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    Kinematic analysis for sliding failure of multi-faced rock slopes

    W.S. Yoon, U.J. Jeong, J.H. Kim *

    School of Earth and Environmental Sciences, Seoul National University, San 56-1, Shilim-dong, Kwanak-gu, Seoul, 151-742, South Korea

    Received 3 October 2001; accepted 29 April 2002

    Abstract

    Most kinematic analyses for rock slope stability have dealt with single-faced slopes (SFS) with a planar surface of a constant

    strike. However, there are many slopes with non-planar surfaces along road cuts and in open pits, etc. Multi-faced slopes (MFS)

    consist of two or more faces with different strikes. Multi-faced slopes have different sliding conditions compared to single-faced

    slopes because of their geometrical characteristics, i.e. convex surface on plan view. On stereographic projection, a sliding

    envelope of a multi-faced slope is a union of envelopes of individual faces formed on the slope surface. Sliding modes of multi-

    faced slopes are divided into two types and they are subdivided into two modes, respectively; Type 1 single or double plane

    sliding and Type 2 single or double plane sliding. Type 1 sliding failures are controlled by the same rule as the single-faced

    slopes as suggested by Hocking [Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 13 (1976) 225]. Type 2 sliding failures can

    occur on multi-faced slopes only. A Type 2 sliding block must have two or more adjacent slope faces. Though two joint sets

    must be developed for Type 1 sliding, Type 2 single plane sliding can occur with only one joint plane in the multi-faced slopes.

    A simple Type 2 single sliding block is composed of one joint plane, two slope faces and the upper natural slope surface. If twojoint planes act as sliding planes for plane failures at two adjacent faces of a multi-faced slope, they form a block of Type 2

    double plane sliding in the slope. On a stereographic projection, a Type 2 sliding zone is defined as the area between the true dip

    lines of two side-slope faces in the sliding envelope of a multi-faced slope. If the true dip lines of one or two joint planes plot

    within a Type 2 sliding zone, Type 2 sliding failure can be possible. D 2002 Elsevier Science B.V. All rights reserved.

    Keywords: Kinematic analysis; Rock slope; Single-faced slope; Multi-faced slope; Stereographic projection

    1. Introduction

    Kinematic analysis, which is purely geometric,

    examines which modes of slope failure are possible

    in a jointed rock mass. Angular relationships between

    discontinuities and slope surfaces are applied to

    determine the potential and modes of failures (Kliche,

    1999). Numerous studies (Markland, 1972; Goodman,

    1976; Hocking, 1976; Cruden, 1978; Lucas, 1980;Hoek and Bray, 1981; Matherson, 1988) have been

    performed to determine failure modes utilizing stereo-

    graphic projection technique since Panet (1969).

    The Markland test (Markland, 1972) is one of the

    kinematic analysis methods designated to evaluate the

    possibility of wedge failure. A refinement to Mar-

    klands test has been discussed by Hocking (1976).

    He differentiated the sliding along one plane (single

    plane sliding) forming the base of the wedge from the

    sliding along the line of intersection of two joints

    0013-7952/02/$ - see front matterD 2002 Elsevier Science B.V. All rights reserved.P I I : S 0 0 1 3 - 7 9 5 2 ( 0 2 ) 0 0 1 4 4 - 8

    * Corresponding author. Tel.: +82-2-880-6733; fax: +82-2-871-

    3269.

    E-mail address: [email protected] (J.H. Kim).

    www.elsevier.com/locate/enggeo

    Engineering Geology 67 (2002) 5161

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    (double plane sliding). Most methods including Mar-

    klands test are restricted to rock slopes with a con-

    stant strike. Even though the angle of the natural slope

    (upper slope surface) has no fundamental effect on thekinematical stability of a slope, it has been used in

    kinematic analysis (Ocal and Ozgenoglu, 1997).

