18th european young geotechnical engineers’ … · 18th european young geotechnical engineers’...

18th EUROPEAN YOUNG GEOTECHNICAL ENGINEERS’ CONFERENCE

Portonovo, Ancona (Italy), June 17-20th 2007

Influence of the parameters of residual shear strength over the stability of landslide terrainsH. ZayakovaVSU “L. Karavelov”- Sofia



1. INTRODUCTION

0

0,05

0,1

0,15

0,2

0 10 20 30 40 50 60 70 80

Shear deformation, sm

Shea

r st

reng

th, k

g/sm

2.

Fig.1. Dependency of residual shear strength and shear deformation for Emen landslide



2.EMEN LANDSLIDE

Fig. 2. View of the landslide section above the road near the Emen village



Fig. 3. Toe of the landslide body above the road



Fig. 4. Stabilized slope along profile 1



Table 1. Dry slope, natural terrain, profile 1, Janbu’s method

φ c Fs Strength decrease Note

degre

e

kP

a - %

13.7 16 1.215 42.4 Residual

14.72 20 1.419 33.9

15.74 24 1.622 25.5

16.76 28 1.825 17.0

17.78 32 2.029 8.5

18.8 36 2.233 0 Peak

Table 2. Water saturated slope, natural terrain, profile 1, Janbu’s method

φ c Fs Strength decrease Note

degre

e kPa - %

13.7 16 1.062 42.4 Residual

14.72 20 1.252 33.9

15.74 24 1.445 25.5

16.76 28 1.636 17.0

17.78 32 1.828 8.5

18.8 36 2.02 0.0 Peak



The performed stability calculations show that:

In the case of absent loading from transport vehicles on the roadbed, when the residual strength values have been reached, the slope can be stabilized only by draining the groundwater by means of the drain ribs and drying the landslide body.

The water saturated slope to the established groundwater level is stable for predicted decrease of the shear resistance to 34 % under the assumption in favour of safety that the strength decrease is simultaneous and of equal sign for all points in the destruction range.

The stabilized slope by means of re-battering, draining and rock counterforce with considering the dynamic impact of the traffic load is practically not influenced by the stressed state of the landslide material, indicating a state of equilibrium.



3. DEBEL DYAL LANDSLIDE

Fig. 5. Water saturated slope along profile 1



Table 4. Dry slope, natural terrain, profile 1, Janbu’s method

φ c Fs Strength decrease%

Notedegree kPa -

6.3 14.2 1.109 47.9 Residual

7.52 16.66 1.309 38.4

8.74 19.12 1.51 28.9

9.96 21.58 1.711 19.3

11.18 24.04 1.914 9.7

12.4 26.5 2.116 0 Peak



φ c Fs Strength decrease%

Notedegree kPa -

6.3 14.2 0.907 47.9 Residual

7.52 16.66 1.07 38.4

8.74 19.12 1.233 28.9

9.96 21.58 1.397 19.3

11.18 24.04 1.561 9.7

12.4 26.5 1.725 0.0 Peak

Table 5. Water saturated slope, natural terrain, profile 1, Janbu’s method, with considered impact of the dynamic loading from the road



The performed stability calculations show that:

In the case of absent loading from the transport vehicles on theroadbed, the slope can be stabilized to decrease of the shear resistance value to 38 % only by draining soil water by means of the drain ribs and drying the landslide body.

The water saturated slope to the established level of the groundwater level is stable for predicted decrease of the shear resistance of up to 28 %, with the assumption in favour of safety that the strength decrease is simultaneous and of equal sign for all the points from the destruction range.



The stabilization of the slope by means of a rock counterforce, situated on the territory of the municipal lands, not only exerts an adverse effect on the landslide body stability, but also has a certain negative effect by qualitatively decreasing the stability.

The re-battering the landslide slope aimed at its stabilization is an economically unprofitable approach with the view of the slope morphology – i.e. it would lead to considerable volumes of excavation works.

The stabilization of the Debel Dyal landslide is realized by means of a rigid reinforced concrete anchored structure combined with drain ribs in the direction of movement of the landslide material within the range of the roadbed.



4. CONCLUSION

The considered landslides prove that the search and application of analogous approaches to the stabilization of natural slopes is acomplicated task.

In all cases, however, the drying of the landslide body at a stage, when the deformations in the massif have not led to the expectedfinal decrease of the shear strength, as well as the dumping of rock or earth material in the toe of the landslide, are favourable for the slope stability. This would also lead to insignificant volumes of repair works for restoring the road level.



The devil is in the details

Thanks for your patience

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