Assessing the abrasivity characteristics of the central Dublin fluvio-glacial gravels – A laboratory study

Tunnelling and Underground Space Technology 96 (2020) 103209

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Assessing the abrasivity characteristics of the central Dublin fluvio-glacial gravels – A laboratory study

T

Emer O'Connora, Miles Friedmanb, Filip Dahlc, Pål Drevland Jakobsend, Dirk van Oosterhoutc, ⁎ Michael Longe, a

Ground Investigations Ireland (GII) (Formerly Research Student, UCD), Ireland Transport Infrastructure Ireland (TII), Dublin, Ireland c SINTEF, Trondheim, Norway d Norwegian University of Science and Technology (NTNU), Trondheim, Norway e School of Civil Engineering, University College Dublin (UCD), Newstead Building, Belfield, Dublin 4, Ireland b

ARTICLE INFO

ABSTRACT

Keywords: TBM Gravels Geotechnical tests Abrasivity Wear

The aim of this paper is to study the abrasiveness of fluvio-glacial gravels located in Central Dublin. It also seeks to identify which test types are the most suitable for assessing the impact of boring tunnels through these materials on tunnel boring machine (TBM) cutterheads. Drilling/sampling of the material proved difficult but geophysical surface wave surveying proved useful. The material was shown to be very dense and to have a large proportion of cobbles and boulders. An extensive suite of laboratory abrasiveness testing was carried out which included tests on gravel samples (e.g. SAT™, SGAT and LCPC) as well as tests on individual cobbles (e.g. point load, Cerchar, Sievers’ J and SJIP). The laboratory results imply a very high impact abrasion (LCPC testing) and low to medium sliding and crushing abrasion. (SAT™ or SGAT tests). Cerchar tests on individual cobbles suggest medium abrasive material in contrast to Sievers’ J/ SJIP testing which indicate low surface hardness. No clear inter-relationship was found between the various test results. Similarly, no strong correlation was proven between results and various geotechnical parameters or with quartz content. The size of individual particles of gravel, cobbles and boulders could be decisive for assessment of wear. However, the larger clasts mostly comprise limestone, which are less abrasive and have a lower surface hardness. The ease of dislocating clasts from the general matrix will have an important effect on the wear on cutterhead steel. Grain angularity and sphericity of the material are important parameters for dislocation of clasts. A limitation of this and similar studies is the lack of tests capable of including particles between 10 mm and cobble size. However, it is clear that no single test can be used to assess the abrasiveness of material like the fluvio-glacial gravels encountered here.

1. Introduction Dublin is well known for its competent lodgement till deposits (known locally as Dublin Boulder Clay) which underlie much of the city (Long and Menkiti, 2007). These deposits are well understood and pose very little geotechnical problems due to their high strength and stiffness and very low permeability. However glacial gravel deposits are also found within the city. For example, a pre-glacial channel originally identified by Farrington (1929), runs east-west across the city centre just north of the present day River Liffey, see Fig. 1. From an engineering point of view, it has significant importance in that is it generally filled with deposits of glacial and fluvio-glacial gravels with cobbles and boulders. The proposed MetroLink metro scheme, also shown in Fig. 1, will run north south through the city centre in tunnel, intercepting the

⁎

channel and also the underlying lodgement till and limestone bedrock. As little experience exits on excavations or any underground works in this channel and given its proximity to many sensitive structures, this proposed development has stimulated research into the channel and the materials contained within it, see for example Long et al. (2012), Friedman et al. (2015), Kealy (2017) and O'Connor (2018). The likely geology calls for the use of a shield tunnel boring machine (TBM) with face support. Closed face tunnelling by its very nature makes interventions to repair and replace worn cutters other than in shafts or station boxes problematic. Thus it is important for the client, manufacturer and contractor to have information on the strength and abrasivity of the materials the TBM will encounter. There are several studies on wear of cutterhead tools (primary wear) and cutterhead structure (secondary wear) in hard rock. Tunnelling in soft ground and

Corresponding author. E-mail address: [email protected] (M. Long).

https://doi.org/10.1016/j.tust.2019.103209 Received 11 March 2019; Received in revised form 13 November 2019; Accepted 15 November 2019 0886-7798/ © 2019 Elsevier Ltd. All rights reserved.

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Fig. 1. (a) Location of pre-glacial trench, MetroLink Scheme and study site in relation to Central Dublin.

wear mechansims and consequences are presented in Nilsen et al. (2007). These are summarised to be possible wear and impacts of on the cutterhead structure, loss of cutterhead diameter and abrasive wear and impacts on soft ground excavation tools. Hunt (2017) states that the most important boulder and cobble properties to consider for the impact on performance and tool life with TBM tunnelling are frequency, distribution, size range, shape, composition, abrasiveness and soil matrix structure. Here the focus is on applying a set of available abrasivity test methods on soil samples obtained from the line of the proposed MetroLink project. The work is directed in particular on which tests are the most suitable for characterising abrasivity of gravels and to evaluate

how to assess the laboratory test results. In order to address these issues an extensive series of in situ and laboratory testing of the gravels was undertaken. Work was carried out in situ and in the laboratories at UCD and at NTNU/SINTEF, Trondheim, Norway. 2. Methodology 2.1. Study site The work described was undertaken at a site just off Lower Dominic St. in Central Dublin. Samples were taken from Borehole LDS01, see Fig. 1a, which is located towards the centre and in the deepest part of 2

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the pre-glacial trench (Kealy, 2017).

2.5. Geotechnical laboratory testing

2.2. Geological background

Geotechnical laboratory testing comprised water content and particle density measurments as well as particle size distribution analyses. These tests were carried out to the procedures outlined in BSI (1990). For the particle size distribution tests particles greater than 100–125 mm in size were initally removed by hand. Large shear box testing (300 mm × 300 mm × 125 mm high) was undertaken because of the range of particle sizes encountered.

The geological maps of the area (www.gsi.ie) show the entire area to be underlain by the limestone bedrock of the Calp/Lucan formation overlain locally by lodgment till and then by a thick sequence of fluvioglacial sand and gravel deposits. The fluvio-glacial sands and gravels are understood to have been deposited during the Last Glacial Maximum of the Irish Ice Sheet (IIS). Kealy (2017) has described four main phases of deposition related to the pre-glacial channel. The sands and gravels were deposited mostly during Phase 2 when the pre-glacial channel served as a conduit for sub-glacial water flow. This resulted in an esker type (sand and gravel) deposit within the channel. During periods where the ice was in contact with rock at the channel edges, lodgement tills were deposited.

