Recent Experiences of Reinforced Soil Retaining Structures in China - Reinforced Soil Engineering: Advances in Research and Practice - page 165

1. Fiber-reinforced cohesive soil has a higher shear strength than an
unreinforced one by increasing the cohesion c, without significant
change of angle of internal friction.
2. Its tensile strength and limit tensile strain increase, and reinforcement
changes the failure pattern of cohesive soil extended.
3. Reinforcement increases the fracture toughness of cohesive soil and
extends the yield zone of crack tip in a cracked specimen.
4. The hydraulic fracturing test result on the hollow cylinder specimen
shows that fiber reinforcement cannot increase the fracturing pressure
of cohesive soil, but can make the soil obtain self-seaming ability.

In Fig. 6, the failure patterns of unreinforced and reinforced cohesive soil
steep slopes are the results of a model test conducted in centrifuge in Tsinghua
University. It is found that fiber reinforcing not only enhances the stability of
steep slope, but also changes its failure pattern. For example, in the case of an
unreinforced clay slope with dry density 0.00155 g/mm 3 , the centrifugal
acceleration at failure is 45 g (correspond to 15.7 m high). In the reinforced one
with the same dry density, it is 100 g (35m high). The unreinforced clay steep
slope fails abruptly without any noticeable sign before collapse, while the
reinforced one fails gradually, which can still bear more loads even after cracks
appear. It is also found that there is a family of failure surfaces, rather than only
one, in the fiber-reinforced clay slope when failure develops. This phenomenon
results from the redistribution of stresses through fiber reinforcing in the slope
(Zheng Jiqin et al., 1996; Jie Yuxin, 1998).

Figure 6 Failure patterns of model steep slopes: (a) reinforced; (b) unreinforced.