POSTER PAPER PROCEEDINGS

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

2 A Review on Different Proposed Methods of Rock and Soil Abrasiveness Estimation for Tunnel Boring Machines Tool Wear Prediction Adel Asadi 1 1 Department of Petroleum Engineering, Science and Research Branch, Islamic Azad University Tehran, Iran. ( address: adelasadi.pe@gmail.com) ABSTRACT Due to the advanced mechanization of the methods of excavation, in particular the increasing use of Tunnel Boring Machines (TBM) in underground construction, knowledge regarding rock and soil abrasiveness is critically required. The wear of the TBM disks indeed governs strongly the performance and efficiency of disk cutters, their rate of replacement, and therefore the costs and time of the tunnel construction. As a result of a vast literature review, the present work illustrates and compares a set of tests for the determination of rock and soil abrasiveness, whose results are used for the estimation of tool wear not only in TBM tunneling, but also in rock and soil drilling, in the use of road headers, in foundation construction, etc. This paper can be used as a brief guide for TBM tool wear prediction before starting field-scale Tunneling, and will help to speed up our further efforts to explore this effect for improving the efficiency of TBMs. Key Words: Rock and Soil Abrasiveness, TBM Tool Wear 1 INTRODUCTION The present study illustrates and compares a set of tests for the determination of rock and soil abrasiveness, whose results are used for the estimation of tool wear not only in TBM tunneling, but also in all excavation projects related to rock and soil drilling Wear and Rock Abrasiveness The term abrasivity describes the potential of a rock or soil to cause wear on a tool. Consequently, abrasivity is an important rock parameter to be determined and to be described in the course of any larger road, tunnel or mining project in order to allow the contractor to assess economical aspects of excavation methods. As the potential to cause wear on a tool depends significantly on the specific circumstances of the observed system (e.g. involved tools, mechanisms of excavation, temperature, applied loads, etc.) it should nevertheless be kept in mind that rock abrasivity can never be an intrinsic physical parameter as for example rock strength. The wear is in many ways similar to the effect of harder minerals on softer ones and is easily represented by the scratch that the hard objects engrave in soft minerals. Plinninger et al., 2002, depicted that Abrasive wear is the predominant wear process in most rock types. Abrasive wear leads to the removal of material from the tool surfaces while it is moving against the rock. This phenomenon is the function of hardness difference between interacting bodies. It is caused by direct contact of tool and hard particles in the rock or contacts between tools and particles in between rock and tool. 1

3 Figure 1. Relation of abrasive wear rate and the ratio of hardness between the interacting materials. Deketh, 1995, mentioned that according to the studies, when the ratio of abrasiveness of two interacting materials exceeds 20% of their Vickers hardness, abrasive wear increases dramatically. When the ratio is less, the abrasive wear is marginal. Atkinson et al., 1986, mentioned that various factors affect the rock abrasiveness and they can be categorized as: Mineral composition Hardness of mineral constituents Grain shape and size Type of matrix material Physical properties of the rock including strength, hardness and toughness 2

4 Figure 2. Parameters infuencing tool wear and excavation performance. The modes of wear are of interest to equipment manufacturers, and are controlled by the following parameters: (i) Petrology: rock strength, joint features, weathering, mineral composition, in-situ stresses, grain-size, shape, elongation, anisotropy, porosity. (ii) Tribology: the wear due to friction, feed force, rotating velocity, and wear due to microscopic processes including abrasion, adhesion, material fatigue or brittle failure of the tool metal. (iii) The rate of wear: the velocity of metal removal from the tool. Table 1. Classification of drill tooth wear rate. Classification Tooth lifetime (m 3 excavated / bit) Lifetime Very low 2000 Very high Low 1500 to 2000 High Moderate 1000 to 1500 Moderate High 500 to 1000 Low Very high 200 to 500 Very Low Extremely High 200 Extremely Low 3

5 The types of wear is of interest to contractors, and are as the followings: (i) Primary wear: the expected wear from normal excavation, permitting replacement at appropriate intervals. (ii) Secondary wear: unplanned and unusually occurs when the primary wear is excessive or unexpected, and may lead to sudden failure. Abrasivity investigation can be based on a wide variety of testing procedures and standards. For the estimation and discussion of such methods it is important to understand that the procedures cover a wide span of scale, ranging from on-site real-scale drilling tests to model tests with simplified tools and microscopic and chemical analysis of rocks and minerals. Depending on its individual scale and testing setup, each method is able to take different factors into account while disregarding others. 4 Figure 3. Scales of abrasiveness investigation.

