Introduction

In the planning stage of the mining and tunneling projects that used mechanical excavators such as tunnel boring machines (TBM) and roadheaders, the different formations’ characteristics are determined in detail by the field and laboratory studies (Bilgin et al. 2014). Based on the data obtained from these studies, the proper cutter selection can be made, and the consumption rate of these selected cutters can be calculated. Cutter consumption rate (CCR) is one of the main parameters affecting the total cost of mining and tunneling projects excavated by mechanical excavators. One of the critical parameters affecting the wear of cutters is the abrasivity of the rocks, which can be estimated in different laboratory test methods (LCPC 1990; Nilsen et al. 2006; Labaš et al. 2012; Alber et al. 2014; Macias et al. 2016). The Cerchar abrasivity index (CAI) test is a well-known and widely used test method for determining the abrasivity of rocks with a simple test procedure. The results of the CAI test are generally used as an influencing parameter to predict the CCR in some theoretical models (Johnson and Fowell 1986; Ozdemir 1998; Rostami et al. 2005; Lee et al. 2013; Sun et al. 2019). These models generally showed that the CCR increased with increasing CAI value.

The relationships between CAI value and other physical and mechanical properties of rocks were examined in detail by many researchers (Kahraman et al. 2014; Er and Tuǧrul 2016; Moradizadeh et al. 2016; Capik and Yilmaz 2017; Zhang et al. 2021). Capik and Yilmaz (2017) analyzed the relationships between CAI and different strength parameters, such as uniaxial compressive strength (UCS) and Brazilian (indirect) tensile strength of 43 different sedimentary and igneous rock samples collected from the Cankurtaran and Salmankas tunnels in Türkiye. They found strong correlations between CAI and the UCS, BTS, and point load strength of rocks, with 0.87, 0.82, and 0.83 R values, respectively. In addition, many researchers found strong relationships between CAI and strength parameters for different rock groups, each generally consisting of rocks with the same origin. Generally, they reported that the CAI of rocks increased with increasing rock strengths such as UCS and BTS (Kahraman et al. 2010; Deliormanli 2012; Rostami et al. 2014; Ko et al. 2016).

Another widely used test method to determine the abrasivity of rocks is LCPC (Laboratoire Central des Ponts et Chaussées), which is defined by French standards (LCPC 1990). The relationships between the abrasivity and strength parameters of the different rock groups, each generally consisting of rocks with the same origin, were also investigated using the LCPC test results (Hashemnejad et al. 2016; Kahraman et al. 2018). Kahraman et al. (2018) statistically analyzed the effects of rock strengths on the LCPC abrasivity coefficient (LAC) for igneous rocks. They found a non-strong and weak correlation between LAC and each UCS and BTS, respectively. They reported that UCS and BTS influence LAC; LAC increases as UCS and BTS increase, but they emphasized that BTS’ influence is not dominant.

In the literature review, it has been seen that strength is an effective parameter of the abrasivity of rocks. However, many parameters, such as water content in field conditions, affect rock strength. Therefore, the effects of the water content of rocks on their strength have been investigated by many researchers (Yilmaz 2010; Li et al. 2012; Wong and Jong 2014; Várhelyi and Davarpanah 2018; Luo 2020). Török and Vásárhelyi (2010) examined the effect of increasing water content on UCS for travertines and found that UCS decreased with increasing water content. The same study also proposed an equation for estimating the UCS in the saturated condition. Zhou et al. (2018) found that wetting significantly increased the tensile strength of sandstone with a low clay mineral content. Other researchers found a similar result for different types of rocks (Karakul and Ulusay 2013; Zhu et al. 2022).

When considering the effects of water on rock strength, it is expected that the abrasivity of the rocks will also be affected by increasing water content. Therefore, the effects of increased water content on the abrasivity of rocks have been analyzed in many studies. Abu Bakar et al. (2016) performed the CAI test on 33 different sedimentary rocks in dry and saturated conditions to investigate water saturation’s effects on rocks’ abrasivity. They observed that the CAI values obtained in saturated conditions were lower than those in dry conditions and reported that the CAI values in water-saturated conditions were approximately 0.8 times less. In another study, Mammen et al. (2009) examined the effects of water content on the CAI of rocks by varying the water content. They reported a reduction of approximately 13% in CAI values in fully saturated conditions compared to the dry ones. In addition, the effects of water content on rock abrasivity were investigated for the LCPC test. Barzegari et al. (2015) analyzed the effects of water content on the LAC of 11 different crushed rock samples. According to the results, the effects of increased water content are not the same for all rock types and showed that abrasivity decreased in 45% of the samples and increased in others. Abu Bakar et al. (2018) investigated the effects of water content on the abrasivity of 20 rock samples with different porosities using the LCPC test method. They reported that with the increasing water content, the LAC value increased to 15% and 30% for low-porous and high-porous rocks, respectively, and then decreased.

