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SOFT SOIL (PROBLEMS & STABILISATION METHOD) Session 2 - 7 Course: S0892 - Ground Improvement Method Year: 2010.

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Presentation on theme: "SOFT SOIL (PROBLEMS & STABILISATION METHOD) Session 2 - 7 Course: S0892 - Ground Improvement Method Year: 2010."— Presentation transcript:

1 SOFT SOIL (PROBLEMS & STABILISATION METHOD) Session Course: S Ground Improvement Method Year: 2010

2 Bina Nusantara COURSE 2 Content: Soft Soil Problems Stabilization Methods: – Preloading & Vertical Drain – Stone Column – Dynamic Compaction – Chemical Stabilization – Reinforcement

3 Bina Nusantara SOFT SOIL PROBLEMS LOW BEARING CAPACITY HIGH SETTLEMENT LIQUEFACTION

4 Bina Nusantara SOFT SOIL PROBLEMS LOW BEARING CAPACITY

5 Bina Nusantara SOFT SOIL PROBLEMS SETTLEMENT

6 Bina Nusantara SOFT SOIL PROBLEMS LIQUEFACTION

7 Bina Nusantara STABILIZATION METHOD PRELOADING & VERTICAL DRAIN Encountered problems on fine grained soft soil are low strength, and high compressibility Preloading by surcharge embankment applied to reduce compressibility and increases soil strength Fine grained soil possessed very low permeability that consolidation process takes very long time Vertical drains provide drainage paths to reach the surface

8 Bina Nusantara PRELOADING & VERTICAL DRAIN BASIC PRINCIPLE Surcharge

9 Bina Nusantara PRELOADING & VERTICAL DRAIN BASIC PRINCIPLE

10 Bina Nusantara VERTICAL DRAIN DESIGN

11 Bina Nusantara VERTICAL DRAIN DESIGN D = 1.05 S D = 1.13 S

12 Bina Nusantara VERTICAL DRAIN INSTALLATION

13 Bina Nusantara VERTICAL DRAIN + VACUUM Vacuum load can reach greater than 80kPa (equals to 4 – 5 m height preloading fills with  = 17 – 18 kN/m 3 ) Rapidly decreases excess pore water pressure Inward lateral movement

14 Bina Nusantara VACUUM CONSOLIDATION

15 Bina Nusantara CONVENTIONAL VD VS VACUUM CONSOLIDATION CONVENTIONAL VERTICAL DRAINVACUUM CONSOLIDATION

16 Bina Nusantara STABILIZATION METHOD VIBRO COMPACTION Compaction of loose granular soils by penetration of a vibratory probe or vibroflot. Should combine with sand/stone column if applied in fine grained soil Affected area by the compaction energy : m

17 Bina Nusantara STABILIZATION METHOD STONE COLUMN

18 Bina Nusantara STONE COLUMN DESIGN BEARING CAPACITY SINGLE STONE COLUMN Where:  v = vertical stress in stone column  hs = passive resistance of surrounding soil (the effect of loading shall be considered)  v ’ = effective friction angle of stone column (35 o – 40 o ) c u = undrained cohesion of surrounding soil P L = Pressuremeter limit presssure Formula 1  Formula 2  Formula 3  Allowable Bearing Capacity FS = Factor of Safety = 3

19 Bina Nusantara STONE COLUMN DESIGN Available design methods with respect to settlement: (1) Equilibrium Method (2) Priebe’s Method (3) Granular Wall Method (4) Greenwood Method (5) Incremental Method and (6) Finite Element Method Derived from unit cell idealisation, stone column is modelled to be a concentric body in a composite soil mass.

20 Bina Nusantara STONE COLUMN DESIGN

21 Bina Nusantara STONE COLUMN NOTES Typical design values per column in range of 200 to 300 kN/column Young modulus of stone column in range of 40 to 70 Mpa The settlement of single stone column under design load usually in range of 5 to 10 mm The maximum settlement of sotne column group is 100mm

22 Bina Nusantara STONE COLUMN INSTALLATION vibrator makes a hole in the weak ground hole backfilled..and compacted Densely compacted stone column

23 Bina Nusantara STONE COLUMN INSTALLATION WET METHOD

24 Bina Nusantara STONE COLUMN INSTALLATION DRY METHOD (TOP-FEED METHOD)

25 Bina Nusantara STONE COLUMN INSTALLATION DRY METHOD (BOTTOM-FEED METHOD)

26 Bina Nusantara STONE COLUMN INSTALLATION BOREHOLE METHOD (RAMMED COLUMN)

27 Bina Nusantara VIBROFLOTATION Vibro Compaction Method by using a self vibrating probe or a vibroflot Vibroflot (vibrating unit) Length = 2 – 3 m Diameter = 0.3 – 0.5 m Mass = 2 tonnes

