ORAL PAPER PROCEEDINGS

Transcription

1 ITA - AITES WORLD TUNNEL CONGRESS April 2018 Dubai International Convention & Exhibition Centre, UAE ORAL PAPER PROCEEDINGS

2 Use of two-component mortar in the precast lining Backfilling of mechanized tunnels in rock formations Justa Cámara, R. 1 1 Master Technical Leader in Tunnels Acciona Construcción SA, Alcobendas Madrid, Spain Abstract: The precast concrete rings used on themechanized tunnel linings show serious problems in the backfilling of the gap between the ring and the excavation face. A new material known as Two-component mortar A+ B have been the one that offer the best results. Component A is a cement based colloidal suspension, with other hydraulic components, and Component B is an accelerator, usually sodium silicate. On the EPB shields, the two-component mortar is applied without problems through the tail shield pipes. In the case of rock formations the two-component mortar application is being reviewed from an application through the segments with some problems due to the conformation of the lining ring and a possible ring ovalization, up to a combination of pipes in the tail shield and the grouting pipes on the top segments. The main aim is to get a full watertightness of the backfilling layer. The paper will review some detais for the solutions adopted in three case studies, Legacy Way road tunnels in Australia, Bolaños-Campobecerros twin tunnels, on the High Speed Railway Line from Madrid to the Northwest of Spain, and Follo Line railway tunnels in Norway where the two-component mortar has been applied combining the tail shield pipes and the segment grouting pipes on the top of the lining. The article also shows the tests have been made for the definition of the characteristics, the implementation process, as well as theincorporated modifications on the machines and precast segments. Justa Cámara, R. 1 1 Master Technical Leader in TunnelsAcciona Construcción SA, Alcobendas Madrid, Spain 1. INTRODUCTION In this paper we will initially do a description of different typologies of TBMs that can be used in the excavation of tunnels in rock formations and their issues in relation with mortar backfilling. After that we will focus the paper in the backfilling of segmental lining gap of this type of mechanized tunnels and possible alternatives of backfilling, and finally we will describe why to use two component mortars in the backfilling of the gap between the rock boring face and the external face of the precast segmental lining, and its capabilities and limitations. Recent experience and development of Hard Rock Tunnel Boring on most large diameter tunnels, especially above 9m in diameter, has shown that improved ground support is a prerequisite to improved monthly advance rates. While it is accepted that TBMs can perform well in good rock conditions, the data is less conclusive about difficult ground conditions. Difficult ground can mean many 2

3 things. It can mean massive high UCS strength rock with high abrasivity. It can mean blocky conditions; severely jointed; squeezing; swelling; or fault zones. It can mean all or some of these adverseconditions coupled with varying amounts of water inflow. In a vast majority of long, large diameter tunnels, most of these conditions are encountered to a greater or lesser extent. The fact is modern TBMs can effectively bore through all types of conditions and far exceed advance rates of Drill and Blast operations in each condition. For example, in good rock conditions of medium hard to soft stable rock, TBMs are without question able to achieve advance rates up to 1,000 meters per month. There are five main types of TBMs that have been used to bore tunnels in rock formations: Main Beam, Single Shield, Double Shield, Earth Pressure Balance (EPB), and Slurry Shield. The most classic of these is the Open Main Beam TBM. The big advantage of this TBM type is the access it provides to rock immediately behind the cutterhead for rock support. The Main Beam TBM is normally used with temporary non-concrete lining, whereas most other types of TBMs are used with segmental lining. We will refer from here on to the closed machines, due to the use of two component mortar is not compatible with the Open Main Beam TBM. The Single Shield is often used in softer formations, though in difficult or hard rock conditions the design has several drawbacks. The TBM relies solely on thrusting off the segments for advance, often requiring larger than necessary segments. The operation is also cyclic: while segments are being placed boring is discontinued. Another big disadvantage is that there is no reverse force reaction to manipulate the shield when it starts to get trapped. A further drawback of the Single Shield is the very poor access to the cutterhead area for ground conditioning with foams and grouts. The Double Shield TBM has in recent years come into fairly common use, with key advantages in hard rock tunnels. The machine body is fully shielded to hold rock in place until the lining is set. Boring and segment erection happen concurrently. However, this TBM type also has its drawbacks. It is long and therefore prone to being trapped. The design is very poor with regard to access to the cutterhead for use of foams and grouts. Figure m Diameter Double Shield TBM, Follo Line project, Norway Though traditionally used in soft ground, EPB-type machines have also been used to excavate rock. In the past 40 years since the first use of EPB machines there have been substantial developments in this type of TBM. Great advances 3

