Shield tunnel construction management case study on the impact of surface settlement

• Main Authors: Chih-Ling Chung, 鍾枝霖
• Other Authors: Chung-Jung Lee
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/05953737111559965342

碩士 === 國立中央大學 === 土木工程學系碩士在職專班 === 99 === As the development of metropolitan areas and international competitiveness are increasing, construction techniques employed in mass rapid transit (MRT) projects have become one of the more important measures of modernization. Even though it has been more than 20 years since the tunnel boring machine (TBM) was introduced for construction projects in Taiwan, there are still arguments about construction techniques particularly when soil property is more complex or the site is adjacent to other structures. In order to control the settlement of the ground surface or protect other structures, the secondary grout injection technique applied inside the TBM (i.e., secondary backfill grouting) is usually employed as an additional measure. In terms of studies of the TBM secondary grout injection technique, the industry is still lacking systematic organization of studies between practices and theoretical analyses. Therefore, the design and choice of secondary grout injection are primarily decided by considering on-site conditions and the proximity of neighboring structures. There is still no comprehensive study of the soil layer. The case study in this paper mainly focuses on the layer of on-site soil which consists of clay or silty sand. As for the shield tunnel excavation, the settlement of the ground surface can be controlled by applying secondary grout injection. In addition, good construction management would be the best way to control the settlement of the ground surface. The case study in this paper is an example which indicates that modified construction management during shield tunnel excavation not only allows the settlement of the ground surface to be controlled properly but also ensures no damage or settlement of the ground of neighboring structures. In this paper, the settlement of the ground surface is estimated based on the settlement calculation proposed by Peck. In addition, the loss rate of ground is used to discuss the settlement of the ground surface controlled by increasing the proportion of polymer admixture and changing the TBM mirror face earth pressure from active to passive. Hence, in this paper the settlements measure with surface-type settlement points and the measured deformations with the convergence points are used as evidence for the effect of construction management on the control of the settlement of the ground surface. In this paper, an MRT project which has been completed was used as an example. According to its result, it is inferred that secondary grouting injection provides good control over the settlement of the ground surface and protection of neighboring structures. However, it has little effect on the clay and silty sand layers. Increasing the polymer admixture and employing passive earth pressure as the mirror face earth pressure for the TBM may also improve control over the settlement of the ground surface. With these discussions, it is expected that theoretical analysis combined with engineering practice may serve as a consistent approach for planning shield tunnel excavation in the future even when complications from soil layers and other factors are not overcome.