两种特殊土混合改良土的工程性质指标数学预估模型与改良机理研究

Study shows that phyllite weathered soil and high liquid limit red clay are poor subgrade filler which have special engineering properties, so the two kinds of special soil should not be used as subgrade filler. Two kinds of special soils’ mixture can improve specific engineering properties in practice, so a new improvement method called “Special soil mixed improvement method” is put forward. The basic idea is using phyllite weathered soil reduce red clay’s high liquid limit and high shrinkage, and using red clay’s high cohesive force to strengthen phyllite weathered soil compaction strength. Firstly, Some kinds of experiments will be carried out ,such as soil particle diameter test, limit moisture content test, shear strength test, uniaxial compressive strength test, compaction, compression test，dry-wet cycle test and image binary processing with MATLAB, etc. Some engineering properties’ indicators changing rules with blend ratio (λ) and compaction coefficient(K) will be put forward after system experiment, such as gradation, liquid and plastic moisture content limit, shrinkage, crack, strength, deformation, etc. Secondly, crack ratio and some railway inspection related indicators influence laws will be studied by small pit test on-site. On the basis of experiment, engineering property indicators’ mathematical prediction models will be put forward by regression analysis. Results of the subject will initially reveal mixed filler modified mechanism, and improve the theory of special soil mixed filler. The subject will promote theory support for special soil mixed filling, and promote technique to break the engineering experience “special soil must be separately, layered filling”.

研究证实千枚岩风化土与高液限红粘土都是有特殊工程性质的不良填料,不宜作为路基填料。实践中两种特殊土混合可以改善土的工程性质，课题据此提出“特殊土混合相互改良”的新方法。基本思想是用千枚岩风化土降低红粘土的高液限性与高收缩率，用红粘土提高压实千枚岩风化土的强度。首先通过混合填料的粒径分析、界限含水率、抗剪、单轴强度、击实、压缩、干湿循环试验和MATLAB图像二值处理，探讨液塑限、收缩、裂隙、强度、变形等指标随掺合比(λ)和压实系数(K)的演变规律。然后开展现场小型试坑试验，研究λ对土的裂隙、铁路检测相关指标的影响规律。在试验基础上，通过编制软件回归分析建立相关工程指标随λ、K的数学预估模型，并提出完善混合改良填料的定量评价方法。课题成果将初步揭示混合填料改良机制，完善特殊土混合填筑相关理论，突破工程中特殊土必须“分开、分层填筑”的经验束缚，为铁路推广特殊土混合填筑改良法提供理论支撑。

课题试验所用千枚岩风化土(简称千枚岩土)和红黏土来源于江西南昌昌北货场工程，设计千枚岩土：红黏土混合比方案分别为5：0、5：1、5：2、5：3、5：4和0：5。通过混合土的土粒比重试验、界限含水率试验、标准击实试验、可击实性试验、膨胀性试验、固结试验、干湿循环试验、微型贯入试验、浸水与非浸水直剪试验，研究得到了混合土基本物理性质指标、膨胀指标、压缩指标、强度指标、裂隙指标等随红黏土掺合比、含水率和压实系数的变化规律，通过编制软件回归分析建立工程性质指标变化规律的数学预估模型,并完善混合改良填料的定量评价方法。基于混合土试验结果，建立了基于路基地基系数K30检测的数值分析模型，研究了K30随掺合比、含水率和压实系数的变化规律。在宏观试验的基础上，通过XRD和电镜扫描从微观级配、矿物成分等方面分析了两种特殊土混合改良的机理。试验研究结果表明，在千枚岩土中掺入红黏土可以有效提高千枚岩土的强度、可压实性，降低千枚岩土的膨胀率，同时降低红黏土在干湿循环作用下的裂隙率，在液限、膨胀变形和收缩变形方面达到了相互改良的效果。数值仿真结果及基于承载力计算表明，混合土在红黏土掺合比大于20%时可以满足铁路路基系数要求，结合裂隙率和路基C组填料对液限值的要求，红黏土掺合比为20%-50%混合土可用于路基填料，最优掺合比为50%。课题首次提出了“特殊土混合相互改良”的方法，达到“以害治害”的目的，对突破特殊土必须“分开、分层填筑”的经验束缚奠定了坚实的基础，为铁路推广特殊土混合填筑改良（法）提供理论支撑。