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Technical Note

Suction-Controlled Ring Shear Test of the Silt and Concrete Interface

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02 April 2024

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04 April 2024

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Abstract
The interface of a structural system in the soil is usually unsaturated. A decrease in the shear strength of the soil-structure interface can degrade the structure, especially under humid conditions. Studying the shear characteristics of the silt-concrete interface using a shear apparatus. Suction-controlled ring shear tests were carried out on the silt-concrete interface for three interface roughness values. The influence of the matric suction (s) and interface roughness (R) on the shear strength index of the silt-concrete interface was analyzed. The test results showed that high values of s and R improved the shear strength of the interface, but the result was affected by the net normal stress (NNS). High values of NNS and R improved the strain-hardening characteristics. NNS, s, and R significantly affected the interface shear shrinkage. The internal friction angle of the saturated interface was smaller than that of saturated silt, whereas the opposite occurred in the unsaturated state. The cohesion and internal friction angle of the interface rose with an increase in R, and they were larger than that of silt. A shear strength model of the silt and interface was established.
Keywords: 
Subject: Engineering  -   Civil Engineering

0. Introduction

The shear characteristics of the soil-structure interface are critical to the design of structures in the soil (such as pile foundations, retaining walls, and soil nails). The interaction between the soil and the structure significantly influences the bearing capacity and stability evaluation of geotechnical engineering. The interface shear test is a direct and simple method widely used to study the shear characteristics of the soil-structure interface ( Li et al., 2021a). The interfaces of most structural systems in the soil are usually unsaturated, and external factors, such as temperature and humidity, affect the matric suction. In particular, humid conditions at the interface alter the matric suction, decreasing the shear strength of the soil-structure interface, deteriorating the structure, and reducing its operating performance.
Researchers have studied the shear characteristics of unsaturated interfaces using suction- and stress-controlled direct shear tests (Borana et al., 2016; Hamid and Miller, 2008; Hossain and Yin, 2012). Peng et al. (2022) performed direct shear tests on the interface between unsaturated soil and steel plates, considering the influence of matric suction and interface roughness. However, due to the limited strain range of the direct shear instrument, it cannot accurately reflect the deformation and failure law of the soil-structure interface after long-distance shearing. Various methods, including direct shear ( De et al., 2022; Borana et al., 2016; Chen et al., 2015; Shi et al., 2020), simple shear (Hossain and Yin, 2015), and ring shear (Sheng et al., 2020) test have been employed to investigate the soil-structure interaction. These studies examined the impact of the water content, stress state, freeze-thaw cycles and temperature, cyclic load (De et al., 2022; Yin et al., 2020; Ravera et al., 2022; Shi et al., 2020; Rui et al., 2020a), and other factors on the interface shear strength and shear strength parameters. Most studies focused on sand, silt sand, and cohesive soil ( Kou et al., 2021; Konkol et al., 2021; De et al., 2022; Chen et al., 2015; Shi et al., 2020). For example, Li et al. (2021c) experimentally studied the interface shear behavior between microbially induced calcite precipitation (MCIP)-treated calcareous sand and steel under different cementation degrees and normal stress conditions . Pei et al. (2021) conducted ring shear tests using loose and dense sand with different roughness values. Monotonic shear tests were performed at the steel interface. Qu et al. (2021) conducted large-scale direct shear tests on the freeze-thaw interface of unsaturated coarse-grained soil using a temperature control system. It is noted that researchers have conducted suction-controlled direct shear tests (Borana et al., 2016). Nonetheless, the shear displacement of the direct shear instrument is limited. The shear area remains the same during the ring shear test (Hong et al., 2009). The shear testing equipment is capable of subjecting the soil specimen to rather large strains. The residual shear stress state in the field can be accurately simulated in the laboratory (Patil et al., 2020). However, a lack of data exists on the silt-structure interface characteristics in suction-controlled shear tests.
The interface of a structural system in the soil is usually unsaturated. Therefore, it is crucial to study the influence mechanism of matric suction on the silt-structure interface under humid conditions. The shear characteristics of the silt-concrete interface were analyzed, and the influences of the net normal stress (NNS), matric suction (s), and interface roughness (R) on the shear stress-shear displacement relationship were investigated. Estimating the shear strength of the unsaturated soil interface is essential in geotechnical engineering (Escario et al., 1986; Fredlund et al., 1978; Borana et al., 2015). Therefore, a calculation model of the interface shear strength index was established. The research results improve our understanding of the unsaturated silt-structure interface in practical applications.

