冰碛湖坝温度场与内部结构变化的耦合机制及其对坝体稳定性的影响研究

The temperature field distributions and its changes of moraine dam of glacial lake not only directly generate the freeze-thaw state of inner dam and the melting of dead ice, but also indirectly imply the outer setting of water and heat and inner structural characteristics of moraine dam. Furthermore, they are closely related to the stabilities of dam itself and are the keys to assess the risks of moraine-dammed glacial lake outburst flood hazards. The basic issues of coupling mechanism between temperature fields and inner structure of moraine dam are urgent to be solved and are of basically theoretical significance and practical application value to do research on the coupling mechanism between the temperature field of moraine dam and the inner structure change and its subsequent impacts on the stability of dam itself based on heat-flow among the moraine dam. A typical in high-breach-risk moraine-dammed lake in Tibet will be selected as the experimental area achieved by the method of multidimensional in-situ surveys of "outer-surface-inner" to moraine dam. The coupling relationships among "water and heat environment of dam-inner structure of dam-shape changes of dam body" is to be regarded as the dominant exploring flow chart on the basis of heat interpretation of "source-flow-converge" inside of moraine dam. It is projected to study the variation processes on the inner structure of moraine dam, the state of penetrated status, the melt of dead ice. The model of the melt of dead ice in inner moraine dam is to be built, coupling mechanisms is to be revealed and more quantitative knowledge about the stability of dam itself is intended to be obtained in the view of the intrinsical attributes of moraine dam. The prospective project is expected to enrich the theories of envolution and development of glacial lake ouburst hazads and consequently provide theoretical supports for the risk assessment and remediation measures of glacial lake outburst flood hazards.

冰碛湖坝的温度场及其变化直接决定坝体内部冻融状态和死冰消融，并间接映射冰碛坝外部水热环境和内部结构特征，与坝体稳定性密切相关，从坝体能量流场的角度，分析和模拟其内部结构的变化，是探讨坝体本身稳定性的关键科学问题。拟申请的项目以西藏典型的高危险性冰碛湖为研究试验区，基于对冰碛坝"外部-表层-内部"的多维度观测，以堤坝"水热环境-坝内结构-坝体形变"之间的能量耦合关系为主线，通过对坝体能量"源-流-汇"的解析，探讨冰碛湖坝的内部结构、渗流管涌状态、埋藏冰消融等的变化过程，建立冰碛坝内埋藏冰消融模型，探究坝体温度场与内部变化间耦合机制及其对坝体稳定性的影响。本研究可望从冰碛坝本身的性状层面上，对冰碛湖坝体稳定性及其变化有进一步量的认识，在冰湖溃决灾害形成和演变机理方面取得创新成果,为冰湖溃决灾害减缓提供理论支撑。

根据计划安排，项目以西藏典型的高危险性冰碛湖—龙巴萨巴湖为观测研究试验区，共执行4次野外考察，积累了一批珍贵的野外观测数据，主要包括：开展了冰碛坝气象观测（2套自动气象站，包括风温湿辐射降水等要素）、冰碛坝内部结构雷达探测；在龙巴萨巴湖冰碛坝布设两个堤坝水热等物理性状观测点，每一个观测点包括0-1.5m间5层地温观测、4层土壤含水量、2层土壤热通量等梯度观测传感器各一套；进行湖盆径流观测，连续进行雨水样、冰样、湖水样、堤坝土样样品采集工作等。.在项目执行期间，课题组成员从冰碛坝能量平衡、冰碛坝温度内部结构变化、冰碛坝消融模拟和堤坝稳定性等方面开展深入研究，发现：（1）在喜马拉雅山区，冰碛坝的稳定性是冰湖溃决灾害的核心要素，堤坝水热状态及其变化是堤坝稳定性的关键指标。（2）观测期间堤坝土壤体积含水量较低，年平均仅为5.2%，峰值出现在积雪和冻土消融之后，最大可达27%；0-1.5m冻土年均温度已经超过0°C，尽管堤坝年均气温为−3.56°C，且约有1.0 W m-2/a的热量向下传递，指示堤坝浅层冻土已经退化，且退化还将不断加深。（3）模型模拟显示，2012-2016年间，堤坝年最大融化深度为2.8-2.9m，年最大融化深度为2.5-2.6m，也就说冬季堤坝出现了厚度约0.3-0.5m的消融夹层；过去55年来，龙巴萨巴湖堤坝最大融化深度呈增大趋势而最大冻结深度呈减小趋势，说明堤坝冻土/埋藏冰在不断消融、退化。（4）龙巴萨巴湖堤坝的稳定在不断下降，堤坝0-1.0m深度堤坝结构松散，全年基本处于未冻结状态，易发生漫顶冲刷溃决，堤坝1-3米深度，夏季处于融化状态，且冬季存在消融夹层，易发生管涌溃决。.项目研究从冰碛坝的水热等物理性状和坝体内部结构变化的层面上，对冰碛湖坝体稳定性及其变化、堤坝溃决的机理等有进一步量的认识，在冰湖溃决灾害形成和演变机理方面取得创新成果，研究成果作为主要内容之一获得湖南省自然科学二等奖1项和科技进步一等1项，并直接服务于西藏水利厅对西藏冰湖溃决灾害警和减缓工作，取得明显的社会效益。