The influence of freeze-thaw cycles on the granulometric composition of Moscow morainic clay
Effect of Freeze-Thaw Cycles on Mechanical Behavior of Compacted Fine-Grained Soil
Effect of Freeze-Thaw Cycles on Mechanical Behavior of Compacted Fine-Grained SoilGuoyu Li, Wei Ma, Shuping Zhao, Yuncheng Mao, Yanhu MuState Key Laboratory of Frozen Soils Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, Gansu, ChinaABSTRACT: A large amount of work has been conducted to study the effect of freeze-thaw cycles on the geotechnical properties of various soils. But less laboratory work has been focused on the effect of number of freeze-thaw cycles and on quantitative relationship between mechanical behavior and freeze-thaw cycles. This study undertook a series of tests including freeze-thaw (FT) (after 0, 2, 5, 11, 21, and 31 freeze-thaw cycles respectively), unconfined compression (UC) and unconsolidated-undrained triaxial compression (UUTC) tests. These tests aim to assess the influence of freeze-thaw cycles on the mechanical behavior of compacted fine-grained soil, to establish correlation between the mechanical behavior and freeze-thaw cycles, and to facilitate the prediction of changes in geotechnical properties of soil. Freeze-thaw cycles notably influence the stress-strain curve reducing the UC strength by 11%, elastic modulus by 32%, and cohesion by 84% after 31 freeze-thaw cycles in comparison with those soils unexposed to freeze-thaw. The angle of internal friction is slightly increased by 1 to 2°. The weakening and deteriorating effects of freeze-thaw on the compacted fine-grained soil are confirmed. They can provide a scientific basis for design consideration of cold-region infrastructures, and for countermeasures against frost heave and thaw settlement.KEY WORDS: Mechanical behavior, freeze-thaw, geotechnical properties, fine-grained soil, frost heave and thaw settlement.1INTRUDUCTIONRepeated freezing and thawing in cold regions strongly weathers and deteriorates the geotechnical properties of densely compacted foundation soil, e.g., change in micro-fabric and loss in strength. It thus might cause damage, and even failure of the foundation of the various man-made infrastructures such as residential buildings, roads, airstrips, pipeline and pile (Alkire and Morrison 1982).According to several laboratory tests (Kim and Daniel 1992, Othman and Benson 1993), the hydraulic permeability of compacted fine-grained soil increases following freeze-thaw cycles. The mechanism of this increase is because micro-fissuring are enlarged during freezing and thawing and because ice melting in soil matrix leaves internal large pore spaces (Chamberlain et al., 1990). Chamberlain and Gow (1979) also mentioned that fine particles might move out of large pore spaces during freezing and thawing. Eigenbrod (1996) also found that freezing and thawing leaded to densification of soft and normally-consolidated clay samples, but other studies showed the opposite to occur for dense samples. Studies showed that freeze-thaw increased density of loose soil but decreased the density of dense soils (Viklander 1998, Yao et al.2008, Li et al. 2011). This so-called dual effect of freeze-thaw process on the density has been verified by the several studies (Su et al. 2008, Wang et al. 2009, Yang et al. 2003). Considerable laboratory work has been performed to study effects of freeze-thaw cycles on geotechnical properties inducing changes in soil strength such as shear strength, elastic modulus, cohesion and internal friction angle for varying densities. Some works showed that freeze-thaw caused a decrease in strength of soils (Culley 1971, Graham and Au 1985, Yong et al. 1985, Aoyama et al. 1985, Lee et al. 1995, Simonsen et al. 2002, Qi and Ma 2006, Wang et al. 2007). However, some researchers found that the strength increased for loosely compacted soils (Ono and Mitachi 1997, Alkire and Morrison 1982). It is therefore known that dense soils tend to swell under freeze-thaw but loose soils are densified.Although a considerable amount of studies have been conducted, they have some disadvantages such as less number of freeze-thaw cycles, lack of quantitative relationship between mechanical behavior and number of freeze-thaw cycles. These limitations make it difficult to predict the developing trend of soil undergoing freezing and thawing. The effect of freeze-thaw cycles on the mechanical behavior has been tested using closed-system freeze-thaw (FT) tests, unconfined compression (UC) tests, and unconsolidated-undrained triaxial compression (UUTC) tests. These tests aim to (1) confirm the weakening effect of freeze-thaw cycles; (2) assess the changing process of the mechanical behavior under the freeze-thaw cycles; and (3) establish the quantitative relationships between them.2TESTING PROCEDUREA fine-grained soil, i.e. silty clay, was collected close to Yonydeng county, Gansu province in Northwestern China. Grain size distribution (Figure 1), liquid and plastic limits, and specific gravity were measured in the laboratory prior to the FT, UC and UUTC tests according to the Chinese standard JTG E40-2007 which resembles the ASTM Standards such as D4318–10, D2166–06, D2850–03a (MC-PRC 2007, Li et al. 2011). The liquid and plastic limits are 26.9 % and 18.7%, respectively. The specific gravity is 2.704. The Proctor compaction test following the standard D698–07 was carried out to determine the maximum dry density and the optimum water content, which are 1.91 g/cm3 and 16.1 %, respectively. The remolded cylindrical samples (125 mm in height and 61.8 mm in