IS 2132 Part 1 : 1986Code of practice for thin-walled tube sampling of soils - Stationary piston sampler

IS 2132 (Part 1) specifies the code of practice for thin-walled tube sampling of soils — stationary piston sampler. Thin-wall tube (Shelby tube) sampling is the gold-standard method for obtaining undisturbed cohesive soil samples for laboratory testing — particularly UCS (IS 2720 Part 10:1991), triaxial (Part 11), and consolidation tests.

Use IS 2132 Part 1 thin-walled tube sampling when: - Cohesive soil characterisation for foundation design - Soft / sensitive clay sampling (where SPT split-spoon disturbance is severe) - Sites where minimal sample disturbance is critical (sensitive structures, dam, bridge) - Sites with deep cohesive layers - Quality geotechnical investigation per IS 1892:1993

Thin-wall tube samples are essential for: - Triaxial UU/CU tests — accurate undrained / consolidated-undrained shear strength - Consolidation tests — accurate compression index Cc + Cv coefficient of consolidation - Permeability tests — undisturbed soil permeability - UCS tests — accurate c_u from undisturbed sample (vs disturbed sample which over-estimates)

Sampling ratio (Area Ratio AR): - AR = (D_outer² − D_inner²) / D_inner² × 100 % - Thin-wall tube: AR < 10 % (good — minimal soil displacement) - SPT split-spoon: AR ~ 100-115 % (significant disturbance) - AR is the key indicator of sample disturbance

Standard tube dimensions (Clause 4): - Inner diameter (ID): 75 mm (3 inch) — most common; 100 mm for large samples - Outer diameter (OD): 76.5 mm at sampling end - Wall thickness: 1.5-2 mm - Length: 600-900 mm typical - Material: stainless steel or galvanised mild steel; smooth interior surface - End: sharpened cutting edge (taper 1:25)

Stationary piston sampler: - Piston initially blocks tube interior - Tube driven down past piston; piston stays at original position - Soil enters tube through open end - Sample of length = tube travel; piston prevents sample compression

Sampling procedure: 1. Drill borehole to sampling depth using rotary or auger drill. 2. Clean borehole bottom — remove cuttings, slurry. 3. Lower piston sampler with piston engaged at bottom. 4. Push sampler steadily into soil at constant rate (or single push using hydraulic force). 5. Recover sampler — gentle withdrawal to avoid suction. 6. Cap sampler ends — wax + plastic caps to prevent moisture loss + disturbance. 7. Label — project, date, depth, BH number. 8. Transport — vertical, padded; avoid shock + temperature extremes.

Acceptance: - Recovery ratio (length recovered / length pushed): 95-100 % expected - Recovery < 90 % indicates poor sampling (caving, leakage); discard sample - Visual inspection: smooth, undisturbed soil; cracks / fissures visible if disturbance occurred

Lab handling: - Extrude sample from tube using hydraulic extruder (push from bottom up) - Trim ends + middle for testing - Test within 7 days of sampling (longer storage causes moisture redistribution)

Sampling cadence: - Per IS 1892:1993: undisturbed sample every 3 m in cohesive layers - Critical strata: every 1.5-2 m - For consolidation: every depth where settlement matters - Multiple samples per stratum for statistical confidence

Soil suitability: - Soft to stiff cohesive soils (c_u 5-100 kPa): excellent sample quality - Very soft sensitive clays: very careful sampling; even thin-wall causes disturbance - Stiff clays: hard to push; may need additional pressure or mechanical advance - Silty / sandy soils: poor recovery; sample disturbance high - Granular soils (sand, gravel): not suitable; sample falls out; use SPT or other in-situ testing

Compared to SPT split-spoon (IS 2131):

| Sampler | Area ratio | Sample quality | Use | |---|---|---|---| | Thin-wall (this code, IS 2132 Part 1) | < 10 % | Excellent | Cohesive; lab UCS / triaxial / consolidation | | Split-spoon (IS 2131) | ~110 % | Disturbed | All soils; SPT N-value + classification |

