Research On Mechanical Characteristic Of Bracing And Retaining Structure In Large Deep Excavation

In recent years,with the vigorous development of China’s infrastructure,more and more high-rise buildings and underground rail are concentrated in urban centers,which generate a lot of deep excavation.Because of density of buildings, narrow space of the city center, extremely complex surrounding environment of the construction, the difficulty of excavation are increasing, and the safety requirements of the excavation are more stringent. Row piles, diaphragm wall, cement walls, against the wall for the arch, soil nail walls and row piles-internal support and various types of other support are used in common pit.Study the mechanical properties of the supporting structure to ensure safe construction excavation has become a hotspot problem into the engineering field. Row piles- internal support is a new type of support structure, which began to be used and developed in the 1980 s, the advantages of facilitate the construction, less investment, short construction period, distortion control are making it a deep foundation pit preferred solution in supporting structure, especially in the application of soft soil conditions.In this paper, based on engineering in the typical soft soil area, the middle and lower reaches of the Yangtze river in wuhan, because the flow separation, from top to bottom sediment particles from coarse to fine, flood land as the typical phase transition rule in the Yangtze river sedimentary detritus carrying hydraulic condition and flood plains, lakes, and studied on both sides under the action of the change of sedimentary environment, on the level terraces formed a set of quaternary holocene lacustrine facies alluvium, the typical soft clay layer and the underlying soil layer of dual geological structure, the formation of foundation pit accident rate is high.At present, achievements were made in aspects of the type of supporting structure, mechanical properties and stability factors by domestic and foreign scholars in the row pile- internal support, but the research is not perfect enough.In this paper, based on the Wuhan Yangtze River Media Building excavation, building piles in deep pits- internal support structure in the Yangtze River level terrace binary geological environment is researched, the supporting structure mechanical characteristics, deformation characteristics, strength properties and failure characteristics and influencing factors of row piles- internal support were focused on. First, by reviewing of literature, status quo excavation was researched, the main characteristics and problems were mastered, then calculation model of row piles- internal support was built by using ANSYS and TianHan(V2005) software, then the earth pressure distribution, supporting structure stress, deformation and failure characteristics were analyzed, finally projects to be implemented relying on the development of monitoring programs. The mechanical properties, failure characteristics and influencing factors of row piles- internal support were mastered through theoretical analysis and comparative analysis of the experimental results, and supporting structure is proposed to optimize the design and improve the corresponding theoretical results for the similar engineering design calculations reference. The main contents and conclusions are as follows:(1)The structure characteristics and soil pressure distribution mode of building piles in deep pits- internal support structure in the Yangtze River level terrace binary geological environment were studied on, which can establish numerical model, and provide theoretical guidance for construction safety monitoring solution.(2)The way of boundary constraint and confining pressure distribution patterns could be the key factor of the support unit design calculation. Based on the TianHan(V2005) software, calculation model of inner support was built, the effects of deformation and damage characteristics in different constraints,different confining pressure distribution on the internal forces of the support were analyzed, which can be reference for the design.(3)Based on ANSYS platform, the finite element calculation model of row piles-internal support was built to realize the simulation of excavation process, the quantitative analysis were made about surrounding soil pressure, internal force on pile internal force, support, etc. Supporting horizontal displacement, bending moment and shear force were significantly increased, while the pile of foundation pit excavation depth, and all indexes reached the maximum and being stable when the excavation reach the design elevation. The strut axial forces presented the same change rule with the increase of excavation depth.(4)The Yangtze River Media Building deep excavation monitoring program was designed for supporting piles, internal support, the surrounding soil, etc. Results shows that supporting pile bending moment, horizontal displacement value arise with the increase of excavation deepen gradually, and axial force on the excavation support deepening increases, and tends to be stable, supporting pile and support within the monitoring value does not exceed the alert. The construction safety was ensured and accumulated data is to revise local rules.(5)The theoretical calculation and monitoring results show that support, supporting pile and the soil pressure in the various mechanical indexes such as monitoring data and numerical results are in good agreement. Monitoring and inversion analysis of the results of numerical calculation show that in a typical binary geologic environment in deep foundation pit supporting structure within the pile- supported peripheral approximate triangular distribution of earth pressure, the supporting plane triangle and rectangular composite confining pressure distribution mode is the most suitable in this project(6)Successful application of the deep excavation engineering pile and concrete support in Wuhan Yangtze river media building ensured the safety of the foundation itself and the surrounding buildings, roads, which has certain social economic benefits and the practical significance,and gained experience of deep foundation pit engineering of the future similar geological environment accumulated.