    If a slope surface has a constant strike, section view

    is more important rather than the geometry on plan

    view. However, many rock slopes consist of several

    faces with different strikes. If upper natural slopes are

    not considered, single-faced slopes (SFS) can be

    defined as slopes having only one face with a constant

    strike, and multi-faced slopes (MFS) can be defined as

    slopes having two or more faces with different strikes.

    Convex- and concave-shaped slopes on plan views are

    defined as positive and negative MFSs, respectively.

    This paper deals with positive MFSs.

    MFSs have different sliding conditions from the

    SFSs because of their geometrical characteristics. For

    example, two or more joint sets are necessary for

    sliding failures of SFSs. These joint sets act as sliding

    planes or release surfaces of sliding blocks. Even if

    only one joint plane is developed, sliding failure can

    occur in MFSs because this joint can intersect two

    conjoined slope faces acted as lateral boundaries of

    sliding block. Therefore, upper natural slope angles on

    section views can be negligible for estimating thestability of rock slopes, but geometries of slope

    surfaces on plan views must be considered to deter-

    mine failure modes and potential. However, many

    MFSs have been analyzed as for SFSs in the processes

    of stability analysis.

    The aims of this paper are: (1) to describe sliding

    modes of MFSs compared with SFSs, and (2) to

    suggest a method of kinematic analysis for MFSs

    based on the Markland test. A real example of MFS

    is subjected to stability analysis.

    2. Sliding failure of single-faced slopes (SFS)

    The wedge failure is a common type in jointed rock

    slopes. Markland (1972) proposed that wedge failures

    occur along the lines of intersection of joints and

    hence, these intersections must daylight in the slope

    faces. In order for the line of intersection to daylight,

    the plunge of the intersection should be less than the

    dip angle of the slope face measured along the trend

    of the intersection. In addition, the plunge of the

    intersection must exceed the friction angle of the joint

    planes.

    In the Markland test (Markland, 1972), the greatcircle of a slope face (SL in Fig. 1) and the circle of

    the friction angle, /, of the joint are plotted on a

    stereographic projection. The zone (the thick-lined

    envelope in Fig. 1) between the great circle (SL)

    and the friction circle is called the sliding envelope.

    This sliding envelope represents Marklands wedge

    failure conditions, i.e. plunge of intersection of the

    joints is less than slope angle and greater than friction

    angle of the joint. If the intersection (L12 in Fig. 1) of

    the two joints (J1 and J2, dotted great circles in Fig. 1)

    is located in the sliding envelope, the wedge failure is

    possible.

    Hocking (1976) divided wedge failures into two

    modes in term of sliding planes of wedges. One is

    single plane sliding (so-called plane failure), and the

    other is double plane sliding which is the general form

    of wedge failure suggested by Markland (1972). If

    two joint planes bound a sliding wedge, single plane

    sliding (upper part of Fig. 1a) is defined as a sliding

    on only one of the joints bounding the base of the

    wedge, but the double plane sliding (upper part of Fig.

    1b) is defined as a sliding on both joint planes parallel

    to the line of intersection. If the true dip (L1) of either(J1) of the joint planes lies within the shaded area

    between the line of intersection (L12) and true dip of

    slope face (LSL), as shown in lower part ofFig. 1a, the

    single plane sliding can occur (Hocking, 1976). Cru-

    den (1978) suggested that if true dip of either or both

    wedge-forming joint planes fall into the area, the

    sliding mode of the wedge is a single plane sliding.

    However, if the line of intersection (L12) locates in the

    sliding envelope and both L1 and L2 lie outside the

    area (shaded area in lower part ofFig. 1b), the double

    plane sliding can occur.Hoek and Bray (1981) proposed two general con-

    ditions of a plane failure by single plane sliding, (1)

    the strike of sliding plane must be parallel or nearly

    parallel (F 20j) to the slope face, and (2) release

    surfaces must be present in the rock mass to define the

    lateral boundaries of the slide. The second condition is

    a critical condition of the plane failure. If the release

    surface does not exist, single plane sliding cannot

    occur, though the strike of sliding plane is parallel to

    the slope face. These release surfaces can be divided

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    into two types: (1) joint planes that intersect the

    sliding plane and (2) free faces that intersect the slope

    surface. These release surfaces lead to differences in

    sliding possibilities between SFSs and MFSs. In

    SFSs, joint planes act as the release surfaces, whereas

    individual faces as well as joint planes can act as the

    release surfaces in MFSs.

