BU3102 Construction Technology III

1. BU3102 Construction Technology III Describe the construction process of concrete and/or steel piles for deep foundation. Show case studies.

4. REPLACEMENT PILES

5. Types of Replacement Piles • Percussion Piles • Flush Bored Piles • Rotary Piles

6. PERCUSSION PILE

7. Percussion Piles Method Percussive excavation equipment using grabbing method

8. Percussion Piles Soil Conditions • Coarse gravel and cobbles, glacial till, marls, or thinly bedded shales and clays. A casing oscillator

10. FLUSH BORED PILE

11. Flush Bored Piles Method • Continuous flight auger with a length in excess of the borehole depth is drilled into the soil to the required depth before concrete is cast Continuous Flight Auger

12. ROTARY PILES

13. Rotary Pile Method • Similar to the construction process in our case study.

14. In some situation, it may be possible to increase the end bearing of the pile by enlarging the base of the pile. • This process is known as under reaming.

15. Closed under-ream tool Opened/working position

16. CASE STUDY ROTARY PILES

17. Project: Water Place Condominium (three 15-storey tower blocks) • Location: Tanjong Rhu Road • Developer: Far East Organization • Piling Contractor: WP Piling Co.

18. Tanjong Rhu Road

19. Site Overview

20. Areas to look at: • Site conditions and surroundings • Soil investigations • Soil properties • Why bored piling is used • Sequence of piling - Relevant tests carried out in the course of piling

21. Site Conditions and Surroundings • Reclaimed land, near to waterfront • Surroundings: private residential condominium blocks across the road • Walking distance to the future Boulevard MRT station

22. Soil Investigation • Collecting soil samples for testing or/and visual inspection • Sequence of strata • Ground water level

23. Soil Stratification: Boreholes

24. Soil profile N-value Moisture(%) Medium stiff sandy silty clay 10-20 20-40 Soft to firm marine clay (upper) <3 60-80 Stiff silty clay 20-30 20-40 Soft to firm marine clay (lower) <5 40-60 Dense to very dense clayey sand >100 20-30 Hard silty clay 60-80 20-40 Soil Properties

25. Marine Clay • Kaolinite rich, soft silty clay, with sandy, silty, peaty and shelly fragments

26. Problems Caused by Marine Clay • Ground heave • Adjacent ground surface subsidence • Negative Skin Friction • Low bearing capacity and long term settlement • High Water Table

27. Why Bored Piles are Used • Vibration, noise and dust kept at minimum • Soil conditions: Marine Clay - Low bearing capacity: Deeper foundations such as bored piles are needed to reach firm stratum - Ground heave and negative skin friction: Displacement piling not possible - Rough concrete pile surfaces enhance grip against subsoils

28. Load Transfer: - Bored piles transfer reasonably heavy loads effectively to firm stratum, with larger cross section and combination of concrete (axial load) and reinforcement (lateral load) to take loads. • Site: Spacious for bored pile construction • Can be installed in very long lengths • Cost: cheaper than steel piling

29. Sequence of Construction Setting out: 1. The surveyor sets out the exact location of the pile. Pegging is done by means of a timber or metal stick or peg.

30. Initial Excavation

31. 3. • Insertion of metal casing. • The casing bypasses the initial sand layers. • It serves to guide and align the drilling process.

32. 4. • The boring operation proceeds. • A boring bucket is used to extract wet soils.

33. The boring bucket with a shuttle to drill & extract the marine clay and carry the soft soils to the surface. • Slurries formulated with Laviopol Sint P& water mixed in a storage tank are poured into the bored hole.

34. The mixture of Laviopol Sint P and water is: drilling mud • Stabilizes the soil • Aid in supporting the sides of the bored hole. • Resists water seepage through the sides.

35. 5. • Drilling mud is continuously added into the hole during boring. • Density, viscosity & pH checks: to be carried out constantly on the slurries. • Ensure correct constituency and mix integrity.

36. Litmus paper to find pH value of drilling mud. Apparatus used to measure drilling mud density.

37. The end of bored hole reach stiff/hard strata 5m minimum penetration depth. 6. • The Resident Engineer confirms the depth by lowering a long measuring tape into the hole.

38. Reinforcement cage is lowered into the hole. Each length of cage is 12m. • Each cage is lowered progressively. • Overlapping: 1 - 1.2m

39. Spacers are installed at random positions around the cage. Spacers are essential to provide sufficient concrete cover all round

40. Once all the cages are put in place, its final position is secured by means of a hook bar.

41. The tremie pipes with different component lengths are connected and lowered into the hole progressively.

42. A hopper is connected to the top section, that acts as a funnel. Metal fork to align hopper

43. 9. • Concrete (Grade 35) is transported to the site. • Prior to concreting, some concrete from the truck is taken out & slump test is carried out. • Cube test is done as concrete is placed in 3 cubes.

44. Once the delivered concrete passes the slump test, the truck proceeds to the designated bored hole. • Concrete is poured into tremie pipe.

45. This concreting method requires the concrete to displace the drilling mud. • As the volume of concrete increases at the bottom of the hole, slurries are pushed out of the steel casing. “Washing Effect”

46. 10. • Tremie pipe is hoisted up and down by the crane. • Drilling mud are collected in a nearby earth pit & pumped back into storage water tank for remixing & reuse for the next pile.

47. Drilling mud displaced gets increasingly thicker. • Tremie pipe starts moving up from the hole. Crane will draw out part of tremie pipe & its length reduced by removing section by section.

48. The steel casing is extracted by means of a vibro hammer. Alternatively, the crane is sufficient to pull out the casing.

49. 15. • Once the concrete is cast, the surveyor/engineer sets up apparatus to check the eccentricity of the cast pile. • The cast pile is eventually back-filled for protection.

50. DISPLACEMENTPILES