Abstract
Field monitoring in the process of excavation of foundation pit is an important measure to reduce the risk. This paper describes a case study of the filed monitoring data during the process of deep foundation pit excavation in soft soil areas. The displacements of the diaphragm wall top were analysed and found that the horizontal displacement showed the convex shape, while the vertical displacement showed the concave shape. Based on the field monitoring data, the deformation mode of lateral displacement of the diaphragm wall belonged to the composite mode. The relationship between maximum lateral displacement and excavation depth showed a strong linear correlation. The horizontal displacements of bracing pillar decreased with the increasing of bracing stiffness, while the effect of bracing stiffness on vertical displacements of bracing pillar could be ignored. The settlement profile computed using the method of Hsieh and Ou was in good agreement with the field observations and better described the development trend of the ground surface settlement. The ratio of the maximum ground surface settlement (δvm) to the maximum lateral displacement of the diaphragm wall (δhm) was in the range of 0.74∼0.88, belonging to the range of 0.5∼1.0 proposed by Hsieh and Ou. This paper provides a reference basis and related guidance for similar projects.
Highlights
As the development of urban construction and underground space exploitation scale, a large number of deep foundation pits appear in the construction of high-rise buildings and underground traffic engineering
The variation regularities of the diaphragm wall deformation, horizontal and vertical displacement of bracing pillar, and ground surface settlement are analysed based on the filed monitoring data during the process of deep foundation pit project in soft soil areas
Vertical displacement and the base plate should be poured timely when finishing excavation. e vertical displacement of the diaphragm wall top near the middle part increased with the increasing of excavation depth at the beginning, and reached an equilibrium level after finishing the fourth bracing
Summary
As the development of urban construction and underground space exploitation scale, a large number of deep foundation pits appear in the construction of high-rise buildings and underground traffic engineering. The variation regularities of the diaphragm wall deformation, horizontal and vertical displacement of bracing pillar, and ground surface settlement are analysed based on the filed monitoring data during the process of deep foundation pit project in soft soil areas. E excavation sequence was required to combine with the installation of local bracing system, in order to ensure that the time lag between excavation of part earthwork and corresponding construction of bracing structure was in the range of allowable design and to control the deformation of foundation pit and surrounding structures. According to the Technical Code for Monitoring of Building Foundation Pit Engineering (GB504972009), the alarming values on monitoring are the cumulative allowed variation of 30 mm or variation rate of 3 mm/d for displacement of the diaphragm wall top, displacement of bracing pillar, and ground surface settlement, while the alarming value on monitoring is the cumulative allowed
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