    3. Sliding failures of multi-faced slopes (MFS)

    3.1. Sliding modes of MFS

    Various modes of failure can occur in MFSs as

    shown in Fig. 2. Single plane sliding (Fig. 2a) released

    by other intersected joint plane is called Type 1 single

    plane sliding. This type of sliding complies with the

    Hocking single plane sliding rule. Fig. 2b shows a

    sliding block formed by only one joint plane without

    any intersected joints. This single plane failure can

    occur because two adjacent faces act as free faces for a

    sliding block. Single plane sliding without the pres-

    ence of any other joint plane can be defined as Type 2

    single plane sliding. The sliding block of Type 2

    single plane sliding must be bounded by two or more

    slope faces and upper natural slope surface.Double plane sliding in MFSs has different char-

    acteristics when compared with double plane sliding

    in SFSs. If one joint is a potential sliding plane of

    single plane sliding in one face and the other joint is a

    potential sliding plane of single plane sliding in an

    adjacent face, double plane sliding along the inter-

    section of two joint planes can occur (Fig. 2d). This

    double plane sliding is called Type 2 double plane

    sliding in MFSs, and Hockings double plane sliding

    for SFSs (Fig. 2c) called Type 1 double plane sliding.

    Fig. 1. Hockings (1976) stereographic solution for sliding of a single-faced slope. (a) Single plane sliding. The sliding direction (thick arrow) of

    the sliding block is same as L1. (b) Double plane sliding. The sliding direction (thick arrow) of the sliding block is same as L 12. SL, great circle

    of slope face; J1 and J2, great circles of joint planes; LSL, true dip of slope face; L1 and L2, true dip lines of J1 and J2; L12, line of intersectionbetween J1 and J2; /= 30j, friction angle of joint planes.

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    Therefore, sliding modes of MFSs can be dividedinto two types: Type 1 single and double plane sliding

    and Type 2 single and double plane sliding. In case of

    Type 1 sliding blocks, two wedge-forming joint planes

    must be necessary, but the number of slope faces is not

    important. For Type 2 sliding, at least two slope faces

    are necessary. If upper slope surface (or natural slope

    surface) is not considered, boundary conditions of

    sliding blocks are summarized as follows:

    Type 1 single or double plane sliding block: two

    joint planes and one slope face (Fig. 2a and c).Type 2 single plane sliding block: one joint plane

    and two slope faces (Fig. 2b).

    Type 2 double plane sliding block: two joint planes

    and two slope faces (Fig. 2d).

    3.2. Stereographic projection technique for simple

    multi-faced slopes

    Fig. 3 is an example of kinematic analysis using

    stereographic projection technique for two-faced

    slopes with different sliding modes. A two-faced slopeis the simplest MFS. The surfaces of a two-faced slope

    form a triangular shape between the two ends (S and SV

    in the middle part ofFig. 3) in plan views. The straight

    line connecting the two ends (S and SV) is defined as

    mean slope line (MS, the dashed line in Fig. 3). RS and

    LS in Fig. 3 are the side-slope faces. The side-slope

    face with a positive side-slope orientation angle meas-

    ured clockwise from MS is called a left side-slope face

    (LS), and the face with a negative side-slope orienta-

    tion angle is called a right side-slope face (RS) in this

    paper. The side-slope orientation angles (a and b in themiddle part of Fig. 3) are defined as the acute angles

    between the strikes of side-slope faces and MS. The

    clockwise angle measured from MS has a positive

    value. MS of the example in Fig. 3 trends EW, and the

    latitudes of LS and RS are N45jW/60jSW and

    N60jE/60jSE, respectively. The side-slope orientation

    angle of LS is 45j (a), and the angle of RS is 30j

    (b). Friction angle of all joints is assumed as 30j.