4 have been made in cutterhead design, use and application of foams, and design of the auger itself. Modern EPBs can be used with the correct additives in just about every type of ground from solid rock to flowing sand. With the correct additives they can also hold water pressure up to and over 10 bars while obtaining good advance rates. However, water pressure in most long, large diameter tunnels can exceed 10 bars. Due to the most detrimental fault of an EPB type machine when used in most rock is very high wear of all components in the cutterhead and screw conveyor. These components are in constant contact with rock and a lot of time rock under pressure. This high wear normally results in numerous interventions, which involve stopping for several weeks or months for repair or replacement of components. In addition the EPB-type machines also experience all the drawbacks of a simple Single Shield. Slurry TBM machines are also used in rock excavation. The development in the design of slurry machines over the last 50 years has been significant. However, there has not been one rock tunnel that has been excavated with a Slurry TBM that would not have been more economical, and completed in a shorter time, by alternate methods. The high wear and complexity of operation in varying ground conditions make the Slurry machine extremely difficult to operate and maintain constant face pressure resulting in very high costs. 2. LESSONS LEARNED IN LARGE DIAMETER ROCK BORING AND CUTTER- HEAD EVOLUTION In the past 15 years, there have been several key lessons learned in large diameter rock boring. The main lesson: In all but homogeneous sedimentary formations, there is a very high degree of rock fallout at the face. This means that at any one time up to 50% or more of the face falls out in advance of boring. The effect is a result of jointing, bedding planes and fissures which occur normally in most rock formations. In these formations the forces of highloading disc cutters in effect act as wood splitters. Small to large blocks of rock are wedged out, causing openings or voids culminating in larger blocks and larger voids. This is typically not a big problem because modern cutterheads are designed for partial face loading; however, problems occur when the voiding progresses outside the cut diameter. This often occurs in severely jointed ground, causing voids or cathedralling above the TBM. This phenomenon occurs whether the machine is an Open TBM or a shielded TBM. Such voids left untreated can cause the TBM to be stuck or eventually, if not properly back filled, can cause segment failure. The second lesson is that the TBM should have sufficient torque to start cutterhead rotation, and keep rotation even with a full face of loose rock against it. Such high cutterhead torque is common on EPB and Slurry TBMs, as they are always operating with a full face of material against the cutterhead. Today rock machines are designed with such high torques. 4 However, unlike EPB or Slurry machines, a rock TBMneeds high cutterhead RPM to achieve good advance rates.with modern variable frequency drives (VFDs) these torque and speed characteristics can be achieved.

5 The third lesson learned is that the amount of material that ends up on the TBM conveyor must be controlled. The volume of rock conveyed out should never be more than what is contained in a normal advance. If too much volume is excavated, then cathedralling is occurring and real problems can begin, requiring ground treatment or special ground support. With modern TBMs it is possible to advance with a full face of loose rock. There are two major types of ground support used in modern tunneling: continuous concrete segmental lining and temporary lining (shotcrete, rock bolts, etc.). Concrete segmental lining is very attractive because the TBM will hold the rock in place until all loose rock and soil can be supported by the segments. In some tunnels, depending on the geology, this process can be successfully achieved. In other tunnels, ground conditioning or temporary support is required even when using segments. For the proper selection of a TBM, the possible extreme conditions that it can address in the total alignment to be bored must be evaluated. Extreme conditions are considered to be squeezing ground and water-filled fault zones. In such conditions features can be built into the TBM to make continuous progress through such zones possible and practical. For squeezing ground there are a number of options that can all be built into the TBM design: overcutting capability, invert thrusting. Even in such conditions, advance rates of 2 to3 meters per day are possible. When encountering water-filled fault zones several measures are available. First, continuous probe drilling 30 to 50 meters in advance of the TBM is recommended in all conditions. 360º probe and grout drilling is an option, while drilling through the face is also available. With today s modern grouts just about any formation of difficult ground can be consolidated. The tunnel operation needs to have a plan plus available materials to grout off fault zones. Figure 2. Grouting scheme in a Double Shield TBM with Jointed Rock at the Face In some extreme conditions, foam in combination with forepoling has been used to support the crown in advance of boring. A good example of foam use was on the Campobecerros tunnels, described after as second case study. 5

6 Figure 3. TBM Cutterhead, Follo Line Project, Norway The most important and key part of the TBM is the cutterhead. These cutterheads have gone through a tremendous evolution. Early designs were mounted with small 11 cutter discs on large spokes with large buckets. There was a generation of domed cutterheads which were thought to be more stable. Over the years, cutterhead bucket openings havegradually gotten smaller and more refined in shape, evenly ingesting the broken rock instead of gathering in large and small chunks. Modern cutterheads are crack resistant by the use of flex-acceptable materials and improved welding techniques. Strategically placed wear-resistant material is now commonly used. Rear-mounted cutters are now standard. The designs are more smooth to reduce torque when against a loose face of rock or large blocks. One of the most recent and biggest steps forward is the use of large 20 cutters, which have long wear life and can withstand the tremendous forces of blocky, hard rock. 3. BACKFILLING THE ANNULAR GAP IN A CLOSED TBM The width of the annular gap is caused by overcut, conicity of the shield skin and design of the seal; its width ranges between 13 and 18 cm. Figure 1 shows the factors influencing the width of the annular gap 6

