Appendix C
The Spady Landslide: Soil Analysis, Pre- and Post-Slope Failure Analysis
* using the *
* Method of Slices *
* *
* Copyright (C) 1992 Ä 96 *
* Interactive Software Designs, Inc. *
* Moscow, ID 83843, U.S.A. *
* *
* All Rights Reserved *
* *
* Ver. 5.200 96 Ä 1265 *
******************************************
Problem Description : post 1997 stability analysis
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SEGMENT BOUNDARY COORDINATES
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10 SURFACE boundary segments
Segment x-left y-left x-right y-right Soil Unit
No. (ft) (ft) (ft) (ft) Below Segment
1 .0 .0 40.0 10.0 2
2 40.0 10.0 70.0 30.0 2
3 70.0 30.0 72.5 32.0 2
4 72.5 32.0 79.0 41.0 1
5 79.0 41.0 83.5 41.0 1
6 83.5 41.0 84.0 39.0 1
7 84.0 39.0 88.0 39.0 1
8 88.0 39.0 88.5 42.0 1
9 88.5 42.0 115.0 48.0 1
10 115.0 48.0 135.0 53.0 1
1 SUBSURFACE boundary segments
Segment x-left y-left x-right y-right Soil Unit
No. (ft) (ft) (ft) (ft) Below Segment
1 72.5 32.0 135.0 32.0 2
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ISOTROPIC Soil Parameters
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2 Soil unit(s) specified
Soil Unit Weight Cohesion Friction Pore Pressure Water
Unit Moist Sat. Intercept Angle Parameter Constant Surface
No. (pcf) (pcf) (psf) (deg) Ru (psf) No.
1 116.0 120.0 242.0 10.00 .000 .0 1
2 117.0 120.0 555.0 10.00 .000 .0 1
1 Water surface(s) have been specified
Unit weight of water = 62.40 (pcf)
Water Surface No. 1 specified by 3 coordinate points
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PHREATIC SURFACE,
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Point x-water y-water
No. (ft) (ft)
1 70.00 30.00
2 80.00 34.00
3 135.00 40.00
A critical failure surface searching method, using a random
technique for generating CIRCULAR surfaces has been specified.
20 trial surfaces will be generated and analyzed.
2 Surfaces initiate from each of 10 points equally spaced
along the ground surface between x = 30.0 ft
and x = 50.0 ft
Each surface terminates between x = 90.0 ft
and x = 120.0 ft
Unless further limitations were imposed, the minimum elevation
at which a surface extends is y = .0 ft
* * * * * DEFAULT SEGMENT LENGTH SELECTED BY XSTABL * * * * *
5.0 ft line segments define each trial failure surface.
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ANGULAR RESTRICTIONS
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The first segment of each failure surface will be inclined
within the angular range defined by :
Lower angular limit := -45.0 degrees
Upper angular limit := (slope angle - 5.0) degrees
Factors of safety have been calculated by the :
* * * * * SIMPLIFIED BISHOP METHOD * * * * *
The most critical circular failure surface
is specified by 20 coordinate points
Point x-surf y-surf
No. (ft) (ft)
1 36.67 9.17
2 41.58 8.23
3 46.54 7.64
4 51.54 7.42
5 56.54 7.56
6 61.51 8.06
7 66.44 8.91
8 71.29 10.12
9 76.04 11.68
10 80.67 13.57
11 85.15 15.80
12 89.45 18.34
13 93.56 21.18
14 97.46 24.32
15 101.12 27.72
16 104.52 31.39
17 107.65 35.29
18 110.49 39.40
19 113.03 43.71
20 115.18 48.04
**** Simplified BISHOP FOS = 1.131 ****
The following is a summary of the TEN most critical surfaces
Problem Description : post 1997 stability analysis
FOS Circle Center Radius Initial Terminal Resisting
(BISHOP) x-coord y-coord x-coord x-coord Moment
(ft) (ft) (ft) (ft) (ft) (ft-lb)
1. 1.131 52.13 76.66 69.24 36.67 115.18 4.463E+06
2. 1.141 52.55 74.75 66.45 38.89 113.19 4.024E+06
3. 1.174 63.95 49.19 46.75 38.89 110.58 3.396E+06
4. 1.174 56.05 48.23 46.71 32.22 102.65 3.234E+06
5. 1.183 48.05 74.07 65.90 36.67 107.80 3.730E+06
6. 1.215 58.50 79.40 66.96 45.56 117.99 3.784E+06
7. 1.216 47.01 60.04 55.22 30.00 99.97 3.297E+06
8. 1.307 45.02 61.17 53.61 34.44 95.61 2.639E+06
9. 1.310 64.50 50.57 39.13 47.78 103.21 1.917E+06
10. 1.336 59.61 71.28 55.45 50.00 109.27 2.449E+06
* * END OF FILE * * *
