RECENT ADVANCES IN MEASUREMENT OF GROUT … · fracture in rock satisfactorily (Draganovic and Stille 2014). That is probably due to the deficiency in their design being based on

$Page 1: RECENT ADVANCES IN MEASUREMENT OF GROUT … · fracture in rock satisfactorily (Draganovic and Stille 2014). That is probably due to the deficiency in their design being based on$
BERGMEKANIKDAGEN • 20 MARS

89

RECENT ADVANCES IN MEASUREMENT OF GROUT PENETRABILITY, IMPROVEMENT OF GROUT SPREAD, AND EVALUATION OF RTGC THEORYNya framsteg i mätning av inträngningsförmåga avinjekteringsmedel, förbättring av spridning av bruket och utvärdering av RTGC-teorin A. N. Ghafar, RISE CBI Betonginstitutet, Division Samhällsbyggnad A. Draganovic, KTH Royal Institute of TechnologyF. Johansson, KTH Royal Institute of TechnologyS. Larsson, KTH Royal Institute of Technology

Abstract This paper presents a short summary of a PhD project conducted on grout penetrability properties in rock fractures. After review of the methodologies developed to measure grout penetrability, three of which that were more recognized in Swedish grouting industry were selected for a comparison. The aim was to determine which one is more reliable and how. The study showed positive aspects of Short-slot. Afterwards, the so-called varying aperture long slot (VALS) was developed to study the gout penetrability at more realistic conditions. Then, a low-frequency rectangular pressure-impulse was employed to improve the grout spread by successive erosion of eventual filter cakes in consecutive cycles. The results showed considerable improvement in experiments using Short-slot. The dissipation of the pressure-impulses was then investigated using VALS,where the remaining amplitudes along the slot were noticeable. Finally, VALS was once again used to examine the performance of the RTGC theory in a more realistic geometry condition. The study showed a relatively satisfactory agreement between the experimental and the analytical results of grout propagation using the hydraulic aperture.

I denna artikel presenteras en kort sammanfattning av ett doktorandprojekt ominträngningsförmågan hos injekteringsmedel i bergsprikor. Efter granskning av de befintliga metoder som utvecklats för att mäta inträngningsförmågan hos injekteringsmedel, tre av dem som var mer erkända i den svenska injekteringsindustrin, valdes för en jämförelse. Syftet med den här studien var att förstå vilken som är mer tillförlitlig och hur. Studien visade positiva aspekter på den Kort spalten. Vidare utvecklades en lång spalt med varierande spaltvidder (VALS) för att studera inträngningsförmågan hos injekteringsmedel under mer realistiskta förhållanden. Sedan användes en lågfrekvent rektangulär tryckimpuls för att förbättra spridningen hos injekteringsmedel genom successiv erosion av filterkakor i konsekutiva cykler. Resultaten visade på en avsevärd förbättring av experiment genomförda med Kort spalt. Spridning av tryckimpulserna undersöktes sedan med VALS, där de återstående

BERGDAGARNA 2018

90

amplituderna längs spalten var märkbara. Slutligen användes VALS för att undersöka utförandet av RTGC-teorin i ett mer realistiskt geometrisk tillstånd. Studien visade en förhållandevis tillfredsställande överensstämmelse mellan försöksresultaten och förutsägelserna av spridningen hos injekteringsmedel när man använde hydrauliska öppningen som medelstorlek på spalten.

Introduction One of the main concerns in subsurface infrastructures is to provide and maintain the sealing required during both construction and operation. Ingress of water into underground projects during the construction increases the time and costs. It can be accompanied by environmental issues such as lowering the groundwater tables, settlement of the structures, and destruction of vegetation. During the operation, it might also be hazardous to human life, e.g., falling icicles in tunnels in cold climate. It reduces the life cycle of the projects and increases the maintenance costs. To provide the sealing required, one of the governing parameters is to obtain sufficient spread of grout in fractures surrounded the facility (Gustafson and Stille 2005; Fransson 2008; Stille 2015). This has been achieved using cement-based and/or chemical grouts (Houlsby 1990; Karol 2003). Despite showing satisfactory spread and sealing efficiency, the use of chemical grout is prohibited in many countries due to several environmental issues (Weideborg et al. 2001). Cement-based grout, which is cheaper with less environmental problems, is more common in the grouting industry. However, in use of cement-based grout, filtration, which occurs due to the arching of the cement particles at a fracture constriction, is an obstacle that restrict the grout spread (Eriksson et al. 2000; Eklund and Stille 2008; Draganovic and Stille 2011). On this basis, this study was dedicated to studying the grout penetrability properties in fractured hard rock.

