Application of Rock Mass Characterization for Det

Original Paper

Application of Rock Mass Characterization for Determining the Mechanical Properties of Rock Mass: a Comparative Study Mahmoud Hashemi1 , Sh. Moghaddas2 and R. Ajalloeian3

Received: 25 July 2008 Accepted: 23 March 2009 Published online: 16 April 2009

Abstract The results of geotechnical explorations, engineering geological investigation (including laboratory and in situ tests) and field observations have been used, along with borehole logging charts, to obtain the rock mass geotechnical data. Based on the data, the rock mass along the Sabzkuh water conveyance tunnel route was classified by rock mass rating (RMR), Q-system (Q), rock mass index (RMi) and geological strength index (GSI) (3 methods). A new series of correlations were established between the systems based on the data collected from the study area. These relationships were then compared with those reported in the literature, and two new relations were recommended. The classifications were utilized to calculate mechanical properties (rock mass strength and deformation modulus) of the rock mass along the tunnel according to available empirical relations, and to distinguish the upper-bound and lower-bound relations.

Keywords Rock mass classification - RMR - Q - RMi - GSI - Mechanical properties - Geotechnical explorations - Tunnel

1 Introduction

1.1 Background

Rock Mechanics and Rock Engineering Springer-Verlag 200910.1007/s00603-009-0048-y

(1) Department of Civil Engineering, Faculty of Engineering, The University of Isfahan, 81744-73441 Isfahan, Iran

(2) Engineering Geology, Sabir Engineering Co., Tehran, Iran(3) Department of Geology, Faculty of Science, The University of Isfahan, Isfahan, Iran

Mahmoud Hashemi Email: [email protected]

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Rock mass classifications play an important role in estimating the strength and deformability of rock masses and in assessing the stability of rock slopes. They also serve as an index to rock rippability, dredgeability, excavibility, cuttability, and cavibility (Bieniawski 1989).

During the past 50 years, there have been numerous efforts around the world to create a suitable engineering rock mass classification system so that the preliminary evaluation of feasibility, development and stability/service of engineering structures/projects, would be possible and fairly reliable. Terzaghis (1946) rock-load classification scheme could be considered to be the first empirical classification system for rock mass. Subsequently, various researchers proposed different rock mass classification systems, including Laufer (1958), Deere et al. (1967), Wickham et al. (1972), Bieniawski (1973), Barton et al. (1974), Hoek (1994), Hoek et al. (1995) and Palmstrm (1995). Many researchers have also tried to correlate the various classification systems [mostly between rock mass rating (RMR) and Q-system (Q)]. Some relations have been proposed by Bieniawski (1976), Rutledge and Preston (1978), Moreno (1980), Cameron-Clarke and Budavari (1981), Abad et al. (1984), Kaiser and Gale (1985), Al-Harthi (1993), Barton (1995), Turul (1998) and Kumar et al. (2004).

The construction of underground structures, such as powerhouses, gas and petroleum storage systems, nuclear waste storage spaces, and water conveyance tunnels are of high importance. The very first step for the design and stability analysis of such structures is to use numerical and analytical modeling methods. The methods use the mechanical properties (deformation modulus and strength) of the rock mass as input parameters.

Typically, a series of field tests, such as plate loading, jacking, flat jacking, or block shear testing, are conducted to obtain the parameters. The tests are expensive and time-consuming, especially when they are done in underground openings.

Therefore, the empirical (indirect) methods for estimating the parameters are the easiest, quickest and simplest alternatives.

During years of developments in rock engineering, various empirical methods have been proposed, where these use the classification systems as a base. To judge the relations, one needs time to verify the relations by applying them at various sites with different types of rocks and conditions for rock mass so that the advantages and disadvantages will be apparent and the relations can be improved. Although none of the relations is absolutely the best, we may find the best one under certain conditions by comparing them.

The estimation of uniaxial compressive strength of rock mass using classification systems is important for correct evaluation of underground structure stability.

For this purpose, various relations have been suggested, including those by Yudbir et al. (1983), Kalamaras and Bieniawski (1993), Singh (1993), Goel (1994), Bhasin and Grimstaad (1996), Singh et al. (1997), Sheory (1997), Aydan and Dalgi (1998), Hoek et al. (2002), Barton (2002), and Ramamurthy (2004).

A literature review of existing relations is presented by Edelbro et al. (2007). They demonstrated that the results of the application of the relations vary significantly, even when one system is used by different, qualified engineers. A comparison between the estimated rock mass with in situ measured rock mass strength indicates the reliability of the various systems.



To determine the engineering properties of rock mass for use in numerical analyses, the evaluation of deformation modulus using the classification systems is essential. Bieniawski (1978) estimated the modulus using the RMR value. Subsequently, various empirical relations estimating the modulus based on the classification systems have been proposed, including those by Serafim and Pereira (1983), Nicholson and Bieniawski (1990), Verman (1993), Verman et al. (1997), Mitri et al. (1994), Singh (1997), Hoek and Brown (1997), Palmstrm and Singh (2001), Barton (2002), Hoek et al. (2002), Kayabai et al. (2003), Gokeoglu et al. (2003), Ramamurthy (2004), Sonmez et al. (2004), and Zhang and Einstein (2004).

It is important to note that the evaluation of all input data for the various above relations is subjective; i.e., different input values are estimates by different people based on the same field conditions. Therefore, different values are derived, even with the same relation.

1.2 The Study Area The Sabzkuh water conveyance project (including the Sabzkuh diversion dam, open channel and tunnel and Choghakhor dam rehabilitation) is designed to transfer 90 million m3 of water annually from the Sabzkuh drainage basin to the Choghakhor dam reservoir. The project is located about 109 km south of Shahr-e-Kord city and 90 km south west of Borujen city, Chaharmahal-Bakhtyari province. The study area is situated on the north side of Zagros mountain between 5050 to 5058 eastern longitude and 3145 to 3158 northern latitude. The surface run-off along the Sabzkuh River may be kept by a diversion dam, which is a 4.5 km long open channel that runs to a main. The main is 8.574 km long, and the water is finally carried to the Choghakhor dam reservoir (Fig. 1). The tunnel cross section has a horseshoe shape with a diameter changing from 4.2 to 3.2 m.