7 In order to minimise settlements at the ground surface and to ensure good embedment and placement of the segmental lining, the annular gap has to be filled with grout continuously during tunnelling. During tunnel advance the grouting of the annular gap and the embedment of the segmental lining are necessary to transmit the forces from the tunnel into the surrounding ground. 3.1 GROUTING MATERIALS Different types of grouting materials have been used in order to ensure good embedment and to minimize settlements in soils tunnelling. Hydraulically setting mortar and twocomponent grout are typically used as grouting materials. In the case of shielded hard rock tunnel boring machines the annular gap was usually backfilled with pea gravel instead of grout untilthe introduction, as innovation, of two component grout in Legacy Way project hard rock tunnels. These materials are described in the following. Hydraulically setting mortar Since the beginning of shield tunnelling mortar is the most common grouting material in Europe. There are high demands on the mortar concerning - embedment of the segm ent lining - minimization of settlements or lining movementsduring construction - sealing against ground water and leakage water - good plasticity to gain ideal mortar workability andpumpability The mortar should in the first place have an excellent pumpability in order to minimize plugging problems in the grout system. However, it should also have good properties of stiffness at the beginning for filling the annular gap to ensure good embedment. The demand for stiffness at the beginning and the demand on good plastic deformation partly contrast each other. Mortar with good features of embedment sometimes have bad pumping properties and vice versa. The stiffening behaviour of the mortar must be regulated in such a way that it is possible to start tunnelling after an interruption. The demands on the hydraulically setting mortar are listed in the following table. Table 1. Typical demands on hydraulically setting mortar to fill the annular gap 7

8 The properties of mortar are governed by its cement constituents. It is possible to divide mortar into active, reduced active and inert systems. In inert systems there is no cement, while reduced active systems have a fraction of cement usually varying between 50 kg/m³ and approximately 200 kg/m³. In table 2 examples for grout mixtures with an active system, reduced active systems and an inert system are shown. Table 2. Grout mixtures with an active system, reduced active systems and an inert system for a major traffic tunnel (Thewes and Budach, 2009) Two-component grouting mortar Grout with two components was developed to achieve good pumpabilty / workability and a quick setting. Both components have slurry consistency in order to pump them close to the annular gap where they are mixed. One component is cement bentonite slurry. The other component is a hardener or activator. After a short reaction time a gel is generated. The reaction time of the grout can be influenced by controlling the volume flow of those both components. Table 3. Example of grout mixture of two-component mortar Backfilling with mortar and pea gravel 8 In certain cases a combination of mortar and pea gravel is also used commonly as grouting material. Firstly, mortar is placed in the annular gap at the bottom to ensure good embedment of the segmental lining. After that pea gravel can be inserted through the segmental lining to prevent settlements. Finally the crown of the tunnel is grouted because the gravel will not achieve a full round embedment. It is important to note that in jointed or fractured hard rock with a high water inflow the annular gap could serve as a sort of drainage layer, where water is collected

9 and flows forward to the excavation chamber of the shield machine. In these cases from time to time a full round injection i.e. with water stopping polyurethane resin has to be done from inside the segment rings. 3.2 GROUTING METHODS Two different methods to fill the annular gap with grouting material have been established. On the one hand it is possible to transport the grouting material through segmental lining into the annular gap; on the other hand grout supply lines can be used to fill the annular ring. The latter method is also called grouting through the tailskin. Grouting through grout holes in the lining segments The lining segments have to be equipped with holes to fill the annular gap with grouting material. The grout holes should have a mechanism to retain the grouting material in the annular gap like non-return valves or plugs. The number of grouting holes depends on the plastic deformation of the grouting material. There is usually one grouting hole per lining segment. After the segments are fitted tubes are inserted in the grouting holes in order to fill the annular gap. The grouting process should start as soon as possible for minimizing lining movements or even settlements. A seal at the end of the tailskin prevents the penetration of the grouting material into the shield machine. By controlling the grouting pressure and the pressure in the excavation chamber, the contact between the mortar and the tunnel boring machine is prevented. Spring steel sheets prevent the penetration of grouting material into the steering gap and into the excavation chamber. Figure 5. Grouting through grout holes in the lining segments (common in hard rock) Cavities in the tunnel crown in the former annular gap with the high of 1 % of the shield diameter can be the result of slump of the primary grout. Secondary grouting is usually necessary and is carried out from 40 to 100 m behind the shield at the end of the back-up system (Maidl et. al, 1996). In soft ground it is necessary to fill the annular gap continuously with mortar. Therefore grouting technology through the tailskin was developed. Using this method, the mortar is pumped through grout supply lines into the gap. 9

10 Generally, the width of the grout supply line changes from a diameter of 65 mm to an oval cross-section which has with the same cross-sectional area. Figure 6 shows the principle of grouting through the tailskin. Two-component mortar was already grouted into the annular gap through the tailskin and through the grout holes of the lining segments (Bäppler, 2008). The mortar is kept from setting within the grout lines by rinsing the lines regularly. To fill the annular gap with the above described materials, different methods are applied to pump the material. Piston pump Piston pumps are the most common pumps to grout the annular gap with hydraulic settled mortar. Piston pumps push the material through a supply line and convey the mortar. The volume of delivered mortar is regulated by the pace of the piston. Piston pumps exist as single or double piston pumps. Double piston pumps are usually installed in tunnel boring machines due to their compact design. Each piston fills one grout supply line with mortar. Figure 7. Double piston pump with installed grout supply line Peristaltic pumps 10 The main component of a peristaltic pump is a flexible tube fitted inside a circular pump casing. The pump draws the material inside the tube by causing a vacuum inside the tube under simultaneous pushing of the material forward by the rotation of rollers on the flexible tube.

