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The size of rock fragments had an influence on Ksat at around 20 % (Figure 4.10), but the Ksat was not

affected by the size or the component ratio of rock fragment at around 35 % and 50 % (Figure 4.11). This indicates the rock fragment sizes and component ratios seem not to be important factors when total rock fragment content increases (Figures 4.8 and 4.9). This needs to be understood with a viewpoint of total rock fragment content. Figure 4.12 presents the Ksat values with the total rock

fragment content regardless of the rock fragment sizes and component ratios. The Ksat values were

not significantly different at the rock fragment contents between 20 % and 48 % and tended to increase gradually from 40 % to 60 %.

Intermediate rock fragment content and K

Urbanek and Shakesby (2009) found that a range of intermediate rock fragment content induces inconstant and variable water flow rates, and this appeared in the region of 20-40 % in the present study. The rock fragments have not only a negative influence on water flow by reducing space available for water flow and increasing tortuosity, but also a positive effect by creating large pores at rock-to-soil interfaces and connecting them as rock-to-rock flow paths (Beckers et al., 2016; Beibei et al., 2009; Mehuys et al., 1975; Sauer & Logsdon, 2002; Urbanek & Shakesby, 2009). These contrary differences occur simultaneously, and the final effect depends on which is larger. The degree of the negative effect directly depends on the volume of rock fragments, as increasing rock fragments reduces the space available for water flow. However, the degree of this positive influence is affected by not only the rock fragment content but also distribution and alignment of the rock fragments. When the favorable distribution and alignment are created, the positive effect would become stronger in spite of the same rock fragment content (Urbanek & Shakesby, 2009). At the low content (17-20 %), in the present study, the size of rock fragment was likely to be a critical factor to decide whether the rock fragments contacted each other or not, as explained in the previous section. However, the intermediate rock fragment content (20-48 %) would be sufficient to generate rock-to- rock connections regardless of the size or the component ratios. In addition, increasing rock

fragment content would increase rock-to-soil interfaces and rock-to-rock connections. While the positive effect gradually increased with the increasing rock fragment within the intermediate content zone, the negative effect was also gradually increased. Consequently, the contrary effects of rock fragments compensated each other, so the Ksat was not significantly changed.

Standard error bars at the intermediate content zone were relatively larger than the other rock fragment content (see Figure 4.12), which means the degree of the positive effect became different whenever the soils were repacked again. Similarly, Sakaki and Smits (2015) found that porosity of repacked soils varied at each time of repacking. This is because a packing procedure or uniformity of repacked soil enable to affect Ksat (Beckers et al., 2016; Zhang et al., 2011) because the

distribution and alignment of rock fragments would be altered every time. The result of the present study suggests the Ksat at the intermediate rock fragment content is variable in a repacked soil

experiment, which makes interpretation of the result more complex.

High rock fragment content and K

Increase in the Ksat at high rock fragment content is consistent with the previous studies. In

particular, many studies have reported that the Ksat rapidly increased when the rock fragment

content was over than 40 % (Beckers et al., 2016; Beibei et al., 2009; Zhang et al., 2011). This would be because a high volume of rock fragment creates large gaps between the rock fragments.

mixture of two sized particles, especially when the ratio of coarser particles was high. Van Wesemael et al. (1995) also reported a strong increase in macropores when the rock fragment content was greater than 50 %. The repacking process was not properly conducted in the present study because of the huge volume of rock fragments, so the unfilled voids were obviously recognized. Moreover, the present study demonstrated the high Ksat at S40G20 (60 %) although the tension infiltration rates

were very low (Table 4.4), which implies a lot of large pores were created in S40G20. Water flows through all of connecting pores regardless of sizes when soil is saturated, but the tension infiltration test in the present study estimated a limited range of connecting pores up to 0.1 cm diameter (Figure 4.13). Therefore, the inconsistent hydraulic properties of S40G20 implies the pores larger than 0.1 cm were created in S40G20. Due to this void, water could flow fast although the rock fragments accounted for large space in the soil. Because this fast flow was caused by the repacking, this may or may not happen under natural conditions.

Figure 4.12. Ksat with total rock fragment content. Error bars are standard errors (n=3). The same

letters indicate no significant difference (n=3, p<0.05). 0 0.05 0.1 0.15 0.2 0 17 20 34 35 40 48 50 60 Ksat (c m m in -1)

Rock fragment content (%) a b bc cd cde cde de cde e

Figure 4.13. Ranges of diameter of connecting pores related to Ksat and infiltration rates with

different tensions.

Relationships between rock fragment content and connecting porosity

Figure 4.14 shows the negative relationship between the rock fragments and the tension infiltration

rates at all tensions. The relationship was strongest at tension 10 cm (R2_{=0.67), and R}2 _values

gradually decreased with decreasing tensions, which means the pores larger than 0.03 cm were likely to reduce the correlation (Figure 4.13). Therefore, sizes of rock-to-soil interfaces and continuous flow paths along the rock fragments, which increased with increasing rock fragment content, seem to be larger than 0.03 cm.

Figure 4.14. Relationships between rock fragment content and tension infiltration rates with four tensions (*: p < 0.05, **: p < 0.01).