6 1.2. TBM With widespread increasing applications of mechanized tunneling in almost all ground conditions, prediction of tunnel boring machine (TBM) performance is required for time planning, cost control and choice of excavation method in order to make tunneling economical. One of the most important factors for the prediction of the cost and finishing time of a tunneling operation using a TBM is the correct prediction of the overall performance. Advance rate (AR) is a principal measure of full-face TBM performance and is used to evaluate the feasibility of the machine and predict advance rate of excavation. Hard rock tunnel boring has become more or less the standard method of tunneling for tunnels of various sizes with lengths over 1.5 to 2 km. estimating the performance of TBM is a vital phase in tunnel design, and for the choice of the most appropriate excavation machine. During the past three decades, numerous TBM performance prediction models for evaluation of TBM have been proposed. In brief, all the TBM performance prediction models can be divided into two distinguished approaches, namely theoretical and empirical ones. Based on rock failure mechanism, theoretical models analyze cutting forces acting on disc cutter to find force equilibrium equations. The theoretical models which are primarily developed by using indentation tests or full-scale laboratory cutting tests provide an estimate of cutting forces based on cutter and cutting geometry and spacing and penetration of the cut. Laboratory cutting tests provide basic understanding of rock fragmentation into the force penetration behavior of rocks. The disadvantage of these tests is that, it does not completely represent the real rock mass conditions as the TBM disc cutters encounter in the field. On the other hand, an empirical method does have some strength (taking into account rock mass conditions) as well as some shortcomings. The main deficiency of the empirical models is the absence of cutting force, cutter geometry, cutting geometry and ability to match machine thrust and torque/power in various ground conditions. In the last couple of decades, with growing use of TBMs in the world and the necessity to accurately predict performance of machines in different ground conditions, many researchers have worked to develop new prediction models or adjustment factors for the common existing models. Growth of TBM manufacturing technology and existence of some shortcomings in the prediction models have made it necessary to perform more research on the development of the new models. Due to the complexity of TBM performance prediction, beyond mathematical and empirical solutions, artificial intelligence (AI) methods have been widely utilized by many researchers. 5

7 TBM advantages and disadvantages could be illustrated as follows: TBM PROS: Higher advance rate Exact excavation profile Automated and continual work process Low personnel expenditure Better working conditions and safety Mechanization and automation of the drive TBM CONS: Geological information needed High investment Longer lead time for machine designing and manufacturing Specific profile (circular) Limits on curve driving Detailed planning required Limits on adaptation to highly variable rock Limits on adaptation to high water inflow Limits on transportation system TBM Tool Wear Some of the most important aspects in the study of the fragmentation of rock due to the action of TBM disks concern the abrasiveness of the rock and the wear of the tools. The wear of the disks in fact means that they have to be substituted, with consequent effects on the efficiency of the excavation, on the speed of advancement and therefore, on the times and costs of constructing the tunnel. After having conducted a detailed examination of the methods that have become established in scientific literature to assess the degree of abrasiveness of rock and the potential speed of tools wear, the methods that allow a prediction to be made of the TBM tool wear are presented. The technological, mechanical and geometrical characteristics of excavation tools, together with the physical, mechanical and geostructural characteristics of the rock, influence the effectiveness and the productivity of excavation. From both the technical and economic point of view, abrasivity is one of the rock properties that are most involved in tunneling. Even if a rock is not too strong for mechanized excavation, tool wear can in fact render the operation costly due to the fact that a change in tools influences the time spent on stops and the cost of the tools themselves. No standard test is universally used for the measurement of the abrasivity of a rock and a large number of different tests are in fact today in use. The difficulty of making standard tests is related to the different modes of the study of the tools in the interaction with the rock: drilling, excavation by TBM discs and so on. The wear mechanism is in fact different according to the type of tool (drilling bit, disc), and how it works i.e., through impact or through rotation and so on. This fact probably depends on the elusive nature of the properties that cause the wear of the tools in rock machining. 6

