## 5 Conclusions  
1. The deviatoric stress-axial strain curves of PCS samples are all strain-softening curves.
2. Under the same confining pressure, with the increase in fiber mass content, the peak stress, strain at peak stress, and residual stress of PCS samples first increase and then decrease. When the fiber mass content is 6%, the modification effect is optimum. Compared with the 0%0 PCS sample, with the change in confining pressure, the peak stress increases from 24% to 29%, the strain at peak stress increases from 85% to 120%, and the residual stress increases from 87% to 110%. With the increase in confining pressure, the modification effect of fiber is gradually improved. Among the tests, the ductility is significantly improved.
3. The incorporation of fiber can increase the cohesion c and the internal friction angle \(\phi\) of PCS samples. When the fiber mass content is 6%, the cohesion c and the internal friction angle \(\phi\) reach the maximum value. Compared with the 0%0 PCS sample, the cohesion c increases by 25.9% and the internal friction angle \(\phi\) increases by 7.4%. It can be seen that the incorporation of fiber improves the cohesion c and the internal friction angle \(\phi\) of the sample, thereby improving the shear strength.
4. When the fiber mass content is fixed, with the increase in confining pressure, the brittleness index of the PCS sample decreases and the ductility increases. Under a confining pressure of 100 kPa, the brittleness index is the highest and the brittle failure is obvious. Under a confining pressure of 400 kPa, the brittleness index reached its lowest value and the brittleness failure shows the most mitigation. When the fiber mass content is 6%, the brittleness index reaches the minimum. Compared with the 0%0 PCS sample, with the increase in confining pressure, the brittleness index decreases from 52% to 79%. The incorporation of fiber can improve the brittle failure behavior of the sample, and the modification effect is enhanced with the increase in the confining pressure.
5. Under the same confining pressure, with the increase in fiber mass content, the failure angle of PCS samples first decreases and then increases. The PCS sample with 6%0 fiber mass content exhibits the minimum failure angle, providing solid evidence that the incorporation of fiber mitigates the brittle fracture form of the sample to some extent.  
As a limitation, the current study only considered small soil specimens. In reality, the situation is more complicated, as there will be impurities such as stones and organic matter. The effect of impurities in a specimen and the effect of specimen size were not considered in this study, but which is worthy of future study.  
The authors confirm contribution to the paper as follow: [PERSON] and [PERSON] proposed the idea and wrote the paper; [PERSON]. ([PERSON]) revised the manuscript; [PERSON], [PERSON] ([PERSON]), and [PERSON] conducted the tests and analyzed the data; [PERSON] reviewed the results and approved the final version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (Grant numbers [41772311]), the Zhejiang Provincial Natural Science Foundation of China (Grant number [LY17E080016]), the Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Science (Grant number [Z017013]), the Scientific Research Projects of Zhejiang Department of Housing and Urban and Rural Construction (Grant number [2017K179]), and the International Scientific and Technological Cooperation Projects of Shaoxing University (Grant number [2019 LGGH1007]).