Abstract
In the case of constructing buried pipes and channels in weak clay zones, the sliding failure due to the weakness of the ground, the sinking due to stress increment and so on are frequently observed. As the cause of the sliding failure of channels, it is regarded as (1) the cracking of ground surface in paddy fields and others and the water pressure acting to it, and R the channel bottom existing on an extremely weakened stratum. And as the cause of the sinking of buried pipes, it was able to be clarified (1) that the foundation of pipes and diversion works is located in ultra-weak clay area with large compressibility, (2) that there is the compacting sinking due to the additional weight of the replaced soil for preventing the rising of the pipes, and (3) that the sinking of the pipes and ground surface occurs when the cavities that arise underground by pulling sheet piles out close.
In order to prevent the lowering of functions of channels and buried pipes, by using the improved cement system materials made by various campanies, the tests were carried out in the laboratory and in a field, and the difference in the improved characteristics was investigated.
The conclusion (1) that as the result of the laboratory test, there was the difference as much as more than ten times in the strength of improved soil according to respective materials on the market, (2) that about 60% of the strength obtained in the laboratory becomes the strength of the improved ground in the field, (3) that unless the proportion of mixing was more than the 6-7%the homogeneity of the improved ground was not obtained, (4) that as for the ground requiring improvement, it is desirable to apply this process to uniaxial compressive strength distribution qu=8+2·Z (kN/m2) or less and so on were obtained.
Further, by constructing buried pipes and channels in fields, the verification of improved ground zones together with the workability and the economical efficiency was carried out.