8 The wear of disks on a TBM machine results in a decrease in the efficiency of the excavation and also greater dead times in which the machine has to be stopped in order to substitute excessively worn disks which are no longer able to work in a satisfactory manner. An analysis of the influence of abrasiveness on the construction times of a tunnel excavated with a TBM machine and as a consequence, on the costs, is a very important aspect in the design phase. Some aspects pertaining to the wear of disks during the excavation of tunnels in rock using TBMs are analyzed in this study, and the most common rock and soil characterization tests with reference to the wear of disks, and the currently available methods used to forecast wear of the tools in literature are presented. 2. ROCK ABRASIVENESS The present work lights on a set of tests for the determination of abrasivity, whose results are used for the estimation of tool wear in TBM tunneling. These methods normally give a fairly reliable estimation of the abrasiveness. The greatest challenge in most cases is to collect representative samples Moh s Hardness All rocks and soils consist of minerals that have a distinctive scratch hardness. To define this hardness, the Moh s hardness scale is the standard reference used. The scale is divided into 10 increments, ranging from talc (with a hardness of 1) as the softest, up to diamond (hardness 10) as the hardest. The scale is naturally linear from a hardness of 1 to 9, with each mineral being able to scratch the one below it in the scale. Among the most common minerals, mica and calcite are very soft (hardness 2.5 and 3, respectively), while feldspar, pyroxene and amphibole may be characterized as medium hard (hardness 6). Quartz and garnet are very hard (hardness 7 and 7-7.5, respectively), and to a great extent, determine the degree of TBM cutter wear. Cutter life can be estimated from the relative percentage of minerals of different Moh s hardness classes (>7, 6-7, 4-5 and <4). For coarse-grained rock and soil this is most commonly determined by petrographic analysis using a microscope. For fine grained rock and soil it is most commonly determined by X-ray diffraction (XRD), sometimes supplemented by differential thermal analysis (DTA). The higher the percentage of hard minerals found at the face, the more abrasive the soil or rock and the shorter the cutter life. In addition to mineral composition, TBM performance is also influenced by many other textural features, such as: Grain size, shape and elongation Grain orientation, directional properties Grain interlocking Micro-fractures and pores The use of Moh s hardness therefore is restricted mainly to preliminary estimates of cutter wear. As far as is known, Moh s hardness has not to date been used directly as an input in any TBM performance prediction model. 7

9 2.2. LCPC Abrasivity Test The LCPC abrasivity testing device is described in the French standard P and has been developed by the Laboratoire Central des Ponts et Chausées (LCPC) in France for testing rock and aggregates. The abrasimeter is built of a 750 W strong motor holding a metal impeller rotating in a cylindrical vessel which contains the granular sample. The rectangular impeller is made of standardized steel with a Rockwell hardness of HRB Figure 4. LCPC abrasivity testing device. 1: Motor, 2: Funnel tube, 3: Steel impeller, 4: Sample container. As stated in the standard, the grain size of the rock sample has to be in a range between 4 to 6.3 mm; rock has to be crushed before the test accordingly. With the aid of the LCPC abrasivity test, the breakability or brittleness of the sample material can be quantified too. A modified classification is given in Table 2. The LCPC Breakability-Coefficient (LBC) is defined as the fraction below 1.6 mm of the sample material after the test: LBC = (M ) M (1) Where LBC is LCPC Breakability Coefficient (%), M1.6 is mass fraction less than 1.6 mm after LCPC test (g), and M is mass of the sample material ( t). 8

10 Table 2. Classification of the LCPC Breakability Coefficient (LBC). HAR Abrasion Index 2.3. CERCHAR Abrasion Index LBC (%) Breakability Classification 0-25 Low Medium High Very High The Cerchar abrasion index test is one of the most common geotechnical parameters for describing and classifying hard rock abrasiveness. Researchers evaluate the Cerchar test as a very quick and simple method for rock abrasiveness classification. Figure 5. The Cerchar abrasivity test machine. The Cerchar test is performed by scratching a freshly broken rock surface with a sharp pin of heat-treated alloy steel. In the Cerchar test, a sharp steel indenter (hardness of 200 kg/mm2) of 90 cone angle is applied to the surface of a rock specimen with a static force of 70 N. The steel point is then slowly moved on by 10 mm. This procedure is repeated five times in various directions on the rock surface, always using a sharpened steel tip. The abrasivity of the rock is obtained by measuring with a microscope the resulting wear flat on the steel cone. The unit of abrasivity is defined as a wear flat of 0.1 mm diameter. 9

