To improve the poor characteristics of low strength and high compressibility of weak silty soil, a series of samples with different cement dosage, fiber content, and fiber length was prepared in this experiment, and unconfined compressive strength (UCS) tests, triaxial tests, and scanning electron microscopy (SEM) tests were carried out to explore the influence of polypropylene fiber on the strength of cement-stabilized soil and analyze the curing mechanism of fiber-reinforced cement soil. The test results show that the factors affecting the UCS of the sample from high to low were: cement dosage, fiber content, and fiber length. An orthogonal test found that the optimal ratio of the sample was cement dosage of 18%, fiber content of 0.4%, and fiber length of 3 mm, and the UCS of the sample can reach 1.63 MPa. The triaxial test shows that when the cement dosage is 15% and the fiber length is 9 mm, the incorporation of fiber can significantly improve the toughness and strength of soil. When the cement dosage is 15%, the UCS with 0.4% fiber content is 1.6 times that without fiber. With the increase of fiber content, the peak stress and axial strain of fiber-cured soil are increased, and the cohesion and internal friction angle are also increased. The failure mode and SEM test of fiber-reinforced cement soil show that when the cement dosage is 15% and the fiber length is 9 mm, the addition of fiber can improve the deformation ability of cement soil and slow down the development of cracks. With the increase in fiber content, the number and width of cracks are significantly reduced, and the failure mode changes from brittle failure to ductile failure.

Shale reservoir has an initial unloading effect during the natural uplift and erosion process, which causes the shale brittleness to change, affecting the design of the fracturing scheme. To consider this, the axial compression loading and confining pressure unloading experiment of shale is carried out, and then the influence of unloading rate on the mechanical parameters, failure characteristics, and the brittleness of rock are analyzed. What is more, a new evaluation method of brittleness characteristics that take the unloading effect into consideration is proposed. The conclusions are as follows: (1) The unloading rate has a weakening effect on the mechanical parameters, such as the destructive confining pressure and the residual strength of the samples. (2) The failure characteristics of shale specimens are a single shear failure in an oblique section under low unloading rate, and multiple shear zones accompanied with bedding fracture under high unloading rate. (3) The brittleness of shale samples is well verified by the brittleness index $B_{d1}$ and $B_{d2}$ during the loading path; nevertheless, it has shortage at the unloading path. This paper proposes a new brittleness evaluation method which can consider the influence of the different unloading rates and unloading points. Furthermore, there is a nice characterization between the brittleness damage and this method.