Introduction
Tunneling and underground construction projects often face challenges related to weak soils, high groundwater pressures, and the need to minimize surface settlement in densely populated urban areas. Jet grouting has become a widely adopted ground improvement technique in these scenarios due to its ability to form strong, impermeable soilcrete columns and panels. This article presents case studies highlighting the practical application, performance, and lessons learned from jet grouting in tunneling and underground works.
Case Study 1: Metro Station Excavation Support in Soft Clay (Asia)
- Project Context: Construction of a deep metro station shaft in soft clay with a high groundwater table.
- Problem: Risk of basal heave and water inflow during excavation.
- Jet Grouting Solution:
- Installed a jet grout bottom plug beneath the shaft.
- Soilcrete columns overlapped to form a continuous horizontal slab.
- Performance:
- Achieved unconfined compressive strength (UCS) of 3–5 MPa.
- Permeability reduced by 3 orders of magnitude.
- Provided a safe and dry excavation environment without excessive dewatering.
- Lesson Learned: Jet grouting bottom plugs are highly effective in preventing basal uplift in deep shafts.
Case Study 2: Tunnel Face Stabilization in Sandy Soil (Europe)
- Project Context: EPB (Earth Pressure Balance) shield tunneling beneath urban infrastructure.
- Problem: Loose sandy soils prone to collapse at the tunnel face.
- Jet Grouting Solution:
- Pre-grouting performed ahead of the tunnel face to stabilize soils.
- Triple-jet system used to ensure sufficient diameter and strength.
- Performance:
- Tunnel face stability maintained, minimizing surface settlement.
- No ground loss recorded during excavation.
- Lesson Learned: Pre-excavation jet grouting can provide temporary ground arching and prevent face collapse.
Case Study 3: Seepage Control in River-Crossing Tunnel (North America)
- Project Context: Subaqueous tunnel crossing beneath a river.
- Problem: High groundwater pressure threatened excavation stability.
- Jet Grouting Solution:
- Jet grout cutoff wall constructed parallel to the tunnel alignment.
- Columns overlapped to create a continuous barrier.
- Performance:
- Hydraulic conductivity reduced from 10⁻³ to 10⁻⁷ m/s.
- Excavation completed without uncontrolled water inflow.
- Lesson Learned: Jet grouting cutoff walls are a practical alternative to slurry walls in permeable soils.
Case Study 4: Settlement Control in Urban Tunneling (Japan)
- Project Context: Construction of a shallow tunnel beneath a congested city center.
- Problem: Concern over ground settlement affecting historic buildings above.
- Jet Grouting Solution:
- Jet grout block formed above the tunnel alignment to act as a load-bearing arch.
- Performance:
- Maximum surface settlement limited to less than 5 mm.
- Adjacent historic structures remained unaffected.
- Lesson Learned: Jet grouting can create soilcrete vaults or arches to redistribute stresses and protect surface assets.
Case Study 5: Emergency Ground Treatment During Tunnel Collapse (South America)
- Project Context: During tunneling through mixed soils, unexpected collapse occurred at the crown.
- Problem: Urgent need to stabilize loose ground and resume tunneling.
- Jet Grouting Solution:
- Rapid-response jet grouting from surface drilled boreholes.
- Created reinforced soilcrete zone around collapse area.
- Performance:
- Tunnel crown stabilized within two weeks.
- Allowed controlled resumption of tunneling without further collapse.
- Lesson Learned: Jet grouting provides a flexible and rapid remedial solution for ground failures in tunneling.
Key Observations from Case Studies
- Versatility: Jet grouting is applicable across a wide range of soils, including sands, silts, and clays.
- Groundwater Control: Highly effective in reducing permeability and preventing inflow in saturated soils.
- Settlement Mitigation: Essential for urban tunneling beneath sensitive structures.
- Emergency Response: Useful for rapid stabilization of collapse-prone ground.
- Limitations: High costs, spoil management, and variability in column geometry remain challenges.
Conclusion
The reviewed case studies demonstrate that jet grouting plays a critical role in tunneling and underground construction, particularly in complex ground and groundwater conditions. Its integration into excavation support, face stabilization, and seepage control strategies ensures construction safety, minimizes risks to adjacent infrastructure, and enables urban projects to advance with reduced disruption.
As tunneling projects continue to expand into more challenging environments, jet grouting will remain a vital tool in the geotechnical engineer’s toolkit, with future improvements focusing on precision, automation, and environmental sustainability.