diameter) were densely compacted and formed by a layer-by-layer compressing devices (a steel mold). Water content and dry density of soil samples were close to the maximum and the optimum.The samples were then sealed with rubber membranes and consolidated for 24 hours for homogeneous water content. After this consolidating period, they were placed into a modelingbox and exposed to cyclic freezing and thawing in a closed system without in- or out-flow of moisture. The air temperature in the modeling box was automatically controlled and adjusted by circulating coolants (Freon or Ethylene Glycol) driven by a compressor, which varied in the range of -30 to 30 °C as shown in Figure 2. One freeze-thaw cycle lasted 24 hours, 16 hours for freezing and 8 hours for thawing. After different freeze-thaw cycles, soil samples were taken out of the box; and the UC and UUTC tests were performed to investigate the effect of freeze-thaw cycles on the changes in mechanical behavior.Figure 1: Grain-size distribution of the soil sampleFigure 2: Temperature change of air in modeling box under freeze-thaw.Soil samples preparation and testing operations were carried out conforming to the related standard JTG E40-2007 (MC-PRC 2007). Dry density of 1.81 g/cm3 and water content of 16.1% of samples were selected for various tests; their resolutions are controlled within ±1%. Three soil samples were used to perform the strain-controlled UC tests at a constant axial strain rate of 2.4% per minute while four soil samples were used to perform the UUTC tests at a constant strain rate of 1% per minute. The applied confining stress in UUTC tests is 50, 100, 200 and 300 kPa respectively. The compression tests terminate until load values decrease with increasing strain. Six groups of soil samples, being used for 0 (i.e. unexposed to freeze-thaw), 2, 5, 11, 21 and 31 freeze-thaw cycles, were used to carry out the related tests. The deformation and load were measured with MTS stress and strain sensors, respectively, with an accuracy of 0.5 % of the full scale. They were automatically recorded by data logger at a certain time interval needed to provide a complete stress-strain curve.3RESULTS FROM UC TESTS3.1Effect of freeze-thaw on unconfined compressive (UC) strengthThe results of the UC tests are given in Figures 3 to 6. Soil samples unexposed were also tested for comparison. Figure 3 shows the stress-strain curves of typical soil samples after different number of freeze-thaw cycles. The stress-strain curves consist of three stages during the strain increase: elastic, plastic, and failure stages respectively (Yang et al, 2010). Failure is taken to correspond to the maximum unconfined compressive stress attained or the stress at 15 % axial strain, whichever occur first during the performance of a test (ASTM, 2006). The soil exhibits the elastic property while the strain is relatively low below about 2% representing the straight portion of the curves. In the plastic stages, the stress-strain curve begins to bend downward with the increasing strain. This bend indicates that the weaker part in soil sample begin to yield, and even to damage. In the failure stage, the stress falls abruptly after the peak point of the curve because the soil sample begins to fail. The failure pattern is typical of brittle one.Figure 3: Stress-strain curve for soil samples after different freeze-thaw cycles.Figure 4: Change in UC strength with increasing freeze-thaw cycles.The UC strength is defined as the maximum axial compressive stress at failure or the corresponding stress at 15% strain if no maximum axial compressive stress is reached, whichever occurs first. The UC strength as a function of the freeze-thaw cycles is shown in Figure 4. The straight line shows the decreasing trend of the UC strength with the increasing freeze-thaw cycles.After 31 freeze-thaw cycles, UC strength has decreased by 11% on average. The soil sample isweakening after repeated freezing and thawing. The linear regression equation is given as follows.σf = -0.589 n+176.4 (r20.33) [1] where σf (in kPa) is the UC strength and n is the number of freeze-thaw cycles, and r2 is thecoefficient of determination. This equation can be used to predict the change in strength of thesimilar soil due to freeze-thaw cycles. This empirical relationship depends on the soil type, watercontent and dry density.3.2Effect of freeze-thaw on failure strain and elastic modulusThe strain at failure and the elastic modulus are defined as failure strain and the slope of thestraight line of the stress-strain curve respectively. They are important parameters characterizingthe mechanical behavior of soil. Figure 5 shows the response of failure strain to freeze-thawcycles. The failure strain decreases with increasing freeze-thaw cycles. It decreases by 11.2% onaverage after 31 freeze-thaw cycles. The freeze-thaw cycles progressively cause the local damagein soil samples.Figure 5: Change in failure strain with increasing freeze-thaw cycles.Figure 6: Change in elastic modulus with increasing freeze-thaw numbers.The elastic modulus progressively decreases with increasing freeze-thaw cycles (Figure 6). Itdecreases by 32% on average after 31 freeze-thaw cycles. The following linear regressionequation is found from the results:E = -0.046 n+6.07 (r20.19) [2] where E (in MPa) is the elastic modulus.According to results of the UC tests, decrease in the UC strength, elastic modulus, and failurestrain confirms the weakening effect of freeze-thaw cycles on soil.4RESULTS FROM UUTC TESTSResults of UUTC tests on samples unexposed to freeze-thaw