Background Several test methodologies have been developed over the years to study penetrability properties of cement-based grout. The disagreement over the results obtained, however, is an indication that those methods might not replicate the filtration process at a real fracture in rock satisfactorily (Draganovic and Stille 2014). That is probably due to the deficiency in their design being based on diverse and occasionally unrealistic assumptions, limitations, and test conditions (Ghafar et al. 2017a). Therefore, our first concern in this study was to investigate among the existing methodologies developed to measure grout penetrability, which one was more reliable and how? Furthermore, a standard method for evaluation of grout penetrability in fractured hard rock has not yet been established. The results obtained from the existing methodologies were difficult to relate to grouting in rock fractures. Therefore, a new methodology to replicate the filtration at a fracture constriction more realistically was required. One of the factors governing the filtration and the grout spread is the applied pressure. A sufficient increase in pressure decreases the filtration and improves the grout spread by increasing the potential for erosion of the unstable filter cakes (Eriksson et al. 1999; Nobuto et al. 2008). High-frequency oscillating pressure superimposed on an underlying constant pressure has been shown to improve the grout spread by virtue of reducing the

grout viscosity due to the high-frequency oscillation (Pusch et al. 1985; Borgesson and Jansson 1990; Mohammed et al. 2015). Besides the promising results, use of dynamic grouting has not yet been industrialized due to the limited efficiency and quick dissipation of the oscillation. This suggested that to improve the grout spread in fractures effectively, a proper solution might be use of different shape and frequency of the applied pressure. One of the major issues in rock grouting is insufficient spread of grout, which deteriorates the obtained sealing and the resulting durability. Moreover, the unnecessary spread of grout beyond the required limits is uneconomic and is sometimes accompanied by environmental issues. Optimization of the grout spread is therefore of huge significance in rock grouting. Hence, several stop criteria have been developed to control the grout spread, from which the real time grouting control (RTGC) theory has got a lot of attention in the Swedish grouting industry. It predicts the spread of grout over time in fractures using the grout’s rheological properties and the applied pressure (Gustafson and Stille 1996, 2005; Gustafson et al. 2013; Stille 2015). It has been developed based on assumptions, the most significant of which is the uniform fracture aperture. Accordingly, all the laboratory works, aimed to verify the theory, were conducted in either pipes or parallel plates with constant apertures (Håkansson 1993; Gustafson et al. 2013). This means that the theory has not yet been investigated in the lab at presence of constrictions similar to the geometry of a real fracture in rock. Accordingly, this study was carried out in four different parts with the objectives summarized as follows: a) Which of the existing test methodologies developed to measure grout penetrability are more reliable and how? b) How can grout penetrability be measured more realistically? c) How can the grout spread be improved effectively using dynamic pressure impulses? d) Is it feasible to employ the RTGC theory to predict the grout spread in an artificial fracture with variable aperture?

Part (A): Measurement of grout penetrability (Existing methodologies) In this part, a review was first conducted on the existing methodologies developed to measure grout penetrability with details presented in Ghafar (2017). The study showed that the disagreements/contradictions over the results obtained using various methodologies were in conjunction with either or a combination of differences between their applied pressures, constriction geometries, and grout volumes, as well as some deficiencies in their evaluation methods. Filter-pump and Penetrability-meter, two recognized methods in Swedish grouting industry, were then selected for a comparison against Short-slot with more realistic test conditions and more accurate evaluation method. To make a fair analogy, the test apparatus and procedure in both Filter-pump and Penetrability-meter were adjusted to operate under as similar test conditions as possible to those in Short-slot. The aim was to better understand the grout penetrability and fairly evaluate the reliability and functionality of the methods. Fig.1 shows five different test setups (T1-T5) used in the experiments with details that can be found in Ghafar et al. (2017a).


91

grout viscosity due to the high-frequency oscillation (Pusch et al. 1985; Borgesson and Jansson 1990; Mohammed et al. 2015). Besides the promising results, use of dynamic grouting has not yet been industrialized due to the limited efficiency and quick dissipation of the oscillation. This suggested that to improve the grout spread in fractures effectively, a proper solution might be use of different shape and frequency of the applied pressure. One of the major issues in rock grouting is insufficient spread of grout, which deteriorates the obtained sealing and the resulting durability. Moreover, the unnecessary spread of grout beyond the required limits is uneconomic and is sometimes accompanied by environmental issues. Optimization of the grout spread is therefore of huge significance in rock grouting. Hence, several stop criteria have been developed to control the grout spread, from which the real time grouting control (RTGC) theory has got a lot of attention in the Swedish grouting industry. It predicts the spread of grout over time in fractures using the grout’s rheological properties and the applied pressure (Gustafson and Stille 1996, 2005; Gustafson et al. 2013; Stille 2015). It has been developed based on assumptions, the most significant of which is the uniform fracture aperture. Accordingly, all the laboratory works, aimed to verify the theory, were conducted in either pipes or parallel plates with constant apertures (Håkansson 1993; Gustafson et al. 2013). This means that the theory has not yet been investigated in the lab at presence of constrictions similar to the geometry of a real fracture in rock. Accordingly, this study was carried out in four different parts with the objectives summarized as follows: a) Which of the existing test methodologies developed to measure grout penetrability are more reliable and how? b) How can grout penetrability be measured more realistically? c) How can the grout spread be improved effectively using dynamic pressure impulses? d) Is it feasible to employ the RTGC theory to predict the grout spread in an artificial fracture with variable aperture?