    In the kinematic analysis, individual faces of the

    MFS keep on their sliding envelopes because all faces

    Fig. 2. Sliding modes of a multi-faced slope (a rectangular three-faced slope) can be divided into two types which are subdivided into two

    modes, respectively. (a) Type 1 single plane sliding and (b) Type 2 single plane sliding. (c) Type 1 double plane sliding and (d) Type 2 double

    plane sliding. Type 2 sliding blocks (c and d) must be bounded by two or more slope faces.

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    are controlled by Hockings rule like a SFS. There-

    fore, the sliding envelope of a MFS is the union of

    envelopes of individual faces forming the slope sur-

    face. In Fig. 3, the sliding envelope (thick-lined) iscomposed of the envelopes of LS and RS. If the

    absolute values of the two side-slope orientation

    angles are increased, the area of the sliding envelope

    is increased.

    Fig. 3a shows the Type 1 single plane sliding

    condition of the two-faced slope. If one (or both) true

    dip of one (or both) of the wedge-forming joints lies

    within the shaded area, bounded by the trend of the line

    of intersection and the true dip line of any face, the Type

    1 single plane sliding is possible (see Fig. 1a).

    In lower part of Fig. 3a, the intersection (L12) of

    two joint planes (J1 and J2) is located within the

    sliding envelope (thick-lined) of the two-faced slope,

    and the true dip line (L1) of J1 joint plane plots in the

    shaded area between L12 and true dip line (LRS) of RS.

    This indicates that Type 1 single plane sliding on J1joint plane can occur within RS.

    Even if only one joint plane is developed in a MFS,

    Type 2 single plane sliding can be possible. Fig. 3b

    shows Type 2 single plane sliding of a two-faced

    slope. The Type 2 sliding block(Fig. 3b) is formed by

    one joint plane (J1) and two side-slope faces in the

    plan view. In order that a sliding block is formed byone joint plane and two or more faces, the acute angle

    (h1 of Fig. 3b) between the strike of the sliding plane

    (J1, dotted line) and MS (dashed line) should lie

    be tw ee n th e tw o si de -s lo pe or ie nt at io n an gl es

    (b< h< a). h has a positive value when measured

    CW from MS. Additionally, the sliding plane should

    daylight in the MFS, and its dip angle should be larger

    than the friction angle.

    In Fig. 3b, h1 is 15j and Type 2 single plane

    sliding on J1 can occur because h1 lies between the

    two side-slope orientation angles; b (

    30j

    ) < h1(15j) < a (45j). Type 2 single plane sliding cannot

    occur within the slope in Fig. 3a because the angle

    (h1 = 45j) of the sliding plane (J1) for Type 1 single

    plane sliding is smaller than a and b; h1 ( 45j) < b

    ( 30j) < a (45j).

    This orientation condition for Type 2 single plane

    sliding can be represented as a Type 2 sliding zone on

    a stereographic projection. If h1 lies between the two

    side-slope angles (b < h < a), the true dip of J1 plots

    within the area between true dip lines of two side-

    slope faces. This area is defined as Type 2 sliding

    zone in this paper. If the true dip of a joint plane is

    plotted in the Type 2 sliding zone, single plane sliding

    can occur without any other joint plane.Type 1 double plane sliding within slopes is con-

    trolled by Hockings double plane sliding condition

    (see Fig. 1b). Fig. 3c shows the condition for Type 1

    double plane sliding for two-faced slopes. The boun-

    daries of the sliding block in Fig. 3c are two joint planes

    (J1 and J2) and one side-slope face (RS). The inter-

    section line (L12) is located within the sliding envelope

    of RS, and the true dip lines (L1 and L2) of the two joint

    planes (J1 and J2) lie outside the shaded area between

    L12 and true dip line (LLS or LRS) of any face (LS or

    RS). Type 1 double plane sliding on both joint planes

    can occur within RS of the two-faced slope.

