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Treatment of C.D.G. with slurry shield TBM Case study in Hong Kong

presented at LTA-UITP Singapore International Transport Congress and Exhibition (SITCE) in October 2013

Yves Chouanard Commercial & Marketing Director MS sas [email protected]

ABSTRACT: Slurry TBMs have been chosen in decomposed granite alignments so as to ensure safe boring conditions, both in Hong-Kong and in Singapore. Despite the fact that, in both cases, the GIBR gives a very wide variety of grain-sizes distributions, it is of major importance for the contractor at bidding stage to come to a sensible evaluation of the quantities of spoils which will be recovered by the Separation Plant, especially the extra-fines portion - 63µm.

The aim of this presentation is to compare the figures extrapolated from the GIBR with the ones obtained on the sites, and to adjust the simulations tools used for the sizing of the different components of the Separation Plant by the STP supplier, especially the excess mud treatment section.

SUMMARY:

1 PRESENTATION OF THE PROJECTS : ............................................................................. 2 1.1 MTR WIL 703 : ............................................................................................................ 2 1.2 XLR 820/821: .............................................................................................................. 3

2 INTERPRETATION OF THE GEOLOGICAL FILE ............................................................... 4 3 TOOLS TO SIMULATE THE PROCESS & THE VOLUMES OF SPOILS GENERATED: ....... 5 4 SUMMARY OF RESULTS OBTAINED ON XLR 820 JOB SITE : ....................................... 6

4.1 SOIL BULK DENSITY : ....................................................................................................... 6 4.2 % OF FINES -63µM : FIRST TUBE : ..................................................................................... 7 4.3 % OF FINES IN THE CDG : SECOND TUBE : .......................................................................... 7 4.4 ABRASIVITY OF THE CDG : ............................................................................................... 8 4.5 QUALITY OF THE SLURRY ............................................................................................... 9 4.6 TREATMENT OF EXTRA-FINES .......................................................................................... 10 4.7 TOTAL SPOILS VOLUME AT THE END OF THE TUNNELS : ........................................................ 11

5 COMPARISON BETWEEN HONG-KONG & SINGAPORE CDGS : .................................. 12 6 CONCLUSION : ............................................................................................................... 12

Treatment of C.D.G. with slurry shield TBM- Case study in Hong Kong

SITCE Conference & Exhibition

Y. Chouanard – Oct. 2013

page 2

1 PRESENTATION OF THE PROJECTS :

1.1 MTR WIL 703 :

Hong-Kong MTR 703 These two tunnels (boring Ø 6.35m, 770m + 490m long) are part of the West Island Line (Sheung Wan to Sai Ying Pun), situated in a very congested urban area. Contract was awarded by MTR Corporation to Dragages, Maeda & Bachy Solétanche Joint Venture. Its first ring was bored in September 2011, and the tunnel was completed in November 2012.

The geological profile was showing about 31% of the drive in CDG, 42% in mixed face, and 21% in rock, with a small section representing 6% in Alluvium.




page 3

1.2 XLR 820/821:

Hong-Kong MTR 820/821 – 2 x 1 800 m3/h These twin tubes, 3.5 + 0.75 km long tunnels on Kowloon side (boring Ø 9.32m) belong to Guangzhou-Shenzhen-Hong Kong Express Rail Project XLR. Contract has been awarded by MTR Corporation to Dragages Bouygues Joint Venture. Its first ring was bored in October 2011, and the tunnels are due to be completed in 2015.

The geological profile was showing about 52% of the drive in CDG, 14% in mixed face, and 35% in rock.




page 4

2 INTERPRETATION OF THE GEOLOGICAL FILE

One of the difficulties in the interpretation of the GIBR is the extrapolation of two critical values of the CDG section, - its dry density (g d), and - its % of extra-fines, because of their direct influence on the sizing of the STP excess mud treatment section.

The GIBR was giving the following information in terms of particle size distribution :

The in-situ densities (g h) were also given within a wide range :

ð an average value of 19kN/m3 was chosen for MTR 703 and 2 for XLR 820/821.

which is a very wide range… from 8 to 80% !

An average value of 30% was chosen for MTR 703 and 32% for XLR 820/821.




page 5

3 TOOLS TO SIMULATE THE PROCESS & THE VOLUMES OF SPOILS GENERATED:

The "Volume & Mass Balance" calculation sheets, or "VMB", have been developed by MS to help in the sizing of a Slurry Treatment Plant with regards to the geology of one particular tunnel project, and to the technical choices of the contractor in terms of instant boring speed and daily progress target.

It includes the following sections :

• a summary of the geological profile of the tunnel,

• the VMB calculations in each geologies,

• a summary showing the critical values given by the VMB in these different geologies, values which will become sizing factors,

• a calculation of the spoils volumes and of the consumables for the entire tunnel.




page 6

4 SUMMARY OF RESULTS OBTAINED ON XLR 820 JOB SITE :

Data GIBR Results from XLR

820

Soils bulk density

gh

Bedrock 2.6 2.6

Mixed face 2.2 2,2

Soft CDG 1.9 2

< 63µm Soft CDG 32%

(extrapolation) 40%

4.1 Soil bulk density :

mostly in CDG.

CDG until ring 250, then mixed face, and full-face granite for last 50 rings




page 7

4.2 % of fines -63µm : First tube :

The average value of fines < 63µm measured on site in CDG is close to 25%, but the conglomerates of clay recovered with the sand/or the gravels, which represents another 5%, should be added, which means that the total is effectively close to 32% on this drive.

