The temperature-dependent shear strength of ice-filled 1 joints in rock mass considering the effect of joint 2 roughness, opening and shear rates

. Global warming causes many rockfall activities of the alpine mountains, especially when ice-10 filled joints in the rock mass become thawed. The warming and thawing of frozen soils and intact rocks 11 was widely studied in the past several decades, however, the variation of shear strengths of ice-filled 12 joints was not fully understood. Recently, some scholars studied the thawing process and strength loss 13 of ice-filled joints at different temperatures, however, the influence of the joint roughness, opening and 14 shear rate on ice-filled joints was not systematically investigated. In this study, a series of compression-15 shear experiments were conducted to investigate the shear strength of ice-filled rock joints by considering 16 the effects of joint roughness, opening and shear rates. The shear strength quickly reduces with increasing 17 temperature, especially above -1 ℃. In addition, the shear strength decreases with increasing joint 18 openings but it increases with increasing joint roughness. When the joint opening is large enough, the 19 effect of joint roughness disappears and the shear strength of ice-filled joints is equal to that of solid ice. 20

the cool seasons because the warming and thawing of joint ice could greatly decrease the strength of rock mass containing ice-filled joints (Weber et al., 2018;Etzelmüller et al., 2022).Yang et al. (2019) claimed that the existence of detached ice block could promote the mobility of ice-rock system and thus cause a more serious geological disaster on alpine rock slope.Therefore, the warming degradation of the icerock interface and the strength loss of ice-filled joints should be comprehensively studied.
In the past decades, the warming degradation of permafrost soils was widely investigated, however, there is little literature reporting the strength loss of rocks containing ice-filled joints.The shear experiment of the ice-rock interface might be first conducted by replacing the rock with concrete in order to make a specific roughness (Davies et al., 2001(Davies et al., , 2017)).These experiments were conducted at the temperature from -5 to 0 ℃.Krautblatter et al. (2012) developed a shear strength model for the ice-filled joints that incorporates the cracking of rock bridges, the friction of rough joint walls, creep of ice and detachment of rock-ice interfaces.Mamot et al. (2018) conducted a systematic study of the shear failure of limestoneice and mica-rich interfaces at constant strain rates from -10 to -0.5℃, and they found that the normal stress and freezing temperature were two important factors influencing the shear strength.However, the uniform joint surfaces were used without considering the influence of joint roughness.Mamot et al. (2021) further predicted the warming stability of permafrost slopes containing ice-filled joints by using the Universal Distinct Element Code (UDEC).The simulation results verified that the warming temperature close to the melting point might drive the slide of a slope with angle of 50°-62°, and the actual slope angle also depended on the joint orientation.The above research mainly investigated the thawing temperature and normal stress on the shear strength of ice-filled joints.The highest normal stress is about 1.438 MPa (Davies et al., 2001), and the maximum range for the temperature was -10 ℃ to -0.5 ℃ https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.(Mamot et al., 2018).However, the freezing depth could exceed 100 m for some alpine caves containing frozen ice (normal stress large than 2 MPa) and the temperature was less than -15 ℃ as observed in the field (Colucci and Guglielmin, 2019).Therefore, a much wider range of temperature and normal stress should be considered when investigating the shear characteristics of ice-filled joints.
In addition, although some scholars began to pay attention to the mechanical properties of ice-filled joint rock mass, the influence of many important factors on the shear strength of ice-filled joints was not investigated, including the joint roughness, shear rate, normal stress and joint opening.Generally, the natural joints have different roughness and openings (Shen et al., 2020).In this study, a comprehensive shear experiment was performed on the ice-filled joints in sandstones.The main purpose was to reveal the influencing mechanism of freezing temperature, joint roughness, shear rate, joint opening and normal stress on the shear strength of ice-filled joints in rock masses.This research can provide a better understanding of the warming degradation process of the ice-filled joints and the thawing disaster of alpine mountains in cold regions.

Collection of sandstones
The red sandstones collected from Yichang city of Hubei province were used in this experiment.This is a typical sedimentary rock and is widely distributed on the surface of the earth.The block samples with approximately equal P-wave (compressional wave) velocities were chosen to make frozen samples containing ice-filled joints.The basic physico-mechanical properties of this red sandstone are given in Table 1.

