Research Needs Masaki KITAZUME, Dr. Eng. Tokyo Institute of - - PowerPoint PPT Presentation

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Research Needs Masaki KITAZUME, Dr. Eng. Tokyo Institute of - - PowerPoint PPT Presentation

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QC/QA for Deep Mixing - Current Practice and Future Research Needs Masaki KITAZUME, Dr. Eng. Tokyo Institute of Technology Factors Affecting Strength Increase 1. Characteristics of Type of binder binder Quantity Mixing water and additives

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SLIDE 1

QC/QA for Deep Mixing - Current Practice and Future Research Needs

Masaki KITAZUME, Dr. Eng. Tokyo Institute of Technology

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SLIDE 2

May 30, 2019

  • M. Kitazume (TIT)

Factors Affecting Strength Increase

1. Characteristics of binder Type of binder Quantity Mixing water and additives 2. Characteristics and conditions of soil Physical, chemical and mineralogical properties of soil Organic content pH of pore water Water content 3. Mixing conditions Degree of mixing Timing of mixing/re-mixing Quantity of binder 4. Curing conditions Temperature Curing time Humidity Confining pressure Wetting and drying/freezing and thawing, etc.

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SLIDE 3

Execution

May 30, 2019

  • M. Kitazume (TIT)

cement silo slurry plant & agitator slurry pumps

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SLIDE 4

Construction procedure

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  • M. Kitazume (TIT)

4 column

binder per min. binder per vol. torque of mixing shaft rpm of mixing shaft speed of mixing shaft depth of mixing shaft time

〇

mixing blades

〇 〇 〇

sand blanket

〇

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SLIDE 5

principle of quality control

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cement factor, F

           c w v f F / 1 1 4

slurry

where F : cement factor (kg/m3) f : flow rate of cement slurry (m3/min) v : speed of mixing blade (m/min) w/c : water cement ratio of cement slurry slurry : unit weight of cement slurry (kg/m3)

           

u u d d

V N V N M T

where T : blade rotation number (n/m) M : total number of mixing blades Nd : blade rotation speed during penetration (rpm) Vd : blade penetration speed (m/min) Nu : blade rotational speed during withdrawal (rpm) Vu : blade withdrawal speed (m/min)

blade rotation number, T

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SLIDE 6

Key factors for quality

  • Effect of number of blades -

May 30, 2019

  • M. Kitazume (TIT)

After Nishibayashi et al., 1985

Entrained rotation phenomenon, disturbed soft soil adheres to and rotates with the mixing blade without efficient mixing, may take place in one shaft blade, which decrease degree of mixing.

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SLIDE 7

Key factors for quality

  • Effect of blade shape -

May 30, 2019

  • M. Kitazume (TIT)

Mixing blade type-A (Abe et al., 1997) Mixing blade type-B, comparison of quality with and without free blade (Enami et al., 1985)

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Vertical wing enhances the up-down movement of soil together with the horizontal movement, that is effective for uniform mixing

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SLIDE 8

Key factors for quality

  • Effect of blade shape -

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  • M. Kitazume (TIT)

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Rake angle

large rake angle enhances the up-down movement of soil together with the horizontal movement, that is effective for uniform mixing

Free blade and bracing plate

to prevent the "entrained rotation phenomenon."

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SLIDE 9

Key factors for quality

  • Effect of mixing efficiency -

May 30, 2019

  • M. Kitazume (TIT)

Blade rotation number, T (times/m)

           

u u d d

V N V N M T

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where T : blade rotation number (n/m) M : total number of mixing blades Nd : blade rotation speed during penetration (rpm) Vd : blade penetration speed (m/min) Nu : blade rotational speed during withdrawal (rpm) Vu : blade withdrawal speed (m/min)

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SLIDE 10

Key factors for quality

  • Effect of speed -

May 30, 2019

  • M. Kitazume (TIT)