11 The Cerchar-Abrasivity-Index (CAI) is calculated from the measured diameter of the resulting wear flat on the pin as shown in equation 2. CAI 10 d c Where CAI is Cerchar Abrasivity Index, d is diameter of wear flat (mm) and c is unit correction factor (c= 1 mm). (2) Fig. 6. Sketch of the steel pin with rectangular shape before the test (left) and after the test (right) with the wear flat d. The advantage of this test is that it can be performed on irregular rock samples. The CAI value is related directly to cutter life in the field. CAI values vary between less than 0.5 for soft rocks (such as shale and limestone) to more than 5.0 for hard rocks (such as quartzite). Classification of rock abrasiveness by CAI value. (Deliormanlı, Table 3. Classification of rock abrasiveness by CAI value. (Deliormanlı, 2012.) CAI mean value Classification Class 0.3 to 0.5 Not very abrasive to 1 Slightly abrasive 2 1 to 2 Medium abrasive to abrasive 3 2 to 4 Very abrasive 4 4 to 6 Extremely abrasive 5 10

12 2.4. The Vickers Test Vickers hardness defines the micro-indentation hardness of a mineral, and provides a Vickers hardness number (VHN). The hardness number is defined as the ratio of the load applied to the indenter (gram or kilogram force) divided by the contact area of the impression (mm2). The Vickers indenter is a square based diamond pyramid with a 130 included angle between opposite faces, so that a perfect indentation is seen as a square with equal diagonals. A virtually linear relation has been found between Moh s hardness and VHN (in log scale) CSM Formulas of the Colorado School of Mines (CSM) model for predicting the penetration are based upon results from linear cutting tests in the laboratory that have been subsequently compared with TBM field data. The main result is a potential function with the normal force per cutter that is needed for a certain penetration (Rostami, 1997). The advantage of this approach is that cutter-heads with different geometries can be individually modelled. However, no rock mass characteristics like discontinuities, stress conditions, ground water etc. are taken into account in the basic model Gehring Model The formula of the Gehring model derives from the analysis of different tunnel projects with a certain machine setup (17 cutters, 80 mm spacing). The formula has a modular structure and a simple linear function crossing the zero point with independent correction factors that allow the consideration of rock mass properties as well as different cutter-head types and geometries. Yet the definitions of some correction factors, e.g. the influence of discontinuities and specific failure energy, are not applicable and therefore in the focus of researchers from the ABROCK research project (Schneider et al., 2012, Entacher, 2013, Wilfing et al., 2014) to be revised as they control penetration rates significantly. The main result of Gehring is the maximum penetration for a certain normal force per cutter. By analyzing data from former tunnel projects as well as performing on-site penetration tests, it has been shown that neither a simple linear function through the origin (Gehring) nor a potential function (CSM) reflect the relationship between force and penetration. This is caused by the fact that in the beginning there is a range where low penetration rates (up to 3 mm/rev) cause relatively high thrust forces due to high energy consumption at the crushed zone. This range is described as subcritical penetration. Once the formed cracks coincide, rock chips are expelled from the face (chipping) and the correlation between force and penetration becomes linear. Therefore, the Gehring model should be modified by using a simple linear function with a certain y-axis offset, which is set by the subcritical penetration and depends on geological conditions and the deformation behavior of the rock. 11

13 2.7. NTNU The philosophy of the NTNU prediction model is to combine the decisive rock properties and the relevant machine parameters. Several steps are involved in the NTNU prediction model for hard rock TBMs in order to estimate time and cost for tunnel excavation: net penetration rate, cutter life as well as advance rate and excavation cost. The model has had a successive development since the first version in 1976 by the NTNU (former NTH). Figure 7. Principle sketch of the NTNU abrasion test. The Abrasion Values AV/AVS represent time dependent abrasion of tungsten carbide/cutter steel caused by crushed rock powder. The same test equipment as for the AV is used to measure the AVS, but instead of the tungsten carbide test pieces used for AV, the AVS test uses test pieces of steel taken from a cutter ring. The two tests are defined as follows: AV: The Abrasion Value is the mean value of the measured weight loss in milligrams of 2-4 tungsten carbide test bits after 5 minutes, i.e. 100 revolutions of testing, by using an abrasion apparatus and crushed rock powder. AVS: As described for AV, but with 1 minute, i.e. 20 revolutions of testing Schimazek s Abrasiveness Factor The abrasiveness properties of rock can be determined by using F-Schimazek s Value. The value represents the abrasiveness of rock towards the tool or cutter wear that used in the excavation work. This index can be evaluated as equation below: 12 F = Qtz f s 100 (3)

