非饱和岩体裂隙中冰层生长试验及单个裂隙壁面上的结霜模型研究

Experiment of ice growth in unsaturated rock fracture and study on frost model on individual fracture wall

裂隙中冰夹层的出现及生长是岩体冻胀风化的重要特征及成因,裂隙岩体是由裂隙和岩石基质构成,裂隙与可视为孔隙介质的岩石性质差异巨大,多数情况下是岩体中水分主要的储存及运移通道,对于不饱和裂隙而言,其中往往同时存在着气态迁移和液态迁移,很难直接用既有的原位冻胀和分凝冰机理解释裂隙中冰层形成及生长过程。为研究非饱和岩体裂隙中冰层出现及分布状况,作者用两块水泥试块拼接成带有单条垂直裂隙的岩体试样,并对试样进行了暖端补水条件下的单向冻结试验,试验结束后,试块中新增了3条水平裂隙和1条垂直裂隙,且裂隙中均有薄冰层出现,试样负温区有显著的结霜现象,整个过程中水分迁移总量达221 mL,且以气态形式为主。基于传热学基本原理,建立了自然对流条件下单个裂隙壁面上的结霜模型,根据试验中试样不同冷表面的特征,将结霜表面分为Ⅰ~Ⅲ类,分别计算了三类冷表面上霜层厚度、密度及单位质量随时间的变化,并利用试验结果对计算结果进行了验证,证明了单个壁面上结霜模型的可靠性。以结霜模型为依据,同时结合相关文献进行分析得到:影响岩体裂隙负温区壁面结霜量的直接因素有裂隙中的对流传热条件、空气相对湿度及负温区壁面面积大小,这三个因素取值越大时,则一定时间内裂隙壁面上的结霜量越多,裂隙中的成冰作用更为显著。裂隙沿程的温度梯度则是更为本质的原因,温度梯度越大时,岩体裂隙中的对流传热作用会更为强烈,负温区壁面面积越大,则一定时间内结霜量越多。

The formation and growth of ice interlayers in rock fractures are significant characteristics and causes of rock frost weathering.Fractured rock masses consist of fractures and rock matrix,which differ greatly in prop⁃erties and can be considered as a porous medium.Water is typically the primary storage and transport channel in the rock mass,while unsaturated fractures often involve both gas-phase and liquid-phase migration,making it difficult to directly explain the formation and growth process of ice layers in the fractures using existing in-situ frost heave and frost segregation mechanisms.To investigate the occurrence and distribution of ice layers in un⁃saturated rock mass fractures,the authors conducted a unidirectional freezing test on two cement test blocks with a single vertical fracture under warm-end water replenishment conditions.After the test,three horizontal frac⁃tures and one vertical fracture appeared in the test block,with thin ice layers forming in the fractures.The nega⁃tive temperature zone of the sample showed significant frosting,and the total amount of water migration during the entire process reached 221 mL,primarily in the gas phase.Based on the fundamental principles of heat trans⁃fer,the authors established a frost model for a single fracture wall surface under natural convection conditions.The frost surfaces were divided into classes I~Ⅲbased on the characteristics of different cold surfaces of the test samples,and the thickness,density,and unit mass of frost layer on the three types of cold surfaces were calcu⁃lated over time.The experimental results validated the calculation results,demonstrating the reliability of the frost model on a single wall surface.Based on the frost model and relevant literature analysis,the direct factors affecting the amount of frost on the negative temperature zone wall surface of rock fractures include the convec⁃tive heat transfer conditions in the fracture,the relative humidity of the air,and the size of the negative tempera⁃ture zone wall surface area.The greater the values of these three factors,the more frost will form on the fracture wall surface within a certain time,and the more significant the ice formation in the fractures.The temperature gradient along the fracture is the essential reason,as the greater the temperature gradient,the stronger the con⁃vective heat transfer in the rock fracture,and the larger the negative temperature zone wall surface area,the more frost will form within a certain time.