After Enami et al., 1986 After Nishibayashi et al., 1985 10

effect of rotation speed effect of penetration speed

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SLIDE 11

strategy for quality control

inject small amount of slurry with low w/c ratio

economic, low ground heaving small size slurry pipe, easy to control flow rate of slurry low w/c ratio (large viscosity) of slurry requires large pump capacity chemical additives for reducing viscosity, install facility

inject large amount of slurry with high w/c ratio

less economic, large ground heaving large size slurry pipe, difficult to control flow rate of slurry in the case of low flow rate large w/c ratio (low viscosity) of slurry does not require large pump capacity no facility for chemical additives

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SLIDE 12

strategy for quality control

large rake angle of mixing blade

up-down movement of soil enhances uniform and large strength large resistance requires large capacity mixing motor, low rpm is required chemical additive or air mist for reducing mixing energy

small rake angle of mixing blade

no up-down movement of soil makes uniform and large strength small resistance requires small capacity mixing motor, high rpm can be achieved no facility for chemical additive or air mist for reducing mixing energy

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  • M. Kitazume (TIT)

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Construction procedure

  • switching penetration injection to withdrawal injection,

bottom and surface treatment -

bottom treatment surface treatment

more cement and mixing are necessary more cement and mixing are necessary

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SLIDE 14

Construction procedure, Example

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200 400 600 800 1000

  • 40.0
  • 30.0
  • 20.0
  • 10.0

0.0 10.0 20 40 60 80 100

depth CL. (m)

Duaration time (min)

mixing blade (bottom) mixing blade (top) water soil layrs water injection binder injection mixing blade torque load

mixing blade cement injection torque water injection rpm

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SLIDE 15

Construction procedure and analysis

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  • 30
  • 20
  • 10

10 100 200 300 400 500

depth CL. (m) Binder factor (kg/m3)

3EE013-09-L - 3EE-1 (Analysis)

BF water

  • 30
  • 20
  • 10

10 2 4 6 8 10

depth CL. (m) W/C ratio

3EE013-09-L - 3EE-1 (Analysis)

W/C water soil layrs column

  • 30
  • 20
  • 10

10 0% 10% 20% 30% 40% 50%

depth CL. (m) Binder content (%)

3EE013-09-L - 3EE-1 (Analysis)

BC water soil layrs column

  • 30
  • 20
  • 10

10 500 1,000 1,500 2,000 2,500 3,000

depth CL. (m) qu (kN/m2)

3EE013-09-L - 3EE-1 (Analysis)

quf quf (estimate) water soil layrs column

W/C ratio Binder factor Binder content Measured and estimated USC

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Quality of overlapping

May 30, 2019

  • M. Kitazume (TIT)

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rolling and pitching of barge

tidal wave, buoyancy force and soil resistance force of mixing shafts and blades weight loss of cement injected multiple mixing units enhance barge movements sufficient anchoring & ballast tanks are required to minimize the barge movements and assure the verticality.

soil resistance force during withdrawal buoyancy force soil resistance force during penetration

weight loss of cement

  • verlap : 0.3 m

stabilized soil columns 100 1 30 3 .   m m y verticalit at -30 m

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SLIDE 17

Quality assurance

  • Core sampling -

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A Denison type sampler, double tube core sampler, or triple tube core sampler are recommended. A large diameter such as 86 mm or 116 mm is recommended.

RQD description of rock quality 0 - 25% very poor 25 - 50% poor 50 - 75% fair 75 - 90% good 90 - 100% excellent length run core Total 10cm pieces core

  • f

length

  RQD

The RQD (Rock Quality Designation) index

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SLIDE 18

Quality assurance

  • Laboratory test -

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Unconfined compression test

specimen: 5 cm x 10 cm loading speed: 1 %/min. data to be reported qu, qur, ef, E50, E50/qu t, d, w (%)

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SLIDE 19

Concluding remarks

Quality control

quality control is essential for assuring the uniformity and strength and the verticality of stabilized soil column

Quality assurance

core sampling and unconfined compression test are necessary

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Thank you for your kind attention

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