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

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 2. Characteristics Physical, chemical and mineralogical properties of soil and conditions of Organic content soil 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. May 30, 2019 M. Kitazume (TIT) 2

Execution cement silo slurry plant & agitator slurry pumps May 30, 2019 M. Kitazume (TIT) 3

Construction procedure 〇 〇 〇 〇 〇 sand blanket mixing blades binder per vol. binder per min. rpm of mixing shaft speed of mixing shaft torque of mixing shaft time column depth of mixing shaft May 30, 2019 M. Kitazume (TIT) 4

principle of quality control cement factor, F    where 4 f  slurry F : cement factor (kg/m 3 ) F    1    : flow rate of cement slurry (m 3 /min) f v 1   w / c v : speed of mixing blade (m/min) w/c : water cement ratio of cement slurry  slurry : unit weight of cement slurry (kg/m 3 ) blade rotation number, T   N N       d u T M    V V  where d u T : blade rotation number (n/m)  M : total number of mixing blades N d : blade rotation speed during penetration (rpm) V d : blade penetration speed (m/min) N u : blade rotational speed during withdrawal (rpm) V u : blade withdrawal speed (m/min) May 30, 2019 M. Kitazume (TIT) 5

Key factors for quality - Effect of number of blades - 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. After Nishibayashi et al., 1985 May 30, 2019 M. Kitazume (TIT) 6

Key factors for quality - Effect of blade shape - Mixing blade type-A (Abe et al., 1997) Mixing blade type-B, comparison of quality with and without free blade (Enami et al., 1985) Vertical wing enhances the up-down movement of soil together with the horizontal movement, that is effective for uniform mixing May 30, 2019 M. Kitazume (TIT) 7

Key factors for quality - Effect of blade shape - 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." May 30, 2019 M. Kitazume (TIT) 8

Key factors for quality - Effect of mixing efficiency - Blade rotation number, T (times/m)   N N       d u T M     V V d u where T : blade rotation number (n/m)  M : total number of mixing blades N d : blade rotation speed during penetration (rpm) : blade penetration speed (m/min) V d N u : blade rotational speed during withdrawal (rpm) V u : blade withdrawal speed (m/min) May 30, 2019 M. Kitazume (TIT) 9

Key factors for quality - Effect of speed - effect of rotation speed effect of penetration speed After Nishibayashi et al., 1985 After Enami et al., 1986 May 30, 2019 M. Kitazume (TIT) 10

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 May 30, 2019 M. Kitazume (TIT) 11

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 May 30, 2019 M. Kitazume (TIT) 12

Construction procedure - switching penetration injection to withdrawal injection, bottom and surface treatment - more cement and surface treatment mixing are necessary more cement and mixing are necessary bottom treatment May 30, 2019 M. Kitazume (TIT) 13

Construction procedure, Example 10.0 1000 0.0 800 water injection cement injection mixing blade -10.0 600 depth CL. (m) mixing blade (bottom) -20.0 400 mixing blade (top) water soil layrs water injection -30.0 200 binder injection torque mixing blade rpm torque load -40.0 0 0 20 40 60 80 100 Duaration time (min) May 30, 2019 M. Kitazume (TIT) 14

Construction procedure and analysis Binder factor W/C ratio 3EE013-09-L - 3EE-1 (Analysis) 3EE013-09-L - 3EE-1 (Analysis) 10 10 0 0 depth CL. (m) depth CL. (m) -10 -10 BF W/C -20 -20 water water soil layrs column -30 -30 0 100 200 300 400 500 0 2 4 6 8 10 Binder factor (kg/m3) W/C ratio Binder content Measured and estimated USC 3EE013-09-L - 3EE-1 (Analysis) 3EE013-09-L - 3EE-1 (Analysis) 10 10 0 0 depth CL. (m) depth CL. (m) -10 -10 quf BC quf (estimate) -20 -20 water water soil layrs soil layrs column column -30 -30 0% 10% 20% 30% 40% 50% 0 500 1,000 1,500 2,000 2,500 3,000 Binder content (%) qu (kN/m2) May 30, 2019 M. Kitazume (TIT) 15

Quality of overlapping rolling and pitching of barge tidal wave, buoyancy force and soil resistance force of mixing shafts and blades weight weight loss of cement injected loss of multiple mixing units enhance barge movements cement sufficient anchoring & ballast tanks are required to minimize the barge movements and assure the verticality. 0 . 3 m 1   stabilized soil columns verticalit y 30 m 100 soil resistance force during withdrawal at -30 m soil resistance force overlap : 0.3 m during penetration buoyancy force May 30, 2019 M. Kitazume (TIT) 16

Quality assurance - Core sampling - 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. The RQD ( Rock Quality Designation ) index   length of core pieces 10cm  RQD description of rock quality RQD Total core run length 0 - 25% very poor 25 - 50% poor 50 - 75% fair 75 - 90% good 90 - 100% excellent May 30, 2019 M. Kitazume (TIT) 17

Quality assurance - Laboratory test - Unconfined compression test specimen: 5 cm x 10 cm loading speed: 1 %/min. data to be reported q u , q ur , e f , E 50 , E 50 / q u  t ,  d , w (%) May 30, 2019 M. Kitazume (TIT) 18

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 May 30, 2019 M. Kitazume (TIT) 19

Thank you for your kind attention May 30, 2019 M. Kitazume (TIT) 20