Soil conditioning for EPB tunnelling in choesionless soil, clay and rock masses and backfilling in shield tunnelling

Transcription

1 2do Congreso Latinoamericano de Túneles y Espacios Subterráneos LAT de septiembre de 2015 Soil conditioning for EPB tunnelling in choesionless soil, clay and rock masses and backfilling in shield tunnelling Daniele Peila Ingeniero en Minas, Politécnico di Torino 67 páginas

2 Mechanized tunnelling in urban areas Through a urban area, a tunnel must be built at a shallow depth in soft ground. The most significant environmental problem that arises is the control of the settlement at the surface, which must be contained within values that are compatible with the safety of the buildings and/or structures on the surface. Courtesy S. Pelizza

3 EPB Shield Ground and water pressure Counter-pressure inside the bulk chamber Excavated volume Extracted volume Excavated volume Extracted volume Conceptual scheme of an the face pressure control of an EPBS The face support is provided by the excavated ground that is kept under pressure inside the excavation chamber (also called plenum ) by balancing the volume of the extracted and excavated material and by the thrust jacks on the shield. The spoil is removed from the excavation chamber by a screw conveyor that allows the pressure control by variation of its rotation speed and its capacity of transportation out 3

4 EPB Shield: EPB machine: example of applications clay silt sand gravel EPB-SHIELD. APPLICATION open shield RANGE AND CONDITIONING. possible coarse soil foam + polymers silty sand foam very coarse soil foam, polymers and filler conditioning necessary foam and additives (clogging - adhesion of soil) sieve size [mm] 4

5 Soil conditioning: WHY In order to fulfill all the requirements for a successful EPB technology application, as well as to extend the applicability of such technology over a wider range of soils, it becomes necessary to inject some additives that transform the soil into a material that shows the required features: Good plasticity Low permeability Pulpy consistency Example of Rome metro For EPB system spoil conditioning is essential in tunnelling process 5

6 Soil conditioning: WHY Reduction of the wear for all mechanical parts of the machine in contact with the soil Better uniformity of the pressure distribution in the bulk chamber Control of the flow of the excavated material through the cutter head Reduction of the friction forces in the bulk chamber Reduction of the permeability with consequent better control of water inflow. Smoother flow of material along the screw conveyor Creation of the plug in the screw Easier spoil handling Prevent the stickness of the clay on the mechanical parts Avoid that the excavated clay will reconstruct as a mass in the bulk chamber 6

7 Soil conditioning: WHAT The most used additives for soil conditioning belongs to following families: Foam (surfactants that are mixed with water and air to create the foam) Long chain polymers (to improve the foam bubbles stability) Anti clogging and lubricating agents (to avoid amalgamation and stickness of the clay) Dispersing agents (to avoid amalgamation and stickness of the clay) Abrasion-preventers Bentonite Filler «Water» (injected in order to plasticize the finer part of the soil) 7

8 SOIL CONDITIONING DESIGN PROCEDURE Step 1 GEOMECHANICAL CHARACTERIZATION Laboratory tests Soil conditioning design Step 2 ENVIRONMENTAL CHARACTERIZATION Step 3 JOB SITE MANAGEMENT AND CONTROL CONDITIONED SOIL CONDITIONING AGENT Lab. environmental tests Choice of environmentally acceptable agents IMPROVEMENT OF THE CONDITIONING SET DESIGN

9 foam design parameters Foam is the most used conditioning agent in choesionless soil Average composition for a normally used foam: Foaming agent 0.5-3% Water 5-10% Air 90-95% Polymer (eventual) <0.1% Foaming agent can have inside a small amount of polymer to stabilize the foam bubbles. 9

10 foam property assessment Foam expansion ratio (FER) Foam bubble size Foam density Foam stability (half time life) (t 50 ): to measure the durability of the foam at atmospheric pressure (different foams can change their properties in 3 min to 1 hour) 10

11 foam properties assessment Half-time life of different foams ( t50 ) FER Foam A 124s 143s 225s 340s Foam B 203s 532s 1204s 1641s Foam C 115s 175s 204s 295s FER FER A B 11

12 SOIL CONDITIONING TESTING There are a few ways to select the correct conditioning regime 1. Laboratory testing 2. Previous history in the same site 3. Trial & error 4. Rules of thumb Laboratory testing is very important, they can define the effectiveness of soil conditioners and indicate the most suitable chemicals. They do not only indicate the type of chemicals but can also determine the effect of water addition as well as the effect of different concentrations. 12

