Study On Load Model&Simplified Analysis Method Of Ultra Deep Foundation Excavation In Sandy Pebble Stratum

The middle air shaft engineering of Lanzhou rail transit line 1 which between Olympic Sports Center and Century Avenue is 33.4m long,20.4m wide,45.1m deep.It is the deepest foundation pit engineering in permeable sandy pebble stratum in China right now.As a major risk project of Lanzhou rail transit line 1,it has the characteristics of high groundwater level,high permeability coefficient and on the brink of the Yellow River.The enclosure structure adopts 60.1m concrete underground diaphragm wall,the main structure adopts the concrete five-layer box frame structure,top-down construction is taken.In order to study the mechanical behavior and load model of super deep shaft,site construction monitoring,FLAC^3D numerical simulation and indoor model experiment research method is used in this paper.The research content is mainly to the diaphragm wall displacement,internal force,water pressure and soil pressure,and the simplified calculation method of the structure,the specific research contents and conclusions are as follows:?1?This paper uses FLAC^3D numerical simulation and construction monitoring to study the top-down construction mechanics behavior of the ultra-deep air shaft.At the same time,the reliability of numerical simulation results is verified.?2?In this model test,the film sensor is used to improve the test method of the traditional earth pressure box.In order to understand the air shaft's water and earth pressure distribution,a complex model test which considers groundwater seepage and top-down construction is designed in this paper.?3?On the basis of indoor model test and FLAC^3D numerical simulation,The soil and water pressure distribution of air shaft is put forward.This paper proposes and improves a simplified structural calculation method for the "two-wall-in-one"&top-down construction of the ultra-deep air shaft,which based on the traditional foundation structure of elastic foundation beam method.Then,compared with the simplified calculation and numerical simulation results,the simplified calculation results is adjusted to meet the practice.