Seismic Behavior of Soldier Pile Support Systems for Deep Excavations in Coarse Grain Alluvium

Soldier pile consists of the passive reinforcement (i.e., no post-tensioning) of existing ground by installing closely spaced steel bars (i.e., nails), which are subsequently encased in grout and transfer the loads from steel piles to soil. As construction proceeds from the top to bottom, concrete is also applied on the excavation face to provide continuity. Soldier pile is typically used to stabilize excavations adjustment to the buildings to prevent surface movement and cracks in the buildings where top-to-bottom construction is advantageous compared to other retaining wall systems. For certain conditions, soldier pile offers a viable alternative from the viewpoint of technical feasibility, construction costs, and construction duration when compared to ground anchor walls, which is another popular top-to bottom retaining system. This paper addresses soil nails that are installed with a near horizontal orientation and are primarily subjected to tensile stresses together steel piles which act as cantilever beam with horizontal nails as supports. Soldier pile can be used for both temporary and permanent structures based on its service life or intended duration of use. Soldier pile is a form of ground retention used when ground conditions comprise of dense to moderately dense soils such as coarse grain alluviums. Soldier pile systems with lateral nails are used in many excavation projects. This method is one of the appropriate support systems in deep excavations. However, most of the researches have been focused on the effects of wall height on the stability of excavations in static conditions, but with increasing of the use of soldier pile systems in seismic regions, the dynamic stability of these structures cannot be ignored. According to increasing of the usage of the soldier pile systems in seismic active zones, it’s important to study the dynamic behavior of these structures. Hence, in this paper, the seismic behavior of soldier pile systems in Tehran coarse grain alluvium has been investigated. The methodology is based on pseudo-static approach to equalize the dynamic analysis. The numerical modelings have been done according to Finite Difference Method (FDM) to this equalization. Based on slope stability theory, it has been shown that the pseudo-static method is a suitable and simple approach to equalize dynamic behavior. Therefore, in this paper, a similar approach has been used to equalize dynamic behavior of soldier pile systems with considering a proposed pseudo-static coefficient. The failure surfaces in dynamic and pseudo-static models efficiency. Network of this case study is the roads network of Fars province that it has 59 nodes and 80 arcs. Two groups of hazardous materials are considered and the risk factor is calculated for each group in all links. Each node can be the potential point of the demand or a point of supply. All paths can be used in both directions, and it has been assumed that the risk of passing hazardous material through the path between two nodes is equal for both directions. Risk index includes three factors, “population under effect”, “the environment assets”, and “the number and importance of road facilities across a link”. Results showed the best possible and the safest and most economical routes, would be obtained by solving the safety model and using the result of this model in the safety-economic model.