Calculation Method And Application Of Unsaturated Collapsibility Of Loess Based On Suction Stress

Loess is a special soil with collapsibility.The coefficient of loess collapsibility is calculated by dividing the collapsibility between the natural moisture content and the saturated moisture content obtained by experiment by the thickness of the sample.Ho wever,as a matter of fact,with the increase of water content,even if the saturated w ater content is not reached,the unsaturated collapsible loess will also occur,and the p henomenon of unsaturated collapsible loess is also very common.At present,the resea rch on the mechanics mechanism and calculation method of unsaturated collapsible loe ss is not enough.The yongjing black mesa area in gansu province as a case study ar ea,the loess sample in four different locations in the conventional wet test,TRIM,la boratory test,on the basis of introducing concept of stress absorption,explored the col lapse deformation and stress response of the relationship between absorption,establishe d the collapsibility of unsaturated loess deformation calculation method,and applicatio n and black mesa area,irrigation simulation verified the collapse deformation caused b y history,forecasts the development trend in the future.(1)The cause of ground subsidence in Heifangtai area is found out.The loess with large pore structure and water sensitivity is the internal cause of collapsible settle ment.The increase of loess moisture content and the rise of water table are the induc ement factors.The serious surface subsidence in the study area is the result of the co mbined action of the saturated subsidence of loess caused by the rise of groundwater level and the unsaturated subsidence of loess caused by the increase of moisture conte nt in the aerated zone under long-term irrigation conditions.(2)The mechanism of loess collapsibility based on suction stress is revealed.Th e TRIM test instrument and the concept of LU suction stress were introduced.Throug h a large number of loess unsaturated characteristic tests,the soil-water characteristic c urve of loess in the research area was established,and the absorption stress function a nd permeability coefficient function under the condition of humidification and dehumid ification were obtained.With the increase of loess water content,the absorption stressdecreases sharply and the permeability coefficient increases sharply.The suction stress of the loess decreases with the increase of the initial loess moisture content.The sm aller the initial moisture content of the loess,the greater the suction stress of the loes s and the greater the collapsible potential of the loess.(3)The calculation method of unsaturated collapsibility of loess is proposed.In the system analysis of collapsibility loess collapsibility and unsaturated past research,o n the basis of introduction of unsaturated soil mechanics theory based on appeal,com bined with the research area of the loess collapsibility test and TRIM test data,analyz es the loess collapsibility deformation and stress response of the relationship between absorption,determines the unsaturated loess collapsibility deformation calculation of ke y parameters,set up for different moisture content change interval of unsaturated loess collapsibility deformation calculation method.(4)Using this method,the total subsidence generated by point irrigation in the s tudy area was simulated to be 2.72 m,of which the unsaturated subsidence was 0.92 m,accounting for 33.8% of the total subsidence.It is predicted that if the groundwater l evel in the study area rises by 5m,a subsidence of 0.3m will occur,with a subsidenc e potential of 0.6m.