植物根系对粘土覆盖层的影响研究

发布时间：2018-06-05 22:22

本文选题：植物根系 + 优势流　；参考：《哈尔滨工业大学》2015年硕士论文

【摘要】：垃圾填埋场封顶覆盖层处于填埋场表层,是保护填埋场不受到外界侵蚀的一道重要措施。封顶覆盖层阻滞降雨入渗至垃圾体内部,减少垃圾渗滤液产量,避免填埋体内部水位过高引起的填埋场失稳。在垃圾降解时,产生各种有害物质,垃圾填埋场封顶覆盖层可以阻挡有害气体无组织扩散至大气中,避免垃圾降解过程中产生的有害物质影响附近居民。覆盖层中上覆耕植土作为植物生长基质,为填埋场生态恢复提供条件。垃圾填埋场封顶覆盖层从垃圾体顶面至表面依次为:排气层、防渗粘土层、排水层和植被层。防渗粘土层作为封顶覆盖层的核心部分,影响着封顶覆盖层的长期服役性能。很多研究表明,粘土防渗层在干湿循环、冻融循环中极易开裂,粘土防渗层一旦开裂,形成裂隙网络,裂隙作为土体中通道,极易产生优势流,使得土体渗透性明显增加,雨水更加容易入渗到垃圾体中。粘土防渗层开裂是影响封顶覆盖层长期服役性能的主要因素。同时在覆盖层生态恢复过程中,植物根系有可能在粘土防渗层中的穿插生长,形成大量根系,水分有可能沿根系优先迁移形成优势流,增大粘土防渗层的渗透性。同时植物根系团聚土颗粒,限制土壤开裂。植物根系对粘土防渗层的综合影响需要进一步研究。本文拟通过含根系的土柱试验综合评价植物根系对土体开裂及优势流的作用。采用分层压实法压实土柱,在土柱中培养植物,运用二值图像法和图像处理技术计算裂隙率。定量分析在植物生长过程中压实粘土表面开裂情况,对比同条件下无植物土柱表面裂隙开展情况。结果显示当压实粘土中有植物根系时,相对于同条件无植物根系的压实粘土,表面开裂能得到一定延缓和限制。通过四组土柱试验,分析覆盖层在不同状态下的渗流特性。首先,进行一组重塑压实土柱渗流试验,此组土柱中既无植物根系也无裂隙,模拟刚压实完成的覆盖层的渗流特性。其次,进行了一组经过一段时间干湿循环后表面产生开裂的重塑压实土柱渗流试验,模拟当植物根系尚未生长至粘土防渗层中,已经产生开裂的覆盖层渗流特性。再次,在土柱中培养植物,在植物生长过程中,土体产生开裂,进行当土中同时含有植物根系和裂隙时的渗流试验,模拟植物根系在粘土防渗层中生长,同时产生开裂时覆盖层的渗透特性。最后为了准确评价植物根系的作用,进行了土体中含有植物根系但未产生开裂的重塑土柱渗流试验。四组试验结果显示植物根系和裂隙都会加大雨水入渗到土壤中。植物根系为水分入渗提供优先迁移通道,植物根系的优势流作用不可忽略。尽管粘土中裂隙在渗流试验中会闭合,一定时期内雨水入渗产生波动,但整个过程中,水分沿着裂隙入渗形成优势流并未被削弱,土体开裂提高了土壤的渗透性。以亮蓝作为染色示踪剂,在含有植物根系但无开裂的重塑土柱中,进行染色示踪试验,定性评价在压实粘土中染剂沿着植物根系的迁移。结果显示随着深度的加大,染剂在截面的染色范围逐渐减小,在根系附近土壤中,染剂存在局部优先迁移。进一步明确了植物根系在覆盖层中的作用。
[Abstract]:The top cover layer of the landfill site is in the surface of the landfill. It is an important measure to protect the landfill from the external erosion. The top cover layer block the rainfall to infiltrate into the garbage body, reduce the output of the landfill leachate and avoid the instability of the landfill site caused by the high water level inside the landfill. The top cover layer of the landfill can prevent the harmful gas from spreading unorganized into the atmosphere, avoiding the harmful substances produced in the process of waste degradation and affecting the nearby residents. The cover layer is covered with soil as the base of plant growth and provides conditions for the ecological restoration of the landfill. The cover layer of the landfill is in turn from the top of the garbage body to the surface. It is: the exhaust layer, the impervious clay layer, the drainage layer and the vegetation layer. The impervious clay layer is the core of the top cover, which affects the long-term service performance of the top cover. Many studies show that the clay impervious layer is very easy to crack during the dry and wet cycle and the freeze-thaw cycle. Once the clay seepage layer is cracked, the fracture network is formed and the fissure is used as the mass medium in the soil. It is very easy to produce the dominant flow, which makes the soil permeability increase obviously, and the rainwater is more easily infiltrated into the garbage. The cracking of the clay impervious layer is the main factor affecting the long-term service performance of the top cover layer. It is possible to migrate the dominant flow along the root system and increase the permeability of the clay impervious layer. At the same time, the plant roots reunite the soil particles to limit the soil cracking. The comprehensive effect of the plant roots to the clay impervious layer needs further study. Using the stratified compaction method to compact the soil column, cultivate the plants in the soil column, use the two value image method and the image processing technique to calculate the crack rate. This paper quantitatively analyzes the cracking of the compacted clay surface during the plant growth and compares the surface fissure of the plant without the plant soil column under the same condition. The surface cracking can be delayed and restricted for the compacted clay with the same condition without plant roots. Through four groups of soil column tests, the percolation characteristics of the cover layer in different states are analyzed. First, a group of remolded compacted soil column seepage tests are carried out, and there is no plant root and no fissure in this group of soil columns. Secondly, a group of remolded compacted soil column percolation tests were carried out after a period of dry and wet circulation, and the seepage characteristics of the cracked covering layer have been produced when the plant roots have not yet grown to the clay impervious layer. Again, the plant is cultivated in the soil column and the soil is cracked during the plant growth process. The percolation test of plant roots and fissures in the soil also simulates the growth of plant roots in the clay impervious layer and the permeation characteristics of the covering layer during the cracking. Finally, in order to accurately evaluate the effect of plant roots, the seepage test of the remolded soil column containing plant roots but not cracking in the soil is carried out. The results of the four groups of experiments are carried out. It is shown that the roots and fissures of plants increase rain infiltration into the soil. Plant roots provide a preferential migration channel for water infiltration, and the dominant flow of plant roots can not be ignored. Although the cracks in the soil are closed during the seepage test, the rain infiltration will fluctuate during a certain period, but the water is formed along the fissure throughout the process. The dominant flow was not weakened, the soil cracking increased the permeability of the soil. With bright blue as a dyeing tracer, the staining tracer test was carried out in the remolded soil column containing plant roots but no cracking. The results showed that the dye was migrated along the root system in the compacted clay. The result showed that the dye was dyed in the cross section with the increase of depth. In the soil near the root system, there is a partial preferential migration of the dye, which further clarifies the role of plant roots in the mulching layer.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU993;TU442

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