and after 11 freeze-thaw cycles aregiven in Figures 7 to 10. The other results for different freeze-thaw cycles are summarized inTable 1 and Figure 11. Figures 7 and 8 show the stress-strain curves of the compacted fine-grained soil under varying confining stresses unexposed and exposed to freeze-thaw cycles.Figure 7: Stress-strain curve at various confining stress for samples unexposed to freeze-thaw.Figure 8: Stress-strain curve at various confining stress for samples after 11 freeze-thaw cycles.The stress-strain curve and failure pattern of the soil samples are similar to those in the UC tests.The mechanical behavior of soil samples also exhibit obvious three stages during loading. Thefailure pattern is typical of brittle failure. Moreover, the deviator stress strength, defined as themaximum deviator stress at failure at a given confining stress, for the soil samples after 11 freeze-thaw cycles is much smaller than the one for samples unexposed to freeze-thaw. In addition, soils exhibit a transition from strain-softening to strain-hardening behavior with the increasing confining stress. The freeze-thaw cycles reduce the confining stress at which the stress-strain curve transits from strain-softening to strain-hardening.Figures 9 and 10 show the Mohr strength lines for soil samples unexposed and after 11 freeze-thaw cycles, respectively. The shear stress and normal stress are denoted as τ and σ respectively. The real Mohr failure envelops are not straight lines. But they can be simplified as straight lines for convenience of analysis as following equations 3 and 4.τ = σ tan (350) + 60[3]τ = σ tan (360) + 28.8 [4]S h e a r s t r e s s (k P a )Normal stress (kPa)07006005004003002001001600120010008006004002000 Figure 9: Mohr strength line for soil samples unexposed to freeze thaw.0200400600800100012001600100200300400500600700Normal stress (kPa)S h e a r s t r e s s (k P a )Figure 10: Mohr strength line for soil samples after 11 freeze-thaw cycles.The cohesion and internal friction angle of soil samples depend on the number of freeze-thaw cycles (Table 1 and Figure 11). The cohesion, the intercept of the Mohr strength line, is considerably reduced due to freeze-thaw (Figures 9 to 11); and the internal friction angle that the strength line makes with the normal stress axial, slightly increases by 1 to 2° (Table 1). The cohesion decreases by 84% on average after 31 freeze-thaw cycles.The results from the UUTC tests show that freeze-thaw reduces the deviator stress strength, cohesion and the confining stress at which strain-softening/hardening transition occurs. Freeze-thaw cycles weaken the structure and reduce the strength of compacted fine-grained soil.Table 1: Changes in cohesion and angle of internal friction after different freeze-thaw cycles Number of freeze-thaw cycles 0 21131Cohesion (kPa)60 42.528.89.8Internal friction angle (°) 35 373636Figure 11: Cohesion as a function of the number of freeze-thaw cycles.Change in mechanical behavior is attributed to the increase in volume of the pore of soil because water volume increases by 9% when it freezes. The volume increase from water to ice makes stress on the surrounding soil particles and pushes them moving out of pore space, even separated each other. In addition, freezing always leads to some joints and fissures due to shrinkage (Othman and Benson 1993, Proskin et al. 2010, Mu et al. 2011). Following the thawing, the removed finer particles and fissures tend to re-position to their original locations. But it is very hard to fully recover for densely compacted soil. This process occurs at each freeze-thaw cycle. As a consequence, a net increase in volume and a weakening of soil sample occurs at each new freeze-thaw cycle. These microstructure variations lead to changes in mechanical properties in macroscopic scale. Concerns should be made on the weathering and weakening process of freeze-thaw to geotechnical properties of compacted fine-grained soils.5CONCLUSIONSFreeze-thaw reduces the UC strength, elastic modulus and failure strain of compacted fine-grained soil, indicating that freeze-thaw has a significantly weakening effect on the compacted soils. The degraded mechanical behavior has a close correlation with the number of freeze-thaw cycles. A correlation has been established to predict and assess the developing trend of the degradation.The results from UUTC tests confirm that repeated freeze-thaw leads to obvious decrease in deviator stress strength, cohesion, and the confining stress at which the stress-strain curve shows a transition from the strain-softening to strain-hardening.ACKNOWLEDGEMENTSThis work was supported by the Program for Innovative Research Group of Natural Science Foundation of China (Nos. No.41121061), National Key Basic Research Program of China (973 Program) (No. 2012CB026106), the Chinese Academy of Sciences (CAS) Western Project (No. KZCX2-XB2-10), Western Communications Construction Scientific and Technological Project (No. 200831800025), National Natural Science Foundation of China (Nos. 41171055, 40971046 and 41023003) and Project of the State Key Laboratory of Frozen Soils Engineering, CAS, (No. SKLFSE-ZY-03).REFERENCESAlkire, B. and Morrison, J., 1982. 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冻融循环对土壤团聚体与微生物特性影响研究进展
