Supports and Anchor Back-Analysis in SVSLOPE®
A feature of SVOFFICE™
Supports (anchor objects) are very important in reinforcing slopes. The latest release of SVSLOPE® provides a comprehensive support for a variety of anchor objects in both 2D and 3D analysis. The anchor objects supported in SVSLOPE® include the following: end anchored support, geotextile, grouted tieback, grouted tieback with friction, micro pile, soil nail, soil nail (Hong Kong practice) and a user defined option that allows the user to specify the support characteristics. The software allows any number of anchor objects to be added to any particular slope analysis.
The design of anchor patterns is more complex in 3D analysis. Therefore, an additional functionality enabling the user to design patterns of anchors in a 3D slope is available. The support systems in 3D can be specified as uniform or non-uniform supports. Non-uniform supports allow random entry of support systems, where each anchor object is added individually. The uniform supports interface allows the user to enter a group of re-occurring supports such as soils nails in a regular pattern. After the pattern is generated, the user is free to modify each individual anchor as needed or add additional anchors. The uniform entry method is therefore highly useful in the fast entry of regular support patterns in a full 3D analysis.
The anchor back-analysis feature allows users to design anchor patterns in order to stabilize slopes. This feature is available in both SVSLOPE® 2D and 3D, therefore it allows the full 3D back analysis of arbitrary patterns which vary spatially in a 3D fashion. This feature is easy to use and may be incorporated in any existing analysis. All the existing supports available in the SVSLOPE® software may be incorporated into an anchor design back-analysis. Supports may be used to match the equivalent horizontal force required by the slope back-analysis. The equivalent horizontal force method also allows the engineer to experiment with combinations of support to reach the target factor of safety. For example, the user may experiment with a combination of grouted tiebacks and soil nails of differing installation lengths.
How does Anchor Back-Analysis work?
The back analysis feature works by allowing the user to specify a target factor of safety and a horizontal support force elevation. The analysis is then run using either the Bishop or Janbu Simplified methods. The results of the analysis will be a recommendation for how much horizontal force is required to raise the factor of safety to the target level. Once the horizontal force is known, the user can then experiment with different anchor designs in SVSLOPE® to replicate this horizontal force. There may be the need to use some anchor combinations to obtain the given factor of safety. The user is encouraged to use his/her professional judgement in each case.
The results of a 3D analysis are of a particular use in that the intersection of the elliptical or fully specified slip surfaces may be taken into account. It should be noted that a 2D analysis assumes a cylindrical slip surface in the third dimension. In reality, most slip surfaces are elliptical. This means that the point at which they intersect various anchors may change at different places on the slip surface. The detail is significant in the design of grouted tiebacks.
SVSLOPE® provides a comprehensive support for a variety of 2D and 3D supports. The anchor back-analysis feature is an additional feature that works by allowing the user to specify a target factor of safety and a horizontal support force elevation. Additional help on the specifics of this implementation is available in the User Manual.