Instrumentation and Evaluation of the Concrete Dome Plug DOMPLU RICHARD MALM. Division of Concrete Structures KTH, SE Stockholm

Transcription

1 i Instrumentation and Evaluation of the Concrete Dome Plug DOMPLU RICHARD MALM Stockholm 2015 TRITA-BKN, Report 147 KTH Civil and Architectural Engineering Division of Concrete Structures KTH, SE Stockholm

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3 Instrumentation and Evaluation of the Concrete Dome Plug DOMPLU Richard Malm TRITA-BKN, Report 147

4 Richard Malm, 2015 KTH Royal Institute of Technology Department of Civil and Architectural Engineering Division of Concrete Structures Stockholm, Sweden, 2015

5 Preface The department of Civil and Architectural Engineering at KTH Royal Institute of Technology, by commission of SKB (Swedish Nuclear Fuel and Waste Management Co), has carried out the work presented in this report. This full-scale test presented, comprises several activities such as measurements of the bentonite seal, water pressure, leakage, etc., which are all analysed and evaluated. These results are however, not included here. Instead, these are presented as separate reports, and the main conclusions and the outcome from the performed full-scale test are presented by Grahm, Malm and Eriksson (2014). KTH has been responsible for the instrumentation and evaluation of the response of the concrete dome. The results presented here, therefore, include the installation of sensors and evaluation of the measured response of the concrete dome plug in the full-scale test performed by SKB in the Äspö Hard Rock Laboratory. Stefan Trillkott and Claes Kullberg have performed the installation of all sensors with the assistance of SKB personnel at site. Writing of the report, analysis and evaluation of measured data have been performed by Dr. Richard Malm. Prof. Anders Ansell and Prof. Em Jonas Holmgren have been responsible for the review. Stockholm, June 2015 Richard Malm i

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7 Summary This report presents the instrumentation and evaluation of the ongoing measurements of the concrete dome plug in the full-scale test DOMPLU performed by SKB (Swedish Nuclear Fuel and Waste Management Co) in the Äspö Hard Rock Laboratory. The installation of sensors was performed in March 2013, about one week prior to casting of the concrete dome. The concrete dome plug was instrumented with several different types of sensors. These were mainly embedded inside the concrete dome, with the purpose to monitor its behaviour and to verify that it performs as expected. The different types of sensors used to monitor the concrete dome were; strain gauges, temperature sensors, joint-meters, LVDT sensors and pressure sensors. The evaluation and analysis of the recorded response of the concrete dome are presented from the point of casting ( ) up to the point where the plug is subjected to a constant water pressure of 4 MPa ( ). The results show that almost all installed sensors have worked successfully and captured the behaviour from a few hours after casting up to the point of contact grouting the concrete dome, which occurred about 3 months after casting. An advanced cooling scheme was used to 1) reduce the heat from hydration, 2) force the concrete dome to release from the rock and 3) create a gap between concrete and rock before contact grouting. One of the design specifications was that the concrete dome should release from the rock, and hence that it could be considered as almost stress free before contact grouting. The cooling procedure in combination with the contact grouting would then result in a thermal pre-stress of the concrete dome plug. One of the aims with this report is to verify if this occurs. The results show that the concrete dome was subjected to restraint during these stages and hence the concrete dome was at least partially bonded to the rock. This conclusion is based on the following observations: 1. High tensile stresses occur in the concrete dome during the first three months, which may result in cracks in the concrete dome. 2. The obtained thermal pre-stress is lower than what would have been obtained if it had released from the rock (about 53% of the theoretical value) 3. The relative displacements between concrete and rock were significantly lower than corresponding expected displacements that would occur if it released During the increasing water pressure, the following response was observed: 1. The joint-meters located in the top of the dome showed a rapid decrease in displacement as the water pressure reached 3.5 MPa. This was likely caused by a iii

8 release in bond between concrete and rock on the upstream side of the slot. Leakage was also detected in this region during pressurization, which further implies a loss of bond on the upstream side of the slot. 2. All strain gauges showed decreasing strain during increasing water pressure, which resulted in that all sensors showing a compressive state of stress. In total 61 sensors were installed to monitor the concrete dome. Unfortunately, not all sensors were functioning during the measuring period whereas: 1. Three of the temperature sensors have failed also losing their strain recordings. Two of these failed during the increasing water pressure. 2. Eleven strain gauges in total have failed, almost all occurred during the increase in water pressure. This indicates that the bentonite seal was not watertight and water pressure was built up on the upstream side of the slot. 3. Two of the LVDT sensors failed to record reliable displacements. iv

9 Contents Preface... i Summary... iii 1 Background Monitoring system Strain gauges Tokyo Sokki Kenkyujo (TML) sensors Geokon Temperature sensors LVDT sensors Joint meters Pressure on the formwork Data Acquisition Drainage cabinet Instrumentation cabinet Data acquisition systems Instrumentation Strain gauges Theoretical placement of installed sensors Actual placement of installed sensors Temperature sensors LVDT Joint meters Pressure on the formwork Cable alignment Data acquisition system Comparison of sensor types v

10 4.1 Strain gauges Comparison between signals from Geokon and TML sensors Notable errors Temperature Comparison between sensor types Notable errors Displacements Signal processing Temperature calibration of raw data Filtering of raw data Reference point for the sensors Results Pressure on the formwork Temperature Early age behaviour Malfunctioning temperature sensors Long-term behaviour Strain Early age response Calculated effect of pre-stress Long-term behaviour Malfunctioning strain gauges Estimation of induced stress Relative displacement between concrete and rock Early age behaviour Long-term behaviour Displacement of the concrete dome Conclusions Installation Monitoring Bibliography A. Appendix Measured data A.1 Strain gauges vi

11 A.2 Temperature sensors A.3 Joint meters vii

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13 1 Background In Sweden, a site has been selected at Forsmark for final disposal of spent nuclear fuel from nuclear power plants. The repository will be located approximately 470 m below the ground surface in crystalline rock. The KBS-3V concept envisages the disposal of spent fuel packaged in copper canisters with cast iron inserts. The long-term safety principles are based on isolation and containment of radioactive waste through the choice of a stable geological environment at depth and the use of a multi-barrier system consisting of engineered barriers (canister, buffer, backfill, and closure) and the host rock. The canisters are emplaced in vertical holes below horizontal deposition tunnels. The holes are lined with pre-compacted blocks of bentonite buffer. The deposition tunnels are backfilled with bentonite blocks and pellets, and closed with a tunnel plug. Deposition tunnel plugs in the KBS-3V repository are not prime safety barriers, but they have temporary functions with the objective of supporting the performance of other safety barriers. Their functions during the operational period of the repository are to: Confine the backfill in the tunnel. Support saturation in the backfill. Provide a barrier against water flow that may cause harmful erosion of the bentonite backfill and buffer. There are two driving forces for the demonstration of plugging and sealing technology in SKB s programme: to decrease uncertainties in the long-term performance of deposition tunnel plugs, and to decrease uncertainties in the description of the initial state of the deposition tunnel plugs. The reference design of the plug will be updated and modified based on DOMPLU outcomes. The update on the reference design basis is required to capture any new learning from the DOMPLU test and quantify any uncertain requirements In order to test the conceptual plug system for the KBS-3V repository, a full-scale test, DOMPLU, was performed at Äspö Hard Rock Laboratory (HRL), as seen in Figure 1-1. The DOMPLU test is based closely on the reference conceptual design of the deposition tunnel plug. In contrast to the earlier plug tests undertaken by SKB, DOMPLU therefore represents a more detailed iteration of the design rather than a fundamental change. The current SKB reference design and DOMPLU design are broadly similar, with the exception of a few modifications intended to test the performance of new materials planned to be introduced as the reference design in the future (e.g. the use of low-ph unreinforced concrete instead of ordinary reinforced concrete for the concrete dome (Malm, 2012)). 1

