Pertemuan 03 Penyelidikan Tanah

1. Pertemuan 03Penyelidikan Tanah Matakuliah : S2094 / Rekayasa Pondasi Tahun : 2005 Versi : 1.1 • Media referensi video : DrillingAndSampling.wmv minicone.wmv

2. Site Exploration and Characterization “Subsurface material properties cannot be specified; they must be deduced through exploration.” Charles Dowding (1979)

3. Objectives • Determine location and thickness of soil and rock strata (subsurface soil profile) • Determine location of groundwater table • Recover samples for laboratory testing • Conduct lab and/or field testing • Identify special problems and concerns

7. Site Exploration; General Strategy • Project Assessment • Literature Search • Field Reconnaissance • Subsurface Drilling and Sampling • Laboratory Testing of Soil Samples

8. Project Assessment • Type, location and approximate dimensions of the proposed development • Existing topography and any proposed grading • Any previous developments

9. Literature Search • Geologic Maps • Soil Survey Reports • Geotechnical Reports • Historic Groundwater Data

10. Geologic Maps

11. Remote Sensing • Conventional Aerial Photographs • Geologic features (landslides, faults), topography, drainage patterns • Site history • Infrared Aerial Photographs • Springs, seepage zones • Useful in slope stability investigations

12. Field Reconnaissance • Any previous developments, grading etc. • Site topography, any signs of slope instability (landslides, soil creep) • Site drainage conditions • Rock outcrops • Site access

13. Field Exploration • Site Boring Layout • Test Borings or Test Pits? • It depends on the type of materials, and what you want to know. • Number and Frequency of Borings • Depth, Sampling Methods and Field Testing

14. Field Exploration

15. III. Subsurface Exploration/Sampling • Borehole Spacing • Site conditions/uniformity • type of structure (bridge, building, landfill) • typically one borehole/2500 ft2 • Also see Table 4.1 (p.108) • Borehole Depths • Magnitude of loading/soil conditions • Also see Table 4.3 (p.109)

16. How Many Borings?

17. How Deep?

18. Look Up and Live! • Safety Awareness • Regular Emphasis

19. Drilling and Sampling of Soils • Subsurface Drilling • Auger Drilling • Solid Stem Auger • Hollow Stem Auger • Rotary Drilling • Bucket Auger • Percussion (or Cable Tool) Drilling

20. Auger Drilling

21. Auger Drilling • Hollow Stem Auger • Casing with outer spiral • Inner rod with plug/or pilot assembly • For sampling, remove pilot assembly and insert sampler • Typically 5ft sections, keyed, box & pin connections • Maximum depth 60-150ft

22. Hollow-Stem Augers

23. Air or Mud Rotary Drilling • http://www.redi-drill.com/ms-index.htm

24. Rotary Drilling • Bit at the end of drill rod rotated and advanced • Soil/rock cuttings removed by circulating drilling fluid • Common drilling fluid; bentonite in water with slurry density 68-72pcf • Air may be used as drilling fluid

25. Cable Tool Drilling • Not common in US in geotechnical explorations • Heavy impact drilling tools lifted and dropped • Impact loosens soil and rock • Cuttings removed with a bailer • Slow process; Used in environmental explorations where drilling fluid is not permitted

26. Rock Drilling, Coring, Augering • http://www.globaldrilsup.com/cat-index.html

27. Soil and Rock Sampling • Disturbed samples • In-place structure is not preserved • Okay for determination of soil index properties • “…Estimating the nature of the formation from the cuttings is like identifying the cow from the hamburgers.” G.F. Sowers

28. Soil and Rock Sampling • Undisturbed samples • Minimizes effects from potential disturbance • Needed for determination of in-situ density, in-situ permeability, soil shear strength and compressibility

29. Soil Samplers • Standard Split Spoon Samplers • Shelby Tube Samplers • Piston Samplers • Heavy Wall Samplers

30. Standard Split Spoon Samplers • Thick wall (0.25in) cylinder • Sampling tube is split along the length • Hammered into the ground

31. Shelby Tube (Thin-wall) Samplers • Thin wall (1/16in) sampling tube • Sampler pushed into the ground hydraulically • Sample extruded from tube

32. Piston Samplers • Minimizes sample disturbance caused by back-pressure

33. Heavy-Wall Samplers • Thicker walls provide better strength & durability • However, it creates more disturbance • Sampler pounded into the ground

34. Groundwater Monitoring • Groundwater level must be determined during geotechnical investigation • Can be accomplished by leaving selected soil borings open

35. In-situ Testing • When it is difficult to obtain “undisturbed” samples • Cohesionless soils, Sensitive clays • In-situ Test Methods • Standard Penetration Test (SPT) • Cone Penetration Test (CPT) • Pressuremeter Test • Flat Plate Dilatometer Test

36. Standard Penetration Test (SPT) • 140 lb (63.5 kg) Hammer • 30in (76 cm) free fall • Drive sampler over 18 inches • Record no. of blows per each 6 inch penetration • SPT blow count=blows for 2nd 6 inch penetration + blows for 3rd 6inch penetration

37. Standard Penetration Test (SPT)

38. Standard Penetration Test (SPT)

39. Types of SPT Hammers

40. Corrections to SPT blow Counts • Factors affecting SPT blow count: • Hammer Efficiency (See Table 4.3) • Borehole diameter (See Table 4.4) • Type of sampler (See Table 4.4) • Rod length (See Table 4.4)

41. SPT Correction Factors

42. SPT Overburden Correction

43. Use of SPT Data • To Determine Relative Density, Dr • From AASHTO Chart • From Eq. (4.3) p.122 • To determine  • From Figure 4.11 (p.123) • To determine C • From AASHTO Chart