14 F is the Schimazek s abrasiveness factor (N/mm), σ is the tensile strength, Qtz% is the percentage of quartz or any other equivalent mineral, and ø stands for the quartz grain size (mm). The higher the F-Schimazek s value, the more abrasive is the rock and vice versa. The classification of abrasiveness by using the F-Schimazek s Value as proposed by Arthur (1996) Rock Abrasivity Index In order to overcome the weaknesses identified for conventional geotechnical wear indices, the Rock Abrasivity Index (RAI) was introduced by Plinninger, The RAI represents a modification to the Equivalent Quartz Content and is applicable mainly to hard-rock but also suitable to weak rock types. Based on laboratory investigations in the scale of minerals and rock, the RAI is calculated for relevant rock types by multiplying the rock s Unconfined Compressive Strength (UCS) and Equivalent Quartz Content (EQC). Even if problems in the determination of UCS or thin section analysis are encountered, there are well known alternatives available (like X-Ray Diffraction Analysis or Point Load Test). Nevertheless it should be kept in mind that the RAI value is a geotechnical wear index, derived from laboratory tests from small scale samples and mineral/rock scale investigations. The representative assessment of RAI value distribution for a whole rock series or project as well as the assessment of other wear-relevant rock mass scale influences remain a challenging task for engineering geologists and rock engineers. When using these two core parameters, the RAI takes into account the content of abrasive minerals (which is especially relevant for abrasive wear) and the strength of the rock (which has found to be relevant for both, abrasive wear and wear due to breaking of tool parts) Mineral Content Methods Geologists calculate rock abrasivity based on the abrasivity of the constituent minerals. In this method, percentage of each mineral in the rock is calculated and multiplied by its respected abrasivity based on different available scale. Among them, Abrasive Mineral Content (AMC), Equivalent Quartz Content (EQC), and Vickers Hardness Number for Rock (VHNR) are the most common tests. AMC uses Moh s scratch hardness, while EQC uses Rosiwal grinding hardness and VHNR benefits from Vickers indentation hardness (an indentation test in which the ratio of the force to the area of the indentation is considered as an index for abrasivity of the material). In EQC method, constituent minerals of the rock will be identified either by microscopic or macroscopic mineral evaluation methods. The Rosiwal hardness of each mineral is divided by Rosiwal hardness of Quartz (120). This way quartz would be 100% and all other minerals hardness will be compared to quartz. The Rosiwal hardness of the mineral will be corrected for the ratio of each mineral in the rock sample (weighted average) and EQC of the rock is determined. 13

15 2.11. Burbank Test It is one of the tests that measure the effect of rock abrasivity on metal parts of mining and crushing machines. This test consists of a metal paddle of the tests alloy and a container which carries the rock samples. Container rotates at 74 rev/min and the paddle rotates in the opposite direction with the 632 rev/min inside it. Therefore rapid wear of the paddle occurs which is an index of the abrasivity of the rock Modified Taber Abraser In this test, a 6 mm thick disc form an NX core should be used. The sample rotates 400 times under the wheel which is under a 250 g load. Debris of the rock and the abrader wheel is removed buy a vacuum to remove the rock that could get stuck in the abrader wheel grits. The abrader weight loss is considered as an index for the rock abrasiveness. Moreover, weight loss of the rock is a measure for its abrasive resistance DIAI Al-Amen and Waller (1992) introduced the Dynamic Impact Abrasion Index test. This test is used for simulating the abrasive wear occurs by fine rock particles. The result is mainly useful for transportation of materials by conveyors, especially at transfer points and chutes. In this test, 1000 g of crushed rock is used. The rock is blown using condensed air into a duct. In the duct, there are steel shims with the hardness of 600 in Vickers scale. The air flow is controlled by a rotameter flowmeter control valve at 138 l/min. The shims will be abraded and the weight loss is measured. The weight loss is compared with the weight loss of the shims when they are facing a standard abrasive material made of artificial corundum Modified Schmidt Hammer Test Besides the available laboratory tests on rock abrasiveness, there are some in-situ or field tests for abrasion measurement as well. Janach and Merminod (1982) used an M-type Schmidt hammer for this use. They modified the front of the hammer and put a hardened steel indenter at the top. They put the indenter at 45 and mentioned that the edge can act in a similar way to a disc cutter of a TBM. The roller has a hardness of 62 HRC and the impact energy for each blow is 30 J. Test should be repeated 20 to 50 times. The indenter is weighed afterwards and the weight loss for the imposed impact energy in mg/kj is considered as an index for rock abrasivity. As they did not have real data, they correlated their results with miniature disc cutters and achieved reasonable results Micro-scale Rock Abrasion Characterization The first step towards the knowledge of the wear attitude of a rock on a tool consists of a petrographic analysis in order to determine the mineralogical composition of the rock with particular attention being paid to the contents of quartz and other abrasive minerals such as feldspar and laminated silicates. 14 Other minerals, which are sometimes present in small quantities, can also confer important wear properties to the rock. The second step consists in conducting mechanical tests on the rock which are listed in table 4.