2.6. X-ray diffraction and differential thermal analysis Samples for X-ray diffraction (XRD) and differential thermal analysis (DTA) were initially crushed in a jaw crusher to less than 5 mm in size and then subsequently made into a fine power form (8–10 μm in size). One to two grammes of the prepared powder was used in the XRD and in the DTA analyses.

2.3. Borehole drilling

2.7. Testing for abrasavity and wear of gravel material

A borehole was drilled mainly for the purposes of obtaining soil samples for abrasivity testing by Irish Geotechnical Services Ltd. (IGSL) at location LDS01 (see Fig. 1). The cable percussive (shell and auger) method was used according to the procedures outlined in BSI (2015). Fines retention is well-known to be a problem with samples of sands and gravels recovered by cable percussive drilling. This is due to the flushing out of this fine material by water in the ground and that which is used to facilitate the drilling process. In order to counteract this the recovered material was initially placed in a steel drum which had holes in its base and which was lined with a geotextile so as to trap the fine material. Samples, generally of mass 20 kg to 30 kg, were then transferred to plastic bags. Recovery of the fluvio-glacial sands and gravels proved to be challenging. Refusal was frequently met due to the density of the material and on encountering cobbles and boulders. In these circumstances chiselling had to be used. It took five days in total to drill the borehole to a depth of 22.3 m. Nonetheless it is considered that the drilling method used was appropriate for the challenging conditions encountered as it was able to recover a wide range of particel sizes. It had been hoped to trial other techniques, for example the sonic drilling method (Brenton et al., 2019; Jeffrey et al., 2011) to recover the samples but cost and time constraints ruled this out. A log of BH LDS01 is shown on Fig. 2. It can be seen that approximately 1.8 m of made ground overlies an upper lodgement till to about 10.5 m. This in turn overlies the fluvio-glacial sands and gravels to a depth of about 22.0 m. A thin layer of the lower lodgement till was found beneath the sands and gravels. Groundwater is encountered towards the base of the made ground. The proven geology is consistent with the geological history of the area as discussed above. Kealy [2017] and others have demonstrated the general heterogeneity of the fluvioglacial sand and gravel deposits. Although the density of the materials is generally high, the actual quantity of sand, gravel, cobbles and boulders varies across the study area. It is difficult to make area-wide conclusions from the results from one borehole. However BH LDS01 is at the deepest section of the trench and contains dense deposits with a range of particle sizes and types well characteristic of the general study area.

A material specific abrasivity test suite was developed for the gravels. The suite comprised a number of well known abrasivity test methods such as the LCPC and Cerchar tests. In addition some more recently developed abrasion test methods such as the Soil Abrasion Test (SAT™), the Soft Ground Abrasion test (SGAT) and the Sievers’ J (SJ) Miniature Drill test were carried out. 2.7.1. SAT™ The SAT™ test was developed at SINTEF/NTNU beginning in 2005 in order to provide estimations of soil abrasivity. An outline of the test is given in Fig. 3. Full details of the development of the test and the test procedures can be found in Nilsen et al. (2007) and Jakobsen et al. (2013a). The test comprises feeding particles less than 4 mm in size onto a rotating disk, passing them beneath a test piece originating from a TBM disc cutter, and measuring the loss in weight of the test piece subsequent to testing for 1 min/20 revolutions. The SAT™ value is detemined by calculating the mean value of the weight loss in the steel pieces in milligrammes. Clearly a significant limitation of the test, with respect to this study, is that it is restricted to particles less than 4 mm in size. 2.7.2. Soft ground abrasion tester (SGAT) Some further limitations of the SAT™ test include the lack of water in the tested sample and the lack of an allowance for soil density, ground stress and the possible addition of soil conditioning additives during tunnelling. These limitations led to the further development of the soft ground abrasion tester by NTNU/SINTEF (Jakobsen et al., 2013b). The SGAT was intended to test the soil in a more in situ like condition and also to allow for investigating TBM parameters such as rate of rotation and thrust on the resulting abrasivity. An outline of the SGAT test is given in Fig. 4. Material up to 10 mm in size is compacted into a 15 cm diameter test chamber at the desired water content and density values. The required pressure is applied and soil conditioning additives are injected if needed. A drilling tool, comprising two orthogonal steel bars 13 cm long, is penetrated into the sample at 50 rpm and at a required penetration rate. The use of the two separate steel bars provides for the possibility of assessing primary wear on the lower bar and secondary wear on the upper bar. The resulting torque and thrust are then continuously measured. After the test the weight loss in the upper and lower steel pieces is determined.

2.4. Geotechnical in situ testing In situ geotechncal testing comprised standard penetration testing (SPT) during the drilling and stiffness measurments using the multichannel analysis of surface wave technique (MASW). This technique allows the geophone spacing, the striking hammer offset distance and the mass of the striking hammer to be altered. By varying these parameters a shear wave velocity (Vs) profile can be obtained over a range of depths (Fig. 2b).

2.7.3. LCPC test The LCPC Abrasivemeter was developed by the Laboratoires Central des Ponts et Chaussées and the test procedures are defined in the French Standard (Normalisation-Française, 1990). It is based on a steel 3

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0

Made ground 1.8 m

0

SPT N (Blows / 300mm) 20 40 60 80 100

0

0

Vs (m/s) 200 400 600 800 1000 10m/4m/5kg 10m/4m/10kg 15m/4m/10kg

Upper lodgement till

6m/2m/5kg 6m/2m/5kg 6m/1m/5kg

10

Offset/geophone spacing/hammer

30

Very dense

Log of BH LDS01

20

IGSL (2017)

Dense

Loose

22.0 m 22.3 m Lower lodgement till

Medium dense

GIIL (2017)

(a) SPT N against depth. Density categorisation after BSI (2002)

30

Very dense

Geotech (2009)

Medium dense to dense

SIL (2005)

20

Loose

Fluvio-glacial sands and gravels

6m/1m/10kg

N=50 means a refusal

Depth (m)

10.5 m

10

(b) Vs against depth. Density categorisation after NIBS (2002)

Fig. 2. Log of BH LDS01, (a) SPT N values and (b) shear wave velocity profiles.

impeller rotating for 5 min very rapidly (4500 rpm) in a 500 g sample consisting of particles 4.0–6.3 mm in size (i.e. clay, silt and sand fraction largely removed). The impeller’s dimensions are 25 mm × 50 mm × 5 mm. The weight loss of the steel impeller is measured and the LCPC abrasivity coefficient (LAC) is calculated as:

LAC =

m0

m M

LCPC Abrasivemeter by comparing the sieve curves of the initial 4.0–6.3 mm sample fraction with the particle size distribution after the test. 2.8. Testing for abrasivity and wear of individual cobbles Cerchar and Sievers’ J testing was carried out on individual cobbles types that are considered to be lithologically dominant throughout the gravels. The Cerchar test is a measure of rock abrasivity whereas the Sievers’ J test is a measure of rock surface hardness and resistance to indentation.

