Study on the height effect of highway embankments in permafrost regions

Thaw settlement is the main embankments distresses of highway in permafrost regions, according to survey data of the Qinghai–Tibet Highway (QTH). It can be effectively mitigated or even controlled by raising the embankment height. In view of this engineering problem, this study proposes the concept of the Height Effect of Embankment in Permafrost (HEEP). The concept represents the deformation and failure rules of embankment resulting from height variations. A thermal-elastic-plastic thaw settlement computational model is used to simulate the settlement processes of embankment, considering scenarios of different mean annual ground temperatures (MAGTs) and different heights. The model is validated by the field monitored data from a specific embankment section along the QTH. It is found that the total deformation of embankment is of considerable value and comes primarily from the thaw settlement of permafrost. Some special structures are recommended to supplement the built embankment, to ensure the stability of embankment in warm permafrost regions. The research results could provide essential theoretical and technological support for the transversal section design of highway embankments in permafrost regions.     

宁夏南部山区生态环境脆弱性评价

通过建立生态环境脆弱性评价指标体系,选择压力-状态-响应模型,对宁夏南部山区生态环境进行了定量评价,得到了各个评价单元的生态脆弱性相对强弱得分,同时运用Arcgis软件对区域的生态脆弱性进行分级.结论表明,评价单元脆弱性主要集中在强脆弱性和中脆弱性之间,其中原州区和隆德县为强脆弱区,泾源县、海原县、西吉县、彭阳县属于中脆弱区.     

A temperature dependent creep damage model for polycrystalline ice

We present a continuum damage model for the temperature dependent creep response of polycrystalline ice under a multiaxial state of stress, suited for ice in polar regions. The proposed model is based on a thermo-viscoelastic constitutive law for ice creep and a local orthotropic damage accumulation law for tension, compression and shear loadings. Orthotropic damage is represented by a symmetric second-order damage tensor and its effect on creep is incorporated through the effective stress concept. The unknown model parameters are first calibrated using published experimental data from constant uniaxial stress tests and then predictions are made for constant strain rate and multiaxial loadings. The predicted results are in good agreement with both experimental and numerical results in the literature illustrating the viability of the proposed model. The model is mainly intended for studying the failure mechanisms of polar ice at low deformation rates with depth varying temperature profiles.     

A new structure to control frost boiling and frost heave of embankments in cold regions

Frost boiling and frost heave are the main factors that cause road damage in cold regions. A new kind of embankment structure, which consists of geotextile, crushed-rock layer and geomembrane, was designed and investigated both in the laboratory and at the field of Budongquan located at Qinghai–Tibet Plateau. Comparison tests were conducted at the same time. The key of the new structure is the porous crushed-rock layer which has smaller thermal conductivity with function of drainage and blocking of moisture migration induced by freezing. Both the laboratory and field research results show that the frost penetration and thawing depths of the new structural embankment are much smaller than those of the coarse-grained soil embankment. Also, the new embankment structure has lower water content in the upper layer and smaller frost heave and thawing settlement than the latter does. In addition, it has good drainage effect. Water coming from the road surface can be drained away from the embankment through the porous crushed-rock layer. All these states that the new structure consisting of the porous crushed-rock layer is superior in frost damage mitigation to the normal structure used in cold regions.     

基于BP人工神经网络的高锰酸盐指数预测模型

高锰酸盐指数(CODMn)作为有机物相对含量的指标之一,同时是河流水质规划的一项重要指标。CODMn预测过程可认为是一种复杂非线性函数关系的逼近过程,利用BP人工神经网络建立CODMn预测模型,将历史样本作为模型的输入进行训练,利用训练好的网络模型进行预测,结果表明该模型具有良好的预测性能。     

青藏高原热融湖对冻土工程影响的数值模拟

热融湖的侧向热侵蚀对周围冻土工程产生较大影响。在柱坐标下,运用带相变的数值热传导模型,预测了热融湖影响下冻土路基的地温场发展状况和可能造成的工程病害。预测结果表明：在不考虑湖岸坍塌后退、面积扩大的情况下,热融湖对冻土路基的热影响主要受湖底年平均温度和湖边到路基的距离两个因子的影响。湖底年平均温度越高,对路基的热影响越严重;湖边到路基的距离越近,对路基的热影响亦越严重。突出的表现在坡脚、路基中心平均地温升高和融化夹层在水平、竖直方向的发展。如果考虑热融湖的湖岸坍塌后退,实际增温要比模拟的结果更明显,影响更严重。     

电缆防火涂料在高速公路隧道中的应用研究对比

在运营中的高速公路隧道,由于防火需要,现在基本都在使用膨胀型电缆防火涂料。本课题通过试验应用对比,确认电缆防火改性涂料(纳米技术)与普通水性电缆防火涂料在高速公路隧道这一特殊环境下的使用效果。为高速公路隧道电缆防火和消防设计提供参考依据。     

混合介质对降温法形成甲烷水合物性质的影响

目前,对沉积物中天然气水合物形成与分解性质的研究主要是在单一介质中进行,但自然界中的天然气水合物主要赋存于混合介质沉积物中。因此,有必要考察不同介质类型对天然气水合物形成的影响。为此,将粗砂、细砂、粉土3种介质按不同方法混合,搭配出6种混合型介质,并采用降温法在其内生成甲烷水合物,研究介质类型对甲烷水合物形成性质的影响及在降温过程中不同介质消耗甲烷气体的特点,为研究介质内水合物形成机制提供理论基础。实验装置由供气、反应和数据采集3个系统组成。结果表明:①不同单一介质对水分的吸持力差别很大,介质混合后水分在其内的分布状态及水分子在介质表面的吸附排列存在较大差异,从而使不同混合型介质内甲烷水合物的最终生成形态不同;②介质类型不仅会影响其内甲烷水合物的形成过程,而且会影响水合物的含气率;③不同介质内甲烷水合物生长过程所处的时间阶段不同。     

季节冻土区保温路基设计参数

在季节冻土区,尤其是在深季节冻土区,冻害对铁路路基寿命有着严重的影响,因而抑制路基冻胀是季节冻土区路基设计的基本原则。本文对铺设保温层的效果,运用土壤冻结条件下水热耦合输移的基本方程和数值方法,模拟分析在不同的埋深、宽度、厚度和施工季节条件下,铺设XPS保温材料板对路基下季节冻土最大季节冻结深度在以后50年内随时间的变化。在数值模拟的基础上,提出在季节冻土区铁路路基工程中埋设保温层的合理深度、宽度及施工季节;总结分析保温板厚度和路基填土高度之间的关系。     

高海拔输电线路的冻土工程问题及对策研究

±500kV直流输电线路横穿整个青藏高原,其生存环境不可避免与冻土和不良冻土现象有紧密的联系。由于冻土具有冻胀、融沉特性及不良冻土现象等问题,因而,输电线路要安全运行,线路选线定位时就必须了解与线路有关的冻土工程问题。本文从影响输电线路选线定位的因素出发,在分析冻土输电线路工程问题的基础上,从多个角度建议了线路建设中的工程对策,为即将开工的±500kV青藏直流联网工程的顺利进行提供科学依据和参考。