3.Assessment of Geotechnical Hazard
    3.1.Assessment of Slope Instability
      3.1.1.Criteria to assess Slope Instability induced by Seismic Ground Motion
        (1)Input/Output
        1. Pre-condition
              1. Assessment of “slope failure hazard induced by seismic ground motion” by local government
        2. Input Data
              1. Assessment result of “slope failure hazard induced by seismic ground motion” by local government
              2. Peak ground acceleration
        3. Output Data
              1. Hazard rank of slope collapse (A/B/C)
        (2)Outline of the Method

        Based on the result that statistically investigated the past example of slope collapse induced by seismic ground motion, criteria to assess slope instability induced by seismic ground motion was created and hazard of each steep slope has been assessed with it. In this judgment table, JMA (Japan Meteorological Agency) seismic intensity of 5+ or 6- is assumed as input earthquake motion. Therefore, the assessment standards are created in consideration of the difference in the strength of earthquake motion in the earthquake damage assessment of local governments in Japan.

        Although the criteria consist of "factor element", "management element", and "reference element", only "factor element" and "management element" are used for hazard assessment in the earthquake damage assessment.

        　

        　

        Table 3.1.1 Criteria to assess slope instability induced by seismic ground motion
        (factor element)

        Item
        Situation
        Note
        　 Score
        (1)

        Height (H)

        [m]
        H<10
        3
        		 　
        10<=H<30
        7
        30<=H<50
        8
        50<=H
        10
        (2)

        Inclination

        ()

        		      <1:1.0
        1
        		 　
        1:1.0≦＜1:0.6
        4
        1:0.6≦
        7
        (3)

        Overhang
        Overhang of slope with structure
        7
        		 “Overhang” means rock slope etc. that is recognized as an overhang at a glance.
        Overhang of slope without structure
        4
        No
        0
        (4)

        Geology
        There are many boulder stones and unstable stones on the surface of a slope
        10
        		 When two or more items are applicable, use upper score. For example, the score may be ten for “soil” with many boulder stones and unstable stones on the surface.
        Cut slope has many boulders
        7
        Weathering alternation and cracks develop into the rock
        6
        Soil with gravel
        5
        Weathering alternated rock
        4
        Cracks developed rock
        4
        Soil
        4
        Clay
        1
        Rock without cracks
        0
        (5)

        Thickness of surface soil
        More than 0.5 m
        3
        		 Surface soil means humus and organic matter on the surface. When very loose collapsed rock exists under surface soil, the rock is contained in surface soil. 
        Less than 0.5 m
        0
        (6)

        Spring
        Exist
        2
        		 “Exist” means that spring always seen.
        Nothing
        0
        (7)

        Frequency of falling stone and collapse
        More than once a year
        5
        		 “falling stone and collapse” means slight falling stone, slope collapse, etc. of a grade which does not do damage to road traffic or a road structure
        Less than once a year
        3
        No
        0
        Total
        		 　 　

        　

        　

        Table 3.1.2 Criteria to assess slope instability induced by seismic ground motion
        (management element)

        Item
        Situation
        Note
        　 Score
        (8)
        Abnormalities of slope
        Exist
        a
        		 　
        Nothing
        c
        (9)
        Abnormalities of slope stabilize constriction
        Exist
        a
        Nothing
        c
        (10)
        Falling stone, collapse which did damage to the house etc.
        Exist
        a
        Nothing
        c
        (11)
        Detrimental act on a slope
        Remarkable
        a
        		 　
        A little
        b
        Nothing
        c

        Table 3.1.3 The assessment standard of slope failure hazard

        Total score of 7 Items of factor element
        13 or less
        14 - 23
        24 or more
        Management element

        (8) - (11)

        		 More than 1 (a)
        (A)
        (A)
        (A)
        1 (b) and 3 (c)
        (B)
        (A)
        (A)
        4(c)
        (C)
        (B)
        (A)

        Example: Assessment standard by Kanagawa Prefecture Office (1993)

        Primary slope failure hazard is assessed from the crosscheck of the totaling score of seven items of factor element, and four items of management element (Table 3.1.3). Final slope failure hazard is assessed from the ground acceleration and the result of primary assessment as shown in Table 3.1.4, which is decided from the example of the slope collapse caused by the 1978 Miyagi-ken-oki Earthquake.