Fig. 1 Location map of the study area

2 Engineering Geological Assessment The lithology of the tunnel route mainly consists of limestone, marly and dolomitic limestones, dolostone, shale and variable sizes of alluvium. The lowest and the uppermost lithologies belong to Camberian and Quaternary, respectively. The Sabzkuh syncline is the main geologic structure at the project area. The axis of the syncline is extended in the NWSE direction in which the Sabzkuh River flows. The Sabzkuh tunnel passes the north limb of the syncline and is extended in the SWNE direction. From the viewpoint of structural geology,



the stratification is regular along the tunnel route from the inlet section to the F11 fault. Moving from the F11 fault towards the outlet, the stratigraphy of the area is disturbed due to the active structural geology, intensive erosion and complex lithology of the area. The morphology of the area mainly consists of high mountains and deep valleys with steep walls. At the project area, there are karstic features and traces, including sinkholes, solution dolines, lapies, poljes and shallow caves, which are locally observed in limestone. A total of six boreholes have been drilled, with overall length of 1,646 m, using wireline and rotary core boring methods along the tunnel route. The longest borehole is 522.1 m long. Currently, approximately ten additional boreholes are being drilled, where these are concentrated in the weak zones and critical areas. Since the overburden is high (around 1,200 m in the middle of tunnel route), the borehole drilling has become very difficult and time- and money-consuming. Therefore, geophysical exploration is preferred for these sections of the tunnel route. In addition, the pilot (probe) horizontal boreholes are planned ahead of main tunnel excavation (Fig. 2).



Fig. 2 The geological map and geotechnical longitudinal cross-section of the tunnel route



For geotechnical evaluation and rock mass classification, the field observation, geophysical exploration, borehole logging, the field tests and laboratory experiments have been used and studied thoroughly. The studies show that the rocks in the area are slightly to moderately weathered.

Regarding the joint conditions, the wall surfaces of the joints are mostly rough. The infillings mainly consist of calcite, ferrous oxide and finely ground (clay to silt size) lithic particles.

The joint pattern along most parts of the tunnel consists of three sets (two joint sets and bedding). In some areas, four joint series are observed (three joint sets and one bedding). The results of laboratory tests that were mainly carried out on the borehole and some field samples show that the uniaxial compressive strength of rocks varies from 10 to 125 MPa (Table 1).

Table 1 Summery of laboratory test results of boreholes and field samples

Segment no.

Tunnel section

Lithology

Value of laboratory tests

From To

Uniaxial comprehensive strength (MPa)

Modulus of elasticity (GPa)

Max. Min. Ave. Max. Min. Ave. 1 0 + 000 0 + 043 Limestone 118 68 85 33 27 31

2 0 + 043 0 + 325 Marlstone and marl 28 12 15 21 15 15

3 0 + 325 0 + 461 Limestone 105 63 85 32 28 30

4 0 + 461 0 + 679

Marly limestone and calcareous shale

74 42 55 25 21 23

5 0 + 679 1 + 247 Limestone 95 52 60 32 26 29

6 1 + 247 12 + 150 Limestone and marly limeston

75 25 38 28 23 24

7 2 + 150 2 + 770 Limestone 110 53 65 30 27 31

8 2 + 770 3 + 088 Dolostone and dolomitic limestone

118 50 67 33 29 32

9 3 + 088 3 + 868 Dolostone and dolomitic limestone

112 50 62 33 28 31

10 3 + 868 4 + 015 Dolostone and marly limestone

98 48 58 29 23 26

Limestone,



The RQD is mostly evaluated from the borehole cores, and in some cases, it is determined using the Palmstrm (1982) method:

where J V is the volumetric joint count and is calculated as:

where s i is the average spacing of ith joint set.

Joint wall aperture is generally higher than 1 mm. In some stations, there are very high joint apertures (more than 50 mm), which are mostly seen on the ground surface. Figure 3 shows one of the cases in which a joint set is observed in a calcareous formation (DaryanFahlian

11 4 + 015 4 + 705 dolostone and dolomitic limestone

108 52 64 31 26 29

12 4 + 705 4 + 715 Marly limestone 45 27 35 22 15 16

13 4 + 715 5 + 120 Dolostone 125 56 70 32 26 30 14 5 + 120 5 + 745 Dolostone 106 53 66 33 27 30

15 5 + 745 5 + 871 Marly limestone 44 25 32 23 15 17

16 5 + 871 6 + 193 Limestone, dolostone and dolomitic limestone

92 55 62 30 26 28

17 6 + 193 6 + 352 Marly limestone 42 25 32 23 15 17

18 6 + 352 6 + 442 Dolostone 100 48 63 30 28 28


90 42 60 32 27 30

20 6 + 576 6 + 823 Marly limestone 42 22 30 22 12 14


90 42 58 28 25 27

22 7 + 980 8 + 059 Brecciated limestone 20 10 15 10 8 8

23 8 + 059 8 + 231 Micaceous shale 41 23 29 23 16 18



Formation). The joint set wall spacing has been widened due to a secondary dissolution process, so that the joint aperture is increased to 1540 cm. The joint has a dip/dip direction of 84/110 and is approximately parallel to the tunnel axis. The joint set wall condition is also rough.

Fig. 3 One of the cases in which a joint set is observed in a calcareous formation (DaryanFahlian Formation)

The geological features of the tunnel route are partially shown in Figs. 4, 5 and 6.



Fig. 4 A shear zone is presented near the outlet between the CHT1 and CHT2 boreholes that are a result of an active fault (F16)

Fig. 5 The joint sets in the Khanekat formation in a level higher than CHT3 borehole and in contact with Neyriz formation. The joint wall condition is rough and dissoluble

Fig. 6 A dissolution and karstic cavity with dimensions of more than a meter in the SarvakIlam formation near the ST202 borehole

A shear zone is also presented in Fig. 4, located near the outlet between the CHT1 and CHT2 boreholes; it is a result of an active fault (F16). The zone is extended to 100 m in width and may affect the rock mass at the tunnel level. The zone consists of lithic pieces with diameters

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ranging from 1 to 100 cm that are connected by a matrix from the original formation. The lithic pieces belong to the Khanekat formation, which consists mostly of limestone, dolostone and dolomitized limestone.

The joint sets in the Khanekat formation at a higher level than the CHT3 borehole and in contact with the Neyriz formation are shown in Fig. 5. The joint wall condition is rough and dissoluble.