江苏农业学报(ＪｉａｎｇｓｕＪ.ｏｆＡｇｒ.Ｓｃｉ.)ꎬ２０２３ꎬ３９(４):１０８０￣１０８８ｈｔｔｐ://ｊｓｎｙｘｂ.ｊａａｓ.ａｃ.ｃｎ郑昕雨ꎬ陈㊀鹏ꎬ韩金吉ꎬ等.冻融循环对土壤团聚体与微生物特性影响研究进展[Ｊ].江苏农业学报ꎬ２０２３ꎬ３９(４):１０８０￣１０８８.ｄｏｉ:１０.３９６９/ｊ.ｉｓｓｎ.１０００￣４４４０.２０２３.０４.０１８冻融循环对土壤团聚体与微生物特性影响研究进展郑昕雨ꎬ㊀陈㊀鹏ꎬ㊀韩金吉ꎬ㊀孟子轩ꎬ㊀王英男ꎬ㊀蔺吉祥ꎬ㊀王竞红(东北林业大学ꎬ黑龙江哈尔滨１５００４０)收稿日期:２０２２￣０９￣０９基金项目:国家自然科学基金项目(３２０７２６６６)ꎻ科技基础资源调查项目(２０１９ＦＹ１００５０６￣０５)ꎻ黑龙江省自然科学基金项目(ＬＨ２０２０Ｃ０４６)ꎻ中央高校基本科研业务费(２５７２０１９ＣＰ０６)作者简介:郑昕雨(１９９９－)ꎬ女ꎬ山东莱芜人ꎬ硕士研究生ꎬ主要从事土壤结构与土壤生态研究ꎮ(Ｅ￣ｍａｉｌ)ｚｈｅｎｇｘｉｎｙｕ＠ｎｅｆｕ.ｅｄｕ.ｃｎ通讯作者:王竞红ꎬ(Ｅ￣ｍａｉｌ)ｙｕａｎｌｉｎ＠ｎｅｆｕ.ｅｄｕ.ｃｎ㊀㊀摘要:㊀冻融循环是高纬度㊁高海拔等气候寒冷地区特有的自然现象ꎬ通过改变土壤水热平衡对土壤理化性质㊁土壤微生物造成影响ꎮ研究土壤冻融循环可以预测土壤结构与生态的发展趋势ꎬ并为研究全球变暖背景下冻融循环与土壤团聚体㊁微生物的相互作用机制提供一定理论依据ꎮ本文通过查阅文献ꎬ综合分析了近年来国内外学者对冻融循环及其对土壤团聚体㊁微生物特性的影响等研究成果ꎬ探讨了土壤团聚体与微生物的相互作用关系ꎬ总结了冻融作用下土壤团聚体粒径分布㊁稳定性和孔隙结构的变化ꎬ阐述了冻融循环对土壤微生物及其群落结构的影响ꎬ并对本领域的研究方向进行了展望ꎬ旨在为研究冻融循环背景下土壤团聚体与微生物的响应提供新的思路ꎮ关键词:㊀冻融循环ꎻ土壤团聚体ꎻ土壤孔隙结构ꎻ微生物群落ꎻ微生物生物量中图分类号:㊀Ｓ１５１.９＋４㊀㊀㊀文献标识码:㊀Ａ㊀㊀㊀文章编号:㊀１０００￣４４４０(２０２３)０４￣１０８０￣０９Ｅｆｆｅｃｔｓｏｆｆｒｅｅｚｅ￣ｔｈａｗｃｙｃｌｅｓｏｎｓｏｉｌａｇｇｒｅｇａｔｅｓａｎｄｍｉｃｒｏｂｉａｌｐｒｏｐｅｒｔｉｅｓ:ａｒｅｖｉｅｗＺＨＥＮＧＸｉｎ￣ｙｕꎬ㊀ＣＨＥＮＰｅｎｇꎬ㊀ＨＡＮＪｉｎ￣ｊｉꎬ㊀ＭＥＮＧＺｉ￣ｘｕａｎꎬ㊀ＷＡＮＧＹｉｎｇ￣ｎａｎꎬ㊀ＬＩＮＪｉ￣ｘｉａｎｇꎬ㊀ＷＡＮＧＪｉｎｇ￣ｈｏｎｇ(ＮｏｒｔｈｅａｓｔＦｏｒｅｓｔｒｙＵｎｉｖｅｒｓｉｔｙꎬＨａｒｂｉｎ１５００４０ꎬＣｈｉｎａ)㊀㊀Ａｂｓｔｒａｃｔ:㊀Ｆｒｅｅｚｅ￣ｔｈａｗｃｙｃｌｅ(ＦＴＣ)ｉｓａｎａｔｕｒａｌｐｈｅｎｏｍｅｎｏｎｉｎｃｏｌｄｒｅｇｉｏｎｓｓｕｃｈａｓｈｉｇｈｌａｔｉｔｕｄｅａｎｄａｌｔｉｔｕｄｅꎬｗｈｉｃｈａｆｆｅｃｔｓｓｏｉｌｐｈｙｓｉｃｏｃｈｅｍｉｃａｌｐｒｏｐｅｒｔｙａｎｄｓｏｉｌｍｉｃｒｏｏｒｇａｎｉｓｍｓｂｙｃｈａｎｇｉｎｇｓｏｉｌｗａｔｅｒ￣ｈｅａｔｂａｌａｎｃｅ.Ｒｅｓｅａｒｃｈｏｎｓｏｉｌｆｒｅｅｚｉｎｇ￣ｔｈａｗｉｎｇｃａｎｐｒｅｄｉｃｔｔｈｅｄｅｖｅｌｏｐｍｅｎｔｔｒｅｎｄｏｆｓｏｉｌｓｔｒｕｃｔｕｒｅａｎｄｅｃｏｌｏｇｙꎬａｎｄｐｒｏｖｉｄｅａｔｈｅｏｒｅｔｉｃａｌｂａｓｉｓｆｏｒｔｈｅｉｎ￣ｔｅｒａｃｔｉｏｎｍｅｃｈａｎｉｓｍｏｆｆｒｅｅｚｉｎｇ￣ｔｈａｗｉｎｇｃｙｃｌｅｗｉｔｈａｇｇｒｅｇａｔｅｓａｎｄｍｉｃｒｏｏｒｇａｎｉｓｍｓｕｎｄｅｒｇｌｏｂａｌｗａｒｍｉｎｇ.Ｂａｓｅｄｏｎｔｈｅｌｉｔｅｒ￣ａｔｕｒｅｒｅｖｉｅｗꎬｔｈｉｓｐａｐｅｒｃｏｍｐｒｅｈｅｎｓｉｖｅｌｙａｎａｌｙｚｅｄｔｈｅｒｅｓｅａｒｃｈｒｅｓｕｌｔｓｏｆｄｏｍｅｓｔｉｃａｎｄｆｏｒｅｉｇｎｓｃｈｏｌａｒｓｏｎｆｒｅｅｚｅ￣ｔｈａｗｃｙｃｌｅａｎｄｉｔｓｅｆｆｅｃｔｓｏｎｓｏｉｌａｇｇｒｅｇａｔｅｓａｎｄｍｉｃｒｏｂｉａｌｃｈａｒａｃｔｅｒｉｓｔｉｃｓｉｎｒｅｃｅｎｔｙｅａｒｓ.Ｔｈｅｉｎｔｅｒａｃｔｉｏｎｓｂｅｔｗｅｅｎｓｏｉｌａｇｇｒｅｇａｔｅｓａｎｄｍｉｃｒｏｏｒｇａｎｉｓｍｓｗｅｒｅｄｉｓｃｕｓｓｅｄꎬｔｈｅｒｅｓｐｏｎｓｅｓｏｆｐａｒｔｉｃｌｅｓｉｚｅｄｉｓｔｒｉｂｕｔｉｏｎꎬｓｔａｂｉｌｉｔｙａｎｄｐｏｒｅｓｔｒｕｃｔｕｒｅｏｆａｇｇｒｅｇａｔｅｓｕｎｄｅｒｆｒｅｅｚｅ￣ｔｈａｗｗｅｒｅｓｕｍｍａｒｉｚｅｄꎬａｎｄｔｈｅｅｆｆｅｃｔｓｏｆｆｒｅｅｚｅ￣ｔｈａｗｃｙｃｌｅｓｏｎｓｏｉｌｍｉｃｒｏｏｒｇａｎｉｓｍｓａｎｄｔｈｅｉｒｃｏｍｍｕｎｉｔｙｓｔｒｕｃｔｕｒｅｗｅｒｅａｌｓｏｄｉｓｃｕｓｓｅｄ.Ｉｎｔｈｅｅｎｄꎬｔｈｅｒｅｓｅａｒｃｈｄｉｒｅｃｔｉｏｎｏｆｔｈｉｓｆｉｅｌｄｗａｓｐｒｏｓｐｅｃｔｅｄꎬａｉｍｉｎｇｔｏｐｒｏｖｉｄｅｎｅｗｒｅｓｅａｒｃｈｉｄｅａｓｆｏｒｔｈｅｒｅｓｐｏｎｓｅｏｆｓｏｉｌａｇｇｒｅｇａｔｅｓａｎｄｍｉｃｒｏｏｒｇａｎｉｓｍｓｕｎｄｅｒｆｒｅｅｚｅ￣ｔｈａｗｃｙｃｌｅｓ.Ｋｅｙｗｏｒｄｓ:㊀ｆｒｅｅｚｅ￣ｔｈａｗｃｙｃｌｅｓꎻｓｏｉｌａｇｇｒｅｇａｔｅꎻｓｏｉｌｐｏｒｅｓｔｒｕｃｔｕｒｅꎻｍｉｃｒｏｂｉａｌｃｏｍｍｕｎｉｔｙꎻｍｉｃｒｏｂｉａｌｂｉｏｍａｓｓ㊀㊀冻融循环(Ｆｒｅｅｚｅ￣ｔｈａｗｃｉｒｃｌｅｓ)指在高纬度㊁高海拔等气候寒冷地区ꎬ由于昼夜及季节温差变化导致土壤反复冻结与解冻的过程ꎮ冻融作用在世界范围内普遍存在ꎬ几乎所有位于４５ʎＮ以上的陆地土壤每年都会经历季节性冻融循环ꎬ甚至个别地区的土壤会经历短期的日冻融[１]ꎮ中国冻土面积约占国土面积的７５％ꎬ其中季节性冻土面积约为５.１４ˑ０８０１１０６ｋｍ２ꎬ占陆地总面积的５３％ꎬ土壤的冻融现象极为普遍[２]ꎮ自２０世纪开始ꎬ由于人类活动的增强ꎬ大气中的主要温室气体浓度增加ꎬ全球变暖趋势已不可逆转[３]ꎬ陆地生态系统冬季变暖㊁积雪变薄和不稳定性增加等现象频发ꎬ随之引发了冻融循环温度与频次的改变[４]ꎮ在冬季积雪较厚的地区ꎬ由于雪是土壤的重要绝缘体ꎬ土壤冻融循环的强度㊁频率主要取决于区域气候条件和绝缘积雪的厚度ꎮ而全球气候变暖会造成积雪厚度和覆盖面积减少ꎬ进而可能造成土壤冻融现象越发频繁[５]ꎮＨｅｎｒｙ[６]已经预测ꎬ在冬季积雪覆盖的地区ꎬ未来３０年的年土壤冻融循环次数会随平均气温的升高而明显增加ꎮ土壤结构是维持全球陆地生态系统的重要因素ꎬ对于保持水分㊁稳定生物多样性㊁维持农业以及抵抗洪水㊁侵蚀和滑坡的能力具有重要作用ꎮ土壤通常可以被看作是由堆积的团聚体和孔隙空间组成的复杂三维结构ꎬ这些团聚体由土壤矿物质㊁有机质和微生物组成ꎬ在土壤形成过程中通过各种物理㊁化学和生物过程结合在一起ꎬ其稳定性是土壤结构的一个重要特征[７￣８]ꎮ土壤团聚体一般可以根据粒径大小分为大团聚体(>２５０μｍ)和微团聚体(ɤ２５０μｍ)ꎬ其中大团聚体由微团聚体组成[９￣１０]ꎬ而微团聚体由更小的结构单元组成ꎬ其结构相较于大团聚体更加稳定[７￣８]ꎮ团聚体的形成可以用Ｔｉｓｄａｌｌ等[１１]提出的团聚体层次模型来解释ꎮ根据这一理论ꎬ不同粒径的团聚体有不同的结合方式ꎮ大团聚体ꎬ特别是粒径大于２ｍｍ的大团聚体ꎬ主要由根和真菌菌丝结合在一起ꎬ其稳定性较低ꎬ受到扰动时会分解为更小的团聚体[１１]ꎻ微团聚体则由各种胶结物和胶黏剂与较小的土壤颗粒(如粉粒和黏粒)结合形成ꎬ这部分团聚体的水稳定性很强ꎬ可以承受强大的机械压力和物理化学压力ꎬ不会被农业生产活动破坏ꎬ能在土壤中存在几十年[８ꎬ１１]ꎮ土壤微生物活性对土壤团聚体的形成和稳定起着至关重要的作用ꎬ大多数土壤微生物的生活环境与团聚体密切相关ꎬ它们既生活在团聚体颗粒内部ꎬ也生活在团聚体颗粒之间ꎬ与土壤一起构成了支持地球上陆地生物食物网的营养基础[１２]ꎮ在过去的几十年里ꎬ冻融循环一直是土壤生态学研究的热点ꎮ土壤的各项物理特性与微生物特性共同影响着土壤生产力ꎬ而冻融循环作为影响土壤生态的重要因素之一ꎬ既会在土壤频繁冻结与解冻的过程中对土壤团聚体粒径分布㊁稳定性和孔隙结构等物理特性造成较强影响[１３￣１６]ꎬ也会改变土壤的生物过程与微生物群落组成[１７]ꎮ目前有研究者认为ꎬ冻融循环促进了土壤团聚体的碎裂和分解ꎬ降低了大团聚体的比例ꎬ提高了微团聚体含量[１８]ꎬ并且随着冻融循环次数的增加ꎬ团聚体的稳定性先升高后降低[１９]ꎮ另有研究发现ꎬ在冻融初期ꎬ微生物受到破坏ꎬ养分流失进入土壤ꎬ土壤养分的有效性显著提高ꎬ但是由于微生物大量死亡ꎬ反复冻融后土壤养分的有效性显著降低[２０]ꎮ在全球变暖背景下ꎬ冻融循环频次与温度发生改变ꎬ对土壤团聚体与微生物也产生了未知影响ꎬ因此研究冻融循环对土壤团聚体及微生物的影响至关重要ꎮ因此ꎬ本文从冻融循环对土壤团聚体与微生物特性的影响㊁团聚体与微生物的相互作用关系等方面对国内外现有研究结果进行了归纳与总结ꎬ并提出了研究展望ꎬ旨在为探讨土壤团聚体与微生物的相互作用以及深入挖掘冻融循环对土壤的影响提供一定的科学依据ꎮ１㊀土壤团聚体与微生物的关系土壤团聚体是土壤的基本结构单位和功能单位ꎬ是由土壤有机质㊁无机结合剂和生物材料通过一系列物理㊁化学及生物过程结合而成的[２１￣２２]ꎮ土壤团聚体与微生物密切相关ꎬ团聚体间和团聚体内部的孔隙为微生物群落提供了适宜其生长的微环境ꎬ而微生物会影响团聚体的形成与稳定性ꎬ二者共同影响了土壤结构与生态ꎮ土壤团聚体和微生物都易受外界环境影响ꎬ自然和人为的扰动均会改变团聚体的粒径组成与稳定性ꎬ此外部分微生物对环境条件的改变也十分敏感ꎮ冻融循环作为一种常见的气候现象ꎬ对土壤团聚体与微生物的影响可以分为２种途径:一是冻融循环改变了团聚体的粒径分布与稳定性ꎬ从而影响微生物的活性与分布ꎻ二是冻融循环影响了土壤微生物活性ꎬ进而对团聚体的形成与稳定性产生影响ꎮ１.１ 不同粒径团聚体对微生物的影响土壤团聚体对于土壤微生物群落生态学和微生物驱动的生物地球化学循环都起到重要作用ꎮ团聚体内部的物理化学条件通常不同于土壤整体的均质化条件ꎬ它为微生物的生存增加了土壤的空间异质性ꎬ每个单独的土壤团聚体都可为土壤微生物群落提供一个独特的环境分区[１２]ꎮ由于团聚体内部空间狭小ꎬ许多微生物捕食者无法进入ꎬ从而为微生物１８０１郑昕雨等:冻融循环对土壤团聚体与微生物特性影响研究进展提供了一个避难所ꎬ防止它们被捕食ꎮ团聚体粒径会影响微生物的分布ꎬ一般认为ꎬ微团聚体中的微生物丰度与微生物多样性均高于大团聚体[２３￣２４]ꎮ不同粒径级的团聚体有不同的优势微生物类群ꎬ细菌㊁放线菌都主要分布于小粒径级的土壤团聚体中ꎬ而真菌在较大粒径级的土壤团聚体中占优势[１２]ꎮ土壤微生物生物量作为衡量土壤肥力的重要指标ꎬ也受到团聚体粒径的显著影响ꎬ微团聚体的微生物生物量显著高于大团聚体[２５]ꎮ此外ꎬ团聚体粒径在影响微生物生理代谢活动方面也有重要意义ꎮ微生物在团聚体结构中占据特定的生态位ꎬ微生物既生活在团聚体颗粒内部ꎬ也生活在团聚体颗粒之间ꎮ与团聚体外部环境相比ꎬ团聚体内部环境水分含量较高ꎬ通气性较差ꎬ因此栖息在其中的微生物以好氧兼厌氧的细菌为主ꎬ而真菌主要以菌丝形态存在其中[２６]ꎮ上述小型生态环境在孔隙结构㊁连通性㊁化学性质和水分含量等方面存在差异ꎬ为微生物提供了空间上异质性的生态位ꎬ可能会产生不同的微生物群落ꎬ而微生物群落直接受到非生物因素的影响和塑造ꎬ也可能产生不同的代谢活动[１２]ꎮ１.２㊀微生物对团聚体结构的影响良好和正常的土壤结构通常伴随着较高的微生物生物量和活性ꎬ疏松多孔的土壤结构可以显著改善土壤中细菌㊁真菌群落的结构和生物多样性ꎮ此外ꎬ提高土壤微生物的多样性和数量对于改善土壤结构具有重要意义[２７￣２９]ꎮ团聚体的形成及其稳定性与微生物群落组成的关系十分密切[１２]ꎮ微生物一般通过２种方式影响土壤团聚体的形成ꎬ一是真菌㊁放线菌通过菌丝的物理结合作用将土壤颗粒机械地缠绕在一起ꎬ形成临时的大团聚体ꎻ二是通过微生物胞外聚合物(包括多糖㊁蛋白质和ＤＮＡ等)的胶结作用将土壤颗粒黏结在一起ꎬ形成持久性微团聚体[２９]ꎮ根据团聚体形成的层次理论ꎬ由根和菌丝组成的精细网络可以束缚土壤颗粒ꎬ是大团聚体形成的主要方式[１１]ꎮ由于菌丝会被细菌分解ꎬ因此菌丝结合的团聚体不能维持很长时间ꎮ由于大团聚体容易受到外界作用力而碎裂ꎬ因此微团聚体更容易形成ꎮ微团聚体之所以能在土壤中存在较长时间ꎬ是因为大多数(７０％)土壤细菌生活在微团聚体中ꎬ一些细菌细胞在团聚体形成过程中被困在矿物基质中ꎬ而另一些细菌细胞在润湿过程中附着在团聚体外部ꎬ通过有机物和微生物胞外聚合物的胶结作用增强微团聚体的稳定性[２３ꎬ３０]ꎮ２㊀冻融循环对土壤团聚体的影响土壤团聚体是土壤的基本结构单位ꎬ团聚体的粒径分布和稳定性等特征对土壤的生产力具有重要意义[３１]ꎮ冻融循环对土壤的孔隙特性㊁团聚体稳定性㊁保水特性等有较强影响[１６]ꎮ由于土壤类型㊁质地㊁初始结构与含水率等自身因素不同ꎬ其对不同冻融温度㊁冻融时间及冻融循环次数也有不同的响应ꎮ２.１㊀冻融循环对土壤团聚体粒径分布的影响冻融循环能够改变土壤团聚体的粒径组成ꎮ目前较为普遍的认知是:在土壤冻结过程中ꎬ土壤颗粒孔隙中的冰晶会发生膨胀ꎬ从而打破团聚体之间的联结ꎬ将大团聚体崩解破碎成微团聚体ꎬ同时ꎬ由于冻结水膨胀产生压力ꎬ使得土壤颗粒重新聚集成新的团聚体ꎬ导致团聚体粒径组成发生变化(图１)ꎮ多数研究发现ꎬ冻融循环促进了土壤团聚体的碎裂和分解ꎬ显著降低了较大粒径级团聚体的比例ꎬ提高了中小粒径级团聚体的比例[１８ꎬ３１￣３４]ꎮ例如ꎬ姚珂涵等[３５]发现ꎬ随着土壤冻融循环次数的增加ꎬ粒径>２ｍｍ团聚体占比显著降低ꎬ而微团聚体占比显著提高ꎮＸｉａｏ等[１４]的研究也发现ꎬ冻融循环降低了粒径>５ｍｍ的团聚体占比ꎬ提高了微团聚体占比ꎮ由此可见ꎬ冻融循环普遍提高了土壤中微团聚体的占比ꎬ对于较大团聚体的结构有破坏效应ꎮ另外有研究发现ꎬ冻融循环会促进大团聚体形成ꎬ降低微团聚体含量[１５ꎬ３６]ꎮＨａｎ等[１７]研究发现ꎬ冻融后土壤中的黏粒含量降低ꎬ砂粒含量增加ꎬ说明冻融循环在破坏原有的土壤团聚体后ꎬ细颗粒重新聚集ꎬ甚至可能形成砂粒ꎮＷａｎｇ等[１５]也发现ꎬ冬季土壤冻融后ꎬ土壤中粒径>１ｍｍ的团聚体的占比升高ꎬ而粒径<１ｍｍ的团聚体的占比降低ꎮ关于冻融对团聚体粒径分布产生的不同结果ꎬ可能有以下几种原因:(１)冻融循环对土壤团聚体粒径分布的影响与冻融循环次数有关ꎬ在最初几次冻融循环中ꎬ微团聚体占比上升ꎬ但是随着冻融循环次数的增加ꎬ微团聚体占比又会下降ꎻ(２)冻融循环对土壤团聚体粒径分布的影响与土壤初始含水率密切相关ꎬ在适宜的土壤含水率条件下ꎬ水分的团聚效应大于冻融的破碎效应ꎬ使得大团聚体占比升高ꎬ而微团聚体占比降低[３５]ꎻ(３)由于冻融循环实质上是土体内水分体积与形态变化引起的土壤特性的改变ꎬ其对大团聚体㊁微团２８０１江苏农业学报㊀２０２３年第３９卷第４期聚体结构都有影响ꎬ且对大团聚体的影响更大ꎮ由此可见ꎬ冻融对土壤中团聚体粒径分布的影响受到土壤质地㊁初始含水率和初始粒径组成的影响ꎮ图１㊀冻融对土壤团聚体粒径分布的影响Ｆｉｇ.