(1)

where m0−m is the weight loss of the steel impeller after one test and M is the soil or rock materials weight (0.0005 t) The soil material's brittleness properties can also be measured by the

Fig. 3. Outline of the SINTEF/NTNU abrasion tester used to perform the Soil Abrasion Test (SAT™) (left) and photo of the test rig (right). 4

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Fig. 4. Outline of the Soft Ground Abrasion Tester (SGAT) (left) and photo of the test rig (right).

2.8.1. Cerchar The Cerchar test is one of the most common approaches used for measuring rock abrasivity. A freshly broken rock surface is scratched over a distance of 10 mm with a sharp pin of heat-treated steel alloy subjected to a static load of 70 N. The Cerchar Abrasivity Index (CAI) is determined from measuring the wear on the pin tip (d) under a microscope to an accuracy of 0.01 mm. CAI is calculated from:

CAI = 10

d c

3. Material parameters of fluvio-glacial sands and gravels Geotechnical engineering parameters are important inputs for selecting the tunnel allignment, designing support of tunnels and shafts and selection of the tunnelling method. For full face tunnelling, the tunnelling methods consist of earth pressure balance shield (EPB) or slurry shield excavation. Originally the selection of EPB or slurry shield was based on the permeability of the soil. Rocky, cobble and gravelly ground with a permeability value greater than 10−5 m/s is suitable for slurry TBMs. EPB TBMs are ideal for soils with low permeability and fine contents. In recent years, various soil conditioning additives that are commonly used in EPB tunnelling have expanded the applicable ground conditions for EPB TBMs. A summary of the geotechnical engineering parameters relevant to this study is as follows.

(2)

where c is a unit correction factor = 1 mm. The test was originally developed by Laboratoire du Centre d‘Études et Recherces des Chabonnages (CERCHAR) de France for coal mining applications. In general two forms of Cerchar testing are available namely the original design described by Cerchar (1986) and as defined in the French Standard (Normalisation-Française, 2000) and a modified system outlined by West (1989). In the original Cerchar design, both the weight and the pin are moved quickly over the rock surface. The test duration should be 1 s according to ISRM (2013) or to Alber et al. (2013). In the West design, as was used here, the rock sample itself is moved relatively slowly using a hand crank. In this case the test duration should be 10 s according to ISRM (2013). Unfortunately the two systems do not necessarily give the same result and output is also a function of parameters such as the pin hardness, see for example Michalakopoulos et al. (2006).

3.1. Clast type An image of a typical gravel sample, as recovered, is shown in Fig. 5. It can be seen that the material comprises a wide variety of competent individual clasts of varying size and lithologies. As the site area is underlain by the limestones and shales of the Calp/Lucan Formation it was expected that limestone might be the dominant lithology in the material. Therefore the clasts were sub-divided into those which were limestone and those which were from other lithologies. This was done by randomly selecting 100 gravel particles from two depths, sub-dviding them into fine (2–6.3 mm), medium (6.3–20 mm) and coarse (20–63 mm) size fragments and manually analysing the clasts in each group. The results, shown on Fig. 6, confirm that the dominant lithology is limestone and that the percentage (by mass) of limestone present increases as the clast size increases. For the fine gravel the occurrence of limestone and other lithologies is approximately equal. Similar results were obtained for the two samples tested. The other lithologies include greywacke sandstone, siltstones, mudstones together with occasional chert, granite and basic igneous rocks.

2.8.2. Sievers’ J The Sievers’ J-Value (SJ) miniature drill test was originally developed by Sievers (1950). SJ establishes a measure of the rock surface hardness or resistance to indentation. SJ is defined as the mean value of the measured drill hole depths in 1/10 mm, after 200 revolutions of the 8.5 mm miniature drill bit. The SJ test is normally performed as 4–8 drillings, depending on variations in the texture of the sample and SJ is reported as the mean value. The SJ test can also be used to determine the abrasiveness of rock, by calculating a Sievers’ J Interception Point (SJIP) (Dahl et al., 2007). The SJIP is determined by finding the intersection point of two tangents formed at the beginning and end of the penetration depth versus time curve in the SJ test.

3.2. Particle shape, angularity, sphericity and fragmentation Consistent with the overall heterogeneity of the material, particle shape, angularity and sphericity are variable within the sequence. The 5

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suggest the material is generally very dense (NIBS, 2003) with its density increasing with depth. It is clear that the MASW data provides a much better characterisation of the material density when compared to the SPT. The variation in water content with depth is shown in Fig. 7a. The average value is some 4.8%. Average particle density (Gs) for the material is about 2.58. Using these average values results in a calculated bulk density (ρbulk) well in excess of 2 Mg/m3 confirming the dense nature of the material. Shear box samples were compacted at their natural water content to a density of about 1.95 Mg/m3. Normal stresses (σn) of 100 kPa, 200 kPa and 300 kPa were used. According to Muir Wood [1990] the maximum mobilised friction angle (ϕ′m) is the sum of the dilation angle (ψ′) and the critical state friction angle (ϕ′cs). The shear box tests results showed that the degree of dilation decreased with increasing σn. The ϕ′m value was similar for all tests and was about 44°. In contrast the maximum mobilised ψ′ value decreased from about 12° at σn = 100 kPa to 6° at σn = 300 kPa.

