Mechanical behavior of soft clay improved with lime cloumn during vertical excavation

1992 Fiscal Year Final Research Report Summary

• Project/Area Number: 03555110
• Research Category: Grant-in-Aid for Developmental Scientific Research (B)
• Allocation Type: Single-year Grants
• Research Field: 基礎・土質工学
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: KIMURA Tsutomu Tokyo Institute of Technology, Professor, 工学部, 教授 (40016506)
• Co-Investigator(Kenkyū-buntansha): HIROOKA Akihiko Tokyo Institute of Technology, Research Associate, 工学部, 助手 (70238400) ; SUEMASA Naoaki Tokyo Institute of Technology, Research Associate, 工学部, 助手 (80206383) ; 竹村 次朗 東京工業大学, 工学部, 助教授 (40179669) ; TAKEMURA Tsutomu Tokyo Institute of Technology, Associate Professor
• Project Period (FY): 1991 – 1992
• Keywords: excavation / sheet pile / soft clay / soil improvement / stability / deformation / earth pressure / centrifuge model test

Research Abstract

A centrifuge excavator with which the process of excavation can be simulated in-flight was developed and a study on the mechanical behavior of soft clay during excavation using the centrifuge excavator is reported here. In this study three series of centrifuge tests were carried out. In the first series, the effect of undrained strength increase with depth on the stability of vertical cuts was investigated by centrifuge model tests in which prepared models were brought to failure by increasing centrifugal acceleration. In the second series, unsupported excavation and excavation with a supporting wall with or without ties were conducted with the excavator for two types of soft clay, namely normally consolidated and lightly overconsolidated clays. Earth pressures on sheet pile walls and deformations of the walls and clay were measured during excavation. In the third series. excavation with supporting wall without tie for normally consolidated clay improved with lime piles in active side were conducted by using the excavator. The effect of improvement and mechanical behavior of improved groud during excavation were investigated.
The analyzes of the test results provided the following conclusions.
1)The mechanism of failure in excavation with sheet pile walls without ties is different for clay grounds with uniform strength and increasing strength. For the former the wall shows translational movement with well-defined linear slip surface both in the active and passive side, while for the latter the wall tilts around the bottom with linear slip surface only in the active side.
2)In excavation with sheet pile walls without ties, the embedment does not contribute to the stability in clay with uniform strength. but stability number increases significantly with depth of embedment in clay with increasing strength.
3)The characteristics of clay in the active state have a dominant effect on the deformations and strains of sheet pile walls.
4)The improvement with lime piles in the active side of sheet pile without tie reduces strains of sheet pile and active pressures on sheet pile walls, and in effective in increasing the stability of excavation.