降雨环境下多年冻土区块石路基传热特性研究

As a key technology to solve disease of thaw settlement, crushed-rock embankment is widely applied in permafrost regions. However, rainfall in the Qinghai-Tibet is gradually increased in the context of global climate warming. In summer rainfall with some of heat will penetrate crushed-rock layers inside, which has an impact on the cooling performance of crushed-rock layers and the hydrothermal state of stratum. At present, it is necessary to carry out research on the heat transfer property of crushed-rock embankment in the condition of rainfall, which is adopted to evaluate heat transfer efficiency and long-term thermal stability. By means of laboratory model experiments in this project, the law of hydrothermal response for crushed-rock layer is analyzed under different rainfall conditions, meanwhile the effect extent of the rainfall on the cooling performance of crushed-rock embankment and the major control factor is revealed. Combined with observed data in laboratory test, theory model of water-thermal-gas coupled is founded on the basis of heat transfer and seepage mechanics in porous media, which is used to investigate convective heat transfer mechanism and water flow law for crushed-rock layer in the scenario of rainfall. The prediction and evaluation of long-term thermal stability and optimization design of geometrical parameters is carried out on the structure type of crushed-rock embankment in practice, contributed for design and computing theory of crushed-rock embankment in permafrost region. It has great significant to not only further understand heat transfer mechanism of crushed-rock layer in the above research results, but also to provide scientific basis and technical supports in the structure design and engineering stability on crushed-rock embankment in permafrost region.

作为解决冻土融沉病害的关键技术，块石路基在多年冻土区得到广泛应用。近年来，随着全球气候变暖，青藏高原降雨呈增加趋势，夏季降雨携带一部分热量将入渗到块石层内部，影响块石路基的降温性能和水热状态。目前，如何评价降雨环境下块石路基的传热功效和长期热稳定性，则有必要深入开展块石路基传热特性的研究。本项目通过室内模型试验，研究不同降雨条件下块石路基水热响应规律，揭示降雨对块石路基降温性能的影响程度和主要控制因素；结合模型试验数据，基于多孔介质传热学、渗流力学理论建立块石路基水热气耦合模型，探索降雨环境下块石层对流传热机理和水分流动规律，开展现有块石路基型式长期热稳定预测和评价，提出块石路基几何优化设计参数，完善多年冻土区块石路基设计计算理论。研究成果对进一步认识块石路基的传热机理具有重要意义，也可为多年冻土区块石路基结构设计和工程稳定性评价提供理论依据和技术支撑。

受全球气候变化影响，青藏高原暖湿化趋势显著，降水条件下雨水携带的部分热量会改变块碎石层内对流传热过程，水分入渗引起基底土层的水热状态和全年热量收支变化，从而对块碎石路基的降温性能和长期稳定性产生影响。本项目通过室内试验观测块石层内温度、热流及空气流速的变化规律，揭示降雨条件下块石层的传热过程及对流特征；在此基础上，分析块石底部土层地温动态变化和水分迁移规律，揭示降雨条件下块石路基的降温效能及影响程度的分析。通过建立理论模型，开展现有块石路基结构型式的长期热稳定评估。研究成果可为多年冻土区块石路基优化设计、结构补强及病害整治提供依据。封闭块石层在降雨下其自然对流与降雨量和厚度有关。随降雨量增加，1.4 m厚的块石层瑞利数最大值逐渐降低，当降雨量达到23 mm时，块石层不发生自然对流；而0.6 m厚的块石层瑞利数最大值则随降雨量增加逐渐增大，自然对流增强。降雨对1.4 m厚度的块石层内部与基底土层有升温作用，而对0.6 m厚度的块石基底土层有降温作用。随着降雨量增加，浅层土体积含水量峰值有一定抬升但差异不大。块石体与土层之间的空隙会被凝结冰部分填充，降雨难以入渗形成水分累积，在多雨地区块石层与土层界面应加强防排水措施。开放块石层在降雨时段各深度处的温度有明显突变，降雨入渗可使基底土层温度最大抬升2.13 ℃；在集中降雨作用下基底土层的平均温度基本呈升温变化，厚度小的块碎石层对降雨的温度响应更为显著。基底土层在降雨过程中体积含水量先急剧上升后缓慢下降，且其对温度的响应滞后于水分变化。随着降雨量增加，土层的体积含水量及变化量整体呈升高趋势。各周期块碎石表面与基底土层的热通量在降雨时段均存在突变并随降雨量增大整体变化量增加。块碎石基底土层随降雨量增大每周期的吸热量和放热量基本呈抬升变化，热收支变化受降雨入渗量和块碎石厚度的影响。