100 mm

Fig. 5. Typical sample of gravels as recovered. 100

Percentage of lithology present (%)

80

3.4. Particle size distribution Limestone at 13.5 m Limestone at 15 m Others at 13.5 m Others at 15 m

On average the particles removed before testing (those greater than 100–125 mm in size) accounted for between 54% and 82% (average 70%) of the material by mass with no pattern with depth (Fig. 7d). Test curves for the remaining fluvio-glacial gravel material are shown in Fig. 8 and confirm the material tested to be a sandy gravel. Generally the PSD tests show consistent results with the possible exception of the test between 13.5 and 14 m which shows a higher sand content. Plots of sand and gravel content with depth are shown on Fig. 7b. The gravel content has been subdivided into that on fine, coarse and medium gravel on Fig. 7c. There is no clear pattern with depth with the various values remaining more or less constant. Arguably there is a small increase in gravel content with depth and a slight reduction in sand content with depth but the differences may be within the accuracy of the test measurements. The material has an average effective size (D10) of about 1.2 mm and a D60 value of 10.4 mm after removing particles larger than 100 mm. The resulting uniformity coefficient (CU) is on average 12 (range 7–21) which corresponds with a medium to well graded material (Craig, 2004).

Limestone clasts 60

40

Clasts from other lithologies

20 Fine gravel

Medium gravel

Coarse gravel

Fig. 6. Percentage (by mass) of clasts of different lithologies.

3.5. X-ray diffraction and differential thermal analysis

particles from the other lithologies are on average more rounded than the limestones. In addition, these particles have a higher sphericity than the limestone clasts. These findings are consistent with these particles having undergone increased transport and erosion. However, some particularly angular and potentially abrasive particles were observed within the other lithologies for example chert, quartz and silicified sandstone. Some fragmentation of the larger limestone cobbles was observed to have occurred during the drilling and recovery process as could be seen from the fresh surfaces. Little fragmentation was observed in the cobbles of the other lithologies.

X-ray diffraction analyses (XRD) were performed on six specimens and differential thermal analysis (DTA) was carried out on five specimens. The results of the XRD tests are summarised in Table 1. The material is dominated by the presence of quartz and calcite. There is little variation with depth except perhaps for the shallowest sample. One sample was tested twice, and the two sets of results are very similar. The presence of, on average, 60% quartz was an unexpectedly high result for an area where the dominant rock type is limestone. This finding could have potentially important implications as quartz is known to be highly abrasive. However, in order to study this further DTA testing was also used to measure the quartz content. DTA is a sensitive and specific technique for the detection of free crystalline quartz. The method utilises the thermal transition representing the reversible alpha to beta crystal inversion of quartz at 573 °C. The prepared specimen is heated to approx. 700 °C during the analysis and the cooled down again to room temperature. The inversions at 573 °C cause an endothermic reaction on heating while an exothermic reaction occurs on cooling. The DTA analysis confirmed the presence of 13–24% (average is 17.3%) quartz (see Table 1). It is unclear why such a discrepancy exists between the two sets of results. However, it is possible that the XRD analysis revealed the

3.3. Density, water content and shear strength As well as the present work by IGSL (2017), data for three additional site investigations are available for the site (Fig. 2). SPT N values are shown on Fig. 2a. It can be seen that there is considerable scatter in the data and there are many refusals (denoted by N = 50). The presence of cobbles and boulders in the material would have contributed to these refusals. In the fluvio-glacial gravels most of the tests refused. According to ENISO (2005) the material can be classifed as dense to very dense. A full in situ Vs profile with depth varying between about 2 m and 30 m was obtained and is shown on Fig. 2b. The Vs values also 6

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Fig. 7. Variation in (a) water content, (b) sand and gravel content, (c) gravel content and (d) mass of material greater than 100 mm/125 mm removed with depth.

presence of microscopic quartz which was not detected by the DTA analysis as it only utilises the alpha – beta crystal inversion of quartz to determine the quartz content in the sample. Microscopic quartz in the form of cryptocrystalline quartz was observed in thin section analysis on a cobble recovered from 16.5 m depth. Silicification of carbonate rocks in which a solution enriched with silica ions supresses calcite and other minerals to form, for example cherts, could also be an explanation for the observed results, see for example Bustillo (2010) or Haldar and Tišljar (2014). However, more work is required in order to verify this.

3.6. Point load strength testing of cobbles A summary of point load strength testing of individual cobbles is given on Table 2. Point load strength, Is(50), may also be used to estimate uniaxial compressive strength (σc) using the expression: c

(3)

= k50 Is (50)

It has been found that the factor k50 varies with the strength of the rock and increases with increasing rock strength. Here the values of k50

100 PSD A 14.5-15m PSD C 11-12.5m

80

PSD D 19.5-20m

Percentage passing (%)

PSD E 18-18.5m PSD F 13.5-14m PSD 1 12.5-13m

60

PSD 2 15-15.5m PSD 3 15.5-16m PSD 4 20.5-21m

40

PSD 5 21-21.5m

20

0 0.001

Clay

0.01

0.1 1 Particle size (mm)

10

100

Silt Fine

Med.

Coarse

Fine

Med.

Coarse

Fine

Med.

Coarse

Fig. 8. Particle size distribution curves for fluvio-glacial sand and gravel. 7

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there is little difference in the results of the two tests (Table 3). Seven LCPC tests were carried out for this project, as shown in Fig. 9c, and the results compared with the abrasivity criteria from Normalisation-Française [1990]. The results suggest that the material is very abrasive and conflict with the SAT™ and SGAT results described above. However, the LCPC test refers to a different form of abrasion and specifically represents a measure of impact abrasion (material degradation due to particle impact) compared to the crushing and sliding type abrasion in the two other tests.

Table 1 Results of XRD and DTA testing. Sample

XRD01

XRD02

XRD03

XRD04

XRD05

XRD06

Depth (m) Quartz Calcite Plagioclase Pyroxene Mica Chlorite K-feldspar Dolomite Amphibole VHNR DTA (% quartz)

11–11.5 41% 43% 7% 2% 2% 2% 1% < 1% < 1% 573 13

14–15 61% 31% 3% 3% < 1% < 1% < 1%

15.5–16 64% 32% 3%

18–19 60% 35% 3%

19–20 62% 34% 3%

21 – 22 67% 28% 3%

< 1% < 1% < 1% < 1%

< 1% < 1% < 1% < 1%

< 1% < 1% < 1% < 1%

< 1% < 1% < 1% < 1%

857 24

896 16

856 19

876

920 Two tests 15/ 17

4.2. Tests on individual cobbles Cobbles up to 21 cm in diameter were recovered during the drilling of BH LDS01. A summary of the abrasivity test results on the cobbles is given in Table 4 as well as on the figures which follow. For this study 11 Cerchar tests were carried out. Cobbles were chosen to represent the rock types encountered in the deposit. The results are shown on Fig. 10a and compared to the abrasivity limits suggested by ISRM (2013). Most of the results fall in the “medium” abrasiveness range. The most abrasive rocks are the sandstone and silicified siltstone. Fossiliferous limestone is slightly more abrasive than non-fossiliferous limestone. Four Sievers’ J tests were carried out for this project on samples which had previously been subjected to Cerchar testing. The SJ results are shown on Fig. 10b and according to the criteria of Dahl et al. (2012) fall in either the “low surface hardness” or “very low surface hardness” categories. Similarly, the SJIP data, shown in Fig. 10c, suggest that any drilling equipment used on these materials will have either “very high” or “extremely high expected tool life”.

