📋 Case Study

Urban Transit Tunnel Alignment Through Mixed-Soil Stratigraphy

Variable soil profile (soft clay → weathered volcanic tuff → dense sand) causing differential settlement and excavation instability

🏗️ Project Overview

3.2 km cut-and-cover metro extension in Jakarta, Indonesia

🎯 Challenge

Variable soil profile (soft clay → weathered volcanic tuff → dense sand) causing differential settlement and excavation instability

🔧 Design Approach

Combined SPT + CPT + seismic refraction survey; staged excavation with jet-grouted secant piles and real-time inclinometer monitoring

📐 Design Diagram

AI-generated project design illustration

📐 Key Calculations

N60-based φ′ estimation

φ′ = 27.1 + 0.3·N60 (for sands)

Result: 36.4°

Guided retaining wall design

Cv from oedometer tests

Cv = (T₉₀ × H²) / (t₉₀ × 10⁶)

Result: 0.82 m²/year

Predicted 18-month consolidation timeline

Lateral earth pressure coefficient (K₀)

K₀ = 1 − sin φ′

Result: 0.41

Reduced passive resistance assumption

📊 Results

0.8 mm/month max differential settlement; 98% on-schedule completion; zero ground loss incidents

💡 Lessons Learned

• •Pre-construction geophysics reduced borehole count by 40%
• •Real-time instrumentation enabled proactive support adjustments

✅ Key Takeaways

• 1Pre-construction geophysics reduced borehole count by 40%
• 2Real-time instrumentation enabled proactive support adjustments