This code provides guidelines for the design, material selection, construction, and quality control of stone columns used for ground improvement. It covers methods like vibro-replacement to increase bearing capacity, reduce settlement, and accelerate consolidation in weak or soft cohesive soils and loose cohesionless soils.
Covers guidelines for the design and construction of stone columns 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
Settlement Reduction Factor (β) = S_c / S (where S_c is settlement with columns, S is settlement without)
Bearing Capacity Improvement Factor (n) = q_u(c) / q_u(s) (where q_u(c) is ultimate capacity of improved ground, q_u(s) is of unimproved ground)
Stress Concentration Ratio (n_s) = σ'_s / σ'_c (where σ'_s is effective stress in stone column and σ'_c is in surrounding soil)
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.