Field Instrumentation, Monitoring of Drilled Shafts for Landslide Stabilization and Development of Pertinent Design Method, Executive Summary Report

摘要

The use of a row of spaced drilled shafts to stabilize unstable slopes along the highways offers many advantages compared to other slope stabilization techniques. Some of these advantages may include: (1) various construction techniques are available for installing drilled shafts in almost any type of soil and rock conditions; (2) lateral load test can be performed to verify the lateral load-carrying capacity of the drilled shafts; (3) the use of drilled shafts avoids the need to address the right-of-way issues that may be needed for other types of slope stabilization methods; (4) the drilled shafts offer a reliable and economical solution compared to other slope stabilization methods; and (5) the drilled shafts are typically structurally capable of resisting long-term environmental effects. Despite a wide application of this slope stabilization technique by highway agencies, there is no universally accepted design method that can yield a safe and economic design outcome. The design process requires engineers to determine optimized combinations of the following key design variables: (1) drilled shafts diameter; (2) spacing between the drilled shafts to ensure the development of soil arching; (3) the necessary socket length of the drilled shafts in the non-yielding rock layer so that the drilled shafts can act as relatively stable structural members against the moving soil; (4) the location of the drilled shafts within the slope body so that the target global factor of safety of the stabilized slope can be achieved using the most economical configuration of the drilled shafts; (5) the forces imparted on the drilled shafts due to the sliding soil mass so that the structural design of the drilled shafts can be performed to meet the structural capacity requirements. Therefore, a research effort to develop and validate a pertinent design procedure is needed.