Investigation of vertical members to resist surficial instabilities

Abstract

This report summarizes the state of the art of using reinforcing structural members to stabilize surficial slope failures. The literature search and review conducted in this study indicated that the use of structural members for stabilizing surficial slope failures is not common practice; however, there is great interest in this methodology. The research team identified the following three innovative methods of surficial slope stability: installing small size structural members by conventional methods; installing launched soil nails, and installing earth anchors. This report includes detailed information regarding the design and analysis methodology for structural members, the material properties of structural members used, construction methods, cost-effectiveness, and case histories. It should be noted that there is little documented information available on this subject. In order to investigate the influence of installing structural members to stabilize surficial slope instabilities in Wisconsin, a comprehensive slope stability analysis was conducted using Wisconsin soil and slope input parameters and various soil strength parameters under dry and saturated conditions. The analysis conducted in this report and by other studies demonstrates the effectiveness of using the structural members in stabilizing surficial slope failures. Based on the information and data available, the methods that have potential merit to stabilize surficial slope failures in Wisconsin in terms of cost-effectiveness and field performance are the small size conventional structural members and the earth anchoring systems. Short-term field performance data demonstrated that plastic lumber is an effective remediation method if installed in closely spaced configuration. Wood lumber and earth anchors also are considered cost-effective. Long-term field performance data on the use of these materials is not available to draw any rational conclusions. Creep of plastic lumber and decay of wood lumber in aggressive environments may impact the behavior of these structural elements in the future and therefore the stability of the slopes they are used to repair.