## 3 Results  
### Ucs  
Figure 6 shows the UCS of BFUSM and BFCSM at varying BF contents and curing times with a length of 12 mm. It is obvious that the UCS of BFUSM and BFCSM both have an increasing trend as curing time increases and reach the maximum strength after curing for 28 days. Without the incorporation of cement (Figure 6a), the fiber content increases from 0.0% to 0.1% and 0.2%, the corresponding strength is 0.45 Mpa, 0.48 Mpa, and 0.67 Mpa, respectively. Thereafter, the fiber content increases to 0.3% and 0.4% and the  
Figure 4: Universal testing machine used for tests: (**a**) UCS test, (**b**) STS test, and (**c**) test system.  
Figure 5: SEM test system: (**a**) vacuum treatment, (**b**) gold spray treatment and (**c**) scanning electron microscope XL-30.  
strength a small decrease to 0.46 Mpa and 0.49 Mpa, respectively. It can be found that at the fiber content of 0.2%, the UCS of BFUSM is the highest. The reason is that when fiber content is higher than 2%, the pull-out effect of fiber is significant, resulting in lower UCS. Hence, a 0.2% dosage is more suitable to reinforce BFUSM. The UCS of SM0.2B at 3 days, 7 days, 14 days, and 28 days is 0.32 Mpa, 0.56 Mpa, 0.60 Mpa, and 0.67 Mpa, respectively. The increasing amplitude of adjacent curing time is 75.61%, 5.77%, and 12.04%, indicating that the UCS of SM0.2B increases the most after curing for 7 days.  
As Figure 6b presented, the UCS of BFCSM increases first and then decreases with the increasing fiber contents, which is coincident with the conclusions of [PERSON] et al. [41]. The UCS of SM2P0B is 1.58 Mpa, the corresponding UCS of SM2P0.1B, SM2P0.2B, SM2P0.3B, and SM2P0.4B is 1.16 times, 1.17 times, 1.07 times, and 1.12 times that of SM2P0B, manifesting that BFCSM reaches the maximum strength at 0.2% dosage, which is the optimal dosage for BFCSM. Since the fiber content is higher than 2% dosage, the pull-out effect of fiber is obvious under compressing, which leads to a decrease in strength. The UCS of SM2P0.2B at 3 days is 1.39 Mpa, the corresponding strength at 7 days, 14 days, and 28 days is 1.07 times, 1.21 times, and 1.33 times that at 3 days, the increasing amplitude between adjacent curing time is 7.16%, 13.22%, and 10.00%, respectively, implying that the UCS of SM2P0.2B has the maximum increasing amplitude after curing for 14 days.  
Comparing Figure 6a and 6b, the UCS of BFCSM is obviously higher than that of BFUSM at the same fiber content and curing time condition [37; 47; 48]. The UCS of SM2P0.2B at 3 days, 7 days, 14 days, and 28 days is 3.39 times, 2.67 times, 2.83 times, and 2.78 times that of SM0.2B, indicating that the cement effect of hydration reaction is more significant than that of BF on UCS, the reason is that BFUSM relies on the fiber to \"build bridges\" between particles to increase UCS of soil. But in BFCSM, the fiber \"build bridges\" in the cement-soil skeleton, which makes particles more closely connected and leads to a significant increase in strength [40]. The multiple relationships between the UCS of SM0.2B and SM2P0.2B remain basically unchanged after curing for 14 days, indicating that after the inclusion of cement, the increasing impact on UCS of the combined action of fiber and cement tends to be stable after 14 days of curing.