Application of combined deep mixing method using blade-mixing and jet-grouting to earth retaining wall with a function of water cutoff wall

In applications of deep mixing to retaining wall, water cutoff wall and bottom sealing barrier etc., the unification of columns is highly required. Although the unification is ensured by overlapping of deep mixing columns generally, jet grouting may be used partially for the cases such as water sealing or unification to other structures. However its slow construction speed and expensive cost become problems frequently. As a method to ensure unification quality while minimizing cost increase, a combined mixing method have been developed, which uses not only blade mixing but also jet grouting for cutting and mixing soil existing in outer area of the blade. In this method, high-pressured binder slurry is injected from the end of a 1.2 m-diameter mixing blade with 20 cm of cutting distance. Due to the small 20 cm cutting distance, a 1.6 m-diameter stabilized column can be constructed with about 1/10 of jet energy required for typical jet grouting machines. This method was applied to a construction of an earth retaining wall that also served as a water cutoff wall. In this project, the water cutoff wall was constructed firstly by regular deep mixing method overlapping in the direction of wall extension. Then, the earth retaining wall was constructed by using the combined mixing method to be unified with the existing water cutoff wall. This combined mixing method created a highly continuous solidified soil at a low cost and in a short time.