ANCHOR DESIGN FOR SLOPE STABILIZATION BY SURFACE LOADING

The increase in slope stability by application of discrete surface loads depends in part on the orientation of the load. For stabilization systems such as anchored geosynthetics, the load orientation corresponds to the angle of anchor installation. A theoretical study is performed to determine the optimum orientation of such anchors in purely cohesionless soils to maximize the increase in slope stability. Three cases are analyzed: a hypothetical surface load without anchorage, surface load with grouted end anchorage, and surface load with driven friction anchors. The last case involves the most interesting analytical solution since the optimum anchor orientation is a function of the slope geometry, the in situ stresses, and the desired increase in factor of safety. The required length and spacing of anchors depend, in addition to the aforementioned factors, on the anchor diameter, the internal friction angle of the soil, the soil-anchor interface the internal friction angle of the soil, the soil-anchor interface friction, the strength of the geosynthetic, and the depth of the potential failure surface. A simplified equation is given for the anchor orientation, and a design chart is presented for determining spacing and length requirements. An example problem illustrates the importance of proper anchor orientation.