Behavior of a Short Fiber Pull-out from Fiber Reinforced Cement Stabilized Soil

Failure mechanism of short fiber-reinforced cement-stabilized soil depends on the interaction between the fiber and the cement-stabilized soil matrix. And the mechanism of fiber reinforcement is revealed by experimental studies and numerical simulations. Firstly, by using the single fiber pull-out test, the results show that the maximum tensile force of single fiber under different embedding lengths increases with the development of age. Then based on a cohesive model, a three-dimensional finite element model is established to simulate the interaction between single fiber and cement-stabilized soil. The comparisons of numerical results and experimental results reflect that viscous interface parameters have vital effects on the interaction between single fiber and cement-stabilized matrix. Introducing the proper cohesive model, numerical results agree well with the experimental results better. Introduction The fibers can inhibit the expansion of cement-stabilized soil, also can improve crack resistance and long-term strength. In recent years, a large number of researchers studies the cement-stabilized soil reinforcement formula [1,2,3] by means of experiments in order to get better effects. According to the experiments, the reinforcement effects mainly depends on six factors: fiber volume fraction, fiber orientation, fiber shape, fiber material properties, matrix material properties, and surface contact characteristics of fiber and matrix [4]. And the understanding of the mechanism of fiber and matrix interaction relies on the single fiber pull-out test, which is a critical problem to decide the role of fiber and its reinforcement effects, and it is also the key point that researchers and engineers have been concerning about. For the accurate measurement of single fiber pull-out curves, many researchers have developed a variety of advanced precision apparatus for single fiber pull-out tests [5,6]. For further insight of fiber and matrix interactions, Cox introduced the shear lag model to established the mathematical model of fiber and matrix interaction [7], which solving stress field and strain field of the composite. Based on the shear lag model or more rigorous three-dimensional model of interaction between fiber and matrix, a large number of research results are obtained by the following researchers [8,9,10]. It is well known that the interfacial viscous effects is very important for the interaction analysis between fiber and matrix. Hsueh [11] considered viscous effects in the interface and the radial shrinkage in fiber pull-out process caused by the Poisson effect. These theoretical analyses are only applicable to simple shapes and boundary conditions, they are inconvenient for application in more complicated conditions. Morrison used the method of preset debonding length to establish the two-dimensional finite element model to calculate the results of fiber debonding and pull-out force, and he found that the effects of fracture energy release rate G and fracture length b was significant for failure modes [12]. Povirk developed a single fiber quasi static analysis depending on friction constitutive relation of pull-out rate, reflecting fiber and matrix interface friction velocity weakening [13]. The above analysis of the interaction between fiber and matrix ignored the viscous contact condition at the interface, and the simulation results needed to be improved further.