全风化千枚岩复合改良土路用性能

Road properties of completely weathered phyllite composite improved soil

为了充分利用全风化千枚岩作为路基填料,设计了红黏土掺和比分别为0、20%、40%、60%和100%,水泥掺量分别为0、3%和5%的组合改良方案,开展了改良土的界限含水率、抗剪强度和无侧限抗压强度试验,分析了改良土的路用性能。试验结果表明:当水泥掺量分别为3%与5%时,复合改良土的液限均低于40%,符合路基设计中液限低于40%的控制要求;改良土的黏聚力随红黏土掺和比与水泥掺量的增大而增大,内摩擦角随红黏土掺和比的增长先增大后减小,随水泥掺量的增大而增大,但两指标在水泥掺量大于3%时增长幅度较小。改良土路基极限承载力计算结果表明:5%水泥改良全风化千枚岩路基极限承载力仅为725.3 kPa,红黏土掺和比为40%改良全风化千枚岩路基极限承载力达到2 198.3 kPa,分别是全风化千枚岩路基承载力的2.34和7.10倍,因此,红黏土改良效果优于水泥;经过比较可得红黏土掺和比为40%,水泥掺量为3%是合理掺和方案,在28 d养护后,路基极限承载力计算值为4 247.7 kPa,液限为32.7%。微观机理分析结果表明:红黏土颗粒小于全风化千枚岩颗粒,当红黏土掺和比大于40%时可以包围千枚岩颗粒的点-点接触,增加了接触点数与接触面积,从而大大提高了改良土路基的极限承载力。无侧限抗压强度试验结果表明:优化方案改良土7 d无侧限抗压强度为487.25 kPa,满足铁路路基设计要求。

In order to make full use of completely weathered phyllite as subgrade filler, the combined improvement schemes were designed, in which red clay blending ratio was 0, 20%, 40%, 60%, and 100%, respectively, and cement content is 0, 3%, and 5%, respectively. The tests of boundary moisture content, shear strength and unconfined compression of the improved soil were carried out, and the road performances of the improved soil were analyzed. The test results of the improved soil show that the liquid limit of the improved soil is lower than 40% when cement content is 3% or 5%, and all improved soils comply with the liquid limit control requirement of the design of railway earth structure(less than 40%). The cohesion of the improved soil increases with the increase of red clay blending ratio and cement content. The internal friction angle of the improved soil increases first and then decreases with the increase of red clay blending ratio, and increases with the increase of cement content. But both shear indexes increase slightly when cement content is more than 3%. The calculation results of ultimate bearing capacity of the improved completely weathered phyllite subgrade show that the ultimate bearing capacity of the subgrade with 5% cement is only 725.3 kPa, and the value of the subgrade with 40% red clay is 2 198.3 kPa, being 2.34 and 7.10 times that of the completely weathered phyllite subgrade, respectively. Therefore, the improvement effect of red clay is better than that of cement. Analysis results show that the rational mixing scheme is that red clay blending ratio is 40% and cement content is 3%. Under the scheme, when the curing age is 28 days, the calculated value of the ultimate bearing capacity of the improved completely weathered phyllite subgrade is 4 247.7 kPa, and the liquid limit of the improved completely weathered phyllite is 32.7%. Microscopic mechanism analysis results show that red clay particles are smaller than fully weathered phyllite particles. When red clay blending ratio is greater than 40%, red clay can surround the point-to-point contact of phyllite particles, and increase the contact points and contact area, which greatly improves the ultimate bearing capacity of the improved soil subgrade. The test results of unconfined compressive strength show that the 7-day unconfined compressive strength of the improved soil in the optimized scheme is 487.25 kPa, which meets the requirement of the design of railway earth structure.