In-situ Immersion Test And Analysis Of Pleistocene Epoch Q₂ Loess At Xi'an Tableland

It has a long history for loess to be foundation of buildings.The collapsibility of loess is a typical issue of engineering geology in loess area,which tremendously impacts the project construction actions and greatly damages the buildings.With implementation of western development strategy of China,various projects on a large scale were continually put into operation,and range of construction extends into loess tableland.The engineering properties of Q₂ loess deep seated or at loess tableland were paid increasing attentions.In engineering practice,it is found that,the engineering properties of Q₂ loess are distinctly different from that of new loess.In order to take precautions against hazard of loess collapsibility and save construction cost,it is necessary to properly determine the collapse pattern of Q₂ loess.On the basis of numerous test results performed by our predecessors,collapsibility of Q₂ loess under overburden pressure at loess tableland was tested,and determination of its collapse pattern was analyzed through water immersion test in a lager test pit and pile load test in submerged soils at new campus of X University,Xi'an city.First,the geotechnical investigation report for the project site shows that,the site is a collapsible one under overburden pressure;second,in field water immersion test in a large test pit,collapse deformation at different locations,collapse deformation in layers of collapsible soils,and deformation of ground surface outside of the pit were measured to determine collapse pattern of the site.The test result indicants that,under overburden pressure and at condition of water immersion over a wide area,no collapse deformation occurred at this site,so the tested site should be determined to be non-collapsible site under overburden pressure;finally,in the process of load test on ram-compaction piles with composite bearing base in water immersion,shaft resistance of the pile was measured,showing that,bearing capacity of ram-compaction piles with composite bearing base after water immersion slightly decreases,and no negative side resistance occurs.After comparison analysis between laboratory tests,water immersion tests in large test pits and pile load tests,middle pleistocene Q₂ loess at the site is determined to be not collapsible under overburden pressure to provide some explicit measured data for further research of collapsibility of Q₂ loess,based on which,analysis of collapse difference of Q₂ loess was conducted so as to give some suggestions for determination of collapse pattern of Q₂ loess.