Structural Evolution and Mechanical Response Mechanism of Loess in Strong Earthquake Area
-
摘要:
黄土因其遇水产生湿陷变形而对工程构筑物的安全性造成严重威胁.强震区黄土遭遇先期地震后其内部结构将发生变化，结构演变与黄土初始含水量密切相关.先期地震对黄土的结构性破坏引起宏观力学特征变化，为揭示强震区黄土结构演变与力学响应的内在机制，基于动三轴对黄土试样预先施加不同PGA（peak ground acceleration）条件下动荷载进行预震处理，模拟强震区先期地震对黄土的扰动，后进行固结不排水试验，分析抗剪强度指标与地震荷载及初始含水量的关联性.试验结果表明，初始含水率为2%时，预先施加地震动荷载的黄土试样与未预先施加动荷载的试样相比，其峰值强度出现了明显降低，且随着预先施加动荷载PGA的增加，峰值强度降幅增加.孔隙水压力随应变的不断增加趋于平缓，有效轴向应力和有效围压随应变的不断增加而持续减小，最终趋于平缓；初始含水量增加至12%，预震处理后的黄土试样强度增大.通过绘制应力路径关系曲线，确定了强震区黄土失稳的临界失稳线，对于同一黄土试样，PGA增加后引起黄土失稳线不断下移，表明黄土中的应力状态随地震动荷载的增加而发生变化.初始含水量为12%时，预震后的黄土试样剪切强度增大，表明含水量增加后，前期地震荷载开始破坏黄土初始结构性，导致试样密度增大，产生强度增加效应.
Abstract:Loess poses a serious threat to the safety of engineering structures because of its collapsibility and deformation when it encounters water. The internal structure of loess in strong earthquake areas will change after encountering historical earthquakes, and the structural evolution is closely related to the initial water content of loess. Structural damage of loess by historical earthquakes also affects its macroscopic mechanical characteristics: In order to reveal the mechanism of the structural evolution and mechanical response of loess in strong earthquake areas, the loess samples were pre-seismically treated with dynamic loads under different PGA (peak ground acceleration) conditions via dynamic triaxial tests, so that the disturbance of historical earthquakes to loess was simulated. Afterwards, the undrained test was carried out to analyze the correlation between the shear strength parameters, the seismic load and initial water content. The test results show that when the initial moisture content is 2%, the peak strength of the loess sample with pre-seismical treatment is significantly lower than that of the sample without pre-seismical treatment, and with the increase of PGA, the peak strength decreases. The pore water pressure eventually tends to be constant with the continuous increase of the strain, the effective axial stress and the effective confining pressure decrease with the continuously increasing strain, and finally tend to be content. When the initial water content increased to 12%, the strength of the loess sample after pre-seismical treatment increased.By drawing the stress path relationship curve, the critical instability line and failure line of the loess in the strong earthquake area are determined. For the same loess samples, the increase of PGA causes the loess instability line to move down continuously, indicating that the stress state in the loess changes with the increase of the earthquake dynamic load. When the initial moisture content is 12%, the shear strength of the loess sample after pre-seismic treatment increases.
