Corner and partition wall effects on the settlement of a historical building near a supported subway excavation in soft soil

Abstract

This paper discusses the settlement characteristics of a historical building near the corner of a supported excavation made in soft soil during the construction of a subway. Measurements from the study site at Daliang Station, Foshan, China are analysed, and the effects of partition walls are explored. The complexity of the corner effects of braced excavations is considered, and deformation forms and damage to buildings near the corners are analysed. Depression, arching, deflection, torsion, differential settlement, and inclination are studied. Finally, partition walls are proposed to reduce the impact of the corner effect on the buildings. We found that the corner effect limits the deflection and deformation of a corner building and has little effect on torsional deformation. Partition walls can significantly reduce the horizontal deformation of underground diaphragm walls and the settlement of corner buildings. The results help to understand the stress behaviour and deformation mechanism of buildings near the corners of braced excavations and on ways to control such deformation.

Introduction

The supported subway excavation in soft soil is a project with various unfavourable conditions (Guo et al., 2019, Huang et al., 2020, Shen et al., 2015). The stress and deformation of its supporting structure is a very complicated three-dimensional problem. The spatial effect of the supported excavation is mainly reflected in the influence of excavation corner effect. Furthermore, the deformation and stress of its surrounding structure and the settlement and deformation of the surrounding surface, buildings, and structures are affected by excavation corner effects (Sun et al., 2017, Yuan et al., 2019, Zeng et al., 2019, Zhang et al., 2012). Its geological disadvantages and the length–width ratio exacerbate the impact of the corner effect (Gotman and Gotman, 2019, Huang et al., 2019; 2019., Mei et al., 2019, Geng and Yu, 2017). Therefore, the existence of the corner effect, to a certain extent, has transformed the settlement deformation characteristics of buildings adjacent to a supported excavation, making their deformation characteristics complex (Finno et al., 2007, Ou et al., 1996, Wang and Zhou, 2011).

Many influencing factors are involved in supported excavations for subways made in soft soil. Such excavations have become a focus of research in geotechnical engineering. Present research mainly emphasizes the following aspects: the deformation and stress of supported excavation enclosure structures (Parthasarathi et al., 2019, Shi et al., 2019, Sun et al., 2019, Wang et al., 2019, Wang et al., 2019, Ni et al., 2015) and their influencing factors (Liu et al., 2019, Liu et al., 2019, Luo and Li, 2019, Wang et al., 2019, Wang et al., 2019); settlement analysis of the surrounding surface and buildings (Li et al., 2019, Liu et al., 2019, Pathirana et al., 2019, Sun et al., 2019); and the stability of groundwater and supported excavations (Zhang et al., 2017, Zhang et al., 2013, Zhang et al., 2020;2020., Xu et al., 2017, Liu et al., 2019, Liu et al., 2019, Li et al., 2019, Kasani and Hamidzadeh, 2018). Nevertheless, research on the spatial effects of supported excavations is insufficient. In actual projects, there are issues such as the excessive deformation of corner buildings. Therefore, corner buildings, especially ancient buildings, have been extensively studied.

The settlement and deformation of buildings adjacent to supported excavations for subway systems in Taipei (Ou et al., 1996), South Korea (Yoo, 2001), Singapore (Wong et al., 1997), Shanghai (Wang et al., 2009), and other places have been studied using on-site monitoring. Furthermore, the construction conditions, geological conditions, housing foundation conditions, time and space effects, and influences of building settlement caused by supported excavations at various construction stages have been studied. The trench construction of underground diaphragm wall-enclosure structure, poor geological conditions, soil erosion between supporting piles and improper construction procedures have been found to induce excessive building settlement (Nakai et al., 2006, Liu and Wang, 2009). Additionally, the relationships between the three-dimensional effect of the envelope structure deformation, ground settlement, and supported excavation deformation and building settlement have been determined (Finno et al., 2007, Pan et al., 2008, Lee et al., 1998), while studying the settlement and inclination of the buildings. Nevertheless, research on corner effects on settlement, deformation, and damage to buildings relevant to corner construction of metro supported excavations in soft soil are needed. The deformation mechanism of corner buildings during the entire process of a supported excavation needs to be further explored. A feasible measure is imperative to reduce corner effects and the impacts of the supported excavation constructions on building settlement.

This paper investigates the settlement characteristics of corner buildings and associated corner effects based on measurements taken during an entire supported excavation in soft soil. Depressions and arches, deflection and torsion, differential settlement, and the inclination of corner buildings near braced excavation are analysed. Based on the idea of the deformation propagation, a measure of the partition walls to reduce the deformation of diaphragm wall and building settlement is proposed. The influences of partition walls with different positions, rigidities and depths on building settlement are analysed. The results provide a theoretical foundation for reducing the influence of the corner effect on the deformation of buildings.