考虑雨水感热的降雨对多年冻土水热变化影响模型研究

青藏高原暖湿化诱发的多年冻土和寒区工程水热变化是第三极冻土生态与地质演化问题的关注焦点。目前降雨影响下的多年冻土地表能量收支建模未考虑雨水温度的影响,忽略了降雨能量脉冲作用。在已有的冻土水热耦合理论的基础上,通过引入考虑雨水感热的地表能量平衡理论,完善了考虑降雨能量的冻土水热耦合模型,基于青藏高原北麓河现场监测验证了模型的有效性,并分析了夏季降雨对地表能量平衡和活动层水热的影响机制。结果表明：考虑雨水感热的修正模型模拟土壤体积含水率、温度和热通量的平均偏差误差分别在±1.198%、±0.704℃和±1.66 W/m²之内,一致性指数分别大于0.877、0.929和0.937;优化后的模型提升了对地表吸放热状态的评估,能够较好地预测了雨后活动层水热的变化;夏季降雨增加地表蒸发潜热和雨水感热,降低地表净辐射、感热和土壤地表热通量使地面降温,降温效果与降雨强度正相关;同时受降雨时段影响,白天降雨事件的降温效果显著,雨水感热促进地表冷却,而夜间雨水短暂加热地表,蒸发潜热的显著作用使地表依旧持续降温。在地表温度梯度降低和雨水入渗的作用下,温度梯度水汽通量减少,液态水通量增加...     

中国天山西部那拉提山地区多年冻土分布特征

那拉提山位于中国天山西部, 其冻土变化过程对区域自然环境变化、 工程活动产生重要互馈作用. 结合即将修建的新疆伊(宁)-库(车)输电线路前期的冻土勘察结果, 对那拉提山地区冻土分布特性、 主要影响因素等进行了探讨. 结果表明: 那拉提山地区冻土分布属于典型的山地多年冻土, 冻土发育区域、 冻土类型和地下冰空间发育特征及冻土温度状况等主要受到海拔、 地形地貌、 地表水分条件等因素的影响和控制. 同时, 该地区大量发育有泥流阶地、 泥流舌、 热融滑塌、 石环、 石河等冰缘现象. 受坡向、 植被、 水分等因素影响, 区域内冻土活动层厚度为0.7~4.5 m, 随着海拔增加, 冻土厚度由阳坡连续多年冻土下界(海拔3 000 m)附近的约20~22 m增加到海拔3 300 m附近的约70~100 m. 自1985年以来, 区域年平均气温上升(约0.088℃·a^-1), 该区域内的冻土退化趋势明显.     

青藏铁路遮阳棚路基试验工程效果实测研究

太阳辐射是导致气温和地表温度升高的主要因素之一,遮挡了太阳直接辐射后可以有效降低地表温度.基于青藏铁路冻土区遮阳棚路基试验工程监测数据,分析了遮阳棚内外的气温差异和路基地温特征.结果表明:遮阳棚能够降低棚内气温,监测期间棚内年平均气温低于天然条件下平均气温值0.6℃;监测期内天然条件下近地表0.1～0.3m范围的气温高于1.0m以上气温近1℃,但在棚体内部仅相差约0.3℃;日最高气温值在棚体内外的单日差值达6.0℃,平均气温值在地面0.1m高度处相差4.2℃,1.5m高度处相差2.1℃;在遮阳棚的作用下,棚体内部及附近土体地温有所降低,且多年冻土上限有一定的抬升,抬升最大幅度达1.0m.监测结果显示了遮阳棚对于保护路基下冻土的良好效果.     

