Effects of freezing-thawing and cyclic loading on pore size distribution of silty clay by mercury intrusion porosimetry
Effects of freezing-thawing and cyclic loading on pore size distribution of silty clay by mercury intrusion porosimetry
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DOI：
10.1016/j.coldregions.2017.11.002
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发表时间：
2018
影响因子：
4.1
通讯作者：
Zhong-Liang Zhang;Z. Cui
中科院分区：
文献类型：
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作者：
Zhong-Liang Zhang;Z. Cui
随着城市轨道交通的发展，软土在地铁振动荷载作用下的长期变形问题引起了研究者和工程技术人员的广泛关注。除了原位试验和室内三轴试验外，显微镜试验也是研究软粘土动力特性的有效手段。此外，粉质粘土冻融前后的孔隙尺寸分布（PSD）的变化研究较少。采用压汞法（MIP）对经过循环三轴试验的粉质粘土冻融前后的微观孔隙结构进行了研究。压汞过程中存在孔径为0.1-0.6 μ m的瓶颈现象。粉质粘土的对数微分孔体积曲线呈单峰型，其中孔隙半径在0.05~0.6 μ m范围内的模式代表团聚体内孔隙。冻融后，无循环加载的样品的最终压汞体积和最可几孔径分别增加约6.0%和30.64%。在相同的循环荷载下，随着冻结温度的降低，汞侵入量增大。频率越低，循环应力比越大，试样的变形越大，最可几孔径越小。频率为2.5Hz的冻融后试样的孔体积（F）比频率为0.5Hz的冻融后试样的孔体积（U）增加了8.74%，而频率为0.5Hz的冻融后试样的孔体积（F）比频率为0.5Hz的冻融后试样的孔体积（U）增加了5.03%。CSR为0.125的冻融后样品的最可能孔径比CSR为0.375的冻融后样品的最可能孔径大约81.2%。压汞试验中的压汞过程类似于沿着干燥持水曲线（WRC）描述的饱和土壤中的空气注入过程。压汞压力和归一化体积分别相当于土壤吸力和土壤中的空气体积。由MIP导出的WRC适用于用货车模型预测土壤水分特征曲线。在压汞试验中，粉质粘土的微观孔隙结构具有分形特征，并符合热分形维数模型。
With the development of urban rail transposition, the long-term deformation of soft clay under the subway vibration loading has drawn wide attention by researchers and engineers recently. In addition to the situ tests and laboratory triaxial tests, the microscope tests also provide an effective way to clarify the dynamic characteristics of soft clay. Moreover, the variations of the pore size distribution (PSD) of the silty clay before and after freezing-thawing have less been investigated. In this paper, the mercury intrusion porosimetry (MIP) tests were conducted to study the microscope pore structures of the silty clay before and after freezing-thawing which had experienced the cyclic loading by the cyclic triaxial tests. A bottleneck phenomenon with the pore radii of 0.1–0.6 μm exists in the mercury intrusion process. The log-differential pore volume curves of the silty clay show a unimodal mode, where the mode with pore radii range from 0.05 to 0.6 μm represents intra-aggregate pores. After freezing-thawing, the final mercury intrusion volume and the most probable pore size of the samples without cyclic loadings increase about 6.0% and 30.64%, respectively. Under the same cyclic loadings, the mercury intrusion volume increases with the freezing temperature decreasing. The lower the frequency and the larger the cyclic stress ratio (CSR) of cyclic loadings are, the larger the deformations of the samples are and the smaller the most probable pore size becomes. The pore volume of samples after freezing-thawing (F) with frequency of 2.5 Hz is 8.74% larger than that with 0.5 Hz, while it is 5.03% of undisturbed samples (U). The most probably pore size of the samples after freezing-thawing with CSR of 0.125 is about 81.2% larger than that with CSR of 0.375. The process of mercury intrusion in MIP tests is similar to the air injection in a saturated soil as described along the drying water retention curve (WRC). The mercury intrusion pressure and the normalized volume are equivalent to the soil suction and the air volume within the soil, respectively. The MIP derived WRC is suitable for the prediction of the soil-water characteristic curves with the van Genuchten model. In addition, the microscope pore structures of the silty clay exhibit fractal characteristics with the thermal fractal dimension model in MIP tests.