Mass movement

Introduction

We can define a mass movement as a soil, mud sediments and stones movement toward down.

This movement can perform with low amount and slowly like soil creep and/or with high amount and speed like a landslide and/or stones falling from slopes and walls. On the world scale, the mass movement has had a few fatalities rather than the overall of fatalities caused from natural disasters. Nevertheles, we can not ignore a high damages at a wide level to a man-mades, and sometimes they result a structures movement and/or roads cut.

It is a necessary that a components of one inclined land first become an unstable and then sliding for a mass movement and this occurs when the separating forces overcome on a resisting forces.This equilibrium has been defined as factor of safety that is shown with F:

F= Factor of safety

F= stress/ resisting force= sum of separating forces/ some of resisting forces.

2-2- Some of the most important of mass movement at 20^th century (Jone.1995):

One inclined surface with a factor of safety less than 1 is an instable, and therefore it is at a suitable requirements for sliding and falling, while one inclined surface with a factor of safety more than 1 is a stable. The inclined surface that it's factor of safety is equal to one, it is at a critical equilibrium requirements.

In general, 6 types of region have been identified for a landfall or a mass movement:

1-     Regions having seismicity

2-     Mountainous environments

3-     Regions that the land is detached in them (Land detach)

4-     Areas covered by thick loess sheets

5-     Regions having improper weather

6-     Regions with a fast development

The mass movement is performed at a different dimensions, and shapes that we can classify them based on the following cases:

-         Materials type: weathered soft sediments or rough and resistance stones.

-         Movement type: movement as flows, sliding or movement of deposits along with classes.

-         Speed: the movement speed can be very low or very high

Hazards risk survey caused from mass movements: The slopes stability amount has been drawn at hazard risk maps. There are two important points for surveying mass movement hazard risk:

1-     To anticipate the fall, slide and creep possibility at slopes.

2-     To determine the position, time and magnitude of event. We must know two points for anticipating a mass movement possibility.

At Grindelwald area, Swiss Alps, the Landslide hazards have been classified as follows(Kienholz 1978):

Avoidance from mass movement:

There are a many ways for avoiding from a mass movement.

First, We must determine an areas having a movement risk given to maps relating to that area and a direct visit from land, then introduce an alternative with regards to the area having a mass movement possibility . At some of areas, the inclined landsare near to the established buildings and there is a falling and sliding possibility of the slopes components over buildings. Here we can increase the safety with making a protective wall that we must build in a piper or parts inside a protective wall in order to pass the penetrated water from upper stream.