Part (A): Measurement of grout penetrability (Existing methodologies) In this part, a review was first conducted on the existing methodologies developed to measure grout penetrability with details presented in Ghafar (2017). The study showed that the disagreements/contradictions over the results obtained using various methodologies were in conjunction with either or a combination of differences between their applied pressures, constriction geometries, and grout volumes, as well as some deficiencies in their evaluation methods. Filter-pump and Penetrability-meter, two recognized methods in Swedish grouting industry, were then selected for a comparison against Short-slot with more realistic test conditions and more accurate evaluation method. To make a fair analogy, the test apparatus and procedure in both Filter-pump and Penetrability-meter were adjusted to operate under as similar test conditions as possible to those in Short-slot. The aim was to better understand the grout penetrability and fairly evaluate the reliability and functionality of the methods. Fig.1 shows five different test setups (T1-T5) used in the experiments with details that can be found in Ghafar et al. (2017a).

BERGDAGARNA 2018

92

Fig. 1 Schematic view of regular Filter-pump (T1), modified Filter-pump manually and mechanically operated (T2, T3), modified Penetrability-meter (T4), and Short-slot (T5)

T1 shows regular Filter-pump, manually operated, using total volume of passed grout as the evaluation method. T2 and T3 are modified Filter-pump, manually and mechanically operated, respectively, both using the weight-time measurement as the evaluation method. Finally, T4 and T5 represent modified Penetrability-meter and Short-slot both using the same evaluation method as in modified Filter-pump. The criteria that were used to evaluate grout penetrability in this study were bmin (the min fracture aperture that a specific grout can penetrate at all) and bcrit (the min fracture aperture that a specific grout can penetrate without filtration) as defined by Eriksson and Stille (2003). These parameters were determined in each test using the graph of weight-time measurement, where constant gradient/mass flow rate was representative for no filtration condition and variation in gradient/mass flow rate was an indication of filtration. The materials used, mixing process, and test plan can be found in detail in Ghafar et al. (2017a). Some results are presented in Fig.2. To the left, various flow rates (red lines) and different total weights of passed grout (black lines) are shown in the results obtained from test setup T2 using the same materials, mesh size, operator, and test procedure. By mechanizing the test setup in T3 (Fig.2 right), with the aim to apply similar pressure in each test constantly, the results showed a better agreement in the experiments conducted at similar test conditions. This shows the extent of influence of the applied pressure on grout penetrability measurement.

Fig. 2 Results of modified Filter-pump (T2) manually operated, (T3) mechanically operated

Some results of test setup T4 are presented in Fig. 3 (left) to show the uncertainties induced by the grout mass/volume. As can be seen, when the grout weight was < 1.0 kg, there was no change of mass flow rate (red line), meaning no filtration in the process. When the grout weight was between 1.0-1.5 kg, there was still no trace of filtration (pink line). However, by exceeding the grout weight from 1.5 kg, change of the flow rate can be seen in the results (brown dashed-lines), which is representative for filtration. Finally, the uncertainties induced by the evaluation methods are presented in the results of test setup T3 in Fig.3 (right). Using the total weight of he passed grout, there is no trace of filtration in the experiments conducted using 61 μm mesh filter, since in all experiments the full capacity of the Filter-pump was filled with grout. But, using the weight-time measurement, change of the flow rate (blue line) is an indication of filtration.

Conclusions Diversity in the applied pressure, grout volume, evaluation method, and constriction geometry were found as the main origins of uncertainty/contradiction in the results of the grout penetrability measurement. Use of Filter-pump and Penetrability-meter is no longer recommended to evaluate grout penetrability, but Filter-pump can still be used for quality control of cement and mixing process. Accordingly among the three methods, use of Short-slot is considered to be more reliable due to more realistic geometry, test condition, and evaluation method.

Fig. 3 Results of modified Penetrability-meter (T4), and modified Filter-pump (T3)


93

Fig. 2 Results of modified Filter-pump (T2) manually operated, (T3) mechanically operated

Some results of test setup T4 are presented in Fig. 3 (left) to show the uncertainties induced by the grout mass/volume. As can be seen, when the grout weight was < 1.0 kg, there was no change of mass flow rate (red line), meaning no filtration in the process. When the grout weight was between 1.0-1.5 kg, there was still no trace of filtration (pink line). However, by exceeding the grout weight from 1.5 kg, change of the flow rate can be seen in the results (brown dashed-lines), which is representative for filtration. Finally, the uncertainties induced by the evaluation methods are presented in the results of test setup T3 in Fig.3 (right). Using the total weight of he passed grout, there is no trace of filtration in the experiments conducted using 61 μm mesh filter, since in all experiments the full capacity of the Filter-pump was filled with grout. But, using the weight-time measurement, change of the flow rate (blue line) is an indication of filtration.