Sampling errors that invalidate sample: - Non-cohesive soil falls out - Cut-off in tube due to oversize particles - Caving of borehole walls - Excessive friction (long sample, friction force > soil shear strength → sample sheared) - Heavy tamping / shock during transport - Long delay between sampling + testing (moisture migration)

Sample disturbance indicators: - Visible fissures + cracks on extruded sample - Compaction at top (piston pressure); use bottom portion - Bow / curvature of sample (eccentric pushing) - Volume change (compressed during sampling)

Storage: - Wax-sealed at both ends - Vertical orientation - Refrigeration (4-10 °C) for extended storage - Test within 7 days; max 30 days

Cost: - Thin-wall tube: ₹500-1500 each (reusable for similar soil types) - Sampling labour: 1-2 hours per sample - Lab tests on the sample: ₹3000-15000 per sample (UCS / triaxial / consolidation)

• IS 2132 Part 2 — non-stationary thin-walled tube sampler.
• IS 2720 Part 4:1985 — soil grain-size analysis (preliminary characterisation).
• IS 2720 Part 5:1985 — Atterberg limits.
• IS 2720 Part 10:1991 — UCS (the main lab test on thin-wall samples).
• IS 2720 Part 11:1993 — triaxial UU.
• IS 2720 Part 15 — consolidation test.
• IS 2720 Part 17 — CBR (less common on thin-wall samples).
• IS 2720 Part 30 — vane shear (in-situ; complement to thin-wall sampling).
• IS 2131:1981 — SPT.
• IS 1892:1993 — site investigation procedure.
• IS 1498:1970 — soil classification.
• IS 6403:1981 — bearing capacity.
• IS 8009 Part 1:1976 — settlement.
• ASTM D1587 — international counterpart for thin-wall sampler.
• ASTM D6151 — international counterpart for stationary piston sampler.
• BS 5930 — UK code for site investigation.

1. Thin-wall sampling in granular soil. Sample falls out; useless. Use SPT or other test for granular. 2. Use SPT split-spoon for triaxial / consolidation testing. AR > 100 % causes severe disturbance; results unreliable. Use thin-wall. 3. Tube end damaged / dull. Cutting edge folds soil; disturbance increases. Inspect + replace tube. 4. No piston in 'piston sampler'. Sample compresses; result inflated. Verify piston engaged. 5. Long delay between sampling + testing. Moisture migration; strength changes. Test within 7 days. 6. No wax seal at ends. Moisture loss; sample dries; strength rises artificially. Wax + cap. 7. Heavy handling / drop. Sample shocked; structure disturbed. Pad; vertical orientation. 8. Excessive recovery in soft clay. Recovery > 110 % indicates over-sampling (heave); discard. 9. Insufficient recovery (< 90 %). Caving / loss; sample not representative; discard. 10. Sample at edge of tube tested. Wall friction zone disturbed; use middle portion. 11. Multiple samples extruded from same tube without cleaning. Cross-contamination; clean tube between uses. 12. No sample identification. Tracking lost; lab can't assign to project. Mandatory labelling.

Investigation cascade for cohesive site:

1. Reconnaissance + boring plan (IS 1892:1993). 2. Borehole drilling with rotary drill. 3. In-situ tests at intervals: - SPT (IS 2131:1981) every 1.5 m - Vane shear (IS 2720 Part 30:1980) in cohesive layers 4. Undisturbed sampling (this code, IS 2132 Part 1): - Every 3 m in cohesive strata - Critical depths - Multiple samples per stratum 5. Lab testing on thin-wall samples: - Index tests (Parts 4, 5) - UCS (Part 10:1991) - Triaxial UU/CU (Part 11) - Consolidation (Part 15) 6. Synthesis: - Soil profile + strength + compressibility - Foundation recommendation - Settlement estimate 7. Foundation design (IS 1080:1985, IS 2911 series).

Thin-wall tube sampling is the foundation of reliable geotechnical characterisation in cohesive soils. Without it, lab tests are compromised; with it, foundation design is well-grounded. For any project on cohesive subgrade, IS 2132 Part 1 sampling is non-negotiable.