The changing water content of formations in field conditions affects mechanical excavators’ excavation performance and cutter wear (Mammen et al. 2009; Bilgin et al. 2014). Hassanpour et al. (2010) analyzed the performance of a double shield TBM in pyroclastic rocks, noting that water indirectly affects machine performance due to its effect on the strength and alteration of the rock mass. Increasing water content causes problems, especially in excavating clay-rich and fine-grained soil and rock formations, and many researchers investigated these problems, especially clogging, for TBM excavations (Thewes and Burger 2005; Hollmann and Thewes 2013; Chen et al. 2022). Chen et al. (2022) emphasized that clogging will reduce the penetration rate of cutters, resulting in excessive wear. In addition, many studies showed similar results for TBMs’ disc cutters (Peila et al. 2019; Avunduk and Copur 2019).

The literature review showed that increasing water content has an effect on the abrasivity of the rocks as well as their strength. Therefore, theoretically, cutter consumption is expected to be less in excavations performed in wet conditions. However, the effects of increasing water content on the CCR can differ based on the characteristics of excavated formations. For example, with increasing water content in the excavations of clay-rich and fine-grained soil or rock, the excavated material can stick to the cutter and cutterhead, resulting in excessive wear of the cutters by blocking them. Previous studies investigating the adhesion of rock materials to the cutter and their effects on cutter wear have generally focused only on TBM excavations. However, similar problems may also occur in excavations using roadheaders, resulting in an unpredictable CCR of roadheaders.

In this study, the adhesion problems of rock materials to cutters and their effects on cutter consumption are investigated for the first time for roadheaders using actual field data. It is determined that during the excavation of CSCs in the Cappadocia region, excavation material in wet conditions adhered to the cutters, which caused an unexpected increase in the CCR of the roadheaders. In addition, this study showed that the CCR calculation made only theoretically may not always give accurate results, especially for changing formation properties. Therefore, the changing formation characteristics should be considered for a more precise CCR estimation. Thus, new equations are developed for CCR estimation based on the adhesion potential of rocks, especially for excavating rocks with an adhesion potential of cutters, such as porous ignimbrites and clay-rich rocks.

Field studies

Description of CSC projects

In the Cappadocia region, the formation generally contains ignimbrites with high porosity, low strength, and easy excavated characteristics. Therefore, many CSCs are excavated annually in this region and used as storage facilities for different fruits and vegetables, especially lemons and potatoes. In addition, there is no need for a mechanical cooling system in CSCs since the formation structure. CSCs generally consist of the main gallery having an entrance and rooms where products are stored on both sides of this gallery (Fig. 1a). Also, there can be more than one main gallery in the same project area.

Fig. 1
figure 1

A general view of CSC (a); CSC excavation in dry condition (b); CSC excavation in wet condition (c)

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In this study, the CCRs of two roadheaders with the same technical properties are recorded during the excavation of ten different CSC projects. The locations of the CSCs are given in Fig. 2. As seen in Fig. 2, Konaklı and Aktaş CSCs are located in Niğde, while the others are located within the provincial borders of Nevşehir. The technical properties of these CSCs, such as their dimensions, are detailed in Table 1. Due to the excavated ignimbrites’ low strength and porous structure, the increasing water content affects their physical-mechanical properties and excavability. In Sulusaray, Nar, and Kayhan regions, excavations are carried out in dry and wet conditions in the same project area due to underground water income. Therefore, in these regions, the CCRs of roadheaders are recorded for dry and wet conditions in different galleries in the same project area. In addition, especially in the winter and autumn seasons when the precipitation is high in the region, the excavation performance of the roadheaders is significantly affected. Also, CSCs in the Cappadocia region can be excavated in all seasons. Therefore, the excavation performance of roadheaders for Çat, Kavak, Konaklı, and Aktaş CSCs is recorded and analyzed in both dry and wet conditions for different CSCs excavated in the same formation in different seasons (Fig. 1b, c).