Table 2 Point load testing of cobbles. Sample No.

Description

Is(50) (MPa)

σc* (MPa)

Strength classification#

1 2 3 4 5 6 7

Limestone Limestone Limestone Sandstone Basic igneous Basic igneous Siltstone

2.74 2.03 2.29 7.56 4.24 3.18 1.88

38.4 28.4 32.1 151.2 67.8 44.5 26.3

Medium strength Medium strength Medium strength Very high strength High strength Medium strength Medium strength

* From NGRM [2000] c = k50 Is (50) and for Is(50) 1.8–3.5 MPa, k50 = 14, for Is(50) 3.5–6 MPa, k50 = 16, and for Is(50) 6–10 MPa, k50 = 20. # From ISRM (1978).

suggested by NGRM (2000) and which are summarised in Table 2 are used. Five of the seven cobbles tested were of medium strength. The two others (the sandstone and basic igneous cobbles) were of high strength and very high strength respectively according to ISRM (1978).

5. Abrasivity testing – Analysis and discussion 5.1. Excavation with respect to measured abrasivity

4. Results of abrasivity testing

Test results from SAT™, SGAT, LCPC, Cerchar and Sievers J are included in this research. The test capability of each test in relation to particle size or presence of cobbles and wear mechanisms are presented in Table 5. The laboratory results imply a very high impact abrasion and low to medium sliding and crushing abrasion. One should evaluate the abrasion mechanisms in combination with geological aspects, for example heterogeneity and lithology, to gain an understanding of the wear rate on the TBM excavation steel. Firstly, the size of individual gravel particle, cobles and boulders could be decisive for the wear, as large clasts need to be broken down in front of the cutterhead while smaller clasts can be extracted with less mechanical effort. Breaking down large clasts in front of the cutterhead by rotation and advance of the cutterhead will imply repeated impact on cutter steel. The indications that larger clasts consist of limestone, are less abrasive and have a lower surface hardness, would probably ease the breakdown of the larger clasts. However, the laboratory analyses leading to this hypothesis do not include clasts larger than 10 mm. Secondly the ease of dislocating clasts and brokendown clasts from the gravel matrix will have an important effect on the wear on cutter steel and excavatability of the ground. Easy dislocation of clasts will require less mechanical effort and result in less impacts of cutter steel to extract clasts from the gravel matrix compared to extraction of interlocked clasts. No cementation or significant presence of cohesive material was observed which leaves grain angularity and sphericity of the material to be the important parameters for dislocation of components. From Table 5, it is clear that there is a lack of tests capable of including particles between 10 mm and cobble size. The study also lacks a testing device that can quantify the abrasivity or impacts of larger clasts in interaction with steel (cutter tools).

The discussion which follows will be separated into testing of the general gravel material and that on individual cobbles. The test results will be given initially. An analysis and comparison of the test results will be performed in Section 5. 4.1. Abrasivity of gravel material A summary of all the abrasivity test results on the gravel material is given on Table 3 as well as on the figures which follow. The results of seven SAT™ tests carried out for this project are shown on Fig. 9a together with the abrasivity classification scheme from Jakobsen et al. (2013a). These values suggest that the material can be classified as having low/medium abrasivity. It is important to remember that this test specifically represents abrasion caused by sliding over and crushing grains. For the SGAT testing the material was compacted at its natural water content to a density of 2 mg/m3. Test results are shown in Fig. 9b. As expected more wear (primary) was recorded on the lower steel bar when compared to that on the upper (secondary wear). Although no formal published classification system exists, experience at SINTEF/ NTNU indicates the values measured are suggestive of low to medium abrasion and are hence consistent with the SAT™ results. There is no clear pattern in the maximum torque recorded in each test as it generally remains relatively constant for all the tests. Some particle size distribution tests were carried out before and after two of the SGAT tests and little difference was found between the two sets of results. In addition the SGAT test at 21.5 m was repeated using material directly as recovered from the borehole. As can be seen 8

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Table 3 Results of abrasivity testing on gravel. SAT™

SGAT

LCPC

Depth (m)

Weight loss (mg)

Depth (m)

Weight loss top (mg)

Weight loss bottom (mg)

Max. Torque (Nm)

Depth (m)

LAC (g/t)

12.25 13.75 15.75 17.75 19.50 20.25 21.25

2.5 2.0 8.5 8.5 9.0 5.5 12.0

11.25 14.5 15.75 15.75 20.25 21.5 21.5

0.026 0.013 0.018 0.017 0.018 0.019 0.018

0.031 0.023 0.017 0.018 0.019 0.020 0.016

15.77 21.98 17.92 20.52 15.81 18.42 19.42

12.25 13.70 15.75 17.75 19.50 20.25 21.25

1090 1214 634 1096 878 690 1050

8

0

5

SATTM (mg) 10

15

20

25

8

SGAT (g)

0

0.01

0.02

0.03

0.04

8

LAC (g/t)

0

800

1600

Upper steel bar LAC

Lower steel bar

12

12

14

14

14

16

16

16

18

18

18

20

20

20

24

Medium abrasion

22 High abrasion

Abrasivity limits are from Jakobsen et al (2013a)

24

(a)

Low to medium abrasion 0

5

10

15

22 SGAT limit 0.03g

20

25

24

Max. torque (Nm) (b)

Extremely abrasive

12

22

10

Very abrasive

10

Medium abrasive

Max. torque

10

Low abrasion

Depth (m)

SATTM

Abrasivity limits are from Normalisation Française (1990)

(c)

Fig. 9. Results of soil abrasivity tests (a) SAT™, (b) SGAT and (c) LCPC.

