Abstract
The muck and mucky soil in Nansha District exhibit characteristics including higher water content, large void ratio, low natural density, high compressibility, and low strength. Compared with marine soft soils in other domestic regions, they exert a more pronounced influence on engineering construction and operation, posing substantial risks and challenges to rail transit network construction and operation. In response to soft soil strata, certain domestic regions and municipalities, such as Shanghai and Shenzhen, have established targeted management requirements in rail transit protection specifications and relevant regulations, including expanded protection zone scope and strict prohibition of displacement piles, to mitigate the impact of engineering design and implementation in soft soil areas on existing rail transit structures. Based on the particular characteristics of soft soil in the Nansha region, this paper analyzes various targeted measures in foundation pit engineering design concerning their effects on operating metro tunnels. Furthermore, utilizing a river-crossing passage project in Nansha District as a case study—the project crosses over Metro Line 4 twice with a minimum vertical clearance of 4.6 m from the metro tunnel—this paper investigates the influence of external foundation pit engineering on rail transit structures from design and control measure perspectives. It proposes conclusions and recommendations such as a support pile length-to-depth ratio L/H>3, the requirement that support walls adjacent to the metro should be rock-socketed, and that isolation walls should function as permanent structures, which hold significant importance for protecting rail transit operation and structural safety under such special geological conditions in the Guangzhou area.
Full Text
Preamble
Analysis of the Impact of Foundation Pit Design and Implementation on Existing Subway Structures in Soft Soil Areas of Nansha
Ou Suihui
Guangzhou Metro Engineering Consulting Co., Ltd., Guangzhou 510000, China
Abstract
The muck and mucky soils in Nansha District are characterized by high water content, large void ratios, low natural density, high compressibility, and low strength. Compared with marine soft soils in other regions of China, these soils exert more pronounced effects on engineering construction and operation, posing substantial risks and challenges to the development and operation of rail transit networks. In response to these conditions, certain cities such as Shanghai and Shenzhen have implemented targeted management provisions in their rail transit protection codes and related regulations, including expanded protection zone boundaries and prohibitions on displacement piles, to mitigate the influence of engineering design and construction on existing rail transit structures in soft soil areas. Based on the unique characteristics of Nansha's soft soils, this paper analyzes various targeted measures in foundation pit engineering design and their impacts on operating subway tunnels. A cross-river channel project in Nansha District, which crosses Metro Line 4 twice with a minimum vertical clearance of 4.6 m from the subway tunnel, serves as a case study to investigate the effects of external foundation pit projects on rail transit structures from both design and control measure perspectives. The study proposes key recommendations including a support pile length-to-depth ratio of L/H>3, the requirement that retaining walls on the subway-adjacent side be rock-socketed, and the use of isolation walls as permanent structures. These conclusions are of significant importance for protecting rail transit operation and structural safety under such special geological conditions in the Guangzhou region.
Keywords: deep soft soil; foundation pit support design; analysis of rail transit protection measures