    Type 2 double plane sliding has a different sliding

    condition from Type 1 double plane sliding. In Fig.

    3d, both joint planes for Type 2 double plane sliding

    can act as sliding planes for single plane sliding. If the

    two wedge-forming joint planes can respectively act

    as sliding planes for Type 1 single plane sliding within

    two adjacent slope faces, and the line of intersection

    also satisfies Type 1 double plane sliding, the block

    formed by the two joints and the two faces will slide

    on both joint planes along the line of intersection. For

    this Type 2 double plane sliding condition, the anglesh1 and h2 in Fig. 3d (the angles between strikes of the

    two joint planes (J1 and J2) and MS) must satisfy the

    following conditions: 0 < h1 < a, and b < h2 < 0. These

    conditions indicate that true dip lines of both joints

    will plot within the Type 2 sliding zone bounded by

    the two true dip lines of side-slope faces in sliding

    envelope on the stereo-net. For example, in Fig. 3d, if

    h1 = 30j and h2 = 20j, then 0< h1 (30j) < a (45j)

    and b ( 30j) < h2 ( 20j) < 0. The true dip lines (L1and L2) of the two wedge-forming joint planes (J1 and

    J2) and line of intersection (L12) are located within theType 2 sliding zone (shaded area), and L12 plots

    between L1 and L2.

    In Fig. 3d, J1 and J2 joint planes can act as sliding

    planes of Type 1 single plane sliding for LS and RS,

    respectively. If the sliding block is formed by only or

    either of two joint planes, Type 2 single plane sliding

    will occur including both slope faces. However, if a

    sliding block is formed by two joint planes (J1 and J2)

    and two slope faces like in Fig. 3d, sliding does not

    occur on either of the two planes, but occur on both

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    planes along the line of intersection. This double

    plane sliding is a Type 2 double plane sliding.

    When two joint sets develop in an MFS rock mass,

    two or more different sliding modes can be possibleand these sliding modes have different conditions to

    those for SFS, because a MFS is composed of two or

    more slope faces.

    3.3. Stereographic projection technique for complex

    multi-faced slopes (MFSs)

    The stereographic overlay technique for two-facedslopes (Fig. 3) can be applied to more complicated

    MFS using the same method. Fig. 4 shows examples

    of three-faced (Fig. 4a) and round-faced (Fig. 4b)

    Fig. 3. Sliding modes (upper), plan views (middle) and stereographic projections (lower) for a two-faced slope (SSV). (a) Type 1 single plane

    sliding. The sliding block is formed by J1, J2 and RS. (b) Type 2 single plane sliding. The sliding block is formed by J1, LS and RS. (c) Type 1

    double plane sliding. The sliding block is formed by J1, J2 and RS. (d) Type 2 double plane sliding. The sliding block is formed by J1, J2, LS and

    RS. LS and RS, left and right side-slope faces; MS, mean slope line; a and b, side slope orientation angles of LS and RS; LLS and LRS, true dip

    lines of LS and RS; h1 and h2, angles between MS and strike lines of sliding planes (J1 and J2); sliding direction, a thick arrow. For key to other

    abbreviations, see Fig. 1.

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    slopes. These examples have the same side-slope

    orientation angles (a = 45j and b = 30j) and MS

    as the two-faced slopes in Fig. 3.

    Surface of a three-faced slope (Fig. 4a) consists of

    LS, RS and the central slope face (CS). Sliding enve-

    lope (thick-lined) of the three-faced slope is a union of

    the three envelopes of the three individual slope faces,

    and the Type 2 sliding zone is a shaded area between

    true dip lines of RS and LS in Fig. 4a.