Preparation of ice-filled joint rock mass
According to the JRC index proposed by Barton and Choubey (1977) ① The original rock blocks were cut into the designed rectangular blocks (100 mm × 100 mm × 50 mm) by using a rock cutting machine.
② These rectangular blocks were used to engrave different rough curves on the surface by using a 3D numerical control engraving machine.The roughness can be controlled by implanting the standard JRC curves into the controlling system of this machine.Each frozen rock sample containing an ice-filled joint was assembled by using a pair of rectangular blocks with the same roughness.
③ The rock blocks were heated in a dry oven at 105 ℃ in order to tightly paste the waterproof tape and prevent the escape of joint water during freezing.

Experimental procedures
The main objective of this study is to investigate the effect of critical factors on the shear strength of icefilled joint rock mass, including the freezing temperature, joint roughness, shear rates, joint opening and normal stress.The joint roughness is a basic index for rock joints, which is always considered when investigating other factors.Therefore, all the samples can be divided into 4 groups, namely the temperature group, shear rate group, joint opening group, and normal stress group.In the pre-test, the shear strength of the ice-filled joint does not change when the temperature is below -5 ℃, however, it greatly decreases when the temperature increases from -5 ℃ to 0 ℃.Therefore, the temperatures are set as -15 ℃, -5 ℃, -1 ℃ and -0.5 ℃, respectively.The shear rates are 0.2 mm/min, 0.4mm/min and 0.8mm/min in the shear rate group.In the joint opening group, the openings of ice-filled joints are 2 mm, 8 mm and 14 mm, respectively.The freezing depth on the earth may be small, however, it can exceed 100 m in some alpine caves, where the in-situ stress is close to 2 MPa.Therefore, in the normal stress group, the normal stresses are set as 0 MPa, 0.5 MPa, 1 MPa, 1.5 MPa and 2 MPa, respectively.Three parallel experiments were performed on each group to eliminate the discreteness of ice-filled joint samples and experiment error.There are approximately 225 ice-filled joint samples prepared in this experiment.The distribution of these ice-filled joint samples were shown in Fig. 2.
All the water-containing joints were frozen in a freeze box at a specific temperature for about 12 h, and they were used to conduct the direct shear experiment on a temperature-controlled shearing instrument under the scheduled low temperature and normal stress.A temperature sensor was implanted into the sample to accurately monitor the internal temperature change of ice-filled joint samples.When the scheduled freezing temperature was reached, the normal stress was applied with a loading rate of 0.2 kN/s.Then the shear process was performed in the displacement mode with the designed shear rate.After the shear experiment, the rupture modes of ice-filled joints were captured and analyzed by using a camera.3 Experimental results

Effect of freezing temperature and joint roughness
In the temperature group, freezing temperatures were set as -15 ℃, -5 ℃, -1 ℃ and -0.5 ℃, and the joint roughness was named by the profile number in  with increasing the freezing temperature, because the bonding strength between ice and joint surface becomes to be weaker, and the shear rupture happens along the ice-rock interface instead of solid ice when the freezing temperature is larger than -0.5 ℃.
In addition, when the freezing temperature is close to 0 ℃, the pre-melting of ice-rock interface induced by the normal stress will cause a reduction of bonding strength.Therefore, the shear strength between bonded ice-rock interfaces is much smaller than the shear strength of solid ice at a high freezing temperature close to the melting point of bulk ice, such as -0.5 ℃.It should be noted that the aggregation phenomenon of rupture ice disappears when T = -0.5 ℃ because the high-temperature ice is ductile failure along the ice-rock interface instead of the joint ice itself.However, the climbing effect still makes a significant contribution to the increase of shear strength.The peak shear displacement and normal displacement also are dependent on the freezing temperature (Table 3 and Table 4).With the increase of freezing temperature, the peak shear displacement increases because the joint ice will change from brittle to ductile (Bragov et al., 2015).Ice is brittle at -15 ℃ and -5 ℃, so the maximum shear displacement before failure is small at this temperature and the shear failure mode displays brittle characteristics.When the temperature increases to -1 ℃, the solid ice becomes to be ductile, therefore a larger shear displacement arises before failure.However, the shear dilatancy reduces with increasing the freezing temperature.Solid ice is a kind of temperature-dependent material, the elastic modulus of which almost linearly decreases with increasing the freezing temperature (Sinha, 1989;Han et al. 2016).The inhibition of normal stress on the shear dilatancy is greater at the high freezing temperature during shear process.
Several typical shear stress-displacement and normal-shear displacement curves for the profile of No. 4 are plotted in Fig. 8.The ice-filled joint shows significant residual shear strength beyond the peak point, which slightly decreases with increasing shear displacement.This residual shear strength is caused by the friction effect between the upper and lower ice-filled blocks.In addition, the normal shear dilatancy displays increasing trend with shear displacement, which is caused by the climbing effect of ice-filled joints.It should be noted that the shear strength has a second rising point at the residual strength stage, because the shear rate is increased from 0.2 mm/min to 1 mm/min in order to accelerate the completion of the shear process.Schulson and Fortt (2012) claimed that the friction between ice interfaces increases   Another finding is that the JRC is not suitable to interpret the influence of joint roughness on the shear strength of ice-filled joints, because the peak shear strength does not monotonically increase with increasing JRC index.The peak shear strength displays an increase-decrease-increase-decrease trend against JRC from No. 2 to No. 10 (Fig. 4). Figure 9 shows that the peak shear strength displays a linear increasing trend with increasing aggregation areas of fragmented ice after failure.The aggregation area of fragmented ice can be treated as the effective climbing area which makes a significant contribution to the improvement of shear strength, because the fragmented ice is produced under compression-shear https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.
stress in the process of climbing the steep bulges.As a consequence, only these steep bulges causing aggregation of rupture ice contribute to the improvement of shear strength.The variation law of shear dilatancy against the roughness also is in accordance with the shear strength of ice-filled joints, but it is different from the change law of JRC (Table 4).In Fig. 6, the gathering of fragmented ice mainly arises in the front of the steepest bulge.It illustrates that the improvement of shear strength of joint ice is caused by a part of the steepest bulge instead of the total roughness.Therefore, JCR may be not suitable for the prediction of shear strength of ice-filled joints.For example, although the JCR of No. 6 is much larger than No. 4, the effective steep bulge to cause ice aggregation after failure is smaller than that of No. 4 (Fig. 7).This phenomenon confirms that the improvement of shear strength is only caused by some noticeable steep bulges instead of the total bulges.