1. Laboratory Tests

1.1. Test Materials

1.1.1. Test Soil

The silt was obtained from a foundation pit engineering project in the Zhongyuan District of Zhengzhou City. The physical and mechanical properties of the silt are listed in Table 1, and the particle size distribution is shown in Figure 1. From Figure 1, it can be seen that the test soil is a typical silt, and its particle size is mainly concentrated in the range of 0.05 to 0.075 mm (approximately 57.8%). So, the test soil is poorly graded silt (fine-grained soil). The sample preparation process is illustrated in Figure 2.

1.1.2. Concrete Interface

The original device is only suitable for ring shear tests on the soil itself. The interface between the silt and concrete is sheared in the test. Thus, the upper load plate was improved (Figure 3). The water to sand to cement ratio was 1:4.26:0.8, and we used 42.5 ordinary Portland cement. Concrete structural surfaces with different roughness values were obtained by changing the particle size of the sand and gravel. The roughness calculation equation used was as follows (Li et al., 2022):
Preprints 102953 i001
where V0 is the volume of sand on the surface of the structure, mm3 ; A0 is the structure surface area, mm2.
We assessed concrete interfaces with three roughness values (Figure 4).

1.2. Test Apparatus

We used the SRS-150 unsaturated soil dynamic ring shear apparatus (GCTS company, United States) (Figure 5). This apparatus is only suitable for ring shear tests of soil. We performed a suction-controlled unsaturated ring shear test. The PCP-15U pressure plate was used to measure the matric suction. A GDS unsaturated triaxial apparatus and a GDS conventional triaxial apparatus were used in the triaxial tests.

2. Test Conditions

The mechanical properties of the interface between unsaturated silt and concrete under suction control were analyzed. The NNS (σn-ua) values were 100 kPa, 200 kPa, and 400 kPa. The mechanical properties of the soil at low matric suction (0-400 kPa) are of interest in practical applications (Gan et al., 1988; Naghadeh et al., 2019). Therefore, the matric suction values (ua-uw) of the unsaturated triaxial test were selected as 0, 50, 100, 200 kPa. When conducting shear tests on interfaces with different roughness on silt, the roughness of the contact surface should not be excessive (Li et al., 2022a). The interface roughness (R) values were 0.11 mm, 0.37 mm, and 0.54 mm. The shear rate has a negligible effect on the interface shear strength at rates of less than 0.1 mm/min. Thus, a shear rate of 0.02 mm/min was selected (Li et al., 2022b; Bhat et al., 2013). The shear displacement of the interface between the silt and concrete reached the peak strength at about 4 mm and was stable. Therefore, a shear displacement of 10 mm and a shearing time of 500 min were used. An unsaturated triaxial test with constant water content and a conventional triaxial test with consolidated undrained conditions were used to calculate the shear strength parameters of silt. The types of silt-concrete interface shear tests are listed in Table 2, and the types of silt shear strength tests are listed in Table 3.

