Knowledge Resource Center for Ecological Environment in Arid Area
| 青藏高原红梁河地区风沙堆积对冻土影响的数值模拟研究 | |
| 其他题名 | Numerical Simulation Study of Influence of Aeolian Sand Accumulation on Permafrost in the Honglianghe Area of Qinghai-Tibet Plateau |
| 王陆阳 | |
| 出版年 | 2018 |
| 学位类型 | 硕士 |
| 导师 | 吴青柏 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 青藏高原由于其独特的自然地理环境不仅有利于各种类型冻土的发育，也直接促进了沙漠化的形成和发展，目前青藏高原沙漠化土地面积约占主要行政区总面积13.96%，铁路沿线沙害地段长约270.50km，约占总长度1/7。沙漠化所产生的风沙堆积不仅会对人类工程经济活动产生直接影响，同时，同地形、植被、水体等一样，风沙堆积也是一种影响冻土状态及分布的重要局地因素，但其对下伏冻土的具体影响目前尚未清楚。通过研究风沙堆积对高原冻土的影响可以明确冻土在积沙下的具体变化和高原冻土环境将来的发展态势，从而有助于公路铁路等工程沙害的预防和治理，进而促进高原地区的经济环境开发。本研究基于传热理论建立数值模型，模拟青藏高原红梁河沙害严重地区季节和多年冻土以及青藏公路沿线多年冻土在风沙堆积下的变化情况，模拟各个场地在21种厚度干湿沙覆盖下50年内的温度及冻融状态变化情况。研究结果显示：(1)青藏高原地区堆积在地表的风积沙层，其导热系数较下伏土体相对较小，进而造成地表与下层土体间热量传输能力大幅度减弱，显著改变土体原有热量平衡状态，进而建立起新的年热量循环平衡关系，这是风积沙层造成土体温度及冻融状态变化的根本原因。无论在哪种场地，随沙厚增加，冷暖季年热循环量均减小，故浅层地温年较差减小。(2)在红梁河季节冻土场地，在干湿沙覆盖下，分别以沙厚20cm至40cm和沙厚100cm至120cm为阈值，随着沙厚增加，活动层内冷季年热循环量和季节冻结层厚度均为先减小后增大；地温年变化层内年热循环平衡和年平均地温均为先增大后减小。因此该场地季节冻土随沙厚增加由逐渐消退趋势转变为逐渐加积趋势。(3)在红梁河多年冻土场地，在干湿沙覆盖下，其沙厚阈值随时间发生改变，总的来说，分别以沙厚20cm至120cm和沙厚30cm至140cm为阈值，随着沙厚增加，活动层内暖季年热循环量和季节融化层厚度均为先增大后减小；在某些沙厚条件下，多年冻结状态退化为季节冻结状态，季节融化层转变为季节冻结层；地温年变化层内年热循环平衡和年平均地温均为先增大后减小。因此该场地多年冻土在部分沙厚下加速退化为季节冻土，在部分沙厚下进化加积。(4)在青藏公路K2933处场地，在干沙覆盖下，其沙厚阈值随时间发生变化，阈值范围大约为60cm至130场面，随着沙厚增加，活动层内暖季年热循环量和季节融化层厚度均为先减小后增大；年变化层内年热循环平衡变化幅度相对较小，年平均地温虽然会以某一沙厚为阈值先增大后减小，但变化幅度不超过0.3℃。此时多年冻土随干沙厚增加先进化后发生退化。在湿风积沙下，随着沙厚增加，活动层内暖季年热循环量和季节融化层厚度均增大，地温年变化层内年热循环平衡和年平均地温均增大，但是年平均地温增大幅度小于0.2℃。因此该场地多年冻土随湿沙厚度增加持缓慢退化状态。(5)积沙导热能力的强弱与沙层含水量有直接联系。含水量为5%的湿沙导热系数是相同厚度干沙导热系数的5至6倍；同时，由于积沙中的水分相变，使湿沙中热量循环量大于干沙。由于以上原因，造成干风积沙下土体热量循环变化幅度大于相同厚度湿沙下土体热量循环变化幅度，进而形成干沙下土体温度、冻融过程的变化均显著与相同厚度湿沙下土体相应变化。(6)风沙堆积对冻土的影响不仅与沙层性质相关，同时也与沙层下伏冻土温度状态、组构和发育趋势相关，积沙场地冻土温度和冻融状态的变化是积沙和冻土二者共同作用的结果。因此，同一状态的积沙对不同类型的冻土可能会有不同的作用，同样的，同一类型的冻土对不同类型的积沙可能也会有不同响应。 |
| 英文摘要 | The Qinghai-Tibet Plateau is not only conducive to the development of various types of permafrost, but also directly facilitating the formation and development of desertification due to its unique environmental conditions. At present, the desertified land area of the Qinghai Tibet Plateau is about 13.96% of the total area, and the sand damage sections are about 270.50km along the railway, which accounts for about 1/7 of the total length. The drift-sand caused by desertification is not only having a direct impact on the social economic activities, but also a kind of important local factor, like topography, vegetation and water, to affect the state and distribution of permafrost. However, the specific mechanism of the influences of the aeolian sand to the underlying permafrost is not clear so far. Through the study of the effect of aeolian sand to the permafrost, the dynamics and its future developing trend of the permafrost environment could be understood in the Qinghai-Tibet Plateau in order to contribute the maintenance and management of the highway and railway engineering from the sand damage, and also be beneficial to the economic development in the plateau.Based on the theory of heat transfer to establish the numerical model, it simulates the variations of the seasonally frozen soil and permafrost in the Honglianghe River and the state of permafrost along the Qinghai Tibet highway under the aeolian sand in this study. The variations of soil temperature and freeze-thaw processes are simulated with 21 different kinds of thickness and moisture contents of drift-sand at each site in 50 years in the work. The results of the study are shown as the follows:(1)When the aeolian sand accumulated on the ground surface on the frozen soil in the Qinghai Tibet plateau, the sand causes substantial decrease of the heat transfer between the ground surface and the soil beneath it due to the smaller heat conductivity coefficient of the sand to the former ground surface , resulting a significant changes of the original soil heat balance and the formation of a new one. This is the fundamental reason of the changes of soil temperature and freeze-thaw processes. Wherever the sites, the annual thermal circulation during the cold or warm season decreases as the increase of the thickness of sand, which leads to the decreasing of the temperature range of the shallow layer.