透壁通风管路堤土体蒸发降温的试验研究

以多年冻土区透壁通风管路堤为研究对象,进行了路堤蒸发降温效果的室内试验,分析了土体水分蒸发对路堤降温效果的影响机制。分析结果表明,路堤通风期间的水分主要通过裸露在管壁小孔的土体表面直接蒸发,其有利于降低路堤温度。暖季空气与管壁的对流换热效应可使路堤土体增温,同时,通过管壁小孔的水分蒸发散热将对路堤产生降温效应,由于融土的未冻水含量较大,使得通过管壁小孔的水分蒸发散热降温作用也较大,这使透壁通风管路堤总体显现出降温效果     

风积沙环境下高等级公路冻土块石路基降温性能分析

青藏高原脆弱的生态系统以及人类工程活动,加剧了青藏工程走廊线性工程两侧沙漠化、荒漠化发展趋势,尤其冻土块石路基面临日益严重的风积沙灾害问题。以多年冻土区高等级公路块石路基为研究对象,采用数值模拟分析风积沙环境下封闭块石路基的降温性能和长期热稳定性。结果表明：风积沙堆积对封闭块石路基下部土层冻土温度的影响程度高于冻土上限,1.0 m湿沙工况降低冻土温度,0.2 m干沙则增大冻土温度。升温背景下,随年平均气温增加风沙堆积对路基冻土上限影响程度增强,干沙增大冻土融化深度,湿沙抬升冻土上限。随冻土含冰量减小,路基中心冻土上限对气候升温敏感性增加,风沙堆积影响减弱。气候升温和风沙堆积条件下,在年平均气温低于-5.5℃时,宽幅沥青路面封闭块石路基能够满足降温要求,使人为冻土上限保持在块石层内。研究成果可为风沙危害区多年冻土块石路基的病害治理和拟建青藏高速公路块石路基设计提供科学依据。     

盐渍土水-热场耦合效应与盐胀变形试验

为了研究西北干旱地区盐渍土在自然气候条件下的水-热场变化特征与盐胀变形规律,在4.5 m深试验坑内埋设了若干套竖向变形观测设备、含水率和温度传感器,对坑内不同深度土层的温度场、水分场和盐胀变形随季节性变化状况进行了为期1 a的动态监测和分析研究。结果表明：0.6 m以上土层相较于其他土层对气候温度变化的响应更加积极、温差变化幅值也更大,且土层间的温差幅值随降温期的不断深入而增大;土体含水率变化主要受降水、蒸发和温度梯度的耦合影响, 0.4 m以上土层水分的变化幅度较其他土层而言更为显著,土层水分迁移沿深度方向表现出分带现象;盐胀变形主要受温度和水分迁移的影响,盐胀变形主要发生在距地表1.0 m土层深度内,主要发展时间在当年11月至次年2月之间。     

高原植物与冻土季节融化层的关系——以西藏土门地区为例

高原地区的植物与冻土季节融化层都受到气候条件的影响,并相互制约。冻土的低温限制植物根系向深处生长发育,而植被又减少地面的阳光直射、土壤增温和水分蒸腾,降低地表温度,使冻土在季节融化期内融化深度不连续,呈块状分布。高原植物的形态特征是对严寒、大风、强光等生态因子的适应。     

半干旱地区地表-地下水系统水热运移与裸土蒸发研究

地表-地下水系统水、热迁移转化与裸土蒸发机理研究对于水量平衡以及地表能量转化具有重要意义。以鄂尔多斯盆地风沙滩地区为研究区,基于原位蒸渗仪长期观测,结合数值模拟,选择2种地下水位初始埋深分别为80 cm（浅埋深）和290 cm（深埋深）的情景,研究了变饱和带水热迁移转化的动力学过程以及对裸土蒸发的影响。结果表明:变饱和带土壤水的运动规律受水头梯度和温度梯度的共同驱动,且在不同水位埋深条件下呈现不同的运动方式;浅埋深条件下,受水头梯度的作用,土壤的毛细上升高度能够到达地表,蒸发条件下土壤水在毛细力驱动下向上运移,土壤内部不存在零通量面,温度对水分运动的影响较小,发现当地下水位埋深小于毛细上升高度时,地下水在毛细力作用下直接贡献土壤蒸发;深埋深条件下,水头和温度是土壤水运动过程的关键因素,位于地表以下18 cm以浅土壤内部出现孤立的零通量面,阻止了土壤水的向上运移,导致蒸发量减小。当地下水位埋深大于毛细上升高度的1.6倍时,地下水不再直接参与土壤蒸发,但会间接地影响包气带的水分转化;因此模拟期间浅埋深的裸土累积蒸发量约为深埋深累积蒸发量的4倍。     

