Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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- 10.2 EXISTING SLOPE STABILITY 10.2.1 Data Gathering
| 10 DESIGN FOR SLOPE STABILIZATION 10.1 OVERVIEW Methods for stabilizing slopes with deep foundation elements, independent of wall structures that buttress the slide force, include in-slope installation of (i) drilled shaft, driven pile, or drilled-in pile systems to add shear resistance across the failure plane or a potential slip surface and (ii) battered driven pile or micropile systems to essentially tie the soil mass of an existing slide together to the more competent ground below the plane of failure. Both design methods rely upon a comprehensive assessment of the existing slope stability, followed by modelling of the interaction between the soil and the installed deep foundation elements. The analysis and design of laterally loaded deep foundation elements for slope stabilization applications involves the evaluation of (i) the geotechnical resistance factor (ϕ) of the slope with the deep foundation elements installed and (ii) the loads for structural design of the foundation elements. The geotechnical resistance factor that applies after the slope has been stabilized with deep foundation elements is not well defined because the earth pressures applied to the elements are dependent on the relative movement of the soil and the foundation elements, which depend on the geotechnical resistance, as well as the stiffness of the pile/shaft elements used to stabilize the slope. This chapter provides a methodology for analysis and design of deep foundation elements for slide stabilization applications. 10.2 EXISTING SLOPE STABILITY 10.2.1 Data Gathering Existing slope conditions should be assessed by review of available information and collection of geotechnical data through a subsurface exploration, including geophysics, and laboratory testing program. Data gathering typically includes the following Topography – Topographic information is essential to development of cross-sections for the slope stability analysis, identification of critical areas, and establishment of limits fora landslide mitigation. Landslide Extent – Observations of known points of shear failure, as evidenced by head scarps, toe bulges, and surface slumps, should be carefully mapped for comparison with the topographic data. Subsurface Profile – Borings should be advanced to a depth suitable to gather information on soil indices and strength, stratigraphy above and below the plane of failure, and the prevailing groundwater conditions. For rapid assessment of overall conditions under emergency slide mitigation circumstances, open-hole borings maybe supplemented by in-situ testing methods, such as cone penetration test (CPT) soundings. For failed slopes, laboratory strength testing may need to include development of residual soil strength data within the failure surface strata. For additional guidance on planning and execution of subsurface exploration programs for slopes, refer to Mayne et al. (2002) and Loehr et al. (2016). Failure Plane Identification -- Preliminary analysis of failed slopes can often be based upon the visual observation of shear failure surface features in combination with topographic data and available pre- failure subsurface information. However, to accurately assess the position of the failure surface, installation of inclinometer casings should be included in the subsurface exploration program, with 132 provisions for subsequent periodic monitoring. In addition, piezometers and groundwater monitoring wells can be installed to better define the groundwater conditions. Download 6.03 Mb. Share with your friends:
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