Effect of shear rates
The shear rates have significant effects on the strength of solid ice as observed in the previous literature (Petrovic, 2003).Low shear rates are used to conduct quasi-static shear experiments, including 0.2 mm/min, 0.4 mm/min and 0.8 mm/min.Figure 10 shows that the peak shear strength slightly decreases with increasing shear rates.Solid ice is a kind of typical elasto-plastic material.When the shear rate is slow, the ice crystal has enough time to shear slip and it will present ductile failure characteristics.At a low shear rate, the free water on the slip interface will reorganize at the water-ice interface to form ice, however, it is hard for the ice crystal to adjust to adapt the shear slip at high shear rates, which will cause the shear rupture of ice crystals and hinder the growth of ice on the water-ice interface (Lou et al., 2019).
Figure 11 shows that a high shear rate will induce brittle failure of joint ice and more fragmented ice crystals are produced.As a result, the shear strength reduces with increasing shear rates from 0.2 mm/min to 0.8mm/min.The previous literature shows that there is a critical loading rate for the transition from ductile to brittle behavior of polycrystalline ice (Timco and Frederking, 1982;Gold, 2018).In this study, the transition point of ice-filled joint is not definitely derived due to the limitation of the shear rate range.

Effect of joint openings
Joint opening is another critical factor influencing the shear strength of ice-filled joints.The maximum height difference of the standard JRC curves suggested by Barton and Choubey (1977)  No. 10, respectively.The joint openings are chosen as 2 mm, 8 mm and 14 mm because 2 mm is smaller than all the maximum height differences while 14 mm is much larger than them.The rupture characteristics of joint ice against the joint opening are plotted in Fig. 12.When the joint opening is 2 mm, the aggregation phenomenon of rupture ice is evident.However, the aggregation phenomenon disappears for the profiles of No. 2, No. 4 and No. 6 when the joint opening is 8 mm.When the joint opening increases to 14 mm, there is not any aggregation of rupture ice arising for all the joints.Figure 13 shows that when the joint opening increases from 2 mm to 14 mm, the shear strength of ice-filled joints decreases.The shear strength of pure solid ice also is measured in the laboratory, which is that the critical filling thickness for the profiles of No. 8 and No. 10 should be larger than 8 mm but smaller than 14 mm.There is aggregation ice arising before large bulges, and these large bulges would prevent the direct shear failure of joint ice and improve the shear strength.
The influence of joint opening and roughness on the shear strength can be explained by using the shear failure path of ice-filled joints as shown in Fig. 14.When d=2 mm, the shear climbing will occur before some large bulges for all the joint profiles.This climbing action induces the aggregation of rupture ice and change of shear path.As a consequence, the shear strength will improve.When d=8 mm, the shear failure path will not be disturbed for the profiles of No.

