دانلود رایگان مقاله مطالعات قابلیت هدایت هیدرولیک و تراکم سازی بکفیل ها

Abstract

Fujian standard sand (Sand-F) was used to simulate a sandy soil layer. Hebei bentonite (Bent-H) and Jiangning clay (Clay-J) were served as additives for studying the hydraulic conductivity and compressibility of sand-bentonite/clay mixture backfills. The results indicate that there is an optimum mixing content (Copt) when Bent-H or Clay-J is mixed with the Sand-F. If the content of bentonite/clay is less than Copt, hydraulic conductivity k > 1.0 × 10− 7 cm/s and porosity and coefficient of compressibility decrease with the increase of the content of bentonite/clay. While the content of bentonite/clay are greater than Copt, hydraulic conductivity k ≤ 1.0 × 10− 7 cm/s and porosity and coefficient of compressibility increase with the increase of the content of bentonite/clay. As the content of bentonite/clay is less than Copt, clay minerals only fill the sand pore space without influencing the sand skeleton and porosity decreases with the increase of the content of bentonite/clay. While the content of bentonite/clay becomes greater than Copt, sand particles become disconnected and porosity increases with the increase of the content of bentonite/clay. A porosity model of sand-bentonite/clay mixtures was derived based on a micro-geometrical principle. Another equation was also developed to calculate hydraulic conductivity values with the changes of the content of bentonite/clay.

5. Conclusions

Based on the discussions of the test results and further analysis, the following conclusions can be made: (1) An optimum mixing content, Copt was found for the sand-bentonite/clay mixture backfills when Sand-F was mixed with a certain content of Bent-H or Clay-J. When the content of bentonite/ clay is less than the optimum mixing content, the hydraulic conductivities of the mixtures are N1.0 × 10−7 cm/s and the coeffi- cients of compressibility and the porosities decrease with the increase of the content of bentonite/clay. As the content of bentonite/clay becomes greater than the optimum mixing content, the hydraulic conductivities becomes b1.0 × 10−7 cm/s and the porosities and the coefficients of compressibility gradually increase with the increase of the content of bentonite/clay. That means that the hydraulic conductivity is b1.0 × 10−7 cm/s and the porosity and the coefficient of compressibility have a minimum value at the optimum mixing content for the mixtures. (2) When the content of bentonite/clay is less than the optimum mixing content, the clay minerals only fill the pore space between the sand particles without affecting the sand skeleton. Thus the porosity of the mixture decreases with the increase of the content of bentonite/clay. As the content of bentonite/clay becomes greater than the optimum mixing content, the total volume of the clay minerals becomes greater than the pore space between the sand particles and the sand particles are suspended among the clay particles. Hence the porosity of the mixture increases with the increase of the content of bentonite/clay. A porosity model of sand-bentonite/clay mixtures has been established based on the micro-geometrical principle of sandbentonite/clay mixture, which can explain the hydraulic conductivity and compressibility of the sand-bentonite/clay mixture with the content of bentonite/clay. (3) Based on the porosity model of the mixtures and the improved Kozeny-Carman Equation, a calculation equation was developed to estimate the hydraulic conductivity of the mixtures with various content of bentonite/clay. The comparisons between the estimated and tested values indicate that the estimated values fall within the range of 0.5 to 1.5 times the tested values. The further improvement for the calculation equation is needed in future studies.