Abstract
This paper studied the excavation of a foundation pit above a running subway tunnel in Hangzhou soft soil. The zoned excavation and top-down construction techniques were adopted to control the deformation caused by foundation pit excavation. The excavation was divided into four parts, named Zone A, B, C, and D. Zone A adopted temporary diagonal bracing, and the control effect of deformation was poor; it was cancelled and changed to rapid excavation and thicker cushion in Zones B, C, and D. During the whole construction process, the lateral displacement and settlement of the diaphragm wall, surrounding ground surface, and building settlement were monitored and analysed. The data showed that the lateral displacement of the diaphragm wall was effectively reduced by the zoned excavation technique, and the maximum lateral displacement value of the diaphragm wall in Zone A was the least; rapid excavation and reduced soil exposure time also could effectively control the deformation, and the lateral displacement of the diaphragm wall in Zone C is less than Zone B and Zone D. The ground settlement is strongly related to the lateral displacement of the diaphragm wall. In order to reduce the surrounding ground and building settlements, efforts should be made to reduce the wall lateral displacement.
Highlights
In recent years, the scale of Hangzhou has expanded rapidly. e development of underground space will cause the redistribution of soil stress and affect the surrounding environment
Scholars had collected a large number of excavation cases, compared the deformation characteristics of foundation pits under various geological conditions with indicators such as the maximum lateral displacement of the excavation and the maximum ground surface settlement, and established empirical parameters in different regions for future design practices [1,2,3,4]
Some scholars conducted statistical analysis on regional foundation pits and formed regional indicators; the maximum lateral displacement of the foundation pit in the hard clay soil area collected by Clough [5], Yoo [6], Long [7], etc., was between 0.05 and 0.20% He (He was the excavation depth of the foundation pit, omitted later). e maximum lateral displacement of foundation pits in soft soil areas collected by Ou [8] and Long [7] was between 0.40 and 0.48% He
Summary
The scale of Hangzhou has expanded rapidly. e development of underground space will cause the redistribution of soil stress and affect the surrounding environment. In order to make full use of the land resources in the central area of the city, the excavation depth of the foundation pit is large and the scope of influence is wide. Some scholars conducted statistical analysis on regional foundation pits and formed regional indicators; the maximum lateral displacement of the foundation pit in the hard clay soil area collected by Clough [5], Yoo [6], Long [7], etc., was between 0.05 and 0.20% He (He was the excavation depth of the foundation pit, omitted later). E maximum lateral displacement of foundation pits in soft soil areas collected by Ou [8] and Long [7] was between 0.40 and 0.48% He. Chinese scholars had performed the analysis of deformation characteristics of foundation pits. Using the top-down construction method, the excavation depth of the foundation pit reached 23.0 m. e method to control the deformation of the project could be available for reference for similar projects of the same type
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