Effect of normal stress
The normal stress group was used to investigate the effect of normal stress on the shear strength of icefilled joints, including 0 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa and 2.0 MPa.The shear strength of ice-filled joints displays a significant increasing trend with increasing normal stress (Fig. 16).The Mohr-coulomb criterion may be used to express the relationship between the shear strength and normal stress as below: tan Where p  = shear stress on plane, n  = normal stress on plane, j c = cohesion of ice-filled joints, j  = internal friction angle of ice-filled joints.
Figure 16 shows Mohr-coulomb criterion can be well used to calculate the shear strength of ice-filled joints against the normal stress.The shear rupture modes of the joint ice are given in Fig. 17 The test results show that the shear strength of smooth ice-rock bonding interface is larger than that of pure solid ice at the freezing temperature from -15 to -0.5 ℃ (Fig. 20a).It implies that the shear failure should be inside the solid ice instead of ice-rock interface.When the freezing temperature increase from -1 ℃ to -0.5 ℃, the shear strengths of the ice-rock interface and the solid ice reduce very quickly.Jia et al. ( 2015) also claimed the same change law of solid ice against the temperature.
However, the experimental results show that the shearing failure of many rough ice-filled joints at -0.5 ℃ is the debonding of ice-rock interfaces (Figs. 5,11,12,17).More shear experiments were carried out on rough ice-rock interfaces with profiles of No. 4 and No. 8 on the same experimental condition (σn = 0.5 MPa, v = 0.2 mm/min).It shows that the shear strength of rock-ice-rock "sandwich" is a little larger than that of ice-rock interface, although the change laws of them against temperature are very similar.Another novel finding is that the shear strength of ice-rock interface is larger than the shear strength of solid ice itself below -1 ℃ (Fig. 20b).Therefore, the shear failure below -1 ℃ displays the cracking of joint ice instead of ice-rock interface, and some aggregation areas of rupture ice occur before large bulges (Figs. 5,11,12,17).However, the shear strength of solid ice is larger than that of ice-rock interface above -1 ℃.This is the main reason for the shear failure of rough ice-filled joints along ice-rock interfaces at -0.5 ℃.The freezing temperature of -1 ℃ is the transition point of shear failure modes.Figure 21 presents that the shear failure is along the ice-rock interface when the freezing temperature is approximate -0.5 ℃, however, the area of ice attached to the joints has a great increment with the decrement of freezing temperature from -0.5 ℃ to -15 ℃.It further illustrates that the shear strength of rough ice-rock interface is larger than that of the solid ice below -5℃.Mamot et al. (2018)  Actually, the roughness is another important factor influencing the shear strength of ice-filled joints, which can improve the ability to resist the shear slide of joints (Fig. 22).The shear strength of the No. 2 ice-filled joint is much smaller than that of No. 8 and No. 10 joints.For the profile of No. 2, the shear strength of ice-filled joint is approximately equal to that of the solid ice when the normal stress is less than 1.5 MPa, because the joint opening of 2 mm also is very close to the maximum height difference.
Therefore, the joint opening will determine the effect of joint roughness.However, the shear strength of solid ice is much smaller compared with the shear strength of ice-filled joints when the normal stress is 2 MPa.It is observed that this normal stress has caused some vertical micro-cracks inside the solid ice.
For the ice-filled joints, the compression damage maybe not remarkable, because both the adhesion of ice-rock interface and bulges will prevent the lateral expansion of solid ice under high normal stress.A larger roughness may provide a much stronger confining effect on the lateral expansion.Although the shear strength increases with increasing JRC number in general, the quantitative relationship between them are hard to determine.Figure 4 shows that the change of shear strength against the JRC number is fluctuating.A novel finding of this study is that the aggregation area of rupture ice before large bulges can be well used to predict the shear strength of ice-filled joints.However, it should be noted that a new index of roughness should be proposed in future research in order to build the shear strength model considering joint roughness.
In addition, if the joint opening exceeds the critical value, the influence of joint roughness on the shear strength of ice-filled joints will disappear.For example, when the thickness of joint ice exceeds 14 mm, the shear strength of all the ice-filled joints is equal to the shear strength of infilling ice.