Conclusions Diversity in the applied pressure, grout volume, evaluation method, and constriction geometry were found as the main origins of uncertainty/contradiction in the results of the grout penetrability measurement. Use of Filter-pump and Penetrability-meter is no longer recommended to evaluate grout penetrability, but Filter-pump can still be used for quality control of cement and mixing process. Accordingly among the three methods, use of Short-slot is considered to be more reliable due to more realistic geometry, test condition, and evaluation method.

Fig. 3 Results of modified Penetrability-meter (T4), and modified Filter-pump (T3)

BERGDAGARNA 2018

94

Part (B): Measurement of grout penetrability (New method) Based on the achievements from the first part of the study, a new test method, so-called varying aperture long slot (VALS), was then developed in the form of a four-meter long artificial fracture to measure grout penetrability properties more realistically. The test apparatus primarily consists of two steel plates (top and bottom plates), bolted together with 11 constrictions of 230-10 μm and chambers of 500 μm in between (Fig.4). Twenty three holes have been constructed on top plate before and after each constriction to locate pressure sensors for tracking the grout front and filtration and erosion processes. Twelve valves have also been designed under the bottom plate that can be used as the inlet and outlet. The rest of the test setup and the evaluation method used are similar to those in Short-slot. The method was applicable to test grout of any kind at static and dynamic pressure conditions up to 15 bar. More details of the materials, method, mixing process, and test plan can be found in Ghafar et al. (2017b). The main advantages of the new method compared to Short-slot are more realistic geometry and the possibility to evaluate bmin and bcrit in one test using only one batch of grout mix. Some results are presented in Fig. 5. As can be seen (to the left), the traces of filtration (change of the flow rate) was observable all the way by opening valves V5-V10, except for valve V11, which was therefore representative for the measure of bcrit. To the right, the same test results are shown but with better resolution. Only in V11, there was no change of flow rate. In this experiment, bmin and bcrit were evaluated as 50 and 230 μm, respectively.

Fig. 4 Schematic depiction of varying aperture long slot (VALS)

Fig. 5 Tracking the filtration in test G1-T1 by opening valves V5-V11

Conclusions The study showed the potential of the method to investigate the fundamental behavior of rock grouting at varying parameters with satisfactory repeatability at both static and dynamic pressure conditions.

Part (C): Improvement of grout spread using dynamic pressure impulses Investigation in parts A & B revealed that among the factors influencing the grout spread, the applied pressure is the key element. Pusch et al. (1985) initiated a series of laboratory and field investigation to examine the influence of high-frequency oscillating pressure on improving the grout spread. Even though the results obtained were promising, the corresponding improvement was not so significant. The mechanism of action was reported as reduction in the grout viscosity due to the high frequency oscillation. The main issues were, however, found as insufficient spread and quick dissipation of the oscillation along a fracture. Nowadays, stepwise pressure increment is the method normally used in the grouting operations in field with much better results. The mechanism of action is erosion of the produced filter cakes due to increase in pressure. However, the main issues are yet filtration of the cement particles and poor spread in fractures < 70 μm. What we did at KTH was to combine these two methods and apply a low-frequency rectangular pressure impulse to improve the grout spread more effectively. The mechanism is, however, interpreted as erosion of the produced filter cakes due to change of flow pattern at consecutive cycles, where improved spread in fractures < 70 μm and longer dissipation length were anticipated. Hence, a test setup similar to that presented in Short-slot was employed by slightly adjustment to change the applied constant pressure to programmable dynamic pressure. The experiments were then conducted at 4s/8s and 2s/2s peak/rest periods. The total weight of passed grout and the min-pressure envelope (i.e. a polyline connecting the minimum pressures obtained in each cycle) were the main evaluation methods used to assess the efficiency of the applied pressure. Using the min-pressure envelope, any upward trend represents the filtration and any downward trend is an indication of erosion (Fig.6). More details of the test setup, evaluation methods, materials, mixing process, and the test plan can be found in Ghafar et al. (2016).


95

Fig. 5 Tracking the filtration in test G1-T1 by opening valves V5-V11

Conclusions The study showed the potential of the method to investigate the fundamental behavior of rock grouting at varying parameters with satisfactory repeatability at both static and dynamic pressure conditions.

Part (C): Improvement of grout spread using dynamic pressure impulses Investigation in parts A & B revealed that among the factors influencing the grout spread, the applied pressure is the key element. Pusch et al. (1985) initiated a series of laboratory and field investigation to examine the influence of high-frequency oscillating pressure on improving the grout spread. Even though the results obtained were promising, the corresponding improvement was not so significant. The mechanism of action was reported as reduction in the grout viscosity due to the high frequency oscillation. The main issues were, however, found as insufficient spread and quick dissipation of the oscillation along a fracture. Nowadays, stepwise pressure increment is the method normally used in the grouting operations in field with much better results. The mechanism of action is erosion of the produced filter cakes due to increase in pressure. However, the main issues are yet filtration of the cement particles and poor spread in fractures < 70 μm. What we did at KTH was to combine these two methods and apply a low-frequency rectangular pressure impulse to improve the grout spread more effectively. The mechanism is, however, interpreted as erosion of the produced filter cakes due to change of flow pattern at consecutive cycles, where improved spread in fractures < 70 μm and longer dissipation length were anticipated. Hence, a test setup similar to that presented in Short-slot was employed by slightly adjustment to change the applied constant pressure to programmable dynamic pressure. The experiments were then conducted at 4s/8s and 2s/2s peak/rest periods. The total weight of passed grout and the min-pressure envelope (i.e. a polyline connecting the minimum pressures obtained in each cycle) were the main evaluation methods used to assess the efficiency of the applied pressure. Using the min-pressure envelope, any upward trend represents the filtration and any downward trend is an indication of erosion (Fig.6). More details of the test setup, evaluation methods, materials, mixing process, and the test plan can be found in Ghafar et al. (2016).

