![1
Geotechnical Engineering–I [CE-221]
BSc Civil Engineering – 4th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/d/forum/2016session-geotech-i
Lecture # 29
15-May-2018](https://image.slidesharecdn.com/29-180924141840/85/Geotechnical-Engineering-I-Lec-29-Soil-Exploration-II-1-320.jpg)
Geotechnical Engineering-I [Lec #29: Soil Exploration - II]
- 1. 1 Geotechnical Engineering–I [CE-221] BSc Civil Engineering – 4th Semester by Dr. Muhammad Irfan Assistant Professor Civil Engg. Dept. – UET Lahore Email: mirfan1@msn.com Lecture Handouts: https://groups.google.com/d/forum/2016session-geotech-i Lecture # 29 15-May-2018
- 2. 2 SOIL EXPLORATION Test Pit 1-2m width 1-4m depth ~100-150 mm dia ~10-60m depth
- 3. 3 SOIL SAMPLES Disturbed Sample (DS) Natural soil conditions (structure, texture, density, natural moisture content, stress conditions, etc.) disturbed during recovery. - Recovered by using shovel, from auger cuttings, etc. Undisturbed Sample (UDS) Natural soil conditions (structure, texture, density, natural moisture content, etc.) undisturbed during recovery. - Recovered using special techniques - ‘undisturbed’ is a relative term. - Impossible to obtain absolute undisturbed soil sample Samples recovered from test pits or boreholes can be of two types;
- 4. 4 Disturbed Soil Samples (DS) Bulk Composite (BS) samples recovered from walls Collected in large bags Test Pits
- 5. 5 Disturbed Soil Samples (DS) From auger cuttings From cuttings in the straight rotary slurry From SPT samples Boreholes Hand Auger Drilling DS from Auger cuttings DS from SPT Split-Spoon Sampler
- 6. 6 (63.5 kg) VIDEO STANDARD PENETRATION TEST (SPT) Split Spoon Sampler
- 8. 8 Weight of the hammer = 63.5 kg Drop height = 30 in (762 mm) No. of blows for penetration of 6 in (0.15 m) is counted No. of blows for First 6 in (0.15 m) = X Second 6 in (0.15 m) = Y Third 6 in (0.15 m) = Z SPT N = Y + Z STANDARD PENETRATION TEST (SPT)
- 9. 9 SPT N (blows/300 mm) Relative Density (%) Friction Angle (degrees) State of Packing 4 20 30 Very Loose 4 – 10 20 – 40 30 – 35 Loose 10 – 30 40 – 60 35 – 40 Medium Dense 30 – 50 60 – 80 40 – 45 Dense > 50 > 80 45 Very Dense SPT N (blows/300 mm) Undrained shear strength, Cu (kPa) Consistency 2 10 Very Soft 2 – 4 10 – 25 Soft 4 – 8 25 – 50 Medium 8 – 15 50 – 100 Stiff 15 – 30 100 – 200 Very Stiff > 30 > 200 Hard SANDS/GRAVELS CLAYS / SILTS
- 10. 10 BOREHOLE LOGS
- 11. 11 Undisturbed Soil Samples (UDS) How to procure UDS? Test pits → Block samples → Easy to recover UDS in clays → In cohesionless soils → UDS recovery very difficult and expensive Test Pits
- 12. 12 Undisturbed Soil Samples (UDS) Test Pits 1. Chiseling out a soil block 2. Pressing a wooden box on soil block 3. Wax being applied to prevent moisture loss 4. Performance of FDT
- 13. 13 UDS in Borehole Shelby tube (Thin-walled tube) → commonly used for recovering UDS in clays UDS in sands → Dennison and/or Pitcher tube Undisturbed Soil Samples (UDS) Boreholes
- 14. 14 Sources of Soil Disturbance? Soil displacement during penetration Inside friction Outside friction Undisturbed Soil Samples (UDS) Boreholes Split-spoon sampler (Thick-walled sampler) DS Shelby tube sampler (Thin-walled sampler) UDS Typical Soil Samplers Area Ratio, Ar Inside Clearance Ratio, Ci Outside Clearance Ratio, Co
- 15. 15 Area Ratio, Ar Defines the degree of disturbance Thicker the wall, greater the disturbance Conceptually, ratio between area of displaced soil to x-area of sample Mathematically, Well-designed sampler → Ar ≤ 25% → Ar ≤ 10% (for Soft Sensitive Soils) Undisturbed Soil Samples (UDS) Boreholes For Split-Spoon Sampler D2 = 51mm D1 = 35mm Ar = 112% 100(%) 2 1 2 1 2 2 D DD Ar
- 16. 16 Inside Clearance Ratio, Ci Defines inside friction offered by sampler as the sample is pushed inside Accommodates for elastic expansion of the sample as it enters the tube Mathematically, Well-designed sampler → Ci should be between 1% - 3% 100(%) 1 13 D DD Ci Undisturbed Soil Samples (UDS) Boreholes
- 17. 17 Outside Clearance Ratio, Co Defines outside friction offered by sampler as the sample is pushed inside Defines the force required to withdraw the tube from borehole Mathematically, Well-designed sampler → Co should not be much greater than Ci → Generally should be between 0 - 2% 100(%) 4 42 D DD Co Undisturbed Soil Samples (UDS) Boreholes
- 18. 18 BOREHOLE LOGS
- 22. 22 THE END In fact, it just the beginning!