A dissolution and karstic cavity with dimensions more than a meter in the Sarvak-Ilam formation near the ST202 borehole is also presented in Fig. 6. The cavity was made by the karstic dissolution process, probably due to the presence of three joint sets. The joint sets aperture measures more than 1 mm. The joint walls are mostly rough and rarely undulating (Moghaddas 2004; Hashemi et al. 2004a, b; Ajalloeian et al. 2004).

3 Rock Mass Classification 3.1 Introduction Over the past five decades, various rock mass classification systems have been proposed by different researchers. All the systems tend to utilize the rock mass characteristics using either quantitative or qualitative methods in rock engineering. The characteristics are undoubtedly the essential requirements for empirical design and numerical modeling. However, none of the systems could utilize all of the characteristics. This may be due to lack of homogenity and isotropy in the material.

The characteristics of a particular rock mass could vary from one site to another site, perhaps due to differences in engineering judgments and site conditions. This has led to the creation of various classification systems instead of a single system.

The most well-known classification systems are briefly explained in the following sections.

3.1.1 The RMR System

Bieniawski (1973) proposed a geomechanical classification system (RMR). The system has been revised many times, and the latest version was proposed in 1989. The system calculates an index by summing the ratings for six main factors: the uniaxial compressive strength of the rock material, the RQD value, spacing, condition and orientation of discontinuities, and ground water conditions.

The system defines the rock mass as one of five classes based on structural geology and strength characterization.

3.1.2 The Q-System

Barton et al. (1974) from NGI presented a tunneling quality index, called the Q-system. The system is widely applied to various underground openings. Multiple revisions have been



proposed for the system (Grimstaad and Barton 1993; Barton 2002), which classifies the rock mass as one of nine classes. The index of the system ranges from 0.001 to 1000 on a logarithmic scale and is calculated as:

3.1.3 The RMi System

Palmstrm (1995) proposed the rock mass index (RMi) classification system. The RMi is a volumetric parameter indicating the approximate uniaxial compressive strength of a rock mass by combining c and a jointing parameter (JP). JP represents the block volume (V b) plus the joint condition (jC). The joint condition can be estimated by joint roughness (jR), joint alteration (jA) and joint size (jL).

The RMi system is similar to the Q-system. For instance, jA and jR in the RMi are approximately similar to J r and J a in the Q-system, respectively.

The system evaluates the rock mass as one of seven classes. In addition, it has been recently revised (Palmstrm 2000; Palmstrm and Singh 2001).

3.1.4 The GSI System

Hoek et al. proposed the geological strength index (GSI) to obtain reliable input data, especially those related to rock mass properties required as inputs into numerical analysis (Hoek 1994; Hoek et al. 1995; Hoek and Brown 1997). In the last decade, the index was further developed and modified, particularly in poor and heterogeneous rock masses for designing projects such as tunnels, slopes and foundations in rocks (Hoek et al. 1998, 2005; Sonmez and Ulusay 1999, 2002; Marinos and Hoek 2000, 2001; Cai et al. 2004).

The GSI has been evaluated using three different methods that are described in the following sections.

3.1.4.1 Evaluation of GSI Based on Field Observations

The GSI was first developed based on field observation: the experienced engineering geologist evaluates the rock mass conditions from outcrops (overview and structural geology). Then, the results are compared with the corresponding evaluation table (Hoek and Brown 1997). Finally, the table yields the GSI.

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RQD rock quality designation J

n the joint set number

J r roughness number of least favorable joint

J a alteration number of least favorable joint

J w the joint water reduction factor SRF stress reduction factor.



3.1.4.2 Evaluation of GSI Based on Other Rock Mass Classification Systems

According to this method, the GSI is determined through other rock mass classification systems, such as RMR (1976 and 1989) and Q (Hoek et al. 1995). The method is mostly convenient for the sites in which the stratification outcrops and rock formations are not present, but GSI estimation is required.

Based on RMR76 (Bieniawski 1976), the GSI is equal to the sum of the ratings for four parameters: UCS, RQD, spacing and condition of discontinuities, but the rating for the groundwater condition and joint orientation are set to ten and zero, respectively (Hoek et al. 1995):

For RMR76 < 18, a new parameter, Q is introduced:

For RMR89 (Bieniawski 1989), the formulation is similar to that of RMR76. The only difference is that the groundwater condition rating is set to 15:

Again, for RMR89 < 23, Q has been used.

It should be mentioned that the minimum rating for RMR76 and RMR89 are 18 and 23, respectively, according to the above conditions.

3.1.4.3 Evaluation of GSI Based on Block Volume and Joint Surface Condition Factor

Cai et al. (2004) recently proposed a new approach based on the block size and condition, block volume (V b) and joint condition factor (J C). The approach was intended to increase the performance of GSI and to make it more quantitative. Block size is determined from the joint spacing, joint orientation, number of joint sets and joint persistence. Compared to the variation in joint spacing, the effect of the intersection angle between join sets is relatively small. Thus, for practical purpose, the block volume for three or more joint sets can be approximated as

where S i is the spacing of each joint.

(2)

(3)

(4)

(5)



The joint surface condition (J C), which is defined by the roughness, weathering, and infilling, is similar to the factor used by Palmstrm (1995) to quantify the joint surface conditional and is defined as:

where J W, J S and J A are the large-scale waviness, small-scale smoothness and joint alteration factor, respectively.

The background of the chart provided by Cai et al. is the same as the chart produced by Hoek and Brown (1997), but the HoekBrown chart has been precisely quantified by Cai et al. using V b and J C.

3.1.5 The RCR and N

Goel et al. (1996) studied the various relationships between Q and RMR and found them to be diverse and divergent. They noted that the UCS of intact rock ( c) indirectly presents the Q formulation. In addition, the SRF is not present in the RMR calculation. Therefore, they assumed that the UCS and joint orientation, and SRF may be dropped from the RMR and Q formulations, respectively.

This led to the creation of two new concepts: rock condition rating (RCR) and rock mass number (N). Based on the correlation between RCR and N values for the 63 case studies from India, and other countries, they proposed the following relationships with a satisfactory correlation coefficient of 0.92:

where RCR = RMR (rating for c and joint orientation) and N = Q (assuming SRF = 1).