多年冻土区典型地面浅层地温对降水的响应

在大气-地面-冻土之间存在复杂的水热变化过程,降水是青藏高原地区主要的水分补给来源,在浅层形成水热变化的不连续层。通过对北麓河地区降水和工程路面(沥青路面、砂砾路面)、天然地面(高寒草原、高寒草甸)浅层(0~80cm)温度数据的原位监测,分析在不同降水量和不同时段浅层的温度变化,结果表明:北麓河地区年降水量逐年增加,增加速率为22.9mma-1。降雨主要集中在5~9月。白天地温对降水的响应比夜间强烈。工程路面夜间的温度变化大于天然地面。在相同降水条件下, 10:00~15:30时段的温度变化量大于16:00~18:00时段。随着降雨量的增加,温度下降幅度增大。砂砾、高寒草原、高寒草甸地面地温对降水的响应深度范围为0~30cm。受路面结构中隔水层的影响,沥青路面为0~20cm,且5cm深度温度的变化幅度大于地表。为进一步研究不同地面类型不同水热传输模式层结的划分提供数据基础。     

煤层地下开采地表沉陷预测的边值方法

采空区上覆岩、土体对地表沉陷的耦合行为可归结为弹性理论的边值问题,由不同性状松散表土层确定的应力边界和岩、土体之间形成的位移边界构成了相应边值问题的定解条件。在已有研究成果的基础上,提出了地表下沉预测研究的边值提法,以探讨地下开采引起的地表沉陷规律。给出了采空区上覆表土层内任一点的位移和地表下沉的计算公式,确定了地表沉陷的范围,并以神东矿区大柳塔1203工作面开采引发的地表沉陷为例给出了工程实例。研究结果表明,采空区上覆岩体对地表及表土层内任一点下沉的影响取决于上部岩层破断后的结构形态;采空区上覆土体对地表下沉量的作用与土体性质及表土层厚度有关,土体对表土层下沉的影响由下而上增大,呈非线性变化,至地表达最大值;地表沉陷区域随表土层厚度的增加而增大,其影响范围远大于采空区。     

透壁通风管路堤的对流换热和蒸发散热

针对透壁通风管路堤中透壁通风管管壁与空气之间的对流换热和土体水分通过管壁小孔的蒸发散热机制,分析了开孔率、风速及含水率等因素对透壁通风管管壁对流换热和水分蒸发散热的影响,并具体给出了管壁对流换热系数和蒸发散热系数的计算公式。冬季路堤由于冻土层未冻水含量较小而使管壁小孔的水分蒸发散热较弱,路堤总的降温效果主要由管壁对流换热效应控制,而暖季通风管内空气与管壁的对流换热效应可使路堤土体增温,同时,由于通风管周围融土的未冻水含量较大,而使得通过管壁小孔的水分蒸发散热较强,可部分或全部抵消对流换热引起的增温效应,而有利于路堤的稳定。     

热管措施下锥柱式桩基础传热过程及降温效果预测研究

针对青藏直流联网工程塔基热稳定性问题,建立空气-热管-土体耦合传热数学模型,并利用该模型开展锥柱式基础传热过程及热管冷却降温效果的模拟预测研究. 结果表明：冷季热管工作期间,其周围地温梯度明显较大且呈“纺锤形”分布. 同时,由于锥柱式基础及其底座为热的良导体,热管产生的冷量通过锥柱式基础及其底座快速向基础底部传递,使得基础下部形成大范围低温冻土,这对主要考虑融沉病害的锥柱式基础而言十分有利. 暖季热管停止工作期间,浅层地温主要受环境温度影响,锥柱式基础附近融化深度大于天然地表下,二者差值约35 cm. 通过热管剖面及无热管作用中间剖面地温对比,发现单一塔腿在4根热管措施作用下,锥柱式基础周围多年冻土地温分布较为均匀,可避免冻土地基的显著不均匀沉降变形. 热管周围土体快速降温过程主要集中在前5 a,之后受气候变暖影响桩基础及天然地表以下上限深度不断增加,多年冻土地温缓慢升高. 50 a气温升高2.6 ℃背景下,锥柱式基础下部多年冻土仍保持冻结状态,能够满足青藏直流联网工程对于冻土地基热稳定性要求.     

