Landslide Stabilization Using a Single Row of Rock-Socketed Drilled Shafts and Analysis of Laterally Loaded Drilled Shafts Using Shaft Deflection Data

An accurate and practical methodology for stability analysis and design of drilled shafts reinforced slopes was developed utilizing limiting equilibrium method of slices. Complex soil stratifications and general failure slip surfaces can be handled in the developed method. The effect of soil arching due to the presence of the drilled shafts was accounted for by using a load transfer factor. The numerical values of the load transfer factor were developed based on 3-D FEM parametric study results. Many of the design variables controlling the slope/shaft systems, such: drilled shafts size, shafts location, shaft fixity (the necessary rock-socket length), and the required spacing between the drilled shafts to prevent soil from flowing around the shafts can be successfully determined from the developed method. The optimum location where the drilled shafts could be placed within the sliding soil mass so that the cost associated with the landslide repair using the drilled shafts is minimized can be searched for and determined from the developed methodology. From geotechnical point of view, the global factor of safety for slope/shaft systems can be determined. From structural point of view, the forces acting on the stabilizing drilled shafts due to the moving ground can be successfully estimated. In addition to the developed design methodology, Real-time instrumentation and monitoring were carried out for three landslide sites in the Southern part of Ohio. Various types of instruments were extensively installed inside the stabilizing shafts and the surrounding soils to monitor and better understand the behavior of slope/shaft systems. The UA Slope program developed by Dr. Robert Liang in corporation with ODOT and FHWA has been used in designing these landslides. The field instrumentation and monitoring processes have provided excellent and unique information on the lateral responses of shafts undergoing slope movements. Also, the results of the instrumented cases have provided that the structural design (moments, shear, lateral deflection, and shaft tip fixity) of the shafts are overestimated (i.e., estimated forces acting on the shafts are high), and the geotechnical design (FS of slope/shaft system: movement and rate of movement) is achieved in two case studies but not fully achieved for the third case. On the other hand, in an effort to develop an efficient analytical method for analysis of laterally loaded drilled shafts using only lateral shaft deflection data, numerical procedures were proposed based on the principle of superposition. The lateral shaft deflections along the shaft length due to superposition of the lateral applied load to the drilled shaft were added together to establish the compatibility equations that govern the lateral behavior of the drilled shaft system. The compatibility equations allow for the determination of the net applied loads to the drilled shaft responsible for specific amount of shaft deflections. Once the loads were determined, basic equilibrium equations were applied to calculate shear forces and bending moments along the shaft length. A computer program was developed implementing the proposed numerical procedures to facilitate numerical computations. Many laterally loaded drilled shaft examples were described and used to verify the validity of the developed method. Included in the cases for validation were two actual full-scale drilled shafts at Jefferson County: (1) landslide repair using drilled shafts; and (2) lateral load test, were demonstrated. Advisors/Committee Members: Liang, Robert.