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基于X-ray CT的古土壤孔裂隙识别与表征
李鑫1,2, 卢玉东1,2, 张晓周1,2, 卢阳春1,2, 杨亚慧1,2
1.长安大学 环境科学与工程学院, 陕西 西安 710054;2.旱区地下水文与生态效应教育部重点实验室, 陕西 西安 710054
摘要:
[目的] 对古土壤内部孔隙裂隙结构的形态、类型、孔径分布进行精确表征,为斜坡中古土壤水力学性质的研究提供重要依据。[方法] 利用X-ray CT对泾阳南塬S5古土壤原状试样进行扫描,利用VG studio Max和AVIZO三维可视化软件,经过滤波处理、阈值分割、三维重建得到了三维可视化数字古土壤模型,计算了二三维孔隙度,基于形状因子提取了古土壤中孔隙和裂隙并进行分类,提出了各类空隙的孔径表征算法。[结果] ①古土壤中孔裂隙并存,在空间上具有显著的垂向性和空间异质性,在空间形态上可由形状因子(SF)区分为裂隙(SF > 40.18)、枝杈状孔隙(7.01 < SF≤40.18)、长柱状孔隙(2.0 < SF≤7.01)、椭球状孔隙(1 < SF≤2)和球状孔隙(SF≤1);②大孔隙度(等效直径大于100 μm)为9.86%,占总孔隙度(41.18%)的23.94%,表明古土壤中以等效直径为100 μm以下的孔裂隙为主; ③孔径分布在0.1~5 mm之间,以0.1~0.7 mm为主,而体积贡献率上以0.7~1.0 mm为主,裂隙最大开度5.1 mm。[结论] 古土壤是一种以中小微孔隙为主,(特)大孔隙和(微)裂隙伴生的双重介质土体,X-ray CT和三维可视化重建技术为古土壤孔裂隙识别和表征提供了一种有效的途径。
关键词:  古土壤  X-ray CT  孔隙  裂隙  泾阳南塬
DOI:10.13961/j.cnki.stbctb.2018.06.035
分类号:
基金项目:长安大学研究生科研创新实践项目“基于工业CT的原状古土壤空隙识别与表达”(2018017)
Pore-fissure Identification and Characterization of Paleosol Based on X-ray Computed Tomography
LI Xin1,2, LU Yudong1,2, ZHANG Xiaozhou1,2, LU Yangchun1,2, YANG Yahui1,2
1.School of Environment Science and Engineering, Chang'an University, Xi'an, Shaanxi 710054, China;2.Key Laboratory of Subsurface Hydrology and Ecological Effects in Arid Region, Ministry of Education, Chang'an University, Xi'an, Shaanxi 710054, China
Abstract:
[Objective] Characterization of the shape, type and spatial distribution of pore-fissure structure in paleosol was conducted accurately in order to provide an important basis for the study of hydraulic properties of paleosol in slopes.[Methods] X-ray CT was used to scan the undisturbed samples of S5 paleosol at southern tableland of Jingyang County, Shaanxi Province. Three-dimensional digital paleosol model was established through filtering, thresholding and reconstruction by using 3D visualization software including VG studio Max and AVIZO. The two and three dimensional porosity were calculated, pores and fissures in paleosol were extracted and classified based on shape factors, and the characterization algorithms for various voids were proposed.[Results] ① The pores and fissures coexisted in paleosol, which was of significant verticality and spatial heterogeneity in space. The voids could be differentiated by the shape factors (SFs) into fissures (SF > 40.18), branching pores (7.01 < SF ≤ 40.18), long columnar pores (2.0 < SF ≤ 7.01), ellipsoidal pores (1 < SF ≤ 2), and spherical pores (SF ≤ 1) on spatial pattern; ② the macroporosity (the equal diameter larger than 100 μm) is 9.86%, accounting for 23.94% of the total porosity (41.18%), indicating that the voids with equal diameter smaller than 100 μm are dominant in paleosol; ③ the pore size distribution is between 0.1~5 mm, in which the pores within 0.1~0.7 mm are in the majority on count, and the pores within 0.7~1.0 mm are in the majority of volume contribution rate, and the maximum fissure opening is 5.1 mm.[Conclusion] Paleosol is a kind of double-medium soil with majority of micro, small, medium pores as well as special large pores or macropores accompanying micro fissures or fractures. In addition, X-ray CT and 3D visualization reconstruction technology provides an effective method for the identification and characterization of pore-fissure structures in paleosol.
Key words:  paleosol  X-ray computed tomography  pores  fissures  the southern tableland of Jingyang County