-
图 2 初始含水量2%土样的动应力应变曲线
Fig. 2. Dynamic stress strain curve of soil sample with initial moisture content of 2%
图 3 初始含水量12%土样的动应力应变曲线
Fig. 3. Dynamic stress strain curve of soil sample with initial moisture content of 12%
图 4 初始含水量2%黄土试样应力应变关系
Fig. 4. Stress⁃strain relationship of loess sample with initial water content of 2%
a.PGA=0.00 g; b.PGA=0.15 g; c.PGA=0.30 g; d.PGA=0.40 g
图 5 初始含水量2%黄土试样有效应力路径
Fig. 5. Effective stress path of loess sample with initial water content of 2%
a.PGA=0.00 g; b.PGA=0.15 g; c.PGA=0.30 g; d.PGA=0.40 g
图 6 初始含水量2%黄土试样孔压应变关系曲线
Fig. 6. Pore water pressure strain relation curve of loess sample with initial water content of 2%
a.PGA=0.00 g; b.PGA=0.15 g; c.PGA=0.30 g; d.PGA=0.40 g
图 7 初始含水量12%黄土试样应力应变关系
Fig. 7. Stress⁃strain relationship of loess sample with initial moisture content of 12%
a.PGA=0.15 g; b.PGA=0.30 g; c.PGA=0.40 g
图 8 初始含水量12%黄土试样有效应力路径
Fig. 8. Effective stress path of loess sample with initial moisture content of 12%
a.PGA=0.15 g; b.PGA=0.30 g; c.PGA=0.40 g
图 9 初始含水量12%黄土试样孔压应变关系
Fig. 9. Pore water pressure strain relation diagrams of loess sample with initial water content of 12%
a.PGA=0.15 g; b.PGA=0.30 g; c.PGA=0.40 g
图 10 含水量为2%黄土试样预震后微结构图
Fig. 10. Schematic diagrams of microstructure of loess sample with water content of 2% after pre⁃dynamic treatment
a.PGA=0.00 g, W=2%;b.PGA=0.15 g, W=2%;c.PGA=0.30 g, W=2%;d.PGA=0.40, W=2%
图 11 含水量为12%黄土试样预震后微结构图
Fig. 11. Schematic diagrams of microstructure of loess sample with water content of 12% after pre⁃dynamic treatment
a.PGA=0.00 g, W=12%;b.PGA=0.15 g, W=12%;c.PGA=0.30 g, W=12%;d.PGA=0.40, W=12%
表 1 试样物理力学参数汇总表
Table 1. Summary of physical and mechanical parameters of the samples
参数 初始含水量2%试样 初始含水量12%试样 初始密度ρ(g/cm3) 1.49~1.52 1.63~1.65 实测含水量w(%) 1.82~2.66 11.67~12.48 液限wL(%) 27.05 27.05 塑限wP(%) 16.35 16.35 塑性指数IP 10.70 10.70 地震峰值
加速度(g)0.20 0.20 比重 2.72 2.72 孔隙比 0.79~0.83 0.65~0.67 饱和度(%) 6.27~8.72 48.83~50.67 
下载: 导出CSV
表 2 抗震设防烈度与设计基本地震加速度值和预震次数的对应关系
Table 2. Correspondence between seismic fortification intensity and design basic seismic acceleration value and pre-dynamic times
抗震设防烈度 6度 7度 8度 9度 设计基本地震加速度值(g) 0.05 0.10(0.15) 0.20(0.30) 0.40 预震次数 - 12 20 30
下载: 导出CSV
表 3 各预震荷载对应下的动应力及动剪应力
Table 3. Dynamic stress and dynamic shear stress corresponding to each pre-dynamic loadin
PGA(g) 0.15 0.30 0.40 Τd(kPa) 4.56 9.13 12.17 σd(kPa) 9.12 18.26 24.34 注：据王谦等(2015).
