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All Journal Indonesian Geotechnical Journal
Hirochika Hayashi
Civil Engineering Research Institute for Cold Region
Earth & Planetary Sciences

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Economical Measures against Soft Ground at High Embankment on Peaty Ground Hijiri Hashimoto; Hirochika Hayashi; Atsushi Hirose; Keita Matsuda
Indonesian Geotechnical Journal Vol. 2 No. 3 (2023): Vol. 2, No. 3, December 2023
Publisher : Himpunan Ahli Teknik Tanah Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.56144/igj.v2i3.55

Abstract

Peat, which is considered a special soil, is widely distributed over approximately 2,000 km2 in Hokkaido, Japan. In terms of engineering properties, peat is extremely high in water content, ignition loss, and void ratio and extremely in low shear strength. Ground improvement methods using cement are effective for the rapid construction of embankments on peaty ground. However, to avoid differential settlement and lateral flow, most of such construction is carried out with an improvement ratio of ap=50%. In this case, the improvement can certainly be expected to be effective. However, it is less economical than other soft ground improvement methods. The challenge is to reduce the cost of improving the ground. Our institution (the Civil Engineering Research Institute for Cold Region, PWRI) has developed an economical measure against soft ground that uses cement with a reduced improvement ratio in combination with a crushed-stone mat (gravel foundation reinforcement), and we conducted the test construction of a 16-meter-high embankment to verify effectiveness of the method. The crushed-stone mat consists of a 50-cm layer of crushed stone covered with a geo-synthetic material. The test construction achieved the following results. (1) Settlement of the embankment was significantly reduced. (2) Slip failure did not occur. (3) Displacement to the surrounding ground did not occur. (4) The geotextile in the crushed-stone mat exhibited less strain than that which would cause the geo-synthetic to exceed its design strength. These results show that this economical measure against soft ground was effective at stabilizing the high embankment constructed on peaty ground.
A Case Study of Peat Ground Improvement by Vacuum Consolidation in Hokkaido, Japan Hirochika Hayashi; Hijiri Hashimoto
Indonesian Geotechnical Journal Vol. 2 No. 3 (2023): Vol. 2, No. 3, December 2023
Publisher : Himpunan Ahli Teknik Tanah Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.56144/igj.v2i3.63

Abstract

This paper presents the field performance of vacuum consolidation method on peat ground and some technical learning from the field trial. Peat is well known to be a soft soil which has particular characteristics, including extremely high compressibility and greatly low undrained shear strength. In case of an embankment building over peat ground, sliding failure and large settlement often occur due to the particular characteristics. For actual construction sites on peat ground, therefore, some kinds of ground improvement methods are commonly used. One of the methods is the vacuum consolidation method which can load vacuum pressure with the soft ground by vacuum pumps and prefabricated vertical drains to accelerate the consolidation and increases the strength of soft ground. Peat ground distributed widely in Hokkaido, the northernmost land of Japan. A full-scale trial construction of vacuum consolidation was conducted in a highway project over peat deposit in Hokkaido of Japan to reveal its performance. Although the undrained shear strength of peat ground at the trial construction site was approximately 10 kN/m2 and extremely low, a 10.7 m high embankment was successfully built in only 45 days. This experimental fact implies that the vacuum consolidation method has extremely high effects in improving the stability of peat ground. Based on a result of the trial construction, it also revealed that the increase of undrained shear strength of the peat ground using vacuum consolidation and the suitable spacing of prefabricated vertical drains for peat ground.
Co-Authors Atsushi Hirose Hijiri Hashimoto Hijiri Hashimoto Keita Matsuda