１㊀Ｅｆｆｅｃｔｓｏｆｆｒｅｅｚｅ￣ｔｈａｗｏｎｐａｒｔｉｃｌｅｓｉｚｅｄｉｓｔｒｉｂｕｔｉｏｎｏｆｓｏｉｌａｇｇｒｅｇａｔｅｓ２.２㊀冻融循环对土壤团聚体稳定性的影响团聚体的稳定性是衡量土壤团聚体抗破坏能力的指标ꎬ是评价土壤质量的关键参数ꎬ也是影响土壤可持续性和作物生产的重要土壤性质[３７￣３９]ꎮ良好的团聚体稳定性对于提高土壤肥力㊁提高土壤农艺生产力㊁提高土壤孔隙度和降低土壤可蚀性具有重要意义[４０￣４１]ꎮ不同土壤团聚体的大小与比例可能有很大不同ꎬ团聚体粒径越大ꎬ团聚体稳定性㊁土壤孔隙特性越好ꎬ土壤的水分输送和空气交换特性也越好[３１ꎬ３９]ꎮ研究发现ꎬ在肥力较好的土壤中ꎬ大团聚体的占比也较高ꎬ提高大团聚体含量对土壤肥力有改善作用[４２￣４４]ꎮ当大团聚体与微团聚体比例适中时ꎬ土壤大㊁小孔隙相互协调ꎬ能够有效调节土壤的透气性与保肥性ꎬ从而影响土壤肥力的释放ꎮ目前ꎬ许多关于冻融循环对土壤团聚体稳定性影响的观点是相互矛盾的ꎮ一些研究发现ꎬ土壤冻融循环破坏了大团聚体的结构ꎬ提高了微团聚体的占比ꎬ从而降低了团聚体的稳定性ꎮ也有一些研究发现ꎬ土壤冻融循环加强了粒子键合ꎬ通常会增加土壤团聚体的总体稳定性[４５]ꎮ在冻融循环条件下ꎬ土壤团聚体稳定性的变化是多种因素共同作用的结果ꎬ冻融循环次数㊁外界环境条件及土壤本身的性质都有可能改变团聚体的稳定性ꎮ冻融循环次数是影响团聚体稳定性的重要因素之一ꎮ团聚体稳定性对冻融循环次数的响应并不是一成不变的ꎬ一些研究者认为ꎬ团聚体稳定性大体上随着冻融循环次数的增加而降低ꎬ并最终趋于稳定[１６ꎬ３６]ꎻ另有研究者指出ꎬ少数几次冻融循环会增加团聚体的稳定性ꎬ多次循环才会降低团聚体的稳定性ꎬ当冻融循环次数达到一定数值后ꎬ土壤结构会形成新的平衡[１９ꎬ４６￣４８]ꎮ出现上述现象ꎬ可能由于频繁的冻融循环对土壤结构㊁孔隙空间和颗粒构型造成了破坏性影响ꎮ在土壤冻融循环过程中ꎬ由于土壤发生反复的收缩和膨胀ꎬ较小粒级的团聚体先聚集成大团聚体ꎬ随着冻融次数增加ꎬ大团聚体又破碎成小颗粒ꎬ也就导致团聚体的稳定性随冻融次数的增加先提高后降低ꎮ土壤冻融循环本质上是土体内水分体积与形态变化引起的土壤特性的改变ꎬ因此ꎬ土壤水分含量对团聚体稳定性的影响不容忽视ꎮ土壤含水量过低或过高都会降低土壤的稳定性ꎬ而当土壤含水量等于或稍低于㊁稍高于田间最大持水量时ꎬ有助于保持土壤团聚体的稳定性[３６ꎬ４６]ꎬ保持适当的土壤含水量可以抵消部分冻融循环给土壤带来的破坏[１４]ꎮ这是因为ꎬ当土壤发生冻融循环时ꎬ土壤孔隙内的水分冻结ꎬ会导致团聚体崩解ꎬ且土壤含水量越高ꎬ冻结导致的团聚体崩解也越严重ꎻ同时ꎬ冻结水通过挤压土壤颗粒ꎬ也会导致团聚体重新聚集ꎬ当土壤含水量等于田间最大持水量时ꎬ土壤团聚体的崩解与聚集会达到一种较为平衡的状态ꎬ从而增强冻融过程中团聚体的稳定性ꎮ土壤质地也是决定冻融循环影响团聚体稳定性的重要因素之一ꎮ由于黏土会在土壤颗粒之间形成坚固的桥梁ꎬ所以黏土含量高的土壤ꎬ其团聚体稳定性也较高[３７]ꎮ研究证实ꎬ冻融对松散沙土的影响大于对黏性较强粉土的影响ꎬ黏土含量高的土壤在冻融条件下的团聚体稳定性显著高于其他土壤[４９￣５０]ꎮ在黏土颗粒中ꎬ许多水分子以结合水的形式存在ꎬ这意味着黏土中的未冻水多于粗颗粒ꎬ因此黏土更不容易发生颗粒破３８０１郑昕雨等:冻融循环对土壤团聚体与微生物特性影响研究进展碎ꎬ黏土含量高有利于提高土壤团聚体的稳定性ꎮ２.３㊀冻融循环对土壤孔隙结构的影响土壤团聚体之间和团聚体内部的孔洞叫做土壤孔隙ꎮ土壤孔隙是水分和气体存在的场所ꎬ也是植物根系延展和土壤微生物活动的空间ꎮ土壤孔隙结构特征与团聚体密切相关ꎮ一方面ꎬ孔隙系统特征对团聚体的稳定性起着重要作用ꎬ土壤孔隙度与团聚体稳定性呈显著负相关关系[３９]ꎻ另一方面ꎬ团聚体粒径与孔隙数和孔径相关ꎬ主要表现在较小的团聚体有利于孔隙数增加ꎬ而较大的团聚体有利于大孔径孔隙的形成[５１]ꎮ孔隙度是受冻融循环影响最基础㊁最直观的孔隙特征参数ꎬ一般认为ꎬ在冻结过程中ꎬ土壤中的水由于体积膨胀ꎬ从而增大了土壤颗粒外壁上的压力ꎬ使土壤颗粒重新排列ꎬ土壤孔隙扩大ꎬ孔隙度增加[１６]ꎬ进而影响团聚体特性㊁微生物生存ꎮ冻融循环次数对土壤孔隙结构有明显影响ꎬ特别是在第１次冻融循环后[１６]ꎮ多项研究发现ꎬ在土壤初始含水量相同的条件下ꎬ随着冻融循环次数增加ꎬ土壤孔隙度呈缓慢增大的趋势ꎬ且在初始冻融循环期间(冻融循环次数少于６次)ꎬ土壤孔隙度显著增加ꎬ土壤颗粒间隙和排列改变ꎻ随着冻融循环次数的增加(６~２０次)ꎬ土壤颗粒重新排列引起的孔隙变化逐渐稳定ꎬ土壤的孔隙度趋于稳定ꎬ土壤结构达到新的平衡[１６ꎬ５２￣５３]ꎮ除此之外ꎬ冻融温度也是影响土壤孔隙结构的重要因素ꎮ冻融温差越大㊁冻结温度越低ꎬ在冻融过程中土壤孔隙度也相应地表现为较大的数值[５２]ꎮ然而ꎬ上述研究得出的孔隙度是基于土壤容重㊁颗粒密度的公式推导出来的ꎬ并不能直接反映土壤孔隙变化ꎮ随着土壤显微分析技术的发展ꎬ利用显微电子计算机断层扫描(ＣＴ)技术和Ｘ射线断层扫描技术研究土壤孔隙的方法日渐成熟ꎬ并且更加直观和准确ꎮ土壤结构的可视化研究结果表明ꎬ冻融循环改变了土壤的孔隙结构ꎬ形成了一个复杂的多孔网络ꎬ增加了孔道网络的复杂性ꎬ并使土壤变得更加疏松ꎬ土壤孔隙度也随冻融循环次数的增加而增大[５４￣５５]ꎮ已有研究者通过Ｘ射线断层扫描技术观察到ꎬ在冻融过程中小孔隙数量增加ꎬ它们相互连接形成较大的孔隙ꎬ而大孔隙又发生断裂ꎬ随后形成几个较小的孔隙ꎬ从而形成复杂而连续的微观结构[５４￣５５]ꎮ另有研究者通过显微ＣＴ技术观察发现ꎬ在１５次冻融循环内ꎬ随着冻融循环次数的增多ꎬ土壤孔隙度不断增大ꎬ在７次冻融循环后土壤孔隙度的增大尤为显著ꎻ当冻融循环次数达到１５次时ꎬ团聚体达到新的稳定状态ꎬ团聚体内部孔隙连通ꎬ呈网络状ꎬ连通的网络状孔隙将大团聚体内部固体颗粒分离ꎬ在大团聚体内部可以观察到明显的微团聚体结构[５６￣５７]ꎮ此外ꎬ土壤孔隙结构与土壤含水量也息息相关ꎮ冻融循环导致土壤结构变化的本质是土壤水冻结时会形成冰晶ꎬ产生冻胀力挤压土壤ꎬ从而导致土壤孔隙等一系列结构发生改变ꎮ土壤含水量越高ꎬ冻结时产生的冻胀力也越大ꎬ对土壤孔隙结构的改变也越大[５８]ꎮ３㊀冻融循环对土壤微生物的影响土壤微生物在调节凋落物和有机质分解㊁生物地球化学循环和土壤养分有效性方面发挥着重要作用ꎬ能够影响植物对养分的吸收㊁生长和生产力[５９]ꎮ此外ꎬ土壤微生物在提高土壤稳定性㊁抵御冻融循环引起的土壤侵蚀等方面也具有重要作用ꎬ如Ｓａｄｅｇｈｉ等[６０]发现ꎬ在冻融循环条件下ꎬ细菌㊁蓝藻菌能显著抑制土壤及其组分流失ꎮ冻融循环对土壤微生物的结构和功能都有很大的影响ꎬ一般从土壤微生物生物量和群落结构等方面进行相关研究ꎮ３.１㊀冻融循环对土壤微生物生物量和活性的影响土壤微生物生物量是土壤有机质的活性部分ꎬ能反映微生物在土壤中的含量和潜力[６１￣６２]ꎮ多数研究结果表明ꎬ冻融循环次数会显著影响微生物活性与生物量ꎬ连续的土壤冻融循环会导致土壤结构破坏ꎬ从而降低微生物生物量和微生物群落活性[１７ꎬ６３￣６５]ꎮ然而ꎬ少数几次冻融循环可能会提高微生物生物量[６６]ꎮ对温带森林土壤进行的野外原位试验发现ꎬ在冻融初期ꎬ微生物遭到破坏ꎬ细胞壁破裂后养分流失并进入土壤ꎬ土壤养分有效性显著提高ꎬ但是由于微生物大量死亡ꎬ反复冻融后土壤养分有效性显著降低[２０]ꎮ此外ꎬ影响微生物生物量变化的主要是细菌ꎬ真菌生物量不易受冻融交替的影响ꎬ可能由于细菌迅速适应并对冻融引起的环境变化作出了反应ꎬ而真菌依赖于其强大的抵抗力才得以保持稳定的生物量[２０]ꎮ有研究者认为ꎬ在冻融循环过程中ꎬ高寒草甸㊁高寒草原土壤的微生物生物量碳㊁微生物生物量氮含量普遍表现出相似的 低￣高￣低 变化模式ꎬ是由于早期冻融过程刺激了高寒草原及高寒草甸土壤微生物ꎬ带来了更高的微生物生物量ꎬ然而随着冻融循环次数的增加ꎬ残４８０１江苏农业学报㊀２０２３年第３９卷第４期留微生物逐渐适应低温条件ꎬ微生物生物量又恢复稳定[６７]ꎮ由此可见ꎬ微生物种类与生活环境的差异可能会导致不同的试验结果ꎮ此外ꎬ冻融对微生物的影响并非不可逆转ꎬ冻结期微生物进入休眠状态ꎬ到了融化期又会活跃起来ꎮ土壤微生物生物量对于不同冻融速率也会作出不同的响应ꎮ有报道显示ꎬ微生物生物量在高冻融速率(>１.４ħ/ｈ)下下降ꎬ在相对较低的冻融速率或中等冻融速率下不受影响[６８]ꎮ通过测定土壤微生物呼吸发现ꎬ在相同时间内ꎬ更多次的冻融循环会导致更多微生物死亡[６９]ꎮ３.２ 冻融循环对土壤微生物群落结构的影响土壤中的微生物以细菌㊁真菌和放线菌居多ꎬ其中细菌约占土壤微生物总数的７０％~９０％ꎬ此外还有少量藻类[７０]ꎮ在冻融条件下ꎬ土壤结构遭到破坏ꎬ水热条件被改变ꎬ细胞外形成冰晶ꎬ导致土壤溶质浓度升高㊁蛋白质变性㊁膜损伤㊁细胞脱水和代谢率降低ꎬ这些变化进一步影响了微生物生境和生态位的形成ꎬ从而影响土壤微生物群落[６５]ꎮ不同微生物对冻融循环的响应是不同的ꎬ细菌㊁真菌㊁放线菌等微生物具有其独特的形态㊁生长策略和环境中的生态位ꎬ因此它们对冻融循环的反应可能是不同的ꎮ目前与冻融相关的研究主要针对真菌㊁细菌ꎬ但是由于研究方法与微生物原生环境的差异ꎬ关于真菌㊁细菌群落对冻融循环的响应还没有统一的结论ꎮ一些研究结果表明ꎬ在相同冻融条件下ꎬ细菌群落的结构和组成相比真菌群落有更大变化[１７ꎬ７１]ꎮ不论是在实验室进行模拟冻融试验还是在野外进行原位冻融研究ꎬ都有研究发现真菌的稳定性大于细菌[１７ꎬ７１￣７２]ꎮ冻融循环对真菌群落生物量㊁多样性和群落组成没有显著影响ꎬ但却明显改变了细菌群落的结构和组成ꎮ冻融前期表层土壤微生物多样性增加ꎬ但在后续冻融阶段ꎬ微生物多样性显著下降ꎬ微生物群落结构经历自然选择ꎮ然而ꎬ细菌受冻融循环的影响也有限ꎮ例如ꎬＹｏｓｕｋｅ等[６３]研究发现ꎬ连续４次冻融循环后ꎬ最低的微生物存活率为６０％ꎬ表明大多数土壤微生物可能对环境波动(如土壤冻融循环引起的温度㊁渗透压变化)具有耐受性ꎮ在冻融时期的不同阶段ꎬ微生物种群结构也不同ꎬ发生冻结时微生物含量表现为放线菌>细菌ꎬ因为放线菌对外界环境的敏感度较低ꎬ对恶劣环境的抵抗力要强于细菌㊁真菌ꎻ但是在融雪期ꎬ细菌在微生物中的比例提高ꎬ这是由于细菌对冻融循环的抗性更强ꎬ且喜湿润并能耐受低氧[７３]ꎮ对中温带土壤冻融的研究也发现ꎬ虽然－１５ħ极端冰冻温度的冻融循环对细菌群落危害很大ꎬ但多次冻融循环对细菌群落组成却没有造成重大影响ꎬ细菌群落仅在第１次冻融后出现了快速反应ꎬ而在随后的循环中ꎬ这种反应往往会减弱[６４]ꎮ此外ꎬ拥有不同冻融历史的土壤对冻融循环的敏感度也不同ꎬ对于经常遭遇冻融的土壤ꎬ其微生物群落可能已经适应了这种条件ꎮ因此ꎬ在一般不受冻融影响的土壤中ꎬ冻融循环对土壤微生物的危害更大ꎬ其群落的恢复也更慢[２８]ꎮ４㊀结语与展望冻融循环显著影响了土壤物理化学特性与微生物特性ꎬ能够调控土壤肥力与保水透气性ꎬ进而影响土壤的农业利用价值ꎬ研究冻融对土壤团聚体与微生物的影响有重要的理论价值和实际意义ꎮ通过分析国内外关于冻融循环影响团聚体与微生物的研究现状ꎬ未来可以在以下几个方面进行深入研究ꎮ(１)目前ꎬ对于土壤团聚体的研究主要集中于其稳定性与粒径分布方面ꎬ对于团聚体内部结构及微生物分布的研究相对较少ꎮ未来研究可利用同步辐射显微ＣＴ技术获取土壤团聚体剖面结构与三维立体结构ꎬ进一步探究团聚体的形成与破碎机制ꎬ并结合对团聚体内部微生物分布的研究ꎬ更系统地了解土壤团聚体与微生物的相互作用机制ꎮ(２)近年来ꎬ利用组学技术开展冻融对土壤微生物特性的研究越来越深入ꎬ例如利用新一代高通量分离培养方法ꎬ结合现有的生物分子测序技术ꎬ分析冻融作用下微生物的代谢过程ꎬ探究其对冻融的适应方法与响应机制ꎬ从而更全面㊁深入地理解冻融循环对土壤微生物的作用与影响ꎮ(３)尽管目前对于土壤团聚体与微生物相互作用的研究不断增多ꎬ但在冻融循环条件下ꎬ土壤团聚体和微生物之间的耦合关系还不明确ꎮ由于土壤团聚体与微生物在空间分布和功能上的相关性ꎬ冻融循环导致的团聚体和微生物的变化也会造成二者间的交互影响ꎮ加强这方面的研究ꎬ对于深入阐明冻融对土壤生态系统和结构系统的影响㊁揭示土壤团聚体与微生物的相互作用关系都具有重要的理论意义ꎮ参考文献:[１]㊀ＲＯＷＬＡＮＤＳＯＮＴＬꎬＢＥＲＧＡＡꎬＲＯＹＡꎬｅｔａｌ.Ｃａｐｔｕｒｉｎｇａｇｒｉ￣５８０１郑昕雨等:冻融循环对土壤团聚体与微生物特性影响研究进展。
大庆地区碳酸盐渍土室内冻胀试验研究