3.2 Correlation Between the Rock Mass Classification Systems As the various engineering rock mass classification systems were being developed, a question arose: if two classification systems are applied to two different sites, how can the rock masses in the two sites be compared. The answer is to establish a correlation between the systems in order to calculate one from another. Since some parameters may be used in one system but not in the other, such correlations may be used as an approximate tool and not as an alternative for routine calculation of another system.

Various researchers have tried to correlate the systems. If the systems are simultaneously applied in various sites, the relations will become more convergent. Some of the relations are listed in Table 2.

Table 2 Comparision of various correlations among the rock mass classifications

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3.3 Results and Discussion

3.3.1 Classification Systems

Each classification system contains various parameters with different ratings. One may find a parameter common between the systems while the rating (dividing the boundaries and assigned values) is different among the systems. Roughness, spacing, alteration, and infilling are some of the parameters. Another difference is that the systems utilize the parameters in different ways and ranges. For example, RQD has a maximum value of 15 in the RMR system, whereas it is directly involved in Q evaluation and varies from 10 to 100. On the other hand, the RQD is a way to calculate block volume (J

v) in RMi system. Some parameters are

present in one system, but absent in another system. Some examples of such parameters are the groundwater condition in the RMi system, the strike and dip of joints and uniaxial compressive strength ( c) in the Q system, and the rock mass stress reduction factor (SRF) in RMR and RMi systems. In addition, the RQD depends on the drilling method, and the effect of the groundwater condition depends on the drainage conditions.

Researcher(s) Correlation (relation no.) Estimated parameter Bieniawski (1976) RMR from Q

Rutledge and Preston (1978) RMR from Q

Moreno (1980) RMR from Q Cameron-Clarke and Budavari (1981)

RMR from Q

Abad et al. (1984) RMR from Q

Kaiser and Gale (1985) RMR from Q

Al-Harthi (1993) RMR from Q

Barton (1995) RMR from Q

Turul (1998) RMR from Q

Kumar et al. (2004)

RMR from Q RMR from RMi

RMi from Q

RCR from N



Considering the range of the ratings, the Q and RMi systems are more sensitive than the RMR. In RMR, a range is established, whereas in the other two methods (Q and RMi, and especially Q), the parameters are individually and directly involved in formulas. Therefore, the main disadvantage for the present systems is the different ranges for a particular parameter in various systems due to their different logic and structure.

As another example, the rating sensitivity of the joint spacing in RMR is less than in RMi and GSI (third method, Cai et al. 2004) because the parameter is very important in determining the block volume, and therefore the final rating in RMi and GSI. Thus, the joint spacing rating for RMi and GSI is more sensitive than RMR.

Finally, none of the systems as considered to be complete. This is also the reason that no consistent relations can be found between the various systems.

The engineering rock mass classification has been done for 23 segments passing rock formations using four systems: RMR89, Q, RMi and GSI (2 methods) (Fig. 7).

Fig. 7 The engineering rock mass classification for 23 segments passing rock formations using 4 systems: RMR89, Q, RMi and GSI (3 methods)

The GSI was determined for almost all the segments using the first method. There were two lithological units (marly limestone of Khanekat Formation and dolostone of Dalan Formation) whose outcrops were not available near the tunnel. Their GSI were evaluated based on the available outcrops away from the tunnel route applying the geological conditions of the tunnel route. The third GSI method (3.1.4.3) was also used for all the segments to compare it with the other two methods of GSI. Figure 7 shows that there was no apparent difference between first and third methods of GSI. Marinos et al. (2005) implied that the determination of GSI from third method is not applicable for tectonically disturbed structures, such as segment 22. They also recommended that where direct assessment of depth conditions is not possible, such as segment 10 (Fig. 3), the GSI in depth can be evaluated by proper adjustment of the depth



condition in their recommended GSI chart.

However, the first GSI method is mainly based on the real GSI characteristic (quick field evaluation of rock mass strength). Both (first and third) methods are similar in the sense that they evaluate the rock mass strength according to the exposed-in-surface (outcrop) conditions, where the rock mass is determined by the number of joint sets, alteration, wall roughness, degree of fracturing (blocky structure) in rock mass. Therefore, GSI does not consider the underground (depth) conditions, such as groundwater, dip and strike of discontinuities (with respect to excavation direction) and in situ stress characteristics.

It is also evident that the third method is similar to the RMi system in the sense that it involves the block volume measurement and joint condition factor. Perhaps, the only difference between the GSI and RMi systems is that GSI does not consider the UCS ( c) of intact rock.

For the rock masses along the tunnel route, the GSI varies in the ranges of 2260 and 2556, for the first (Hoek et al. 1995) and third (Cai et al. 2004) methods, respectively.

Moreover, based on the surface field evaluation, and considering the shear zones due to faults activities, the rock mass along the tunnel lies in the Disintegrated-Blocky class, as per the GSI system.

The other systems such as RMR89, Q and RMi evaluate the rock mass as very poor and fair, exceptionally poor and poor, and low and high quality, respectively.

Overall, based on the qualitative description of rock mass, the Q is the most conservative method (considering the weakest description for rock mass), whereas the RMi gives the radical (strongest) description for rock mass.

Along segment 1: as compared to other segments, RMR and Q present high values and evaluate the rock mass similarly to the RMi description, probably due to low overburden, reasonable strength of intact rock (leading to SRF 1) and dry conditions for groundwater in this segment. In addition, the rock mass is mostly blocky, leading to higher values of RMi and GSI (Fig. 7).

Along segments 8 and 9: the RMi yields higher values than Q because of the thick bedding, high values of J

v or the block volume formed by discontinuities, high RQD and the uniaxial

compressive strength of intact rock, whereas these parameters are not involved in the Q calculations, except RQD and ci (indirectly). The high SRF due to high overburden and groundwater condition are the other reasons for the low Q values. In this segment of the tunnel, the RMR and GSI values are also high due to the above reasons.

Along segment 21: due to a relatively low overburden, and therefore, low SRF, the Q value is increased even more than that for RMi. In addition, the RMR and GSI values are relatively low and high, respectively, due to groundwater conditions and other effective factors.