13 SOIL CONDITIONING TESTING The transformation of a soil using foam Result Rome metro 13

14 MOST IMPORTANT AND USED LABORATORY TESTS ON CONDITIONED COHESIONLESS SOIL Slump test Permeability test Wear test Screw drive extraction test 14

15 Slump test The purpose of this test is to determine a global and plastic behaviour of the treated ground. The conventional slump cone standard as for fresh concrete is used Values of cone fall between 10 and 20 are usually suggested as optimal in technical literature. 15

16 Slump test Slump test: soil assessment Sand + gravel 16

17 Slump test Slump test: soil assessment 17

18 Slump test Turin metro soil Detail of Turin soil. Cobbles (left) and <20mm fraction (right) 18

19 Slump test Turin metro soil 19

20 Slump test Rome metro pozzolanic soil FIR = 25% w = 10% FER = 16 20

21 Slump test Rome metro pozzolanic soil Rome metro soil 21

22 Foam-soil mix stability - time effect 22

23 Permeability test 23

24 Permeability test FIR 40% FIR 60% Modified permeability tests on fluvial sand at pressure p = 1 bar for different FIR values Not conditioned FIR 40% FIR 60% Modified permeability test on Rome pozzolanic soil at pressure p = 1 bar for different FIR values 24

25 Wear test direction of rotation wear disk force applied to the disk pressure applied on the soil wear disk soil soil tank Different type of tests have been proposed. No standard exist. Figure 5 Scheme of the proposed test The described test is the one used at the Politecnico di Torino 25

26 Wear test Used conditioning sets for the different soils that where tested SOIL conditioning parameters FIR [%] FER [-] water content [%] fracured limestone alluvional soil alluvional soil alluvional soil alluvional soil 4. test a alluvional soil 4. test b fractured dolerite. test a fractured dolerite. test b quartz sand. test a quartz sand. test b

27 Laboratory screw conveyor device Displacement wire transducer Torquemeter Pressure cell on the top of the tank Pressure cell on the bottom of the tank Pressure cells along the screw conveyor Precision scale Tank height: 800mm Screw lenght: 1500mm Tank diameter: 600mm Screw diameter: 168mm Some different test devices have been proposed. No standard exist. The described test device is the one used at the Politecnico di Torino 27

28 Laboratory screw conveyor device Better transmission of the pressures from the tank to the screw conveyor and along the screw conveyor itself. Saturated sand Conditioned sand 1 bar 1 bar Vinai et al.,

29 Laboratory screw conveyor device Conditioned soil Wet sand 29

30 Laboratory screw conveyor device 160 Monogranular sand Dry sand Saturated sand FIR 40% w 5% FIR 40% w 10% FIR 40% w 20% torque [Nm] time [s]

31 Rock mass conditioning A growing field of application of EPB technology is the conditioning of difficult rock masses where the presence of polluting material is foreseen and must be controlled, or where it is necessary to prevent explosive gasses coming from the rock mass in the machine. The operative procedure of EPB technology, using the machine in closed mode, can prevent the dispersion of all this dangerous materials in the underground environment. It is possible to condition the rock mass crushed by the rock cutters? THE ANSWER IS YES IF A PROPER CONDITIONING SET IS USED 31

32 Rock mass conditioning The test have been carried out with three different Italian geological formations: Monte Morello limestone Sillano strong argillite Voltri calceshist The Monte Morello formation is a mix of limestone and marl layers with a variable mono-axial compressive strength, ranging between 9 and 50 MPa, depending by the content of marl in the sample The Sillano formation is an argillitic formation with a rock mass made mainly of argillite with layers of marl, silt, limestone and calcarenite The Voltri formation are quartzous-micaceous calceshists. 32

33 Rock mass conditioning Grain size distributions of muck produced by rock TBMs from technical literature Used grain size distributions 33

34 Rock mass conditioning 34

35 Rock mass conditioning Stable cavity at the screw conveyor entrance during and extraction test in Monte Morello formation with the conditioning parameters set with the slump test. FER = 15, FIR = 40% and w = 3%. A second test was carried out on the Monte Morello limestone using a set of conditioning parameters that achieves a more fluid mix i.e. with a larger amount of foam: FER = 15, FIR = 70% and w = 3%. Using these values, it was possible to extract the conditioned crushed rock and to correctly control the flowing process through the screw conveyor as shown by the diagram of the monitored parameters. 35