Potential application for prediction of rock avalanches in a warming climate
In recent years, there are many large rock avalanches occurred in the Alps.The rock avalanches that occurred on the Brenva galcier, the Punta Thurwieser and the Drus are some of the recent examples, which have strong impacts on the high mountain infrastructure stability and landscape evolution (Mamot et al., 2018).The rock avalanches are related to the degradation of bedrock permafrost and ice-filled joints.Our study shows that the peak shear strength of ice-filled joints increases with the increase of roughness and normal pressure.This implies that the rockfall will be more stable with higher roughness and normal pressure.In addition, when the joint openings increase, the peak shear strength will decrease, https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.and large joint openings will reduce the effect of joint roughness.The peak shear strength of ice-filled joints decreases with the increase of freezing temperature.Moreover, when the freezing temperature is close to 0 ℃, the pre-melting of ice-rock interface induced by the normal stress will cause a reduction of bonding strength.This result can explain the phenomenon that the boundary of ice-filled joint between frozen and unfrozen become unstable, especially in summer.The peak shear strength of ice-filled joints decreases with the increase of shear rate.It is hard for the ice crystal to adjust to adapt the shear slip at high shear rates so the rockfall may happen.
As the global temperature rises, collapse disasters of ice-filled rock mass caused by warming and thawing often occur in permafrost regions.A constitutive model can be further constructed according to the experiment results.Then combining with a numerical software, this constitutive model can be used to predict the disaster of rock avalanches in the cold region in the future research.Although Mamot et al. (2018) has established a constitutive model for joints, the constitutive model only considers temperature and normal stress, however, the influence of the joint roughness, opening and shear rate is ignored.Through our study, it is evidenced that the joint roughness, shear rate, joint opening and temperature are physical quantities that must be considered in the constitutive model.A constitutive model including these physical quantities will be proposed in our future research.

Conclusions
Above all, this study has provided a comprehensively experimental study on the shear process of icefilled joints, considering the influence of freezing temperature, joint roughness, shear rate, joint opening and normal stress.The following conclusions can be drawn based on this research: (1) The shear strength of ice-filled joints decreases with increasing temperature.The shear failure mode change from shear cracking of joint ice to the debonding of ice-rock interface when the temperature increases to -0.5 ℃, because the bonding strength of ice-rock interface is less than that of solid ice at -0.5 ℃ (v = 0.2mm/min, σn = 0.5 MPa).
(2) The joint roughness can improve the shear strength of ice-filled joints.The shear strength of ice-filled joints linearly increases with increasing the aggregation area of rupture ice before some large bulges.
However, the relationship between the JRC index and the shear strength is poor.In addition, the effect of joint roughness is related to the joint opening and normal stress.
(3) The shear strength of ice-filled joints decreases with increasing joint opening.When the joint opening increases from 2 mm to 14 mm, the aggregation of rupture gradually disappears and the shear strength of ice-filled joint is equal to that of solid ice.Therefore, the joint roughness does not make any contribution to the shear strength when the joint opening exceeds a critical value, which is related to the maximum height difference of joint surface.
(4) The shear strength of ice-filled joints decreases when the shear rate increase from 0.2 mm/min to 0.8 mm/min.The infilling ice will change from ductile failure to brittle failure by observing the rupture ice on the joint surface.The aggregation area of rupture ice also decreases while the brittle rupture phenomenon is more serious with increasing shear rate.
(5) The shear strength of ice-filled joints linearly increases with increasing normal stress, which well satisfies the Mohr-coulomb criterion.The aggregation area of rupture ice also increases with increasing normal stress.In addition, the improvement of shear strength of the ice-filled joints caused by normal https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.
stress is much larger that of solid ice, because the bulges of the joint surface can prevent the lateral expansion of ice under compression.

⑤
https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.④ The joint opening was divided into different specified thicknesses which were controlled by 100 inserting rubber strips, and a piece of waterproof tape was pasted on the surface in order to store water.101 When the waterproof tape was tightly bonded on the rock surface, liquid water should be injected 102 into the artificial joint until no water leaks out.After that, the water-filled joint rock mass was put into a 103 steel mold to freeze in a freezing chamber.The steel mold was used to control the joint opening because 104 the volume of joint water would expand during freezing.Then ice-filled joint samples can be derived 105 after freezing at -20 ℃ for 12 h.The manufacturing procedure and related ice-filled joint samples were 106 shown in Fig. 1.

Figure 2 .
Figure 2. Distribution of rock samples containing ice-filled joints.T: Temperature.v: Shear rates.d: Joint openings.