14 The excavation of the tunnel used for the full-scale test started in the autumn 2012 and the concrete dome plug was cast in March During the full-scale test, the installation of the whole plug system was tested. Among other things, it was tested that the filter was capable of draining the tunnel during hardening of the concrete until the contact grouting was conducted. After this, the saturation and function of the bentonite seal was tested. After the bentonite seal had reached sufficient saturation, in October 2013, the water pressure was increased on the upstream side of the plug using a compression chamber. This was performed so that the filter would be filled with water and thereby increasing the water pressure above natural conditions. It was planned to artificially increase the water pressure so the plug was subjected to a total pressure of 7 MPa and keeping it on this level for a few years. The intention was that the evaluation presented in this report was to be based on this level of water pressure. However, due to water escape from the pressure chamber, a project decision was made where the water pressure was instead kept constant at 4 MPa, which has been the case since February 2014 according to Grahm et al. (2015). After this, the intention is to perform a load test on the concrete dome subjected to a total pressure of 10 MPa. At the point of writing this report, it is not yet decided if or how this load test will be performed. (Grahm et al. 2015) Figure 1-1 Layout of Äspö HRL at level -450 m showing the location of the DOMPLU test in test tunnel TAS01. The concrete dome plug was instrumented with several different types of sensors. These were placed in the concrete in order to monitor its behaviour and to verify that it performs as expected. Some of the most important issues that these sensors were used to deal with are as follows; 2

15 1. If the concrete dome plug releases from the rock due to its early autogenous shrinkage possibly in combination with cooling. The relative displacement between concrete and rock was therefore monitored with joint meters. 2. All previous calculations have assumed that the concrete dome plug is almost stressfree prior to contact grouting (based on the assumption that it releases from the rock). The development of stresses inside the concrete dome is also important to monitor as the external pressures from water and swelling of bentonite clay are applied. This was verified with embedded strain gauges in the concrete dome. 3. That the heat generated in the hardening concrete dome develops as expected and that the cooling of the concrete dome plug is successful in preventing high temperatures during hydration. It is important to make sure that the concrete dome is subjected to low stresses prior to contact grouting and that it hardens and develop material properties as intended. The temperature was verified with thermocouples embedded in the concrete and with ambient air temperature sensors. 4. The pressure on the formwork from self-compacting concrete is normally higher than from conventional (vibrated) concrete. Hence, this pressure was measured to verify the actual one. 5. The water pressure and the pressure from the bentonite seal will act as loads on the concrete dome plug. These must therefore be measured to relate the measured response of the concrete dome plug to the applied external load. The water and swelling pressure of bentonite clay was measured in a separate programme and is hence not presented in this report. 6. The deformations of the concrete dome are important to measure in order to verify that it carries the load through arch action. The deformations of the concrete dome were be monitored with LVDT displacement transducers. This report describes the evaluation of the measured response of the concrete dome in the full-scale test and presents the early results from casting of the concrete up to the point of contact grouting and the early saturation of the bentonite seal. 3

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17 2 Monitoring system The concrete dome, DOMPLU, was instrumented with several types of sensors in order to measure and monitor its behaviour. The purpose of this section is to describe the different types of sensors used in the full-scale test. The following types of sensors were used; Joint meters (TML type KJA-A) 6 sensors LVDT (HBM type WA) - deformation sensors 3 sensors Strain gauges (TML type KM-AT) 24 sensors Strain gauges (Geokon 4200) 4 sensors Temperature sensors (PT 100) ambient air temperature 2 sensors The different types of sensors are described in the following sections. A sketch of the approximate placement of the sensors is shown in Figure 2-1. In the figure, three views of the concrete dome plug is shown together with the placement of the instrumentation. The actual placement of the sensors is later described in Section 3. 5

18 Geocon strain gauges: - (1) embedded strain gauges parallel to each joint meter (Geocon 4200) - (3) embedded strain gauges (Geocon 4200) TML strain gauges: - (5) embedded strain gauges parallel to each joint meter (TML KM-100 AT or KM-200 AT) - (18) embedded strain gauges (TML KM-100 AT or KM-200 AT)) LVDT (3) Joint meters between the plugg and the rock (TML KJA-5 or KJA-10) - (2) parallell to the tunnel direction - (1) vertical in the tunnel roof - (3) perpendicular to the contact Figure 2-1 Sketch of instrumentation in the concrete dome. 6

19 2.1 Strain gauges The strain gauges used in this experiment were all cast inside concrete. This means that they were placed in the formwork prior to casting. As soon as the concrete had sufficient strength to bond to the sensors, these started to register the strain in the concrete. Most of the sensors used, were combined strain and temperature sensors. This is further discussed in Section 2.2. Thereby, it was possible to follow the strain and temperature variation in the concrete dome plug during different stages such as hydration and cooling of the plug. The majority of the strain gauges, 23 sensors, used in the full-scale test was TML (Tokyo Sokki Kenkyujo) sensors, see Figure 2-2 a), TML Co. Ltd. (2013). Out of these 23 sensors, 14 were also equipped with thermocouples to measure the temperature. In order to achieve redundancy, sensors of a separate manufacturer Geokon, Geokon Inc. (2013), were also used in the full-scale test. By this redundancy, it was possible to compare the results from the different kinds of sensors and to be able to get results even if one type of sensors should fail. Four Geokon strainguages were used and all of these also measured the temperature. a) b) Figure 2-2 Strain gauges combined with thermocouples, a) TML b) Geokon Tokyo Sokki Kenkyujo (TML) sensors The KM series strain transducers are designed to measure strain in materials such as concrete, synthetic resin, which undergo a transition from a compliant state to a hardened state. Their low modulus (1000 N/mm 2 ) and waterproof construction are ideally suited for internal strain measurement during the very early stages of curing. They are impervious to moisture absorption, producing excellent stability for long-term strain measurement. The built-in thermocouple sensor of the KM-AT enables actual temperature measurement in addition to strain measurement. The specifications for the TML strain gauges are given in Table 2-1. (TML Co. Ltd. 2013) Table 2-1 Specifications of TML strain gauges, TML Co. Ltd. (2013). Type KM-100A KM-100 AT Capacity (strain) ± ± Non-linearity 1 % of RO 1 1 % of RO 1 Temperature range -20 to +80 C -20 to +80 C 1 Rated Output (RO) 2.5 mv/v ( strain) 7

20 2.1.2 Geokon 4200 Strains are measured using the vibrating wire principle: a length of steel wire is tensioned between two end blocks that are embedded directly in concrete, as seen in Figure 2-3. Deformations (i.e. strain changes) of the concrete will cause the two end blocks to move relative to one another, thus altering the tension in the steel wire. The tension is measured by plucking the wire and measuring its resonant frequency of vibration using an electromagnetic coil. Advantages of these vibrating wire sensors are excellent long-term stability, maximum resistance to the effects of water and a frequency output suitable for transmission over long cables. All components are made of stainless steel for corrosion protection. The specifications for the Geokon strain gauges are given in Table 2-2. (Geokon Inc. 2013) Table 2-2 Specifications of Geokon strain gauges, Geokon Inc. (2013). Type 4200 Capacity (strain) ± Non-linearity < 0.5 % of FSR 1 Temperature range -20 to +80 C 1 FSR (Full Standard Range) strain Figure 2-3 Geokon 4200 strain gauge. 2.2 Temperature sensors Out of the 23 TML strain sensors, 14 also measure the temperature (type TML KM-100AT). In addition, all four Geokon 4200 sensors also measure the temperature inside the concrete. In total, this means that the temperature inside the concrete is measured at 18 positions. All sensors that measure temperature have been named with the same name as the strain gauges, but with the letter T in the end, i.e. ST01T etc. Besides this, two sensors are also mounted outside the concrete dome plug, in order to measure the ambient air temperature. These two temperature sensors are of type Pentronic PT 100, Pentronic (2015). The PT100 sensors are protected by vulcanized India rubber which makes the sensor submersible and the probe tip has a protective stainless steel cap. These sensors are placed to measure the temperature close to the concrete dome plug, in the area 8