16 Table 4. The most widespread tests for abrasion measurements (Innaurato et al., 1990). Principle of measurement Impact tests Attrition tests Bit wear tests Drillability Rebound tests Indentation tests Scratch tests Test name Protodyakonov test NTI test Dorry test Taber test CERCHAR test NTI test DIGET test Siever s test NTI test CERCHAR test DIGET test Schmidt impact Hammer test Shore test Vickers test Knoop test NCB cone indener test Mohs hardness CERCHAR test The Department of Georesourcesand Land at the Politecnico di Torino has performed research on rock hardness at a micrometric scale since the Seventies. Rock hardness is expressed through the frequency distribution of the hardness (Italian Norm UNI 9724, part 6), which measured with a Knoop penetrator (pyramidal shaped diamond) under a load of 1.96 N at 40 points on the specimen. The microhardness value (HK), measured in MPa, can be obtained from the following expression: HK = P (CP L2) (4) Where Cp is a conversion coefficient, which is equal to , P is the force applied to the penetrator (kgf), and L is the maximum length of the sign left on the tested sample (mm). The frequency distribution diagram obtained from 40 readings is used to characterize the rock. The same procedure can also be followed to test the metal which the tool is composed. It is important to determine the HK75 parameter, which corresponds to the micro-hardness value with respect to which 75% of the conducted tests supply a lower micro-hardness value. Innaurato and Mancini, 1996, showed on the basis of in situ investigations and laboratory tests utilizing mini-disks on rock samples, that the wear of tools is closely related to the HK75 parameter of the rock. The relation that connects the wear of the tools to the HK75 parameter is of an exponential type, with a slight initial increase of the wear with an increase in the HK75 parameter and the wear then increases in a remarkable way for high HK75 values. The same authors showed how an accurate estimation of the degree of wear of the disks of a TBM machine can be obtained by conducting a detailed analysis of the 15

17 ordinate distribution of the micro-hardness measurements in conjunction for the rock and the excavation tool. By comparing each single micro-hardness value measured on the rock (HKRi) with all the micro-hardness values measured on the excavation tool (HKTj), it is possible to determine the probability of HKR being greater than HKT. The degree of wear of the tool can be associated to this probability. 3. SOIL & SOFT GROUND ABRASIVENESS A variety of excavation tools are used for tunneling in soil and soft ground. Disc cutters are used generally when the rock mass exhibits a uniaxial compressive strength in excess of 20 MPa. In mixed and soft ground conditions, disc cutters are used to break hard faces into smaller fractions which can be mucked out through slurry lines or the EPB screw conveyor. All TBM parts in contact with the soil are exposed to wear LCPC Abrasivity Test For soils, the choice of a suitable testing procedure to determine the abrasivity is much more limited than for rocks. A determination of the equivalent quartz content or the Cerchar abrasivity test is only practical for large components like coarse gravels and blocks. The only established way of determining abrasivity of soil is the LCPC abrasivity test, which was developed especially for Granulate by the Laboratoire Central des Ponts et Chausées (NF P18-579). As in Büchi et al., 1995, the test is only described for rock, a detailed procedure for soil testing has been proposed in Thuro and Käsling, The investigation method described in Nilsen et al., 2006, according to the statements given, is only suitable for material with grain size less than 1 mm and therefore is only feasible for silty sands and smaller grain sizes or comparable material. When testing soil material, some considerations have to be done in order to agree with the technical recommendations of maximum grain size 6.3 mm due to the arrangement of the impeller and the capacity of the engine. 16 Testing the grain sizes between 4 and 6.3 mm of the soil sample. This fraction has to be obtained by sieving. This leads to low abrasivity values, which do not represent the real abrasivity of the entire soil sample. Testing the grain sizes less than 6.3 mm of the sample accordingly, also leads to low values. Note, that originally the LCPC test was not intended to contain fine-grained materials less than 4 mm. Testing the entire soil sample and crushing the grains larger than 6.3 mm in a crusher.

