Naoaki Suemasa

Centrifuge Model Tests on Seismic Slope Failure

In this study, experimental analyses were carried out to investigate characteristics of slope failure by earthquakes and potential risks of secondary failure. A 1/50 scale model slopes were made of Kanto loam to simulate the shallow unsaturated soil in slopes. Seismic acceleration was applied on a shaking table in centrifuge, so that shear strain in the shallow unsaturated soil increased as the number of seismic cycles. It was found that the slopes failed as a result of accumulation of the plastic shear strain. In addition, changes in height and angle of slopes were measured in the upper remaining section after seismic failures. The potential risks of secondary failure (R v ) were analyzed using Taylor’s stability chart. It was ensured that the value of R v on the upper section decreased as the collapsed soil increased.

Failure Mechanism of Anchored Retaining Wall Due to the Breakage of Anchor Head

In this research, a case history of temporary earth support collapse is first illustrated briefly and the mechanisms of accident occurrences are introduced, with the results showing that the shallow penetration of piles mainly caused the sequences of collapse. In order to understand these failure characteristics and mechanisms, centrifuge model tests using an in-flight excavator were carried out. The failure mechanism of the retaining wall in this labour accident was first demonstrated using centrifuge model tests by Toyosawa et al. Failure mechanism of anchored retaining wall, 667–672 (1996). In this paper, we added some viewpoints regarding the mechanism of the retaining wall and it was thus clarified that the active and passive earth pressures in the retaining wall increased during excavation and then the anchor head exceeded the capacity with respect to tensile stress. As a result, the retaining wall and ground behind the wall collapsed suddenly.

Correlation Between CPT and Screw Driving Sounding (SDS)

Cone penetration test (CPT) is probably the most popular in situ testing method in the world today. Various design parameters, such as undrained strength and relative density, as well as indices for liquefaction assessment, can be derived from the CPT. However, the use of CPT in many roading projects and in subdivision developments may be constrained by the number of tests or project cost; hence, alternative in situ testing technique to supplement the CPT is necessary. Screw Driving Sounding (SDS) is a new in situ test in which a machine drills a screw point into the ground in several loading steps while the attached rod is continuously rotated. During the test, a number of parameters, such as torque, load, speed of penetration and friction, are measured at every rotation of the rod; these provide a robust way of characterising soil stratigraphy. In this paper, the principle of SDS testing is described. SDS tests were performed at various sites in New Zealand where CPT data are available. Then, a side-by-side comparison between CPT and SDS is performed to derive correlations between the CPT tip resistance (qc), sleeve friction (fs) and soil behavior type index (Ic) and the SDS parameters. Based on the results, it is observed that qc correlates well with the penetration energy in SDS while fs and Ic are related to the average torque and change in torque, respectively. The good correlation obtained between CPT and SDS indicates that SDS can supplement CPT results for a more cost-effective geotechnical investigation.

Impact loading experiment on methods to fix lifelines using anchors to prevent accidental falls from slopes

Slope disasters such as slope failures often occur in Japan due to various natural phenomena. Shotcrete and other slope works are carried out to protect social infrastructure and dwellings from slope disasters. Lifelines and safety belts are used to prevent falling accidents and ensure the safety of the workers who engage in slope works. A number of standard lifeline fixing methods are widely used and reported, but their engineering rationale is unclear. In the present study we considered the proper diameters, driving depths, and shapes of the anchors used to fix lifelines, in order to prevent friction and wear of the lifelines and better maintain safety during work on slopes. This paper reports the results of an impact loading experiment performed with experimental banking simulating a construction work site on a slope. Language: ja

INSTABILITY OF MOBILE CRANES DUE TO THE GROUND PENETRATION OF OUTRIGGERS CAUSED BY BRITTLE FAILURE OF THE GROUND

ホイールクレーンなどの移動式クレーンは, アウトリガによって作業中の機体を安定させる. しかし, これが地盤に沈下したことによる転倒災害が多く発生している. 本研究では支持地盤の破壊によるアウトリガの沈下挙動に着目し, その破壊沈下特性の違いが移動式クレーンの転倒に与える影響を遠心模型実験と数値計算によって検討した. その結果, 表層が固結した2層地盤ではその脆性的な破壊によって, アウトリガが急激に沈下するために移動式クレーンは動的に不安定化し, 静的転倒角に比べて少ない機体傾斜でも転倒することがわかった. そのため移動式クレーンの転倒危険度を, 地盤破壊危険度と運動学的沈下危険度の最大値によって評価することを提案し, 地盤工学的な使用限界を示した.