【作者】 李健；

【导师】 汪明武； 张胜；

【作者基本信息】 合肥工业大学 ， 建筑与土木工程（专业学位）， 2014， 硕士

【摘要】 石灰改良膨胀土的强度虽较原状膨胀土强度具有明显的改善，但常因施工扰动引起变形而产生应力松弛，而应力松弛较大时可引发工程灾害和造成重大经济损失，故开展非饱和石灰改良土的应力松弛试验研究，对揭示非饱和石灰改良膨胀土应力松弛规律和确保石灰改良膨胀土地基处理工程安全具有重要的理论意义和工程应用价值。本文利用GDS非饱和土三轴仪，系统开展了掺石灰4%改良膨胀土的土水特性和非饱和强度试验，以及在不同应变水平、应变速率和加载方式下的应力松弛试验，并通过流变理论和经验模态分解理论分析了应力松弛试验结果，进而基于SEM、EDA试验和图像定量分析技术分析相应的微结构变化特征，总结了石灰改良膨胀土的土水特性、无侧限抗压强度、非饱和三轴强度和应力松弛规律，主要得出如下结论：（1）土水特征试验结果表明：非饱和改良土进气值约为300kPa，改良土的脱湿和吸湿循环过程的“滞后”现象明显。（2）无侧限抗压强度试验得出石灰改良土多为脆性破坏，无侧限抗压强度峰值随含水量的增加而减小，相应的轴向应变则随含水量的增大而增大。非饱和三轴强度试验结果表明峰值强度所对应的应变都在1.5%以下，且曲线整体表现为应变软化特征。其他试验条件相同下，剪切速率较慢时获得强度相对更大。（3）应力松弛试验结果表明试验获取的松弛曲线形态基本相似，属于不完全松弛。对于不同应变水平的松弛试验，试样松弛稳定阶段的应力一般随着应变水平的增大而减小。对于不同应变速率的松弛试验，试样在应力松弛阶段的初始松弛速率随着试验应变速率增大而增大的规律。分级加载的松弛试验结果表明，试样后期强度受前期加载引起的累积损伤影响。（4）应力松弛试验数据的经验模态分解结果证实了昼夜温差的变化对GDS松弛试验具有影响，且反映了松弛曲线的多尺度变化。（5）微观定量研究表明所选取的改良土试样孔隙面积以0.3-5um2范围为主，孔隙平均直径为1.57um。（6）理论模型反演研究得出，对分别加载试样，基于西原模型的模拟值与试验实测值基本吻合；对分级加载试样，Burgers模型模拟结果较Maxwell模型模拟效果好。更多还原

【Abstract】 After the lime improvement treatment, it has significantly improved strengthcharacteristics of expansive clay. However, due to the process of constructiondisturbance on site, stress relaxation phenomenon is occured in the lime-treatedexpansive soil, and the larger relaxation of stress in soil may result in engineeringdisasters and great economic loss. Therefore, stress relaxation research of unsaturatedlime-treated expansive soil will not only enrich the rheological theory but also provide abasis for ground treatment.Using GDS triaxial apparatus, experiment was conducted to discuss hydraulicproperties and strength characteristics of unsaturated lime-treated expansive clay.Meantime, a series of stress relaxation tests under different strain level, strain rate andload pattern were carried out, and the rheological element models were introduced to fitthe measured stress relaxation results. Besides, the scanning electron microscope(SEM)and energy dispersion analysis(EDA) tests were applied to discuss soil microstructurecharacteristics. The tests results lead to the following conclusions:(1) From the measured soil water characteristics curve of lime-treated expansiveclay, the drying and wetting curves exhibit hysteresis and the air-entry value was about300kPa.(2) The specimens presented brittle fracture during the unconfined compressionstrength tests, and the peak strength decreases with the increase of water content, whilethe peak strain exhibits a reverse trend. In unsaturated triaxial strength tests, specimensshowed strain softening characteristic, and the peak strains are less than1.5%. Besides,the slower specimen was sheared, the higher peak strength was.(3) All the stress relaxation curves were of similar shape, and the final stress wouldnot decay to zero. For relaxation tests under different strain level, stress in stablerelaxation stage generally decreased with the increase of strain level. For specimensunder different strain rates, the quicker specimen was sheared, the higher initialrelaxation rate was. In the step loading stress relaxation test, former load history willdamage specimen to certain extent, and this damage accumulates with number of step.(4) The stress relaxation curve of specimen BB is decomposed into multi-timescales series with empirical mode decomposition(EMD) method. The decomposedresults show that the series has period that about1day, which confirms that temperaturedifference between day and night affected GDS stress relaxation tests. (5) Based on micro-quantitative analysis, the selected specimen pore areas aremainly in0.3-5um2range, and the pore average diameter is1.57um.(6) Nishihara model is of good fitting result to describe stress relaxation propertiesof lime-treated expansive clay under stage loading tests. While Burgers model showedbetter fitting effect than two-element generalized Maxwell model in depicting specimenviscoelastic under step loading test.更多还原