28 Bina Nusantara VIBROFLOTATION

29 Bina Nusantara VIBROFLOTATION INSTALLATION

30 Bina Nusantara STABILIZATION METHOD DYNAMIC COMPACTION A method of improving the ground using that involves very high energy waves by hammering the earth Pounders weighing 15 to 40 tons are released in free fall from a height of 10 to 40 m. Most suitable for granular soil

31 Bina Nusantara DYNAMIC COMPACTION Cost effective method for: - sand densification - soil compaction - ground compaction - land fill treatment - unconsolidated fill or soil treatment

32 Bina Nusantara DYNAMIC COMPACTION

33 Bina Nusantara DYNAMIC COMPACTION For design, suitability assessment, and determination of optimum field operation parameters rely mainly on : - Empirical Equations - Field Pilot Tests - Past experiences

34 Bina Nusantara DYNAMIC COMPACTION

35 Bina Nusantara DYNAMIC COMPACTION DESIGN Effective Depth Improved

36 Bina Nusantara DYNAMIC COMPACTION DESIGN Applied Energy

37 Bina Nusantara DYNAMIC COMPACTION DESIGN Design Chart

38 Bina Nusantara DYNAMIC COMPACTION DESIGN Design Procedure

39 Bina Nusantara DYNAMIC COMPACTION MECHANISM IN COHESIONLESS SOIL

40 Bina Nusantara DYNAMIC COMPACTION NOTES Important notes for deep compaction (1) Effective depth will not exceed 15 m in practice (Lukas, 1986). (2) Depth of compaction (D) is proportional to the square root of the impact energy (Metric Ton*Meter) /drop. Different relations have been proposed. D = (W*h) 1/2 for cohesive material (Menard and Broise, 1975) D = 0.5 (W*h) 1/2 for cohesionless material (Leonards et al., 1980) Actually, D = 0.3~0.7 (W*h)1/2 from field observation. Use a higher value for loose soils. (3) Maximum improvement occurs within a zone between 1/3 to 1/2 the depth of compaction. (4) If a line is attached from the crane to the weight, the efficiency of the energy reduces by 20% (Lukas, 1986). (5) The ground water has to be at least 2 m below existing ground or 0.6 m below the bottom of craters. (6) An area of 5,000 to 10,000 m2 is required to be economical. (7) Vibration and noise (115 to 120 dB at source) may be a concern to the nearby developments. Figure 1.3 shows the estimated vibration velocity due to the compaction (Lukas, 1986). (8) Minimum 34 ~ 50 m clearance from any structure. (9) The number of repeated drop on the same spot should be limited to drops (Lukas, 1986)

41 Bina Nusantara STABILIZATION METHOD CHEMICAL STABILIZATION INJECTION GROUTING DEEP SOIL MIXING JET GROUTING

42 Bina Nusantara CHEMICAL STABILIZATION

43 Bina Nusantara INJECTION GROUTING 1. install grout pipes using drilling or driving techniques. 2. The mortar-like grout, injected under certain pressure through the pipes. The grout pipe is then lifted some distance (0.3 to 1.5 m), and the injection process is repeated. 3. Grouting can stiffen and strengthen the soil layer by in creasing its density, and acting as a reinforcement. Grouting may also be used to re-level a structure that has been damaged by differential settlements.

44 Bina Nusantara DEEP SOIL MIXING Soil Mixing is the mechanical blending of the in situ soil with cementitious materials. Strengthen soft and wet cohesive soils in a very short time period Treatment is possible up to depths of 30 m

45 Bina Nusantara DEEP SOIL MIXING

46 Bina Nusantara JET GROUTING Uses high kinetic energy (20-60 MPa) liquid spurt (jet) for chopping up the ground around and mixing it with binding agent. Can be used for treating most soil types

47 Bina Nusantara JET GROUTING TYPES

48 Bina Nusantara JET GROUTING

49 Bina Nusantara CHEMICAL STABILIZATION – RESULT

50 Bina Nusantara STABILIZATION METHOD REINFORCEMENT

51 Bina Nusantara REINFORCEMENT BASIC PRINCIPLE

52 Bina Nusantara REINFORCEMENT MATERIAL GEOSYNTHETIC


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