3. Results

3.1. Interface Shear Properties

Figure 6, Figure 7, Figure 8 and Figure 9 show the test results for different values of the NNS, matric suction, and interface roughness, respectively.
(1)
Effect of net normal stress (NNS)
Figure 6 shows the silt-concrete interface shear results for different NNSs and matric suctions at an interface roughness of 0.11 mm. The shear stress of the specimen increases with the horizontal displacement (Zhang et al., 2020b). The shear stress stabilizes when the horizontal displacement reaches a critical value, which is consistent with a large-scale direct shear test result (De et al., 2022). The critical value and initial shear stiffness increase with the NNS ( Li et al., 2021; Zhang et al., 2020b; Rui et al., 2020b). The NNS has a significant effect on the interface shear stress. As the NNS increases, the soil at the interface is compacted, the contact surface between the silt particles and concrete increases, and the interface friction coefficient increases. Therefore, the shear displacement required to achieve a stable shear stress is larger, and the shear strength at the interfaces increases.
When the suction is 200 kPa, shear dilation occurs at the interface at lower NNS, and shear shrinkage and dilation are observed at higher NNS (Figure 6d). The shear shrinkage is significant at low matric suction; the higher the matric suction, the more significant the dilatancy. The larger NNS, the greater the volume shrink and the smaller the shear dilatancy (Qu et al., 2021). When the matric suction is low, and the NNS is high, the silt particles are broken during the shearing process, and the particle may be damaged or ruptured, resulting in an increase occlusal friction and soil compression. During the interface shearing process, the soil grains tend to rearrange and possibly roll over the concrete counterface as a result causing dilation (Borana et al., 2015).
Figure 7 shows the silt-concrete interface shear results for different NNSs and roughnesses at matric suction of 50 kPa. The NNS has a significantly greater impact on the interface shear strength than R. The interfaces exhibit shear shrinkage. As shown in Figure 7(a), weak strain-softening occurs at lower NNS, whereas strain-hardening is observed at NNS of 400 kPa.
(2)
Effect of matric suction (s)
Figure 8 shows the silt-concrete interface shear results for different NNSs and s when R is 0.11 mm. The increase of s significantly increases the interface shear strength (Li et al., 2021; Borana et al., 2015; Borana et al., 2016). The interface shear strength of unsaturated soil is significantly higher than that of saturated soil. As the NNS increases, the effect of s on the interface shear strength is improved, and a nonlinear relationship exists between s and the residual shear strength. As s increases, the bound water film on the surface of the soil particles becomes thinner, and the cementation effect of the soil particles increases. As the contact area between the soil and concrete increases, the interface friction and the interface shear stress increase. All shear stress-displacement curves do not exhibit softening characteristics for higher matric suction. These results are different from the research observations of Li et al. (2021) for the silt.
The interface shear shrinkage tends to exhibit shear dilatancy as s increases, which is similar to the findings of Borana et al. (2015); however, this trend decreases with an increase in the NNS. The effect of the NNS on shear dilatancy is greater than that of s; therefore, the NNS has a larger influence on the interface strength than s. The preparation of remolded soil samples requires pre-compaction. Part of the force during the test compacts the soil samples compacted, and the other part is transformed into potential energy. During the shear test, the soil sample structure is destroyed during the shear test, releasing the potential energy and resulting in the volume expansion of the soil sample. When the NNS is high, the expansion force cannot offset the NNS; thus, the volume expansion is limited. This phenomenon can be explained according to the test conclusions drawn by Yu et al. (2022). The curves of shear stress-horizontal displacement for interfaces indicate gradual hardening behavior at higher suction and partial hardening/ softening behavior at lower suction, which is contrary to the results on completely decomposed granite soil by Borana et al. (2016).
(3)
Effect of interface roughness (R)
Figure 9 compares the silt-concrete interface shear results for different NNS and R values, with a constant s value of 50 kPa. The interface with greater R gains a higher peak shear strength value, which was consistent with the conclusion of the other shear test (Borana et al., 2016; Yu et al., 2022). As R increases, the friction and bite force at the interface between the silt and concrete increase, causing the formation of a thicker shear band, which requires a greater force to produce relative displacement (Li et al., 2021). Additionally, the interface shear stress and vertical deformation increase. The contribution of R to the interface shear stress depends on the NNS level. When the NNS is high, the contribution is significant.
Strain-softening occurs when R is 0.11 mm (Figure 9(a) and(b)), and strain-hardening is observed when R is 0.37 and 0.54 mm, indicating that high value of R results in strain-hardening, which is contrary to the law of the dense sand (Pei et al., 2021). As R increases, the shear shrinkage becomes more significant (Li et al., 2021). However, due to the higher NNS, the soil is compacted, reducing its compressibility (Borana et al., 2016). The difference in the shear shrinkage of the specimens at different R values is small when the NNS is 400 kPa.

