【作者】 魏大川；

【导师】 谌文武； 郭青林；

【作者基本信息】 兰州大学 ， 工程·地质工程（专业学位）， 2019， 硕士

【摘要】 在土遗址赋存的东北、西北、青藏高原地区内,冬季常有降雪,甚至春秋季雨雪天气均有存在。降雪覆盖在土遗址表面,当白天温度上升至一定程度,积雪层缓慢融化,雪水从顶部入渗的方式对土遗址表面、顶部产生浸泡作用,使得土遗址顶部含水率增高,水分的迁移影响了土体颗粒骨架的强度、颗粒排列方式等要素,使土遗址在土体微观结构上发生变化。土体粒凝聚力下降,最终崩解,表现为顶部的酥碱,在外力(风沙吹蚀、人为因素等)作用下轻易的剥落。当温度降低至零度以下,积雪层融化速度逐渐减缓,其孔隙内的雪水冻结,积雪层变成冰雪混合体,覆盖雪层由干燥、片状的雪花密实化、粗颗粒化。低温使得进入土遗址的液态雪水相变成固态冰,由于冰、水的密度差异,相变后固态冰晶体积大于水,这种体积变化进而挤压孔隙是土颗粒骨架发生变形的又一个原因。为了探究积雪覆盖下遗址土劣化特征和治理措施,本文进行了以下几方面的研究:同样的积雪覆盖条件下,不同融化温度时,遗址土的劣化破坏特征与机理;同样试验温度时,对比薄层、厚层积雪覆盖,未冻水(雪水)直接入渗条件下,遗址土的劣化破坏特征与机理;使用三种方式加固土样(加固材料为SH溶液),进行积雪覆盖下冻融循环试验,探究其物理力学性质的变化,并对试验后的加固样进行崩解实验,探究其在静水中的耐崩解性。(1)研究发现,在积雪覆盖条件下的冻融循环中,当积雪厚度与冻结温度一定时,试验结束后3℃融化温度下土体顶部酥碱、裂缝较为严重,6℃时次之,9℃时土样外观基本无变化。对于干密度相同的土体,不同融化温度时,试验结束后土体的物理力学性质不同。10次循环后,6℃融化温度下土体的冻胀率最高,9℃时次之,而3℃时最小;试验结束后,三种融化温度下纵波波速、抗压强度相差不大,而表面硬度随着融化温度增高而增大。(2)相同冻融环境下,积雪覆盖、未冻水(雪水)直接入渗对土遗址的影响差距较大。积雪覆盖条件下试样在冻融循环过程中的物理力学性质劣化特征、外观,与等量未冻水(雪水)直接入渗后的试样有较明显的差别。就物理性质来说,积雪覆盖使得土体冻胀较小,但表面易出现酥碱和泥皮翻卷,顶部易产生裂缝和掉块。就力学性质来说,当积雪量少时对土体的破坏程度小于未冻水(雪水)直接入渗,而积雪量多时,积雪覆盖使得土体劣化得缓慢,为应对由积雪覆盖引起的土遗址病害提供了时间。(3)SH在积雪覆盖条件下的冻融循环中表现出较好的加固效果,土样未出现酥碱、裂隙,强度也有所提升。试验结束后,SH拌合加固后土体仅表面出现少量掉渣,物理力学性质随SH固含量(0.4%、0.5%、0.6%)增高而增大。(4)表面喷洒加固对强度提高不大,但对表层土颗粒锁固效果好,没有掉渣产生,在浓度选择上,1.0%效果性价比更高;SH拌合+表面喷洒加固后土体几无变化,相同喷洒浓度下,SH固含量越高加固效果越好。通过崩解试验证明,三种加固方式下的土体在在积雪覆盖下冻融循环后仍能保持较好的水稳性,崩解试验期间未出现崩解现象。更多还原

【Abstract】 In the northeast,northwest and Qinghai-Tibet plateau where the ruins are located,snow often occurs in winter,even in spring and autumn.Snow cover the surface of the site.When the daytime temperature rises to a certain extent,the snow layer slowly melts,increases the water content of soil.The way of snow water infiltration from the top has an immersion effect on the surface and top of the site,the migration of moisture affected the strength of the soil particle skeleton,particle arrangement and other elements,which reduces the cohesion of the soil particles,changes the soil’s microstructure and finally disintegrates.It eventually leads to the efflorescence on the top and scaling off under the external forces(wind erosion,human factors,etc.).When the temperature drops below 0℃,the melting speed of the snow layer gradually slows down,and the snow water freezes in its pores,making the snow layer become a mixture of snow and ice.The dry and flake snow is densified and coarse-grained.The low temperature makes the liquid snow water entering the soil into solid ice.Because of the density difference between ice and water,the solid ice crystal volume is larger than that of water after phase transformation.This volume change and then squeezing pores is another reason for the deformation of soil grain skeleton.In order to explore the deterioration characteristics of the site soil under snow cover and control measures,the following aspects are studied in this paper: Under the same snow cover condition and different melting temperatures,the deterioration and failure characteristics and mechanism of the site soil were analyzed;At the same test temperature,the deterioration and failure characteristics and mechanism of the site soil were compared under the conditions of thin,thick snow cover and direct infiltration of unfrozen water(snow water);Three methods were used to reinforce the soil(the material is SH),and the freeze-thaw cycle tests under snow cover were carried out to explore the changes of its physical and mechanical properties.In addition,the disintegrating experiment was carried out on the reinforcement samples to explore their disintegrating resistance in water.(1)The results show that in the freeze-thaw cycles under snow cover,when the snow thickness and freezing temperature are constant,the cracks and efflorescence on the top of soil are more serious when melting temperature is 3℃,followed by 6℃,and the appearance of soil samples are basically unchanged at 9℃.For soils with the same dry density,the physical and mechanical properties of soils after the test are different when melting temperatures are different.After 10 cycles,the frost heave rate of soil is the highest when melting temperature is 6℃,followed by 9℃,while 3℃ was the smallest.After the test,the longitudinal wave velocity and compressive strength of soil at the three melting temperatures have little difference,but the surface hardness increases with the melting temperature rise.(2)Under the same freeze-thaw environment,the influence of snow cover and direct infiltration of unfrozen water(snow water)on earthen ruins are quite different.Under the condition of snow cover,the deterioration of physical and mechanical properties and appearance of the samples during freeze-thaw cycles are obviously different from those of the samples directly infiltrated by the same amount of unfrozen water(snow water).In terms of physical properties,snow cover makes the frost heave rate of soil smaller,but efflorescence,cracks,scaling off are prone to occur on the top.As for mechanical properties,when the snow cover is small,the damage to the soil is less than that of the direct infiltration of unfrozen water(snow water).While if the snow cover gets thicker,the soil deteriorates slowly,this allows people to deal with diseases caused by the snow cover.(3)SH shows good reinforcement effect on soil in freeze-thaw cycles under snow cover.There are no crisp efflorescence and cracks in the soil samples,and the strength has also been improved.After the test,only a small amount of slag dropping appeared on the surface of the soil mixed with SH.The physical and mechanical properties increase with the solid content increasement(0.4%,0.5%,0.6%)of SH.(4)Sprinkling SH on the soil surface has little effect on strength improvement,but it has good locking effect on soil particles,so there is no slag dropping.In concentration selection,1.0% is better.After mixing + sprinkling SH,the extrinsic features of reinforced soil samples hardly change during the tests.Under the same spraying concentration,the higher the solid content,the better the reinforcement effect.The tests show that the three kinds of reinforced soil can maintain good water stability after freeze-thaw cycles under snow cover,and there is no disintegration during the disintegration test.更多还原