清华大学课题组发表“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”成果丨GDS空心圆柱扭剪系统应用实例

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：

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。

GDS空心圆柱扭剪试验系统HCA

*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 ε_q, (b) volumetric strain ε_v vs. deviatoric strain ε_q, (c) peak deviatoric stress q_max vs. σ′, (d) initial shear modulus G_i vs. σ?′, and (e) initial dilatancy D_i vs. σ?′.

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 τ_zθ – effective stress p′ and shear stress τ_zθ – shear strain γ_zθ relationships of intact specimen (CIU015), (c–d) shear stress τ_zθ – effective stress p′ and shear stress τ_zθ – shear strain γ_zθ 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 + aN_L??; R_L20 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 γ_u^max under CSR=0.15 and 0.25:(a) γ_u^max vs. cycle number N, (b) r_u^max vs. normalized cycle ratio N/N_L, along with the fitting curve following Baziar’s excess pore-pressure model.

Figure 14 Development of double-amplitude shear strain γ_DA under CSR = 0.15 and 0.25: (a) γ_DA vs. cycle number N, (b) γ_DA vs. maximum pore pressure ratio r_u^max, 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 τ_zθ – shear strain γ_zθ relationship of intact specimen, (b) shear stress τ_zθ – shear strain γ_zθ relationship of reconstituted specimen; (c) secant shear modulus G vs. cycle number N, and (d) G_j/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.

GDS空心圆柱扭剪试验系统 关键特点及优点

GDSHCA基于5Hz 的轴向动态系统性能示例

GDSHCA典型试验数据

轴向位移反馈控制

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