INSIDE CROSSRAIL S WESTERN DRIVES. journal THERMAL IMAGING FOR SCL STRENGTH TRIGGERS REVISITED. Dec 2013/Jan 2014

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1 Tunnelling The international journal for the tunnelling industry Dec 201/Jan 2014 journal SEE PAGE 18 BANGKOK ADVANCE TJ VISITS THAILAND TO SEE HOW THE BLUE LINE ETENSION IS FARING SEE PAGE 26 BRISBANE S LEGACY A NOVEL TBM DISASSEMBLY METHOD AT THE LEGACY TUNNEL EPLAINED SEE PAGE 44 SLURRY REMOVAL TWO LONDON TUNNEL SITES AID SLURRY REMOVAL TECHNOLOGY THERMAL IMAGING FOR SCL STRENGTH TRIGGERS REVISITED INSIDE CROSSRAIL S WESTERN DRIVES

SPOIL TREATMENT Treating chalk spoils Yves Chouanard, Commercial Director with MS refers to two London tunnelling projects explaining in detail the methods used for the treatment of the chalk spoils

88m diameter, 6,904m length and its geology of more than 98% in chalk, is a real challenge in terms of spoil treatment.

2 SPOIL TREATMENT Treating chalk spoils Yves Chouanard, Commercial Director with MS refers to two London tunnelling projects explaining in detail the methods used for the treatment of the chalk spoils during TBM advancement THAMES WATER S LEE TUNNEL in the UK s East London, with its Slurry TBM driven 8.88m diameter, 6,904m length and its geology of more than 98% in chalk, is a real challenge in terms of spoil treatment. The total volume of the chalk slurry after separation of the flints (5 to 25%, average 15%) represents more than 1,2000m of liquid slurry. In such geology, where 95% of the solids could be transformed into extrafines, well below the cut off point for cyclones or centrifuges, several method have been tried in the past to facilitate the disposal of the spoils, but none met the requirements of the contractor, both in terms of costs and final result. This article will describe the methods and results achieved by the Morgan Sindall/Vinci Construction Grands Projets/Bachy Soletanche Joint Venture MVB in reaching a consistency of more than 75% solids by weight, and thus drastically reducing the volume of spoils thereby easing their disposal. The article will also give an overview of the results obtained on another tunnel site in similar geology in London, the Crossrail Thames Tunnel, being constructed by the Hochtief/Murphy Joint Venture HMJV. After their success in the award winning CTRL 20 tunnel, where the discharge of the centrifuges was mixed with cement before placement, HMJV accepted a re-thinking of its excess mud treatment method, having been convinced by the argument in favour of filter-presses enabling them to use an alternative approach to slurry management. the chalk and Thanet sand encountered along its alignment, elsewhere EPB machines run in London clay, sand and gravel. Boring started in October 2012, and is due to be completed early Geology The Lee Tunnel runs predominantly in the Seaford Chalk formation, with a small section of overlaying fine clayey Thanet sands. This Chalk consists of white, sometimes light grey, low to medium dense, weak to moderately weak chalk, with layers of flints ranging from 5 to 25%, with an expected average value of 15%. A bulk density of 2kN/m has been assumed for the design. At the time of the sizing of the separation plant, it was pointed out that there were two questions which were not fully answered in the GIBR and which were of major importance for the sizing of the Separation Plant: one was the ability of the chalk to go into suspension, and the other was the filterability of the resulting slurry. MS therefore received 2 tons of samples that have been tested in our laboratory. Preliminary work and lab tests In addition to the TBM diameter and the slurry volume in circulation, the key figures to The Crossrail Thames Tunnel is in the same geology : only the proportion of Thanet sand in the drive is slightly greater : The two tunnel sites The Lee Tunnel is part of a scheme to store and send to treatment the sewage and rainwater from London, which presently overflows into the River Thames. The 6.9km long Lee Tunnel runs through East London, and will eventually carry sewage from London's largest combined sewer overflow from the Abbey Mills Pumping Station in Stratford to the Beckton Sewage Treatment Works (STW) in Newham. The tunnel works started in February 2012, and the entire scheme is expected to be completed in The 2.6km long twin tubes for the Thames Tunnel is the only Crossrail route which crosses the River Thames. It is also the only slurry shield TBM of this project, because of 44 TUNNELLING JOURNAL

