Slow-moving landslides are common in mountainous area worldwide. Most of them mobilizes slowly over long periods of time, which causes continuous damage to proximal infrastructure and habitats. Most notably, some slow-moving landslides can experience catastrophic acceleration at some point in their life cycle, with potentially fatal consequences. It is therefore important to interpret the dynamics of such class of landslides. Although, there are several factors that can lead to downslope sliding and velocity change, this thesis focuses on the dynamics of slow-moving landslides driven by precipitation. Upon rainfall infiltration, pore-water pressure transients tend to develop within the landslide body, a mechanism often explained through linear and/or nonlinear diffusion models. Consequently, the normal effective stress, which governs the deformation and resistance against downslope movement, will change. On such basis, this thesis proposes to tackle the dynamics of slow-moving landslides from a physics-based standpoint, by placing emphasis on the role of the inelastic deformation behavior of the materials within the basal shear zone of a landslide, as well as on its role in modulating the corresponding coupled hydrological-mechanical processes responsible for the motion of landslides. Viscoplastic models, which can take rate-dependent strength of earthen material into account, have been widely used to quantify the slow-moving landslide’s sliding behaviors. Yet, typically used viscoplastic model assume a lack of pre-failure viscosity, an assumption that contradicts laboratory tests on soil specimens, as well as filed measurements based on remote sensing. Starting from this insight, this thesis proposes a new hybrid rheological law aimed at predicting viscous behavior prior to frictional failure, while ensuring accurate computation of the post-failure sliding dynamics. The hydro-mechanical model resulting from the proposed viscoplastic rheology is eventually assessed on the basis of data from several study sites, showing that the model can be used to describe distinct types of landslide motion spanning from episodic to quasi-continuous sliding. In addition to time-dependent soil behavior, this thesis has also addressed the link between the landslide dynamics and the volume change of the shear zone material. For this purpose, a fully coupled simulation framework accounting for inelastic deformation and simultaneous excess pore pressure transients within the shear zone has been formulated. Although the proposed approach is applicable to very general constitutive models, its capabilities have been tested with reference to the standard perfectly plastic Mohr Coulomb model, which has been used to interpret landslide dynamics in case of both dilative and contractive frictional shear zone response. Numerical simulations of creeping landslides have been used to validate the ability of proposed methodology to capture movements induced by precipitation. In all the inspected scenarios, a satisfactory match between data and simulations was possible for positive dilation coefficients, which led to spontaneous generation of negative excess pore pressure and self-regulated post-triggering velocity. Conversely, simulations based on vanishing dilation (hence, reflecting the approach of critical state) were shown to produce sharp acceleration and large runout, typical of catastrophic events. These results encouraged further analyses aimed at incorporating more sophisticated constitutive laws able to recover critical state as a function of the rate and magnitude of the landslide movements. The final stages of this thesis therefore focused on the analysis of transitions from slow-moving landslides to runaway failures. This objective was pursued by linking the newly formulated hydro-mechanical framework with a classic critical state plasticity model (i.e., Modified Cam Clay). Simulation on model slopes were therefore used to show that the proposed methodology captures runaway acceleration even without abrupt changes of the hydrologic forcing. By analyzing the failure mechanisms, an index reflective of the potential for runaway failure was proposed, which can be used to track the stability of a slow-moving landslide. Notably, the examination of how a slope is weakening upon rainfall based on the magnitude and duration of its creep movement is conducted. The model is finally used to explain the dynamics of landslide movements in a number of study sites. The results show that the proposed framework can be used to disclose whether a moving landslide possesses the signature of a weakening shear zone material and is thus likely to develop runaway failure upon rainfall cycles. It is shown that the proposed index can successfully differentiate stable, episodic landslide events from gradually weakening downslope movements that are gradually converging towards a runaway failure solely on the basis of high-quality parameter calibration of measurements collected during the stable creeping stage.

Creator

• Li, Xiang

DOI

• https://doi.org/10.21985/n2-sspt-yq33

Subject

• Geotechnology
• Civil engineering

Language

• en

Alternate Identifier

• etdadmin_upload_927309
• http://dissertations.umi.com/northwestern:16221

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright