Soil Nail Design Optimization of 100 ft Deep Excavation Project in San Diego, CAÂ-Paper

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The Heights project in San Diego required a permanent soil nail wall up to 100 ft high and 1,000 ft long to replace an existing hillside and accommodate a seven-story residential development with underground parking. The original design used nails up to 115 ft long, large-diameter reinforcing bars, and 13-in. permanent facing, resulting in high construction costs.<br /><br />PB&A reviewed and optimized the design using SNAIL PLUS for static and seismic stability analyses and FHWA procedures for nail-force and facing design. The revised design shortened the total nail length by 44% and reduced reinforcing steel weight by 65%. It also varied nail sizes and facing thickness with depth; the facing was reduced from 13 to 10 in., cutting concrete use by 23%. Together, these changes lowered construction costs by approximately $800,000 and improved construction productivity and scheduling.<br /><br />The project also required evaluating a potential future SDG&E transmission tower near the wall. PLAXIS 2D finite element analyses modeled the soil nail wall and the tower’s 10-ft-diameter, 60-ft-deep drilled-shaft foundation under specified loads. Initial analyses showed that the proposed foundation could be installed only in a limited area while meeting SDG&E’s deflection and rotation limits. The wall design was therefore locally revised, including changes to nail lengths and facing, to increase stiffness and expand the acceptable installation area.<br /><br />The case demonstrates how balancing nail tensile, pullout, and facing resistance can avoid unnecessary material use while maintaining stability and accommodating nearby infrastructure.

Keywords

soil nail wall

San Diego

slope stabilization

SNAIL PLUS

FHWA design

seismic stability

reinforcing steel reduction

PLAXIS 2D

drilled-shaft foundation

construction cost savings