11 Progressive cavity pumps Progressive cavity pumps contain a horizontal spiral within a tube to transport the material due to the friction at the spiral blade. Between the inside of the tube and the outside of the spiral blade there is little space. By using a progressive cavity pump a continuous flow of material is achieved. Progressive cavity pump were used for tunnelling projects only to transport two-component mortar. Just as for peristaltic pumps, the transport of mortar is not economical and not practical due to high wear and the extensive time needed for maintenance. 4. LEGACY WAY PROJECT CASE STUDY In this project two double shield TBMs have been used and the backfilling was made combining a tailskin injection with a segment injection. Figure 8. Legacy Way launching portal 4.1 EQUIPMENT A total of 4 grout pumps are allocated for tailskin injection and 6 grout pumps are allocated for segment injection as follows: Figure 9. Grout pump arrangement on TBM Tailskin injection 11

12 The mixing nozzle of the tailskin grout port will be assessable after the regripping as per illustration shown in fig 9. Maintenance and replacement of the mix nozzle should be carrying out after the re-gripping and before building of the next ring. Figure 10. Tailskin grout port section view It is very important the placement of control panels well located and manned by the grout pump operator for controlling Figure 11. Data Display for tailskin and segment injection the pumping flow rate and other grouting parameters. Regrouting panel is located at injection point in the segment ports. Grout injection nozzle through segments Minimum 6 sets of the grout nozzle and hose were used for the injection through segments 12

13 Figure 12. Grout nozzle set-up Grout port access at each stage For stages 2 to 6 grouting the grout ports are assessable as per illustrations below: Figure 13. Grout point access at different stages Figure 14. Stage 2 grout ports accessible at erector platform 13

14 4.2 MATERIALS Table 4. Legacy Way approved mix design for component A The proposed liquid sodium silicate content is at 9% and 10% ratio of component A volume. Table 5. Target mortar mix design requirements Grout accessories The non-return valve is to prevent grout back flow after injection and is fitted in the grout socket during segment fabrication stage. The screw caps with O-ring are previously fitted on the segment and should be fitted immediately after completion of injection of one grout port. Grout sockets 14 Two grout sockets are embedded in segment V1 to V8 and 1 grout socket in V9. The grout sockets are caped before the extrados of the segment. Before injection

15 through the segment the cap of the grout sockets must be penetrate through. Figure 15. Grout sockets through segment (plan view) 4.3 METHODOLOGY Batching of the grouting material The key of batching the grout at the mixer on surface is to ensure the material mixed in the mixer is following the mix design. To achieve the mix design, the weight of the raw material such as cement, bentonite, fly ash, water and retarder to be discharged to mixer can be adjusted at the grout plant control panel. The actual mix for each batch will be logged to verify the batch is mixed according to the mix design. The tolerance of the material dosing is as follows: Cement +10kg / -5kg Fly Ash + 10kg/ -5kg Bentonite +/- 3kg Inhibitor additive Mapequick CBS 1 +/- 0.2kg Water +/- 10kg Transfer Components A and B from Surface to Staging Tank on TBM After the grout plant on the surface is synchronized with the grout plant on TBM and when both control panel on surface and on TBM gantry are both switched to automatic mode, the component A and B pump on the surface will be automatic activated and transferring the components from surface to their staging tanks on TBM gantries until the upper threshold of the staging tank are reached. The surface pumps can also be operating manually from surface control panel. Stage 1 Grouting It is crucial to provide immediate support at the invert of the ring whenever the built ring becomes suspended from the tailskin. Generally when the tailskin moves forward and forming a 300mm clearance between the spring plate and previous grout, back filling of the annulus void of the lower 120 degree should start. 15

16 In double shield mode the tailskin will move forward by retracting the main thrust cylinder and extension of auxiliary thrust cylinders during re-gripping process. In single shield mode, the tailskin will move forward as machine advances. For 8 P a g e the Legacy Way Project, double shield mode will be applied in general cases. The grout crew will connect the bi-component grout line at stage 2 (lower) grout ports and start grout pumps 1 to 6 (illustrated in fig 9) to inject grout for stage 1 injection. For double shield mode: The flow rate of the pumps can be adjusted to accommodate the re-gripping rate of 200mm/min in semi auto mode. Total grout = m3 per ring Grout lower 120 degrees = 5.11 m3 per ring In special cases the TBM is re-gripped two times within one advance. For Single shield mode: The pumping rate is adjusted based on the advance rate. The grout volume for each ring (5.2m3). The intermediate volume at 1m retraction of the main thrust cylinder (2.6m3) is also checked. Stages 2 to 5 Grouting When operating in double shield mode, on completion of re-gripping the TBM operator switchs the TBM operation to Advance and Ring Build Mode. Here, the tailskin remains still and the injection through the segment is then undertaken from the bench. When the TBM is in Single Shield Mode, the injection through the segment takes place during Ring Build mode. The grout crew prepares the grout injection points after regripping operation. The grout volume and flow rate is adjusted based on proof drilling result or other site observation made. The engineer must oversee the volume injection and differential pumping pressures are recorded correctly. 16 Figure 16. Predicted grout pattern at designed flow rate and volume

