Field instrumentation, monitoring of drilled shafts for landslide stabilization and development of pertinent design method.

731670733PDFTech ReportFHWA/OH-2010/15134238LandslidesSlope stabilityRock drillingOhioOhio. Dept. of TransportationLiang, Robert Y.University of Akron. Dept. of Civil EngineeringUnited States. Federal Highway AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-Soils and GeologyUS Transportation CollectionThe design method for using a single row, spaced drilled shafts, socketed into a firm rock strata, to stabilizean unstable slope has been developed in this research. The soil arching due to the presence of spaceddrilled shafts in a slope was observed in 3-dimensioanl finite element simulations and field monitoring data.A comprehensive 3-D finite element parametric study was used to derive an empirical equation to quantifythe arching induced load transfer. A limiting equilibrium based slope stability analysis method, incorporatingthe arching effect, was developed and coded into a PC based program UA SLOPE 2.1, to allow for analysisof the factor of safety of the shaft/slope system and the earth thrust on the drilled shaft. The developedanalysis and design method was validated based on more than 40 cases of 3-dimensional finite elementsimulations, covering a wide range of slope geometry, soil strength parameters, and the drilled shaftdiameter, spacing, and location conditions. Three slope stabilization projects in Ohio involving the use ofdrilled shafts were monitored with instrumentations to obtain a 3-year performance data of the stabilizedslope and to validate the design based on the developed method. In addition, a field testing program at theATH-124 Project site was conducted to quantify arching during several stages of surcharge load inducedslope movements. The developed UA SLOPE 2.1 program was verified by comparisons with the calibratedfinite element simulation results of this field surcharge loading condition. The UA SLOPE 2.1 program isrecommended for use in finding an optimized design (i.e., location, diameter, and spacing) of the drilledshafts to stabilize an unstable slope