3 SPOIL TREATMENT This table shows for each section of the process the quantities of each element, in volume and mass, calculated for the set boring speed. a summary showing the critical values given by the VMB in these di erent geologies values which will become sizing criteria a calculation of the spoils volumes and of the consumables for the entire tunnel, with two solutions: with decanter centrifuges r-presses. and with These calculation sheets already gave a number of key parameters for the sizing of the STP at bidding stage, but certain parameters needed co rmation. VOLUME AND MASS BALANCE example Vmb a Soil reference : 0% % Saturated soil moisture 15,0% % broken down soil Excav vol Boulders and chips m Broken up soils grainsize distribution % Excav vol 5,0% Pebbles >6mm h d 0% Total / Ring Wet Tons (t/h) Wet Tons t/h t/ring Tons of dry solids (t/h) Tons of Dry Matter h d C - Seaford Chalk 5% flints TBM PERFORMANCE SOILS DISTRIBUTION Boulders and chips SLURRY TREATMENT PLANT m Ring length 8,88 m Excavated surface 61,9 m Excavated volume 111,5 m /h 24,0 Rings per day 8,9 t/ring Excavated meters/day 40,8 5,6 m Sand 6-6mm % m t/h t/ring Extra-fines <6 95,0% 5,9 m 18 t/h 17 t/ring Primary slurry concentration % 111,5 m 189,5 t/h 179,0 t/ring Total 9,5 t/h 4,9 Dewatered Product Humidity in % of wet weight 8% Revolving screen Dewat. Screen 18% Filter-press 24% > 6 mm Sand 2,65 2,65 Extra-fines Bentonite 2,65 2,50 1,00 Consumables Balance and spoils evacuation Per ring Bentonite t Lime 0,5 t 12,2 t Per day t 8 kg/m Fresh slurry concentration (Kg/m) kg/m addition 14,9 m 57,6 m Lime dosage in % of cakes 0, % Spoils evacuation 2,8 t 56,9 t Bento. dosage % / total MS (P1-1) Bento. conc. in slurry at P1.1 kg/m Excess dry matter (< 6 m) % bento. in dewatered sands (item.8) 0% Cakes incl. moisture & lime 414,7 % of clarified water for fresh mud dillution Spécific Density ( s),0 cm/min Excavation speed Excavation diameter 95% % Massic flow (Tons/hour) Volumic flow (m/hour) Total 169,8 t/h on 24 h / day 224,1 t/h Flow / ring Volume Description Item > 6mm Sand Bento. > 6mm Sand Bento. Total (T/h) Density Mass (T) Tons per day Ref. P.1.1 Discharge ,8 66,4 228,0 1,2 1781,9 2156,2 1 Loss in soil 2 1,2 2 Interface soil/tbm 9,4 9,4 P2 Discharge 4,6 67,9 1688, , ,4 1688,4 2514,2 1, ,9 274,5 4 Clear water addition Soil Recirc. extra-fine extra-fine (m/h) (m) > 6 mm 6,6 0,1 0,6 4,2 9,5 0,1 0,2 0,6, 2,4 4,0 9,7 2 6 Sandy slurry 7 67,9 1995, ,1 250,9 1884,9 264,8 Sands 6-6mm Soil Recirc. extra-fine extra-fine 7 8 Cakes 9 15,0 52,9 56,9 125,0 9,6 140,1 56,9 27,2 1, ,0 224, Dessanded slurry 67,9 1995, ,1 250,9 1884,9 264,8 Excess slurry 11 15,0 52,9 71,8 49,6 9,6 140,1 71,8 551,5 415,2 520,9 11 Recycled slurry ,0 187,2 116,0 1556,2 140, 496,0 116,0 1952,4 1469,7 184,9 Clarified water 1 14,8 14,8 14,8 14,8 297, 297, Excess from B addition 15 14,9 14, Dilution water 16 12,2 12, ,048 0 Fresh slurry 18 12,2 12,2 Regenerated slurry 19 5,0 187,2 1886,8 140, 496,0 228,0 1,2 1781,9 2156,2 19 Lime addition 20 0,9 0,5 0,6 0,8 0,5 20 A B C D E F G H I J K L M N O P Q R Bentonite-primary slurry take in consideration for sizing the Slurry Treatment Plant are: the boring speed in the di erent geologies, giving the maximum instantaneous values of volumes and tonnages of solids to be handled the daily progress target, giving average values of consumables (bentonite, water ) and 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 targets. It also helps to study the consequences of any mod of a parameter, such as density, viscosity, or instant and daily boring progress targets in terms of sizing of the components 1 18 Laboratory tests MS received a 500kg bag of samples in September 20 and another in April 2011, both from a nearby quarry, and performed another set of tests in April 2012, after start of the work, with samples from Abbey Mills, and the Pumping shaft. The aims of these laboratory tests were : to check the % of chalk going into suspension, as a function of the attrition time in a concrete mixer which simulates the transport duration to measure the liquid and plastic limits to carry out rheologic tests to perform pressing tests, with chamber and membrane plates of di erent thicknesses, and with di erent additions: lime, polymer, and other "drying" products. These tests co rm di erent assumptions made by calculation sheets and lead to the choice of the di erent working parameters after discussion with the Contractor: return density, viscosity, ltration additives, etc. Percentage of chalk going into suspension - This rst test has been performed in a concrete mixer to simulate the transport duration, and to estimate the percentage of chalk going into suspension as a function of the attrition time: or in terms of consumables. It includes the following sections: a summary of the geological pr of the tunnel, based in the available GIBR the VMB calculations for each geology: based on the owsheet here after, these calculation sheets show the volumes and tonnages to be handled by the di erent sections of the STP: scalping, desanding, desilting, slurry management, excess mud treatment, water management and bentonite preparation. The res in the red circles on the t (above top diagram) refer to the row number of each VMB calculation sheets. TUNNELLING JOURNAL 45

