Effects Analysis Of Excavation Width On Retaining Structure And Soils Nearby

The number of multi-strutted excavations constructed in many major cities around the world has been increasing in recent decades. Current excavation studies mainly focus on the deformation of retaining structure and surrounding soils, but the width of excavation has seldom been considered. Besides, the commonly used design software is based on elastic foundation beam method, which cannot take the excavation width into consideration. However, rich engineering practices show that ’narrow’ excavations have easily-controlled deformation compared with regular excavations. As a result, the stiffness and depth of retaining structure and the scale of pit reinforcement can be decreased to some extent.1, Finite element software, PLAXIS, was adopted for analysis. Different kinds of unit type and soil constitutive models were described in detail. Six groups of analysis model with various width/depth ratios were established (depth=15m, width=6m,15m,30m,45m,60m, and75m, while the width/depth ratios=0.4,1,2,3,4and5, respectively). The effects of ratios on the soil settlement near excavation, horizontal displacement and bending moment of retaining wall, bottom heave and strut axial force were fully studied. The results indicated that it was necessary to consider the excavation width while designing the retaining structure.2, Under different width/depth ratios, the effects of retaining structure stiffness were different, so were the retaining wall length and pit reinforcement. These effects were thoroughly studied, and the optimal feasibility of ’narrow’ excavation was clear.3, A ’narrow’ excavation case was adopted. That was a subway station in Shanghai. The excavation depth was38m and width was22m. The wall length of this case was smaller than similar cases, while the monitoring data didn’t show large wall displacement. This case revealed the economy and feasibility of considering excavation width.