Stepped Soil Nnail Walls Design Example
In this example we will design three stepped soil nail walls. The model is created and analyzed with SnailPlus - Slope Stability Analysis and Soil Nail Walls Design Software.
A. Project Description
This design example presents a case with three stepped soil nail walls. Three soil layers are considered, and a 0.6 ksf surcharge is included at the top. The figure below presents the completed soil nail wall model.
The analysis is performed according to FHWA Geotechnical Circular No. 7 soil nail wall design standards. Initial construction is modeled with temporary factors with the initial shotcrete. In the last stage, design settings are changed to represent long term permanent wall conditions.
B. Example Video
C. Soil Nail Wall Analysis Results
The following images summarize some of the software results. Usually, the overall stability will be most critical. However, with multiple stepped walls, it is important to examine each soil nail wall separately. In SnailPlus, this can be modeled in separate stages where each step is examined separately.
In permanent soil nail walls, the desired safety factor according to FHWA should be greater than 1.5. In this example, the analysis indicates that a safety factor of 1.27 is achieved. To increase the safety factor, a soil nail wall designer can:
a) Increase soil nail lengths
b) Decrease soil nail spacing
c) Use a bigger bar
Usually, increasing the soil nail lengths would be the first choice.