第12卷第1期2021年3月黑龙江大学工程学报J ou—H of Engineering of Heilongjiang UniversityV c012,N c.1Mar.,2021DOI：10.13524/j.2095-C08x.2021.01.003大庆地区碳酸盐渍土室内冻胀试验研究郭琳1lb,王正君1c'1b!*,赵安平2,宫<1t!1b,姜荣辉1t!1b,王嘉峪2(1.黑龙江大学a.寒区水利工程重点实验室；b.水利电力学院；c.建筑工程学院，哈尔滨150080；2.山东农业大学水利土木工程学院，山东泰安271017)摘要：为了研究冻融循环对大庆地区碳酸盐渍土的冻融特性的影响，以含盐量和含水量为变量进行冻融循环试验，分析冻融作用下含盐量和含水量对该类型土的工程性质和工程性态的影响。
借助GDS三轴仪进行固结不排水剪切，探究冻融循环次数对碳酸盐渍土强度的影响，解释盐胀病害发生机理、发展规律和影响因素。
结果表明，含盐量和含水量对盐渍土冻融循环过程中位移的变化均有明显影响，即随着含盐量的增加，冻结过程中负温面积呈先减小后增大的趋势；随着冻融循环次数的增加，黏聚力逐渐减小，而内摩擦角先增大后减小。
关键词：盐渍土；冻融；冻胀特性；三轴剪切试验中图分类号：TU502文献标志码：A文章编号：2095-008X(2021)01-0017-04 Laboratory frost heave test of carionatr soii ie Daqing areaGUO Lin1x1b,WANG Zheng-Jun111.&,ZHAO An-Cing1c'&,GONG Ying1a'1b,JIANG Rong-Hui1x1b,WANG Jio-Yu2(1.HeCowgjiang University a.Key Lab of Water Hydraulic Engineering t Coll Regions； b.School eg Hydraulic and Electric Pooer； c.School O Cct Engiming,Harbin150080,China； 2.Collegr O Hyyraultc and Civil Engiming,Shandong Agricultural Uniersity Tai f an271017,Shandong,China)Abstract:To study the inOuenco of freeze-thaw cyde on the freeze-thaw charactenstico of corbonate soil in Daqing d—e,the freeze-thaw cyde test was corned out wiO slt content and water content as veriables,and the effects of slt content and water content on the engineering prope—ies and engineenng properties of tOe soil were analyzed. The effect of freeze-thaw cycles on the strengtO of corbonate soil was studied by using GDS013X131apparatus and the mechanism,developmeniaw and infuencing factors of salt expansion4:56X0were explained.The results show that the slt conWnt and water conWnt have obvious inauency on the displacement change of saline soil during freeze-thaw cycie,that is,with the inc—vso of sait content the negtWe temperature xe v frst de—vsvs and then increeses；with the inc—co of feeze-thaw cycles,the cohesion dec—vses g—duty,whiie the inte—ai ffetion angie inc—ases first and then dec—ases.Key words:cyrbonate soii;freeze-thaw;f—st heave charactenstid;twaxiai shear test收稿日期：2020-C6-22；修订日期：2020-08-11基金项目：国家自然科学基金项目(51678221)；国家重点实验室开放项目(SKLFSE201615)；黑龙江省应用技术研究与开发计划引导项目(GZ16B013)作者简介：郭琳(1995-),女，硕士研究生，研究方向：建筑材料与无损检测'E-maii：*****************&通讯作者：王正君(1971-),男，教授，博士，硕士研究生导师，研究方向：建筑材料与无损检测'E-maii：wzjsir@163..om 赵安平(1977-),女，副教授，博士，研究方向：地质工程、岩土工程及冻土工程'E-maii：2008047@hlju..du,on引文格式：郭琳，王正君，赵安平，等.大庆地区碳酸盐渍土室内冻胀试验研究]J].黑龙江大学工程学报，2021,12(1)：17-20.・18・黑龙江大学工程学报第12卷0引言盐渍土指自然环境土和盐土以及盐性土体土体，具溶陷、盐及腐蚀性等特性的特殊土体［门。
含水率和冻融循环对筋土界面剪切特性的影响
第 55 卷第 2 期2024 年 2 月中南大学学报(自然科学版)Journal of Central South University (Science and Technology)V ol.55 No.2Feb. 2024含水率和冻融循环对筋土界面剪切特性的影响孟亚1，徐超1, 2，贾斌3，左彬澧1(1. 同济大学 地下建筑与工程系，上海，200092；2. 同济大学 岩土及地下工程教育部重点实验室，上海，200092；3. 中国电力工程顾问集团华东电力设计院有限公司，上海，200063)摘要：制作了一套可实现温度控制的筋土界面直剪试验设备。
为了研究含水率、界面温度、冻融循环次数对筋土界面剪切特性的影响，开展11组土工格栅−砂土界面直剪试验。
研究结果表明，筋土界面的黏聚力和摩擦角均随含水率的增加而减小，当含水率提高时，筋土间的抗剪强度减弱。
加筋可显著提高冻土的抗剪强度，当界面温度为−10 ℃时，土工格栅−砂土界面剪应力峰值较冻结后砂土的剪应力增加了约20%。
筋土界面剪应力随着界面温度的降低而增大，当界面温度在0 ℃以下时，剪应力较大且剪应力−剪切位移曲线会出现峰值强度和残余强度，而在无冻结情况下，筋土界面剪应力稳定值基本相同。
冻融循环后筋土界面的抗剪强度减小，筋土界面的黏聚力和摩擦角均随着冻融循环次数的增加而减小，但在4次冻融循环后趋于稳定。
研究成果可为冻土地区土工格栅加筋土结构的设计和应用提供理论依据。
关键词：土工格栅；直剪试验；筋土界面；剪切特性；冻融循环中图分类号：TU445 文献标志码：A 文章编号：1672-7207（2024）02-0586-09Influence of water contents and freeze-thaw cycles on shearbehavior of geogrid-soil interfaceMENG Ya 1, XU Chao 1, 2, JIA Bin 3, ZUO Binli 1(1. Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China;2. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education,Tongji University, Shanghai 200092, China;3. East China Electric Power Design Institute Co. Ltd., China Power Engineering Consulting Group,Shanghai 200063, China)收稿日期： 2023 −07 −19； 修回日期： 2023 −09 −26基金项目(Foundation item)：国家自然科学基金资助项目(41772284)；安徽省交通运输行业重点科技项目(2022-KJQD-008)；中国电力工程顾问集团华东电力设计院有限公司科研项目(30-K2023-G01) (Project(41772284) supported by the National Natural Science Foundation of China; Project(2022-KJQD-008) supported by the Key Technology Program in the Transportation Industry of Anhui Province; Project(30-K2023-G01) supported by the Scientific Research Program of the East China Electric Power Design Institute Co. Ltd. of China Power Engineering Consulting Group)通信作者：孟亚，博士研究生，从事土工合成材料加筋土结构的研究与应用；E-mail ：******************.cnDOI: 10.11817/j.issn.1672-7207.2024.02.012引用格式： 孟亚, 徐超, 贾斌, 等. 含水率和冻融循环对筋土界面剪切特性的影响[J]. 中南大学学报(自然科学版), 2024, 55(2): 586−594.Citation: MENG Ya, XU Chao, JIA Bin, et al. Influence of water contents and freeze-thaw cycles on shear behavior of geogrid-soil interface[J]. Journal of Central South University(Science and Technology), 2024, 55(2): 586−594.第 2 期孟亚，等：含水率和冻融循环对筋土界面剪切特性的影响Abstract:A set of temperature-controlled direct shear test apparatus for the interface of reinforced soil was developed. Eleven groups of direct shear tests were conducted to study the influence of water contents, interface temperatures, and freeze-thaw cycles on the shear behavior of the geogrid-soil interface. The results show that the cohesion and friction angle of the geogrid-soil interface both decrease with the increase of water contents, as does the shear strength at the geogrid-soil interface. The reinforcement can obviously improve the shear strength of the frozen soil. When the interface temperature is −10 ℃, the peak shear stress at the geogrid-soil interface increases by about 20% relative to the unreinforced soil. The reinforcement provided by the geogrid increaes as the interface temperature drops. The shear stress is higher and the shear stress-shear displacement will show the peak strength and residual strength when the interface temperature drops below 0 ℃, whereas in a non-frozen state, the interface exhibits lower shear stress with a consistent stable value. The shear strength of the geogrid-soil interface decreases after freeze-thawing. Furthermore, both the cohesion and friction angle of the geogrid-soil interface decrease with the increase of freeze-thaw cycles number but tend to stabilize after four freeze-thaw cycles. The research results have reference for the design and application of geogrid reinforced soil structures in permafrost and seasonal frozen regions.Key words: geogrid; direct shear test; geogrid-soil interface; shear behavior; freeze-thaw cycle加筋土结构具有抗震性能好、施工快、减碳环保等特点，被广泛应用于公路、铁路等工程中[1−3]。