4. Discussion and Analysis

4.1. Interface Shear Strength

The test results show that the stress-strain curve has no significant peak, and a negligible difference is observed between the peak stress and the residual stress. Therefore, we analyzed the effect of matric suction and interface roughness on the residual effective cohesion and internal friction angle of the interface. The relationship between the residual shear strength of the silt-concrete interface and the NNS is fitted as follows:
τr = σ0 tanφ0+c0
where τr is the residual shear strength of the interface (kPa), σ0 is the net normal stress (kPa), φ0 is the effective internal friction angle of the interface (°), and c0 is the effective cohesion of the interface (kPa).
Figure 10 shows the fitted relationship between the interface residual shear strength and NNS under different s values for R = 0.11 mm. The effect of matric suction on the residual effective cohesion and effective friction angle of the interface residual shear strength is shown in Figure 11.
The results in Figure 10 show that the residual shear strength of the interface increases with the increase in s and NNS. The results were consistent with the direct shear test results (Li et al., 2021; Yu et al., 2022). When NNS is consistent, a nonlinear correlation is present between matric suction and residual shear strength of the interface.
Figure 11 shows that as s increases, c0 exhibits a significant nonlinear growth with a decreasing growth rate, demonstrating that s contributes significantly to cohesion within a certain range (Marinho et al., 2020). As the matric suction increases, the amount of weakly bound water around the silt particles decreases, and the level of cementation of insoluble salts increases. The water film becomes thinner, increasing the molecular attraction between the soil particles, resulting in increased cohesion (Qu et al., 2021). As s increases, φ0 generally increases. φ0 is very small in the shear stage of the saturated silt and concrete interface. φ0 exhibits no significant change in the unsaturated state, which is similar to the result for the silty sand and the medium-coarse sand interfaces (De et al., 2022), and the matric suction has a negligible effect. However, the matric suction has a significant effect on φ0 at low values (0-50 kPa).
In summary, the effective shear strength index of the interface is significantly different in the unsaturated and saturated states, and the contribution of the matric suction to c0 is much larger than that of φ0.
Figure 12 shows the fitted relationship between the interface residual shear strength and NNS under different R values for a matric suction of 50 kPa. The changes in c0 and φ0 with a change in the interface roughness are shown in Figure 13.
Figure 12 indicates that the interface residual shear strength increases nonlinearly as the interface roughness increases (Yu et al., 2022). The contribution of the interface roughness to the interface residual shear strength strongly depends on the NNS level. The contribution is larger at a higher NNS.
Figure 13 shows that c0 and φ0 increase with the R nonlinearly, but the growth rate of c0 is higher. The growth rate gradually decreases (Pei et al., 2021). The main reason is that the interface roughness increases, causing more soil particles to be embedded in the concrete groove, enhancing the interlocking between the soil and the soil in the groove (De et al., 2022; Zhang et al., 2020a). The friction between the soil and the smooth part of the concrete is weakened, but the interlocking is enhanced in the groove, causing a slight increase in φ0.
The effective cohesion is more affected by the change in suction. However, it seems that the interface roughness plays an important role on the change of cohesion. Although the silt-concrete interface presents the highest cohesion for high suction, its value rapidly decreases with the reduction in suction. The similar phenomenon had been reported in other research papers (Marinho et al., 2020).