17 Inject Grout through Segment at Crown The Stage 6 injection point is accessible at level 3 of gantry 1 at 8m back from the tailskin as per illustration in fig. 16. This operation is envisaged to take place 12m behind tailskin for each advance to prevent stage 6 grouting run off. Excessive grout volume The total target volume injected including all stages is 16.2 m3. The theoretical volume per ring is m3 The estimated excess is 5.7%, which was monitored and the design volume of each stages, adjusted on base of proof drilling and other site observations. Maintain Grout Injection Line and Accessories It is important to regularly clean and maintain the grout injection line and accessories to reduce the delay of grout blockage, leakage and plant failure. The most likely blockage occurs after the mixing points of Component A and B. In some occasions Component B may back flow into the Component A line regardless of non-return valve fitted on the end of Component A line. Mitigation of this problem is to stop the Component B short before stopping Component A, use water to flush the Component A lines and grout nozzle for every stoppage. This process will be automatically carried out by the grouting system for tailskin injection as programmed. As for segment injection, the lines will be cleaned manually using water every shift. The grout pump operator should monitor this closely to ensure this procedure is being carried out. In addition to this, high pressure water will be utilized to clean the grout port in the tailskin each day during maintenance hours. It is crucial to clean and maintain the grout accessories such as grout nozzles, connection points when they are not in use. The nozzle should be cleaned every time they are removed from the segments. The rubber O-ring inside the connection adaptor should always be checked prior connection and any damaged O-rings should be replaced. The diagram below demonstrates a simple layout of the Component A system, and will be used to explain the Component A line maintenance procedure. Figure 17. A line Maintenance Schematic Dagram 17

18 Secondary grouting The grout mixture used will be a combination of Ordinary Portland cement and potable water, at a ratio w/c in the range of by weight. Admixtures may be used in the mixture subject to technical approval. The grout will batched on the TBM and injected through the grout ports in the segments using a Putzmeister S5 worm pump (or similar) with standard nozzles and hoses, similar to the two component grout injection system detailed above. The grout will be injected at 1 bar pressure above hydrostatic pressure. The hydrostatic pressure was defined by the designer. The pressure is monitored at the point of injection by a pressure gauge. The accepted criteria for the batched grout is as per the specifications in the below table 5. BOLAÑOS-CAMPOBECERROS TUNNELS CASE STUDY Figure 18. Bolaños-Campobecerros tunnels launching portal 18

19 This is an excellent case in waterproofing of tunnels applying two component mortar in a single shield rock TBM. This project is part of the Northwest-North High Speed Railway Line in Galicia, Spain. The contractor has been the Joint Venture formed by ACCIONA Infrastructures, FCC, CYES Construction and Contratas y Ventas Company. The tunnel s clearance is 52 m2. The section is circularshaped, with an excavation diameter of 9.90 m, lining segments of 37 cm thick and an internal diameter of 8.76 m. An evacuation platform of 1.62 m of accessible surface (total width of 1.86 m) and a service platform of 1.48 m were used. A single shield TBM (Tunnel Boring Machine) for hard rock has been used during the two drives. It is a Herrenknecht TBM that has been refurbished for this work. The drilling diameter is 9.9 m. The TBM s shield length is 10 m, whereas the total length (including the back-up) is 120 m. The main work of this contract was the boring of straight alignment of Bolaños-Campobecerros Tunnels. It s a twin tunnel for single track, whereas each bored tunnel is aprox. 6,079 m long. The second tunnel completion date was December According to the previous geotechnical studies carried out during the designing stage, the expected water pressure at certain points of the excavation was 140 m water column, with water flow peaks up to 100 l/s. This is why the main concern in this project was the use of an improved waterproofing gap backfilling system. To comply with the watertighness requirement was used as backfilling a two component mortar, instead of conventional mortar, to fill the gap generated between the drilling diameter and the external diameter of the lining. Similar to the resins used for stabilization of tunnel fronts, the two component mortar is a mortar formed by two components (A, with cement, bentonite, water and a retarder; and B, liquid sodium silicate used as accelerator) that once it is injected in its advance by tunneling machine- previously adapted for this function- it produces a reaction around the perimeter of the ring that in only few seconds creates a hardened and high strength gel (0.4 MPa during the first 24 hours). This gel almost immediately fixes the lining pieces to the ground, spreads homogeneously through the gap and isolates the segments completely from the water. This also prevents different movements of the ring segments due to the delay in the mortar s setting. This solution already used by Acciona Infrastructures with good results in the urban tunnel excavation of Legacy Way in Brisbane (Australia), is replacing in the last five years the conventional mortar for mechanized underground works, although it is the first time that it is used in for single shield tunnel boring machine in a rock formation. The bentonite is prehydrated al least 24 hours before incorporating in the batching plant. 19