21 enclosed by the plastic sheet. Two sensors have been chosen in order to achieve redundancy regarding measurements. The temperature range for these sensors is -50 to +105 C. Figure 2-4 Ambient air temperature sensor, PT 100, from Pentronic (2015). 2.3 LVDT sensors Three LVDT (Linear Variable Differential Transformer) sensors were installed on the downstream side of the concrete dome plug in order to measure the relative displacement between the dome plug and the surrounding rock. These sensors were thereby installed after dismantling the formwork for the concrete dome. The LVDT sensors are illustrated in Figure 2-5 and their specifications are given in Table 2-3. The HBM WA inductive displacement transducers were used, due to their high mechanical durability and insensitivity to rough conditions, combined with their relatively low cost, HBM (2009). The sensors sustain virtually no mechanical wear, and the force reaction on the measurement object is negligible. The HBM WA displacement transducer is based on an inductive quarter bridge in accordance with the differential coil principle, i.e. where the sensor has three solenoidal coils placed end-to-end around a tube and as the core moves, the position of the primary coils relative to the two secondary coils changes and causes the induced voltages to change. Key Feature(s) Displacement probe and transducer with detachable transducer plunger Durable, robust, inductive measuring principle Good thermal stability in the event of temperature gradients Space-saving, compact design Pressure-resistant transducer for measuring displacement in hydraulic cylinders Acceleration resistance ensures long service life Option: high temperature version up to 150 C Output signal of individual choice, alternatively: 10mV/V, 80mV/V, V 9

22 Table 2-3 Specifications of HBM LVDT sensor, HBM (2009). Type Nominal displacement WA mm Linearity deviation < ±0.2 % to ±0.1 % Temperature range -20 to +80 C Effect of temperature < ±0.1 % Figure 2-5. Displacement sensors, HBM LVDTs. a) b) 2.4 Joint meters Six TML (Tokyo Sokki Kenkyujo), TML Co. Ltd. (2013), joint meters were used to measure the relative displacement in the rock concrete interface. These sensors are used to measure joint opening displacement of mass concrete. The KJA-A Joint-Meter is embedded in an exclusive socket mounted to concrete blocks made of mass concrete or other materials, and is used to measure joint opening displacement. An optional model with built-in thermocouple unit also exits; however, this was not used in this project. A principal sketch of a joint meter is shown in Figure 2-6. Specifications of the joint meters used in the full-scale test of the concrete dome plug are presented in Table 2-4. At the specific position, where a joint meter is going to be installed, a hole is drilled in the rock and a socket is mounted. The joint meter is then attached to the socket. A photo of the socket used for mounting the joint meter is shown in Figure 2-7 a) and a photo of a joint meter is shown in Figure 2-7 b). 10

23 Table 2-4 Specifications of TML joint meters. Type Capacity (displacement) KJA-A 10 mm Non-linearity 1 % of RO 1 Temperature range -20 to +80 C 1 Rated Output (RO) 1 mv/v ( strain) Embedded in rock Figure 2-6 Joint meters, TML KJA-A, from TML Co. Ltd. (2013). Embedded in concrete a) b) Figure 2-7 a) Installed fixture for mounting the joint meter, b) joint meter, TML KJA-A. 11

24 2.5 Pressure on the formwork Five pressure sensors are installed in the formwork, intended to measure the pressure caused by the concrete. The sensors used for this, were of the type Wika S10 (Wika, 2011), with the specifications given in Table 2-5. The pressure sensors were mounted on steel rings attached to the formwork. The membrane of the pressure sensor, on the upstream side of the formwork, was placed in level with the formwork. A metal socket was installed in the formwork and the form pressure sensor was thereafter fixed in the socket. A sketch of the joint meter and its socket is shown in Figure 2-8 a) and a photo of the form pressure sensor is shown in Figure 2-8 b). Table 2-5 Specifications of Wika S10 pressure sensors, Wika (2011). Type Wika S11 Capacity (pressure) 0 4 bar Accuracy 0.25 % Non-linearity 0.5 % Temperature range in media (concrete) Temperature compensated range -30 to +100 C 0 to +80 C a) b) Figure 2-8 Pressure sensor, a) sketch of the sensor and the metal socket, b) photo of Wika S10. 12

25 2.6 Data Acquisition The cables from the sensors inside the concrete dome plug were drawn first to four drainage cabinets and thereafter the cables are drawn to the instrumentation cabinet. The purpose of drainage cabinets was to prevent water from transporting inside the cables, i.e. between the metal core and the plastic sheeting, to the instrumentation cabinet. Experiences from the previous prototype experiments showed that this may be an issue, hence this extra protective measure to save the measuring equipment Drainage cabinet A sketch and a photo of the drain cabinets are shown in Figure 2-9. The cables from the sensors are inserted into the cabinet from the bottom, and the cables going from the cabinet to the instrumentation cabinet are leaving from the top of the drain cabinet. a) b) Figure 2-9 Drain cabinets, a) sketch of the drain cabinet with its dimensions in mm, b) photo of a drain cabinet Instrumentation cabinet The instrumentation cabinet, was of type ELDON ASR , and with the dimensions, h=1402 mm, b=805 mm and d=405 mm. This instrumentation cabinet, includes all data acquisition systems, and also a laptop. The cabinet is heavy and therefore requires a rigid framework in order to fix it to the rock wall. A sketch of the framework used to mount the instrumentation cabinet is shown in Figure

26 a) b) Figure 2-10 Framework for mounting the instrumentation cabinet The instrumentation cabinet is illustrated in Figure The cables are connected at the bottom of the instrumentation cabinet. Figure 2-11 Instrumentation cabinet. a) b) 14

27 2.6.3 Data acquisition systems Separate data acquisition systems were used to collect the data from the different types of sensors. This is due to the fact that in some cases the sensors required different acquisition systems or the fact that the different measurements e.g. pressure on the formwork measurements and the rest were carried out for different time periods. The HBM Spider 8-SR01 system with 16-bit resolution was used to sample the data from the pressure sensors, as shown in Figure 2-12, and its main specifications are given in Table 2-6. In combination with this data logger, a laptop with the software HBM Catman Pro was used. Table 2-6 Specifications of HBM Spider8 system. Type Spider8 Accuracy class 0.2 Linearity deviation (in relation to nominal value) 0.05 Operating temperature range -20 to +60 C Effect of temperature < ±0.1 % Figure 2-12 HBM Spider8 system. For data acquisition from all permanent sensors during the whole field test, i.e. strain gauges, LVDT and temperature sensors, the following multichannel loggers were used: Gantner Q.bloxx A104 For Geokon strain gauges (including their temperature signals) Gantner Q.bloxx A106 For TML Strain gauges, joint meters and LVDT sensors Gantner Q.bloxx A104 For ambient air temperature sensors and thermocouple signal of TML strain gauges A photo of the loggers from Gantner is shown in Figure 2-13 a) and specifications for the Gantner loggers are presented in Table 2-7. In order to transfer the signals (strain and temperature) from the Geokon sensors into the Gantner system, a VibWire-108 module was 15

28 used. In Figure 2-13 b) a photo of the VibWire module is shown and its specifications are given in Table 2-8. Table 2-7 Specifications of Gantner loggers. Used for Type Q.bloxx A104 Q.bloxx A106 Q.bloxx A107 Geokon Strain gauges (including their temp) TML Strain gauges, TML Joint meters & HBM LVDT Ambient temperature (PT100), and Temperature signal of TML strain gauges No used Accuracy % % % Linearity error < 0.02 % FS < 0.02 % FS < 0.01 % FS Operating temperature range -20 to +60 C -20 to +60 C -20 to +60 C Temperature accuracy < ±0.5 C - ±0.15 C Relative humidity 5 % up to 95 % 5 % up to 95 % 5 % up to 95 % Resolution 24 bit 24 bit 24 bit a) b) Figure 2-13 Data loggers, a) Gantner Q.bloxx A104, A106 and A107, b) VibWire