下载: 导出CSV
表 4 预震处理前后干密度、孔隙比、饱和度对比
Table 4. Comparison of dry density, pore ratio and satu- ra tion before and after pre-dynamic treatment
初始含水量 2% 12% 预震前干密度(g/cm3) 1.49~1.52 1.63~1.65 预震后干密度(g/cm3) 1.492~1.522 1.65~1.67 预震前孔隙比 0.79~0.83 0.65~0.67 预震后孔隙比 0.78~0.82 0.64~0.66 预震前饱和度(%) 6.27~8.72 48.83~50.67 预震后饱和度(%) 6.28~8.73 49.45~51.31
下载: 导出CSV
表 5 初始含水量2%黄土试样偏应力峰值汇总
Table 5. Summary of peak deviatoric stress of loess sam- les with initial moisture content of 2%
PGA(g) 100(kPa) 150(kPa) 200(kPa) 0.00 70.00 81.31 89.36 0.15 68.04 76.59 85.82 0.30 62.95 72.09 82.96 0.40 53.86 63.00 75.96
下载: 导出CSV
表 6 初始含水量2%的CSL临界失稳线斜率
Table 6. Slope of CSL critical instability line with initial water content of 2%
试样 临界失稳线
的斜率KPGA=0.00 g 1.79 PGA=0.15 g 1.67 PGA=0.30 g 1.50 PGA=0.40 g 1.39
下载: 导出CSV
表 7 初始含水量2%黄土试样孔隙水压力稳定值汇总
Table 7. Summary of stable values of pore water pressure of loess sample with initial water content of 2%
PGA(g) 100 (kPa) 150 (kPa) 200 (kPa) 0.00 83.89 125.24 176.82 0.15 88.01 128.52 180.30 0.30 90.23 133.41 185.64 0.40 93.20 138.65 190.43
下载: 导出CSV
表 8 初始含水量12%黄土试样偏应力峰值汇总
Table 8. Summary of peak deviatoric stress of loess samples with 12% initial water content
PGA(g) 100(kPa) 150(kPa) 200(kPa) 0.15 87.91 114.74 134.48 0.30 92.79 119.38 140.02 0.40 105.05 125.99 150.74
下载: 导出CSV
表 9 初始含水量12%的CSL临界失稳线斜率
Table 9. Slope of CSL critical instability line with initial water content of 12%
试样 临界失稳线的斜率K PGA=0.15 g 1.28 PGA=0.30 g 1.56 PGA=0.40 g 1.73
下载: 导出CSV
表 10 初始含水量12%黄土试样孔隙水压力稳定值汇总
Table 10. Summary of stable values of pore water pressure of loess sample with initial water content of 12%
PGA(g) 100(kPa) 150(kPa) 200(kPa) 0.15 88.50 146.29 192.88 0.30 80.84 139.91 187.63 0.40 77.78 128.58 178.73
下载: 导出CSV
表 11 初始含水量2%和12%土样抗剪强度
Table 11. Shear strength of soil samples with initial water content of 2% and 12%
PGA(g) 内摩擦角
c(°)黏聚力
φ(kPa)初始含水量
2%试样0.00 18.64 18.22 0.15 17.16 16.74 0.30 14.86 13.85 0.40 12.32 10.53 初始含水量
12%试样0.15 18.98 20.35 0.30 19.86 23.72 0.40 24.27 25.11
下载: 导出CSV
-
An, L., Deng, J., Guo, P., et al., 2019. Correlation between Microscopic Parameters and Dynamic Elastic Modulus of Loess. Chinese Journal of Geotechnical Engineering, 41(Suppl. 2): 105-108(in Chinese with English abstract). Chen, J. B., Chen, X. W., Jing, X. J., et al., 2021. Ergodicity of Turbulence Measurements upon Complex Terrain in Loess Plateau. Scientia Sinica (Terrae), 51(2): 299-313(in Chinese). doi: 10.1360/SSTe-2020-0128 Chen, W. W., Liu, W., Wang, J., et al., 2019. Relationship between Saturation Degree and B Value for Loess. Rock and Soil Mechanics, 40(3): 834-842(in Chinese with English abstract). Cheng, G. Y., 2003. Study on the Correlation between Saturated Sand Shear Wave Velocity and Liquefaction Resistance(Dissertation). Tianjin University, Tianjin(in Chinese with English