Ken-ichi Tokida

Field Investigation into Effectiveness of Compaction Grouting

AbstractThe common design approach of compaction grouting for ground improvement works is oversimplified and does not account for the effects of soil properties and grouting variables. The obtained improvements therefore appear inconsistent with the predicted ones. This paper presents the results of a field test conducted at Tokyo International Airport to evaluate the effectiveness of compaction grouting under well-controlled conditions. The test consisted of 87 compaction grout piles injected in three cases of different pile diameters and spacings. The paper also discusses the effects of soil properties, replacement ratio, and injection sequence on the effectiveness that is evaluated in terms of the standard penetration test N-value and cone penetration test tip resistance, and the variation of effectiveness with depth. A new design procedure that accounts for the effects of initial soil properties is introduced. It has been found that the injection sequence has a significant effect on the grouting mecha...

A probabilistic evaluation of the size of earthquake induced slope failure for an embankment

The seismic design method for earth structures considers only the safety factor, subsidence and sliding displacement. However, the estimation of the size of slope failures is necessary to judge the remaining function of an embankment after an earthquake event. The size of slope failures due to an earthquake is investigated by considering the heterogeneity of the ground strength and was based on slope stability analysis of two case histories: the 2001 Geiyo Earthquake (Mj6.7) and 2009 Suruga Bay Earthquake (Mj6.5). As a result, we propose a method for slope failure size estimation based on the maximum slip surface. The proposed method enables a rational assessment of the functional loss of an embankment in terms of the slope failure size.

Damages of Coastal Structures through Field Survey on the 2011 Off the Pacific Coast of Tohoku Earthquake

現地調査の限られた事例から,海岸保全施設の被害特 性,盛土構造の被害特性および落堀の発生特性に関して, 得られた課題および知見は,以下の通りである. (1)海岸保全施設の被害特性と課題・知見 防潮堤,離岸堤,砂浜,消波ブロックなどの各種の海 岸保全施設に着目して現地調査を実施した.これらの施 設の被害の有無,程度の状況から,津波に対する防潮構 造の計画あるいは設計に関する留意事項について,既に 指摘されている事項も含め,本地震の津波から得られた 課題および知見は,以下のように提示できる. a)防潮堤の越流侵食による破堤過程 防潮堤の大規模で全体的な破壊事例が写真-1(岩沼市 北新田地先)である(矢印は押し波の方向).津波の越 流による裏法先の侵食が,裏法,天端,さらに表法に拡 大したことが破壊過程である.言い換えると,表法の侵 食は皆無,軽微であり,防潮堤の耐津波性は裏法先の地 盤あるいは裏法の耐侵食性に依ることが示唆される. b)防潮堤の前面形状と耐津波性・津波減勢性 津波に対する防潮機能には,防潮堤本体の耐津波性お よび防潮堤による津波減勢性があると考えられ,津波対 策ではこの両視点からの評価が必要である.防潮堤の前 土木学会論文集B2(海岸工学) Vol. 68,No. 2,2012,I_1406-I_1410