4.3 % of fines in the CDG : Second tube :

On the second tube, the average value of fines < 63µm measured on site is close to 35%, with peaks on the last 50 rings up to 39%, but again, the conglomerates of fines recovered with the sand/or with the gravels should be added, what represents another 5%, i.e. the total is this time close to 40% with peaks up to 45%.These two examples demonstrate the variability of the ground, and especially the % of fines.




page 8

4.4 Abrasivity of the CDG :

One major issue in the treatment of CDG is the perfect desanding of the slurry, while resisting to it very high abrasiveness : in these CDG, 56% of the rock is considered as "Very Abrasive" (Cerchar Abrasiveness Index 2 to 4), and 41% "Extremely Abrasive" (CAI 4 to 6).

Rock Abrasiveness

Percentage Distribution

Class (after Cerchar)

CAI

(Cerchar Abrasiveness Index) Not Very < 0.5 0%

Slightly 0.5 to 1

0%

Medium to Abrasive 1 to 2

2.6%

Very 2 to 4

56.4%

Extremely 4 to 6

41%

Quartzitic > 6 0%

An "integral" desanding and desilting of the slurry is therefore required, and a special care should be brought to the wear protection.




page 9

4.5 Quality of the slurry

MTR 703 : low cover, urban area lead to high quality of slurry in terms of rheologic properties : Density YV Filtrates

CDG 1,147 7,5 Pa 52 mL

Rock 1,094 1,9 Pa 147 mL

Mixte 1,138 2,7 Pa 49 mL

XLR 820 : less constraints, but natural viscosity due to the activity of the fines (up to 6 Pa, without bentonite addition), bigger diameter and other constraints such as the cement contamination of the slurry. Sand

content (elutriometer)

Density

YV

Filtrates

Ring / Day

Average 1,5% 1,136 4 Pa 80 mL 8 r/d

Max 3,5% 1,23 6 Pa 170 mL 12 r/d

Min 0,5% 1,03 1 Pa 60 mL 6 r/d




page 10

4.6 Treatment of extra-fines

40 to 45% fines < 65µm in the ground, means for a Ø 9.3m tunnel 120 to 140 m3 of excess mud per bored meter ending in the excess mud tank. For two tunnels bored concurrently with a total daily progress target of 40m, it is 4,800 to 5,600 m3 of sludge to be processed daily.

Only Filter-presses enable a transformation of this liquid sludge volume into solid cakes, with an average moisture content of 27% (water weight on total cake weight) :

Filter-Press cakes

Filter-press productivity in CDG :

Bentonite

concentration in excess mud

Filtrates (API-30

min)

Average Yield Value

Lime addition

Excess mud

average density

FP15-C80-M16 production

in m3/h of excess mud

in t/h of solids

XLR 820

0 kg/m3 ~80 ml

3 Pa

(natural viscosity of

fines)

2%

(+coagulant) 1.207 30 - 36 10 - 12 t/h

MTR 703

0 to 40 kg/m3 ~50 ml 6~7.5 Pa 5% 1.167 30 - 37 8 - 10 t/h




page 11

4.7 Total spoils volume at the end of the tunnels :

Taking the example of XLR 820/821, the original assumption of 30% fines <63µm in the CDG lead to a total of 175,000 tones of solids < 63µm after completion of the two tunnels, and to the following volumes:

Excess mud volume

Excess mud density

Reduction ratio

Original volume in excess mud tank : 600,000 m3 1,182

In case of treatment by decanter centrifuge 325,000 m3 1,335 / 1.8

After treatment by Filter-Press 132,500 m3 1,822 / 4.5

Disposal of soils by barges / storage on ground




page 12

5 COMPARISON BETWEEN HONG-KONG & SINGAPORE CDGS :

COMPLETELY DECOMPOSED GRANITE COMPARISON HONG KONG vs SINGAPORE

Parameter Hong Kong Singapore

ROCK

Names of granites Kowloon and Sha Tin

granites Bukit Timah and Jurong

granites

In situ density (γh) 2,5 to 2,6 2,4 to 2,6

Dry density (γd) 2,4 to 2,5 2,25 to 2,5

Permeability 10-7 to 10-9 m/s 10-6 to 10-9 m/s

Abrasivity Very abrasive to quartzitic Very abrasive to quartzitic

CDG

grades V&VI

Densities Min Medium Max Min Medium Max

In situ density (γh) 1,7 2 2,1 1,7 2 2,1

Dry density (γd) 1,2 1,6 1,8 1,2 1,6 1,8

Grain size distribution

Min Medium Max Min Medium Max

% > 6 mm 0,0% 10,0% 25,0% 0,0% 5,0% 15,0%

Sand (63 µm - 6 mm) 35,0% 50,0% 90,0% 30,0% 55,0% 75,0%

Extra-fines (< 63 µm) 10,0% 40,0% 60,0% 25,0% 40,0% 55,0%

Liquid limit 30 - 70% 40 - 80%

Plastic limit 10 - 45% 10 - 35%

Plastic index 10 - 50% 10 - 60%

Permeability 10-5 to 10-8 m/s 10-6 to 10-8 m/s

6 CONCLUSION :

Boring with a Slurry Shield TBM in Completely Decomposed Granite is challenging as it requires:

• a perfect separation of the excavated solids,

• a mastery of the rheologic properties of the slurry,

• a right solution to treat the big volume of extra-fines spoils.

The experience gained in Hong Kong could be perfectly applicable to Singapore geology and environment.