abstract). Cui, S. H., Pei, X. J., Huang, R. Q., et al., 2020. Excess Interstitial Water Pressure within Sliding Zone Induced by Strong Seismic Shaking: An Initiation Model of the Daguangbao Landslide. Chinese Journal of Rock Mechanics and Engineering, 39(3): 522-539(in Chinese with English abstract). Gao, G. R., 1981. Classification of Microstructures of Loess in China and Their Collapsibility. Science in China (Ser. A), 24(7): 962-974. Gao, G. R., 1996. The Distribution and Geotechnical Properties of Loess Soils, Lateritic Soils and Clayey Soils in China. Engineering Geology, 42(1): 95-104. https://doi.org/10.1016/0013⁃7952(95)00056⁃9 Jiang, M. J., Zhang, F. G., Hu, H. J., et al., 2014. Structural Characterization of Natural Loess and Remolded Loess under Triaxial Tests. Engineering Geology, 181: 249-260. https://doi.org/10.1016/j.enggeo.2014.07.021 Liu, W., Chen, W. W., Wang, Q., et al., 2020a. Effect of Pre⁃Dynamic Loading on Static Liquefaction of Undisturbed Loess. Soil Dynamics and Earthquake Engineering, 130: 105915. https://doi.org/10.1016/j.soildyn.2019.105915 Liu, W., Chen, W. W., Yang, F., 2021. Influence of Long⁃Term Seismic Effect on Mechanical Properties of Loess. China Earthquake Engineering Journal, 43(4): 965-976(in Chinese with English abstract). doi: 10.3969/j.issn.1000-0844.2021.04.965 Liu, W., Wang, Q., Lin, G. C., et al., 2020b. Effect of Pre⁃Dynamic Loading on Dynamic Liquefaction of Undisturbed Loess. Bulletin of Earthquake Engineering, 18(13): 5779-5806. https://doi.org/10.1007/s10518⁃020⁃00917⁃w Ma, L. N., Qi, S. W., Guo, S. F., et al., 2022a. Investigation on the Deformation and Failure Patterns of Loess Cut Slope Based on the Unsaturated Triaxial Test in Yan'an, China. Journal of Earth Science (in press). https://doi.org/10.1007/s12583-021-1554-4 Ma, P. H., Peng, J. B., Zhuang, J. Q., et al., 2022b. Initiation Mechanism of Loess Mudflows by Flume Experiments. Journal of Earth Science (in press). https://doi.org/10.1007/s12583-022-1660-y Mao, Y. D., Wang, Z. X., Pang, Z. B., 2021. Two Significant Stages in the Aridification of the Eastern Chinese Loess Plateau since 1.2 Ma. Earth Science, 46(1): 272-280(in Chinese with English abstract). Min, L. R., Fan, H., 1988. The Formation of the Loess Plateau in China and the Discussion on the Causes of Loess. Chinese Science Bulletin, 33(9): 690-692(in Chinese). doi: 10.1360/csb1988-33-9-690 Ministry of Housing and Urban Rural Development of the People's Republic of China, 2016. Code for Seismic Design of Buildings GB 50011-2010. China Construction Industry Press, Beijing(in Chinese). Ministry of Transport of the People's Republic of China, 2011. Code for Geological Investigation of Highway Engineering JTGC20-2011. People's Communications Press, Beijing(in Chinese). Pei, X. J., Zhang, X. C., Guo, B., et al., 