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UBC Theses and Dissertations

Regional geology, groundwater flow systems and slope stability Hodge, Robert A.L.


The purpose of this thesis is to show, using computer simulation of flow systems in a variety of hypothetical slopes, how different geological environments affect the groundwater flow regime, which in turn is fundamental to the stability of a slope. Galerkin's method is used to derive a finite element program to model two dimensional, saturated, steady state flow through anisotropic and heterogeneous rigid porous media. An understanding of the regional geology is required in order to understand the regional flow system. The following points are illustrated. a. In anisotropic media, the most adverse groundwater condition for slope stability occurs when the major axis of conductivity lies down the dip of the slope. b. Depending on their characteristics, faults, contacts and dykes can be either detrimental or favourable in their effect on the flow system. Careful field investigation is required to establish that effect. c. Deep weathering commonly causes a confining zone of low conductivity, a situation very detrimental to stability. d. Stress relief fractures on valley walls can adversely influence the effect of groundwater on stability. e. A regional aquifer can cause high pore pressure development beneath a valley. f. Fluctuations in the regional groundwater system can cause instability in Pleistocene terraces. g. The presence of an underlying less conductive zone or unit can have an adverse effect on the flow system. Conductivity contrasts of less than two orders of magnitude can cause pore pressure development critical to stability. Three other points are demonstrated which have direct application to slope stability analysis and control. 1. The pressure head distribution on rock wedges can be nonlinear rather than the commonly assumed linear distribution. 2. The introduction of a reservoir at the toe of a slope can influence the groundwater regime well above the reservoir surface; even a low reservoir can cause, the change required to cause instability. 3. Piezometric measurements and drainage systems must penetrate through any less conductive unit that might be acting as a slide plane.

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