SPOIL TREATMENT To maintain a safety margin, it was decided to consider for the sizing - the possibility that 0% of the chalk will come into solution, and - only 5% of.

volume of excess slurry and to optimize the cycle time of the lter-presses, a high value of return slurry density was chosen, up to a maximum of 1.42.

4 SPOIL TREATMENT To maintain a safety margin, it was decided to consider for the sizing - the possibility that 0% of the chalk will come into solution, and - only 5% of. Rheologic tests - These tests have been performed to measure the VP (plastic viscosity), VA (apparent viscosity), Yv (Yield Value), Filtrates API, at di erent concentrations: To minimize the volume of excess slurry and to optimize the cycle time of the lter-presses, a high value of return slurry density was chosen, up to a maximum of Nevertheless, after start-up, much higher values of the real mined chalk viscosities have been measured on site, and as a consequence this return density has been reduced to 1.0, to avoid settlement and building up troubles in storage tanks. 46 TUNNELLING JOURNAL

SPOIL TREATMENT Pressing tests - Hundred of tests have been performed: to measure the filterability of the slurry at different concentrations, with different additives or "drying" agents, and with

It was therefore decided to choose 40mm cakes, delivering a final water content of 25 to 0%, with an addition of 0.

In Chalk, chamber plates have been chosen to maximize the useful volume, and a minimum number of filter-presses equipped with membrane plates will be kept for the treatment of the bentonitic mud

5 SPOIL TREATMENT Pressing tests - Hundred of tests have been performed: to measure the filterability of the slurry at different concentrations, with different additives or "drying" agents, and with different cloth permeability to optimize the feed pressure and cycle time sequences to optimize behavior of the cakes during the discharge operation and to avoid the risk of sticking to the cloth. It was therefore decided to choose 40mm cakes, delivering a final water content of 25 to 0%, with an addition of 0.5 to 1% of lime (many other products were tested, but lime demonstrates a higher performance). In Chalk, chamber plates have been chosen to maximize the useful volume, and a minimum number of filter-presses equipped with membrane plates will be kept for the treatment of the bentonitic mud recovered in Thanet sands, The technical challenges Flexibility of the STP - The two geologies encountered not only lead to a different behavior of the slurry, but also require different rheologic properties, which demand a very flexible design of the separation plant, in order to be able to handle: high density chalk pulp, containing very abrasive flints, where the main concern should be a control of the density and an optimization of the spoils volume, clayey Thanet sand, possibly coming in sticky conglomerates, where the concern should be the stability of the face. A first stage with a revolving trommel (cut size 6mm) was chosen, as well as a double cycloning stage, with a lower cut at 45μm (d50). Different wear protection methods have also been tested - rubber, wear resistant steel, ceramic linings (tiles or molded parts). Slurry management - With an instant boring speed of 80 to 0mm/minute, the "in-line" and "in real time" slurry control in terms of density becomes a critical issue, and the MS patented "slurry management" proved its efficiency. TUNNELLING JOURNAL 47

SPOIL TREATMENT Excess mud treatment This is the major challenge of this Tunnel Work, which becomes even more challenging due to the fact that a very small di erence in the moisture content gives a

