Effects Of Different Electrical Solutions On Strength And Permeability Of Saturated Porous

Seawater intrusion occurs when seawater is drawn into freshwater aquifers. This natural process is intensified by sea level rise and over pumping of aquifers. During this progress, the lever and chemical constitution of underground water changed a lot. A lot of chemical reaction occurred when the water and soil blend together, such as adsorption, erosion, ion exchange, sedimentation, crystal, etc. And the structure and the physical characteristic of the soil changed, too. The surface nature and micro-structure of the soil changing with the hydrochemistry, and the strength and permeability were affected by these facts, and then the erosive velocity of the estuarine and coastal changed as well as the strength of coastal buildings. Actual soil and micro-glass balls were chosen in this article to study the mechanism of the soil characteristic affection through a micro way, in order to be helpful for the prevention of seawater intrusion.The effect of the hydrochemistry on the characteristic of the soil taken from Laizhou Wan was discussed in this article through two parts:one is size distribution the other is strength. The methods of these tests are type-A hydrometer test, ultrasonic size analyzer test and shear strength test. The results were showed as follows:(1) The hydrochemistry affection controls the diameter of the particles, in which experiment it is indicate that different kind of salt have different affection on particles. Under the same salt content, the diameter of fine sediment increased with the increase of electrolyte concentration to some extent. As a result of the comparison, the order of different degrees of influence is (in descending): CaCl2>MgSO4>MgCl2>NaCl. Different impact between single salt and sea water is also illustrated. It is simply studied the reason of changing diameter on the condition of different hydrochemistry environment.(2) The experiment indicates that shear strength change a lot because of the salinity of NaCl, and the effect was intensified by water content. It is thought that the salinity affect the double electric layer and the thickness of water film on the surface of the particle. The thickness of double electric layer changes, because of which the particles get together or detach from each other, meanwhile, cohesion between particles changes because of the changing of the thickness of water film.Because of the complex of the soil, it was hard to identify the influencing factor of the soil. Micro-glass ball is hollow, most of which is made of Si, Al and O. In order to exclude the broken, agglomerate and colloid release, the micro-glass ball was chosen to modify the soil to see the permeability and strength changing with the solution, and the results was showed as follows:(1) The permeability of 4 kinds of the micro-glass ball was studied in the condition of different solution. Consider the micro-glass ball sample as a kind of porous media, permeability of sample were tested by variable-head permeameter in different condition of percolating fluid. The results of these experiments showed the osmotic coefficient is closed related to Dav, and verified one of these models established by formers. The osmotic coefficient is active related to the electrical conductivity, and the effect of CaCl2 is larger than NaCl. The CaCl2 and NaCl changed the effective porosity through changing the thickness of the hydration layer of the particles, and the osmotic coefficient could be changed as large as 5-6 times.(2) The experiments show that, when the water content rising within a certain scope range, the soil cohesion firstly increases and then decreases. The peak appear in 26 percent. The result maybe relates to water-film cohesive force and the traction role of water molecules. The solutions of different concentrations (NaCl and seawater) can influence soil strength, which are researched in the study too. Under certain conditions of moisture content, as the concentration increasing, the changing curve of the soil cohesion showed a trend of first rising and then declining. The maximum appears respectively in 6g/100ml (NaCl) and 5%(seawater). NaCl has a larger influence on the micro-glass ball than seawater when the electrical conductivities are similar, and it may because the combination of different ions decrease the effect.