Landslide Monitoring System

CHAPTER I INTRODUCTION

Landslides are down slope movements of rocks, debris or earth under the influence of gravity, which may cover a wide range of spatial and temporal scales. Most landslides occur at steep slopes, but they can also happen in low relief areas in connection with excavations by rivers or construction work. Landslides  can  be triggered  by natural  environmental  changes  or by  human activities. Earthquakes, volcanic activity, heavy rainfalls and changes of ground water level are typical natural triggering mechanisms for landslides, which amplify the inherent weakness in rock or soil. Landslide may result in severe human casualties, property losses and environmental degradation. [DER2003]

While landslides are a naturally occurring environmental hazard they have recently increased in frequency in certain areas due to human activity. They can be classified by rate of movement (from several centimetres a year or creep...to many miles per hour), type of material (bedrock, unconsolidated sediment, or organic debris) and nature of movement (slide, slump, flow or fall). Debris flows are fast moving flows of mud and rock and they are the most numerous and dangerous of all the landslides.  Debris flows generally occur during periods of intense rainfall or snow melt. They usually begin on the top of steep hills with saturated soil  as  they are so  dangerous because they move quickly,  destroy without  warning,  and  obliterate  everything  in  their  path.   They  can  destroy homes, knock down trees, and obstruct streets and roadways. [GEO2003]

Landslide monitoring system is useful in places that are prone to landslide especially on  a  hilly  or  mountainous  area.  The  developers  project  which  is entitled MCU-Based Landslide Monitoring System using GSM Technology includes the following features. The installation of GSM and alarm feature to give an early warning to the community, the alarm will trigger automatically through the use of a bionic horn that serves as a warning signal to the residents of a particular  community.  It will also send SMS notification to the registered number of the residents for them to have time to evacuate immediately.

1.1       Background of the Study

Landslides are not individual events, they occur in conjunction with other factors. Landslides occur when the hill or mountain side is unstable.

Factors that can allow gravity to overcome the resistance of earth material are: Erosion is the process by which soil and rock are removed from the Earth's surface by exogenetic processes such as wind or water flow, and then transported and deposited in other locations. Addition of moisture - Moisture equals weight and water from heavy rainfall, flooding, rapid snow melting, glacier melting, and an increased water table can all saturate the hillside and cause a landslide. El Nino, the weather phenomenon that can increase precipitation, led to thousands of landslides.   Shocks   and   Vibrations   -   Earthquakes,   typically   those   of   4.0 magnitudes and above, can create stresses that weaken slopes. Earthquakes tend to produce the largest and most destructive landslides. Overdevelopment - Human activities such as construction, building, transportation, building dams and canals,

and mining can disturb large volumes of earth materials. In fact, landslide damage is increasing every year as our population expands further into hilly regions. Deforestation - As the human population grows the demand for clear land for crops and housing grows too.

So forests, with trees that hold the soil in place, are logged, burned, and developed. And while this alone will usually not cause a landslide, the land becomes much more susceptible to heavy rains and floods and landslides can occur with much less rain than if a forest was still there. Wildfires, either natural or manmade, also have the same effect. [GEO2003]

There  are  six  (6)  types  of  landslide  debris  flow,  earth  flow,  debris landslide,   sturzstrom,   shallow   landslide   and   lastly   deep-seated   landslide. A debris flow is a form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water mobilize as slurry that flows down slope. It includes less than 50% fines. This type of landslide commonly caused by intense surface-water flow, due to heavy precipitation or rapid snowmelt, that erodes  and  mobilizes  loose  soil  or rock  on  steep  slopes.  Earth  flows  have  a characteristic  "hourglass"  shape.  The  slope  material  liquefies  and  runs  out, forming   a   bowl   or depression   at   the   head.   However,   dry   flows   of granular material  are  also  possible.  Debris  landslides  generally  start  with  big rocks that start at the top of the slide and begin to break apart as they slide towards the bottom. A sturzstrom is a rare, poorly understood type of landslide, typically with a long run-out. Often very large, these slides are unusually mobile, flowing very far over a low angle, flat, or even slightly uphill terrain. Shallow

landslide  in  which  the  sliding  surface  is  located  within  the  soil  mantle or weathered bedrock (typically to a depth from few decimeters to some meters). It can often happen in areas that have slopes with high permeable soils on top of low permeable bottom soils. And lastly deep-seated landslides in which the sliding surface  is  mostly deeply  located  below  the  maximum  rooting  depth  of  trees (typically to depths greater than ten meters)

There are also different soil types. All five is a combination of just three types of weathered rock particles that make up the soil: sand, silt, and clay. How these three particles are combined defines your soil’s type—how it feels to the touch, how it holds water, and how it’s managed, among other things.

1.   Sandy Soil has the largest particles among the different soil types. It’s dry and gritty to the touch, and because the particles have huge spaces between them, it can’t hold on to water. Water drains rapidly, straight through to places where the roots, particularly those of seedlings, cannot reach. Plants don’t have a chance of using the nutrients in sandy soil  more  efficiently as  they’re swiftly carried  away by the runoff. The upside to sandy soil is that it’s light to work with and warms much more quickly in the spring.