Hydrothermal pattern of frozen soil in Nam Co lake basin,the Tibetan Plateau

Hydrothermal processes and the regimes of frozen soil formed in alpine regions with glaciers and lake area are complex and important for ecological environment but have not been studied in Tibet. Based on soil temperature and moisture data from October 2005 to September 2006 collected in the Nam Co lake basin, Tibetan Plateau (TP), those questions were discussed. The mean annual air temperature was −3.4°C with 8 months below 0°C. Air and soil temperature varied between −25.3~13.1°C and −10.3~8.8°C, respectively. Soil moisture variations in the active layer were small with the minimum value of 1.4%, but were influenced greatly by snowmelt, rainfall and evaporation, varying up to 53.8%. The active layer froze later, thawed earlier and was thinner, however, the lower altitude limit of permafrost is higher than that in most areas of TP. The effects of soil moisture (unfrozen water content) on soil temperature, which were estimated through proposed models, were more significant near ground surface than the other layers. The surface soil temperature decreased with snowcover, the effect of cold snow meltwater infiltration on soil thermal conditions was negligible, however, the effect of rainfall infiltration was evident causing thermal disruptions.     

Thermal Characteristics of the Embankment with Crushed Rock Side Slope to Mitigate Thaw Settlement Hazards of the Qinghai-Tibet Railway

Abstract: Permafrost (perennially frozen ground) appears widely in the Golmud-Lhasa section of the Qinghai-Tibet railway and is characterized by high ground temperature (≥ ?1°C) and massive ground ice. Under the scenarios of global warming and human activity, the permafrost under the railway will gradually thaw and the massive ground ice will slowly melt, resulting in some thaw settlement hazards, which mainly include longitudinal and lateral cracks, and slope failure. The crushed rock layer has a thermal semiconductor effect under the periodic fluctuation of natural air. It can be used to lower the temperature of the underlying permafrost along the Qinghai-Tibet railway, and mitigate the thaw settlement hazards of the subgrade. In the present paper, the daily and annual changes in the thermal characteristics of the embankment with crushed rock side slope (ECRSS) were quantitatively simulated using the numerical method to study the cooling effect of the crushed rock layer and its mitigative ability. The results showed that the ECRSS absorbed some heat in the daytime in summer, but part of it was released at night, which accounted for approximately 20% of that absorbed. Within a year, it removed more heat from the railway subgrade in winter than that absorbed in summer. It can store approximately 20% of the “cold” energy in subgrade. Therefore, ECRSS is a better measure to mitigate thaw settlement hazards to the railway.     

Technical approaches on permafrost thermal stability for Qinghai–Tibet Railway

Widespread warm permafrost with a high ice content is a key problem for the roadbed stability of the Qinghai–Tibet Railway. A new approach is proposed to alleviate the effect of global warming and engineering construction on permafrost by cooling the roadbed and positively protecting the permafrost. Measures for cooling the roadbed by adjusting solar radiation, conduction, and convection are studied and applied to prevent ground ice from thawing and to ensure roadbed stability in permafrost regions. The results of monitoring permafrost embankments at Beiluhe and along the Qinghai–Tibet Railway show that the measures adopted for cooling the roadbed are very effective in raising permafrost table and reducing the soil temperature.     

青藏铁路通风路基边界条件研究

In permafrost regions, many methods about active cooling embankment are put forward, one of these representations is ventilated embankment, its cooling effect is the result of the air convection in the duct, and this leads to reducing the annual average ground temperature. The present work in this article is to determine the boundary conditions of the ventilated embankment and natural ground in numerical work. There are several effects which influence boundary conditions, they are: radiation, evaporation,phase change, convection and embankment material etc. Radiation and convection are the main effects in those. We mainly consider sun radiation in this article. The added-surface effect in ventilated embankment lowers its temperature, so the temperature on the wall of the ventilated embankment is different from the temperature in atmosphere. There are two methods in determining the surface temperature, experimental method and experiential method. Detailed research is discussed in the article.     