4.2. Comparison of Silt Strength and Interface Shear Strength

The shear strength indicators of the silt and the silt-concrete interface (S-I) for different matric suction and interface roughness values were analyzed. Figure 14 shows the shear strength indexes of the silt and S-I for different suction (R=0.11 mm). Figure 15 depicts the shear strength indexes of the silt and S-I for different R values (s=50 kPa).
As s increases, the difference in cohesion is not significant, and a linear relationship is observed (Figure 14). However, a significant difference in the internal friction angle between silt and interface occurs. Matrix suction predominantly affects the moisture content of the silt, thereby influencing the silt cohesion and consequently impacting the cohesion of interface. It is likely that the high proportion of silt particles in the concrete grooves caused the shear zone is within the silt and it appears not to follow the actual interface with the concrete. This is similar to the findings of other researchers (Borana et al., 2015; Marinho et al., 2020). Therefore, the interface shear behavior is similar to the shearing of the silt. The interface cohesion depends on the soil type. As the state changes from saturated to unsaturated, the internal friction angle of S-I increases, whereas that of the silt decreases slightly. This may occur due to an increase in matric suction, which reduces the amount of pore water and increases the pore space (Wang et al., 2022). An increase in the contact area between the soil particles and the interface increases the friction force and the internal friction angle. However, the soil particles are broken and redistributed, reducing the interlocking between the soil particles and the internal friction angle of the silt. The interfacial shear strength decreases with the decrease in the unsaturated soil matric suction (Wang et al., 2022). It is noted that whether it is silt or silt-concrete interface. The cohesion increased significantly with the matric suction , but the internal friction angle fluctuated in a small range and exhibited no significant change. The internal friction angle of the saturated silt interface is observed to be lower than that of the silt, demonstrating a significant relationship with the critical value for the matrix suction. Interestingly, as matrix suction progressively increases, the internal friction angle of the interface will gradually align with that of the silt.
Figure 15 shows that the difference in the cohesion and internal friction angle between S-I and the silt is very small when R is 0.11 mm. As R increases, the cohesion and internal friction angle of S-I increase. The shear strength of S-I was found to be greater than of the silt (Li et al., 2021b). The reason is that the microscopic concave-convex structures between the contact surfaces come into more as R increases, increasing the contact area between the surfaces, the bite force, the friction force, and the internal friction angle. The cohesion increases due to the more capillary contacts of the soil with the interface. A rough interface produces higher cohesion and friction force during interface shearing, increasing the shear resistance and energy loss. In addition, the interface roughness affects the contact area of the interface, influencing the interface’s mechanical properties and stability (Gholampour et al., 2019).

