Tamotsu Matsui

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...

Calibration Chamber Modeling of Compaction Grouting

Compaction grouting, despite its many applications, has some problems that are basically attributed to the minimal guidelines to predict treatment effectiveness and the relatively little understanding of grouting mechanisms. To physically model and investigate compaction grouting in the laboratory under controlled conditions, large-scale calibration chamber, sand deposition, and injection systems have been developed. The chamber that has been developed is of the double-wall type and can independently control the sample stresses and deformations and impose different boundary conditions. Compared to the available double-wall chambers, the developed chamber has several innovative features. It is larger in size and self-reacting, applies the vertical stress at the top of the sample, provides for a rigid boundary at the base of the sample, and provides for upheave of the sample surface. The developed sand deposition system adopts the principles of pluvial deposition through air to prepare uniform soil samples at controlled relative densities. The developed injection system can inject actual compaction grouts. The developed systems are described in this paper. Some typical testing results are also presented and discussed to assess the chamber performance and illustrate the corresponding grouting mechanisms. The results reveal satisfactory performance of the developed systems and proper modeling of compaction grouting.

A CASE STUDY ON OLD RIVERBED AND DISASTER BY EA RTHQUAKE AND INUNDATION

本研究の事例に取り上げた矢作川流域のほとんどが花崗岩地帯であり，沖積平野の広範囲に砂が堆積している．近年，住宅や工場・道路などへの利用が多い旧河道や後背湿地では，地震時に堆積砂が液状化し，豪雨時に低湿地が浸水する被害を受けやすい．本研究では，矢作川の旧河道や後背湿地の生成過程と現状を歴史的文献・資料，地盤調査・工事資料，現地踏査などにより把握すると共に，浸水や液状化による災害に対する危険性を検討した．その結果，河床低下により矢作川本川の越水の危険性は減少傾向にあるが，支川の内水排除対策が今後の重要課題であり，また本川や各支川の旧河道及び低湿地における浸水や液状化に対する危険箇所が数多くあることを具体的に明らかにした．さらに，開発に伴う災害危険区域の増加傾向と共に遊水地の必要性も指摘した．