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Title:Movement of landslides in stiff clays and clay shales
Author(s):Kane, Thierno I
Director of Research:Mesri, Gholamreza
Doctoral Committee Chair(s):Mesri, Gholamreza
Doctoral Committee Member(s):Stark, Timothy D; Long, James H; Marshak, Stephen
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):First-time slides
reactivated landslides
land development on natural and man-made slopes
clay shales
stiff clays
shear strength
residual shear strength
slope stability
factor of safety
load-controlled direct shear tests
laboratory creep tests
time to slope collapse.
Abstract:The rate of slope movement has major socio-economic implications on the rapid global urbanization, with estimated annual fatalities resulting from landslides near 5000 and economic losses amounting to over $15 Billion U.S. dollars. Yet, the stability of natural and man-made slopes is generally evaluated using limit equilibrium methods expressed as a ratio of resisting and driving forces (termed Factor of Safety), which provides no information on the rate or extent of the movements. Quantifying the rate of slope movement would be extremely valuable for the planning, design and construction of structures and infrastructures on natural and man-made slopes. This dissertation uses the factor of safety to estimate transient movement rate which in turn is used to predict time remaining to catastrophic collapse of first-time slope failures. It also proposes a method to predict the rate of movement of reactivated landslides for the governing environmental conditions using the global factors of safety. For this purpose, the movement of 11 first-time landslides and 36 reactivated landslides, documented worldwide, were analyzed. In this study, to relate the time remaining to rupture of first-time slides to the factor of safety, existing time to failure prediction methods for first-time slope failures were critically reviewed, evaluated and updated to include interpreted field observations of first-time slides in intact ground and first-time slides with part of the slip surface at the residual condition. The load-controlled drained and undrained laboratory test data on undisturbed and remolded soft- to stiff- clays, reported in the literature, were analyzed. An empirical correlation for secant residual friction angle for a wide range of clay compositions with plasticity index in the range of 10 to 250%, was extended to 8 different effective normal stresses in the range of 10 to 700 kPa. Load-controlled laboratory drained direct shear tests were conducted on 12 different stiff clay and clay shale compositions, for testing durations up to 4 months, to investigate the movement behavior of reactivated landslides. Published records of 60 reactivated landslides were examined, and 23 landslides with detailed information on subsurface condition, observed rates of movement and groundwater pressures, were related to the factor of safety in reference to the residual shear strength. A comparison of field behavior to that observed in the laboratory tests were used to estimate the thickness of the shear zone of reactivated landslides. The proposed method to estimate the rate of reactivated landslide movement from the factor of safety was validated using 13 additional landslides documented in the literature. In summary, the factor of safety is a global parameter determining the rate of slope movement because it implicitly includes shear stresses, groundwater pressures and the shearing resistance of the ground. Using the proposed approach of relating the time remaining to collapse to the factor of safety, the catastrophic 1963 Vaiont slide in Italy was re-interpreted as a first-time landslide with subhorizontal base of the slip surface at the residual condition. On the other hand, it was illustrated that reactivated landslides in stiff clays and clay shales move at all factors of safety; however, will not accelerate catastrophically. The proposed method, allowing the prediction of movement rate, will permit the planning, design and constructions of structures and infrastructures on reactivated landslides.
Issue Date:2019-11-20
Rights Information:Copyright 2019 Thierno Kane
Date Available in IDEALS:2020-03-02
Date Deposited:2019-12

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