BERGDAGARNA 2018

96

Fig. 6 Min-pressure envelope

Fig. 7 Results of min-pressure envelope obtained using 30 μm slot at 2s/2s peak/rest

period Among the results obtained, the total weight of passed grout showed roughly 3 times improvement in the experiments conducted at 4s/8s and 11 times improvement at 2s/2s peak/rest periods using 30 μm slot compared to the results obtained from the static pressure tests. The min-pressure envelope presented in Fig. 7 with random upward and downward trends shows the counterbalancing filtration and erosion as the main reason to keep the slot open for a longer period to obtain more penetration.

Conclusions: The low-frequency rectangular pressure impulse showed a substantial control on filtration and improved the grout spread within parallel plates with constrictions ≤ 70 μm, where the results of 2s/2s peak/rest period showed a better efficiency than 4s/8s. However, the potential comment on the method was yet quick dissipation of the pressure-impulses along a fracture. On this basis, in the next step of the study, the dissipation of the pressure-impulses was examined in a considerably longer artificial fracture. Hence, VALS was once again introduced with pressure sensors located at 2.7, 2.0 m, and at the beginning of the slot. The details of the test setup, evaluation methods, materials, mixing process and test plan can be found in Ghafar et al. (2017c). Some results are presented in Fig.8. The blue line is the pressure variation at the beginning of the slot, the red line at 2.0 m and the green line at 2.7 m. As can be seen, even though the shape of the applied pressure is different, but we got 46% and 25% of the initial amplitude of the applied pressure after 2.0 and 2.7 m with aperture range of 230-60 and 230-40 μm, respectively.

Pres

sure

Time

Valve fully opened

Valve fully closed

No filtration Aperture fully

opened Filtration Fully plugged aperture No ΔP

Erosion

Min-pressure envelope Fig. 8 Results of the pressure-time measurements using pressure sensors at 0.0, 2.0, and 2.7 m from the slot’s beginning in grout test with 2s/2s peak/rest periods

Conclusion: The study showed the potential of the method on improvement of grout spread in fractured hard rock specially in apertures <70 μm.

Part (D): Evaluation of the RTGC theory in more realistic condition The RTGC theory is a stop criteria for estimating the grout spread to provide a reliable and economic tight zone around any underground facility. Due to one of the primary assumptions, i.e. uniform fracture aperture, the theory has been mainly tested using laboratory setups with constant aperture. In addition, the aperture size that previously used in the early stages of the development of the theory was hydraulic aperture, bh. However, it is not bh that governs the grout take in grouting operations; it is the fracture’s mean physical aperture, bphy. This, which is used nowadays in application of the RTGC theory, is roughly twice the size of bh. The questions in the last part of the study were therefore whether it is feasible to employ the RTGC theory to predict the grout spread in an artificial fracture with variable aperture and how good the quality of the predictions would be using bh or bphy. To examine the theory in this part, VALS was once again used but with pressure sensors located at 0.99, 1.71, and 2.43 m from the slot’s beginning to track the grout front. Fig.9 presents the flow chart that summarizes the formulations for prediction of the grout propagation over time using RTGC theory for 1D flow condition. In this flow chart, bh can be obtained through some water tests using the cubic law, whereas bphy can be simply calculated using the average of the aperture sizes of the slot between the inlet and the outlet (Ghafar 2017). Finally, the viscosity and yield stress, which are needed as in-data in the calculations, can be obtained using some routine rheological measurements. More details of the materials, methods, and test plan can be found Ghafar (2017).


97

Fig. 8 Results of the pressure-time measurements using pressure sensors at 0.0, 2.0, and 2.7 m from the slot’s beginning in grout test with 2s/2s peak/rest periods

Conclusion: The study showed the potential of the method on improvement of grout spread in fractured hard rock specially in apertures <70 μm.