29 Table 2-8 Specifications of VibWire-108 logger. Type VibWire-108 Used for Geokon Strain gauges No used 1 Linearity error Operating temperature range 0.05 % FS -50 to +70 C Temperature accuracy ±0.1 C Resolution 32 bit The assembly of all data acquisition systems in the instrument cabinet is shown in Figure Figure 2-14 All data acquisition systems as installed in the instrument cabinet. 17

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31 3 Instrumentation In this section the placement of the instrumentation is described, i.e. where all sensors were placed and to document the installation process. The position of some of the sensors, i.e. all strain gauges and the pressure sensors, were measured with a total station. For these sensors, first the theoretical placement of the sensors is presented and afterwards the actual placement in the test. The other sensors, as the joint meters, ambient temperature sensors and LVDTs were not measured with a total station. Hence for these sensors only the theoretical position is presented. Regarding the joint meters for instance, the theoretical placement is judged to be quite exact since the theoretical placement was used as coordinates for the drilling machine. In order to describe more easily the theoretical placement of the different sensors, the plug is defined in four sections in its thickness direction, as illustrated in Figure 3-1. In the figure, the approximate drawing of cables is also shown, the cable alignment is later described in Figure 3-1 Defined sections in the dome plug and approximate cable placement. In order to describe the theoretical placement of all sensors as sketch of a local coordinate system is shown Figure 3-2. After installation, the actual placement of the strain gauges and the form pressure sensors was then measured with a total station, as mentioned earlier. 19

32 Downstream view 90 o Cross-sectional view y y 180 o z R/2 R x 0 o Upstream surface x z Downstream surface 270 o Section Figure 3-2 Sketch of the concrete dome plug, used for describing the placement of sensors. No sensor was placed closer than 400 mm to a concrete surface, i.e. the concrete cover is more than 400 mm for all sensors embedded in concrete, in order to reduce the risk that the sensors and their cables could be potential leakage paths. All sensors are named with starting with the letters PXD, which refers to the full-scale test. At the end of each sensor name, the specific names for each sensor are defined Strain gauges are named ST01 ST27, Thermocouples of the embedded strain gauges are named ST01T ST27T (with the same name as the strain gauges but with the letter T at the end) Joint meters are named JM01 JM06, LVDT are named LVDT01 LVDT03 Ambient air temperature sensors are named PT01 PT03. Since the name of sensors in SKBs data system SICADA has to consist of nine characters, zeros are added in the name of each sensor between the letters PXD and the specific sensor name if needed, i.e. for instance PXD0ST01T or PXD00ST Strain gauges Theoretical placement of installed sensors In Table 3-1, the different types of sensors, their direction and their theoretical placement is described. The placement of each sensor is given in the local coordinate system, previously shown in Figure 3-2. It should be noted that the placement of the sensors shown in Table 3-1, are approximate and the detailed placement of these sensors is instead shown later in this section. The four Geokon sensors are denoted as no 1, 14, 21 and 27 in Table 3-1. In the table, the dimensions, diameter (D) and length (L), of each type of sensor is also presented. 20

33 Table 3-1 Installed strain gauges. Type Manufacturer Name Section Direction Placement Assembly Note 1 Strain Geokon PXD00ST centre cooling pipe 2 Strain TML PXD00ST centre cooling pipe 3 Strain TML PXD00ST centre cooling pipe Geokon 4200 (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) 4 Strain TML PXD00ST centre cooling pipe TML KM-100A TML KM-100AT 5 Strain TML PXD00ST centre cooling pipe (incl temp) 6 Strain TML PXD00ST centre cooling pipe TML KM-100A 7 Strain TML PXD00ST centre cooling pipe TML KM-100A TML KM-100AT 8 Strain TML PXD00ST *radius cooling pipe (incl temp) TML KM-100AT 9 Strain TML PXD00ST centre cooling pipe (incl temp) TML KM-100AT 10 Strain TML PXD00ST centre cooling pipe (incl temp) TML KM-100AT 11 Strain TML PXD00ST centre cooling pipe (incl temp) 12 Strain TML PXD00ST centre cooling pipe TML KM-100A TML KM-100AT 13 Strain TML PXD00ST ,5*radius cooling pipe (incl temp) Geokon Strain Geokon PXD00ST ,5*radius cooling pipe (incl temp) 15 Strain TML PXD00ST ,5*radius cooling pipe TML KM-100A TML KM-100AT 16 Strain TML PXD00ST ,5*radius cooling pipe (incl temp) TML KM-100AT 17 Strain TML PXD00ST ,5*radius cooling pipe (incl temp) TML KM-100AT 18 Strain TML PXD00ST ,5*radius cooling pipe (incl temp) 19 Strain TML PXD00ST *radius cooling pipe/rock TML KM-100A 20 Strain TML PXD00ST *radius cooling pipe/rock TML KM-100A 21 Strain Geokon PXD00ST *radius cooling pipe/rock Geokon 4200 (incl temp) TML KM-100AT 22 Strain TML PXD00ST (9:00) Perpendicular to the rock rock (incl temp) 23 Strain TML PXD00ST (9:00) Upstream direction rock TML KM-100A TML KM-100AT 24 Strain TML PXD00ST (12:00) Perpendicular to the rock rock (incl temp) 25 Strain TML PXD00ST (12:00) Upstream direction rock TML KM-100A TML KM-100AT 26 Strain TML PXD00ST (3:00) Perpendicular to the rock rock (incl temp) Geokon Strain Geokon PXD00ST (3:00) Upstream direction rock (incl temp) Type: TML KM-100A Type: TML KM-100AT Type: Geokon 4200 Dimensions: D= 20 mm, L= 104 mm Dimensions: D= 20 mm, L= 104 mm Dimensions: D= 19 mm, L= 153 mm 21

34 3.1.2 Actual placement of installed sensors The placement of all strain gauges in the full-scale test was measured with a total station, and the measured coordinates for all strain gauges are presented in Table 3-2. The coordinates given in Table 3-2 are specified in the format used in SKBs SICADA system called Äspö 96, which is a global coordinate system for the whole Äspö HRL. Table 3-2 Measured placement of strain gauges. Coordinates (m) Type Manufacturer Name X Y Z 1 Strain Geokon PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain Geokon PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain Geokon PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain TML PXD00ST Strain Geokon PXD00ST

35 Almost all sensors were placed within a close range of the desired location. However, one of the sensors ST08 was placed on the upstream side of the plug rather than the downstream side of the plug, see Figure 3-3. Unfortunately, this sensor was thereby installed close to a cooling pipe, so the temperature measured at this location was highly affected by the temperature in cooling system. According to the measurements with the total station, the sensor ST19 was placed far from its intended position and was mounted in the centre of the dome. However, based on the photos taken of the installed sensors it can be seen that this sensor is not located in the centre of the dome, see Figure 3-4. Instead, the sensor is actually placed close to its intended position and thereby the measurement of its position is incorrect, see Figure 3-4. Figure 3-3 Installed sensor ST08, placed close to a cooling pipe.. 23

36 Figure 3-4 Photo of sensors installed in the centre of the dome. Most of the sensors were mounted near the cooling pipes. In these cases, the sensors were typically attached to short reinforcement bars which were attached to the cooling pipes. A total of 11 sensors (sensors ST01 ST07 and ST09 ST12) were placed in the centre of the dome, at different depths. Since these were to be placed with an angle of 45 degrees, they were mounted on spiders as shown in Figure 3-5. Four spiders were then mounted on a rod, so that the installation of these sensors was prefabricated and could easily be mounted on the cooling pipes. All sensors attached with spiders are shown in Figure 3-6. Figure 3-5 Spiders used to mount strain gauges in the centre. 24

37 Figure 3-6 Strain gauges attached with spiders. Those sensors that were mounted near to the rock, typically less than one meter, were also attached to reinforcement bars which were bolted into the rock. An example of the installed strain gauges (ST22 and ST23) near the rock surface is shown in Figure 3-7. In this figure, the two joint meters (JM01 and JM02) installed are also shown. In the photo, the grouting tubes can also be seen which are used to grout the concrete dome approximately 3 months after casting. In Figure 3-8 the strain gauges and joint meters installed close to the top of the slot are shown and in Figure 3-9 the strain gauges and joint meters installed at 9 o clock. 25

