清华大学课题组12月5日在岩土工程学术期刊《Engineering Geology》发表了题为“Experimental investigation and analysis of monotonic and cyclic behaviour of a natural sand in intact and reconstituted states”（天然结构性砂土原状与重塑状态单调及循环力学特性的试验研究）的学术文章。本研究联合运用空心圆柱扭剪仪、冻结-切削制样系统及X射线CT平台，对深井原状砂与重塑砂开展单调、循环和各向异性剪切试验，提出“颗粒互锁主导”模型，系统揭示天然结构-力学耦合机制，证实原状砂剪切模量与抗液化强度均为重塑样的两倍，为沉积型砂土工程性状评价提供直接依据。
https://doi.org/10.1016/j.enggeo.2025.108497
*论文版权归原作者和出版方所有，本文仅为学习交流。
以下是对这项成果的简要介绍：
论文摘要
地质沉积过程中形成的砂土结构对其力学性能起关键控制作用，直接影响工程设计。然而，获取原状样品的困难阻碍了对原位砂土行为的全面认识。
本研究在深井沉井内取得高质量原状样，现场冷冻并采用专用装置精确削样；同时以相同级配和密度的风干雨落法制备重塑样进行对比。利用空心圆柱扭剪仪系统开展单元试验，比较两类试样在单调与循环荷载下的响应；进一步通过各向异性单调试验、无约束干燥试验及X射线CT扫描，揭示原状砂独特力学特性的根源。
结果表明：单调加载下，原状样剪切模量超过重塑样两倍，初始剪胀显著增强，而峰值强度相当；不排水循环加载时，原状样抗液化能力为重塑样的两倍以上；值得注意的是，两类试样在不排水循环过程中超孔压的归一化累积及其与剪应变的关系几乎一致。排水循环加载下，原状样收缩性更弱、模量更高。各向异性力学模式的差异对整体性能差异贡献有限，颗粒互锁才是控制该砂土行为的主导因素。本研究可为具有相似地质成因的工程场地砂土力学行为提供参考。
试验设备
本研究使用了GDS空心圆柱扭剪试验系统HCA等设备。
空心圆柱系统通过控制施加到土样上的三个主应力的大小和方向，可以给土样施加十分复杂的应力路径。可选动态和静态的系统以及局部的小应变测量。GDS空心圆柱系统可用于很多试验，包括本构模型的验证，地震活动中土体动力响应研究等。
相关图表
*图表为论文截图，版权归论文原作者和出版方所有，本文仅为学习交流。
Figure 1 Hollow cylinder torsional shear apparatus at Tsinghua University
Figure 3 Schematic diagram of the process for obtaining the hollow cylindrical intact specimen: (a) schematic cross-section of the site profile, (b) sand blocks packed in containers with multi-layer cushioning, (c) sand block segmented into four cuboids, (d) specimen trimmed into an eight-sided prism, (e) trimming of outer diameter and height to desired dimensions, and (f) trimming of inner diameter to desired dimensions.
Figure 4 Photos of the trimming device and trimmed specimens: (a) Electrical lathe used for trimming frozen specimens, (b–c) dimensional measurements of the trimmed specimen, and (d) the specimen with inner and outer membranes.
Figure 6 Air pluviation apparatus for hollow cylindrical specimen preparation and its performance: (a) schematic of the pluviation setup, (b) relationship between aperture size and specimen density.
Figure 8 SEM images of intact and reconstituted specimen particles across gradation ranges: 0.5–1 mm, 0.355–0.5 mm, 0.2–0.355 mm, 0.2–0.25 mm, 0.15–0.2 mm, 0.075–0.15 mm, and <0.075 mm. (a–g) Intact specimen; (h–n) reconstituted specimen.
Figure 9 Loading stress paths: (a) triaxial test, (b) monotonic anisotropy test, and (c) cyclic test.
Figure 10 Comparison between triaxial compression test results on intact and reconstituted specimens: (a) deviator stress q vs. deviatoric strain εq, (b) volumetric strain εv vs. deviatoric strain εq, (c) peak deviatoric stress qmax vs. σ₃′, (d) initial shear modulus Gi vs. σ₃′, and (e) initial dilatancy Di vs. σ₃′.
Figure 11 The effective stress path and shear stress–strain hysteresis curve for specimens subjected to undrained cyclic shearing with CSR of 0.15: (a–b) shear stress τzθ – effective stress p′ and shear stress τzθ – shear strain γzθ relationships of intact specimen (CIU015), (c–d) shear stress τzθ – effective stress p′ and shear stress τzθ – shear strain γzθ relationships of reconstituted specimen (CRU015).
Figure 12 Comparison of liquefaction resistance for intact and reconstituted specimens. (The data points represent experimental results, and the curves are fitted using the equation CSR = c + aNL⁻ᵇ; RL20 denotes the cyclic stress ratio required to generate an excess pore-pressure ratio of 0.95 in 20 loading cycles.)
Figure 13 Development of maximum excess pore pressure ratio γumax under CSR=0.15 and 0.25:(a) γumax vs. cycle number N, (b) rumax vs. normalized cycle ratio N/NL, along with the fitting curve following Baziar’s excess pore-pressure model.
Figure 14 Development of double-amplitude shear strain γDA under CSR = 0.15 and 0.25: (a) γDA vs. cycle number N, (b) γDA vs. maximum pore pressure ratio rumax, with the fitted curve based on the empirical relationship proposed by Chen et al. (2020).
Figure 15 Volumetric strain of the intact and reconstituted specimen under drained cyclic shearing: (a) CSR = 0.7, (b) CSR = 0.25.
Figure 16 Shear stress–strain responses of intact and reconstituted specimen under drained cyclic shearing with CSR = 0.7 for 30 cycles: (a) shear stress τzθ – shear strain γzθ relationship of intact specimen, (b) shear stress τzθ – shear strain γzθ relationship of reconstituted specimen; (c) secant shear modulus G vs. cycle number N, and (d) Gj/G1 vs. cycle number N.
Figure 17 Comparison of deviatoric stress ratio – deviatoric strain relationships for ISs and RSs at various drained loading directions: (a) 0°, (b) 30°, (c) 60°, and (d) 90°, as well as the comparison of volumetric strain – deviatoric strain relationships for ISs and RSs at various drained loading directions: (e) 0°, (f) 30°, (g) 60°, and (h) 90°.
Figure 19 Comparison of deviatoric stress ratio – deviatoric strain relationships for ISs and RSs at various undrained loading directions: (a) 0°, (b) 30°, (c) 60°, and (d) 90°, as well as the effective stress paths (deviatoric stress – mean effective stress relationships) for ISs and RSs at various undrained loading directions: (e) 0°, (f) 30°, (g) 60°, and (h) 90°.
Figure 20 Comparison of the anisotropic degree of intact and reconstituted specimen in undrained tests: (a) peak strength, (b) maximum excess pore-water pressure vs. principal stress direction.
Figure 22 Self-standing test of intact (IS) and reconstituted (RS) specimens: (a) the frozen specimens stand; (b) the reconstituted specimen collapses after drying; (c) the intact specimen collapses after a very gentle disturbance.
Figure 23 X-ray tomography visualization of particle and contact identification: (a–b) Reconstructed images of the intact and reconstituted specimens; (c–d) Vertical y–z sections showing detected contacts for each specimen type.
研究亮点
创新取样技术获取保持原位结构的原状砂
对原状与重塑砂开展系统的单调与循环试验
原状砂模量、剪胀性及抗液化能力显著更高
原状与重塑砂各向异性特征总体相似
颗粒互锁被确认为原状砂力学行为的主控因素