20 Equally relevant have been the innovations implemented to improve the quality of the rings and, therefore, their sealing. These include a new waterproofing system with double EPDM rubber gaskets in the lining segments that, by doubling the gasket sealing that surrounds each segment, placing them one close to the external face and other near to the internal face, increases the sealing capability; and, in addition, it reduces the deformation distributing the loads more uniformly. This double gasket results in a compression effect at least one of the two profiles when the ring can developes some ovalization and/or slight distortion in the rotation and, subsequently, a predictable watertightness improvement. Figures 19. Typical lining segment with double gasket 20

21 Figures 20. Lined tunnel view Another innovation has been the modification of the conicity of the ring, using an angle equivalent to a minimum radius of 350 meters (lower than what can describe the TBM, which is 400 meters), which corrects the small deviations described by the TBM with respect to the theoretical alignment, avoiding the risk of propping up in the shield tail. The tunnel s layout minimum radius is 7,280 m. Finally, trapezoidal segments have been used instead of the usual rectangular ones. According to the companies, this change improves the longitudinal compression of the joints, avoiding pathologies that could be caused by the loads of the pushing jacks. The result is an additional compression component to that of the erector in all radial joints, which does not occur in rectangular segments. The tunnel section excavated by drill & blast was also lined with the same precast segments used for the lining with the TBM. The rings were set by the TBM along the machine was skidded up to the auxiliary tunnel frontal face. Main Challenge: In single shield TBMs, application of the two component mortar through the segments has had some problems due to the possible ovalization of the ring and the water ingress through the back filling. Challenge solution: In Bolaños-Campobecerros tunnels ACCIONA has applied and improved the solution that was implemented before in Legacy Way project (Australia). The tail shield of the TBM was modified to apply the two component mortar as backfilling, as well as improved the structural ring behaviour and the global watertighness with the placement of double rubber gasket keeping the trapezoidal segment geometry. 6. FOLLO LINE PROJECT CASE STUDY Nowadays it is frequent that the contract specifications require a tight tunnel, even in cases with high water pressures in the rock formation to be drilled. This is the case of the Follo Line project where up to 16 bars of hydrostatic pressure are reached. In this project four double shield TBMs have been used and the backfilling was made combining a tails kin injection with a segment injection. 21

22 Figure 21. Double Shield TBM assembly in cavern 6.1 EQUIPMENT Backfilling equipment on TBM Table 6. Characteristics of Bi-component pumps All eight pumps will be used for tail skin injection; two of these pumps will also be used for secondary grouting 22

23 Tailskin injection Figures 22. Component B pumps and tank, gantry 5 The tailskin injection is being performed from eight double lines. Of the 2 lines shown only one is being used for normal injection operations having the second one available as a reserve line in case of blockages. The mixing nozzle of the tailskin grout port will be assessable after the re-gripping as per illustration shown in figure 10. Maintenance and replacement of the mix nozzle should be carried out after the re-gripping and before building the next ring. Before maintenance shift, the ring must therefore not be built. before building the next ring. Figure 23. Position of grout socket in s 23

24 6.2 MATERIALS Mix design and mortar requirements The proposed mix design per batch of component A used at the moment is the following: Table 7. Bi-component proposed mix design The proposed sodium silicate content is at %7 - %6 ratio of component A volume. Requirements for the component A and B are as follows: Table 8. Bi-component mortar requirements 24

25 Grout socket One grout socket is embedded in each segment. The grout sockets are caped before the extrados of the segment. Before injection through the segment the cap of the grout sockets must be penetrate through with an approximate 25mm drill bits. The non-return valve shall be installed to prevent grout back flow after injection and will be fitted in the grout socket after penetrated the segment and before starting of grout injection. Grout caps will only be installed in segments that will be used for secondary grouting and tertiary grouting. Figure 24. Disassembled grout socket with non-return valve, socket and grout cap Injection nozzle through segment Bi-component grout shall be complete seal the grout socket at the completion of each segment injection. This is achieved by avoiding flushing of the lines with component A through the grout socket before removing the injection packer. A three way valve will be introduced just before the segment injection packer so when the injection if finished and the pressure has been reached the three way valve will be switched so that the bicomponent flow will re-directed towards the flushing line. This way the grout socket will be full with compacted bicomponent grout and will ensure a complete seal of the grout socket. The grout operator will than switch off the component B pump so that component A will run through the mixing nozzle and flushing lines for around 5 L. When the injection and the flushing is completed, the nozzle will be detached from the segment port, cleaned and maintained properly. See figure METHODOLOGY Transfer component A and B to staging tank on TBM To operate the backfill grouting system in auto mode requires two functions. First is the synchronisation of the grout plant on the surface with the grout injection system on TBM. The second is to switch both control panel on surface and on TBM gantry to automatic mode. In this case the component A and B pump on the surface will be automatic activated andtransferring the components from surface to their staging tanks on TBM gantries until the upper threshold of the staging tank are 25

