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Enhancements for the DOST-KASC Landslide Susceptibility

Assessment Procedure

Daniel C. Peckley Jr., PhDGeotechnical Engineering Group, Institute of Civil Engineering

University of the Philippines - Diliman

Outline

1) Realities that led to the conduct of the DOST-KASC Landslides Project

2) Overview of the DOST-KASC Landslides Project and Landslide Assessment Procedure

3) Realities and insights requiring enhancements for the DOST-KASC Landslide Assessment Procedure

4) Proposed enhancements

Realities that led to the DOST-KASC Landslide Study (1/2)

• More than 98% of rain-induced landslides are shallow-depth landslides.

• The poor and disadvantaged are the most vulnerable to any natural disasters, rain-induced landslides included:

- lack or poor understanding of the susceptibility of their communities to landslides

- limited choices, e.g. place to settle

- limited or no capacity to adapt or use technologies to protect themselves

Realities that led to the DOST-KASC Landslide Study (2/2)

• LGUs and community leaders also have very limited understanding of landslide susceptibility

• Although a prevalent problem, there are very few geologists and engineers knowledgeable on landslide susceptibility assessment, especially site-specific assessments and detailed investigations.

DOST-KASC Landslides ProjectMain objective: development of site-specific but simple, graphical hazard

assessment procedure for rain-induced, shallow-depth landslides.

1.1 Peer-reviewed by a committee of

local experts involved in landslide

studies and/or actual mitigation works

and the Disaster Response Hyperbase

(DRH) of Japan NIED-EDM

1.2 Pilot-tested in 8 communities

affected by landslides due to Typhoon

Pepeng (2009)

1.3 Used in training-seminars organized

by:

a) CIERDEC and NEDA-CAR

b) Community and Family Services

International (CFSI) together with the UN

High Commission on Refugees (UN-

HCR)

c) Other NGOs in Luzon

Survey of Landslide and Imminent Landslide Sites

Landslide data on which the procedure is based:

geotechnical surveys of around 243 landslide and

imminent landslide sites >> 60 sites planned.

Include sites hit by Typhoon Pepeng in Mt. Province, Benguet and Baguio City:

Conferences and Workshops- KASC with LGUs in Kalinga & other CAR-SUCs, 6 Nov 2009

- Earthquake Exposure and Vulnerability Workshop by PHIVOLCS and

Geoscience Australia, 14 Nov 2009

- PICE-DMAPS at the 35th PICE National Convention in Baguio City, 28

Nov 2009

- 2nd Regional Conference on Geo-Disaster Mitigation in ASEAN, Bali

Indonesia, 25 Feb 2010

- 2nd UNESCO-IHP & DRH Workshop , Hanoi, Nov. 9, 2010;

Published online on the DRH Website, maintained by the DPRI, Kyoto

UniversityPICE-DMAPS – 35th PICE Nat’l Convention Hands-on demonstration of SWST

Takes off from fundamental idea that capacity or strength S should always

be greater than the applied load L:

(S>L or Fs = S/L > 1)

Bridge capacity or strength = 30T

Weight of truck or load = 25TFs = = 1.2 Bridge capacity or strength = 30T

Weight of truck or load = 36TFs = = 0.8

a,slope angle = 15o, aRating = 2

Clayey soil, SRating = 5

SRating = 5

aRating = 2Fsbasic = = 2.5

a, slope angle = 32o,

aRating = 8

Clayey soil,

SRating = 5

Tension cracks

SRating = 5


Susceptibility assessment procedure (1/8)

10o,

SRatings for soils were quite easy to establish; significant amount of data

on f and cohesion c of soils.

For granular materials, e.g. sand, gravel and non-plastic silt,

Fs = tanf/tanα

f – angle of friction

α – angle of slope


SRating: an index related to the f and cohesion c of the

slope material

aRating: an index related the angle slope a

α

Fs = SRating/αRating,

HR3: Highly fractured and disturbed hard rock

For rocks, mass strength is primarily characterized by the cracks and discontinuities present in the rock mass and its intact rock strength.


hard rock – as hard or harder than

concrete; penetration by 4”

common wire nail with a

hammer is not possible.

size of blocks mostly between

10cm (4inches) to 60cm

(around 2ft)

SRating = 25


Determining the SRating for rock masses:

- Used the Hoek-Brown Criterion (2002) to obtain equivalent angles of friction f and cohesion c.

Hoek-Brown criterion parameters:

1) Geologic strength index (GSI) – based on the

extent and characteristics of discontinuities

present in the rock mass

2) Intact strength si

3) Disturbance factor D

equivalent angles of friction f and cohesion c

Thus, for both soils and rocks, SRating is derived from f and c.