    The surface of a round-faced slope has unlimited

    number of faces (Fig. 4b). The side-slope faces of this

    slope can be considered as the two tangential faces at

    two ends of the slope surface as shown in Fig. 4b. The

    sliding envelope (thick-lined) of a round-faced slope

    is a union of unlimited number of envelopes, and the

    Type 2 single plane sliding zone (shaded) is the area

    between dip direction lines of two tangential faces of

    the sliding envelope. If the orientations of the two

    Fig. 3 (continued).

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    side-slope angles (a and b) are constant, the sliding

    zone increases with an increase in the number of slopefaces.

    4. Case study

    To evaluate the proposed method, a fracture survey

    and kinematic analysis was carried out on the exposed

    rock slope faces in a quarry of Jurassic granite in

    Seoul, Korea, where building stones were quarried

    until 1979. Recently, this site has been developed for

    housing. However, sliding failures have occurred

    several times during re-excavation and site prepara-tion. A rock slope in Fig. 5 is an example of these.

    The rock slope has a steep-quarried surface with a

    gentle upper slope surface. The quarried surface (Fig.

    5) is a typical two-faced slope having LS and RS. The

    latitudes of LS and RS are N12jE/75jSE and

    N40jW/75jNE, respectively. The lengths of LS and

    RS are about 25 and 60 m, respectively. The trend of

    MS is N25jW, and side-slope orientation angles of LS

    and RS are 32j and 15j, respectively. Two joint

    sets are developed in the rock mass of the slope.

    Fig. 4. Stereographic projections for (a) a three-faced slope and (b) a round-face d slope. CS is the central slope face, and LCS is true dip of CS.

    The shaded area is a Type 2 sliding zone. For key to other abbreviations, see Fig. 3.

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    Latitudes of Set 1 joints (J1) and Set 2 joints (J2) are

    N14jW/43jNE and N82jW/75jSW, respectively.

    A major sliding failure occurred by single planesliding within both slope faces. This sliding block is

    formed by J1 (sliding plane) and two side-slope faces.

    This sliding is Type 2 single plane sliding on J1 plane.

    Sliding plane is partly intersected by another joint.

    J1 does not satisfy the plane failure condition

    (h

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    the Type 2 sliding zone (shaded area) between true dip

    lines, LLS and LRS, of the sliding envelope (Fig. 7).This result indicates that Type 2 single plane sliding

    on J1 joint planes can occur including both slope

    faces, as shown in Fig. 5. This case study shows that

    the suggested kinematic analysis method is a more

    effective method to determine characteristics (i.e.,

    modes, locality and potential, etc.) of sliding failures

    in multi-faced slopes.

    5. Conclusions

    A single-faced slope is straight in plan view, but a

    multi-faced slope, which consists of two or more

    faces, is not straight in plan view. This difference in

    surface geometries in plan view can trigger different

    sliding conditions related to boundary conditions of

    sliding blocks. Sliding modes and the stereographic

    projection technique for stability analysis of multi-

    faced slopes are as follows.

    (1) Sliding modes in multi-faced slopes are divided

    into two types based on number of slopes involved in

    Fig. 6. Kinematic analysis to estimate the sliding potential of the

    rock slope shown in Fig. 5 using the stereographic projection

    technique for single-faced slope. (a) Right slope (RS). Type 1 single

    plane sliding can occur on joint plane J1 (N14jW/43jNE). (b) Left

    slope (LS). Type 1 double plane sliding can occur along the line of

    intersection between joint planes J1 and J2 (N82jW/75jSW). For

    key to other abbreviations, see Fig. 3.

    Fig. 7. Kinematic analysis to estimate the sliding potential of the

    rock slope shown in Fig. 5 using the stereographic projection

    technique for multi-faced slope. Type 2 single plane sliding on joint

    plane J1 as well as Type 1 single plane sliding are possible. For key

    to other abbreviations, see Fig. 3.

