Abstract: In a deep excavation, the maximum displacement of earth retaining structures (e.g., diaphragm wall) usually occurs below the information level. In order to reduce the displacement, the deep cement mixing technique is often used to improve the ground 2 to 3 m below the information level. Because of the high heterogeneity in the strength of cement-admixed soils, the conservative design value for strength is generally adopted in practice. In this study, two main sources for the heterogeneity in the strength of cement-admixed soils are considered, namely, the positioning error in column installation and the non-uniformity within each single column. The unconfined compressive strength of cement-admixed soils is simulated as the three-dimensional random field, and the random field serves as the input parameter in finite element analysis. Based on such kind of finite-element analysis, the design overall strength of a cement-treated slab subjected to lateral loading can be considered as the mean value minus its standard deviation multiplied by a reduction factor. The reduction factor is explored for various scenarios. The results of this study are likely to offer guidelines for comparable projects in practice.