冻融循环作用对土体性质的影响研究现状
冻融循环作用对土体性质的影响研究现状摘要：冻融作用对于冻土地区的实际工程建设有很大的影响，所以冻融作用也是工程建设中十分重要的研究课题。
本文首先简要介绍了冻融引起的灾害，冻融循环试验的仪器方法和冻融循环改变土的物理力学性质等方面。
关键词：冻土，冻融循环试验，冻融作用0.引言冻融作用是实际建设工程中十分重要的影响，所以研究土冻融作用后的物理力学性质尤为重要。
冻融灾害是季冻区工程建设的重要问题之一。
已川藏铁路为例，土体经过冻融作用使得边坡发生失稳滑动，冻土边坡表层土体强度降低，是以川藏铁路为例季节性冻土边坡破坏的主要因素[1]。
因此，为减少冻融循环引发的工程灾害，研究冻融循环作用对土体性质的影响是十分必要的。
1.研究冻融循环试验的仪器与方法室内土的冻融试验一般将试件放置于圆筒模型内，根据试验要求会在内部装上温度探测器来监测土样内部的温度变化，将土样放入恒温箱中，可以用位移器来监测试样在冻融过程中的产生位移变化。
此外，在冻融过程中有开放式的，完全封闭式的，半封闭式，对于冻融试件有加围压和轴压两种加压方式。
冻结方式对各个研究者而言也各不相同，可以按照施加冷源的位置来分类，一般有单向冻结，单向融化，偶尔有双向冻结，单向融化等。
冻融对土的物理力学性质的影响一般用剪切、压缩固结、静三轴、动三轴等试验考察土工程性质在冻融循环作用下的改变。
2.冻融作用引起土物理性质的变化学者研究发现冻融循环可以使土的液塑限发生一定的变化[2]，也可以使土的颗粒级配发生变化[3]。
通过大量试验表明土样在冻融过程中内部会出现细小裂隙，而土样中的冰晶也会发生融化导致土样内部大孔隙的形成，因此土样的孔隙比减小，但渗透系数一般会有所增大[4]。
通过学者研究表明渗透性是土样在冻融过程中变化最为显著的。
Chamberlain等[5]研究表明，冻融后渗透性与孔隙比变化有一定的关系。
后来学者齐吉琳[6]等通过大量研究表明不同密实度的土的在冻融试验中渗透性会有不同的变化趋势，但整体呈现增大趋势。
粗骨料对再生混凝土力学性能影响研究
青海交通科技2020—4粗骨料对再生混凝土力学性能影响研究马兰（青海民族大学西宁810007）摘要随着废弃结构物的拆除量日益增加，建筑垃圾越来越多，如果将其随意填埋或露天堆放，会造成严重的土地资源浪费和环境污染。
鉴于此，笔者利用万能试验机和冻融机开展室内试验，首先分析了干燥状态和饱和状态下再生混凝土抗压强度、拉伸劈裂强度等随粗骨料取代率变化趋势，随后从质量损失率和相对动弹性模量两个方面评价了再生混凝土（粗骨料替代率60%）抗冻性能随冻融循环次数的变化规律，并对其劣化模型进行了拟合，以期为类似的再生混凝土设计提供理论指导"关键词粗骨料再生混凝土力学性能影响因素Effect of coarse aggregate on mechanical properties of recycled concreteMa5#(Qinghai Nationnalities University#Xining810007#China)Abstraci With the increasing demolition of abandoned structures#there are more and more construction waste.If V is buried or piled up in the open,it wili couse serious waste of land resources and environmentai p^lu-tion.fn view of this,the author uses universai testing machine and freeze一tiaw machine to cerre out indoor tests. Firstiy,the change trend of performance of concrete with the replacement rate of coarse aggreaate t de and saturated state is analyzed-Then,the frost resistancc of recycled concrete(60%replacement rate of coarst aggreaate) with the numbes of freeze一thaw cycles is evvluated from two aspects of mass loss rate and relative dynamic modulus of elasticity fn ordes te provide theoreticyl guidance fos similas recycled concrete design,the deterioration model wasftted.Key wortt coarss aggreaate;recycled concrete;mehaicol property;inOuenco factos随着我国城市建筑和基础交通设施建设的飞速发展,废弃结构物的拆除量也日益增加，使得建筑垃圾越来越多。
风火山隧道冻融循环条件下岩石损伤扩展室内模拟研究_张淑娟
(a)
(b)
图 2 温度控制周期图 Fig.2 Temperature control period during the tests
2003 年 7 月 23 日收到初稿，2003 年 9 月 26 日收到修改稿。 * 国家杰出青年科学基金(40225001)、国家自然科学基金(40171019)资助课题。 作者 张淑娟 简介：女，1975 年生，博士，2000 年 7 月毕业于长安大学水文地质与工程地质专业，主要从事寒区岩土工程方面的研究工作。E-mail： sjzhang@。
(1 中国科学院寒区旱区环境与工程研究所冻土工程国家重点实验室 兰州 730000) (2 铁道部第一勘察设计院桥隧处 兰州 730000)
摘 要 借助与程控装置配套的 CT 技术，研究了青藏高原风火山隧道拱顶和侧拱处的砂质泥岩在冻融循环条件下
的损伤扩展特性，并讨论了该条件下引发损伤的主要因素。此结果可为寒区隧道及类似工程的安全运营提供参考，
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岩石力学与工程学报
2004 年
1引言
随着寒区经济的发展，人们在这些地方大兴土 木，如道路工程、水利工程、隧道工程、工业与民 用建筑等的建设。在我国进行了青藏公路、格尔木 至拉萨输油管线、光纤通讯工程、大坂山隧道等著 名的工程，正在建设的有青藏铁路工程、青康公路 工程。这些工程活动越来越多地触及到岩体，从而 导致人类工程及开采活动对岩体的影响及其二者之 间的相互作用加剧， 再加上岩体赋存于地下水渗流 场、应力场与温度场多场并存的复杂地质环境之中， 就易于诱发多种地质灾害，如大坂山隧道，在冬季 出现洞顶挂冰，路面形成冰椎，夏季洞壁发生严重 的渗漏水等现象，还没正式起用的昆仑山隧道也出 现了类似的情况，对于这一切，表面上看起来是影 响了交通的正常运营，可是否存在潜在问题呢？大 家知道寒区隧道由于施工、机车运行和气温等外界 条件的影响，衬砌背后的多年冻土会形成一个冻融 交替的冻融圈，而水是寒区隧道产生病害的根源， 也是冻融圈作用的主要影响因素；又岩体本身是一 种自然损伤材料，含水量较高，冻结后冰体产生不 均匀冻胀力和冻胀变形，而这种力和变形在融化过 程中又不能完全恢复，从而加剧了岩体内部的胀缩、 损伤开裂等一系列物理、力学的交替变换，随着冻 融循环次数的增多，这将对岩体工程的稳定性产生 重要影响。对于常温下岩石的损伤，国内外已作了 大量研究[1～3]，相比之下，对其冻融损伤的研究并 不多见，尤其是国内。
冻融作用下不同饱和度红砂岩损伤力学特性
第51卷第12期2020年12月中南大学学报(自然科学版)Journal of Central South University (Science and Technology)V ol.51No.12Dec.2020冻融作用下不同饱和度红砂岩损伤力学特性宋勇军，车永新，陈佳星，任建喜，毕冉，陈少杰(西安科技大学建筑与土木工程学院，陕西西安，710054)摘要：为研究不同饱和度条件下冻融循环作用对岩石损伤规律及力学特性的影响，以饱和度分别为30%，50%，70%，90%和100%的红砂岩为对象，进行冻融循环、电镜扫描(SEM)及单轴压缩试验，分别得到不同冻融循环次数后岩样孔隙率、SEM 图像及应力−应变曲线，建立不同饱和度冻融受荷岩石宏观统计损伤演化方程，从细微观角度系统分析饱和度影响下冻融受荷岩石的劣化机制。
研究结果表明：随着冻融循环次数增加，孔隙率呈现先快后慢的增长趋势，且当饱和度大于70%后，孔隙率迅速增大。
低饱和度下岩样矿物颗粒黏结紧密，颗粒边界不明显，孔隙较少；随着饱和度增大，胶结物的溶蚀作用逐渐加速，颗粒间胶结减弱，溶蚀孔洞增多；岩样冻融循环后裂隙平均长度和孔隙平均面积均随饱和度增大逐渐增长。
岩样整体呈剪切破坏，剪切破坏面随饱和度增大逐渐增多并贯穿整个岩样。
峰值强度和弹性模量随饱和度增大呈“上凸式”指数减小，当饱和度达到70%后，降幅迅速增大；随冻融循环次数增加，峰值强度和弹性模量呈“下凹式”指数降低，冻融循环10次后，降幅趋于减小。
饱和度为70%、冻融循环为10次是该红砂岩损伤劣化的界限值。
相比冻融循环作用的损伤劣化影响，饱和度对岩石性质的改变更显著。
关键词：饱和度；冻融循环；扫描电子显微镜；力学特性；损伤演化中图分类号：TU452文献标志码：A开放科学(资源服务)标识码(OSID)文章编号：1672-7207（2020）12-3493-10Damage mechanical properties of red sandstone with differentsaturation during freeze-thawSONG Yongjun,CHE Yongxin,CHEN Jiaxing,REN Jianxi,BI Ran,CHEN Shaojie(School of Architecture and Civil Engineering,Xi'an University of Science and Technology,Xi'an 710054,China)Abstract:To investigate the effects of freeze-thaw cycles on rock damage and mechanical properties in different saturated states,red sandstone with different saturations (30%,50%,70%,90%and 100%)were selected for freeze-thaw cycle,scanning electron microscope (SEM)and uniaxial compression tests.The porosity variation,SEM image and stress-strain curve of rock samples were obtained after the action of freeze-thaw cycles.The macroscopic statistical damage evolution equations of frozen-thawed rocks with different saturated states were established.The degradation mechanisms of frozen-thawed and loading rocks were systematically analyzed under the