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    sliding block formation which are further subdivided

    into two modes, respectively; Type 1 single and

    double plane sliding and Type 2 single and double

    plane sliding.(2) Type 1 single and double plane sliding are

    controlled by the same rules for single-faced slopes. A

    Type 1 sliding block has at least two wedge-forming

    joint planes.

    (3) Type 2 single and double plane sliding are

    controlled by the rules different than for single-faced

    slopes. A Type 2 sliding block involved at least the

    two slope faces, and two or more slope faces of the

    sliding block act as release surfaces. Type 2 single

    plane sliding can occur with only one joint plane and

    involves two or more faces of a multi-faced slope. For

    Type 2 double plane sliding, the intersection of the

    two wedge-forming joints must satisfy the Type 1

    double plane sliding condition, and the joints must

    satisfy the Type 1 single plane sliding condition on

    two adjacent slope faces, respectively.

    (4) On a stereographic projection, individual faces

    of a multi-faced slope have their own sliding enve-

    lopes. The sliding envelope of a multi-faced slope is

    defined as the union of the envelopes of individual

    faces forming the slope surface. If the absolute values

    of the two side-slope orientation angles and the

    number of faces of the multi-faced slope increase,the area of the sliding envelope increases.

    (5) On a stereographic projection, Type 2 sliding

    zone is defined as an area between true dip lines of the

    two side-slope faces of the sliding envelope. If one (or

    two) true dip line(s) of joint(s) is (are) plotted within

    the Type 2 sliding zone, Type 2 single (or double)

    plane sliding is possible, involving two or more faces

    of the multi-faced slope. This Type 2 sliding cannot be

    predicted by kinematic analysis technique developed

    for a single-faced slope.

    Acknowledgements

    This research was performed for the Natural

    Hazards Prevention Research Project, one of theCritical Technology-21 Programs, funded by the

    Ministry of Science and Technology of Korea. The

    BK 21 program through SEES has supported part of

    this study. We thank Dr. W.Y. Kim of KIGAM, Dr.

    Y.S. Kim and S.J. Yeo of SEES, Korea, Dr. J.R.

    Andrews of University of Southampton, UK and two

    anonymous reviewers for helpful comments.

    References

    Cruden, D.M., 1978. Discussion of G. Hockings paper A method

    for distinguishing between single and double plane sliding of

    tetrahedral wedges. Int. J. Rock Mech. Min. Sci. Geomech.

    Abstr. 15, 217.

    Goodman, R.E., 1976. Methods of Geological Engineering in Dis-

    continuous Rocks. West Publishing, San Francisco.

    Hocking, G., 1976. A method for distinguishing between single and

    double plane sliding of tetrahedral wedges. Int. J. Rock Mech.

    Min. Sci. Geomech. Abstr. 13, 225226.

    Hoek, E., Bray, J.W., 1981. Rock Slope Engineering Institution of

    Mining and Metallurgy, London.

    Kliche, C.A., 1999. Rock Slope Stability SME, Littleton, CO.

    Lucas, J.M., 1980. A general stereographic method for determining

    possible mode of failure of any tetrahedral rock wedge. Int. J.Rock Mech. Min. Sci. Geomech. Abstr. 17, 5761.

    Markland, J.T., 1972. A useful technique for estimating the stability

    of rock slopes when the rigid wedge sliding type of failure is

    expected. Imp. Coll. Rock Mech. Res. Rep. 19, 10.

    Matherson, G.D., 1988. The collection and use of field discontinuity

    data in rock slope design. Q. J. Eng. Geol. 22, 1930.

    Ocal, A., Ozgenoglu, A., 1997. Determination of sliding mode of

    tetrahedral wedges in jointed rock slopes. Rock Mech. Rock

    Eng. 30, 161165.

    Panet, M., 1969. Discussion on Graphical stability analysis of

    slopes in jointed rock. By K.W. John. J. Soil Mech. Found.

    Div., Proc. ASCE. 95 (SM2), 685686.

    W.S. Yoon et al. / Engineering Geology 67 (2002) 5161 61