18 According to the original grain size distribution the crushed and therefore more angular material has to be added to the original material again. Depending on the scope of the abrasivity determination, the fines less than 4 mm have to be used for the test or excluded. For a geotechnical interpretation of the obtained abrasivity values, a grain size distribution analysis of the soil material before the test (and crushing) is essential. In addition, a mineralogical and petrological analysis of the components should be performed. The fines below 2 mm can be analyzed by X-ray diffractometer, whereas the larger components can be determined manually or optically Mill Tests These three following tests are similar in many ways. The tests apparatuses and procedures consist of a rotating drum consisting a soil sample mixed with steel balls or pins. These tests have been developed to determine road surface quality by measuring the degradation of geological materials. These mill tests expose steel samples to a combination of impact and abrasive wear. However abrasive wear on these samples is likely to be less significant due to low contact stresses between the steel and soil. Water and other additives can be introduced to mill tests in order to evaluate their influence on abrasive wear Nordic Ball Mill Test This test has been used to determine the influence of rock conditioning additives on the abrasivity properties of crushed rock and natural oil samples. Figure 8. The Ball Mill Test apparatus. The test used in the NTNU/SINTEF laboratory is a modified version carried out without the use of steel ribs, and with a rubber-lined drum designed to reduce wear caused by steel interacting with steel. The test procedure is easy and straightforward. 17

19 Los Angeles Abrasion Test This test consist of a cylinder with a rotation speed of between rpm. The test duration may be between 100 and 500 revolutions. The steel samples comprise between six and twelve 47 mm diameter balls, each ball weighing between 390 and 420 g. Figure 9. The Los Angeles Abrasion Test apparatus. The quantity of soil or aggregates used during a single test is 5000 g, with a sample size greater than 1.6 mm diameter. In order to determine road aggregate properties, soil or aggregate degradation indices are measured after first 100, and then again after 500 revolutions. As an alternative to evaluating the degradation of soil and aggregates, this test can also be used to measure weight loss incurred by the steel balls for soft ground abrasivity applications Micro Deval Test The test is commonly used in Canada to determine abrasion caused by aggregates. The test principle is to place an aggregate sample together with a fixed volume of wear in a jar mill. The jar mill contains steel balls similar to the Los Angeles Abrasion Test. 18 Figure 10. The Micro Deval Test apparatus.

20 The aggregate sample, weighting 1500 g, is soaked in two liters of water for one hour prior to testing. Following preparation, the sample is placed in the Micro Deval jar mill together with 5000 g of steel balls, each 9.5 mm in diameter. The drum is sealed and rotates at 100 rpm. The Test duration is dependent on the grain size curve of aggregate, and varies between 95 and 120 minutes. In addition to the degradation of soil and aggregates, this test can also be used to measure weight loss incurred by the steel balls for soft ground abrasivity applications Dorry s Abrasion Test Dorry s abrasion test uses the resistance of aggregates to surface wear by abrasion induced by a rotating steel plate and is determined by measuring the volume loss of the aggregate specimen. Figure 11. Dorry Abrasion Test. In the test, two samples of soil or crushed rock materials are prepared and placed in a rectangular molds. The steel samples are mounted against a circular rotating steel wheel in diametrically opposing clamps. The aggregate abrasion value (AAV) is given by the percentage of weight loss incurred by samples Miller Slurry Test In the USA there is a standardized test, called the Miller test (ASTM G75-01), which was originally developed in the oil industry for deep vertical borings, but deals with a similar abrasion problem as on Slurry-TBM drives. This test can be used to collect data from which the relative abrasivity of a slurry related to a standardized steel surface can be known, additionally the response of different materials to an abrasive slurry can be investigated. The test consists of a tray covered with a layer of Neoprene on the bottom and filled with the test slurry (e.g. bentonite slurry + soil). A standardized steel block is dipped into the test slurry and is loaded with a fixed weight (22,24N is applied as a normal force). 19

21 Figure 12. Miller test to determine the Slurry Abrasivity (Miller Number), and the Slurry Abrasion Response (SAR Number). The steel block is driven in a reciprocating motion through the test slurry for 6 hours. The mass loss of the steel block is measured and gives the Miller Number which is an index of the relative abrasivity of slurries in terms of wear of a standard reference material. The wear damage on the standard wear block is worse as the Miller Number gets higher. If materials other than the standard steelblock are used the measured mass loss indicates the Slurry Abrasion Response (SAR Number) Ball-on-Plate Test The Tribology Gemini Centre at NTNU and SINTEF has been conducting tribological tests similar to the Miller Slurry Test, in order to determine abrasive and corrosive wear. The tests have been run both on reciprocating ball-on-plate apparatus, and by using the Rubber Wheel test. The reciprocating ball-on-plate test consists of a 6 mm diameter steel ball moving back and forth with a stroke length of 10 mm, either across a rock sample or in a slurry environment. The steel ball has a normal force of 5 N. 20

