📋 Case Study

Historic Masonry Bridge Retrofit on Alluvial Floodplain

Low-density floodplain deposits (OCR ~1.2), high seasonal water table, and risk of scour undermining abutments

🏗️ Project Overview

Seismic retrofit of 1892 stone arch bridge over Mississippi tributary in Missouri

🎯 Challenge

Low-density floodplain deposits (OCR ~1.2), high seasonal water table, and risk of scour undermining abutments

🔧 Design Approach

Mini-pile underpinning + graded filter blanket + real-time piezometer network; phased load transfer verified by strain gauges

📐 Design Diagram

AI-generated project design illustration

📐 Key Calculations

Ultimate skin friction (qₛ)

qₛ = α × cᵤ (α = 0.55 for mini-piles)

Result: 110 kPa

Defined pile length requirement

Scour critical velocity (V꜀)

V꜀ = K × (g × D₅₀)⁰·⁵

Result: 1.82 m/s

Informed flow training structure geometry

Settlement under dead load (Schmertmann)

δ = Σ(Δσ × I × Δz / Eₛ)

Result: 8.3 mm

Below allowable 10 mm tolerance

📊 Results

Completed within historic preservation constraints; monitored settlement < 0.3 mm/year post-retrofit

💡 Lessons Learned

• •Mini-piles minimized vibration impact on historic masonry
• •Graded filters prevented internal erosion despite frequent saturation cycles

✅ Key Takeaways

• 1Mini-piles minimized vibration impact on historic masonry
• 2Graded filters prevented internal erosion despite frequent saturation cycles