38 Figure 3-7 Strain gauges ST22 & ST23 and joint meters JM01 & JM02 installed near the rock, at 3 o clock. Figure 3-8 Strain gauges ST24 & ST25 and joint meters JM03 & JM04 installed in the top, at 12 o clock. 26

39 Figure 3-9 Strain gauges ST24 & ST25 and joint meters JM05 & JM06 installed at 9 o clock. 27

40 3.2 Temperature sensors Most of the temperature sensors were embedded in the same sensors as the strain gauges, hence, the installation of these and their position have already been described in the previous section. The thermocouple signal of the embedded strain gauges is presented in Table 3-3. In the table, the dimensions, diameter (D) and length (L), of each type of sensor is also presented. Table 3-3 Installed strain gauges with thermocouples. Type Manufacturer Name Section Direction Placement Assembly Note 1 Strain Geokon PXD0ST01T 1 0 centre cooling pipe 2 Strain TML PXD0ST02T centre cooling pipe 3 Strain TML PXD0ST03T 1 90 centre cooling pipe 5 Strain TML PXD0ST05T centre cooling pipe 8 Strain TML PXD0ST08T *radius cooling pipe 9 Strain TML PXD0ST09T 3 90 centre cooling pipe 10 Strain TML PXD0ST10T 4 0 centre cooling pipe 11 Strain TML PXD0ST11T centre cooling pipe 13 Strain TML PXD0ST13T 1 0 0,5*radius cooling pipe 14 Strain Geokon PXD0ST14T ,5*radius cooling pipe 16 Strain TML PXD0ST16T 4 0 0,5*radius cooling pipe 17 Strain TML PXD0ST17T ,5*radius cooling pipe 18 Strain TML PXD0ST18T ,5*radius cooling pipe 21 Strain Geokon PXD0ST21T *radius cooling pipe/rock 180 (kl: 22 Strain TML PXD0ST22T 4 9) Perpendicular to the rock rock 90 (kl: 24 Strain TML PXD0ST24T 4 12) Perpendicular to the rock rock 26 Strain TML PXD0ST26T 4 0 (kl: 3) Perpendicular to the rock rock 27 Strain Geokon PXD0ST27T 4 0 (kl: 3) Upstream direction rock Type: TML KM-100AT Type: Geokon 4200 Dimensions: D= 20 mm, L= 104 mm Dimensions: D= 19 mm, L= 153 mm Geokon 4200 (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) Geokon 4200 (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) Geokon 4200 (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) TML KM-100AT (incl temp) Geokon 4200 (incl temp) Two ambient air sensors PT01 & PT02 were also installed during this test. Initially, these were placed on preliminary positions, quite close to the two cooling machines. This can be seen on the output from these sensors, where the measured temperature from these sensors increased as the cooling machines were in operation. However, when the casting was finished and the formwork had been removed, these air sensors were moved to their permanent positions shown below. 28

41 Both PT temperature sensors were placed on the downstream side of the concrete dome plug, in an area enclosed by a plastic sheet. The PT01 temperature sensor was mounted 10 cm from the centre of a scaffolding beam structure used to mount the LVDT displacement sensors (see Figure 3-12). The other temperature sensor, PT02, was mounted near the rock, at midheight, on the downstream side of the concrete dome plug. The placement of the two ambient air temperature sensors is shown in Figure 3-10 and Figure PT02 PT01 Figure 3-10 Scaffolding used for mounting the LVDT sensors, and placement of PT100 sensors. a) b) Figure 3-11 Installed ambient temperature sensors, a) PT01, b) PT02 29

42 3.3 LVDT All LVDT sensors were made by HBM and are shown in Figure 2-5. The placement of the sensors is also described in Table 3-4. The coordinate system used for describing the placement of the sensors was previously shown in Figure 3-2. In the table, the dimension, diameter (D) and length (L), is also given for the type of sensor used. Table 3-4 HBM LVDT sensors Type Manufacturer Name Section Direction Placement Assembly Note 1 LVDT HBM PXDLVDT centre Scaffolding 2 LVDT HBM PXDLVDT ,5*radius Scaffolding 3 LVDT HBM PXDLVDT *radius Scaffolding Type: HBM LVDT WA-10 Dimension: D= 12 mm, L= 130 mm All LVDT sensors measure the relative displacement between the dome plug and the surrounding rock. The sensors were mounted on a scaffolding beam structure on the downstream side of the concrete plug, as seen in Figure 3-12 a). The scaffolding beam structure was mounted after dismantling the formwork for the concrete dome. In order to adjust the LVDT sensors so that they measure the horizontal displacement, wedges were designed and attached directly to the downstream surface of the dome plug, as illustrated in Figure 3-12 b). LVDT03 LVDT02 LVDT01 a) b) Figure Scaffolding used for mounting the LVDT sensors, and their approximate position. 30

43 Figure 3-13 Scaffolding and installed LVDT sensors. a) b) c) Figure 3-14 Installed LVDT sensors, a) LVDT01, b) LVDT02, c) LVDT03. 31

44 3.4 Joint meters Joint meters were placed to measure the relative displacement between the rock and dome plug on the left and right side of the downstream side of the slot and also in the top of the dome plug, i.e. placed at 9, 12 and 3 o clock. At each location, two joint meters were mounted, where one sensor measure the displacement perpendicular to the rock surface. Two other joint meters, placed at 3 and 9 o clock, measure the displacement in the upstream downstream direction, and the last joint meter placed at 12 o clock, measures the vertical displacement. The names of the different joint meters and their placement are shown in Table 3-5 and Table 3-6. The coordinate system presented in these two tables was previously shown in Figure 3-2. In Table 3-5, the dimension, diameter (D) and length (L), is also given for the type of sensor used. Table 3-5 Installed joint meters. Type Manufacturer Name Section Direction Placement Assembly 1 Jointmeter TML PXD00JM (kl: 9) Perpendicular to the rock rock 2 Jointmeter TML PXD00JM (kl: 9) Upstream direction rock 3 Jointmeter TML PXD00JM (kl: 12) Perpendicular to the rock rock 4 Jointmeter TML PXD00JM (kl: 12) Vertical direction rock 5 Jointmeter TML PXD00JM (kl: 3) Perpendicular to the rock rock 6 Jointmeter TML PXD00JM (kl: 3) Upstream direction rock Type: TML KJA-10A Dimension: D= 40 mm, L= 270 mm Table 3-6 Theoretical placement of installed joint meters. Coordinate (m) Type Manufacturer Name x y z 1 Jointmeter TML PXD00JM01-3,32 0,00 2,29 2 Jointmeter TML PXD00JM02-3,15 0,00 2,49 3 Jointmeter TML PXD00JM03 0,00 3,32 2,29 4 Jointmeter TML PXD00JM04 0,00 3,65 1,93 5 Jointmeter TML PXD00JM05 3,32 0,00 2,29 6 Jointmeter TML PXD00JM06 3,15 0,00 2,49 It should be noted that the coordinates in the table above are based on theoretical shape of the rock, and was used to determine the placement of the sensors. The actual placement of the joint meters was not measured with the total station and was not documented. These theoretical coordinates were used for positioning the drilling machine. Hence, the only deviation between theoretical coordinates and actual placement of the sensors is related to 32

45 tolerances regarding placement of the drilling machine. The procedure of mounting the socket in order to install the joint meters is shown in Figure 3-15 and Figure Photos of the installed joint meters have already been shown, see Figure 3-7 for joint meter JM01 & JM02, Figure 3-8 for joint meter JM03 & JM04 and Figure 3-9 for joint meter JM05 & JM06. Figure 3-15 Photo of two sockets used to mount the Joint meters. Figure 3-16 Photo of two sockets used to mount the Joint meters 33

