The depth of soil layer which influenced by climate in Hefei is studied by way of climate environmental data and field experiment of water content. It can be found that the calculated depth of the layer according to climate environmental data is smaller than the real value. On this foundation

the determination method of treatment depth for subgrade paved with expansive soil is proposed based on the relationship of swelling pressure and unloaded expansibility. The correlative curve of the expansive pressure and the unloaded expansibility is established by means of swelling pressure test of eighteen representative soils selected from Hefei. It provides reliable references for determining the treatment depth of subgrade. Finally

some suggestions of treatment depth for the different structure positions of subgrade are given.