26 reached. The surface pumps can also be operating manually from surface control panel, but this should be limited for exceptional cases. Backfilling concept The backfill grouting concept is to complete primary grouting cycles with injection through the shield for the lower 269 degree of the tunnel annulus. Followed by complete the secondary backfilling of remaining top 91 degree of tunnel annulus through segment. This concept has follow benefits: Injection through the shield to minimize possibility of breaking the segment behind grout ports Pressurized backfill in the tunnel crown to minimize the requirement extensive proof drilling which minimize the leaking grout ports. Minimize pressure on spring plate reduce the delay related grouting contaminating the grippers. Measures to be put in place to ensure successful operation as follows: All 8 pump shall be utilize during TBM shield grouting during re-gripping to minimize flow rate requirement. The segment and invert grouting will be branch off two of the 8 pumps. Short gel time(10-6 sec) Define pressure limit for different level Ability of control gel time in an effective manner Grout system maintenance regime Grout volume/pressure control guidelines Primary grouting It is crucial to provide immediate support at the invert of thering whenever the built ring becomes suspended from the tailskin. The primary grouting shall start when the tailskin moves forward and forming a 300mm clearance between the spring plate and previous grout. All 8 pumps will be ultilise to provide adequate flow rate capacity. The grout will flow from all injection ports except the two lines at the top of the tail skin forming a support to the ring of 265 degrees. In double shield mode, the tailskin will move forward by retracting the main thrust cylinder and extension of auxiliary thrust cylinders during re-gripping process. In single shield mode the tailskin will move forward extending only the auxiliary cylinders as the machine advances. For the Follo line Project, 4 double shield mode TBMs were utilised in general cases. 26 Figure 25. Bicomponent layer behind the concrete lining

27 Injection flow capacity For double shield mode: Theoretical grout volume Total grout = m3 per ring Grout from tailskin 268 degree = 8.42 m3 per ring Target volume and pressure The total target volume for bicomponent primary grout is 8,42 m3. The target pressure for primary injection shall be 0,5 to 1 bar. The initial volume and pressure target refer to the parameter below. These parameter shall be optimized during the first grouting cycles based on actual experience obtained. Figure 26. Initial grout volume and pressure In semi auto mode the flow rate, need to be pre-defined so the target volume can be achieved by end of the stroke. For single shield mode: The pumping rate will be adjusted based on the advance rate. The engineer will provide instruction of the adjustment of the pumping rate accordingly. Secondary grouting. The injection of the remaining 95 degrees will be executed with the secondary grouting through the segments at specific grout socket injection location. The injection will take place from the mobile platform at the top deck of the bridge or from the stairs that connect the top deck to the middle deck (see Figure 27 and Figure 28 for location of secondary grout injection ports and available working platforms). 27

28 Figure 27. Location of grouting ports for secondary grouting and available working platforms As the pump used for injection through the segments is the same that will have to be used for the tailskin injection the segment injection has to be completed in the time frame of one advance. For double shield mode: Figure 28. Mobile platform for secondary grout injection Injection every 2 rings using one single pump when grout sockets in the crown are available. Injection every 3 rings, using 2 pumps, injecting both right side and left side when 2 grout sockets are available. 28

29 For single shield mode: The injection will have to take place during ring building and finish before restart of the excavation: More pumps are available for secondary grouting; it is assessable, case by case if only one or more pumps need to be used. The injection is performed approximate 6 rings behind the last installed ring using special injection nozzles. Switching operations between tailskin injection and segments injection As said in the previous paragraphs, all the pumps will be in operation during re-gripping injection. Four of these lines can be used for secondary grouting, the ball valves will be opened so component A can flow towards the segment injection point. As an alternative the hose can be disconnect and switch to either tailskin injection or segment injection grout lines. Bi-component mix for secondary grouting The Component A mix will be the same as the tailskin injection. The dosage of Sodium silicate will be different. The final mix will have then a higher gel time to be able to inject two or more rings in one time. This dosage difference will have an impact on the short-term strength but, as this is an injection for the top part only, it does not need this early strength to sustain. the ring. The mix will have a dosage of component B at approximate %6. Cleaning and Maintenance Cleaning of component A pipes is crucial and the same method described for Legacy Way is followed. 7. INSPECTION AND TESTS / CHECKLISTS Grout testing Two category of grout testing are carried out during grouting operation: 1. regular grout testing to ensure the design strength and other grout requirement are met and to monitor the consistency of the grout performance 2. Grout restart testing - After long term grout idling to verify if the idled grout is still usable Regular tests Testing of the grouting material are undertaken at the frequency below until the result has consistently met the grout requirement. Typical testing includes strength, bleeding, gel time, Marsh funnel test etc. Grout testing at the grout plant will be undertaken by trained Grout Plant assistants or the operator who has been fully trained by additive manufacturer technical support. 29