2017. Experimental Case Study of Seismically Induced Loess Liquefaction and Landslide. Engineering Geology, 223: 23-30. https://doi.org/10.1016/j.enggeo.2017.03.016 Sun, J. Z., 2005. Loess Science (Part 1). Hong Kong Archaeological Society, Hong Kong(in Chinese). Sun, P., Li, R. J., Jiang, H., et al., 2017. Earthquake⁃Triggered Landslides by the 1718 Tongwei Earthquake in Gansu Province, Northwest China. Bulletin of Engineering Geology and the Environment, 76(4): 1281-1295. https://doi.org/10.1007/s10064⁃016⁃0949⁃4 Toyota, H., Takada S., 2017. Variation of Liquefaction Strength Induced by Monotonic and Cyclic Loading Histories. Journal of Geotechnical and Geoenvironmental Engineering, 143(4): 04016120. https://doi.org/10.1061/(asce)gt.1943⁃5606.0001634 Wang, J. D., Xu, Y. J., Zhang, D. F., et al. 2021. Study on the Effect of Loess Vibration on Permeability. Scientia Sinica (Terrae), 51(5): 763-782(in Chinese). doi: 10.1360/SSTe-2020-0293 Wang, Q., Wang, P., Wang, J., et al., 2015. Effect of Microstructure Properties on of Dynamic Residual Deformation Behavior of Saturated Loess. Chinese Journal of Geotechnical Engineering, 37(Suppl. 2): 143-147(in Chinese with English abstract). Wang, S. Y., Luna, R., Onyejekwe, S., 2016. Effect of Initial Consolidation Condition on Postcyclic Undrained Monotonic Shear Behavior of Mississippi River Valley Silt. Journal of Geotechnical and Geoenvironmental Engineering, 142(2): 04015075. https://doi.org/10.1061/(asce)gt.1943⁃5606.0001401 Wang, S. Y., Luna, R., Onyejekwe, S., 2015a. Postliquefaction Behavior of Low⁃Plasticity Silt at Various Degrees of Reconsolidation. Soil Dynamics and Earthquake Engineering, 75: 259-264. https://doi.org/10.1016/j.soildyn.2015.04.014 Wang, S. Y., Luna, R., Zhao, H. H., 2015b. Cyclic and Post⁃Cyclic Shear Behavior of Low⁃Plasticity Silt with Varying Clay Content. Soil Dynamics and Earthquake Engineering, 75: 112-120. https://doi.org/10.1016/j.soildyn.2015.03.015 Wang, S. Y., Luna, R., Yang, J. S., 2013. Postcyclic Behavior of Low⁃Plasticity Silt with Limited Excess Pore Pressures. Soil Dynamics and Earthquake Engineering, 54: 39-46. https://doi.org/10.1016/j.soildyn.2013.07.016 Wu, Z. J., Zhang, D., Wang, S. N., et al., 2020. Dynamic⁃Response Characteristics and Deformation Evolution of Loess Slopes under Seismic Loads. Engineering Geology, 267: 105507. https://doi.org/10.1016/j.enggeo.2020.105507 Xie, D. Y., Qi, J. L., Zhu, Y. L., 1999. Soil Structure Parameter and Its Relations to Deformation and Strength. Journal of Hydraulic Engineering, 30(10): 1-6(in Chinese with English abstract). doi: 10.3321/j.issn:0559-9350.1999.10.001 Yasuda, S., Harada, K., Ishikawa, K., et al., 2012. Characteristics of Liquefaction in Tokyo Bay Area by the 2011 Great East Japan Earthquake. Soils and Foundations, 52(5): 