Moisture is an important part of calcareous soil. During construction, the moisture in the soil causes the physical and chemical interaction between lime and soil to meet the needs of the formation strength of lime soil; Moisture makes lime soil have certain plasticity during compaction, so it can be rolled to the required degree of compaction; Moisture makes the lime soil have a certain humidity in the curing process, which meets the need of moisture in the strength formation process. Therefore, the optimum water content is also the key index to control the construction quality of lime soil.

Theoretically, the optimum water content of lime soil is the sum of the optimum water content of plain soil, the water needed for evaporation during mixing and the water needed for lime reaction. The optimum water content of lime soil with different soil quality and lime content is different, which needs to be obtained through experiments. When the lime soil is rolled under the optimum water content, the maximum compactness can be obtained. Water content should be tested separately during mixing and at the beginning of rolling. When rolling, the water content of the mixture can be slightly higher than the optimal water content of 0.5% ~ 1%, which is to make up for the water loss during rolling. Excessive water content will not only affect the possible density and strength of lime soil, but also significantly increase the drying shrinkage of lime soil, resulting in drying shrinkage cracks in the structural layer. If the water content is too small, it will also affect the possible density and strength of lime soil.