复杂条件下冻土块石路基的环境适应性及对策研究

The block-stone embankment is the key technology of solving permafrost problem. It has successfully solved the problem of permafrost of Qinghai-Tibet Railway, and is widely used in other subgrade engineering in permafrost regions. In practice, the "block-stone embankment" is confronted with new-severe problems: the adaptability to complex conditions, such as the sand filling and accumulation, snow cover and rain infiltration etc., and the strategy of mitigating the adverse influence. This project tries to propose a thermal analysis model, based on convection heat transfer theory in porous media, frozen soil heat transfer theory and seepage theory, under the complex conditions, and finite element calculation formula is derived. The structure changing property will be investigated after the rock layer is filled with sand by field experiment and field investigation of the real sand filled embankment of Qinghai-Tibet Railway. And then, the interface of temperature difference of driving force of natural convection will be determined. The characteristics of heat and moisture in the block stone layer will be studied by experiment by simulating precipitation. The boundary conditions of the sand cover and snow cover will determine by field observation, respectively. Based on the proposed model and observed conditions, numerical method is used to estimate the adaptability of block-stone embankment to the complex conditions. Field and laboratory test are used to validate the simulation results and the model will be improved according to the comparison result. After the thermal regime characteristics of block-stone embankment under complicated conditions are determined, prevention techniques will be put forward and be simulated, tested and optimized. The research results can provide theoretical basis and technical support for risk evaluating and treatment of the Qinghai-Tibet Railway subgrade threatened by sand, and for the disease prevention and control of the proposed the Qinghai-Tibet Expressway and other roadways influenced by complex conditions in permafrost regions.

“块石路基”是解决道路冻土问题的关键技术，成功解决了青藏铁路的冻土难题，并在其它冻土路基工程中被广泛应用。在实践中“块石路基”面临严峻的新问题：风沙填堵堆积，积雪和雨水入渗等复杂条件下的适应性及应对策略。本项目以多孔介质对流换热理论、冻土传热理论和渗流理论为基础，建立复杂条件下块石路基水热分析模型、推导有限元计算公式。通过试验研究风沙填堵后块石层内部结构的变化规律，确定发生自然对流的温差界面；通过试验研究块石层内的水热特征；通过现场观测确定风沙/积雪的热平衡边界。然后用数值方法对复杂条件下块石路基的环境适应性进行评价，用现场及室内试验结果对模型进行验证、改进。在确定复杂条件下块石路基温度场特征后，提出防治技术方案，并对方案效果进行模拟和试验验证，对技术方案进行改进优化。研究成果可为青藏铁路沙害路基病害评估与治理，拟建青藏高速公路及其它受复杂条件影响的冻土路基的病害防治提供理论依据和技术支撑

多年冻土区道路工程的稳定性受控于气候及工程活动影响下多年冻土自身的稳定。青藏铁路的修建为我国乃至世界多年冻土道路的修筑提供了成功的范例和技术支撑。“块石路基”成为解决多年冻土区路基融沉病害的关键技术之一。然而在实践中，“块石路基”面临风沙，积雪和降水条件下的环境适应性问题。.本项目基于传热、渗流理论，采用理论分析、现场试验、室内试验和数值分析方法，从基本参数、理论模型到工程技术对青藏高原风积沙物理特征，积沙和积雪的热边界条件，风积沙、降雨对块石路基水热特征及长期稳定性和风沙、积雪及积水环境下的工程应对技术及效果开展了深入研究。课题组建立了新的风积沙导热系数计算模型，明确了青藏工程走廊风积沙微观物理特征及风积沙与块石混合材料热物理参数和渗透特性；明确了积沙、积雪条件下的路基热边界条件，建立了青藏工程走廊工程热边界计算模型；建立了降雨入渗的水热耦合分析模型，并阐明了降雨对冻土普通路基，冻土块石路基的热影响规律；定量评价了风沙填堵对块石降温性能的影响规律，给出了风沙填堵情况下块石层自然对流发生的临界温差，阐明了风沙填堵、堆积对冻土块石路基长期稳定性的影响规律；提出了预防、治理风沙堆积、地表积水、边坡积雪冻土块石路基问题的L型通风管技术和热管方案，并对其效果进行了数值分析。结果表明：新的风积沙导热系数计算模型具有很好的准确性；降雨对路基浅层土体水分含量影响显著。降雨条件下路基浅层土体的水分含量迅速升高，可达10%。路基-15cm深处土体含水率在冻结期和融化期的差值可达到12%，-45cm以下土体的含水率差值则不超过2%；风沙填堵大幅降低块石路基降温功能，路基将不能保持稳定，必须采用额外措施；热管、L型通风管、防雪棚可有效解决路基风沙和积雪问题。成果可为多年冻土区重大工程（青藏铁路、拟建青藏高速、高寒边防公路）及一般性工程在复杂条件下的长期稳定性评价、病害整治和预防提供理论依据和技术支撑。