Mixed Soldier Pile and Rock Anchor Deep Excavation in Carrollton, Texas
Designed with DeepEX Software
Construction of a new pump station at the Elm Fork Water Treatment Plant in Carrollton, Texas required a 56 ft deep excavation. Substrata conditions consisted of 20ft of fill, and clays over shale rock. The solution was to provide a soldier pile and timber lagging wall supported by one level of tiebacks in the upper 20 ft and step the excavation in rock by stabilizing the rock mass with anchors. To save on pile costs, the initial excavation was benched and the soldier piles were installed from a lower elevation.
The soldier pile deep excavation was designed and constructed by Lance Kitchens, P.E. of Russo Construction, using our DeepEX software. Deep Excavation assisted Russo with the design review and setup of the deep excavation model. An aerial image of the deep excavation can be seen below:
Figure 1 Aerial image of completed shoring wall in Carrollton, Texas
Conditions like this requires careful examination of various design conditions. First, the soldier pile wall and tieback system needs to be designed to resist the earth and any surcharge loads. Because the tiebacks are inclined and the pile wall is embedded in rock, the vertical anchor load component will immediately be transferred to the pile and pile socket. In this case it is typical to examine the stability of rock wedges from the pile tip sloping down to the rock face. DeepEX examined automatically such conditions by also considering the effect of rock anchors in the stability.
Excavation of the vertical rock faces also reduces the available passive resistance on the soldier piles. In this case, the available passive resistance depends on the number of rock anchors, their length, and on the intersection with potential slip surfaces. In DeepEX, the passive resistance on the soldier piles was examined by having the program investigate different sliding surfaces and finding the critical conditions.
Last, the global stability of the whole soldier pile excavation-rock anchor supported system had to be considered. In DeepEX, an automatic search algorithm was utilized to find the most critical potential sliding mass.
In this project, DeepEX was instrumental as it allowed the designer to fully consider all aspects of the deep excavation design in one package.
Figure 2 Support of Excavation Analysis with Soldier Pile and Rock Anchors in DeepEX
Figure 3 Viewing the mixed soil-rock excavation face supported by soldier piles and rock anchors