Study On The Deformation And Destruction Characteristics Of Piled Raft Foundation In The Combination Area With Loess Digging And Filling Region

Yan’an is located in the south of Shaanxi province, belonging to the typical mountain valley type cities. Loess hilly gully topography determines the shortage of available land resources, which seriously limits the development of the city. The urban population density of Yan ’an is 1.5 thousand people per square kilometer, higher than the super city such as Beijing and Shanghai in some areas, which leads to densely built areas, traffic congestion and insufficient public infrastructure. Expanding the new urban development space and gradually improving the urban functions is the priority thing of Yan’an city’s development. According to the development strategy of Yan’an,They will build a double old Yan’an city in gully areas surrounding the old one by cutting the mountain, filling in the ditch, stretching out. The "mountain city" project of Yan’an in collapsible loess regions now is the world’s largest engineering in geotechnical, also the first in the world history of city construction. Because of the large filling area of construction site, thick filling-up thickness and high-level collapsibility, the foundation deformation, uneven settlement problem and so on for the high fill foundation problem become the core problem of the construction site safety, also an important topic needs to be urgently further researched in construction of the loess high-fill areas.There are a great deal of researches of city-building in mountain area,but relatively scattered, not systematic and deep. The loess hilly gully region cut mountain to build new district still have no study, so there is no mature experience for reference at home and abroad. In this paper, based on Shaanxi province Science and Technology Creative Engineering Plan Projects- major geological and geotechnical engineering research of Yan’an loess ravine and gully region construction- construction site engineering planning and design technology study. Mainly aimed at Yan’an district development strategy of ―cutting the mountain to fill in the ditch‖, conducted the piled raft foundation model experiment filling area. Analysis the basic patterns of stress, deformation characteristics of piled raft foundation under the uneven settlement, to understand the effect of piled raft foundation to eliminate the loess even deformation in the combination area of digging and filling site, analysis the feasibility and disaster prevention and control measures for the construction of loess high-fill site and comprehensive analysis the stress and deformation of the digging and filling loess foundationThe main results of the study is below:(1) The large scale physical model test of the piled raft foundation is carried out, and the stress and deformation characteristics of the piled raft foundation under different ground conditions are analyzed;(2) The relevant conclusions of the model test are verified and replenished by numerical simulation method, and the bearing behavior and deformation mechanism of the piled raft foundation across the loess digging and filling site are further studied;(3) Combine the results of model test and numerical simulation, structure safety monitoring methods for the construction project of the loess digging and filling site are presented.