Soil Improvement Using Grouting
A three-part investigation into cement and chemical grouting of sandy soils — from a failed laboratory carboy trial to a successful field-scale pressurized injection system, followed by chemical grouting with sodium silicate and its behavior inside concrete.
Cement–Water Grouting
Two attempts: a laboratory trial that failed, and a field-scale pressurized system that succeeded.
Objective & Setup
Evaluate the effectiveness of cement grout in improving sandy soil inside a transparent plastic water carboy. A perforated pipe (perforations every 15 cm) delivered grout while a sealed bottom plug forced horizontal flow.
Grout bled to the surface and accumulated as a solid crust around the injection pipe. The soil beneath remained entirely untreated.
- • Grout failed to penetrate inter-granular voids.
- • Cement suspension separated; fluid escaped upward.
- • Rigid carboy boundary restricted natural dissipation.
- • Gravity alone could not overcome pore resistance.
Engineering Diagnosis
Pressurized Grouting System
Modified Mix (Mix 2)
Higher fluidity via a leaner mix and a superplasticizer, injected under controlled pneumatic pressure into pre-wetted sand.
System Components
Field Preparation
- • Test pit excavated in natural sand to 50 cm.
- • Surface cleared and levelled.
- • In-situ sand containing 10% fines.
Borehole & Casing
- • 1.0 m casing pipe, 4.5″ diameter.
- • Perforated uniformly every 15 cm.
- • Bottom sealed with a plug for lateral flow.
Confinement
- • Annular cement plug, 15 cm radius, 4-day cure.
- • Sandbag surcharge on top of cured plug.
- • Pre-flushed with clean water before grouting.
Pressurized grout injection produced a consolidated, high-strength grouted soil body — confirming that pressure control, confinement, and mix fluidity are the decisive parameters.
Chemical Grouting — Sodium Silicate (Na₂SiO₃)
A low-viscosity inorganic grout that penetrates fine voids at low pressure — with a critical limitation revealed under saturated conditions.
Key Characteristics
- • Ultra-low viscosity (2–10 cP).
- • High penetrability in sand & silt.
- • Low injection pressure required.
- • Eco-friendly, sustainable chemistry.
Reference: Warner, 2004.
Hardening Mechanism
Mixed with an activator (Calcium Chloride, CaCl₂), the reaction triggers instant polymerization, forming a dense hydrated silica gel that fills the pore spaces.
Expected Enhancements
- • UCS: 0.5 – 3.0 MPa (sandstone-like).
- • Permeability reduced by orders of magnitude.
- • Effective seepage cut-off across grouted zone.
Chemical grout successfully solidified within the sand matrix, achieving high structural cohesion and the expected strength gains.
Grout failed to solidify or cure — zero strength gain due to the presence of water.
Reference: Yonekura & Miwa, 1993.
Why It Fails in Saturated Ground
- • Dilution — excess pore water prevents proper polymerization.
- • Leaching — groundwater flow washes the grout away before curing.
- • Conclusion — inefficient and unsuitable for zones with high groundwater tables.
Sodium Silicate as a Concrete Admixture
Adding Na₂SiO₃ directly to concrete mixes — a controlled destructive test on 15 × 15 × 15 cm cubes.
Mix Design (per 2 cubes)
Failure Mechanisms
Reference: Taylor, 1997.
28-Day Compressive Strength
| Mix | Failure Load (kN) | Compressive Strength (MPa) | Change |
|---|---|---|---|
| Control (0% silicate) | 606.9 | 26.9 | 100% reference |
| Sodium silicate 2.5% | 467.5 | 20.7 | −23.0% |
| Sodium silicate 5.0% | 380.0 | 16.8 | −37.5% |
Inside concrete, sodium silicate acts as a structural pollutant — severely hindering standard cement hydration and producing progressively weaker mixes as dosage increases. The admixture is counterproductive for compressive strength.
Synthesis Across the Three Phases
From failed carboy trials to pressurized field grouting and the chemistry of sodium silicate.
Phase 1 — Cement Grouting Trials
Failed to achieve required permeability and homogeneous stabilization.
- • Bleeding & sedimentation: high water caused separation within 23 min.
- • Surface clogging: low water raised viscosity, blocking pores up to 60 cm.
- • Gravity limits: 1.5 m pipe height lacked pressure to overcome pore resistance.
Phase 2 — Sodium Silicate Grouting
- • Viscosity and particle stability adjusted successfully.
- • Full-depth penetration achieved.
- • Homogeneous distribution throughout the sand.
- • Increased UCS & dry density; decreased permeability.
Load–Settlement Behavior
Plate load tests compared grouted samples against a loose sand baseline (13.1 kN/m³, ultimate load 0.09 kN). Grout ratios were tested from 10:1 down to 4:1.
| Load (kN) | Settlement (mm) |
|---|---|
| 0 | 0 |
| 0.01 | 0.03 |
| 0.02 | 0.05 |
| 0.03 | 0.07 |
| 0.04 | 0.08 |
| 0.05 | 0.13 |
| 0.07 | 0.33 |
| 0.08 | 0.44 |
What the Three Phases Prove
Efficiency depends strictly on grout penetration through the sand pores — controlled by viscosity, pressure, and confinement.
Chapter 1 — Bibliography
- 1.Clough, G. W., & Baker, W. H. (1986). Grouting for Support of Deep Excavations. Journal of Geotechnical Engineering, ASCE.
- 2.Hausmann, M. R. (1990). Engineering Principles of Ground Modification. McGraw-Hill.
- 3.Karol, R. H. (2003). Chemical Grouting and Soil Stabilization. CRC Press.
- 4.Mitchell, J. K., & Santamarina, J. C. (2005). Fundamentals of Soil Behavior. John Wiley & Sons.
- 5.Taylor, H. F. (1997). Cement Chemistry. Thomas Telford Publishing.
- 6.Warner, J. (2004). Practical Handbook of Grouting: Soil, Rock, and Structures. John Wiley & Sons.
- 7.Yonekura, R., & Miwa, M. (1993). Fundamental Properties of Sodium Silicate Grouts. Soils and Foundations.