Backfill grouting is the construction method to fill sup the gap between TBM excavation and segmental lining, which called “Tail Void”.
Prevent the ground movement and surface settlement
due to the volume loss at the tail void.
Stabilize the segmental lining in the ground.
Improve water tightness of the segmental lining.
Generate uniform strength of the ground to
make the TBM moving forward successfully.
Therefore, the choice of backfill grouting is to to achieve the above purposes. Consideration for the soil conditions, we use plastic-like consolidation type of backfill grouting. Not only the plastic-like consolidation type of backfill grouting can improve the efficiency of the injection, but it can generate the strength of the grouting material earlier to stabilize the ground. So backfill grouting can minimum the problems of early land subsidence and subsidence after some time in the future.
To fully fill at the tail void.
The volume of grouting material wouldn’t change during the mid and late hardening period.
Grouting material would generate the same strength as the ground formation in early stage, and would distribute good pressure and pressure transmission effects.
Would not produce any material separation and sedimentation.
Can be injected over long distances without any clogging, and can be sustained with long time construction.
Using plastic-like consolidation construction materials, the grouting materials can be injected in the same place continuously.
Good water sealing to avoid the dilution of groundwater after the gelation of grouting material.
Grouting material does not contain harmful substances which leads to secondary disasters after gelation.
Plastic-like consolidation type backfill grouting materials must comply with the above characteristics. It shall be conducted all kinds of laboratory tests prior to construction, to confirm the ability to meet the strength and other item requirements of the specification.
Plastic-like consolidation type backfill grouting material is made from A liquid (ash slurry) mixing with B liquid (sodium silicate). The mixing proportion of A and B liquid is based on geological conditions.
(1)The reference volume of grouting material proportion:
|A Liquid||B Liquid|
|Cement 220~320kg||Bentonite 30~100kg||Stabilizer 2~10L||Water 800~920L||Sodium silicate 50~100L|
（2)The reference value of each test item:
|Test Item||Test Contents||The Reference Value (N/mm2 )|
|Uniaxial compressive strength||Test for consolidation strength||1 Hour 0.02 or higher||1 Day 0.5 or higher||28 Days 1.5 or higher|
|Solid Time||Test for gelation time||3~20 seconds|
|Bleeding of A liquid||Test for pressure piping performance||<5% (1 hour)|
|Fluidity value||Test for fluidity performance||8~13 seconds|
Cement proportion: 3.15 Bentonite proportion: 2.79 Stabilizer proportion: 1.28 Sodium silicate proportion: 1.38
In the construction site, the appropriate proportion shall be selected in accordance with the actual site condition to adjust the proportion for benefit the construction. Followings are the backfill grouting material proportion example in Taipei MRT Hsin-Chuang Line Section CK-570B.
|A Liquid||B Liquid|
|Test Item||The Reference Value (N/mm2)|
|Uniaxial compressive strength||1 Hour 0.8||1 Day 10||28 Days 18|
|Solid Time||8~16 seconds|
|Bleeding of A liquid||0~5%|
|Fluidity value||8~13 seconds|
Cement proportion: 3.15 (comply with CNS 61, Portland Type I Cement) Bentonite proportion: 2.79 (comply with A.P.I 13A) Stabilizer proportion: 1.28 Sodium silicate proportion: 1.38 (comply with CNS 2238, #3)