全风化千枚岩复合改良土试验研究及路基沉降数值分析

Experimental study on fully weathered phyllite composite improved soil and numerical analysis of subgrade settlement

为了充分利用江西北部地区广泛分布的千枚岩土和红黏土,设计红黏土掺和比(λ)分别为0,20%,40%,60%和100%,水泥掺量(ζ)分别为0,3%和5%的组合改良方案,开展水泥、红黏土复合改良千枚岩土的固结试验与直剪试验研究,并基于试验数据建立数值模型,分析压实路基的工后沉降。固结试验表明:复合改良土的压缩模量(Es)随λ的增大近似线性增大,ζ从0增长至3%时Es增长迅速,而ζ从3%增长至5%时Es增长幅度较小;当λ=40%时,水泥掺量范围为0~3%和3%~5%时,Es相对水泥掺量为0时分别增长了116.6%和4.6%,因此水泥建议掺量为3%。直剪试验表明:黏聚力(c)随着λ的增大而大幅增大,内摩擦角(φ)随着λ的增大呈现出先增大后减小的规律;水泥掺量增加对抗剪强度指标均有提高作用,但提高幅度远远小于红黏土的作用。水泥与红黏土改良千枚岩土对比表明:水泥对千枚岩土的Es增长效果优于红黏土,红黏土对千枚岩土抗剪强度指标的提高效果优于水泥。有限元分析表明:路基沉降量随λ的增大而减小,变化规律可以用二次函数表示;路基沉降在水泥掺量0~3%范围内降低显著,在水泥掺量3%~5%范围内降低幅度较小;当λ=60%时,水泥掺量范围为0~3%和3%~5%时,路基沉降量相对水泥掺量为0时分别降低了108.2%和4.8%。根据高速铁路设计规范的沉降控制要求,建议改良方案为红黏土掺和比40%~60%,水泥掺量为3%的组合,此时对应的工后沉降量分别为15.0 mm和13.4 mm。

In order to make full use of phyllite soil and red clay which are widely distributed in the northern part of Jiangxi Province, China, the combined improvement schemes were designed, in which red clay blending ratios(λ) were 0, 20%, 40%, 60% and 100%, and cement content(ζ) were 0, 3% and 5%, respectively. The consolidation test and direct shear test of composite improved soils were carried out. Based on the test data, a numerical model was established to analyze the post-construction settlement of compacted subgrade. The consolidation tests show that the compressive modulus(Es) of the composite improved soil increases approximately linearly with the increase of λ. Es increases rapidly when ζ increases from 0 to 3%, while Es increases relatively small when ζ increases from 3% to 5%. Es increases by 116.6% and 4.6% respectively relative to the cement content of 0 when the improvement scheme is “λ=40%+ζ=0~3% and ζ=3%~5%”, so the recommended cement content is 3%. The direct shear test shows that with the increase of λ, the cohesive(c)increases rapidly and the internal friction angle(φ) increase initially and decrease subsequently. The increase of cement content has improved the shear strength indices, but the improvement is much smaller than the effect of red clay. The comparison between cement and red clay improved phyllite shows that cement is more effective in increasing Es of phyllite than red clay, and red clay is more effective in improving shear strength indexes of phyllite than cement. Finite element analysis shows that the post-construction settlement of the subgrade decreases with the increase of λ and the change law can be expressed as a quadratic function. Subgrade postconstruction settlement decreases significantly in the range of cement content of 0~3%, and decrease is smaller in the range of cement content of 3%~5%. While λ =60%, the subgrade settlement is reduced by 108.2% and 4.8% relative to the cement content of 0 when the cement content ranges from 0 to 3% and 3% to 5%,respectively. According to the settlement control requirements of the code for design of high-speed railway, it is suggested that the improvement scheme is a combination of red clay blending ratio of 40% to 60% and cement content of 3%, and the corresponding post-construction settlement is 15.0 mm and 13.4 mm respectively.