10 <br />sand = 38%<br />m...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-08<br />sand = 35%<br />mi...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D03-05 <br />sand = 22%<br />m...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-07 <br />sand = 18%<br />m...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />DISCUSSION<br />Experimental results demo...
Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />CONCLUSIONS<br />The model dynamic sequen...
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Analogue experiments using hollow microsphere.

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  1. 1. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />DAVID ROSSI<br />USE OF HOLLOW GRANULAR MATERIALS TO SIMULATE DETACHMENT FOLDING <br />AND DEFORMATION PARTITIONING <br />IN SANDBOX THRUST WEDGES<br />
  2. 2. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />INTRODUCTION<br />In analogue modelling the use of PURE SAND in normal gravity experimental condition approximates the upper crust as homogeneous brittle material obeying the Mohr-Coulomb failure criterion.<br />The experimental simulation of sedimentary successions characterised by alternating weaker and stronger layers needs the use of granular materials OTHER THAN LOOSE SAND. <br />For this reason we tested in laboratory the mechanical behaviour of a new materials:<br />HOLLOW ALLUMINIUM and SILICEOUS MICROSPHERES.<br />The aim of the present study is to simulate in laboratory the development of a multilayers asymmetric detachment folds.<br />
  3. 3. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />MATERIAL<br />Hollow aluminium hydroxid microspheres“MICROBALLS”and hollow siliceous microspheres“SI-CEL”are produced with different particle sizes and colours.<br />Tested materials have grain size of respectively 25 mm (si-cel) and 40 mm for (microballs).<br />MICROBALLS<br />SI-CEL<br />
  4. 4. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />DENSITY DETERMINATION<br />Plot of data displaying the relationship between mass increase and height increase of the sediment column (h) for the investigated material.<br />Density of MICROBALLS0.39 g/cm3± 0.65%<br />Density of SI-CEL0.15 g/cm3± 1.41%<br />0<br />5<br />
  5. 5. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />SHEAR TEST DATA<br />Shear tests were carried out in a Casagrande direct shear box.<br />MICROBALLS  = 0.46  = 24.70± 0.009<br />SI-CEL = 0.44  = 23.90± 0.008<br />
  6. 6. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />COHESION<br />The variability range of the extrapolated cohesion value has been calculated by estimating the interception probability () at 99% along the shear axis as (Sokal and James Rohlf, 1987):<br />C’ - T*Es ≤  ≤ C’ + T*Es<br />MICROBALLS C’ = 6 Pa - 1.6 ≤ C’ ≤ 9.8<br />SI-CEL C’ = 1.5 Pa  is virtually zero<br />
  7. 7. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENTAL SETUP <br />The efficacy of the tested microspheres as decollement material in sandbox analogue modelling has been tested in numerous experiments with different configurations of the undeformed sand-microsphere multilayers.<br />The undeformed multilayer of the models was constructed by sieving loose granular materials above a basal sheet of drafting film ( = 0.47).<br />The total thickness of the undeformed sand-microsphere multilayer was comprise between 10.2 mm to 15.5 mm.<br />The scale factor for lengths is 5*10-6 and therefore 1 cm in the box represent about 2 km in nature.<br />
  8. 8. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-12 <br />sand = 100%<br />microsphere = 0%<br />mm<br />
  9. 9. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-06<br />sand = 66%<br />microsphere = 34%<br />Ratio between sand (s) and microsphere (m) thickness:<br />Lower half s/m = 5<br />Upper half s/m = 0.9<br />mm<br />
  10. 10. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-10 <br />sand = 38%<br />microsphere = 62%<br />Ratio between sand (s) and microsphere (m) thickness :<br />Lower half s/m = 0.3<br />Upper half s/m = 0.5<br />mm<br />
  11. 11. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-08<br />sand = 35%<br />microsphere = 65%<br />Ratio between sand (s) and microsphere (m) thickness :<br />Lower half s/m = 0.4<br />Upper half s/m = 0.9<br />mm<br />
  12. 12. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D03-05 <br />sand = 22%<br />microsphere = 78%<br />Ratio between sand (s) and microsphere (m) thickness :<br />Lower half s/m = 0.1<br />Upper half s/m = 0.6<br />mm<br />
  13. 13. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />EXPERIMENT D01-07 <br />sand = 18%<br />microsphere = 82%<br />Ratio between sand (s) and microsphere (m) thickness :<br />Lower half s/m = 0.06<br />Upper half s/m = 0.6<br />mm<br />
  14. 14. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />DISCUSSION<br />Experimental results demonstrate that the lower shear strength ofMICROBALLSand SI-CELmicrospheres seems very useful to simulate weaker layers within the brittle crust.<br />The advantage of using hollow microspheres instead of silicone putty to simulateweak decollement layersis that the former obey the Mohr-Coulomb failure criterion avoiding significant scaling problems like that in theSAND-SILICONEinterface.<br />Thesinking trendof sand (or glass microspheres) into the viscous silicone putty produces mixed layer at the sand-silicone interface with a complex, non Newtonian rheology.<br />
  15. 15. Dipartimento di Scienze della Terra <br />Universita’ “La Sapienza” di Roma<br />CONCLUSIONS<br />The model dynamic sequences allowed us to trace specific kinematic evolution.<br />As a consequence, the contraction produces two different deformation processes in different regions of the multilayers:“Fault-bendandFold-propagation foldingcharacterizing thelower half sequencesof the deforming multilayers, whiledetachment foldingdominates in theupper half”.<br />Results of the sandbox experiments emphasizes the primary role of the mechanical stratigraphy in the control of the deformations structural style within thrust wedges.<br />

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