Severity Analysis.ppt

SEVERITY OF INSTABILITY AND REPAIR PRIORITIES

Repair priorities  Technical

capability  Financial status  Level of interest  Condition of people’s participation  Loss of lives and property  Cost benefit ratio  Other factors

Technical criteria for prioritization

Types of landslides depending on technical capability The sites that can be treated with the help of vegetative systems plus some light engineering to protect the young plants,  The sites that can be treated with small scale civil engineering structures in association with vegetative systems,  The sites that can be treated with civil engineering technology but that might be expensive, the risk of failure may be high, and  The sites that is not possible to stabilize or not worthwhile to treat. 

DEPTH OF FAILURE 

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Up to 25 mm -surface failure caused by erosion 25 - 100 mm -shallow mass failure, probably due to liquefaction of surface layers 100-250 mm -deeper mass failure that can involved water contributed both from infiltrating rain water and rising ground water 250-1000mm -deep mass failure probably to ground water pore pressure more than 1000mm -very deep mass failure due to, or assisted by, high ground water pore pressure

LENGTH OF FAILURE  Up

to 15 m  15 - 75 m  75 - 150 m  more than 150

- minor failure - substantial failure - large failure m - major failure

HISTORY OF SLIDE

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Not moved within the last 5 years -Old slope, may now be stable , unless disturbed by road construction Moved this year for the first time - Active failure, further development may be very difficult to assess Moved within the last 5 years but not this year Recent failure, at present inactive Moved every year by initial mechanism diminishing -Continual failure, but holds possibilities for improvement by remedial works Moved every year by initial mechanism-constant or getting worse - Continual failure with little or no possibilities for further improvement

LIFE PROGRESSION OF SLIDE  Stable

slope formed, or stabilise naturally  further movement expected, by less serious mechanism  Repeated movement expected, by initial mechanism or other equally serious

Procedure for setting priorities  High

priority is given to those sites if Repair is considered feasible by vegetation or vegetation in conjunction with small scale civil engineering structures.  Less priority is given to those sites If repair is feasible by medium scale or large scale standard civil engineering methods.

Prioritization History Life progression

No movement in last 5 years

Moved this year for the first time

Moved within last 5 years but not this year

Moves every year by initial mechanism – diminishing

Moves every year by initial mechanism -constant or worsening

Stable slope formed, or will stabilize naturally

Priority 4 no need may be help

Priority 4 no need may be help

Priority 4 help to stabilize

Priority 2

-

Repeating by less serious mechanism

Priority 2

Priority 3

Priority 2

Priority 1

-

Repeating by same or worse mechanism

-

As per depth of failure

As per depth of failure

As per depth of failure

Civil engineerin g only

Prioritization based on depth of failure Depth of failure

Mechanism

Priority

Less than 25 mm.

Erosion

1

25-100mm.

Shallow flow

1

100-250mm.

Deep flow or shallow slide

2+ civil engineering works

250-1000mm

Medium depth slide

NA-civil engineering works alone

More than 1000mm

Deep slide

NA-civil engineering works alone

Scoring system Factors

Land slides 1 2 3 .. .. .. .. .. ..

Remarks

Thank you!