Fig. 2
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The locations of the CSCs

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Table 1 Mean field excavation performance data of roadheaders for ten CSC projects
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Geology of project areas

The CSC projects are located in the Cappadocia region, one of Türkiye’s most attractive tourist centers. The region’s landscape generally consists of the tuff layers eroded by water and wind effects. The CSCs studied within the present study were excavated in the Neogene-Quaternary aged volcanic (pyroclastic) rocks in the Cappadocia Volcanic Complex (CVC). The CVC has a width of 40–60 km and an extension of more than 250 km in the NE-SW direction (Toprak et al. 1994). This region is bounded by the Taurus mountain belt in the south, the Kirsehir region in the north, and the Hasan Mountain and Erciyes Mountains in the east and west, respectively.

The geology of the Cappadocia region generally consists of pre-Neogene granitic rocks, Neogene sedimentary rocks, Neogene aged volcano-sedimentary, and Quaternary volcanic rocks. A general stratigraphic vertical column of the region is given in Fig. 3. The Neogene-Quaternary volcano-sedimentary in the region is mainly composed of ignimbrites. The stratigraphy of the ignimbrites (tuffs) in the region is classified as Kavak, Zelve, Sarımaden, Sofular, Cemilköy, Tahar, Gördeles, Kızılkaya, Valibaba, and Kumtepe from the oldest to the youngest (Le Pennec et al. 1994; Aydar et al. 2012). Sulusaray, Nar, Kavak, Kayhan, and Çat CSCs are located in Zelve and Kavak ignimbrite units, while RCSs in Aktaş and Konaklı are located in Kızılkaya ignimbrites. Generally, the colors of these tuffs are gray, off-white, and straw yellow, varying from fine to coarse-grained. Also, they are interbedded with clay and marly clay beds (Aydan and Ulusay 2003; Ulusay and Aydan 2018).

Fig. 3
figure 3

A general stratigraphic vertical column of the Cappadocia region (Temel 1992; Temel et al. 1998)

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Field performance of roadheaders

Within the scope of field studies, field performance data of two roadheaders with the same technical properties were recorded during the excavation of ten different CSCs. The roadheaders have an axial type cutterhead with 200-kW cutting power and 130 cm diameter, and also, there are 64 conical cutters on the cutterhead.

In the Cappadocia region, excavated ignimbrite formations generally have a homogeneous structure with very few discontinuities. Also, the excavated porous ignimbrites have low strength. There is generally no need for any support system in CSC excavations. Therefore, CSCs can be excavated by roadheaders more quickly and efficiently than tunnel and mine excavations. However, tuff formations in the Cappadocia region generally have high quartz content, and this causes high cutter consumption for the roadheaders. In addition, since the porous ignimbrites in the region have low strength, increasing water content causes stability problems in the CSCs’ walls. Therefore, water is not sprayed from the roadheaders during excavation, which causes excessive consumption of the cutters due to overheating.

However, CSCs are often excavated in wet conditions, especially in winter and autumn, as porous ignimbrites absorb water at a high rate due to their porous structure. Due to the increased water content, the excavated fine-sized rock material sticks to the cutters. It blocks cutters and negatively affects the CCR of the roadheaders (Fig. 4). Therefore, field CCRs of roadheaders were recorded in both dry and wet conditions to analyze these effects.

Fig. 4
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Rock materials adhering to the cutterhead in wet condition (left); clear cutterhead in dry condition (right)

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The recorded field data included the daily cutting rate and daily cutter consumption of roadheaders, which are the main parameters for determining the CCR. While the daily excavation rate means the amount of material excavated in a day, the cutter consumption rate refers to the number of worn and replaced cutters in a day. Also, the CCR is defined as the cutter loss per excavation of 1 m3 of rock. The excavation of a CSC located in the Cappadocia region is usually completed in 3–4 months. In this study, the field excavation performances of roadheaders in both dry and wet conditions are recorded for at least three weeks for each CSC project. The arithmetic averages of the recorded daily field data of roadheaders are calculated, and the mean values obtained are given in Table 1. In CSC projects, the conical cutters in the cutterhead usually wear from their steel body, not their tungsten carbide bit. Therefore, these cutters are not replaced with new ones; they are only reused after welding the worn steel body (Fig. 5). Reused cutters after welding are used for excavations in both dry and wet conditions. Therefore, when recording the field CCRs of roadheaders, whether the changed cutters are new or not is ignored.

