Experimental Study On Seepage Degradation Of Reshape Saturated Loess Under Seepage

This paper relies on the national natural science foundation project"The Research of Properties Deterioration Mechanism of Loess Engineering and Life Prediction of Loess Structures".On the summary predecessors' achievements, by doing experiments in the laboratory to simulates natural condition of earth dam under long-term seepage effects using acid solution as penetration fluid accelerate the degradation process of remolded saturated loess samples, this paper explored the essence of degradation on remolded saturated loess samples under long-term seepage condition to research Q3 remolded loess in Yangling through the measurements of the permeability coefficient, the leaching quantity of calcium ions infiltration and its rate leaching rate.The main conclusions are as follow:(1) The permeability coefficient k reduces as the penetration processed during the Seepage of the remolded saturated loess. In the early stage, soil particles migration had a big frequency and k reduced in larger extent; while later soil particles migration had Small frequency and k reduced slowly.(2) A complex chemical reactions happened between the salts of Loess and both hydrogen ions and acetic root ions of Penetration fluid, Mainly by hydrogen ions and carbonate reaction. Some gas is trapped in the pore which reduces the effective channel of penetration fliud in the conventional penetration test, but in the Triaxial penetration test, the effect of gas to permeability coefficient can be ignored because carbonic acid which was formed after the reaction of hydrogen ions and carbonate could hardly be decomposed into carbon dioxide gas owing to confining pressure and back pressure exists.(3) For any dry density of penetration samples, the permeability coefficient reduce as the increase of PH value of the seepage fluid in lower confining pressure, The variance of the permeability coefficient corresponded with different PH value also decreases as confining pressure increasing and The permeability coefficient is no longer follow the above rules when the confining pressure increases at 300kPa, meanwhile the influence of the permeability coefficient on the confining pressure has exceeded the influence of the PH value. Different dry density and consolidation penetration confining pressure, different PH value mutual coupling determined the size of the permeability coefficient.(4) After long-term seepage condition, the essence of loess degradation are the action between Penetration liquid and Loess particles which caused irreversible changes of porosity ratio. The main exemplifications are as follow: 1) The seepage force caused Particles migration; 2) The gas was bring in through permeability fluid; 3) Particles sticky gathered force was constantly lost through the loss of Cementation content among particles which caused a further particle migration. Three aspects eventually reflect that Uneven distribution of porosity ratio along the Seepage direction. Minimal porosity ratio face appeared which eventually determined The size of the permeability. the influence of gas can be ignored in the triaxial penetration tests, but it cannot be ignored in the Conventional penetration tests.(5) Porosity ratio of the distribution along the seepage direction or the face of minimum porosity ratio can be used as the damage index of loess penetration degradation. the ratio between minimal porosity ratio and Initial porosity ratio is defined as the damage rate of loess seepage condition by the author ,which can be used to describe degradation degree of the loess permeability under long-term seepage condition. For the Conventional penetration tests, both the minimal porosity ratio and the influence of gas needed to be considered.