Software Discussion Provider Analysis: Rocscience, Inc.-PPT Presentation

PPT Presentation

Pdf Summary

The presentation evaluates a proposed 40-foot-deep excavation in Boston, where marine clay, an adjacent building, and nearby traffic create significant risks of base heave, instability, and ground movement. Because site characterization was based on a single borehole, some soil properties were estimated from literature.<br /><br />The team used RS2 for staged, 2D plane-strain finite-element analysis with coupled consolidation, groundwater effects, strength reduction, and modeled slurry walls and tiebacks. Excavation proceeded in 2-foot stages, with dewatering to 4 feet below the excavation. Alternative wall embedment depths and anchor layouts were assessed. RS3 provided 3D finite-element analysis, while Slide2 and Slide3 were used for limit-equilibrium stability checks.<br /><br />Support configurations were compared using wall deflection, bending moments, shear, anchor forces, settlement, and base heave. On the side next to the building, heavier anchorage was considered to control movements; the four-row layout produced a reported maximum horizontal displacement of about 1.85 inches and movement next to the building of about 0.57 inches. Calculated anchor forces remained below stated tendon capacities in the reported cases. The analyses also highlighted the importance of selecting appropriate constitutive models, especially for distinguishing soil loading and unloading behavior.<br /><br />Limit-equilibrium factors of safety were higher in 3D than in 2D: Janbu results were 1.31 and 1.20, respectively, and Spencer results were 1.85 and 1.62. The 2D and 3D finite-element results showed generally comparable trends, including similar maximum horizontal displacement and anchor forces.<br /><br />The study concludes that alternative support designs can be evaluated across analysis methods to identify a suitable, economical scheme. It also emphasizes that reliable site investigation and modeling assumptions are critical. Computing times ranged from under a minute for 2D limit equilibrium to just over three hours for the 3D finite-element model.

Keywords

Boston excavation

marine clay

base heave

slurry walls

tiebacks

finite element analysis

groundwater dewatering

limit equilibrium

anchor forces

soil stability