In this study, the improvement effect of bearing capacity of the soil cement method has been clarified. In the case the improved ground is applied to the bearing ground of the structure, it is need more consideration that the mechanical properties of the improved soil and the influence of the improvement range. First of all, the bearing capacity test apparatus is developed and is used to demonstrate some tests. From the result of these tests, it is clear that the load-displacement curves of the improved ground show obviously the peak strength, though, the strength decreases suddenly after peak strength. Moreover, it is found out that the increase of bearing capacity depends on the width of the improved area. Furthermore, in the case when improvement area is small, the slip line can be observed almost straightly, on the other hand, it can not be observed when the improved area is large. Secondly, based on the result of the tests, two failure modes and the evaluation equations of the bearing capacity are proposed using the velocity field method. According to the result of the comparison of tests results and proposed evaluation equation, the bearing capacities don't match well.
In general, in case the bearing layer is deep, it is adopted that the deep foundation, such as pile, caisson and so on. These foundations have been adopted and it have enough results, furthermore, the technical investigation for economy have been discussed. On the other hand, the soil improvement method such as deep mixing soil stabilization using soil cement method, which developed the improvement of soft ground, is made drastic progress recently. Therefore, if it is adopted the spread foundations instead of the deep foundation in the improved soft ground, it is expected the reduction of the construction cost.