5.2. Inter-test relationships for gravel tests

Table 4 Results of abrasivity testing on individual cobbles. Cerchar Depth (m)

Rock type

CAI

9.25 11.25 11.25 11.25 13.75 13.25 13.25

Fine grained limestone Fossiliferous limestone Non-fossiliferous limestone Coarse sandstone Fossiliferous limestone Fine grained limestone Fine to coarse grained limestone Silicified siltstone Sandstone Fine grained limestone Non-fossiliferous limestone

2.5 2.4 1.9 2.3 2.5 1.9 1.9

14.25 16.25 19.25 21.5

2.8 3.1 2.2 1.8

Sievers J

SJIP

Sievers J (mm/ 10) 39.0 37.5

SJIP (s)

80.1

31.7

85.3

The data presented in Fig. 9 and Table 3 show no clear inter-relationship between the three main gravel tests types, i.e. SAT™, SGAT and LAC. Jakobsen (2014) suggested there was a weak linear relationship between SAT™ and LAC, but no such trend was found here. Perhaps this is not surprising given each test is a measure of different forms of abrasion.

28.3 31.3

5.3. Abrasivity versus geotechnical properties Jakobsen (2014) showed that by combining SAT™ values and the geotechnical uniformity coefficient (CU), an estimation of TBM cutter tool life can be derived which incorporates both the grading curve and the abrasive properties of the soil. For example, a high SAT™ and a high CU (> 10) would suggest a higher expected wear rate than for a high SAT™ and CU = 5. The relationship between SAT™ and CU found here is shown in Fig. 11a.

20.2

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CAI

14

12

12

Non-fossiliferous limestone Fossiliferous limestone 14 Silicified siltstone

14

16

16

18

18 Non-fossiliferous limestone

20

20 22

Extremely high

Very high

High

Medium

Non-fossiliferous limestone

Low

0

SJIP (s)

10

20

24

Abrasivity limits are from Dahl et al. (2012)

Abrasivity limits are from ISRM (2013)

(a)

30

40

SJIP 10

Sandstone

Extremely low Very low

8

10

16

24

20 40 60 80 100 SJ

Non-fossiliferous limestone, fossiliferous limestone and sandstone

12

22

Sievers J (mm/10)

Fine grained limestone

10

Depth (m)

8

0

18 20 22 24

(b)

Extremely high expected tool life

6

High expected tool life

4

Very low surface hardness

CAI

Low surface hardness

2

Medium surface hardness

8

0

Very high expected tool life

E. O'Connor, et al.

Abrasivity limits are from Dahl et al. (2007)

(c)

Fig. 10. Results of rock abrasivity tests (a) Cerchar, (b) Sievers’ J and (c) SJIP.

Attempts were made to correlate the various abrasivity test results (SAT™, SGAT and LAC) against other geotechnical properties e.g. water content and Vs. There is a weak correlation between increasing SAT™ and increasing Vs as can be seen in Fig. 11b. However, no such trend is apparent for the relationships between SGAT and LAC and Vs. The measured range of water content values was too low to allow any trends to be observed. The measured data have been plotted in the format suggested by Thuro and Käsling (2009) in Fig. 11c, i.e. D50 values plotted against LAC. The data fall in the zone “coarse grained soils with low content of crystalline components”.

to be very poor based on a study of 22 samples taken from the Lower Inn Valley railroad tunnel project in Austria. The relationship between SAT™, SGAT and LAC data from this study and quartz content is presented on Fig. 12. There is no clear relationship between any of the three sets of test results and quartz content. The SAT™ data, when compared to DTA quartz content agree reasonably well with the trend suggested by Jakobsen (2014). The DTA values also seem consistent with classification of Thuro and Käsling (2009) and the pattern of results presented in Fig. 11c. As explained previously the quartz content values from XRD seem to be very high. Several authors have also attempted to relate abrasivity to Vicker’s hardness number (VHNR – see Table 1). This parameter is derived from the results of XRD testing. Like the XRD quartz content the derived values seem very high and are considered to be unreliable.

5.4. Abrasivity versus quartz content There has been much discussion in the literature on the relationship between abrasivity and quartz content. Several studies have suggested that abrasivity increases with increasing quartz content. For example Thuro et al. (2007) suggest an increase in quartz content increases LAC. Beckhaus (2010) shows a strong relationship between increasing equivalent quartz content (EQC) and increasing LAC. The EQC is a measure of the total content of minerals in the material which are sharp for grinding (Thuro and Käsling, 2009). Köhler et al. (2011) reviewed the work of Beckhaus and found the relationship between LAC and EQC

5.5. Abrasivity of individual cobbles Test results on individual cobbles presented on Fig. 10 and Table 4 show no clear relationship between the different tests. Dahl et al. (2012) suggested a relationship of decreasing Sievers’ J with increasing CAI but no such trend is evident here. The sandstone cobble shows the highest abrasiveness (CAI) value but the lowest surface hardness. This is possibly due to the CAI measurement being a combination of

Table 5 Overview of abrasion tests included in this study with corresponding test capabilities. Test

Applicable particle/cobble size

Steel – particle/cobble interaction

Abrasion as classified

SAT™ SGAT LCPC Cerchar Sievers J’

0–4 mm 0–10 mm 4.0–6.3 mm Cobble Cobble

Scraping abrasive wear Scraping abrasive wear, some impacts (high speed) impacts Scraping abrasive wear Scraping abrasive wear

Low to medium abrasivity Low to medium abrasivity Very abrasive Mostly medium abrasive Very high or extremely high expected tool life

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16

0

10

20

8 4 0

30

LAC (g/t)

SATTM (mg)

SATTM (mg)

4

Extremely abrasive

1600

12

8

0

2000

16

12

Zone of coarse grained soils with high content of crystalline components

1200

400 0 0

200 400 600 800 1000

CU

Medium abrasive

0

4

8

12

16

D50 (mm)

Vs (m/s)

(c)

(b)

(a)

Zone of coarse grained soils with low content of crystalline components

Very abrasive

800

Fig. 11. Soil abrasivity and geotechnical testing (a) SAT™ versus Cu, (b) SAT™ versus Vs and (c) LAC versus D50 – modified from Thuro and Käsling (2009).

indentation and abrasion. Sandstone has a relatively high quartz content (and thus high abrasiveness) and medium to low hardness (a lot of indentation). Thuro et al. (2007) suggest that coarser particles are more abrasive than finer particles. This may not be the case here as Fig. 6 shows that the finer material contains less limestone clasts than the coarser material. This could indicate that the limestone cobbles and boulders are less abrasive/lower hardness than the soil lithologies originating from granites. Thuro et al. (2007) also attempted to link CAI values to LAC data as shown on Fig. 13a and found a strong linear relationship between the two sets of values (n = 74, R2 = 0.91). Their motivation was to explore existing relationships between the CAI and TBM cutter tool life. The data for this project fits reasonably well, if a little on the high side of this trend. There is only a slight trend between increasing CAI and increasing quartz content as shown in Fig. 13b. This is in contrast with the findings of West (1989) who found that the EQC was the most significant geological factor influencing the CAI value but is consistent with work of Plinninger et al. (2002) who investigated 109 rock types with a wide range of CAI values and could not find a relationship between EQC and the CAI value (Köhler et al., 2011).

