【作者】 黄伟；

【导师】 汪时机；

【作者基本信息】 西南大学 ， 土木与建筑环境， 2018， 硕士

【摘要】 膨胀土是一种对环境因素较为敏感的特殊粘性土,特别是温度和水分的变化易引起膨胀土的干湿循环效应,从而导致其产生胀缩变形。由此引起的土体吸水膨胀软化和失水收缩开裂现象,会造成土体抗压性能的劣化,进而使得其上的建筑物产生开裂、倾斜等破坏。针对膨胀土存在的上述问题,目前常采用物理、化学或生物等措施改善膨胀土的性能。其中水泥改性是一种适用性强、效果显著的膨胀土改性处治方法。而针对膨胀土的改性措施,现有的研究主要考虑改性材料本身的影响,而较少考虑到环境因素的影响。而改性后的膨胀土常处于侵蚀、干湿交替等复杂环境中,因而研究环境因素和干湿交替对膨胀土改性效果的耦合影响效应,对提出合理的膨胀土改性措施具有非常重要的意义。选取安徽省合肥市滨湖新区的膨胀土为研究对象,设计了室内改性试验,首先对比研究了不同水泥掺量（0、5%、10%、15%）对膨胀土改性效果的影响,并且通过3次干湿循环试验（含水率变化幅度在10%至20.35%之间）及相应的无侧限抗压试验,对比研究了水泥掺量的变化所引起的相应土体的体积变化率的波动情况,以及相应土体的峰值荷载位移曲线的变化趋势,从而得出水泥掺量的变化对膨胀土的胀缩特性和抗压性能的影响。在此基础上,研究了纯净水、不同浓度（1.5%、9%、18%）及不同种类（MgCl₂、NaCl、Na₂SO₄）的化学溶液在干湿循环作用下对水泥改性膨胀土的侵蚀效应。根据试样的宏观裂隙开展及体积的变化和相应的荷载位移曲线及峰值强度,得到了水泥改性膨胀土在不同侵蚀环境下的力学特性随干湿循环次数的变化规律,并对相应的作用机理进行了深入阐述。研究结果表明,随着水泥掺量的增加,膨胀土的胀缩变形得到有效抑制,其抗压性能得到有效改善,并且在干湿循环作用下的稳定性得到提高。而侵蚀环境的干湿循环作用对水泥改性膨胀土的力学特性有显著的影响,且随着侵蚀溶液的浓度和干湿循环次数的递增而变得愈加显著。低浓度的侵蚀溶液在高频次的干湿循环下对土体抗压性能的影响,与高浓度的侵蚀溶液在低频次的干湿循环下对土体抗压性能的影响趋于一致。而仅有高浓度的硫酸钠溶液的干湿循环作用所引起的土体的胀缩变形相对纯净水存在明显差异,其他不同浓度的各溶液的干湿循环作用对土体的胀缩变形的影响则与纯净水比较接近。研究成果可为水泥改性膨胀土在侵蚀、干湿交替等复杂环境下的稳定性及耐久性研究提供科学依据,对膨胀土地区的工程设计和地基处理具有一定指导意义。更多还原

【Abstract】 Expansive soil is a kind of special cohesive soil that is sensitive to environmental factors,especially the changes of temperature and moisture can easily cause the dry and wet cycle effect of expansive soil,which leads to its expansion and contraction deformation,which causes the water swelling and softening of soil.Dehydration shrinkage cracking phenomenon,will cause the degradation of the soil compressive performance,and then make the building on it crack,tilt and other damage.In view of the above-mentioned problems in expansive soils,physical,chemical or biological measures are often used to improve the performance of expansive soils..Cement modification is a kind of expansive soil modification method with strong applicability and significant effect.For the modification measures of expansive soil,the existing research mainly considers the impact of the modified material itself,and less considers the influence of environmental factors.However,the modified expansive soil is often in the environment of erosion,wet-dry alternation,and so on.Therefore,it is very important to study the coupling effect of environmental factors and alternating wet and dry changes on the effect of expansive soil modification..The expansive soil in Binhu New Area,Hefei City,Anhui Province was selected as the research object.An indoor modification test was designed.Firstly,the effect of different cement content（0,5%,10%,and 15%）on the modification performance of expansive soil was compared.And through 3 times of dry and wet cycle test（the change rate of moisture content is between 10%and 20.35%）and the corresponding unconfined compression test,the volume change rate of corresponding soil caused by the change of cement content was studied comparatively.The variation of the peak load-displacement curve of the soil and the fluctuation of the corresponding soil,and thus the effect of the change of the cement content on the expansion and contraction characteristics and compressive performance of the expansive soil.Then,the corrosion effects of pure water,different concentrations（1.5%,9%,18%）and different types（MgCl₂,NaCl,Na₂SO₄）of chemical solutions on cement-modified expansive soils under wet and dry cycles were studied.According to the macro crack development and volume change of the sample,the corresponding load-displacement curve and the peak strength,the change law of mechanical properties of cement-modified expansive soil under different erosive environments with the number of dry-wet cycles is obtained,and the corresponding effects are obtained.The mechanism is elaborated in depth.The results show that with the increase of cement content,the swelling and shrinkage deformation of expansive soil is effectively suppressed,its compressive performance is effectively improved,and the stability under the action of dry and wet cycle is improved.The dry and wet cycles of the erosion environment have a significant effect on the mechanical properties of cement-modified expansive soils,and become more pronounced as the concentration of the etching solution and the number of wet-dry cycles increase.The effect of low concentration of erosion solution on the compressive strength of soil under high-frequency wet-dry cycles is consistent with the effect of high concentration of erosion solution on the compressive performance of soil under low-frequency wet-dry cycles.However,only the high-concentration sodium sulphate solution’s wet-dry cycle has obvious differences in the expansion and contraction of the soil relative to the pure water,and the effects of the wet-dry cycles of other solutions with different concentrations on the expansion and contraction of the soil are affected.The water is closer.The research results can provide scientific basis for the study of the stability and durability of the cement modified expansive soil under the complex environments such as erosion and dry-wet alternating,and it has certain guiding significance for the engineering design and foundation treatment of the expansive soil area.更多还原