36 Rock mass conditioning FER = 15, FIR = 40% and w = 3% FER = 15, FIR = 70% and w = 3% 36

37 Rock mass conditioning The test in calceshists shows that when conditioning crushed rock with a reduced percentage of fines and very irregular grain shape. The grain shape, much more flat that with the limestone and the argillite, in this case is conditioned by the position of the shistosity of the rock mass, and dries very much during the test. For this reason as for the Monte Morello test it is necessary to use higher values of foam injection ratio and water added in the mix: FER = 15; FIR = 75% and w = 7% then the one defined with the slump test. The data recorded during this second test showed that in this case it was possible to achieve good test result 37

38 LABORATORY TESTS ON CONDITIONED CLAY Vane test Shear test Cone pull-out test Adhesion test Mixing test Slump test Screw coveyor extraction test 38

39 Behaviour of clay The excavation of choesive soils by EPBS can be problematic due to the problem of clay adhesion at the cutterhead, excavation chamber surfaces, in the screw conveyor and in the mucking system (belt conveyor and/or muck cars). This adhesion can lead to the clogging of the screw conveyor or of the bulk chamber and to delay and slowering of the advance rate of the machine NEED OF SPECIFIC ADDITIVES 39

40 Behaviour of clay Methods for definition of clogging and stickness (Ball et al., 2009) 1) analyses of the soil moisture content in relation to Atterberg Limits including adhesion limits (Atterberg, 1974). The terms stickiness and adherence are typically given to soil that adheres to metal. The sticky limit, or adhesion limit, is the lowest water content at which soil adheres to a nickel spatula when drawn lightly across the soil paste s surface. 40

41 Behaviour of clay 2) analyses of the relationship between soil consistency index (Ic) and soil plasticity index (Ip) proposed by Thewes (1999) Ic = (LL-wc)/(LL-PL) LL = Liquid Limit PL = Plastic Limit Wc = water content Ip=LL-PL as Consistency Index I C 1,50 1,40 1,30 1,20 1,10 1,00 0,90 0,80 0,70 0,60 0,50 0,40 0,30 hard hardstiff stiff soft pulpy Medium clogging risk Low clogging risk High clogging risk Plasticity Index I P [%] 41

42 Behaviour of clay Modified abacus for clay (Thewes ; 2004; Hollmann and Thewes, 2011) Ic = (LL-wc)/(LL-PL) Ip=LL-PL LL = Liquid Limit PL = Plastic Limit Wc = water content 42

43 Behaviour of clay The right picture clearly shows that the inner part of the chip is not conditioned and the conditioned mud is only outside the chip. The excavation produces a muck composed by clumps of variable sizes, depending on the penetration of the cutting tools into the tunnel face, and a matrix of finer material pulverised by the action of the tools and by the continuous mixing into the bulk chamber. The extracted material appears like clay clumps surrounded by the conditioned powdered fraction. Example of clay chip sample as collected on the conveyor belt of an EPB machine excavating in a clay formation.

44 Used polymers The used polymers with clay, can be divided into dispersing agents and lubricating agents. The dispersing agents act by increasing the negative surface charge on clay particles. The result is the reduction of the natural tendency of clay particles to re-aggregate thanks to their attraction forces. Langmaack suggests that in order to have the desired effect, among other effects, the dispersing molecules have to adsorb on the surface of the clay particles. Therefore, they should have a high charge density to separate the clay particles, creating a steric barrier. The lubricating agents act to create a sealing film on the clay clumps, avoiding water absorption and facilitating the reciprocal sliding of clay clumps and of the clay on steel parts of the machine. The ideal effect of this polymer would be the creation of a film, around the cohesive clay clumps, which allows the clumps themselves to slide.

45 Mixing test Bell et al. (2009) 45

46 Cone test 46

47 Behaviour of clay During the excavation the clay is detached by the cutter head tools in chips. The conditioning study should therefore take into account the behavior of the clay chips and not only the behavior of clay powder mixed with the additive Test able to take into account this aspect should be developed Soil 1 Soil 2 Example of a sticky clay conditioned with foam only

48 Slump test The slump tests results obtained with water, foam anti-adhesive polymer permits a relevant reduction of the clogging between the soil grains, giving the soil a plastic behavior similar to the optimal results that can be obtained with granular soils. Soil 1 Soil 2 The effect of this polymer is the coating of the clay grains with a lubricating film, thus facilitating the reciprocal sliding of the clay grains or clay clots between each other and preventing the ri-aggregation of the clay

