FEM-Based Parametric Optimization for Driven Soil Nail Systems: Development of Performance-Based Design Charts for Slope Stability and Deformation Control

Abstract

The current study uses a database-driven optimization approach employing FEM analysis in PLAXIS 2D based on the Mohr-Coulomb constitutive model. An automation work flow in Python created 38,880 numerical simulations, among which 17,587 met the geometry and performance criteria. Based on the resulting database, it is possible to assess the effect of the major design parameters on slope stability, deformations, and reinforcement requirement, thus creating design charts for practical engineering purposes. A 30% nail length increase resulted in 10% higher FOS and 12% lower displacement. On the other hand, a 30% increase in backfill angle decreased FOS and increased displacement by 40–45%. At the same time, a 30% increase in face angle did not influence FOS (+/-1%) while decreasing displacement up to 14%. Face angle increase from 0° to 10° led to an increase of the maximum excavation depth from 6 m to 10 m due to reduction of lateral earth pressure and better interaction between the wall and soils. Excavation depth increase by 30% decreased FOS by 10% and displacement by 120%, thus determining the main design parameter. Despite the fact that deeper excavation depths required much larger nails and linearly growing spacing, inclined walls needed much smaller reinforcement increase. About 1,100 models were constrained by deformation criteria while only 350 were controlled by FOS criteria, indicating that deformations were controlling design optimization in most cases. The proposed database and design charts provide the basis for optimized soil-nailed excavation system design.