        　

        Table 3.1.4 Hazard rank division with ground acceleration
        (Kanagawa Prefecture Office, 1993)

        Hazard rank

        Ground acceleration
        (C)
        (B)
        (A)
        More than 316 gal
        B
        A
        A
        141 - 316 gal
        C
        B
        45 - 141 gal
        C
        B
        Less than 45 gal
        C

        A: High hazard, B: Moderate hazard, C: Low hazard

        (3)Reference

        Kanagawa Prefecture Office (1993) Kanagawa-ken seibu zisin higai soutei chousa houkokusho (in Japanese. Webmaster translates the title “Report of earthquake damage assessment in Kanagawa Prefecture”).

      3.1.2.Kochi Prefecture Office (1993)
        (1)Input/Output
        1. Pre-condition
              1. Preparation of slope classification map
        2. Input Data
              1. Peak ground acceleration
        3. Output Data
              1. Collapse potential (Number of collapse)
        (2)Outline of the Method

        Sorimachi (1978) and Okuzono et al. (1980) have studied the relation between acceleration of earthquake motion and number of slope collapse caused by the 1978 Izu-ooshima-kinkai Earthquake. Kochi Prefecture Office (1993) assumed the number of slope collapse per square kilometers classified by acceleration as shown in Table 3.1.5 using above results, results of Tamura (1978), and collapse example caused by the 1946 Nankai Earthquake. The table shows collapse potential weighted by score according to acceleration.

        　

        Table 3.1.5 Assumed number of slope collapse per square kilometers classified by acceleration (slope steeper than 30 degrees)

        Acceleration
        		 Number of Collapse
        400 gal or more
        8
        350 gal - 400 gal
        6
        300 gal - 350 gal
        4
        250 gal - 300 gal
        2
        200 gal - 250 gal
        1
        Less than 200 gal
        0.2

        　

        As slopes collapse easily if an angle of inclination surpasses 40 degrees, the number of collapse in the area of 40 degrees or more in the collapse example of the 1964 Niigata Earthquake was doubled.

        (3)Note

        Because the easiness of collapse is subject to local geology, this method is not compensated for other regions.

        (4)Reference

        Kochi Prefecture Office (1993) Kochi-ken zisin taisaku kiso chousa houkokusho (in Japanese. Webmaster translates the title “Report of earthquake damage assessment in Kochi Prefecture”).

        Okuzono, S., H. Haneda and K. Iwatake (1980) Study of slope collapses caused by earthquakes, Soil Mechanics and Foundation Engineering, 28, 45-51 (in Japanese with English abstract).

        Sorimachi, Y. (1978) Zisin ni yoru shamen houkai no jittai, Civil Engineering Journal, 20, 30-35 (in Japanese. Webmaster translates the title “Study of slope collapses caused by earthquakes”).

        Tamura, T. (1978) Zisin ni yori hyousou katuraku gata houkai ga hassei suru hanni ni tsuite, Geographical review of Japan, 51, 662-672 (in Japanese. Webmaster translates the title “Study on the extension of area with surface failure and landslide caused by earthquake”).

      　

      3.1.3.Fukuoka Prefecture Office (1997)

        (1)Input/Output
        1. Pre-condition
              1. Preparation of registers of steep slopes and collapse hazard area
        2. Input Data
              1. Inclination, Shape of slope, Vegetation, Knick line of slope in the registers
              2. Peak ground acceleration
        3. Output Data
              1. Slope collapse potential (A/B/C)
        (2)Outline of the Method

        Slope failure potential is assessed using registers of steep slopes and collapse hazard area.

        First, geomorphological and geological factors tending to generate collapse commonly caused by the three earthquakes (the 1964 Niigata Earthquake, the 1968 Ebino Earthquake, the 1975 Ooita-ken-chubu Earthquake) are selected as general properties of slope collapse using the result of Laboratory of Nihon Doro Kodan (1980, 1981) as shown Table 3.1.6.

        Second, weight (score) for peak ground acceleration is set as Table 3.1.7 by use of the relation between peak ground acceleration and collapse rate by Fire and Marine Insurance Rating Association of Japan (1994).

        At the last, slope collapse potential is classified as Table 3.1.8 from collapse examples caused by the above three past earthquakes.