Along segment 22: there is a likely intersection of a shear zone and the tunnel in depth. Therefore, the rock mass classification calculations are very difficult for almost all the systems. Due to the high crushing effect, the block volume value is very low, leading to minimum values for RMi and GSI. The Q values are also low, due to an important factor



(SRF). The RMR evaluation is also low due to various factors, such as very low strength and groundwater conditions.

These were the most effective parameters, whereas the other parameters could be effective as well.

In segments 12, 15, 17 and 20: the values of all the systems are low and almost similar. This may be due to the intersection of the tunnel with a deep low-strength layer that belongs to the base of the Khanekat formation, which consists of marlstone, marly limestone, and siltstone.

3.3.2 Proposed Correlations Between the Systems

In the earlier studies, a series of correlations have been established, and various relations were proposed which are mostly between the Q and RMR (Table 2).

Correlated data from the Sabzkuh tunnel, along with the other correlations available in literature (10 cases), are presented in Fig. 8.

Fig. 8 Correlated data from the Sabzkuh tunnel, along with the other correlations available in the literature (10 cases)

It is shown that the closest relation to the Sabzkuh tunnel data is the one proposed by Rutledge and Preston (1978).

The recommended relation for the Sabzkuh tunnel data is

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Figure 9 shows the correlation between RMi and RMR values for the Sabzkuh tunnel route

Fig. 9 Correlation between RMi and RMR values for the current case and comparing with relation by Kumar et al. (2004)

It is observed that there is no similarity between the above relation and the available literature (Kumar et al. 2004).

Figure 10 presents the correlation between Q and RMi for the Sabzkuh tunnel data

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Fig. 10 Correlation between Q and RMi in this case and available literature (Kumar et al. 2004)

A comparison of the above relation with available literature (relation 20, Table 2, Kumar et al. 2004) shows that the relations match well, especially for low values of Q (Q < 0.35). However, relation (20) by Kumar et al. 2004 did not show good agreement with the Sabzkuh data for high values of Q (Q > 0.35).

Figure 11 presents correlation between N and RCR for the Sabzkuh tunnel data as:

Fig. 11 Correlation between N and RCR in this case and available literature (Goel et al. 1996 and Kumar et al. 2004)

Comparison of the recommended relation and available literature (Goel et al. 1996; Kumar et

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al. 2004) shows that the proposed relation in the current study lays between the two relations in available literature.

Figure 12 shows the correlation between RMR and GSI (Hoek et al. 1995) in the current study as:

Fig. 12 Correlation between RMR and GSI (Hoek et al. 1995) in the current study

This relation is calculated based on the first method of GSI (Hoek et al. 1995) and RMR89.

Figure 13 shows the correlation between the first method of GSI (Hoek et al. 1995) and the third method of GSI (Cai et al. 2004) in the current study with a strong correlation coefficient:

Fig. 13 Correlation between first method of GSI (Hoek et al. 1995) and third method of GSI (Cai et al. 2004) in the current study

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It is evident that there is little difference between the two methods.

4 Determination of Mechanical Properties for Rock Masses

4.1 Uniaxial Compressive Strength of Rock Mass

4.1.1 Background

Various parameters have been used as input for different empirical relations to get the UCS of rock mass. The parameters are mostly related to classification systems and the rock mass constants. However, the uniaxial compressive strength of intact rock is used in the majority of the relations. Some of the relations are presented in Table 3.

Table 3 Various relations for estimation of rock mass strength

Researchers Equation (in terms of MPa) (relation no.) Limitation Yudbir et al. (1983)

Kalamaras and Bieniawski (1993)

Singh (1993) (kN/m3)

Goel (1994) N = Q (with SRF = 1) B = tunnel width (m)

Bhasin and Grimstaad (1996)

Sheory, 1997

Aydan and Dalgi 1998

Hoek et al. (2002)

s = exp[(GSI 100)/(9 3D)] a = 1/2 + (1/6)(eGSI/15 e20/3) Q c = Q 0 ci/100



The following points are interesting regarding the relations presented in Table 3. First, Yudbir et al. modified the original intact rock criterion (Bieniawski 1973) for rock mass. In addition, Singh et al. (1997) evaluated the relation given by Bhasin and Grimstaad (1996). They concluded that the relation is convenient for good classes of rock mass (Q > 10, ci > 100 MPa). They also evaluated the relation given by Singh (1993) and concluded that the relation can be properly used for weak classes of rock mass (Q < 10, ci > 2 MPa). Ramamurthy (2004) found the following relation for rock mass:

where Jf is the joint factor and is set to 0 and 500 for intact rock and rock mass, respectively, in site conditions. In addition, Ramamurthy (2001) found the following relation as:

Substituting (38) into (39), the relation is obtained as given by Ramamurthy (2004), which is very similar to the relation proposed by Kalamaras and Bieniawski (1993) (Table 3).

In addition, the RQD0 is the oriented RQD in the loading or measurement direction (in the TBM model, it is in the tunneling direction).

4.1.2 Results and Discussion

The rock mass strength estimated using the above relations shows a wide range (Fig. 14).

Barton (2002) Q 0 = Q (with RQD0)

Ramamurthy (2004)

(38)

(39)



Fig. 14 The rock mass strength estimated using relations available in literature

The relations proposed by Goel (1994) and Singh (1993) estimate high values (upper bound) for cm, whereas the relation proposed by Barton (2002) and Yudbir et al. (1983) yields low values (lower bound).

Some relations, such as those proposed by Aydan and Dalgi (1998) and Kalamaras and Bieniawski (1993), give average (medium) values. It seems that the relation given by Hoek et al. (2002) that is widely used in geotechnical softwares is somewhat conservative. As explained earlier, the relations given by Kalamaras and Bieniawski (1993) and Ramamurthy (2004) give similar results.

The cm parameter decreases as the stability and strength condition of the rock mass becomes weaker, due to the direct effect of ci and the values given by the classification systems.

Interestingly, none of the relations directly consider the tunnel dimension (diameter) as a parameter, except the relation given by Goel (1994).

For the upper bound relations, the variation of cm is much higher, whereas the input parameter of the relations (such as intact rock strength) varies in a small range (for example for segments 1 and 2 with strong and weak rock masses, respectively) (Fig. 14).