4.3. Calculation Model of the Shear Strength of the Silt-Concrete Interface

The improved Mohr-Coulomb strength formula to effectively predict the shear strength of unsaturated soils, as follows (Yao et al., 2009):
τ s = c g + ( σ n − u a ) tan ϕ g
where τs is the shear strength of unsaturated soils, σn is the normal stress, ua is the pore air pressure on the failure surface during shear failure, and cg and φg are the cohesion and internal friction angle of the soil, which are are functions of the water content, respectively.
Matrix suction is closely related to water content (Ling., 2009) . And the matrix suction is affected by interface friction angle and cohesion. The interface shear strength between the silt and the silt-structure interface can be expressed as follows:
τ f = c ′ ( u a ) + σ n tan ϕ ′ ( u a )
where τf is the interface shear strength, c'(ua) and φ'(ua) are the interface cohesion and interface friction angle, which are are functions of the matric suction of unsaturated silt, respectively.
The results in Section 4.2 indicate a significant relationship between the strength index of silt and the shear strength index of the interface. This relationship can be expressed as follows (Potyondy et al., 1961):
c ′ ( u a ) = f c c g
ϕ ′ ( u a ) = f ϕ ϕ g
where fc and fφ are the influence parameters of the interface roughness on the cohesion and the internal friction angle, respectively.
cg and φg are calculated by the following formula (Ling and Yin, 2007):
c g = c 50 + k c ( w − w 50 )
ϕ g = ϕ 50 + k ϕ ( w − w 50 )
where c50 and φ50 are the cohesion and internal friction angle when Sr=50%, respectively; Sr is the degree of saturation; kc and kφ are parameters that express the effect of the change in soil water content on the cohesion and internal friction angle, respectively; w50 is the water content of the soil when Sr=50%.
The interface roughness is normalized. Consider the effect of relative roughness of the interface. The influence parameters fc and fφ can be expressed as:
f c = b 1 R n + R 0 c = b 1 R D 50 + R 0 c
f ϕ = b 2 R n + R 0 ϕ = b 2 R D 50 + R 0 ϕ
where R is the interface roughness, mm; D50 is the median particle diameter, which is 0.06 mm; Rn is the relative roughness of the interface, defined as the ratio of the interface roughness to the median particle size; b1 and b2 denote the influence parameters of the relative interface roughness on the interface cohesion and friction angle, respectively. R0c and R0φ represent the influence parameters on the interface cohesion and the friction angle, respectively, when the interface is smooth (R=0 mm).
The fc and fφ of different interface roughness values are fitted with the relative roughness of the interface. The results are shown in Figure 16.
Therefore, b1=0.05, b2=0.01, R0c=1.34, and R0φ=0.96. We can derive the following relationship:
τ f = ( b 1 R D 50 + R 0 c ) ( c 50 + k c ( w − w 50 ) ) + σ n tan [ ( b 2 R D 50 + R 0 ϕ ) ( ϕ 50 + k ϕ ( w − w 50 ) ) ]
The proposed model can accurately predict the interface shear strength for different interface roughness conditions.

5. Conclusions

A suction-controlled silt-concrete interface ring shear test was carried out to study the influence of matric suction and interface roughness on the interface under different stress states. A mathematical model for calculating the interface shear strength was proposed. The main conclusions are as follows:
(1)
The shear strength was significantly higher for the unsaturated than the saturated interface. Increases in the NNS, matric suction (s), or interface roughness (R) improved the interface’s shear strength. A higher NNS had a larger effect of s or R on the interface strength. The NNS affected the interface shear strength more than s or R. Increasing NNS or R improved the interface’s strain-hardening properties, whereas increasing s had the opposite effect. As s increased, the interface shear shrinkage was weakened, and shear dilation was more likely. However, the shear shrinkage was enhanced with increases in NNS or R.
(2)
The interface residual shear strength (τr) had a nonlinear positive correlation with s or R. τr increased with the NNS. The contribution of s or R to τr was larger when the NNS was high. The effective cohesion of the interface (c0) increased significantly and nonlinearly as s or R increased. The effective shear strength index of the interface differed significantly between the unsaturated and saturated states. The effective internal friction angle (φ0) of the unsaturated interface was significantly larger than that of the saturated interface. When s was low, it contributed significantly to c0 and φ0, and the contribution to the former was much larger than to the latter. As R increased, φ0 only increased slightly.
(3)
As s increased, the difference in cohesion between the silt and the silt-concrete interface (S-I) was not significant, but the internal friction angle was significantly different. The interfacial cohesion depended on the soil and the interface type, whereas the internal friction angle depended on s. The internal friction angle of the saturated interface was smaller than that of the saturated silt, but the internal friction angle of the interface in the unsaturated state was larger than that of the silt. As R increased, the unsaturated interface cohesion increased. R may have affected the contact area and stress of the interface, influencing the mechanical properties and stability of the interface. The shear strength of S-I was higher than that of silt.
(4)
A relationship model of the shear strength of the silt and the silt-structure interface considering the influence of the interface roughness was established. The influencing parameters were determined by inverse fitting. The model accurately predicted the shear strength of the silt-concrete interface under different R conditions.