        　

        Table 3.1.6 Geomorphological and geological factors which influence earthquake collapse and score (Fukuoka Prefecture Office, 1997)

        Item
        Situation
        Score
        Inclination
        - 10 [degrees]
        -5
        11 - 20 [degrees]
        -3
        21 - 30 [degrees]
        -1
        31 - 40 [degrees]
        +1
        41 - 50 [degrees]
        +2
        51 - 60 [degrees]
        +3
        61 - [degrees]
        +5
        Shape of slope
        Convex
        +2
        Flat
        -2
        Concave
        -3
        Vegetation
        Bare ground
        +3
        Broadleaf tree
        +1
        Needle-leaf tree
        -1
        Knick line
        Exist
        +2
        No
        -2

        　

        Table 3.1.7 The score to the level of peak ground acceleration influencing earthquake collapse (Fukuoka Prefecture Office, 1997)

        Peak ground acceleration a [gal]
        Score
        0<=a< 100 
        -5
        100<=a< 250
        -4
        250<=a< 350
        -3
        350<=a< 450
        -2
        450<=a< 550
        -1
        550<=a< 700
        +1
        700<=a< 800
        +2
        800<=a< 900
        +3
        900<=a<1,000
        +4
        1,000<=a
        +5

        　

        Table 3.1.8 Slope collapse potential and collapse rate (Fukuoka Prefecture Office, 1997)

        Rank
        Score
        Potential 
        Collapse rate caused by three earthquakes
        A
        -1 or more
        High
        77 %
        B
        -6 to -2
        Relatively high
        48 %
        C
        -7 or less
        Low
        22 %

        (3)Note

        Because the easiness of collapse is subject to local geology, this method is not compensated for other regions.

        (4)Reference

        Fukuoka Prefecture Office (1997) Zisin ni kansuru bousai assessment chousa houkokusho(in Japanese. Webmaster translates the title “Report of earthquake damage assessment in Fukuoka Prefecture”).

        Laboratory of Nihon Doro Kodan (1980) Zisin ni yoru kiken shamen chushutsu no tame no chousa (in Japanese. Webmaster translates the title “Study for extraction of dangerous slope for seismic ground motion”).

        Laboratory of Nihon Doro Kodan (1981) Zisin saigai no chikei chishitsu teki youin bunseki chousa (in Japanese. Webmaster translates the title “Study for geomorphological or geological factor analysis of earthquake disaster”).

        Fire and Marine Insurance Rating Association of Japan (1994) Shamen kyu-keishachi no zisin ji no houkai higai ni kansuru kenkyu, Research Report for Earthquake Insurance No. 37 (in Japanese. Webmaster translates the title “Study on collapse of slopes and steep slopes induced by earthquake”).

    　

    　

    　

    3.2.Assessment of Ground Failure in Reclaimed Land

      3.2.1.Miyagi Prefecture Office (1988)
        (1)Input/Output
        1. Pre-condition
              1. Grasp of distribution of reclaimed area
        2. Input Data
              1. JMA (Japan Meteorological Agency) seismic intensity
              2. Thickness of filling
              3. Inclination of old geographical feature
        3. Output Data
              1. Damage rank (A/B/C/D)
        (2)Outline of the Method

        Miyagi Prefecture Office (1988) created damage judging standard based on results of an investigation of reclaimed area damage caused by the 1978 Miyagi-ken-oki Earthquake. The target-reclaimed area is a large-scale one for housing lots with an area of 10 or more hectares.

        Fig.3.2.1 Relation among the inclination of the old geographical feature, the thickness of filling and the extent of damage of house (Miyagi Prefecture Office, 1988)

        　

        Table 3.2.1 Damage judging standard of reclaimed area damage
        (Akita Prefecture Office, 1997)

        Classification
        JMA (Japan Meteorological Agency) Seismic intensity scale
        Less than 4-
        4+ to 5-
        5+
        6-
        6+ to 7
        1
        C
        B
        A
        2
        D
        C
        B
        A
        3
        D
        C
        B
        A
        4
        D
        C
        B

        　

        Table 3.2.2 Summary of Damage (Miyagi Prefecture Office, 1988)

        Level
        Damage 
        House 
        Underground object
        Ground
        A
        Heavy
        		 House collapsing Damage occurs Collapse or crack are seen
        B
        Moderate
        		 Possibility of house collapsing Possibility of damage Possibility of small crack, collapse etc.
        C
        Slight
        		 Low possibility of damage Possibility of damage depending on places Possibility of small collapse depending on places
        D
        No
        		 No damage No damage No damage

        (3)Note

        Because the easiness of collapse is subject to the construction method of reclaimed area, this method is not compensated for other regions.

        (4)Reference

        Akita Prefecture Office (1997) Akita-ken zisin higai soutei chousa houkokusho (in Japanese. Webmaster translates the title “Report of earthquake damage assessment in Akita Prefecture “).

        Miyagi Prefecture Office (1988) Miyagi-ken zisin higai soutei chousa (in Japanese. Webmaster translates the title “Report of earthquake damage assessment in Miyagi Prefecture”).