The stability of Yinzhong highway fails to satisfy the requirements of the highway engineering. In order to know the deformation features of this highway during its construction, the FEM analysis software of NCAP-2D is used. The geotechnical material's nonlinear features, such as elastic-plastic relations, nonlinear joints, non-tensile characteristics, and orthotropic properties of the layered rock mass, are considered in the software. The Drucker-Prager yield criterion is applied in the numerical models, and the construction process of pile forming and soil filling are simulated with an element-free method. The basic data of displacement and stress after excavation are obtained when compared with those before excavation. Piles with different gaps and broken piles are simulated, and the plastic zone and displacement characteristics are analyzed. The results show that the top of jet grouting pile is in relatively obvious plastic state, because some loads on the soil between piles are transmitted to the piles. At the same time, the top of the piles experiences larger lateral displacement than the bottom, which could enhance the basement stability. The plastic zone and the displacement have a positive correlation when the gap between piles is changed, and the same for the soil and piles. But the area around the pile's top is where breakage would occur with whatever change of pile's gap. The plastic zone would obviously be concentrated around the broken piles, which would influence the foundation reinforcement effect. According to the field load test, after the treatment by high pressure jet grouting, the bearing capability of the foundation is, respectively, 2.08 times and 2.97 times of that of the untreated recently deposited loess and soft loess. And the actual monitoring settlement is only about 0.17 times of the calculated value. So, the treatment in this paper's situation has a good strengthening effects. The conclusion in this paper provides some guidance for highway's construction in the similar situations.