Fig. 5
figure 5

New conical cutters (a); cutter with a worn steel body (b); welded and reused cutters (c)

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Laboratory studies

Physical and mechanical property tests

Block samples are collected from each CSC project area. It should be noted that the collected samples from excavations in wet conditions are specially packaged with a stretch wrap so that their water content would not change. Then, NX core samples are taken and sized from these blocks to determine the physical and mechanical properties of the rocks. The rocks’ density, UCS, and BTS values are obtained in dry and wet conditions by laboratory tests performed according to the standards recommended by ISRM (2007). At least seven test samples are used for each rock type in the UCS and BTS tests. Also, the apparent porosity and water absorption by the weight of rocks excavated in wet conditions were determined by laboratory studies. The average values of the physical and mechanical properties of rocks obtained in both dry and wet conditions are given in Table 2.

Table 2 The mean physical and mechanical properties of rocks collected from the project areas
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Cerchar abrasivity index tests

The Cerchar abrasivity index test (CAI) is a widely used test with a simple test method to determine the abrasivity of rocks. CAI tests are performed according to ISRM standards using the original Cerchar device and steel pins with a 90° conical tip and Rockwell hardness of HRC 54–56 (Alber et al. 2014). Five different CAI tests are performed on dry and wet test samples with a fresh crushed rough surface for each rock type (Fig. 6). After each test, the wear rate of the steel pin tips is measured under a stereomicroscope, and the average value obtained is recorded as the CAI value of the rock. The mean CAI values of the rocks obtained in both dry and wet conditions are given in Table 2.

Fig. 6
figure 6

Cerchar abrasivity index tests on dry and wet samples

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Determination of the adhesion potential of rocks

Field studies have shown that fine-sized porous ignimbrites adhere to the cutterhead and cutters during excavation in CSC projects. Therefore, it aims to explain rocks’ adhesion potentials with laboratory studies. For this purpose, a laboratory-type mixer with a rotating steel arm is used (Fig. 7a).

Fig. 7
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The used mixer (a), preparation of test sample (b), adding a certain amount of water (c)

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The fine-sized rock materials with a weight of 100 g, in size of < 500 μm, are prepared for each rock type after the grinding process in a ball mill (Fig. 7b). These fine-sized rock materials are first dried in an oven at 105 °C for 24 h. By adding water to the prepared fine-sized rock materials in the sample box, test samples with different water contents (3%, 7%, 10%, 15%, 20%, 25%, 30%, 35%, and 40%) are obtained for each rock type. Then, the steel arm is placed in the sample cup containing the fine-sized test sample with certain water content and rotated inside the materials for 2 min at a speed of 30 rpm. After each test, the adhering materials to the steel arm are collected and weighted (Fig. 8). The weights of material adhering to the steel arm, obtained at nine different water contents, are given in Table 3. As seen in Table 3 and Fig. 8, fine-sized rock materials begin to adhere to the steel arm even at low water content (3%, 7%), but maximum adhesions occurred at water content values of 20% and 25%. Adhesion also occurs at 30%, 35%, and 40% water content, but it is seen that the adhesion rate decreases at these water content values.

Fig. 8
figure 8

Rock materials that adhere to the steel arm in different water contents; dry (a), 3% (b), 10% (c), 15% (d), 25% (e), 30% (f), 35% (g), and weighing of the adhering rock material (h)

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Table 3 Weights of the fine-sized test materials adhering to steel arm at different water contents
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XRF analysis

X-ray fluorescence (XRF) is an analysis method that characterizes rock materials. Therefore, XRF analyses are applied to determine the rocks’ elemental content. The results of the XRF analysis are given in Table 4. The content of SiO2 is quite relatively in all rocks, ranging from 61.25 to 76.29%. In other words, the rocks excavated for CSC construction in the Cappadocia region appear to have high abrasive mineral content.

