To deal with the problem of long-term settlement of the operating expressway, the Guan Yun section of the operating Lianyungang-Yancheng expressway, of which the embankment is improved by the lateral radiation grouting technique, is selected for analysis. A numerical model based on ABAQUS software is established to investigate the reinforcement mechanism of the embankment using the lateral radiation grouting technique. The proposed numerical model is then validated by comparing the calculation results of the ground heave, surface settlement of the ground after grouting, soil lateral displacement and excess pore pressure with the measurement in the field test. Subsequently, parametric study is conducted based on the presented numerical model. The results show that lateral radiation grouting technique can efficiently control the settlement of operating expressway and 5 cm reduction of settlement is achieved in field test section. The increasing of the grouting ratio is the primary factor which leads to the larger ground heave as well as the larger compression modulus of soil; and ultimate settlement decreases linearly with increasing of grouting ratio. Higher soil strength leads to insignificant effect of reinforcement, whereas no significant influence of heave is observed. The effect of grouting is more significant with the time in advance to reinforcing the ground. Thus it can be helpful to the compensation of previous settlement and the control of following settlement. The simple lateral radiation grouting technique has an advantage on reducing operating expressway settlement without influencing the traffic operation.