A study on measuring method of in-situ Ko-value for sandy and gravelly soils

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It is very important to know the in-situ stress of soils, because the strength and deformation characteristics of soils are significantly affected by stress level. Unfortunately, until now, there is no efficient method was developed for measuring the in-situ horizontal stress of sandy and gravelly soils. A new method was developed in the present study to measure the horizontal stress in sandy and gravelly soils. A cylindrical shape test probe, with 6 load transducers mounted on the outside surface of the test probe was installed into the frozen ground hole, which was made by coring the frozen ground to obtain high-quality undisturbed samples. After the probe was installed into the frozen ground hole, the frozen ground was allowed to thaw. When, the frozen ground was completely thawed, the stress measured by load transducers show the horizontal stress in the ground. The effect of temperature change of ground during thawing and the hydraulic pressure were canceled. Field test were perfor … More med at a reclaimed land located at Tokyo Bay. Though the preliminary test, the test probe was found to have some electric troubles. It was refined and used in main test for reclaimed land after it was stabilized by Sand Compaction Method. The Ko-value of the compacted sandy soil measured by the present method was ranging 0.41 to 0.98. These values are well consistent with the Ko-value(0.92-1.06) obtained by using Vs-equivalent method using high quality undisturbed samples which is also proposed previously by the authors. These results indicate that the proposed method developed in the present study is useful for measuring the in-situ horizontal stress for sandy and gravelly soils. Based on the internal friction angle obtained from CD tests on high-quality undisturbed samples of reclaimed land before compaction, Ko-value was estimated to be 0.38 by using Jaky's equation. These results firstly show that the Ko-value of the reclaimed land increased from 0.38 to about 1.0 due to sand compaction. Less