This code provides guidelines for improving soft, compressible soils by using vertical drains combined with preloading. It covers the design, material selection, installation, and monitoring required to accelerate soil consolidation and increase its strength before construction.
Covers guidelines for the design and construction of vertical drains and preloading for ground improvement.
Quick Reference Values
Typical Grout Viscosity (Marsh Cone)35-50 seconds
General Grouting Pressure Limit20-25 kPa per meter of depth (to avoid hydrofracture)
Typical Target Permeability post-grouting< 10^-5 cm/s
Bleeding Limit for Cement Grout< 5% of volume
Max Water Temperature for GroutingNot more than 27 °C
Key Formulas
Time factor for radial consolidation: Th = (ch * t) / de²
Degree of consolidation (radial): Uh = 1 - exp(-8Th / F(n)) where F(n) is a function of drain spacing and smear effect
Combined degree of consolidation: Uc = 1 - (1 - Uv)(1 - Uh)
Practical Notes
Verification of ground conditions via boreholes is critical before finalizing the grouting method and parameters.
Continuous monitoring of grout pressure and volume (grout take) is essential to control the process and avoid ground heave or damage to nearby structures.
Post-grouting tests, such as permeability tests (e.g., Lugeon test) or in-situ strength tests, are necessary to validate the effectiveness of the ground improvement.