MetroLink tunnels through these materials on TBM cutterheads. The main findings of the study are as follows:

• Drilling/sampling of the material proved difficult using the shell and • • • • • • •

6. Conclusions

•

0.04

1600

12

0.03

1200

8 Test data - XRD

4

Test data - DTA

LAC (g/t)

16

SGAT (g)

SATTM (mg)

The aim of this paper was to study the abrasiveness of fluvio-glacial gravels located in Central Dublin and to identify which test types are the most suitable for assessing the impact of boring the proposed

auger technique, but geophysical surface wave surveying proved useful. The material is very dense, has a high friction angle and generally medium strong cobbles. There is a large proportion of cobbles and boulders in the material. These needed to be removed prior to particle size distribution testing. The remaining material grades as a sandy gravel. The quantity of limestone present increases with particle size. X-ray diffraction testing surprisingly shows a high percentage of quartz (average 60%). In contrast DTA testing shows about 17% quartz which is in line with expectations. The discrepancy may be due to the presence of microscopic quartz fragments. Cerchar (individual cobbles) tests suggest medium abrasive material. Sievers’ J (individual cobbles)/SJIP testing suggest low surface hardness/very high expected tool life. These results contrast with the Cerchar tests and are possibly due to the Cerchar measurement being a combination of indentation and abrasion. The laboratory results imply a very high impact abrasion (LCPC testing) and low to medium sliding and crushing abrasion. (SAT™ or SGAT tests). This result is significant in that breaking down large clasts in front of the cutterhead will imply repeated impact on cutterhead steel. There is no clear inter-relationship between SAT™, SGAT and LCPC

0.02 XRD

0.01

0

0

20

40

60

Quartz content (%) (a)

80

0

400

DTA

Jakobsen (2014)

0

20

40

800

60

Quartz content (%) (b)

80

0

0

20

Fig. 12. Relationship between (a) SAT™, (b) SGAT and (c) LAC versus quartz content. 11

40

60

Quartz content (%) (c)

80

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2000

4 Extremely abrasive

3

1200 2

1

400 0

Trendline from Thuro et al. 2007 LAC = 273*CAI

Very abrasive

800

CAI

LAC (g/t)

1600

Medium abrasive

0

2

4

0

6

CAI (a)

0

10

20

30

40

Quartz DTA (%) (b)

Fig. 13. Relationship between (a) LAC and CAI and (b) CAI and quartz content.

•

• •

results nor is there any strong correlation between these tests and the various geotechnical parameters or with quartz content. The size of individual particles of gravel, cobles and boulders could thus be decisive for the wear, as large clasts need to be broken down in front of the cutterhead while smaller clasts can be extracted with less mechanical effort. The indication that larger clasts consist of limestone, are less abrasive and have a lower surface hardness, would probably ease the breakdown of the larger clasts. The ease of dislocating clasts and broken-down clasts from the gravel matrix will have an important effect on the wear on cutter steel and excavatability of the ground. Grain angularity and sphericity of the material are important parameters for dislocation of components. A limitation of this and similar studies is a lack of tests capable of including particles between 10 mm and cobble size.

abrasivity of rock by the CERCHAR abrasivity test. Rock Mech. Rock Eng. https://doi. org/10.1007/s00603-013-0518-0. Beckhaus, K., 2010. Die Abrasivität von Gesteinen und ihre baubetriebliche Auswirkung auf die Bohrpfahlherstellung. Bauaktuell 1, 1. Brenton, D., Condron, A., Whitelaw, C., 2019. Sonic drilling and sample quality on the Olympic Park ground investigation. Ground Eng. 27–32. BSI, 1990. BS 1377:1990 – Methods of Test for Soils for Civil Engineering Purposes – Parts 1 to 9Rep. British Standards Institution, London, UK. BSI, 2015. BS5930 – Code of Practice for Ground Investigations. British Standards Institution. Bustillo, M.Á., 2010. Silicification of continental carbonates. In: Alonso-Zarza, A.M., Tanner, L.H. (Eds.), Carbonates in Continental Settings: Processes, Facies and Applications. Elsevier, Oxford, pp. 153–174. Cerchar, 1986. Centre d’É tudes et des Recherches des Charbonages de France. The Cerchar abrasiveness index. Report GAI-JTr/JS No. 86-538. Verneuil. Craig, R.F., 2004. Craig's Soil Mechanics, seventh ed. Spon Press. Dahl, F., Bruland, A., Jakobsen, P.D., Nilsen, B., Grøv, E., 2012. Classifications of properties influencing the drillability of rocks, based on the NTNU/SINTEF test method. Tunn. Undergr. Space Technol. 28, 150–158. https://doi.org/10.1016/j.tust.2011. 10.006. Dahl, F., Grøv, E., Breivik, E., 2007. Development of a new direct test method for estimating cutter life based on the Sievers’ J miniature drill test. Tunn. Undergr. Space Technol. 22 (1), 106–116. Drucker, P., 2011. Validity of the LCPC abrasivity coefficient through the example of a recent Danube gravel. Geomechanik und Tunnelbau 46 (6), 681–691. https://doi. org/10.1002/geot.201100051. ENISO, 2005. BS EN ISO 22476-3: 2005 + A1:2011. Geotechnical Engineering – Field Testing – Part 3: Standard Penetration Test. British Standard/European Standard/ International Organistion for Standardisation. Farrington, A., 1929. The pre-glacial topography of the Liffey basin. Proc. R. Irish Acad. 38 (B), 148–170. Friedman, M., Foroughi, H., Higgins, P., 2015. The geotechnics of infrastructure development in Dublin, Ireland. In: XVIth European Conference on Soil Mechanics and Geotechnical Engineering (ECSMGE). Thomas Telford Ltd., Edinburgh, Scotland, pp. 265–270. https://doi.org/10.1680/ecsmge.60678. ISBN 978-0-7277-6067-8. Haldar, S.K., Tišljar, J., 2014. Introduction to Mineralogy and Petrology. Elsevier. Hunt, S.W., 2017. Tunneling in cobbles and boulders. In: 10th Annual Conference on Breakthroughs in Tunneling – Short Course. Rosemount, Chicago, IL, pp. 1–46. IGSL, 2017. Irish Geotechnical Services Ltd. Report on Ground Investigation at Lower Dominic St. Dublin, Report No. 20006, April. ISRM, 1978. Suggested methods for determining tensile strength of rock materials. Int. J. Rock Mech. Min. Sci. Geomech. Abstr. 15, 99–103. ISRM, 2013. International Society for Rock Mechanics (ISRM) suggested method for determining the abrasivity of rock by the CERCHAR abrasivity test. Jakobsen, P.D., 2014. Estimation of soft ground tool life in TBM tunnelling. PhD thesis. Department of Civil and Transport Engineering, Norwegian University of Science and Technology (NTNU). Jakobsen, P.D., Bruland, A., Dahl, F., 2013a. Review and assessment of the NTNU/SINTEF Soil Abrasion Test (SAT™) for determination of abrasiveness of soil and soft ground. Tunn. Undergr. Space Technol. 37, 107–114. https://doi.org/10.1016/j.tust.2013. 04.003. Jakobsen, P.D., Langmaack, L., Dahl, F., Breivik, T., 2013b. Development of the soft ground abrasion tester (SGAT) to predict TBM tool wear, torque and thrust. Tunn. Undergr. Space Technol. 38, 398–408. https://doi.org/10.1016/j.tust.2013.07.021. Jeffrey, K., Hill, I., Hameed, A., 2011. Deposit knowledge for efficient production. Final Report MIST Project MA/7/G/5/002. University of Leicester. Kealy, S., 2017. Three dimensional geological and geotechnical model of the pre-glacial channel central Dublin. MEngSc Thesis. School of Civil Engineering, University

