Mechanical properties of composite improved phyllite soil under uniaxial compression
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摘要: 针对千枚岩土作为路基填料强度不足的问题，提出一种水泥与红黏土联合改良千枚岩土的方法，通过无侧限抗压强度试验，研究了水泥与红黏土复合改良千枚岩土浸水与不浸水试样的应力-应变曲线，分析了无侧限抗压强度与变形模量随红黏土掺和比与水泥掺量的变化趋势。试验结果表明：随着红黏土掺和比的增大，当水泥掺量为0时，红黏土改良千枚岩土的应力-应变曲线为典型的弹塑性特征，而当水泥掺量不为0时，复合改良土的应力-应变曲线近似表现为线弹性特征，红黏土改良千枚岩土与复合改良土的无侧限抗压强度与变形模量均增大；在浸水条件下，红黏土改良千枚岩土试样发生崩解导致无侧限抗压强度和变形模量降低至0，复合改良土无侧限抗压强度和变形模量减小，水泥掺量分别为3%与5%时，软化系数分别为0.45~0.62与0.71~0.93，因此，复合改良土水稳性更优；水泥与红黏土复合改良千枚岩土时，无侧限抗压强度增加幅度大于水泥与红黏土单独改良增幅之和，实现了“1+1>2”的改良效果，即协同作用，因此，宜采用复合改良方案改良千枚岩土；水泥掺量为3%与红黏土掺和比为20%可以作为满足规范350 kPa强度要求的经济复合改良方案，为了增强水稳定性、快速填筑和协同作用的充分发挥，可以考虑水泥掺量为5%与红黏土掺和比为40%的复合改良方案。Abstract: To address the issue of insufficient strength of phyllite soil as a subgrade filler, a composite improvement method using cement and red clay to improve phyllite soil was proposed. Through unconfined compressive strength tests, the stress-strain curves of composite improved phyllite soil under soaked and unsoaked conditions were studied, and the variations of unconfined compressive strength and deformation modulus with red clay mixing ratio and cement content were analyzed. Experimental results show that with the increase of red clay mixing ratio, the stress-strain curve of red clay modified phyllite soil exhibits typical elastoplastic characteristic when cement content is 0. When cement content is not 0, the stress-strain curve of composite improved phyllite soil approximates linear elastic characteristic, and the uniaxial compressive strengths and deformation moduli of red clay modified phyllite soil and composite improved phyllite soil increase. Under soaked condition, red clay modified phyllite soil disintegrates to result in a reduction of unconfined compressive strength and deformation modulus to 0. For composite improved phyllite soil, the unconfined compressive strength and deformation modulus decrease, with softening coefficients of 0.45-0.62 and 0.71-0.93 for cement contents of 3% and 5%, respectively, showing better water stability. When phyllite soil is improved by using cement and red clay, the increase in uniaxial compressive strength is better than the sum of the increments achieved by using cement and red clay alone, realizing an improvement effect of "1+1>2", that is, synergy. Therefore, it is advisable to adopt the composite improvement scheme to improve phyllite soil. Cement content of 3% and red clay mixing ratio of 20% can be used as an economic composite improvement scheme to meet the strength requirement of 350 kPa. In order to enhance water stability, rapid filling and full play of synergy, the composite improvement scheme of cement content of 5% and red clay mixing ratio of 40% can be considered.
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图 4 未浸水复合改良土的应力-应变曲线
Figure 4. Stress-strain curves of unsoaked composite improved soils
图 6 未浸水与浸水试样的应力-应变曲线对比
Figure 6. Comparison of stress-strain curves between unimmersed and immersed samples
图 7 λ对复合改良土力学参数的影响
Figure 7. Effects of λ on mechanical parameters of composite improved soils
图 8 η对复合改良土力学参数的影响
Figure 8. Effects of η on mechanical parameters of composite improved soils
图 9 浸水复合改良土力学参数的变化规律
Figure 9. Variations of mechanical parameters of composite improved soils under water immersion
表 1 试验材料物理指标
Table 1. Physical indices of test materials
土类 液限/ % 塑限/ % 塑性指数 最大干密度/ (g·cm-3) 最优含水率/ % 土粒比重 红黏土 48.4 26.4 22.0 1.75 17.81 2.69 千枚岩土 43.3 28.9 14.4 1.64 19.32 2.76 
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