46 3.5 Pressure on the formwork The theoretical placement of the pressure sensors is shown in Figure Figure 3-17 Placement of sensors for the pressure on the formwork. Pressure sensors are illustrated as red circles. The vertical placement of these sensors was also measured with a total station. The specifications and location of the pressure sensors are presented in Table 3-7. Due to the complex formwork it was difficult to install the pressure sensors exactly at theoretical locations, instead they were placed as close as possible. The placing of these sensors was not judged to be vital as long as the coordinates for the actual sensors was given. The coordinates are specified in the format used in SKBs SICADA system called Äspö 96, which is a global coordinate system for the whole Äspö HRL. 34

47 Table 3-7 Measured placement of installed joint meters. Vertical coordinate Type Manufacturer Name Z 1 Form pressure Wika S10 PXD00FP Form pressure Wika S10 PXD00FP Form pressure Wika S10 PXD00FP Form pressure Wika S10 PXD00FP Form pressure Wika S10 PXD00FP Photos of the installed pressure sensors on the downstream side and upstream side of the formwork are shown in Figure Figure 3-18 Mounted sensors for the pressure of the formwork. 3.6 Cable alignment The cables from all sensors cast inside concrete were not bundled. The reason for this was to make sure that the cables would not cause a leakage path through the concrete. In addition, to prevent leakage, the cables were drawn in a loop to extend the possible leakage path. A photo of the cable alignment is shown in Figure In order to protect the cables, a plastic tube, with a length of approximately 0.5 m was placed around the cables at the interface where they intersect the formwork, as seen in Figure

48 Figure 3-19 Cable alignment from cast-in sensors. Figure Final cable alignment of cast-in sensors. 36

49 3.7 Data acquisition system As presented earlier in a previous section, the cables were drawn from the sensors to drain cabinets as a safety measure to prevent water transport inside the cables to the data acquisition system. In Figure 3-21 the drain cabinets and the coupling of cables are shown. Figure 3-21 Drain cabinet and cables. The cables were then drawn from the drain cabinet to the instrumentation cabinet where the data acquisition systems were located, see Figure Figure 3-22 Instrumentation cabinet and drain cabinets. 37

50 In Figure 3-23, all sensors are installed and the measuring system is up and running. In the measuring cabinet, a laptop is installed. The laptop had the software Gantner Test Commander/TestNode installed making it possible to follow the measurements during the casting etc., as seen in Figure Figure 3-23 Measurement cabinet, with all sensors installed. 38

51 Figure 3-24 Laptop with measuring software Gantner Test Commander/Test Node. 39

52

53 4 Comparison of sensor types The purpose of this section is to observe the raw data output from the different type of sensors and to compare the output from sensors with the different manufacturers. The presentation of the measured behaviour, and evaluation of the full-scale test, is later given in Section Strain gauges Comparison between signals from Geokon and TML sensors There are no sensors that were placed to give exactly the same results. However, some of the sensors were placed at similar positions to give similar results and thereby giving the possibility to compare the results from the different types of sensors, i.e. Geokon and TML. For instance, four sensors were installed horizontally in the centre of the concrete dome, and their measured response is shown in Figure 4-1. In the figure, an increasing (positive) strain implies that the strain gauge is elongated and vice versa. However, in the measurements of strain it is difficult to define the zero reference value, which is discussed in Section 5.3. As seen in the figure, the three TML sensors gave similar results, but the absolute strain differs between the gauges. This is expected, since the gauges were in different sections in the thickness direction and also since the distance from each sensor to the cooling pipes differs. The Geokon sensor gives similar results for the first part of the cooling and also after the cooling is switched off. However, during the stage with maximum cooling there is a significant difference in the behaviour of the different types of sensors. The strain in the Geokon sensor is much less than in the TML gauges. The response that is measured in the TML gauges is as expected, i.e. since the temperature is reduced, a decrease in strain should appear. 41

54 Strain (temperature compensated) [µs] ST01 ST04 ST07 ST Time after casting [hr] Figure 4-1 Comparison of all horizontal strain gauges in the centre section. Just to make sure that this difference in strain obtained from the different sensors is dependent on the temperature, the temperature for the different sensors is shown in Figure 4-2. Not all of the TML strain gauges that were shown in the previous figure had thermocouples, therefore the temperature measured at the closest sensor is used instead. This applies to strain gauges ST04 and ST07 where the temperature measured at strain gauges ST05 and ST09 has been used instead. As it can be seen in Figure 4-2, there is only a small difference between the temperature measured by the different sensors and this small difference in temperature cannot be the reason for the differences in strain as shown previously. 42

55 Measured temperature [ C] ST01T ST05T ST09T ST10T Time after casting [hr] Figure 4-2 Comparison of measured temperature in the (or near) horizontal strain gauges in the centre section Notable errors All four Geokon sensors also show some occasional voltage impulses in the recordings, these are of electrical origin and erroneous and could therefore be disregarded. These sensors are of the type Geokon and are named ST01, ST14, ST21 and ST27. The same phenomenon also occurs for their temperature signals, i.e. ST01T, ST14T, ST21T and ST27T. These impulses should be filtered out in order to show the correct response. An example of the occasional impulses that occur in the Geokon sensors is shown in Figure 4-3. The TML sensors may show minor influences of these occasional voltage impulses, which also should be filtered out from the response. The TML sensors also shows slightly higher influence of background noise compared to the Geokon sensors. 43

56 800 ST Strain [µs] /13 04/12 05/12 06/11 07/11 08/10 09/09 10/09 11/0811/18 Time, date Figure 4-3 Example of voltage impulses in the output signal from the Geokon sensors. 4.2 Temperature Comparison between sensor types Figure 4-4 shows a comparison between the measured temperature obtained with the two different types of sensors installed in the concrete. As it can be seen in the figure the two different types of sensors give almost identical results. There is only a small deviation in temperature, less than 0.5 C. 44

57 20 ST01T ST02T ST03T Temperature [ C] /13 04/12 05/12 06/11 07/11 08/10 09/09 10/09 11/08 11/18 Time, date Figure 4-4 Difference between temperatures measured with Geokon (ST01T) and TML (ST02T & ST03T) Notable errors All four Geokon sensors show occasional voltage impulses in the recordings, these are of electrical origin and erroneous and could therefore be disregarded. These sensors are of the type Geokon and are named ST01T, ST14T, ST21T and ST27T. These impulses should be filtered out in order to show the correct response. The TML sensors may show minor influences of these occasional voltage impulses, which also should be filtered out from the response. The TML sensors also shows slightly higher influence of background noise compared to the Geokon sensors. 4.3 Displacements All displacement sensors works as intended. However, the level of background noise is quite high in the recorded signals. This is due to the fact that only minor displacements are measured between the concrete dome and the surrounding rock, as seen in Figure

58 Displacement [mm] /12 03/13 04/12 05/12 06/11 07/11 08/10 09/09 10/09 11/08 11/18 Time, date JM01 JM02 JM03 JM04 JM05 JM06 Figure 4-5 Measured displacements between rock and concrete dome plug, obtained from the joint meters. 46

59 5 Signal processing 5.1 Temperature calibration of raw data All measured values have to be adjusted using calibration coefficients. For the following results, this has already been performed through the data acquisition system. However, the measured strain should also be compensated for the surrounding temperature, as seen in Eq. [1], in order to obtain the real strain. ε C ε 0 + C T [1] = ε β where, ε is the real strain C ε gauge calibration factor ε 0 raw strain data C β compensation factor ΔT temperature change The results obtained from the measuring system were already calibrated, hence the strain obtained from the system was thereby calculated asε = C ε ε 0. The compensation factor for the TML strain gauges is presented in Table 5-1. Table 5-1 Compensation factors for TML strain gauges. Compensation factor C β Compensation factor C β Gauge (10-6 C -1 ) Gauge (10-6 C -1 ) ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST ST

