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BACKFILL GROUTING INJECTION

Introduction

Backfill grouting is the construction method to fill sup the gap between TBM excavation and segmental lining, which called “Tail Void”.

There are 4 main purposes when using this method:

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.

Characteristics of backfill grouting

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.

Materials and proportion

1. Characteristics of plastic-like consolidation type backfill grouting material

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.

A liquid: cement, bentonite, stabilizer, and water: It must be able to remain fluidity for a long time, and does not produce material separation. Cement: As a hardening agent, to from the strength of grouting material.Bentonite: Its floating and swelling effect can increase water-sealing and fluidity of A liquid slurry. Stabilizer: Can increase the liquidity of liquid slurry and delay the hardening time of consolidation in order to reduce the probability of clogging in the tube.

B liquid: Sodium silicate. It is a special sodium silicate which enables a rapid condensation of mixing and reacting with alkaline material of liquid A to harden the material in a short time.

2. Using benchmarks for Plastic-like consolidation type backfill grouting material

(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

Proportion selection in the Construction site:

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+B=1m3

A Liquid B Liquid
品名 Cement Bentonite Stabilizer Water Sodium silicate
Proportion 1 260kg 30kg 2.5kg 830l 75l
Proportion 2 240kg 30kg 2.5kg 836l 75l

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)

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