Table 4 XRF analysis results of rocks
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Theoretically estimation of CCR of roadheaders

There are some models in the literature to predict the CCR of roadheaders based on the CAI values of excavated rocks (Johnson and Fowell 1986; Copur et al. 1998; Ozdemir 1998; Comakli 2019a). The equations of the suggested models by different researchers are given in Table 5. CCR values were calculated for dry and saturated conditions using these models to analyze the effect of increasing water content on theoretically estimated values. The obtained results are given in Table 6. As seen in Table 6, in all three models, it is seen that the values obtained for the saturated conditions are lower than those obtained for the dry condition. In other words, the values obtained from the models revealed that the CCRs of roadheaders for all CSC projects would be lower in wet conditions than in dry conditions.

Table 5 The suggested theoretical models for predicting the CCR of roadheaders
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Table 6 Theoretically estimated CCR values (cutter/m3)
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Results and discussions

In this study, the effects of the changing formation properties of excavated porous ignimbrites with the effects of the increasing water contents on the CCR of roadheaders were investigated. Firstly, the effects of the increasing water content of rocks on their strength and abrasivity properties, which are the effective parameters on the CCR of mechanical excavators, were analyzed.

The histogram showing the percentage decrease in UCS and BTS values with the effect of increasing water content is given in Fig. 9. While the reductions in UCS values are between 53.3 and 37.6%, they range from 69.0 to 29.1% in BTS values. Also, the average decreases in UCS and BTS values are obtained as 46.34% and 51%, respectively. Many previous studies report that increased water content reduces rocks’ strength, similar to this study (Li et al. 2012, 2020; Wong and Jong 2014; Zhou et al. 2016). Hawkins and McConnell (1992) reported that the difference between UCS values obtained in dry and saturated conditions for the clay-rich Cretaceous Greensand was 78%. Rajabzadeh et al. (2012) also noted a reduction of 70% in saturated conditions for UCS of limestones.

Fig. 9
figure 9

Histogram showing the percentage of losses in UCS and BTS of rocks with the effect of increasing water content

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The CAI test is a simple laboratory test method widely used to determine the CCR of roadheaders. Therefore, the effect of the increasing water content on the CAI values of porous ignimbrites excavated in CSC projects is also investigated in this study. The relationships between the CAI values obtained in dry (CAIDry) and wet (CAIWet) conditions are statistically analyzed. An average 23.71% decrease in CAI values of rocks was found due to increasing water content. The graphical illustration of the relationship between CAI values, obtained in dry and wet conditions, is presented in Fig. 10. As seen in Fig. 10, a moderate linear relationship exists between the CAIDry and CAIWet values. The equation of this relationship is given in Eq. 1. Abu Bakar et al. (2016) obtained a result similar to that of this study for sedimentary rocks.

$$CA{I_{Wet}}=0.6719 \times CA{I_{Dry}}+0.1258$$
(1)
Fig. 10
figure 10

Relationship between the CAI values obtained in dry and saturated conditions

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The results of the laboratory tests revealed that the increase in the water content of porous ignimbrites reduces the strength and abrasivity properties. Also, similar results have been reported for different rock types in previous studies in the literature (Abu Bakar et al. 2016; Comakli 2019b). In addition, using a small-scale linear rock-cutting test device, Mammen et al. (2009) performed rock-cutting tests on argillaceous quartz sandstone with different water contents. They evaluated the wear rates of cutting tools and found that the wear rate in saturated conditions was about 20% of that in fully saturated conditions. Abu Bakar and Gertsch (2013) performed full-scale rock-cutting tests on dry and fully saturated brittle sandstone in another study. They reported that the water saturation has a reducing effect on the thermal fatigue of conical cutters. According to both the results obtained from this study and previous studies, it is expected that the CCR values of roadheaders will decrease in the excavation of wet formations.

On the other hand, there are some models previously developed by researchers based on the CAI values of rocks to estimate the CCR of roadheaders theoretically. CCR values were also calculated using these models in Table 5 to theoretically analyze the effect of increased water content on cutter consumption. The results of the theoretical models in Table 6 show that the estimated CCRs for roadheaders will theoretically be lower in wet conditions in each model. The percentage reductions of theoretically calculated CCRs in wet conditions are given in Fig. 11. As seen in Fig. 11, the highest reductions are estimated by Johnson and Fowell (1986) model for all CSC projects; they range from 21.20 to 54.04%. On the other hand, since the Comakli (2019b) model was developed for pyroclastic rocks, the lowest reductions are estimated from this model.