60 The Geokon strain gauges (denoted ST01, ST14, ST21 and ST27) should also be compensated for the surrounding temperature. According to Geokon Inc. (2013), the temperature compensation factor for the Geokon strain gauges can be set to 12.2*10-6 C -1, which corresponds to the expansion coefficient of steel. 5.2 Filtering of raw data The raw data contains background noise and occasional voltage impulses. These may occur, for instance, due to cooling equipment, the pressurizing equipment, work in adjacent tunnels or as a result of random errors in the measurement and/or data acquisition equipment. In order to make the measured results more accessible all measured data should be processed through a digital filter. This has been performed with the numerical software MatLab from the MathWorks Inc. The noise caused by the cooling or pressurizing may be considered as a sinusoidal function, and therefore it should have a natural frequency, which could be attenuated with a band-pass filter. However, because a rather low sampling frequency is used in the full-scale measurements (i.e. one recording every 5 minute) the pulsation caused by the cooling and/or pressurizing system is likely to have higher frequencies. Hence, it would thus be impossible to apply a suitable band-pass filter and smoothing filters were instead used to attenuate noise in the signals. Different types of filters suitable for the DOMPLU measurements have already been analysed by Kristiansson (2014), who give further information about the different filters. In this report, the following types of smoothing filters were considered as most suitable: Savitzky-Golay smoothing filter Robust locally weighted regression (rlowess) Both of these smoothing filters have been used in this report since the behaviour of the sensors may vary and thereby may require different approaches to remove the background noise. For instance, the TML joint-meters showed quite large, relatively high frequency, oscillations due to background noise. The real deformations instead have much lower frequencies. Therefore, in order to filter these curves, the Savitzky-Golay smoothing filter uses the least square fit method to minimize the mean-square error for a defined polynomial curve based on a predefined interval of recordings. The Geokon strain gauges showed significant effects from voltage impulses, which completely dominated the behaviour. In order to remove these impulses, a different kind of approach had to be used compared to the previously mentioned method. Therefore, the robust locally weighted regression method was used. In this method, an interval is defined where the smoothing is performed so that recordings within this interval are given a specific weight where points closer to the studied point are given higher importance and vice versa. The 48

61 smoothed value is given by a weighted linear least square method regression using a linear polynomial. The filters used for the different types of sensors are presented in the table below. Table 5-2 Applied smoothing filters for different types of sensors, from Kristiansson (2014). Type of sensor Type of smoothing filter Interval (points) Polynomial order TML strain gauges Savitzky-Golay 15 3 Geokon strain gauges Rlowess 5 - TML temperature Savitzky-Golay 17 2 Geokon temperature Rlowess 5 - Ambient air Savitzky-Golay 61 5 TML joint-meter Savitzky-Golay 71 5 LVDT Rlowess 5 - In the following figures, Figure 5-1 to Figure 5-7, the difference between the original raw data and the filtered data are shown. One graph is shown for each type of sensor used. As it can be seen in the figures, the appearance of the background noise differs between the types of sensor used. For instance, the noise level is relatively high on the signals from the joint meters, see Figure 5-6. The reason for this is discussed further in Section 6.4. In addition the LVDT sensors shows occasional jumps in the signals as seen in Figure 5-7 and the reason for this is discussed later in Section 6.5. Despite the appearance of the background noise, it can be seen that the filtered signal in all cases represent a very good match of the actual trends in the measurements. Thereby, the filtered curves are considered as suitable representations for the recorded behaviour, and are used for post-processing the results from the measurements Temperature [ C] Original data Filtered data 04/01 05/01 06/01 07/01 08/01 09/01 10/01 11/01 12/01 01/01 02/01 03/01 04/01 05/01 06/01 07/01 08/01 09/01 09/29 Time, date [MM/DD] Figure 5-1 Comparison of original and filtered temperature data from TML sensor ST01T. 49

62 Temperature [ C] Original data Filtered data 04/01 05/01 06/01 07/01 08/01 09/01 10/01 11/01 12/01 01/01 02/01 03/01 04/01 05/01 06/01 07/01 08/01 09/01 09/29 Time, date [MM/DD] Figure 5-2 Comparison of original and filtered temperature data from Geokon sensor ST03T. 22 Original data Filtered data Temperature [ C] /01 05/01 06/01 07/01 08/01 09/01 10/01 11/01 12/01 01/01 02/01 03/01 04/01 05/01 06/01 07/01 08/01 09/01 09/29 Time, date [MM/DD] Figure 5-3 Comparison of original and filtered temperature data from PT sensor PT01. 50

63 S 0 0 Original data Filtered data Strain (µs) /01 05/01 06/01 07/01 08/01 09/01 10/01 11/01 12/01 01/01 02/01 03/01 04/01 05/01 06/01 07/01 08/01 09/01 09/29 Time, date [MM/DD] Figure 5-4 Comparison of original and filtered strain data from TML sensor ST02. 0 Original data Filtered data Strain (µs) /01 05/01 06/01 07/01 08/01 09/01 10/01 11/01 12/01 01/01 02/01 03/01 04/01 05/01 06/01 07/01 08/01 09/01 09/29 Time, date [MM/DD] Figure 5-5 Comparison of original and filtered strain data from Geokon sensor ST21. 51

64 Deformation (mm) Original data Filtered data /01 05/01 06/01 07/01 08/01 09/01 10/01 11/01 12/01 01/01 02/01 03/01 04/01 05/01 06/01 07/01 08/01 09/01 09/29 Time, date [MM/DD] Figure 5-6 Comparison of original and filtered displacement data from TML sensor JM Deformation (mm) Original data Filtered data 0 06/01 07/01 08/01 09/01 10/01 11/01 12/01 01/01 02/01 03/01 04/01 05/01 06/01 07/01 08/01 09/01 09/29 Time, date [MM/DD] Figure 5-7 Comparison of original and filtered displacement data from HBM sensor LVDT02. 52

65 5.3 Reference point for the sensors All embedded sensors gave recordings already before the concrete dome was cast. However, until the concrete has reached sufficient strength so that it bonds to the sensors only unreliable results will be obtained. The time for the concrete to bond may differ between the different sensors, based on factors such as the design of the sensor and its location inside the concrete dome. For instance, the Geokon strain gauges have quite large flanges at their end, which improves the early bond and thereby allows for obtaining early recordings. Different methods for selecting the reference point were studied by Kristiansson (2014) and the method chosen in this report is based on one of these approaches. Below three approaches to determine the zero level reference point are summarized. Approach 1: Bond at hydration In the first approach studied, the zero value was defined at the time when the hydration heat started to develop, i.e. when the temperature started to increase at each specific sensor. The sensors that did not measure the temperature were assigned the temperature of the closest temperature sensor. Finding the point when the temperature started to increase could easily be extracted, however, the results showed that with this approach resulted in significant differences in the early response of sensors at similar locations and Kristiansson (2014) therefore discarded this approach. The instrumentation plan was chosen in order to obtain some redundant results and therefore these sensors are expected to give approximately the same recordings. Approach 2: Bond at sudden change in strain In the second approach studied, it was assumed that slip occurs between the sensor and the concrete until the concrete has reached sufficient strength. When the concrete reaches sufficient strength, this should be visible on the strain recordings where a series of sudden changes in behaviour was followed by a smooth curve with no direct discontinuities. However, this approach also showed that sensors at similar positions varied to a great extent. One reason for this may be that the sudden change in strain differed significantly between the sensors where some seemed to bond instantaneously while others bonded more gradually. This approach was discarded by Kristiansson (2014) due to the large differences between sensors at similar positions. Approach 3: Zero level at similar behaviour The final approach studied was based on the second approach; however, one additional aspect considered was that sensors in similar positions and measuring in the same direction also should give similar type of behaviour. The sensors should act stable after they bonded to the concrete, i.e. the appearance should not change significantly, if one time point was selected as reference compared to another point a few hours later. Kristiansson (2014) further developed this approach to also reduce the tensile strain that may occur after significant drops in strain. This resulted in that the time for bond varied between 20:40 at March 13 th to 15:40 at March 14 th. 53