It is clear that no single test can be used to assess the abrasiveness of material similar to the fluvio-glacial gravels encountered here. This conclusion is consistent with the work of Köhler et al. (2011) who also found that it is difficult to predict tool wear in soils by using just one parameter (e.g. LAC) only. Similarly Drucker (2011) studied the use of the LCPC test to assess the abrasivity of Danube gravel from Vienna. She found that the LCPC test does not allow an overall conclusion to be made on the abrasiveness of the material due to the influence of the heterogeneous cobble fraction. Declaration of Competing Interest The authors declared that there is no conflict of interest. Acknowledgments The authors are grateful for assistance in the field work by Irish Geotechnical Services Ltd. (IGSL) who drilled the borehole at Lower Dominic Street and to Andy Trafford, geophysical consultant, who undertook the MASW surface wave testing. Paul Quigley and Hugh Byrne of IGSL also gave invaluable assistance and advice on the laboratory testing. The work described was funded by the Geological Survey of Ireland Short Call Scheme (2016) and Transport Infrastructure Ireland. References Alber, M., Yaralı, O., Dahl, F., Bruland, A., Käsling, H., Michalakopoulos, T.N., Cardu, M., Hagan, P., Aydın, H., Özarslan, A., 2013. ISRM suggested method for determining the

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E. O'Connor, et al. College Dublin. Köhler, M., Maidl, U., Martak, L., 2011. Abrasiveness and tool wear in shield tunnelling in soil. Geomechanik und Tunnelbau 4 (1), 36–53. https://doi.org/10.1002/geot. 201100002. Long, M., Daynes, P.J., Donohue, S., Looby, M., 2012. Retaining wall behaviour in Dublin's fluvio-glacial gravel, Ireland. Instit. Civ. Engineers J Geotech. Eng. 165 (GE5, October), 289–307. Long, M., Menkiti, C.O., 2007. Geotechnical properties of Dublin Boulder Clay. Géotechnique 57 (7), 595–611. Michalakopoulos, T.N., Anagnostou, V.G., Bassanou, M.E., Panagiotou, G.N., 2006. The influence of steel styli hardness on Cerchar abrasiveness index value. Int. J. Rock Mech. Min. Sci. 49, 321–327. Muir Wood, D., 1990. Soil Behaviour and Critical State Soil Mechanics. Cambridge University Press, Cambridge, UK. NGRM, 2000. Norwegian Group of Rock Mechanics. Handbook No. 2, Engineering Geology and Rock Engineering. NIBS, 2003. National Institute of Building Sciences/Building Seismic Safety Council – National Earthquake Hazard Reduction Program – Recommended provisions for seismic regulations for new buildings and other structures (Federal Emergency Management Agency 450), in Part 1: Provisions. Building Seismic Safety Council, Washington, DC. Nilsen, B., Dahl, F., Raleigh, P., Holzhäuser, J., 2007. The new test methodology for

estimating the abrasiveness of soils for TBM tunnelling. In: Rapid Excavation and Tunneling Conference (RETC), pp. 104–106. Normalisation-Française, 1990. P18-579. Granulats: Essai d’abrasavite et de broyabilite. ANFOR Association Française de normalisation, Paris. Normalisation-Française, 2000. ANFOR NF P94-430-1. Roches - Détérmination du pouvoir abrasive d'une roche. Partie 1: Essai de rayure avec une pointe. ANFOR Association Française de normalisation, Paris. O' Connor, E., October 2018. The pre-glacial channel central Dublin, a geotechnical investigation of material abrasivity and its influence on TBM tool selection. MEngSc thesis. School of Civil Engineering, University College Dublin. Plinninger, R.J., Käsling, H., Thuro, K., Spaun, G., 2002. Versuchstechnische und geologische Einflussfaktoren beim CERCHAR-Abrasivitätstest (CAI). Geotechnik 25 (2), 110–113. Sievers, H., 1950. Die Bestimmung des Bohrwiderstandes von Gesteinen. Glückauf 86 (37/38), 776–784. Thuro, K., Käsling, H., 2009. Classification of the abrasiveness of soil and rock. Geomechanik und Tunnelbau (2), 179–188. Thuro, K., Singer, J., Käsling, H., Bauer, M., 2007. Determining abrasivity with the LCPC test. In: Eberhardt, E., Stead, D., Morrison, T. (Eds.), First Canada - U.S. Rock Mechanics Symposium. Taylor and Francis, London, Vancouver, B.C, pp. 827–834. West, G., 1989. Rock abrasiveness testing for tunnelling. Int. J. Rock Mech. Min. Sci. 26, 151–160.

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