Control of post-construction settlement by replacing subgrade with foamed cement banking

When using the preloading method to reinforce expressway soft subsoil, owing to the short preloading period and other reasons, some road sections usually exhibit large settlement rate and do not satisfy the settlement and stability requirement before the starting of pavement construction. Treatment is needed to control the post-construction settlement in a short period. A case study of controlling the post-construction by adopting the foamed cement banking (FCB) to replace parts of subgrade of Shanghai-Jiaxign-Huzhou-Hangzhou Expressway (Lianshi-Hangzhou section) in Zhejiang Province is introduced. According to the laboratory immersion tests, the correction method is put forward for soil-free FCB, as its design bulk density is affected by the water. A settlement prediction method is established, which can reflect the overloading-unloading-reloading procedure for FCB replacing the subgrade, and it is used to calculate the FCB replacement capacity of FCB. In addition, the stability criteria are proposed by using the effective overloading ratio to correct the conventional settlement rate, and a simple method is also presented to estimate the replacement volume of FCB according to the measured settlement rates. Finally the results of the theoretical method are compared with the measured data.