66 Methodology to define measurement reference point The methodology chosen in this report is based on the principle where the reference point is defined after sudden change in strain. However, since the different type of strain gauges and their direction will affect the result, these have been sorted into four categories; Horizontal, Vertical, Inclined and Close to the slot. The reason for this is that sensors measuring in different directions show significant variations in behaviour. This is for instance apparent when comparing sensors in the horizontal direction with the sensors in the vertical direction, see Figure 5-8 and Figure 5-9 respectively. The vertical sensors show in general significant drops in strains just before a smooth curve is recorded. For the horizontal sensors, this drop seems to be more gradual and this behaviour may both decrease and increase until a smooth curve appears. In Figure 5-8 it can be seen that after approximately 21:00 the day of casting ( ), i.e. about 2 hours after starting to the final casting, the sensors give similar behaviour. The vertical sensors also seem to stabilize at the same time as the horizontal strain gauges. However, some of the vertical sensors such as ST03, show an increasing parabolic shape of strain directly after the drop, see Figure This increase in strain was removed in the approach used by Kristiansson (2014), by assuming that the reference point was near the time when the strain curve levelled out. This was based on the assumption that the concrete dome should be subjected to compressive strain. However, this observed increase in strain for the vertical strain gauges is however likely to be caused by the heat generated by hydration, as seen in Figure Strain ([µs]) Strain gauges in horizontal direction (0 degrees) ST01 ST04 ST07 ST10 ST13 ST16 ST :00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 Time Figure 5-8 Measured behaviour of horizontal strain gauges during the first day after casting. 54

67 Strain ([µs]) Strain gauges in vertical direction (90 degrees) ST03 ST06 ST08 ST09 ST12 ST15 ST18 ST :00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 Time Figure 5-9 Measured behaviour of vertical strain gauges during the first day after casting. Strain [mus] :00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 18 Temperature [ C] :00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 Time Figure 5-10 Behaviour of sensor ST03 at time of bond (upper graph) and corresponding measured temperature (lower graph). The inclined sensors are, as expected, behaving as a combination of the horizontal and vertical sensors, as seen in Figure These sensors also seem to bond to the concrete at approximately 21:00 at the day of casting. 55

68 Strain gauges in inclined direction (45 degrees) ST02 ST05 ST11 ST14 ST17 ST20 Strain ([µs]) :00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 Time Figure 5-11 Measured behaviour of inclined strain gauges during the first day after casting. Four of the strain gauges mounted near the slot are measuring in a horizontal direction while two strain gauges (ST24 and ST25) are measuring in the vertical direction. As can be seen in Figure 5-12, the behaviour of the sensors near the slot is comparable to that of the horizontal sensors previously shown in Figure 5-8. However, one of the vertical sensors shows the same type of increase as strain gauge ST03 (shown in Figure 5-10). It is expected that tensile strain/stress may develop in the crest since it is intended that the concrete dome should release from the rock, at least at the crest. 56

69 150 Strain gauges close to the slot Strain ([µs]) 0-50 ST22 ST23 ST ST25 ST26 ST :00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 Time Figure 5-12 Measured behaviour of strain gauges close to the slot during the first day after casting. All sensors seem to bond to the concrete at almost the same time, 20:00 21:30, but it varies slightly between the sensors depending on their location and its direction and in general. Therefore, all strain gauges were defined with the same reference time 22:00. The small difference in strain from selecting a unique value for each sensor or a general time for zero level is marginal, only a few micro-strain. The Geokon sensors had quite large flanges and thereby allowed for measurements much earlier than the TML sensors. This resulted in that none of these sensors showed the same large drops in strain as the TML sensors. These sensors are thereby likely to have been able to capture the variation in strain much earlier than the TML sensors. This can for instance be seen in the behaviour of one of the Geokon strain gauges (ST01) which is located in the centre of the dome. The Geokon sensor shows typical textbook behaviour, see for instance Emborg (1989), regarding early strain/stress behaviour in concrete, as seen in Figure 5-13 a) where compressive strain occurs directly after casting but after a while transcends to tensile strains. During the first hours after pouring the concrete, it behaves completely plastic and no stresses can be measured. After this, the concrete strength starts to increase and due to the increased temperature from the hydration, compressive stresses occur in the concrete. When the heat generated by the hydration reduces resulting in a decreased temperature in the concrete, tensile stresses develops. (Emborg, 1989) This is illustrated in Figure 5-13 b). 57

70 30 20 Strain gauges in horizontal direction (0 degrees) ST01 10 Strain ([µs]) :00 12:00 18:00 00:00 06:00 12:00 18:00 00:00 Time a) b) Figure 5-13 Early strain/stress development in concrete. a) Measured behaviour of the dome plug with a Geokon sensor, b) results from typical measurements of laboratory experiments from Larson (2003). 58

71 6 Results In this section, the filtered results from the point of casting the concrete dome plug ( ) up to the point where the plug is subjected to a constant water pressure of 4 MPa ( ) are presented. 6.1 Pressure on the formwork The pressure on the formwork is measured at five locations over the height of the form/dome. The sensors are numbered from 1 to 5 based on their height above the ground, meaning sensor no 1 is at the bottom and sensor no 5 is close to the top. In Figure 6-1, the pressure is shown as a function of time, measured at each sensor. The sampling rate in these measurements is one reading each minute. As it can be seen, the maximum pressure at each location of the sensors occurs quite soon, just a few hours after the concrete reached that position. This means that the hardening of concrete in the bottom has started even before the whole plug is cast. Thereby, the maximum theoretical hydrostatic pressure of 160 kn/m 2 (at the bottom) will never occur. Instead the maximum pressure measured close to the bottom is approximately 25 kn/m 2. The maximum form pressure is typically 35 kn/m2 measured at all sensor positions. However, there is a voltage impulse in the sensor no 5, increasing from about 30 kn/m 2 to a maximum of approximately 80 kn/m 2 for a period of four minutes. According to the staff at site during casting, the contact grouting tubes were pressurized at the end of casting in order to cleanse the tubes. This pressure impulse, may thereby be a result of this action. Otherwise, the rapid increase in pressure may also be due to a pressure increase from the concrete pumps at the final stage of casting the concrete dome plug. The pressure was increased to make sure that the whole volume was filled with concrete and to prevent air voids inside the formwork. It can be seen in the measuring result that all sensors indicate a change in pressure at this time, but to a smaller extent, as seen in Figure 6-2. Other explanations, however, judged more unlikely are that this value is due to measuring error or due to movement of the formwork (and thereby the sensor) during casting. 59

72 Form pressure (kpa) Sensor 1 Sensor 2 Sensor 3 Sensor 4 Sensor :00 12:00 18:00 00:00 06:00 12: Time (hh:mm) Figure 6-1 Measured pressure on the formwork for the five pressure sensors. Form pressure (kpa) Sensor 1 Sensor 2 Sensor 3 Sensor 4 Sensor :30 20:35 20:40 Figure 6-2 Measured pressure on the formwork for the five pressure sensors, zoomed in on the impulse that occurred. A 3D representation of the pressure as a function of time is shown in Figure 6-3. It can be seen from this figure that the full hydrostatic pressure distribution never developed, i.e. when 60

73 the upper part of the dome was cast, the bottom part had already hardened and thereby gave a low pressure. Figure 6-3 Measured pressure on the formwork as a function of height and time. 6.2 Temperature Early age behaviour The concrete dome is cast with embedded cooling pipes, which are used to control the temperature during different stages of constructions. An advanced cooling scheme was used to control the temperatures in the dome at different stages: A) Reduction of the hydration heat effect B) Cooling of the dome in order to force it to release from the rock C) Additional cooling of the dome prior to contact grouting Figure 6-4 shows the temperature variation in the cooling pipes, during the first four months of the experiment. The ambient temperature in the tunnel is normally between 13 and 15 C. In Figure 6-4, the ambient temperature has been illustrated as 14 C, meaning that if the temperature in the cooling pipes is equal to this, then the cooling system is turned off. 61