Fig. 11
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Histogram showing percentage changes of theoretically estimated and field-recorded CCRs for excavations in wet compared to dry conditions

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CCRs are theoretically expected to decrease in CSC excavations in wet conditions, according to both the reductions in UCS, BTS, and CAI values of the excavated rocks and the estimated results obtained from theoretical models given in Table 5 for saturated conditions. However, of course, field data is more reliable than the results obtained from theoretical models. Therefore, the relationships between the field CCRs of the roadheaders given in Table 1, obtained from excavations in dry (CCRDry) and wet conditions (CCRWet), were analyzed in detail. Field CCR values vary between 0.052 and 0.026 cutter/m3 in dry excavation conditions and between 0.070 and 0.039 cutter/m3 in wet excavation conditions. The percentage changes between the CCRDry and CCRWet are also given in Fig. 11. As seen, the CCR values of roadheaders are increased at different rates, ranging from 33.5 to 10.8% in wet conditions compared to the dry conditions for all CSC projects. Moreover, the relationships between the field CCRDry and CCRWet values of roadheaders are statistically analyzed. A positive linear correlation is found, with a 0.76 correlation coefficient (R2), between the field CCR values obtained in both conditions (Fig. 12). The relationship equation is presented in Eq. 2.

$$FieldCC{R_{Wet}}=1.1066 \times CC{R_{Dry}}+0.0082$$
(2)
$$FieldCC{R_{Dry}}=0.0531 \times CA{I_{Dry}} - 0.0336$$
(3)
$$FieldCC{R_{Wet}}=0.0528 \times CA{I_{Wet}} - 0.0031$$
(4)
Fig. 12
figure 12

Relationship between the field CCR values recorded in dry and wet excavation conditions

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On the other hand, the field CCRs of roadheaders are correlated with the laboratory CAI values for dry and wet conditions, as CAI is a reliable test method to predict the CCR of roadheaders (Fig. 13). As seen, a moderate correlation is obtained between field CCRDry and laboratory CAIDry values, similar to the correlations obtained in previous studies for CSC projects (Comakli 2019a, b).

Fig. 13
figure 13

Relationships between laboratory CAI values and field CCR values of roadheaders for dry and wet conditions

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As seen in Fig. 11, while CCR in wet conditions was theoretically expected to be lower than in dry conditions, actual field data showed that CCRs increased in wet conditions for all CSC projects compared to values obtained in dry conditions. In addition, the correlations between the CAI and field CCR data revealed that CAI is insufficient to estimate the CCR of roadheaders used in excavating wet formations. Therefore, it is understood that the changing formation conditions during excavations in wet conditions adversely affect the CCR of roadheaders, which theoretical approaches do not take into account. In this study, it has been evaluated that the main reason for the increase in CCR in wet conditions was the fine-sized rock materials adhering to the cutters. Namely, fine siliceous particles adhere to the cutters and form an abrasive material between the cutters and the rock in wet conditions and then wear down the cutters. In contrast, fine siliceous particles are essentially separated from the rock by the cutters without prolonged contact with the cutters in dry conditions.

Since the excavated porous ignimbrites have low UCS and high porosity, crack propagation and chip formation are generally limited (Comakli 2019b). For this reason, excavated rock materials in CSC projects are usually in fine-sized 1030form (Fig. 14). Also, these rock materials contain clay, as stated in the paper published by Comakli (2019b). For this reason, rock materials of fine size block the cutters by adhering to them and increasing friction on the cutter surface, resulting in abnormal wear on the steel body of the cutters and increased CCR (Fig. 5b). In addition, it can be noted that the high SiO2 content of the rocks adhering to the cutters also increases CCR. In short, in CSC excavations, it is observed that the main difference between excavations in dry and wet conditions is the adhesion of the excavated fine-sized rock materials to the cutterhead and cutters in wet conditions. Therefore, the relationship between field CCRWet and the water content of rocks excavated in wet conditions was statistically analyzed, and a positive linear correlation was found with a 0.71 correlation coefficient (R2) (Fig. 15). The equation of the relationship is given in Eq. 5.