influence of saturation from microscopic perspective.The results show that,as the number of freeze-thawDOI:10.11817/j.issn.1672-7207.2020.12.023收稿日期：2020−04−20；修回日期：2020−06−23基金项目(Foundation item)：国家自然科学基金资助项目(11972283，11872299，11802230)；陕西省自然科学基金资助项目(2017JM1039)(Projects(11972283,11872299,11802230)supported by the National Natural Science Foundation of China;Project(2017JM1039)supported by the Natural Science Foundation of Shaanxi Province)通信作者：宋勇军，副教授，从事岩石力学与地下工程研究；E-mail ：****************第51卷中南大学学报(自然科学版)cycles increases,the porosity increases quickly firstly and then slowly.When the saturation is greater than70%,the porosity increases rapidly.In low saturated states,the mineral particles of rock sample are tightly bonded,the grain boundary is not obvious,and the pores are few.As the saturation increases,the dissolution of the cement is gradually accelerated,the cementation of particles is weakened,and the dissolution holes increase.After the freeze-thaw cycle of the rock sample,the average length of cracks and the average area of pores gradually increase withthe increase of saturation.The rock sample shows shear failure,and the shear failure surface increases gradually with the increase of saturation and penetrates the whole rock sample.The strength and elastic modulus of rock samples decrease with the increase of saturation as the"upward convex"index.When the saturation reaches70%,the decreasing amplitude increases rapidly.The strength and elastic modulus of rock samples decrease with the number of increases of freeze-thaw cycles as the"under concave"index.After10freeze-thaw cycles,the decreasing amplitude tends to decrease.The saturation value is70%,and the freeze-thaw cycle is performed10 times as the limit value of the damage deterioration of the rock pared with the damage and degradation effects of freeze-thaw cycles,the saturated states changes more significantly for rock properties.Key words:saturation;freeze-thaw cycle;scanning electron microscope(SEM);mechanical properties;damage evolution随着“一带一路”国家战略的提出，西部寒区矿山和隧道等岩土工程建设逐渐增多，冻融环境下岩体的力学特性和工程稳定性问题受到广泛关注。
GB 2762-2012《食品中污染物限量》对乳及乳制品类的新要求
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阿托西班在不同年龄胚胎着床失败患者冻融胚胎移植的妊娠结局分析
实用妇产科杂志2021年2月第37卷第2期Journal of Practical Obstetrics and Gynecology2021Feb.Vol.37,Ao.2・147・文章编号:1003-6946(2021)02-0147-05阿托西班在不同年龄胚胎着床失败患者冻融胚胎移植的妊娠结局分析李馥洁，裴莉，黄国宁，叶虹(重庆市妇幼保健院生殖与遗传研究所重庆市人类胚胎工程重点实验室重庆市生殖医学临床研究中心.重庆400013)【摘要)目的：探讨阿托西班对于胚胎着床失败患者进行冻融胚胎移植(FET)的影响。
方法：回顾性分析388例着床失败且行FET患者的临床资料，比较<35岁和M35岁着床失败患者在移植前使用阿托西班治疗组(n=193)和未使用阿托西班对照组(n=195)的胚胎情况及妊娠结局等。
结果：对于着床失败1~2次的患者，无论<35岁还是M35岁的患者中，阿托西班组和对照组的胚胎着床率、生化妊娠率和临床妊娠率比较差异均无统计学意义(P>0.05)o在着床失败M3次反复着床失败(RIF)的患者，年龄<35岁的患者中阿托西班组的胚胎着床率、生化妊娠率和临床妊娠率分别为33.06%,57.14%和52.38%,均显著高于对照组的22.46%,46.48%和32.39%(P<0.05)；年龄M35岁的患者中，阿托西班组和对照组的胚胎着床率、生化妊娠率和临床妊娠率比较，差异均无统计学意义(P>0.05)o移植前使用单剂量阿托西班治疗后，妊娠期并发症发生率、早产率、低出生体质量儿发生率及出生缺陷发生率与对照组比较，差异均无统计学意义(P>0.05)。
结论：移植前使用单剂量阿托西班是安全的，对改善年龄<35岁RIF患者妊娠结局有积极作用。
【关键词】胚胎着床失败；阿托西班；冻融胚胎移植；临床妊娠中图分类号:R321-33文献标志码：AAnalysis of the Influence of Atosiban on the Pregnancy Outcome of Freezethaw Embryo Transfer in Patients with Different AgesLI Fujie,PEI Li,HUANG Guoning.et al(Reproductive and Genetic Institute,Chongqing Health Center for Women and Children.Chongqing Key Labora・tory of Human Embryo Engi n eeri n g.Ch o n g qing Clin i cal Research Center for Reproductive Medici n e,Ch o ngqing 400013,China)Corresponding author：YE Hong[Abstract]Objective：To observe the effect of Atosiban on frozervthawed embryo transfer(FET)treatment for patients with the history of embryo implantation failure.Methods：The clinical data of388patients who underwentfreeze-thaw embryo transfer with the history of implantation failure were analyzed retrospectively.Patients were divided into treatment group(n =193)with atosiban injection,and control group(n=195)without Atosiban injectionbefore transplantation.The embryo status and pregnancy outcome of patients with implantation failure aged<35years and^35years were compared between the two groups.Results：For patients with implantation failure1or2times,there was no significa n t d i ff e re n ee in embryo impla n tation rate,biochemical preg n ancy rate,and clinicalpregna n cy rate between the atosiba n group and the control group(P>0.05)in patie n ts aged<35years an d m35years.I n patients with RIF(>3times),the embryo implantatio n rate,biochemical preg n ancy rate,a n d clinical pregnancy rate of the Atosiban group in patients<35years old were33.06%,57.14%,and52.38%respectively,which were significantly higher thanthose in the control group(22.46%.46.48%and32.39%,respectively)(all P<0.05).Among patients aged m35years,there was no significant difference in the embryo implantationrate,biochemical pregnancy rate and clinical pregnancy rate between Atosiban group and the control group(P>0.05).After sin g le-dose Atosiba n treatment before transplantatio n,there was no sign i fica n t d i ff e re n ee in the inci・dence of complications during pregnancy,premature birth rate,the incidenee of low birth weight infants and the incidence of birth defects compared with those in the control group(P>0.05).Con e lusions：The use of single-通讯作者:叶虹，E-mail:yehongl210@实用妇产科杂志2021年2月第37卷第2期Journal of Practical Obstetrics and Gynecology2021Feb.Vol.37,\o.2•148•dose Atosiban before transplantationis safe and could significantly improve pregnancy outcomefor RIF patientsyounger than35years.[Key words]Embryo implantation failure；Atosiban；Frozen-thawed embryo transfer；Clinical pregnancy1978年7月世界第1例“试管婴儿”诞生至今.体外受精-胚胎移植（in vitro fertilization embryo transfer,IVF-ET）经历了四十余年，取得了突飞猛进的发展。