The other case studies by Edelbro et al. (2007) revealed that the N, Yudhbir-RMR76, RMi, Q-,



and HoekBrown-GSI methods appeared to yield reasonable agreement with the measured strengths. These methods are thus considered the best candidates for realistic strength estimation, provided that care is taken when choosing values for each of the included parameters in each method. This study has also clearly shown the limits of the presently available strength estimation methods for rock masses, and further work is required to develop more precise, practical, and easy-to-use methods for determining the rock mass strength (Edelbro et al. 2007).

4.2 Deformation Modulus of Rock Mass

4.2.1 Background

The deformation modulus of a rock mass is apparently different from that of intact rock. To obtain the modulus of a rock mass, there are direct (in situ) methods, which require extensive and costly field operations, similar to those needed to obtain cm.

Therefore, indirect empirical relations were proposed to calculate the E m

based on a particular classification system for rock mass. Some of the relations are listed in Table 4.

Table 4 Various relations for estimation of rock mass deformation modulus

Researchers Equation (relation no.) Limitation Bieniawski (1978)

RMR > 50

Serafim and Pereira (1983)

RMR 50

Nicholson and Bieniawski (1990)

Verman (1993), Verman et al. (1997)

H > 50 m

Mitri et al. (1994)

Singh (1997) Q < 10

Palmstrm and Singh (2001)

1 > RMi > 0.1 1 < RMi < 30 ci < 100 MPa

Barton (2002) Q c = Q (ci/100)

Hoek et al. ci 100 Mpa



a = 0.160.35, (0.16 for hard rocks and 0.35 for weak rock)

b D is the disturbance factor or the effect of blast damaged stress relaxation (D = 01)

cWD is the weathering degree (14) E i and E m are in GPa, ci in MPa and H is overburden in meter

In addition, values of deformation modulus of intact rock (belonging to various lithologies) from laboratory tests are given in Table 1.

Regarding the relation proposed by Verman (1993) and Verman et al. (1997), it is assumed that the deformation modulus of the rock mass increases with RMR and tunnel depth. This depth dependency of the deformation modulus is likely to be more pronounced in weaker rock masses and is almost absent in strong, brittle rock masses, due to the effect of the confining pressure (Verman et al. 1997).

The relation given by Ramamurthy (2004) was also derived by substituting relation (38) in the following (Ramamurthy 2001):

4.2.2 Results and Discussion

The above relations were used to estimate the E m along the tunnel route (Fig. 15). It seems that the convergence of the results calculated by the E m relations is greater than the results given by the cm relations.

(2002) ci > 100 Mpa

Kayabai et al. (2003)

Gokeoglu et al. (2003)

Ramamurthy (2004)

Sonmez et al. (2004)

Zhang and Einstein (2004)

Hoek and Diederichs (2006)

(40)



Fig. 15 Estimated Em by various relations available in literature along the tunnel route

It can be concluded from Fig. 15 that the relation provided by Ramamurthy (2004) gives the lowest value of E m. Therefore, it is the most conservative relation when compared to the other relations. The relation by Singh (1997) gives the second lowest values. The other two relations, provided by Mitri et al. (1994) and Gokeoglu et al. (2003) yield the highest values of E m.

It seems that the relation by Hoek and Diederichs (2006) is more sensitive than that of Hoek et al. (2002) to the variation of D values. By increasing the D parameter from 0 to 1, the relation by Hoek and Diederichs (2006) shows more reduction than the relation by Hoek et al. (2002). In addition, the modulus values generated by the Hoek and Diederichs (2006) relation are close to that given by the relation proposed by Singh (1997) in weak lithologies.

The other relations provided by Bieniawski (1978), Serafim and Pereira (1983), and Hoek et al. (2002) generate medium values for E m. The relations proposed by Palmstrm and Singh (2001) present medium E m values, but these are not applicable for RMi > 30 and RMi < 0.1, which is the case for segment 22.

The relation provided by Kayabai et al. (2003) seems to be illogical and, when compared to



the other relations, it is basically a different relation.

Of course, the relation provided by Kayabai et al. (2003) has been modified by Gokeoglu et al. (2003). The latter also yields results totally different from the other relations, probably due to a decrease in ci values.

The two relations given by Verman (1993), Verman et al. (1997), and Singh (1997) consider the overburden as a parameter, which is a crucial factor, especially at high overburden values. These two relations overall give reasonable values of E

m.

As the overburden increases, the E m values also become higher according to both relations.

It should be recalled that determination of the deformation modulus in loading and unloading cases shall be differentiated.

5 Conclusions The rock mass along the Sabzkuh tunnel has been divided into 23 segments and classified using RMR, Q, RMi and GSI (2 methods). The GSI varies in the ranges of 2260 (Disintegrated-Blocky) and 2556, for the first and third methods, respectively. Please note that the quantification of GSI (Cai et al. 2004) is not applied in tectonically disturbed rock masses in which the structural fabric has been destroyed, such as segment 22. In such rock masses, the application of the original qualitative approach (Hoek et al. 1995) based on careful visual observations is recommended (Marinos et al. 2005).

The other systems, such as RMR and Q and RMi, evaluate the rock mass as very poor and fair, exceptionally poor and poor and low and high quality, respectively. Overall, the Q and RMi yield the most conservative and radical descriptions of rock mass, respectively.

Based on Sabzkuh tunnel data, the following relations are proposed (Table 5). The relations in the lower two rows of Table 5 are introduced for the first time in the available literature. Note the RMR value was obtained by summing the rating of all influence factors (six parameters). However, these relations may not be taken to be unique because they are related to a certain rock mass type. Moreover, the effects of anisotropy, dissolution and karstification are not considered in these relations.

Table 5 The recommended relations based on the Sabzkuh tunnel data

Equation (relation no.) r Fig. no. RMR = 5.37 ln Q + 40.48 (22) 0.73 8 RMR = 7.5 ln RMi + 36.8 (23) 0.69 9 RMi = 1.082Q 0.4945 (24) 0.73 10 RCR = 6 ln N + 33.84 (25) 0.59 11 GSI (Hoek et al. 1995 ) = 0.692 RMR89 + 22.32 (26) 0.86 12



The closest QRMR correlation to the Sabzkuh tunnel data is the Rutledge and Preston (1978).

The relations proposed by Goel (1994) and Singh (1993) estimate high values (upper bound) for cm, whereas the relations proposed by Barton (2002) and Yudbir et al. (1983) yield low values (lower bound); this shows a wide range for cm. For the upper bound relations, the variation of cm is very sensitive to variation in the input parameter.