$$FieldCC{R_{Wet}}=0.0056 \times w - 0.0527$$
(5)
Fig. 14
figure 14

Fine-sized excavated porous ignimbrites in dry conditions during the excavation (left); while transported by belt conveyor (right)

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Fig. 15
figure 15

Relationships between the water content of excavated porous ignimbrites and CCR recorded in wet conditions

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Similar problems with the excavated formation sticking to the cutterhead and cutters are more common in TBM excavations. These problems, named clogging problems, generally occur in the excavation of soil formations by the earth pressure balance (EPB) TBMs and were analyzed in previous studies by different researchers (Hollmann and Thewes 2013; Zumsteg et al. 2016; Thewes and Hollmann 2016; Avunduk and Copur 2019). In general, researchers reported that clogging problems negatively affect the excavation performance of TBMs (Alberto-Hernandez et al. 2017; Avunduk and Copur 2019). Also, roadheaders are used in excavating low-strength and clay-containing formations such as tuff, marl, and claystone. Therefore, similar problems should be considered in roadheader excavations.

Many researchers have investigated the adhesion potential of excavated formations for TBM excavations using different laboratory testing methods (Thewes and Hollmann 2016; Avunduk and Copur 2019; Barzegari et al. 2020; Kang et al. 2022). Since the excavated fine-sized porous ignimbrites behave like soil, the adhesion potentials of these rocks are determined in different water contents with a simple laboratory setup in this study. The relationships between the field CCRWet and the weight of the adhering rock materials (WAM) to the steel arm obtained in different water content values are statistically analyzed. Field CCRWet is correlated with the WAM obtained at all water content values, respectively. However, a meaningful correlation is obtained for only 15%, 20%, and 25% water content values, but not found for others. This situation is expected because the water content of the porous ignimbrites collected from the project areas varies from 20.04 to 23.37%. The graphical illustrations of the relationships between field CCRs and the WAM are given in Fig. 16, and the equations of these relationships are also provided in Eqs. 6, 7, and 8. As seen in Fig. 16, the field CCRWet increased with the increasing WAM at each water content value. In other words, these results showed that fine-sized rock materials sticking to the cutters have an enhancing effect on the CCR of the roadheaders during the excavation of CSC projects.

Fig. 16
figure 16

Relationships between field CCR of roadheaders and weight of rock material adhering to the steel arm

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For 15%,

$$FieldCC{R_{Wet}}=0.0086 \times WA{M_{15}} - 0.0304$$
(6)

For 20%,

$$FieldCC{R_{Wet}}=0.007 \times WA{M_{20}} - 0.0313$$
(7)

For 25%,

$$FieldCC{R_{Wet}}=0.0057 \times WA{M_{25}} - 0.018$$
(8)

In addition, it should be noted that the WAMs of the porous ignimbrites excavated in CSC projects were determined by a simple test method in the present study. However, using the LCPC test, another widely used test method to assess the abrasivity of rocks and soils, similar results to the results obtained in this study were revealed by different researchers (Barzegari et al. 2015; Hashemnejad et al. 2016; Abu Bakar et al. 2018). These studies have generally reported that the abrasivity of rocks or soils increases, especially at a given water content value, and that extra water added later can be beneficial to reduce rock abrasivity. While performing the potential adhesion determination tests, similar behaviors were observed for porous ignimbrites in this study. Therefore, it can be considered that the LCPC test method can give more accurate results to determine the abrasivity properties of porous ignimbrites excavated in CSC projects under wet conditions.

The results obtained from the correlations showed that both WAM and w are effective parameters on field CCR in wet conditions during the excavation of CSCs. Thus, the stepwise multiple regression analysis methods were performed to obtain a more reliable equation, based on WAM and w, to predict the CCR of roadheaders during the excavation of porous ignimbrites in wet conditions. To get the best model, the WAM values obtained at 15%, 20%, and 25% water content values were analyzed, respectively. The best equation with 0.84 R2 value was obtained based on WAM15 and w and given in Eq. 9. Then, the estimated CCR for wet conditions obtained from Eq. 9 were correlated with the actual field CCRWet values. The graphical illustration of the relationship between estimated and recorded real CCRWet values is given in Fig. 17. As seen in Fig. 17, there is a strong linear correlation between the field and estimated CCR values for wet conditions. Thus, it can be confirmed that the newly developed equation can be used to predict the CCR of roadheaders during the excavation of rocks that have adhesion potentials to the cutters, such as low-strength ignimbrites and clay-rich rocks in wet conditions. The statistical results of Eq. 9 and the other equations are given in Table 7.

