Narrator: The objective of this video is to explain why landslides occur on the slopes, and to show how human occupation can influence these disasters. |
Images of landslides, newspaper stories etc. (0:27-1:18) |
The problem occurs in several regions of Brazil, especially in the rainy season, and is repeated every year, causing loss of life, social and psychological damage. In the last 3 years, just over a thousand people died in landslides in several cities in the state of Rio de Janeiro. Much larger numbers of people, including children, the elderly and the sick, were displaced or made homeless. Added to this is the physical damage caused by the destruction of homes, roads and water and sewage networks. |
The poor who occupy inappropriate areas in a disorderly fashion are the ones who suffer the most from this.To understand the causes of these disasters, it is important to analyze the slope’s subsoil. |
One of the most common types of landslides occurs where there is a thin layer of residual soil onto the rock. The thickness of the soil layers below the surface is of a few meters. Below the soil there is rock. |
Narrator: When it rains, the water penetrates the ground through the soil layer until it reaches the rock, when it changes direction and flows down the slope. |
Animation: A slope profile, showing a thin soil layer is shown. Blue arrows indicate the downward movement of the rain until it reaches the rock. Then the arrows change direction (parallel to the rock top), and the water level rises within the soil. The drawing shows a wet region within the soil and blue downward arrows parallel to the terrain. (1:19-1:44) |
If the rain continues, the soil is saturated and the water causes a force that drags the soil down the slope. |
Part 2: building the small-scale experiment of landslides (1:45-2:37) |
Narrator: This model was created to represent a slope. The glass wall allows you to visualize what happens. An inclined plane made of polystyrene represents the rock. The soil is placed on top of it. A tank system with colored water and an electric pump represent the entry of rainwater into the land. |
Model: footage of the model assembly. |
Part 3: conducting the experiment addressing the natural factors (2:37-3:32) |
Narrator: The water level rises and increases the pore pressure in the terrain, but the strength of the soil is still enough to prevent a landslide. |
Model: Steady water flow scenes in the model. (2:37-2:56) |
Narrator: However, if the rain continues to soak the soil, the water level will rise until the strength of the soil is overcome. |
Model: Scenes of water level rising and slope failure in the model. (2:56-3:14) |
At this point, the landslide occurs. |
Narrator: As we can see in this video, the soil slides on the rock and hits everything in front of it with great energy. |
Model: Scenes of the slide in slow motion. (3:14-3:32) |
Part 4: conducting the experiment addressing the anthropogenic factors |
4.a - cut and fill in a slope (3:32-5:02) |
Narrator: A landslide can happen more easily if the slope is steeper. How does this happen? It is common to make excavations in the ground to have a level where a house or a street can be built. This makes the back slope steeper and easier to slide off. |
Animation: step-by-step execution of two excavations on a slope, resulting in two plateaus and the “construction” of a toy house on one plateau and a toy road on the other. Then two landslides hit the house and the road. |
Model: show the failure of the small-scale model caused by the excavation procedure (no flow). (3:32-4:37) |
Narrator: an embankment fill may be placed on the slope to make room for construction of houses or roads. If this construction is not performed properly, a slide can be triggered by it. |
Animation: shows the embankment image that looks stable (section equal to the end of the excavation animation). |
Narrator: Despite its “safe” appearance, the embankment fill constructed without care saturates during heavy rains, loses strength and slides. |
Animation: shows the slide hitting the houses. (4:37-5:02) |
4.b - solid waste dumped on the land (5:02-5:12) |
Narrator: It's even worse when one dumps rubble and solid waste on the slope. |
Animation: show an accumulation of solid waste on the slope. |
Narrator: This material may be weak and slide easily when it rains. |
Animation: show the slide of solid waste and debris down the slope reaching the house below. |
Part 5: Final Considerations (5:12-6:12) |
Narrator: The objective of this video was to explain how and why landslides occur on the slopes, and show how the occupation can influence the occurrence of disasters. |
Collection of images of slopes and slope failures (5:12-5:38) |
Credits (5:38-6:12) |
We hope you have understood why landslides occur and which are the actions that should be avoided to improve the safety of the slopes. |