Part (D): Evaluation of the RTGC theory in more realistic condition The RTGC theory is a stop criteria for estimating the grout spread to provide a reliable and economic tight zone around any underground facility. Due to one of the primary assumptions, i.e. uniform fracture aperture, the theory has been mainly tested using laboratory setups with constant aperture. In addition, the aperture size that previously used in the early stages of the development of the theory was hydraulic aperture, bh. However, it is not bh that governs the grout take in grouting operations; it is the fracture’s mean physical aperture, bphy. This, which is used nowadays in application of the RTGC theory, is roughly twice the size of bh. The questions in the last part of the study were therefore whether it is feasible to employ the RTGC theory to predict the grout spread in an artificial fracture with variable aperture and how good the quality of the predictions would be using bh or bphy. To examine the theory in this part, VALS was once again used but with pressure sensors located at 0.99, 1.71, and 2.43 m from the slot’s beginning to track the grout front. Fig.9 presents the flow chart that summarizes the formulations for prediction of the grout propagation over time using RTGC theory for 1D flow condition. In this flow chart, bh can be obtained through some water tests using the cubic law, whereas bphy can be simply calculated using the average of the aperture sizes of the slot between the inlet and the outlet (Ghafar 2017). Finally, the viscosity and yield stress, which are needed as in-data in the calculations, can be obtained using some routine rheological measurements. More details of the materials, methods, and test plan can be found Ghafar (2017).

BERGDAGARNA 2018

98

Fig. 9 Prediction of the grout propagation using the RTGC theory for 1D flow condition

A comparison between the experimental results (the green lines), the predictions using bh (red line), and the predictions using bphy (blue line) are presented in Fig.10. As can be seen, the predictions using bh are in much better agreement with the experimental results.

Conclusion: The predictions of grout propagation obtained from the RTGC theory using bh, the way that the theory was used previously in the early stages of the development, showed relatively good agreement with the experimental results for all the tested materials. However, the predictions using bphy, the way that the theory is nowadays used in the field applications, showed considerably faster spread. This suggests that use of bphy does not always give a better approximation of the fracture apertures than bh to employ in predictions using the RTGC theory.

Fig. 10 Experimental and predicted grout propagation over time for grout R1 (G2-T1and G2-T2)

References Borgesson, L., and L. Jansson. 1990. “Grouting of Fractures Using Oscillating

Pressure.” In International Conference on Mechanics of Jointed and Faulted Rock: 875–82. Vienna, A. A. Balkeme, Rotterdam.

Draganovic, A., and H. Stille. 2011. “Filtration and Penetrability of Cement-Based Grout: Study Performed with a Short Slot.” Tunnelling and Underground Space Technology 26 (4): 548–59. doi:10.1016/j.tust.2011.02.007.

Draganovic, A., and H. Stille. 2014. “Filtration of Cement-Based Grouts Measured Using a Long Slot.” Tunnelling and Underground Space Technology 43: 101–12. doi:10.1016/j.tust.2014.04.010.

Eklund, D., and H. Stille. 2008. “Penetrability due to Filtration Tendency of Cement-Based Grouts.” Tunnelling and Underground Space Technology 23 (4): 389–98. doi:10.1016/j.tust.2007.06.011.

Eriksson, M., T. Dalmalm, M. Brantberger, and H. Stille. 1999. “Separations-Och Filtrerings Stabilitet Hos Cementbaserade Injekteringsmedel (Raport 3065 in Swedish).” Royal Institute of Technology-KTH, Stockholm, Sweden.

Eriksson, M., H. Stille, and J. Andersson. 2000. “Numerical Calculations for Prediction of Grout Spread with Account for Filtration and Varying Aperture.” Tunnelling and Underground Space Technology 15 (4): 353–64. doi:10.1016/S0886-7798(01)00004-9.

Eriksson, M, and H Stille. 2003. “A Method for Measuring and Evaluating the Penetrability of Grouts.” In 3rd International Conference on Grouting and Ground Treatment, 1326–37. New Orleans, Louisiana, United States: ASCE. doi:10.1061/40663(2003)79.

Fransson, Å. 2008. “Grouting Design Based on Characterization of the Fractured Rock, Presentation and Demonstration of a Methodology (Technical Report R-08-127).” Swedish Nuclear Fuel and Waste Management AB (SKB), Stockholm, Sweden.

Ghafar, A.N. 2017. “An Experimental Study to Measure Grout Penetrability, Improve the Grout Spread, and Evaluate the Real Time Grouting Control Theory.” Doctoral Thesis, Royal Institute of Technology, Stockholm, Sweden.

Ghafar, A.N., S. Ali Akbar, M. Al-Naddaf, A. Draganovic, and S. Larsson. 2017a. “Uncertainties in Grout Penetrability Measurements ; Evaluation and Comparison of Filter Pump , Penetrability Meter and Short Slot.” Geotechnical and Geological Engineering. Springer. doi:10.1007/s10706-017-0351-4.

Ghafar, A.N., A. Mentesidis, A. Draganovic, and S. Larsson. 2016. “An Experimental Approach to the Development of Dynamic Pressure to Improve Grout Spread.” Rock Mechanics and Rock Engineering 49 (9). Springer: 3709–3721. doi:10.1007/s00603-016-1020-2.

Ghafar, A.N., S. Sadrizadeh, A. Draganovic, F. Johansson, U. Håkansson, and S. Larsson. 2017c. “Application of Low-Frequency Rectangular Pressure Impulse in Rock Grouting.” In Grouting 2017: Grouting, Drilling, and Verification. ASCE Geotechnical Special Publication 288: 104-113. doi:10. 1061/9780784480793.010.