(2)In QH-4 site, when covering the dry or wet sand, with the sand thickness threshold by 20cm to 40cm and 100cm to 120cm respectively, both of the thermal circulation in the active layer during the cold season and the thickness of the seasonally freezing layer decrease firstly and then increase; the thermal circulation balances in the layer of annual temperature fluctuation and the annual mean ground temperature (MAGT) increase firstly and then decrease. As a result, the trend of seasonal frozen soil changes from gradual fading to gradual aggradation.(3)In QH-5 site, when covering the dry or wet sand, the sand thickness threshold varies with time. In general, with the sand thickness threshold by 20cm to 40cm and 30cm to 140cm respectively, both the thermal circulation in the active layer during warm season and the thickness of seasonally thawed layer increase firstly and then decrease, Some of the permafrost can degrade to seasonal frozen soil and some of the seasonal thawed layer turn to seasonal frozen layer in some situations with specific sand thickness, and the thermal circulation balances in the layer of annual temperature fluctuation and MAGT decrease firstly and then increase. As a result, the permafrost degrades to seasonal frozen soil with some specific sand thickness and aggrades with some other specific sand thickness.(4)In K2933 site, when covering dry sand, the sand thickness threshold varies from 60cm to 130cm with time both of the thermal circulation in the active layer during the warm season and the thickness of seasonally thawed layer decreases firstly and then increases, and the varying range of the annual thermal circulation balance is relatively small in the layer of annual temperature fluctuation. Although the MAGT increases firstly and then decreases with a certain sand thickness threshold, the range of this variation is less than 0.3℃. In this situation, the permafrost aggrades firstly and then degrades with the increasing of sand thickness. On the other hand, when covering the wet sand, the thermal circulation in the active layer during the warm season and the thickness of seasonally thawed layer increase with the increasing of sand thickness, and the thermal circulation balance in the layer of annual temperature fluctuation and MAGT increase with the increasing of sand thickness, though the range of the increasing of MAGT is less than 0.2℃. In this situation, the permafrost degrades slowly with the increasing of sand thickness.(5)There is an obvious difference of thermal conductance between dry sand and wet sand. The heat conductivity coefficient of wet sand with water content of 5% is 5 to 6 times higher than that of dry sand. In addition, the thermal circulation of wet sand is also larger than that of dry sand with same thickness due to the phase change of water. According to the reasons above, the varying range of the thermal circulation of wet sand is larger than that of dry sand with same thickness, so the changes of the soil temperature and freeze-thaw process of wet sand are all greater than those of the same thickness under dry sand.(6)The impact of aeolian sand on the frozen soil is related not only to the properties of sand, but also to the temperature, structure and the development trend of the frozen soil under the sand. The temperature state and the freeze-thaw dynamics of the frozen soil is the result of mutual work of sand and soil. Therefore, same condition of sand may result in different impacts to the frozen soil. Equally, same type of frozen soil may respond differently to different types of sand. |
| 中文关键词 | 青藏高原 ; 风沙堆积 ; 多年冻土 ; 季节冻土 ; 数值模拟 |
| 英文关键词 | Qinghai-Tibet Plateau Aeolian Sand Permafrost Seasonally Frozen Ground Numerical Simulation |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288139 |
| 推荐引用方式 GB/T 7714 | 王陆阳. 青藏高原红梁河地区风沙堆积对冻土影响的数值模拟研究[D]. 中国科学院大学,2018. |
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