Rock mass strength rating, SRating

Slope material: Rocks SRating

HR1: Massive & intact hard rock, s > 2m 100

HR2: Blocky, well-interlocked hard rock, 0.6m<s< 2m 45

HR3: Highly fractured hard rock, 0.1m < s < 0.6m 25

HR4: Disintegrated, protruding rocks & boulders

(may include soft rock fragments)

13

SR1: Massive & intact soft rock 30

SR2: Fractured soft rock 15


Soil mass strength rating, SRating

Slope material: Soils SRating

HS1: Stiff, dense gravelly, sandy, silty and clayey soils

(with significant amount of cementation)

25

SS1: Gravelly soils 10

SS2: Sandy soils 8

SS3: Silty/clayey soils 5


Slope rating, αRating

Range Mean αRating

α ≥ 75° (or with overhang) 82.5° 100

60° ≤ α < 75° 67.5° 32

45° ≤ α < 60° 52.5° 17

30° ≤ α < 45° 37.5° 10

15 ≤ α < 30° 22.5° 5

α ≤ 15° 7.5° 2

a,slope angle

clayey soil

5m

soil sampling points

10m

No drainage

Road

10m


Fs considering other factors:

Fsbasic = SRating/αRating, if only slope angle and material were considered.

To consider other factors:

Fs = vFactor*fFactor*(SRating – sRed – dRed) lFactor* αRating

vFactor – vegetationfFactor – occurrence or signs of failuresRed – reduction when spring/s can be found on the slopedRed – reduction when drainage condition is poorlFactor – present land use (increase in load)


To make the procedure easy to understand:

(1) Always started with the simple idea that capacity or strength

S should always be greater than the applied load L:

(S>L or Fs = S/L > 1)

Bridge capacity or strength = 30T

Weight of truck or load = 25TFs = = 1.2 Bridge capacity or strength = 30T

Weight of truck or load = 36TFs = = 0.8

a,slope angle = 15o, aRating = 2

Clayey soil, SRating = 5

SRating = 5


a, slope angle = 32o,

aRating = 8

Clayey soil,

SRating = 5

Tension cracks

SRating = 5


HR3: Highly fractured and disturbed hard rock

hard rock – as hard or harder than

concrete; penetration by 4”

common wire nail with a

hammer is not possible.

size of blocks mostly between

10cm (4inches) to 60cm

(around 2ft)

SRating = 25

2) Prepared figures and photos, which served as visual aids in

classifying rocks and soils

Photos - HR3: Highly fractured and disturbed hard rock

3) Used simple terminologies that they can easily relate with, e.g.

the definition of hard rock

hard rock – as hard or

harder than concrete;

penetration by 4” common

wire nail with a hammer is

not possible.

size of blocks mostly

between 60cm (2ft)

to 2m (around 6ft)

SRating = 45

HR2: Blocky, well-interlocked hard rock

The folded-paper technique to measure α

4) Introduced simple tools and procedures to determine

assessment parameters, e.g. measuring the slope angle α

5) Communicated with community members in the vernacular

6) In training-seminars, participants were given the opportunity

to actually apply the procedure and to present the results to

other participants and the trainers/facilitators for feedback and

comments

Validation/Levels of Stability

Factor of Stability FsNo. of

sites

No. of

sites that

failed

%age

failure

Fs > 1.2: Stable 5 0 0

1.0 < Fs < 1.2: Marginally stable 7 0 0

0.7 < Fs < 1.0: Susceptible 38 27 71%

Fs < 0.7: Highly susceptible 193 184 95%

Total 243 211 87%

To make them appreciate the proposed procedure more,

validation of the assessment procedure with data from 243

landslide and imminent landslide sites, was presented.

Realities and insights requiring enhancements for the DOST-KASC Landslide Assessment Procedure

1) Landslide disaster reduction and mitigation does not end in

assessments and investigations!

2) Based on these assessments and investigations, a menu or

alternatives of site-specific, practical and cost-effective

mitigation measures should be identified. In landslide

disaster mitigation, there is no such thing as a one-size-fits-

all solution.

3) Costs and capacity to implement and adapt mitigation

measures are primary considerations.

4) Very few engineers are knowledgeable and experienced in

designing and implementing practical and cost-effective

mitigation measures. They have no local guidelines to follow

and are unaware of the limitations of these mitigation

measures.

Proposed Enhancements (1/2)

1) Enhance or upgrade the procedure into Guidelines:

1.a) more detailed site-specific assessments and

investigations

1.b) design and implementation of mitigation measures

considering local conditions

1.c) ballpark and detailed cost estimation

2) Enhancements should be a collaborative work among

2.a) Geologists and geotechnical engineers

2.b) Research institutions: NIGS, UP-ICE, Others

2.c) Concerned government line agencies:

2.c.1) DPWH

2.c.2) DENR-MGB

2.c.3) DOST: PHIVOLCS, PAGASA

Proposed Enhancements (2/2)

3) Emphasis now should be on mitigation measures

- practical and cost-effective

- explore and pilot-test the use of commonly available

construction materials, e.g., cyclone wires

- users have the capacity to adapt and use new

technologies

4) Widespread introduction and implementation among

LGUs and communities vulnerable to landslides

Thank you very much

Courtesy of Dr. Daag, PHIVOLCS

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