Ghafar, A.N., S. Sadrizadeh, K. Magakis, A. Draganovic, and S. Larsson. 2017b. “Varying Aperture Long Slot (VALS), a Method for Studying Grout Penetrability into Fractured Hard Rock.” Geotechnical Testing Journal. ASTM. 40 (5): 871–882. doi:10.1520/GTJ20160179.

Gustafson, G., J. Claesson, and Å. Fransson. 2013. “Steering Parameters for Rock Grouting.” Applied Mathematics 2013: 1–9. doi:10.1155/2013/269594.

Gustafson, G., and H. Stille. 2005. “Stop Criteria for Cement Grouting.” Felsbau: Zeitschrift Für Geomechanik Und Ingenieurgeologie Im Bauwesen Und Bergbau 25 (3): 62–68.

Gustafson, G, and H Stille. 1996. “Prediction of Groutability from Grout Properties and Hydrogeological Data.” Tunnelling and Underground Space Technology 11 (3): 325–332.

Houlsby, A.C. 1990. Construction and Design of Cement Grouting: A Guide to Grouting in Rock Foundations (Vol. 67). John Wiley & Sons.

Håkansson, U. 1993. “Rheology of Fresh Cement-Based Grouts.” Doctoral Thesis, Royal Institute of Technology-KTH, Stockholm, Sweden.

Mohammed, M.H., R. Pusch, and S. Knutsson. 2015. “Study of Cement-Grout Penetration into Fractures under Static and Oscillatory Conditions.” Tunnelling and Underground Space Technology 45: 10–19. doi:10.1016/j.tust.2014.08.003.

Nobuto, J., M. Nishigaki, S. Mikake, S. Kobayashi, and T. Sato. 2008. “Prevention of Clogging Phenomenon with High-Grouting Pressure.” Doboku Gakkai Ronbunshuu C. 64 (4): 813–832 (in Japanese with English abstract). doi:10.2208/jscejc.64.813.

Pusch, R., M. Erlström, and L. Börgesson. 1985. “Sealing of Rock Fractures A Survey of Potentially Useful Methods and Substances (Technical Report 85-17).” Swedish Nuclear Fuel and Waste Management Co (SKB), Stockholm, Sweden.

Karol, R.H. 2003. Chemical Grouting and Soil Stabilization, Revised and Expanded. 3rd ed. Taylor & Francis. doi:10.1201/9780203911815.

Stille, H. 2015. Rock Grouting-Theories and Applications. Rock Engineering Research Foundation-BeFo, Stockholm, Sweden.

Weideborg, M., T. Källqvist, K.E. Ødegård, L.E. Sverdrup, and E.A. Vik. 2001. “Environmental Risk Assessment of Acrylamide and Methylolacrylamide from a Grouting Agent Used in the Tunnel Construction of Romeriksporten, Norway.” Water Research 35 (11): 2645–52. doi:10.1016/S0043-1354(00)00550-9.


99

References Borgesson, L., and L. Jansson. 1990. “Grouting of Fractures Using Oscillating

Pressure.” In International Conference on Mechanics of Jointed and Faulted Rock: 875–82. Vienna, A. A. Balkeme, Rotterdam.

Draganovic, A., and H. Stille. 2011. “Filtration and Penetrability of Cement-Based Grout: Study Performed with a Short Slot.” Tunnelling and Underground Space Technology 26 (4): 548–59. doi:10.1016/j.tust.2011.02.007.

Draganovic, A., and H. Stille. 2014. “Filtration of Cement-Based Grouts Measured Using a Long Slot.” Tunnelling and Underground Space Technology 43: 101–12. doi:10.1016/j.tust.2014.04.010.

Eklund, D., and H. Stille. 2008. “Penetrability due to Filtration Tendency of Cement-Based Grouts.” Tunnelling and Underground Space Technology 23 (4): 389–98. doi:10.1016/j.tust.2007.06.011.

Eriksson, M., T. Dalmalm, M. Brantberger, and H. Stille. 1999. “Separations-Och Filtrerings Stabilitet Hos Cementbaserade Injekteringsmedel (Raport 3065 in Swedish).” Royal Institute of Technology-KTH, Stockholm, Sweden.

Eriksson, M., H. Stille, and J. Andersson. 2000. “Numerical Calculations for Prediction of Grout Spread with Account for Filtration and Varying Aperture.” Tunnelling and Underground Space Technology 15 (4): 353–64. doi:10.1016/S0886-7798(01)00004-9.

Eriksson, M, and H Stille. 2003. “A Method for Measuring and Evaluating the Penetrability of Grouts.” In 3rd International Conference on Grouting and Ground Treatment, 1326–37. New Orleans, Louisiana, United States: ASCE. doi:10.1061/40663(2003)79.