$$FieldCC{R_{Wet}}= - 0.68+(0.04 \times w)+(0.05 \times WA{M_{15}})$$
(9)
Fig. 17
figure 17

Relationship between actual field and estimated CCR values for excavation of wet formations

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Table 7 Statistical results of the regression models
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Conclusions

This study presents the effects of the changing formation properties on the CCR of roadheaders with the effect of the increasing water content during the excavation of the CSCs located in the Cappadocia region. For this purpose, the field CCRs of roadheaders in dry and wet conditions are recorded during the excavation of ten different CSC projects. Then, laboratory tests were carried out on the collected dry and wet rock samples from CSC project areas, and the adhesion potentials were determined by a simple test method. In addition, the CCRs of roadheaders were theoretically estimated for each CSC project using three different models suggested by previous studies. The obtained results from both field and laboratory studies were statistically analyzed to evaluate the effects of increasing water content on the CCR of roadheaders, and the conclusions are summarized as follows:

  • The strength and abrasivity properties tested in the laboratory of excavated porous ignimbrites decreased with the increasing water content; the average reduction in UCS, BTS, and CAI is 46.34%, 51%, and 25.51%, respectively.

  • CCRDry and CCRWet were correlated, and a positive linear relationship was found with an R2 of 0.67.

    $$CA{I_{Wet}}=0.6719 \times CA{I_{Dry}}+0.1258$$

  • While CCR in wet conditions was theoretically expected to be lower than in dry conditions, actual field data showed that CCRs increased in wet conditions for all CSC projects. Therefore, this study proved that the theoretical estimation of CCR of roadheaders based on only laboratory test results is insufficient, and the changing formation properties should be considered.

  • Field studies revealed that the formations excavated by roadheaders were generally obtained in fine-sized form during excavation. Also, excavated porous ignimbrites containing clay and the resulting fine-sized rock materials adhere to the cutters due to increasing water content and have a significantly increasing effect on CCR.

  • The adhesion potentials of the porous ignimbrites excavated in CSC projects were determined for different water contents by weighing the adhering rock materials to the test arm (WAM). It is observed that the adhesion potential of thin materials increased up to 20% and 25% water content values and was at its maximum at these values. It started to decrease at 30%, 35%, and 40% water content values.

  • Determined WAMs in each water content were correlated with the field CCRWet, and strong positive linear relationships were found in each of the 15%, 20%, and 25% water content values with an R2 of 0.62, 0.71, and 0.64, respectively.

    $$\begin{array}{l}FieldCC{R_{Wet}}=0.0086 \times WA{M_{15}} - 0.0304\\FieldCC{R_{Wet}}=0.007 \times WA{M_{20}} - 0.0313\\FieldCC{R_{Wet}}=0.0057 \times WA{M_{25}} - 0.018\end{array}$$

  • Also, the correlations between the field CCRWet values and WAMs proved that the adhesion potential of the porous ignimbrites has a significant effect on the CCR of roadheaders during the excavation of wet conditions.

  • A new equation with R2 of 0.84 was developed to estimate the CCR of roadheaders used in wet conditions to excavate the rocks that may stick to cutters under increased water content.

    $$FieldCC{R_{Wet}}= - 0.68+(0.04 \times w)+(0.05 \times WA{M_{15}})$$

  • In the excavation of CSC projects, water is not sprayed from the roadheaders due to durability problems. However, it is noted that water sprayed from roadheaders may reduce CCR by removing rock material that adheres to cutters during excavations in wet conditions.,

This study investigated the effects of adhesive rock materials on the cutter wear of roadheaders for only low-strength porous ignimbrites excavated in CSC projects in Cappadocia. However, more field data from excavating different rock types, such as marl and claystone, are needed to investigate this issue in more detail in future studies. In addition, it should be emphasized that when investigating the effects of the increasing water content of clay-contain rocks on cutter consumption of roadheaders, it would be more beneficial to consider the mineralogical and petrographic properties of the rocks. Thus, it is planned that more detailed similar studies on clay-contain rocks will be conducted in the future, also considering their mineralogical and petrographic characteristics.