Both density and viscosity parameters can be adjusted automatically and independently. content = 26.

avoid pollution of the large reserve of good quality bentonite by cement particles, and to keep this good quality slurry available when getting out of this area when a higher quality is required and

6 SPOIL TREATMENT Excess mud treatment This is the major challenge of this Tunnel Work, which becomes even more challenging due to the fact that a very small di erence in the moisture content gives a huge di erence in the chalk spoil consistency and aspect: This system measures (F1) the incoming slurry volume and density after desanding & desilting, and compares these values to the settings required at P1 pump. It opens accordingly the monitored valve MV1 to send the right the volume of excess slurry to waste mud tank, and adjusts the dilution water volume (F) and Bentonite (F2) addition if required. Both density and viscosity parameters can be adjusted automatically and independently. content = 26.6% ( humidity ratio = 21%) This system has also two other operating modes : a possible by-pass of the B1 (regenerated slurry) tank, when starting the TBM in a concrete injected area, in order to avoid pollution of the large reserve of good quality bentonite by cement particles, and to keep this good quality slurry available when getting out of this area when a higher quality is required and another mode to facilitate the preparation of an hyperbaric intervention on the TBM head, by sending a large quantity of bentonitic slurry directly to the TBM, bypassing the large B1 reserve Working conditions If we take the example of Crossrail C working conditions, we can ion of the slurry in the Table below: summarize the content = 5.1% (humidity ratio = 26%) Lee Tunnel - with an average return density of 1.21 and an excess mud density of 1.25, the excess mud volume represents 245m for one ring, of which 140 tons of solids and 290m of water. With the current weekly progress of 200m, it represents 29,000m of excess mud to be processed! On the entire tunnel drive, what should be recovered is 624,400 tons of solids <6µm, which gives the following comparison between the di erent available solutions (move to top of next page): In Thanet Sand: Density Plastic Viscosity (MPa.s) Baroïd Filtrates (ml) Baroïd Cake thickness (mm) ph Value In Chalk: Density 1.21 Plastic Viscosity (MPa.s) Filtrates (ml) TUNNELLING JOURNAL 160 Baroïd Cake thickness (mm) ph Value

SPOIL TREATMENT Decanter centrifuge (based on the figures obtained on CTRL 20*), and Filter-presses (present results obtained on this site): Solids Pulp/Cake content Consistency Excess mud Decanter

return density of 1.21 and an excess mud density of 1.25, we have 180m of excess mud for one ring, of which 7 tons of solids and 152m of water.

7 SPOIL TREATMENT Decanter centrifuge (based on the figures obtained on CTRL 20*), and Filter-presses (present results obtained on this site): Solids Pulp/Cake content Consistency Excess mud Decanter centrifuge (*) 624,400 tons 1,000m 1,55,000m 624,400 tons 624,400 tons 275,000m 2000m 50m 45,900m = -75,000m 44% 2% Pasty Solid cake 208% Liquid Filter-presses Crossrail C - with the same average return density of 1.21 and an excess mud density of 1.25, we have 180m of excess mud for one ring, of which 7 tons of solids and 152m of water. On the entire tunnel drive, we should recover about 8,000 tons of solids <6µm, which gives the following comparison between decanter centrifuge and Filter-presses (water content figures are slightly different from Lee Tunnel values, as they are average values of the different soil conditions and the proportion of chalk with regards to Thanet sand and mixed soils are different): Excess mud (*) Warren, Phear, Schultheis, Gregg, 200: "Treatment and Placement of Chalk Spoil from the CTRL Thames Tunnel". Solids Pulp/Cake In addition to the reduction of the total volume of the spoil, and to the drastic change in its consistency, we should notice another big saving, which is the possibility to re-use the filtrate water from the Filterpresses for dilution of the slurry, after correction of the ph, flocculants used instead with centrifuges would make it difficult. content Consistency 8,000 tons 225,000m 266,000m 208% Liquid Decanter centrifuge Filter-presses 8,000 tons 8,000 tons 55,000m 9,000m 96,000m 800m = -16, 000m 51% 6% Pasty Solid cake Conclusion The results obtained on these two sites have demonstrated : the advantages of a precise management of the slurry characteristics in real time, adjusting density & viscosity independently the superiority of filter-presses for the treatment of Chalk spoils, both in terms of final water content of the cakes, and in terms of consistency. TUNNELLING JOURNAL 49

rapid tunnelling thanks to efficient SePArAtion. Low-impact mechanized tunnelling: Integrated solutions.

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