Data availability statement

All data or models that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgements

This work was supported by the Cultivation Fund of Zhengzhou University in 2021 (JC21439018) and the Natural Science Foundation of Henan Province (222300420555). All support is gratefully acknowledged.

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Figure 1. The grain size distribution curve of silt.
Figure 1. The grain size distribution curve of silt.
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Figure 2. Sample preparation process.
Figure 2. Sample preparation process.
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Figure 3. Improved shear loading device.
Figure 3. Improved shear loading device.
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Figure 4. Concrete interface with different roughness.
Figure 4. Concrete interface with different roughness.
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Figure 5. SRS-150 dynamic ring shear apparatus for unsaturated soil.
Figure 5. SRS-150 dynamic ring shear apparatus for unsaturated soil.
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Figure 6. Effect curve of net normal stress on shear stress-shear displacement under different matrix suctions.
Figure 6. Effect curve of net normal stress on shear stress-shear displacement under different matrix suctions.
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Figure 7. Effect curve of net normal stress on shear stress-shear displacement under different interface roughness.
Figure 7. Effect curve of net normal stress on shear stress-shear displacement under different interface roughness.
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Figure 8. Shear stress-shear displacement curve under different matrix suctions.
Figure 8. Shear stress-shear displacement curve under different matrix suctions.
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Figure 9. Shear stress-shear displacement curve under different interface roughness.
Figure 9. Shear stress-shear displacement curve under different interface roughness.
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Figure 10. Fitting line under different matrix suctions.
Figure 10. Fitting line under different matrix suctions.
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Figure 11. Shear strength index changes with matrix suction.
Figure 11. Shear strength index changes with matrix suction.
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Figure 12. Fitting line under different roughness.
Figure 12. Fitting line under different roughness.
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Figure 13. Shear strength index changes with roughness.
Figure 13. Shear strength index changes with roughness.
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Figure 14. Comparison of shear strength indicators under different matrix suctions. (R=0.11 mm).
Figure 14. Comparison of shear strength indicators under different matrix suctions. (R=0.11 mm).
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Figure 15. Comparison of shear strength indicators under different interface roughness. (s=50 kPa).
Figure 15. Comparison of shear strength indicators under different interface roughness. (s=50 kPa).
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Figure 16. Determination of influencing parameters.
Figure 16. Determination of influencing parameters.
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Table 1. The physical and mechanical properties of the silt.
Table 1. The physical and mechanical properties of the silt.
Natural moisture content
w（%）		 Natural density
ρ（g/cm3）		 Specific gravity
Gs 		Liquid limit
wL（%）		 Plastic limit
wP（%）		 Plasticity index
IP
13.24 1.82 2.71 21.6 15.2 6.4
Table 2. The types of silt-concrete interface shear tests.
Table 2. The types of silt-concrete interface shear tests.
NO. σn-ua（kPa） ua-uw（kPa） R（mm） NO. σn-ua（kPa） ua-uw（kPa） R（mm）
M1 100 0 0.11 M10 100 200 0.11
M2 200 0 0.11 M11 200 200 0.11
M3 400 0 0.11 M12 400 200 0.11
M4 100 50 0.11 N1 100 50 0.37
M5 200 50 0.11 N2 200 50 0.37
M6 400 50 0.11 N3 400 50 0.37
M7 100 100 0.11 N4 100 50 0.54
M8 200 100 0.11 N5 200 50 0.54
M9 400 100 0.11 N6 400 50 0.54
Table 3. The types of silt shear strength tests.
Table 3. The types of silt shear strength tests.
NO. σn-ua（kPa） ua-uw（kPa） NO. σn-ua（kPa） ua-uw（kPa） NO. σn-ua（kPa） ua-uw（kPa）
S1 100 0 S4 100 50 S7 100 100
S2 200 0 S5 200 50 S8 200 100
S3 400 0 S6 400 50 S9 400 100
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