The Ramamurthy (2004) relation gives the lowest (lower bound) value of E m, whereas the Mitri et al. (1994) and Gokeoglu et al. (2003) relations yield the highest (upper bound) values of E m.

The tunnel overburden is involved directly in E m calculations only by Verman (1993), Verman et al. (1997) and Singh (1997) relations. As the overburden increases, the E m values also become higher according to both the relations.

The relation by Hoek and Diederichs (2006) is more sensitive than Hoek et al. (2002) to the variation of D values. Moreover, the modulus values by the Hoek and Diederichs (2006) relation are similar to those generated by the Singh (1997) relation in weak lithologies.

Acknowledgments Thanks are expressed to the Mahab-Ghods Consulting Engineers Company, especially R. Banihashemi and A. Ahangaran for providing a site visit. We also thank professor Hoek, professor Palmstrm and professor Gokeoglu for providing useful points while writing this paper.

References

GSI(Hoek et al. 1995) = 0.917 GSI(Cai et al. 2004) + 3.18 (27) 0.9 13

Abad J, Caleda B, Chacon E, Gutierrez V, Hidlgo E (1984) Application of geomechanical classification to predict the convergence of coal mine galleries and to design their supports. In: 5th Inter. Cong. Rock Mech., Melbourne, pp 1519

Ajalloeian R, Hashemi M, Mogshaddas Sh (2004) The Engineering Geology Assessment of Sabzkuh Water Conveyance Tunnel Route, Central Iran, In: Viana da Fonseca & Mayne (eds) Proc. Int. Conf. on Site Characterization (ISC-2), Porto, Portugal, pp 13971402

Al-Harthi AA (1993) Application of CSIR and NGI classification systems along tunnel no. 3 at Al-Dela Descant, Asir Province, Saudi Arabia. In: Cripps JC, Coulthard JM, Culshaw MG, Forster A, Hencher SR, Moon CF (eds) The Engineering geology of weak rock. Balkema, Rotterdam, pp 323328

Aydan , Dalgi S (1998) Prediction of deformation behaviour of 3-lanes Bolu tunnels through squeezing rocks of North Anatolian Fault Zone (NAFZ). Regional symposium on sedimentary rock engineering, Taipei, pp 228233

Barton N (1995) The influence of joint properties in modelling jointed rock masses. Keynote Lecture. In: 8th Cong. ISRM, Tokyo



Barton N (2002) Some new Q value correlations to assist in site characterization and tunnel design. Int J Rock Mech Min Sci 39:185216

Barton N, Lien NR, Lunde J (1974) Engineering classification of rock masses for the design of tunnel support. Rock Mech 6(4):189236

Bhasin R, Grimstaad E (1996) The use of stressstrength relationship in the assessment of tunnel stability. Tunnel Under Space Tech 11(1):9398

Bieniawski ZT (1973) Engineering classification of jointed rock masses. Trans S Afr Inst Civil Eng 15(12):335344

Bieniawski ZT (1976) Rock mass classification in rock engineering. In: Proc. Symp. On Expl. For Rock Eng. Johannesburg, South Africa, Balkema, Rotterdam, pp 97106

Bieniawski ZT (1978) Determining rock mass deformability: experience from case histories. Inter J Rock Mech Min Sci Geomech Abstr 15:237247

Bieniawski ZT (1989) Engineering rock mass classifications. Wiley, New York, p 251

Cai M, Kaiser PK, Uno H, Tasaka Y, Minami M (2004) Estimation of rock mass deformation modulus and strength of jointed hard rock masses using the GSI method. Inter J Rock Mech Min Sci 41:319

Cameron-Clarke IS, Budavari S (1981) Correlation of rock mass classification parameters obtained from borecore and in situ observations. Eng Geol 17:1953

Deere DU, Henderson AJ, Patton FD, Cording EJ (1967) Design of Surface and near surface construction in rock. In: Proc. 8th US Symp. Rock Mech., AIME, New York, pp 237302

Edelbro C, Sjberg J, Nordlund E (2007) A quantitative comparison of strength criteria for hard rock masses. Tunnel Under Space Tech 22(1):5768

Goel RK (1994) Correlations for predicting support pressures and closures in tunnels. Ph.D. Thesis, Nagpur University, Nagpur, India, 154

Goel RK, Jethwa JL, Paithakar AG (1996) Correlation between Bartons Q and Bieniawskis RMR: a new approach. Int J Rock Mech Min Sci Geomech Abstr 33(2):179181

Gokeoglu C, Sonmez H, Kayabai A (2003) Predicting the deformation moduli of rock masses. Int J Rock Mech Min Sci 40:701710

Grimstaad E, Barton N (1993) Updating the Q-system for NMT, Int. Sym. Sprayed Concrete,



Fagernes, Norway, Norwegian Concrete Association, Oslo, Norway, pp 2028

Hashemi M, Ajalloeian R, Moghaddas Sh (2004a) Rock Mass stability analysis for underground excavation support system, the Sabzkuh water conveyance Tunnel, Iran, In: Ahmadi M (ed) 2nd edn. Iranain Rock Mechanics Conf. (IRMC2004), Tehran, IRAN

Hashemi M, Ajalloeian R, Moghaddas Sh (2004b) Rock mass characterization for underground excavation support system, the Sabzkuh water conveyance tunnel, Iran. Int J Rock Mech Min Sci 41(3):532533

Hoek E (1994) Strength of rock and rock masses. News J ISRM 2(2):416

Hoek E, Brown ET (1997) Practical estimates of rock mass strength. Int J Rock Mech Min Sci 34(8):11651186

Hoek E, Diederichs MS (2006) Empirical estimation of rock mass modulus. Int J Rock Mech Min Sci Vol 43:203215

Hoek E, Kaiser PK, Bawden WF (1995) Support of underground excavation in hard rock, A.A. Balkema, Rotterdam, p 215

Hoek E, Marinos PG, Benissi M (1998) Applicability of the geological strength index (GSI) classification for weak and sheared rock massesthe case of the Athens schist formation. Bull Eng Geol Env 57(2):151160

Hoek E, Carranza-Torres CT, Corkum B (2002) Hoek-Brown failure criterion-2002 edition, In: Bawden HRW, Curran J, Telsenicki M (eds) Proceedings of the fifth North American rock mechanics Society (NARMS-TAC 2002) symposium, Mining Innovation and Technology, Toronto, Canada, pp 267273

