I would intuitively express, regardless of other factors or parameters, the more human intervention and modifications on the slopes are introduced, the more prone to sliding the slopes become........

I agree, but it can be challenging to quantify. Even besides human intervention that may cause slope failures, there's another issue. Landslide inventories provide a basis upon which to measure causes and effects of landslides, yet the data are usually biased by the observer's location (e.g., are there roads transportation routes that allow people to identify and document landslide?). More eyes on watch and more assets threatened mean that it's just more likely that a landslide that affects a road or populated area be cataloged than a landslide that happens dozens of kilometers away from sight or human impact. Can you link certain environmental characteristics of your study area to landslide occurrence, and do these characteristics differ with proximity to roads? Do you see a greater frequency or magnitude of landslides near roads, and does this mean that roads exacerbate the situation? Satellite image interpretation may help identify past landslides or looming threats.

I would say that it depends on geographical context, type of slide, and also the scale of analysis.

For my part of the world (Norway), I would say that within those areas where you find redundant roads and road density is high, slides are rare. Where the terrain is steep, the density of roads is low (little redundancy), and many types of rapid mass movement occur "frequently" (hitting roads 1000-2000 times a year). Quick clay slides, however, occur in quite flat terrain where road density may be high.

Analyzing one road, I would say that the less intersections, the higher the exposure to slides. Adding hairpin bends, exposure is even higher.

It is difficult to draw conclusions just from browsing, but take a look at this map service (Integrated database for rapid mass movements in Norway):

http://skredatlas.nve.no/ge/Viewer.aspx?Site=Skredatlas&MapType=Skredhendelser&Extent=-100000,6410000;1140000,7960000

I agree with you that if road density becomes too important, it may in someway armor the ground surface, as it tends to happen in highly urbanized areas. But I keep thinking that as you increase slope intervention, the area should tend to destabilize. Untouched (more natural, which does not mean at all that it may not naturally slide down, like quick clays), it would tend to be more stable than modifying it.

An interesting issue mentioned by Eric is the bias on observation introduced by the fact that occurring along roads they may be more reported and counted than happening in open or virgin (meaning away from roads) areas. This last aspect should be overcome by using remote sensing!!!!!

Roads and vehicle density can act as a triggering factor for landslides. But the slope cutting activities for making or developing roads will be a direct factor for land slides in hilly areas. While considering the major causes of landslides such as heavy rain,steep slope,drainage density and frequency and land use land cover etc.. the road density relationship having a lesser importance

Thanking you,

Joice....

Dear colleague

It seems that you are dealing with vibrations that will work as a triggering mechanism to failure. Please, see the attached thesis that might be of help to you. Good luck

If you revise my first comment, I have indicated "regardless of any other parameter or factor". By this, we must assume that topographic modification in the comparison is the only and one factor taken into account. And this was done trying to give an answer to the original question.

Thank you for your response and suggestions. It was very useful discussion.

Let me know if I understand correctly. You are asking for a way to know the human risk (deaths, economicaly and in time of return to the operation) in the case of one of the slopes fail. Isn't it?

I am just working in the same, I hope to keep in touch with you.

Let me send you the next links for:

http://140.112.12.21/issmge/missing/scnotes.pdf

http://www.amazon.com/Assessment-Geotechnical-Engineering-Gordon-Fenton/dp/0470178205

http://www.infomine.com/library/publications/docs/Griffiths2011.pdf

By knowing the probability of failure and the probability of traffic (cars under the slope) you may have an idea of the consequences (deaths, economically and in time of return to the operation of the way).

It's also important to kow the volume of the landslide and the speed of it. You sholud know the volume with the analysis.

Dear colleague,

I just think that the relation between rainfall and the geology of the surface where the roads are located are factors of high influence. In our island, Mallorca, we have a road network in the mountains that is scarce but yearly the same spots are afected by landslides triggered when high amounts of rain fell in few hours so I think is more a problem of precipitation and geology that a problem of road density.

In my experience, one of the main impacts of roads on landslides is improper drainange control. Landslides result when water is "pirated" from one basin to another due to plugged culverts, poor cross-drains, long ditchlines, etc. Other important contributors include side-casting, and undercutting slopes - cut and fill issues.

I agree with Marten. Surface water and seepage contributes to the landslides. Roads should have table drains and culverts and catch drains and batter drains should be on the slopes to direct the water. Steep slopes is also prone to landslides.

Dear Ramesh,

As Marten told, the roads usually don't generate directly impacts to the stability of soil/rocks (of course if respected regular physical stability rules), but change the drainage systems and when this changes are not properly you can induce the water concentration and trigger a landslides.