有机质与黏粒含量对黑土压缩-回弹特性的影响

为探明有机质和黏粒对黑土压缩-回弹行为的影响,以典型黑土区耕作土壤为研究对象,通过人工添加腐植酸、人工分离-提取-添加黏粒、恒温恒湿培养的方法各配制3个梯度的重塑土。采用室内固结的方法,通过压缩系数、压缩指数及回弹指数的测定与分析,研究了2种含水量条件下黑土压缩与回弹对有机质和黏粒含量变化的响应行为。结果表明:(1)压缩指数均随有机质含量的增加而增大,且在高含水量时二者呈极显著正相关,有机质含量最高时压缩指数为0.246 3,但有机质含量对回弹无显著影响。(2)无论含水量高低,压缩指数均与黏粒含量呈极显著正相关,而回弹指数随着黏粒含量的增加逐渐降低,且在低含水量时二者呈显著负相关。(3)含水量不同,有机质与黏粒对黑土压缩-回弹特性的影响亦不同;黏粒对黑土压缩-回弹行为的影响更为显著。

Effect of Organic Matter and Clay Content on Compression-Rebound Characteristics of Black Soil

AbstractObjective]The problem of vulnerability of soils to compaction damage is getting more and more serious,thus arousing more and more concerns. But for long,researches on mechanical compaction in the black soil region focused mainly on changes in physical structure of the soil. Motivated by the phenomenon that organic matter content in the soil is gradually declining while clay content rising with cultivation going on,this study began to tackle the problem of how the soil responds to the phenomenon in soil mechanics.Method] In order to explore mechanism of the black soil getting compacted under cultivation and factors affecting the compaction and rebound behavior,soil samples were collected from a long-been cultivated black soil field and prepared into test samples different in organic matter content and clay content by spiking humic acid and water. The remolded samples had 3 levels of organic matter content,i.e. 44.93 g kg-1,69.13 g kg-1 and 93.13 g kg-1,and 2 levels of water content,i.e. 20% and 30%. The samples were incubated for 30 days under 25℃ in temperature and 65% in humidity. Then the samples were analyzed for organic matter content with the total organic carbon analyzer of the German Elementar Corporation. In line with the Stokes principles for precipitation,clay particles were separated from the natural soil,fractionated and blended with the remolded soil samples with known clay content at a required ratio and some water to ensure that the remolded soil samples had 3 levels of clay content,i.e. 18.57%,29.37% and 56.33%. From the perspective of soil mechanics,an indoor consolidation experiment was conducted with the samples for determination and analysis of compression coefficient,compression index and rebound index and effects of organic matter and clay content on black soil compression-rebound behavior relative to soil moisture content.Result] Results show as follows:(1)Compression index increased with increasing organic matter content. In the treatments high in water content,an extremely significant and positive correlation was found between compression index and organic matter(p<0.001),with the maximum compression index being 0.2463 in the treatments the highest in organic matter. In the initial phase of consolidation(0~12.5kPa),compression coefficient also rose with rising organic matter content. Soils higher in organic matter content were higher in potential risk of compaction. The soil compression susceptibility increased significantly with increasing organic matter content,because organic matter was one of the most important cementing substances in soil aggregates, very high in hydrophilicity,and capable of thickening the water film between soil particles,and hence enhanced compressibility of the soil. But no significant correlation between soil organic matter content and rebound index was found in both situations.(2)Clay in the soil was considered as the most active one of the mineral components,and higher than organic matter in cohesive force,so it may affect soil physical and mechanical properties more significantly. Clay content was found significantly and positively related to compression index(p<0.001)in this study,regardless of water content,which means that with increasing clay content,soil compression susceptibility increased,but soil resiliency decreased. In soils low in water content,rebound index was found significantly and negatively related to clay content. The joint effect of clay and water on rebound behavior of black soil was quite obvious.(3)Thickness of the water film between soil particles was not a constant and varied with soil water content,thus affecting plasticity of the soil, and hence causing the effects of organic matter and clay to differ,and the two to interact in affection soil mechanics parameters. Compared to organic matter,clay affected compression and rebound behaviors of the black soil more significantly. Whatever,further work should be done on effect of the interaction of organic matter content,clay content and water content in the initial phase on compaction and rebound behaviors of the soil.Conclusion]The compression sensitivity increased with the increase of organic matter content and presented an extremely significant positive correlation under high water content condition,suggesting the higher of organic matter content,the greater risk of compaction. Rebound index showed a decreasing trend with increasing organic matter content. Soil compression sensitivity significantly enhanced with increasing clay content,and there was an extremely significant negative correlation between them under low water content condition,while the resilience gradually weakened. Compared with organic matter,clay content played a more significant role on soil compression-rebound behavior.