青藏高原冬春积雪和季节冻土年际变化差异的成因分析

利用青藏高原上72个常规气象观测站的逐日积雪厚度、冻结深度、气温、降水和地表温度资料,分析了高原积雪和季节冻土年际变化差异的原因.结果表明:气温和地表温度对高原积雪和季节冻土都有重要的影响,而降水对积雪的影响很重要,但是对季节冻土的影响则比较小.高原积雪对季节冻土有较大的影响,在积雪达到一定厚度以后,积雪的保温作用会影响冻结深度的变化,积雪越厚,保温作用越强;积雪越浅,保温作用越弱,当积雪小于某一厚度时其主要起降温作用.积雪的保温作用可能是积雪与季节冻土年际变化差异的原因之一.     

封闭条件下抛石路堤降温效果及机理的试验研究

在多年冻土地区道路工程的修筑与维护中, 如何保证多年冻土不退化所采取措施的长期可靠度问题日益为人们所关注. 通过室内试验研究了实际工程中半开放半封闭抛石路堤受到风沙或积雪填埋后,在不同温度变幅条件下的降温效果. 实验结果发现: 在满足一定厚度时, 封闭条件下的块石层仍具有良好的降温效果, 具有可变等效导热系数的特性, 在实验中充分体现了"热二极管效应". 在外界温度变幅较大的条件下, 降温速度和降温效率均大于温度变幅较小的情况. 通过对块石层顶底温差与其顶部温度变化关系, 以及块石层内温度场特征的分析, 证实了封闭块石层内自然对流的真实存在和对流的运动发展趋势. 试验结果为抛石路堤降温的长期可靠性提供了依据.     

Spatial and Temporal Distribution and Variations in the Near-surface Soil Freezing Days across China, 1956-2006

Using surface soil daily minimum temperature from 845 meteorological stations across China, the long-term (1971-2000) mean and spatial distribution of the near-surface soil freezing days were estimated with annual values of the number of near surface soil freezing days. The time series for the number of freezing days were constructed and compared with air temperatures in the same period.Resultsshowed that long term mean value in the number of the near surface soil freezing days increased with the increasing latitudes and altitudes over China. Near-surface soils were frozen for more than 200 days in the Qinghai Tibet Plateau, northern Xinjiang and northeast of China. The boundaries of permafrost zones coincide with the contour of (220±10) days of near-surface soil freezing. Using the mean number of 15 days of near-surface soil freezing as criterion, we found that the southern boundary of seasonally frozen ground is around the 25°N line, and the regions south of 22°N are essentially unfrozen regions. The time series of the number of freezing days showed a significant linear trend with change with a slope of -0.22days/year over a period from 1956 through 2006. After the 1990s, the linear slope was up to -1.02 days / year, indicating that the rate of decrease in the number of near-surface soil freezing days has accelerated. Changes in the number of near surface soil freezing were in a negative correlation with air temperature, i.e., the number of near-surface soil freezing days decreases with increase in air temperature.Backgroundcolor represents the contour values of the departure of near-surface soil freezing days from the 1971-2000 mean; Black dashed line is the boundary of permafrost regions, red dashed line is the boundary between frozen and unfrozen ground regions in China     

祁连山区黑河流域季节冻土时空变化研究

季节冻土的时空变化对地—气水热交换、地表能量平衡、地表水文过程、生态系统及碳循环等有着非常重要的影响.利用黑河流域11个气象站40多年的气温数据和5 cm深度处的土壤温度数据,建立了月平均气温与土壤冻结天数之间的关系.同时应用月平均气温与冻结天数的相关关系和5 km网格化月平均气温及30 m分辨率的DEM数据,编制了黑河流域逐月季节冻土分布图,并按其空间分布特征,将逐月地表冻融状态划分为:完全冻结、不完全冻结和不冻结3种.系统研究了黑河流域2000-2009年逐月季节冻土分布及冻结概率的时空变化特征.在季节分配上,黑河流域完全冻结面积最大值出现在1月;不完全冻结面积最大值在11月;而不冻结面积最大值在6月和7月.在年际变化上,完全冻结状态的离差值在冷季变化大,暖季变化小;不完全冻结状态在一年的回暖期和降温初期,年际变化较大;不冻结状态分别在4月和10月变化较大.冻结概率在1月达到最大值,6月和7月降低到最小值.在空间分布上,黑河流域季节冻土的逐月分布与变化和冻结概率主要受海拔高度控制,纬度的影响次之.