Freeze-thaw deterioration of saline earthen sites under snowmelt or rainfall infiltration
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摘要: 采用含水率、电导率、弹性波速及无侧限抗压强度等指标，结合试样表观及微结构变化研究了含盐土遗址在融雪或降雨入渗的初始条件下经历冻融循环的劣化机制。结果表明：在冻融循环过程中，试样含水率因融雪与降雨入渗的水分补给及蒸发散失而先增加后减小并趋于稳定，盐分随水分迁移后分别在试样高度5，3.5 cm处富集；水分入渗增加了土粒间的水膜厚度，试样弹性波速和无侧限抗压强度显著下降；随着冻融循环的进行，水分蒸发散失，试样波速和强度逐渐回升，盐分和降水形式是影响试样强度恢复的关键因素。当Na2SO4含量大于0.4%时，其含量的增加会降低试样强度恢复比，NaCl的加入提高了试样强度恢复比，但降低了强度回升速度。经历12次冻融循环后，融雪入渗使易溶盐充分弥散而有助于土体强度恢复，顶部水盐富集导致试样顶面形成酥碱和翻卷的泥皮；降雨入渗使试样微裂隙发育且大孔隙（> 16 μm）占比增大，湿润锋处水盐富集导致试样侧面出现横向裂缝，试样强度回升速度和幅度均较小。Abstract: The changes of samples after freeze-thaw cycles under the initial conditions of snowmelt or rainfall infiltration are characterized considering the water content, conductivity, elastic wave velocity and unconfined compressive strength. Furthermore, the freeze-thaw deterioration mechanism of the saline earthen sites is studied based on the macroscopic and microstructure changes of the samples. The results show that during the freeze-thaw cycles, the water content of the samples increases first, then decreases and tends to be stable due to the water supply and evaporation loss of snowmelt and rainfall infiltration, and after migration with water, the salt is enriched at the height of 5 and 3.5 cm, respectively. The supplied water increases the thickness of bound water film between soil particles, and the elastic wave velocity and unconfined compressive strength of the samples decrease significantly. With the progress of freeze-thaw cycles, the water evaporates, and the wave velocity and strength of the samples increase gradually. The salt content and precipitation form are the key factors affecting the strength recovery of the samples. When its content is more than 0.4%, the increase of the content of Na2SO4 will reduce the strength recovery ratio of the samples. The addition of NaCl improves the strength recovery ratio of the samples, but slows down the strength recovery rate. After 12 freeze-thaw cycles, the snowmelt infiltration makes the soluble salt fully disperse in the samples, which is conducive to the recovery of soil, the accumulation of water and salt at the top of the samples leads to the formation of salt efflorescence and rolled mud. The rainfall infiltration makes microcracks develop and the proportion of macropores (> 16 μm) increase, the accumulation of water and salt at the wetting front leads to transverse cracks at the side of the samples, and the strength recovery speed and amplitude of the samples are small.
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全球性的气候问题与突发自然灾害使得岩土及地下工程灾变问题不断凸现，给岩土工程安全与运营构成巨大挑战。岩土体作为地球表面最为广泛存在的地质材料具有复杂的物理力学特性与显著的时空变异性。岩土工程物理模拟试验技术通过融合多学科知识模拟和再现岩土体在自然与工程状态下的物理力学行为，为复杂岩土工程问题的解决提供强力支撑。“交通强国”等重大国家战略的实施也给岩土工程带来了巨大的历史机遇。岩土工程防灾减灾问题由于其普遍性、迫切性和前沿性也成为岩土及地下工程领域研究的新热点。随着科技的进步，岩土工程物理模拟试验技术也正从传统的重力场模拟、离心试验，向数字与智能化转变，而世界级超大型试验设备的建设，更将极大驱动我国岩土工程物理模拟试验技术的未来发展。
为促进我国岩土工程物理模拟试验技术学术交流，由中国水利学会岩土力学专业委员会和中国土木工程学会土力学及岩土工程分会共同主办，交通运输部天津水运工程科学研究院、南京水利科学研究院、中交天津港湾工程研究院有限公司以及天津大学承办的第十届岩土工程物理模拟学术研讨会于2024年8月在天津市滨海新区举行。本届会议是继武汉(2011年)、杭州(2013)、北京(2017)、喀什(2023)会议后全国岩土工程物理模拟试验技术领域的又一次学术盛会。会议筹备期间共收到投稿论文113篇，经过审稿委员会的审议向《岩土工程学报》（增刊）推荐稿件51篇，并在学报2024年增刊1专刊出版。同时，本届研讨会举办了砂土场地桩基水平承载力平行试验，并以特邀报告、主题报告、青年学者报告等在内的形式开展广泛深入的交流，展现最新模拟技术和研究成果，探讨岩土工程物理模拟试验技术在交通强国基础设施建设与防灾减灾研究中的应用，以促进岩土工程物理模拟试验技术对我国重大战略和重大工程的技术支撑作用。
感谢对本届会议召开鼎力相助的交通运输部天津水运工程科学研究院及各有关单位，感谢向本届会议投稿的各位专家和同行，感谢审稿专家对本次会议审稿工作的辛勤付出。尤其是《岩土工程学报》编辑部，为使本届会议的论文集面世，做了大量工作，专门编辑出版了本期增刊，特此表示感谢。
第十届全国岩土工程物理模拟学术研讨会组委会 -
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图 2 西北土遗址赋存地区冬季平均气温
Figure 2. Average temperatures in regions of earthen sites in Northwest China in winter
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图 3 不同冻融循环次数后试样含水率
Figure 3. Water contents of samples after different freeze-thaw cycles
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图 5 不同冻融循环周期后试样弹性波速变化
Figure 5. Variation in elastic wave velocity of samples after different freeze-thaw cycles
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图 6 不同冻融循环周期后试样无侧限抗压强度变化
Figure 6. Variation in unconfined compressive strength of samples after different freeze-thaw cycles
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图 7 不同模拟条件下试样抗压强度恢复比
Figure 7. Recovery ratios of unconfined compressive strength of samples under different simulation conditions
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图 8 经历12次冻融循环后试样顶、侧面劣化特征
Figure 8. Deterioration characteristics of top and side of samples after 12 freeze-thaw cycles
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图 9 冻融循环前后试样微观结构
Figure 9. Microstructures of samples before and after freeze-thaw cycles
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图 10 冻融循环前后试样孔径分布曲线
Figure 10. Pore-size distribution curves of samples before and after freeze-thaw cycles
表 1 土体基本物理性质
Table 1 Basic physical properties of soils
试样 相对质量密度 塑性
指数粒径分布/% > 0.075 mm 0.075~0.005 mm < 0.005 mm 遗址土 2.72 11.1 4.98 85.69 9.33 试验土 2.72 10.7 3.62 88.76 7.62 
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表 2 土体易溶盐离子含量
Table 2 Content of soluble salt ions in soils
(mg/L) 试样 Cl− NO− 3 SO2− 4 Na+ K+ Mg2+ Ca2+ 遗址土 324.44 4.37 519.18 301.49 8.03 58.91 98.91 试验土 443.83 9.57 498.91 371.11 10.31 60.02 91.49
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表 3 试验分组设置
Table 3 Setting of test groups
组别 Na2SO4/% NaCl/% 组别 Na2SO4/% NaCl/% S1 0.2 0 SC1 0 1.0 S2 0.4 0 SC2 0.2 0.8 S3 0.6 0 SC3 0.4 0.6 S4 0.8 0 SC4 0.6 0.4 S5 1.0 0 SC5 0.8 0.2
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