Tesis doctoral de Nuria Merce Pinyol Puigmarti
Landsliding is an important problem when facing the design, construction and operation of dams and reservoirs. Impoundment of the slope toes as well as the rapid drawdown may trigger the movement of first-time landslides or reactivate ancient landslides often located in reservoir sites. This thesis deals with the particular case of landslides around reservoirs defined as a mobilized mass that slides on a well-defined shearing surface without experiencing a major degradation. in the first part of the thesis the mechanism of rapid drawdown is discussed as a fully coupled flow-deformation problem for saturated/unsaturated conditions. additional risk appears when landslide accelerates and is able to enter the reservoir at high speed creating impulsive waves. The discussion on the different phenomena leading to the fast acceleration is today very active. Probably the lack of well- documented cases makes the advancement of knowledge difficult. The mechanism to explain the rapid acceleration of landslides favoured in this thesis is based on thermal effects on the sliding surface that induce the generation of pore water pressure and therefore, the reduction of the frictional strength. The governing equations (mass and heat balance equations and constitutive equations) formulated in the shear band have been written and integrated together with the motion equation of the slide. With the aim of finding practical criteria to decide the actual risk of slide acceleration due the phenomena analysed, a closed-form solution has been obtained for the case of planar landslides under the hypothesis of incompressible water, solid particles and porous media. For a rational range of the most relevant parameters, comparison between analytical and numerical (relaxing the assumptions introduced in the analytical development) solutions shows a remarkable similarity and reveals that the closed-form solution is accurate enough for practical applications. the thermo-hydro-mechanical approach discussed is applied in the case of vaiont landslide. The stability of this landslide before the failure is first discussed by means of a simple explanation introducing the internal strength of the mobilized rock. The analysis is consistent with the available data (slide geometry, residual strength, material properties and laboratory tests). When the self-feeding mechanism of pore pressure generation due to heat resulting from the frictional work is introduced in the dynamic analysis of the vaiont model, the high velocity actually observed is predicted. sensitivity and scale analysis have been performed for the case of a planar landslide and for the geometry of vaiont. Three parameters have been found important to explain the acceleration of the motion: the thickness of the shearing band, its permeability and its stiffness. In fact, permeability and thickness can be related since both depend on the particle size distribution. Calculated results indicate that the permeability of the shear band is a key parameter. A threshold of permeability established around 10-8 to 10-10 m/s marks the transition for a potentially risky slide (when the permeability is lower) to a safe one (for higher values of permeability). for very large landslides, critical combinations of band permeability and band thickness result in a substantial increase in temperature. At high calculated values of temperature (hundreds or even thousands of ºc), the analysis presented is not applicable. Evaporation or advance constitutive equations including rock melting should be included. in a final chapter a recent large landslide located in canelles reservoir is analyzed. the slide is regarded as a potential risk for the operation of the dam and the reservoir. some of the developments made in the thesis, namely the solution of rapid drawdown and the thermal coupled model for fast landsliding, are applied to canelles. The chapter describes the methodology adopted which can be applied in similar cases.
Datos académicos de la tesis doctoral «Landslides in reservoirs. a coupled thermo-hydromechanical approach«
- Título de la tesis: Landslides in reservoirs. a coupled thermo-hydromechanical approach
- Autor: Nuria Merce Pinyol Puigmarti
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 13/09/2010
Dirección y tribunal
- Director de la tesis
- Eduardo Alonso Pérez De ágreda
- Tribunal
- Presidente del tribunal: sebastií Olivella pastallé
- claudio Olalla marañon (vocal)
- luciano Picarelli (vocal)
- Antonio Soriano peña (vocal)