Structural damage effect on dynamic shear modulus of Zhanjiang clay and quantitative characterization
-
摘要: 湛江黏土是一种具有高结构强度的灵敏性黏土,其强度包络线在固结围压达到结构屈服应力时存在明显转折,为了考察小应变条件下该黏土的动剪切模量随围压水平演化规律,开展了原状样与重塑样在不同围压水平下的共振柱试验与三轴CU试验,探讨考虑土体结构性损伤影响的动剪切模量表征方法。结果表明,重塑土最大动剪切模量Gmax随有效围压的变化可用Hardin公式很好表征,而原状土Gmax随有效围压的变化呈现先增大后减小特征,其转折点对应围压大于结构屈服应力,但最大动剪切模量与不排水剪切强度比值或经孔隙比函数归一化后的最大剪切模量随有效围压变化的转折特征点与结构屈服应力相当。出现上述现象的缘由在于该黏土Gmax同时受土体压硬性的正效应与结构损伤的负效应双重影响,当固结压力小于结构屈服压力时,正效应占主导,反之则相反。针对Hardin公式未考虑结构性损伤的影响与难以延伸极端应力水平的不足,提出具有更广适宜性的描述模式。基于不同固结压力下该黏土的静刚度与微观结构演变性状,阐明了结构性损伤对其动剪切模量影响的物理机制,并间接印证了提出表征公式的合理性。
-
关键词:
- 湛江黏土 /
- 动剪切模量 /
- 结构损伤 /
- 共振柱试验 /
- Hardin改进公式
Abstract: The Zhanjiang clay is a kind of sensitive clay with high structural strength, whose failure envelope has a significant breakpoint when the confining pressure reaches the structural yield stress. The resonant column tests and CU triaxial tests are performed on undisturbed and remoulded specimens to investigate the evolution rules of dynamic shear modulus with confining pressure under small strain, and the characterization method for dynamic shear modulus considering the structural damage effect is also discussed. The results show that the values of Gmax of remoulded and undisturbed specimens with the confining pressure are different: the former can be well described by the formula of Hardin, while the latter increases initially then decreases; and confining pressure at the the turning points are higher than the yield stress, however, the turning points of the ratio of shear modulus to shear strength or the normalized shear modulus by the void ratio function with confining pressure are close to the yield stress. The reason is that the values of Gmax of the structured clay are influenced by both the positive effect of compressive hardening and the negative effect of structural damage, and the former is predominant when the confining pressures are less than the yield stress, otherwise it is opposite. Focusing on the deficiencies of the formula of Hardin without considering the structural damage effect and difficultly extending to the extreme stress level, a widely suitable expression mode is proposed. Based on the change of static rigidity and microstructure of Zhanjiang clay with consolidation pressure, the physical mechanism of influence of structural damage on dynamic shear modulus is illustrated, and the rationality of the proposed formula is confirmed indirectly. -
[1] KU T, MAYNE P W. Yield stress history evaluated from paired in-situ shear moduli of different modes[J]. Engineering Geology, 2013, 152(1): 122-132. [2] SENETAKIS K, ANASTASIADIS A, PITILAKISB K, et al. The dynamics of a pumice granular soil in dry state under isotropic resonant column testing[J]. Soil Dynamics and Earthquake Engineering, 2013, 45: 70-79. [3] HARDIN B O, BLACK W L. Vibration modulus of normally consolidated clay[J]. Journal of Soil Mechanics and Foundations Division, ASCE 1968, 94(2): 453-69. [4] PARK D. Evaluation of dynamic soil properties: strain amplitude effects on shear modulus and damping ratio[M]. Ithaca: Cornell University, 1998. [5] KAGAWA T. Moduli and damping factors of soft marine clays[J]. Journal of Geotechnical Engineering, 1992, 118(9): 1360-1375. [6] 沈珠江. 软土工程特性和软土地基设计[J]. 岩土工程学报, 1998, 20(1): 100-111. (SHEN Zhu-jiang. Engineering properties of soft soils and design of soft ground[J]. Chinese Journal of Geotechnical Engineering, 1998, 20(1): 100-111. (in Chinese)) [7] 谭罗荣, 孔令伟. 特殊岩土工程地质学[M]. 北京: 科学出版社, 2006. (TAN Luo-rong, KONG Ling-wei. Engineering behavior of special rock and soil[M]. Beijing: Science Press, 2006. (in Chinese)) [8] ZHANG X W, KONG L W, LI J. An investigation of alterations in Zhanjiang clay properties due to atmospheric oxidation[J]. Géotechnique, 2014, 64(12): 1003-1009. [9] 孔令伟, 张先伟, 郭爱国, 等. 湛江强结构性黏土的三轴排水蠕变特征[J]. 岩石力学与工程学报, 2011, 30(2): 365-372. (KONG Ling-wei, ZHANG Xian-wei, GUO Ai-guo, et al. Creep behavior of Zhanjiang strong structured clay by drained triaxial test[J]. Chinese Journal of Rock Mechanics and Engineering, 2011, 30(2): 365-372. (in Chinese)) [10] 臧 濛, 孔令伟, 郭爱国. 静偏应力下湛江结构性黏土的动力特性[J]. 岩土力学, 2017, 38(1): 33-40. (ZANG Meng, KONG Ling-wei, GUO Ai-guo. Effects of static deviatoric stress on dynamic characteristics of Zhanjiang structured clay[J]. Rock and Soil Mechanics, 2017, 38(1): 33-40. (in Chinese)) [11] 沈珠江. 理论土力学[M]. 北京: 中国水利水电出版社, 2000. (SHEN Zhu-jiang. Theoretical soil mechanics[M]. Beijing: China Water & Power Press, 2000. (in Chinese))
计量
- 文章访问数: 383
- HTML全文浏览量: 7
- PDF下载量: 381
下载:
