Study On Slope Support Of Deep Foundation Pit Of Chengdu Expansive Soil

At present,the rapid development of urban construction in Chengdu,with the development of underground space,a large number of deep foundation pit project came into being.Deep foundation pit engineering is extremely important and complex,many engineering personnel because of its lack of understanding,and produce a large number of accidents.Expansive soil is a typical cohesive soil with wet swelling and shrinkage properties,which is all over the east of Chengdu.The engineering design personnel often the special properties of the expansive soil lack of knowledge,making a large number of deep excavation problems,resulting in serious accidents,the Chengdu area of deep excavation engineering on expansive soils supporting research has very important practical significance.The main research results and conclusions are as follows:In this paper,the research status of expansive soil and deep foundation pit is discussed briefly,and several kinds of common foundation pit supporting forms are studied.The influence of water content on the shear strength and swelling force of expansive soil was determined by direct shear test and swelling force test.The fuzzy comprehensive evaluation method is established and applied to the optimization of the deep foundation pit supporting scheme.Finally,according to the results of laboratory tests,the FLAC3 D software is used to analyze the deformation of the foundation pit under 4 different working conditions,and propose the treatment method of the deep foundation pit supporting in Chengdu region is analyzed and compared.1,Through the shear test of expansive soil under 8 different water content,obtained:(1)The shear strength of expansive soil is greatly affected by the change of water content,and the shear strength decreases gradually with the increase of water conten;(2)Under different moisture content,expanded clay concrete value and internal friction of poly the angle of soil;(3)Expansive soil cohesion and internal friction angle and moisture content between the two expressions:0.14258.8wc e-= 、?0.05118.0we-=;(4)The expansion of clay expression between the two angle and the moisture content of cohesion and internal friction;(4)the shear strength of expansive soil under consideration moisture condition: tan()hw bwt =sde +ae.2,Through the swelling force test under 8 different moisture content,obtained:(1)The expansion force of the change of water content influence;(2)The change between the swelling force and the water content is linearly decreasing with the increase of the water content;(3)The water rate is low,there is great potential for the expansion of expansive soil,the engineering effect of great uncertainty.3,Set up a hierarchical fuzzy comprehensive evaluation method,and the scores of each factor of foundation pit are affected by research and consulting experts,to optimize the expansive soil deep foundation pit supporting scheme using the optimization method to get the most suitable for the expansive soil of deep foundation pit supporting scheme for pile retaining.4,According to the particularity of the expansive soil,set 4 conditions,and modeled by FLAC3 D software,analyzed 4 kinds of displacement of foundation pit wall,under the condition of soil at the bottom of the pit uplift,subsidence differences and enclosure deformation,and puts forward some suggestions: Chengdu expansive soil in deep foundation pit support design,can be combined with engineering experience and hydrogeology the situation,the expansive soil shear strength index decreasing,in the expansive soil layer within the horizontal direction to the horizontal force inside the foundation pit,in order to consider the effect of moisture content on the mechanical properties of expansive soil,the support design and excavation deformation situation is more consistent,accurate guide construction,excavation of foundation pit for escort.