Case study of cutter soil mixing (CSM) method on hard soil conditions

A vertical cut off wall for water barrier was constructed at the final landfill disposal site in Oita prefecture of Japan to prevent the inflow of groundwater from the surroundings of the landfill site and leakage of leachate (sewage) to the outside. Due to existence of hard rock formations existed in the target ground to construct the cut off wall for water barrier, a Trench cutting Re-mixing Deep wall (TRD) construction method using a pre-drilling by a double rock auger in combination was planned for excavation of cut off wall for water barrier, initially. However, if this plan was adopted, there should be tight schedule for the construction due to pre-drilling. The alternative with CSM (Cutter Soil Mixing) construction method which does not require pre-drilling even in hard rock formation was proposed and the excavation was carried out with CSM method against relatively less hard rock formations. Also, a new machine imported from overseas was used for CSM construction method. Since, in Japan, there is no previous experience for drilling of hard formation layer with the new CSM machine, a pre-test was carried out. In the pre-test, the quality of the soil mixing wall and its drilling capacity against the hard rock formation were checked. The pre-test result was included in the construction cycle for CSM method with the new machine. From this point of view, case study of construction with CSM method which was applied to vertical cut off wall for water barrier of waste landfill waste disposal site in Japan is described and the pre-test performance of rock drilling is summarized in this paper.