Figure 3 .
Figure 3. Shear experiment procedure and equipment 140

Fig. 5 .
There are several aggregation regions of rupture ice close to large climbing bulges on the surface of joints.The peak shear strength of ice-filled joints is related to the aggregation area of rupture ice; because a large shear force is required to promote the solid ice to shear slide along the slope of bulges.The aggregation area and location along the rough profile of joints after shear failure are plotted in Fig.6.It can be observed that the aggregation ice appears before several high bulges and the aggregation location is almost independent of the freezing temperature if aggregation ice occurs.The climbing bulges in front of the aggregation ice are noticeable and influential.It implies that the influence of joint roughness on the shear strengths of these ice-filled joints may be only controlled by several noticeable bulges instead of the JRC index.Figure 7 shows that the shear strengths of No. 6 and No. 10 display obvious reduction trends, which may be in accordance with the ice aggregation area.The ice aggregation area decreases https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.

Figure 4 .
Figure 4. Shear strength against joint roughness at different freezing temperatures.Experimental condition: v = 0.2

Figure 5 .Figure 6 .
Figure 5. Shear rupture modes of ice-filled joints at different freezing temperatures.The yellow lines show the main aggregation of rupture ice.Ice after rupture will aggregate in roughness bulges perpendicular to the shear direction.

Figure 7 .
Figure 7. Aggregation area of rupture ice increases with the reduction of freezing temperature.Experimental https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.when the shear rates increase from 0.06 mm/min to 0.6 mm/min.Therefore, the sudden rise of residual 209 shear strength can be attributed to the accelerated shear rate.210 211

Figure 8 .
Figure 8. Shear strength and normal displacement versus the shear displacement for the profile of No. 4 in the

Figure 9 .
Figure 9. Peak shear strength linearly increases with increasing aggregation areas of rupture ice.Experimental

Figure 11 .
Figure 11.The shear rupture characteristics of joint ice under different shear rates.Experimental condition: T = - approximately 0.83 MPa on the condition that T = -5 ℃, v = 0.2 mm/min and σn = 0.5 MPa.When the joint opening is 14 mm, the shear strengths of ice-filled joint are approximately 0.83 MPa and they are independent of the joint roughness.When the joint opening is 8 mm, the shear strengths of ice-filled joint are very close to the shear strength of pure solid ice (0.83 MPa) for the joint of No. 2, No. 4 and No. 6.The reason is that 8 mm has exceeded the critical filling thickness of these joints (No. 2, No. 4 and No. 6), therefore the shear strength of these ice-filled joints is only controlled by the solid ice instead of joint roughness.In addition, there is not any significant ice aggregation on the joint surfaces of No. 2, No. 4 and No. 6 when the joint opening is 8 mm, and the shear failure happens inside the joint ice.However, for the ice-filled joints of No. 8 and No. 10, the shear strengths are larger than 0.83 MPa, which illustrates https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.
2, No. 4 and No. 6, however, the shear failure path changes due to the climbing action for the profiles of No. 8 and No. 10, in which a significant aggregation of rupture ice is produced.Therefore, the shear strengths of ice-filled joints for the profiles ofNo.2, No. 4 and No. 6  are approximately equal to the solid ice, while the shear strengths for the profiles of No. 8 and No. 10 are much larger than 0.83 MPa.When d = 14 mm, the shear failure happens inside the joint ice for all joint profiles, therefore, the shear failure path and shear strength will not be influenced by the joint roughness and no aggregation of rupture ice occurs.The shear dilatancy deformation of the ice-filled joints in Fig.15has further proved the climbing actions, including all the profiles with joint opening of 2 mm, and the profiles of No. 8 and No. 10 with joint opening of 8 mm.The climbing effect of the No. 2 ice-filled joint with opening of 2 mm is not remarkable, therefore the shear dilatancy is very small and the shear strength also is close to pure solid ice (0.83 MPa).Regardless of the critical filling thickness, the present study shows that the shear strength of ice-filled joints decreases with increasing joint openings from 2 mm to 14 mm, and it is related to the joint roughness below the critical infilling thickness.When the filling ice exceeds the critical thickness, the shear strength https://doi.org/10.5194/tc-2022-155Preprint.Discussion started: 10 October 2022 c Author(s) 2022.CC BY 4.0 License.ofice-filled joints is equal to the shear strength of solid ice under the same condition.It should be noted that the critical filling thickness for each roughness will be determined in future studies.

Figure 12 .Figure 13 .
Figure 12.The shear rupture characteristics of ice-filled joints with different openings.Experimental condition: T =

Figure 20 .Figure 21 .
Figure 20.Influence of freezing temperature on the direct shear strength of ice and ice-filled joints.Experimental399

Table 3 .
The peak shear displacement at the peak points of shear strength (mm) 212