22 Figure 13. Reciprocating Ball-on-Plate Test. The degradation of the steel ball is measured using an SEM microscope, and is used to provide a qualitative evaluation of the wear mechanism (abrasive wear, corrosive wear or a combination known as tribo-corrosion) Rubber Wheel Test The test consists of a container holding slurry (a chemical environment including soil) and a rubber wheel which lifts the slurry and exposes it to a steel sample applying a force of 220 N. The rubber wheel has a linear speed of 2 m/s, equivalent to 200 rpm. Figure 14. Schematic diagram of Rubber Wheel test. 21

23 The degradation of the steel sample is measured using an SEM microscope in a similar manner to that used for the reciprocating ball-on-plate test. Evaluation of the rubber wheel test shows that it is able to measure abrasive wear particles and ribo-corrosive wear on the introduction of liquid and additives Japanese Tunneling Society Method This society has developed a formula for the estimation of ripper tool wear as follows: K D N L V In which: K: Coefficient of Wear (mm/km) D: TBM diameter (mm) N: Cutter head rpm L: Tunnel length (km) V: TBM performance (mm/min) The wear coefficient K is the most problematic factor in the formula, and the society supplies no information about how the coefficient is measured other than by the application of experience data. According to Nakamura, 2012, Japanese contractors use their own, empirically derived, wear coefficients Penn State Soil Abrasion Testing System The Penn State University research group was the first to develop and describe a dedicated abrasion test for in-situ (and similar) soils. The apparatus consists of a rotating blade at a fixed position (depth) within the soil sample. It provides an opportunity to evaluate the influence of water content variations and rotation speeds on a soil sample. The consolidation of the soil is not controlled and the excavation tool does not penetrate fresh soil material during testing. The PSAI testing system is capable to test soils consisting up to cobble dimensions, at 0 to 10 bars pressure. The research conducted at the university shows that overpressure shows no significant influence on the rate of the wear of the propeller. However, it clearly demonstrates that water content, and thus the compactibility of the soil, influences the rate of wear, and that finer-grained soils produce less wear than coarser particles. (5) 22 Figure 15. Illustration of the Penn State Soil Abrasion Testing.

24 This testing system apparatus suggests that it is able to measure abrasive wear, impact/erosive wear when coarse particles are introduced, and tribo-corrosive wear on the introduction of liquid and additives Turin Test The University of Turin (Politecnico Torino Tunnelling and Underground Space Center and Laboratory) has collaborated with UTT Mapei to develop a laboratory apparatus to carry out comparative wear tests on conditioned soils. The test comprises a tank containing a soil sample and a circular metal disc exposed to wear. The soil sample is compressed with 2 kpa confinement pressure both prior to and during testing. The tool is maintained in a fixed position, and as such no penetration is involved. Figure 16. Illustration of the Turin Test device. An evaluation of the literature concerning the Turin Test apparatus demonstrates that it can measure abrasive wear, impact/erosive wear (when coarse particles are introduced), and tribo-corrosive wear on the introduction of liquid and additives NDAT Barzegari et al., 2013, have developed a test called the Newly-Developed Abrasion Test (NDAT). The test apparatus consists of a rotating steel plate exposed to samples of soil or crushed rock. The apparatus can carry out tests under pressure and can also test the influence of soil conditioning additives. Figure 17. Illustration of NDAT method. 23

25 An evaluation of the literature concerning this test demonstrates that it can measure abrasive wear particles and tribo-corrosive wear on the introduction of liquid and additives. Due to the large contact area between the rotating plate and the soil, the influence of impacts is expected to be less than that observed for tests such as Turin Test and the Penn State Soil Abrasion System SGAT The design and development of the Soft Ground Abrasion Tester is a direct outcome of the PhD study done by Jakobsen, The thesis demonstrates the ability of the SGAT apparatus to measure torque and thrust requirements in connection with small-scale drilling operations in soft ground. The apparatus also enables an evaluation of how variation in parameters such as compaction, water content, soil conditioning type and quantity influence thrust, torque and tool life. Figure 18. The SGAT apparatus. There is currently no field data against which to test the validity of the SGAT. However, qualitative observations of one of the tested samples of a tunnel project indicates that the test provides promising results. 4. CONCLUSION This paper can be used as a brief guide for TBM tool wear prediction before starting field-scale Tunneling, and will help to speed up our further efforts to explore this effect for improving the efficiency of TBMs, as it is a concise and up to date review on the available proposed methods of rock and soil abrasiveness determination for TBM tool wear prediction. 24

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