30 Table 9. Grout testing frequency chart Bleed Measurement The bleed of the grout mixture shall be measured using a 1 litre measuring cylinder as per specified in ASTM C940. The bleed is visually measured at 2,1 and 4 hours. The bleed is recorded and reported as a percentage. Marsh funnel The viscosity of the grout shall be measured using the Marsh Funnel. The funnel shall be calibrated with water to give a time of 26 Seconds ± 0.5 seconds, daily. The marsh funnel reading taken immediately after sampling will be used for regular grout test. Grout Density Test Grout Density Test shall be carried out in accordance with the specified Code. Gel Time Testing The A Solution is poured rapidly into the B Solution and poured rapidly back and forth until the grout is no longer pourable. This time is recorded and the test repeated for accuracy. Compressive strength Cube testing to be carry out in accordance with specified Code. Compressive strength test at 1 hour should be carried out on 6 samples, if the viscosity measurement did not achieve the predetermined criteria. If all of the grout cubes is above design requirement of 0.1 Mpa the grout should be deemed usable; if any of the grout cube is lower than 0.1Mpa a 2nd test should be conducted. 30

31 Temperature Measurement Figure 29 Cube Testing Mould Gangs When the grout testing is undertaken, the temperature shall be recorded of both the Ambient and Grout Temperature at the beginning and end of the test run, and recorded on the relevant testing format. The temperature measurement will be taken in the TBM as well as at the grout plant. Shrinkage Test Shrinkage test shall be carrying out in accordance AS or other equivalent code modified to adopt curing condition of %100 humidity. Daily review and action plan The result must be reviewed by project engineer daily. Any abnormal result must be investigated and action taken on case by case basis. The actions may include: Review batching dockets Repeating test under supervision of the engineer Isolate silo if the raw material does not perform Stop batching if deemed necessary Stop grouting if deemed necessary Grout restart test Grout restart tests are considered necessary when the component A is left in the system for more than 12 hours, due to planned or unplanned shut down. Viscosity Measurement A sample of grout shall be taken at the grout pipe and agitated with manual paddler mixer for minimum 5 min. The average of 3 tests of viscosity measurement shall be taken. If the average is within the range of 3 -/+ 32sec. the grout shall be deemed acceptable for reuse. If the Marsh funnel test falls outside the criteria, 1 hour cube strength of the same sample should be tested. Proof Drilling Backfilled annulus void will be proof drilled at strategic locations as per following criteria: Initially every 10 ring at 2 locations. The frequency can be 31

32 adjusted based on proof drilling results. Once a level of confidence has been reached between the primary injection records and proof grouting result this level of testing can be reduced. Method of proofing drilling involves drilling 20mm bore hole through the segment grout port to the rock with battery drill. 8. CONCLUSIONS The two component system injection for backfilling while excavating with closed shield TBMs is progressively substituting the traditional use of hydraulically setting mortar, even in rock formations, with single or double shield. It is crucial to have a well-schooled operating team familiar with ground support including foams and grouts. The reasons why to use two component mortars in the backfilling of the gap between the boring face and the external face of the precast lining segments, are mainly the following: Reduces the risks of choking pipes and pumps Guarantees a complete filling with the pressure of all annular voids created after the TBM tail passage Locks the segmental lining into position, avoiding movement owing to both segmental self-weight and the thrust forces, hoop stresses, generated by the TBM Bears the loads transmitted by the TBM back-up weight Ensures a uniform and homogeneous segment ring confining and an immediate contact between the ground and the lining Avoids puncture loads by ensuring the application of symmetrical and homogeneous loading along the lining Complements the waterproofing of the tunnel jointly with the concrete lining and rubber gaskets (i.e., if the lining has cracks due to a wrong installation, back-fill grout should help to mitigate any water inflow). Strong improvement of lining waterproofness, even in case of high water pressure Great minoration of lining movements due to the buoyancy during grouting process and reduced inducted settlements on surface Better quality in the final lining assembly and tunnel finishing Becomes as a barrier against vibration transmission Better excavation performance rates The secondary grouting is a key factor to assure the tunnel watertighness and it is performed approximate 6 rings behind the last installed ring. 9. REFERENCES Bappler, K. (2008). Entwicklung eines Zweikomponenten- Verpressystems fur Ringspaltverpressung beim Schildvortried, Taschenbuch fur den Tunnelbau 2008, Verlad Gluckauf GmbH, Essen, Maidl, B., Herrenknecht, M. and Anheuser,L. (1995). Mechanised Shield Tunnelling, Ernst&Sohn, Berlin. 32 Thewes M., and Budach C. (2009). Grouting of the annular gap in shield tunnelling An important factor for minimisation of settlements and production

33 performance, Proceedings of the ITA-AITES World Tunnel Congress 2009 Safe Tunnelling for the City and Environment, Budapest, May Home, L. (2009). Modern Large Diameter Rock Tunnels, Fjellsprengningsteknikk, Oslo, 27-26, November

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