Hoek E, Marinos PG, Marinos VP (2005) Characterization and engineering properties of tectonically undisturbed but lithologically varied sedimentary rock masses. Int J Rock Mech Min Sci 42(2):277285

Kaiser TK, Gale AD (1985) Evaluation of Cost and Emprical Support Design at B.C. Rail Tumbler Ridge Tunnels. Canadian Tunnelling, Tunnelling Association of Canada, Wiley, New York, pp 77106

Kalamaras GS, Bieniawski ZT (1993) A rock mass strength concept for coal seams, In: Peng SS (ed) 12th Conf. Ground Control in Mining, Morgantown, pp 274283

Kayabai A, Gokeoglu C, Ercanoglu M (2003) Estimating the deformation modulus of rock masses: a comparative study. Int J Rock Mech Min Sci 40:5563

Kumar N, Samadhiya NK, Anbalagan R (2004) Application of rock mass classification system for tunneling in Himalaya, India Paper 3B 14, SINOROCK2004 Symposium. Int J Rock Mech Min Sci 41(3):531



Laufer H (1958) Classification for tunnel construction (in German). Geologie und Bauwesen 24(1):4651

Marinos P, Hoek E (2000) GSI: a geologically friendly tool for rock mass strength estimation. In: Proceeding of the GeoEng 2000. The international conference on geotechnical and geological engineering, Melbourne, Technomic publishers, Lancaster, pp 14221446

Marinos P, Hoek E (2001) Estimating the geotechnical properties of heterogeneous rock masses such as flysch. Bull Eng Geol Env 60:8292

Marinos V, Marinos P, Hoek E (2005) The geological strength indexapplications and limitations. Bull Eng Geol Environ 64:5565

Mitri HS, Edrissi R, Henning J (1994) Finite element modelling of cable-bolted stopes in hardrock groundmines. In: SME Annual Meeting. Albuquerque. New Mexico, pp 94116

Moghaddas Sh (2004) Evaluation of engineering geology characteristics of rock mass along the Sabzkuh water conveyance tunnel, M.Sc. thesis, Engineering Geology group, Department of Geology, Faculty of Science, The University of Isfahan (UI), Isfahan, IRAN, p 124

Moreno TE (1980) Application de las c1assificaciones geomechnicas a los tuneles de parjares. 11 Cursode Sostenimientos Activosen Galeriasy Tunnels. Foundation Gomez Parto, Madrid

Nicholson GA, Bieniawski ZT (1990) A nonlinear deformation modulus based on rock mass classification. Int J Min Geol Eng 8:181202

Palmstrm A (1982) The volumetric joint counta useful and simple measure of the degree of jointing, In: Proc. IV Inter. Congress of IAEG, New Delhi, 1982, pp 221228

Palmstrm A (1995) RMi: a rock mass classification system for rock engineering purposes. Ph. D. Thesis. The University of Oslo, 400

Palmstrm A (2000) Recent development in rock support estimates by the RMi. J Rock Mech Tunn Tech 6(1):119

Palmstrm A, Singh R (2001) The deformation modulus of rock masses- comparisons between in situ tests and indirect estimates tunnelling. Underground Space Tech 16:115131

Ramamurthy T (2001) Shear strength response of some geological materials in triaxial compression. Int J Rock Mech Min Sci 38:683697

Ramamurthy T (2004) A geo-engineering classification for rocks and rock masses. Int J Rock Mech Min Sci 41:89101



Rutledge JC, Preston RL (1978) Experience with engineering classifications of rock. In: Proc. Int. Tunnelling Symp. Tokyo, A3.lA3.7

Serafim JL, Pereira JP (1983) Considerations of the geomechanics classification of Bieniawski. In: Proc. of Int. Symp. Eng. Geol. Underground Construction., LNEC. Lisbon. 1, II. 33II. 42

Sheory PR (1997) Empirical rock failure criterion. Oxford IBH Publishing co. and A.A. Balkema, Rotterdam, Netherlands, p 176

Singh B (1993) Workshop on Norvegian method of tunneling. CSMRS, New Delhi, India

Singh S (1997) Time-dependent deformation modulus of rocks in tunnels. M. E. Thesis, Civil Engineering Department, University of Roorkee, India, p 180

Singh B, Viladkar MN, Samadhiya NK, Mehrotra VK (1997) Rock mass strength parameters mobalized in tunnels. Tunn Under Tech 12(1):4754

Sonmez H, Ulusay R (1999) Modifcations to the geological strength index (GSI) and their applicability to stability of slopes. Int J Rock Mech Min Sci 36:743760

Sonmez H, Ulusay R (2002) A discussion on the HoekBrown failure criterion and suggested modification to the criterion verified by slope stability case studies, Yerbilmleri. Earth Sci 26:7799

Sonmez H, Gokeoglu C, Ulusay R (2004) Indirect determination of the modulus of deformation of rock masses based on the GSI system. Int J Rock Mech Min Sci 41(5):849857

Terzaghi K (1946) Rock defects and loads on tunnel support. In: Proctor RV, White T (eds) Rock tunnelling with steel supports. Commercial Shearing co., Youngstown, pp 1599

Turul A (1998) The application of rock mass classification systems to underground excavation in weak limestone, Ataturk dam. Turkey Eng Geol 50:337345

Verman M (1993) Rock masstunnel support interaction analysis, Ph.D. Thesis, University of Roorkee, Roorkee, India, p 267

Verman M, Singh B, Viladkar MN, Jeyhwa JL (1997) Effect of tunnel depth on modulus of deformation of rock mass. Rock Mech Rock Eng 30(3):121127

Wickham GE, Tiedman HR, Skinner EH (1972) Support determination based on geologic predictions, In: Proc. Rapid Exc. Tunneling Conf., AIME, New York, pp 4364

Yudbir F, Lemanza W, Prinzel F (1983) An empirical failure criterion for rock masses. In: Proc. 5th Int. Cong. ISRM, Melbourne, vol 1. Balkema, Rotterdam, pp 131138

Zhang L, Einstein HH (2004) Using RQD to estimate the deformation modulus of rock masses. Int J Rock Mech Min Sci 41(2):337341



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