Fluid-solid Coupling Analysis On The Urban Land Creation In The Loess Hilly-gully Region

In recent years, with the rapid development of the national economy and the implementation of the western development strategy, western city is accelerating progress process, and then it is urgent to expand the scale of city. However, the western territory of our country is very mountainous, and the construction land is gravely insufficient, "Central dispersal and external expansion, found city in the mountains" has become the inevitable choice. Located in the loess hilly-gully region, urban land creation engineering project under Yan’an new district construction is to solve the contradiction between urban construction and land resources. After the urban land creation engineering project in the loess hilly-gully region, the valleys were buried by fillings, and the drainage of surface runoff and springs is blocked, which promotes suriace runoff to groundwater that affects the stability of excavation and embankment in loess hilly-gully region. Phreatic water is turned to confined water because of the hardening measures to the site. In addition, the laying of blind ditch exacerbate complicated of urban land creation engineering further. Therefore, it is necessary to analyze the stability of urban land creation engineering project under the influence of groundwater in loess hilly-gully region.Taking the first-stage project of new district building in Yan’an as an example, the present paper has established a 3D geological model by GOCAD, ANSYS and FLAC3D software, based on the field data collection, generalized geological model, etc. And then 10 integrated models of urban land creation engineering were completed as typical geological sections that were chosen along the flow direction of Qiaoer Valley. According to the geotechnical engineering impact induced by hardening measures and drainage, a series of modeling scheme was designed in the simulation, such as no hardening-no drainage, hardening-no drainage and hardening-drainage. Applying the characteristics that interlace unit can be generated automatically by attaching to the specified surface in FLAC3D, the present paper has successfully created irregular groundwater level for simulation. On that basis, this paper studied the distribution feature of stress and pore pressure field from vertical and horizontal aspects in fluid-solid coupling module. Finally, the paper contrasted the characteristic of stress and pore pressure under different conditions vertically through selecting monitoring points in the place of main blind ditch as observation points and analyzed the drainage effect of different types of blind ditch through selecting section 7 as typical section.Main conclusions as follows:Stress distribution tends to be centralized around the blind ditch paved in Neogene red clay and Quaternary loess under the condition of hardening-drainage. While stress concentration caused by stratum missing is more badly than what caused by the laying of blind ditch in any working conditions, which should be attention. Not all of blind ditches along the flow direction work, and different types of blind ditches laid in the same section horizontally take different effects. Pore pressure shows a trend of decrease after increase in the process of the groundwater flowing from secondary blind ditch to main blind ditch. After the groundwater of secondary blind ditch collecting at the main blind ditch, pore pressure of main blind ditch will increase and gradually be stable once the groundwater didn’t drain out timely in main blind ditch.