A Simplified Approach to Design Jet-Grouted Bottom Sealing Barriers for Deep Excavations in Deep Aquifers

Chengyong Cao,Chenghua Shi,Mingfeng Lei

doi:10.3390/app9112307

Abstract

This paper presents a simplified methodology for the design of jet-grouted bottom sealing barriers (temporary water-tightness structures) for deep excavations that was undertaken in deep aquifers. The bottom sealing barriers are usually required to prevent uplift failure against the water head below. Additionally, jet-grouted bottom sealing barriers are never perfect due to the uncertainties of jet grouting columns at the site, so the design must carefully consider the analysis of seepage. For these reasons, the proposed calculation procedure focuses on two different failure mechanisms (i.e., “instability failure” and “seepage failure”) of massive bottom sealing barriers. Subsequently, the design parameters of the jet-grouted bottom sealing barriers (e.g., depth and thickness) for an excavation case were determined while using the proposed design procedure. The field pumping test results show that the water-tightness performance of bottom-sealing barriers performed at site is good, which ensures that the water level inside the excavation can reach the desired level and the groundwater drawdown outside can be minimized. The leakage flow rate of bottom-sealing barriers is lower than the designed maximum allowable seepage when the water level inside stabilizes at the final period of the pumping test.

Highlights

IntroductionThe development and utilization of underground space engineering (such as subways, underground stores, and underground parking, etc.) has become an important way of urban construction in China to achieve sustainable urban development
The development and utilization of underground space engineering has become an important way of urban construction in China to achieve sustainable urban development
This paper proposes the calculation method of jet-grouted bottom sealing barriers considering seepage failure mechanism, which is based on the hypotheses without considering the fluctuation of groundwater level during pumping inside the excavation

Summary

Introduction

The development and utilization of underground space engineering (such as subways, underground stores, and underground parking, etc.) has become an important way of urban construction in China to achieve sustainable urban development. Deep excavations are an important part of urban underground space engineering construction, which is usually high-risk construction project because of great difficulty and danger during excavation. There are Marine and Continental sediments of Quaternary Period with a large thickness that is below the water table in China’s coastal areas (e.g., Tianjin, Shanghai, and Fuzhou, etc.), which are mainly composed of miscellaneous fill, silt, clay, sand, and gravel, etc. The confined aquifers usually have a high piezometric head in these areas. In these cases, groundwater control is a rather difficult work for deep excavation in these coastal areas. Dewatering must be carried out prior to the excavation in order to prevent water inflowing towards the excavation during the excavation

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Conclusion