Kinematic Analysis Markland_plot1
Transcript of Kinematic Analysis Markland_plot1
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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.
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