Two landslides, in close proximity to each other, occurred in stiff clayey silts derived from weathered volcanics of the Yamhill Formation. Initial testing of the general overburden soils gave consistent residual strength values of φ'r = 33°. However, samples taken at the failure zone, determined by inclinometers, gave much lower residual strengths which were in close agreement to the back-calculated strengths for the landslides. The laboratory φ'r of 9° and 22° described in the two case studies differ significantly, probably reflecting variable weathering and soil alteration. It is concluded that samples for strength testing need to be taken from the failure zone in these soils.

  • INTRODUCTION

  • CASE STUDY 1

  • CASE STUDY 2

  • CONCLUSIONS

  • ACKNOWLEDGEMENTS

  • REFERENCES

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