793-810. https://doi.org/10.1016/j.sandf.2012.11.004 Yasuda, S., Tohno, I., 1988. Sites of Reliquefaction Caused by the 1983 Nihonkai⁃Chubu Earthquake. Soils and Foundations, 28(2): 61-72. https://doi.org/10.3208/sandf1972.28.2_61 Zhang, Y., 2019. Study on the Evolution of Loess Structure and Its Constitutive Model in Acidic Environment (Dissertation). Xi'an University of Technology, Xi'an(in Chinese with English abstract). Zhu, Z. Y., 1992. Neotectonics and Neotectonic Movement of the Loess Plateau and Its Adjacent Regions. Quaternary Sciences, 12(3): 252-264(in Chinese with English abstract). Zhuang, J. Q., Peng, J. B., Xu, C., et al., 2018. Distribution and Characteristics of Loess Landslides Triggered by the 1920 Haiyuan Earthquake, Northwest of China. Geomorphology, 314: 1-12. https://doi.org/10.1016/j.geomorph.2018.04.012 Zhuang, Y., Xing, A. G., Cheng, Q. G., et al., 2020. Characteristics and Numerical Modeling of a Catastrophic Loess Flow Slide Triggered by the 2013 Minxian-Zhangxian Earthquake in Yongguang Village, Minxian, Gansu, China. Bulletin of Engineering Geology and the Environment, 79(1): 439-449. https://doi.org/10.1007/s10064⁃019⁃01542⁃x 安亮, 邓津, 郭鹏, 等, 2019. 黄土微观参数指标与动弹性模量关联度研究. 岩土工程学报, 41(增刊2): 105-108. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC2019S2028.htm 陈晋北, 陈霄文, 荆肖军, 等, 2021. 黄土高原复杂地形条件下湍流观测的各态历经性检验. 中国科学: 地球科学, 51(2): 299-313. https://www.cnki.com.cn/Article/CJFDTOTAL-JDXK202102009.htm 谌文武, 刘伟, 王娟, 等, 2019. 黄土饱和度与B值关系试验研究. 岩土力学, 40(3): 834-842. https://www.cnki.com.cn/Article/CJFDTOTAL-YTLX201903002.htm 程国勇, 2003. 饱和砂土剪切波速与抗液化强度相关性的研究(博士学位论文). 天津: 天津大学. 崔圣华, 裴向军, 黄润秋, 等, 2020. 强震过程滑带超间隙水压力效应研究: 大光包滑坡启动机制. 岩石力学与工程学报, 39(3): 522-539. https://www.cnki.com.cn/Article/CJFDTOTAL-YSLX202003008.htm 刘伟, 谌文武, 杨芳, 2021. 地震长期效应对黄土力学性质的影响. 地震工程学报, 43(4): 965-976. doi: 10.3969/j.issn.1000-0844.2021.04.965 毛永栋, 王治祥, 庞志斌, 2021. 黄土高原东部(山西阳曲)1.2 Ma以来黄土记录的两次显著干旱化事件. 地球科学, 46(1): 272-280. doi: 10.3799/dqkx.2019.278 闵隆瑞, 范蕙, 1988. 中国黄土高原的形成及其黄土成因的探讨. 科学通报, 33(9): 690-692. https://www.cnki.com.cn/Article/CJFDTOTAL-KXTB198809014.htm 孙建中, 2005. 黄土学(上篇). 香港: 香港考古学会. 王家鼎, 许元珺, 张登飞, 等, 2021. 黄土振动促渗效应研究. 中国科学: 地球科学, 51(5): 763-782. https://www.cnki.com.cn/Article/CJFDTOTAL-JDXK202105010.htm 王谦, 王平, 王峻, 等, 2015. 微结构特性对饱和黄土动残余变形的影响研究. 岩土工程学报, 37(增刊2): 143-147. https://www.cnki.com.cn/Article/CJFDTOTAL-YTGC2015S2029.htm 谢定义, 齐吉琳, 朱元林, 1999. 土的结构性参数及其与变形强度的关系. 水利学报, 30(10): 1-6. https://www.cnki.com.cn/Article/CJFDTOTAL-SLXB199910000.htm 张耀, 2019. 酸性环境下黄土结构的演变及其本构模型研究(博士学位论文). 西安: 西安理工大学. 中华人民共和国住房和城乡建设部, 2016. 《建筑抗震设计规范》, GB 50011-2010. 北京: 中国建筑工业出版社. 中华人民共和国交通运输部, 2011. 《公路工程地质勘察规范》, JTGC20-2011. 北京: 人民交通出版社. 朱照宇, 1992. 黄土高原及邻区新构造与新构造运动. 第四纪研究, 12(3): 252-264. https://www.cnki.com.cn/Article/CJFDTOTAL-DSJJ199203006.htm -
点击查看大图
计量
- 文章访问数: 580
- HTML全文浏览量: 543
- PDF下载量: 43
- 被引次数: 0