49 Dynamic adhesion test Picture and scheme of the dynamic adhesion test equipment

50 Static adhesion test Picture and scheme of the static adhesion test equipment

51 Tests on clay clumps

52 the effectiveness of a lubricating polymer strongly depends on the plasticity index of the clay. The higher this index, the more effective the use of this type of polymer is. On the contrary, when the soil has a lower clogging tendency (i.e. with a lower plasticity index) the use of the lubricating polymer can cause an increase in the amount of foam needed, due to the water absorption effect of the polymer itself. This effect also increases the stiffness of the mix, with a related increase of the cutterhead torque needed. However, the injection of this polymer in low plasticity index soils can be recommended to obtain both a more homogeneous conditioned soil and long-lasting mechanical characteristics, as the lubricating polymer does not decade easily and quickly, also when used at very low quantities (c = 0.1%) as done in this research; Tests on clay clumps The tests carried out enable us to define some important considerations related to the conditioning of clay with the most commonly used types of products (water, foam and waterpolymer solution) for EPB shield tunnelling: the water content is crucial for the conditioning of clays. the addition of a correctly defined amount of foam makes it possible to obtain a plastic behaviour of the mix that properly transmits the pressure. An important reduction of the adhesive tendency of the clayey soil can be observed when the clay has a high plasticity index (i.e. around to 45 50%), the addition of foam with polymer can be more effective and useful than the standard foam.

53 Backfill grout methods Not more used in soil only in rok masses 53

54 Backfill grout: Grouting continuously through the TBM tail-skin wire brush 2 wire brush 1 wire brush 3 grout tail skin grout segment tail skin sealing grease tail skin sealing grease 54

55 Factors to Consider Injection system: - one component or two component grout - through segments or tail skin Control of workability up to 72 h Stability of the mix avoiding segregation and bleeding Pumpability of the mix Compressive strength after 1 cycle time or 1 hour and 28 days (approximately the same as the ground strength) Shrinkage on drying Durability (modern tunnels are designed for a hundred year lifespan) Environment (some countries object to using silicates) Economics 55

56 Backfill grout: Grouting continuously through the TBM tail-skin 56

57 Mix Possibilities Cement water Cement mortar (sand) Slurry (cement bentonite) Inert mortar Pea-gravel and cement Clay (Russia) 57

58 Action of bacbackfill grout It stops the ground movement once the segments are erected; It reduces/eliminates settlement (especially in critical urban areas); It prevents the ring moving and locks it into position especially on exiting the tailskin; It provides a homogeneous area around the ring which avoids point loading; It helps to reduce the effect of hoop stress induced by the TBM shove rams; It enhances the waterproofing of the ring 58

59 Action of bacbackfill grout 59

60 Two component mix 60

61 Case histories of two components backfill mix: Rome metro C Hardened two component mix below the segments and the soil as shown in the excavation of the station Centocelle. (photo Mapei s archive) Water Bentonite Cement Retarding agent by MAPEI Accelerator admixture by MAPEI kg kg kg 3-7 l l Two component mix used in Metro C Line in Rome (values per m3) (Pelizza et al., 2011) 61

62 Case histories of two components backfill mix: Warsaw metro View of the hardened grout as can be seen in the enlargement for a station. It is possible to observe how the mix fills completely the void annulus (photo Mapei s archive). Water Bentonite Cement IV B 32.5 N Retarding agent BY MAPEI Accelerator admixture BY MAPEI 809 kg 40 kg 300 kg 5 l 65 l Two component mix adopted in the metro line of Warsaw (values per m 3 ) (Mapei data) 62

63 Case histories of two components backfill mix: Madonado Tunnel View of the hardened grout as can be seen in the enlargement for a station. It is possible to observe how the mix fills completely the void annulus (photo Mapei s archive). Water Bentonite Cement TYPE IV Retarding agent BY MAPEI Accelerator admixture BY MAPEI 796 kg 35 kg 350 kg 5 l 61 l Two component mix adopted in the Madonado tunnel (values per m 3 ) (Mapei data) 63

64 Results of the uniaxial compressive tests on samples cured in a sealed bucket filled with sand with a controlled humidity content and maintained at a temperature of about C. The used mix is the mix type A (bentonite content of 30 kg/m3)

65 Results of the uniaxial compressive tests on samples cured in a sealed bucket filled with sand with a controlled humidity content and maintained at a temperature of about C. The used mix is the mix type A (bentonite content of 30 kg/m3)

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