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WHY DO HILLSLOPES MOVE AT SOME TIMES AND NOT AT OTHERS?

WHY DO HILLSLOPES MOVE AT SOME TIMES AND NOT AT OTHERS?. Forces, Resistances and Thresholds. FORCES . RESISTANCES . IF FORCE GREATER THAN RESISTANCE , HILLSIDE MOVES OR “FAILS”. IF RESISTANCE GREATER THAN FORCE , HILLSIDE IS STABLE. FORCE = MASS X ACCELERATION.

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WHY DO HILLSLOPES MOVE AT SOME TIMES AND NOT AT OTHERS?

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  1. WHY DO HILLSLOPES MOVE AT SOME TIMES AND NOT AT OTHERS? Forces, Resistances and Thresholds

  2. FORCES RESISTANCES IFFORCEGREATER THAN RESISTANCE, HILLSIDE MOVES OR “FAILS”. IFRESISTANCEGREATER THAN FORCE, HILLSIDE IS STABLE.

  3. FORCE = MASS X ACCELERATION

  4. FORCE = MASS X ACCELERATION 1. MASS IS THE MASS OF THE HILLSIDE MATERIAL!

  5. FORCE = MASS X ACCELERATION 1. MASS IS THE MASS OF THE HILLSIDE MATERIAL! 2. ACCELERATION? ……….

  6. FORCE = MASS X ACCELERATION 1. MASS IS THE MASS OF THE HILLSIDE MATERIAL! 2. ACCELERATION? ……… DOWNSLOPE MOVEMENT UNDER THE INFLUENCE OF GRAVITY …… ACCELERATION DUE TO GRAVITY.

  7. ACCELERATION DUE TO GRAVITY ACTS PERPENDICULARLY.

  8. 0° INTRODUCE A HORIZONTAL SLOPE, 0°.

  9. 0° W PLACE BLOCK OF EARTH MATERIAL, WEIGHT, W, ON THE SLOPE

  10. 0° W ARBITRARILY DEFINE “DOWNSLOPE” AS TO THE LEFT.

  11. 0° W NONE OF THE FORCE OF GRAVITY IS ACTING IN THE DOWNSLOPE DIRECTION

  12. 0° W W 30° INCLINE THE PLANE TO 30°

  13. 0° W W 30° DOWNSLOPE DIRECTION NOW CLOSER TO DIRECTION OF GRAVITY

  14. 0° W W W 30° 60° INCLINE THE PLANE TO 60°

  15. 0° W W W 30° 60° DOWNSLOPE DIRECTION EVEN CLOSER TO DIRECTION OF GRAVITY

  16. 0° W W W 30° 60° 90° W INCLINE PLANE TO THE VERTICAL, 90°

  17. 0° W W W 30° 60° 90° W ALL OF GRAVITY NOW ACTING IN THE DOWNSLOPE DIRECTION.

  18. 0° W W W 30° 60° 90° W PROPORTION OF ACCELERATION DUE TO GRAVITY ACTING IN THE DOWNSLOPE DIRECTION IS INCREASING.

  19. 0 X W.g 0° W W W SIN(0°) = 0 30° 60° 90° W

  20. 0 X W.g 0° SIN(0°) = 0 W W W 30° SIN(30°) = 0.5 0.5 X W.g 60° 90° W

  21. 0 X W.g 0° SIN(0°) = 0 W W W 30° SIN(30°) = 0.5 0.5 X W.g 60° SIN(60°) = 0.87 0.87 X W.g 90° W

  22. 0.0 X W.g 0° SIN(0°) = 0.0 W W W 30° SIN(30°) = 0.5 0.5 X W.g 60° SIN(60°) = 0.87 0.87 X W.g 90° SIN(90°) = 1.0 W 1.0 X W.g

  23. Mean slope-angle frequency distribution and size frequency distribution of landslide masses in Higashikubiki area, Japan.Junko Iwahashi, Shiaki Watanabe and Takahiko Furuya GeomorphologyVolume 50, Issue 4, 1 March 2003, Pages 349-364

  24. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE?

  25. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 1. Changes in Weight2. Changes in Slope

  26. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? Nevado del Ruiz, Colombia. 1. Changes in Weight • Add water to slope – fill pore spaces 62 lbs per cu ft. 8 lbs per gallon Sichuan Province, China. Armero, Colombia.

  27. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 1. Changes in Weight • Add water to slope – fill pore spaces • Build on it! Saskatoon, Canada Bournemouth, England

  28. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 2. Changes in Slope • Erosion of bottom of slope. Colorado, US Devon, England

  29. WHY WOULD FORCES ON A HILLSIDE FLUCTUATE? 2. Changes in Slope Virginia • Erosion of bottom of slope. • Road/rail cuttings. Thailand Thailand

  30. WHAT ARE THE RESISTANCES TO MOTION ON A HILLSIDE? Normal Stress: “Normal” meaning at right angles to (the slope). Stress implies the component of the acceleration due to gravity, NOT, acting in a downslope direction, but actually holding the hillside in place.

  31. WHAT IS NORMAL STRESS ? Downslope 90° 0° W Normal Stress

  32. W 30° Normal Stress: Moves away from gravity (decreases) as slope increases. Downslope Component: Approaches gravity as slope increases.

  33. W N.S = Cos (Slope) . W. g. 30° Normal Stress: Moves away from gravity (decreases) as slope increases. Downslope Component: Approaches gravity as slope increases.

  34. WHAT ARE THE RESISTANCES TO MOTION ON A HILLSIDE? Normal Stress: Cosine Slope. Friction: Degree to which particles lock together and resist movement.

  35. Angle of internal friction (repose)

  36. Angle of internal friction (repose) GENERALLY: Big grains High friction Small grains Low friction

  37. WHAT ARE THE RESISTANCES TO MOTION ON A HILLSIDE? Normal Stress: Cosine Slope. Friction: High for big grains, low for small. Cohesion: The force that holds together molecules or like particles within a soil.

  38. Cohesion GENERALLY: Clays High cohesion Large grains Low cohesion

  39. FORCES RESISTANCES Weight Slope Normal Stress Friction Cohesion

  40. FORCES RESISTANCES Weight Slope Normal Stress Friction Cohesion WATER HAS DIFFERING ROLES IN THE BALANCE DEPENDING UPON THE QUANTITY OF WATER PRESENT.

  41. HYGROSCOPIC WATER

  42. FORCES RESISTANCES Vs. Weight Slope Normal Stress Friction Cohesion HYGROSCOPIC No Role

  43. CAPILLARY WATER

  44. FORCES RESISTANCES Vs. Weight Slope Normal Stress Friction Cohesion CAPILLARY Resistance Negative Pore Water Pressures

  45. FREE or GRAVITATIONAL WATER

  46. FORCES RESISTANCES Vs. Weight Slope Normal Stress Friction Cohesion GRAVITATIONAL Force Positive Pore Water Pressures

  47. Mass Movement Experiment for Floridians

  48. Mass Movement Experiment for Floridians Sand Castle – Steep Slopes

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