Fransson, Å. 2008. “Grouting Design Based on Characterization of the Fractured Rock, Presentation and Demonstration of a Methodology (Technical Report R-08-127).” Swedish Nuclear Fuel and Waste Management AB (SKB), Stockholm, Sweden.

Ghafar, A.N. 2017. “An Experimental Study to Measure Grout Penetrability, Improve the Grout Spread, and Evaluate the Real Time Grouting Control Theory.” Doctoral Thesis, Royal Institute of Technology, Stockholm, Sweden.

Ghafar, A.N., S. Ali Akbar, M. Al-Naddaf, A. Draganovic, and S. Larsson. 2017a. “Uncertainties in Grout Penetrability Measurements ; Evaluation and Comparison of Filter Pump , Penetrability Meter and Short Slot.” Geotechnical and Geological Engineering. Springer. doi:10.1007/s10706-017-0351-4.

Ghafar, A.N., A. Mentesidis, A. Draganovic, and S. Larsson. 2016. “An Experimental Approach to the Development of Dynamic Pressure to Improve Grout Spread.” Rock Mechanics and Rock Engineering 49 (9). Springer: 3709–3721. doi:10.1007/s00603-016-1020-2.

Ghafar, A.N., S. Sadrizadeh, A. Draganovic, F. Johansson, U. Håkansson, and S. Larsson. 2017c. “Application of Low-Frequency Rectangular Pressure Impulse in Rock Grouting.” In Grouting 2017: Grouting, Drilling, and Verification. ASCE Geotechnical Special Publication 288: 104-113. doi:10. 1061/9780784480793.010.

Ghafar, A.N., S. Sadrizadeh, K. Magakis, A. Draganovic, and S. Larsson. 2017b. “Varying Aperture Long Slot (VALS), a Method for Studying Grout Penetrability into Fractured Hard Rock.” Geotechnical Testing Journal. ASTM. 40 (5): 871–882. doi:10.1520/GTJ20160179.












BERGDAGARNA 2018

100

Geotechnical Special Publication 288: 104-113. doi:10. 1061/9780784480793.010. Ghafar, A.N., S. Sadrizadeh, K. Magakis, A. Draganovic, and S. Larsson. 2017b.

“Varying Aperture Long Slot (VALS), a Method for Studying Grout Penetrability into Fractured Hard Rock.” Geotechnical Testing Journal. ASTM. 40 (5): 871–882. doi:10.1520/GTJ20160179.












PROGNOSVERKTYG FÖR INFRASTRUKTURSKADOR I KIIRUNAVAARAGRUVANS LIGGVÄGG

Prognosis tool for predicting infrastructure damage in the Kiirunavaara Mine footwall Mikael Svartsjaern, Itasca Consultants AB* Karola Mäkitaavola, LKAB

*Tidigare vid Luleå Tekniska Universitet

Sammanfattning Vid skivrasbrytning av den lutande malmkroppen i Kiruna påverkas det omgivande berget på båda sidor av malmkroppen. Liggväggen påverkas till synes i mindre grad än hängväggen då inverkan från brytningen, på markytan, är signifikant mindre. Påverkan på bergmassan under jord i liggväggen, gällande spänningsomlagringar och uppsprickning, kan dock vara kritisk, då hängväggsuppblockningen medför att gruvans infrastruktur i huvudsak förlagts i liggväggens bergmassa. Ny infrastruktur bör generellt placeras så nära malmkontakten som möjligt för att minimera drivningskostnader och transportavstånd men samtidigt på tillräckligt avstånd för att undvika skador relaterade till spänningsomlagringen under brytning.

I detta arbete har ett prognosverktyg tagits fram för att uppskatta den maximala framtida utbredningen av brytningsrelaterade infrastrukturskador i Kirunagruvans liggvägg. Verktyget har tagits fram, och applicerats, i samarbete mellan LKAB och Luleå Tekniska Universitet. Till grund ligger systematisk skadekartering under jord, där brytningens inverkan följts i hela liggväggen under fem år samt numeriska analyser i UDEC och PFC. Modellresultaten har också jämförts med mikro-seismikdata för att validera den simulerade brottsutvecklingen. Brottsutvecklingen i liggväggen visas ske i frånvaro av de vanliga numeriska brottsindikationerna t.ex. koncentrationer av töjningar i så kallade skjuvband. Istället består ”uppsprickningen” av samverkande lokala brott vars beteende kopplas till graden av avlastning.

Abstract The sublevel caving of the inclined orebody at Kiruna affects the rock mass on both sides of the ore. The footwall is affected seemingly to a smaller degree than the hangingwall as the effects of mining, particularly on the ground surface, are significantly smaller. The effects on the rock mass underground, specifically in regard to stress redistribution and fracturing could however be of critical importance as the caving of the hangingwall results in virtually all mining infrastructure being positioned inside the footwall rock mass. New infrastructure should in general be placed as close to the ore contact as possible to minimize production costs and transportation distances but

Documents

RECENT ADVANCES IN MEASUREMENT OF GROUT … · fracture in rock satisfactorily (Draganovic and Stille 2014). That is probably due to the deficiency in their design being based on