南海北部陆坡区深海软土宏微观特征与力学特性研究

蒋明镜; 刘阿森; 李光帅

doi:10.11779/CJGE20220081

南海北部陆坡区深海软土宏微观特征与力学特性研究 English Version

蒋明镜^{1, 2, 3,},
刘阿森²,
李光帅²

1.
苏州科技大学土木工程学院, 江苏苏州 215009
2.
天津大学建筑工程学院, 天津 300350
3.
同济大学土木工程学院地下建筑与工程系, 上海 200092

基金项目:

国家自然科学基金重大项目 51890911

国家重点研发计划项目 2019YFC0312304

海南省重点研发计划项目 ZDYF2021SHFZ264

详细信息

作者简介:
蒋明镜(1965—)，男，教授，博士生导师，主要从事天然结构性黏土、砂土、非饱和土、太空土和深海能源土宏微观试验、本构模型和数值分析研究。E-mail: mingjing.jiang@mail.usts.edu.cn

中图分类号: TU447
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出版历程
- 收稿日期: 2022-01-16
- 网络出版日期: 2023-03-15
- 刊出日期: 2023-02-28

Macro- and micro-characteristics and mechanical properties of deep-sea sediment from South China Sea

1.
School of Civil Engineering, Suzhou University of Science and Technology, Suzhou 215009, China
2.
School of Civil Engineering, Tianjin University, Tianjin 300350, China
3.
Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China

摘要

摘要: 针对中国南海深海软土的研究对于南海资源开发利用具有重要意义。由于取样困难，目前针对深海软土的研究较少，另外深海软土赋存环境特殊，其特性与常规软土有显著差异。通过基础物化特性试验、环境电镜扫描（ESEM）、一维固结及蠕变试验、常规三轴试验、对南海深海软土的材料特性、微观结构、压缩及蠕变特性、三轴剪切特性进行研究分析。试验结果表明该深海软土具有高含水率、低密度、高孔隙比、高饱和度的特点，为高液限粉土，矿物成分中以方解石和伊利石为主。电镜扫描结果显示该深海软土呈片状层理堆积结构，存在疏松架空骨架和贯通孔隙，能储存大量孔隙水，土体中存在生物残骸。一维固结及蠕变试验中，深海软土压缩性强，次固结变形大，固结系数随着竖向压力的增加而减小，次固结系数随着竖向压力的增加先增大后减小。在固结不排水三轴试验中，该深海软土表现出应变硬化特征，有效应力路径呈现先加载后卸载的特征，固结排水三轴试验中，应变硬化的特征更显著，有效应力路径呈现持续加载的特征。
- 深海 /
- 软土 /
- 微观结构 /
- 压缩 /
- 剪切 /
- 固结试验 /
- 三轴试验
Abstract: The research on deep-sea sediment is meaningful for the exploitation and utilization of resources in the South China sea. Because of the difficulties in getting the natural deep-sea sediment, there are scarce researches on it. Besides, the mechanical properties and microstructures of the deep-sea sediment are different from the ordinary soft soil due to the unique geological environment. In this study, the basic material tests, ESEM tests, oedometer tests, 1D creep tests and conventional triaxial tests are conducted to investigate the material properties, microstructures, compression and creep characteristics and shear strengths of the deep-sea sediment. As shown in the results, the deep-sea sediment is a kind of silt with a high liquid limit, high water content, low bulk density, large void ratio and high saturation. The analysis of mineral composition shows calcite and illite are abundant. The micro-pictures show a lamellar layered stacked structure with loose skeleton and large pores, which attributes to the large void ratio and high water content, and there are some biological remains. In the oedometer and 1D creep tests, the deep-sea sediment shows high compressibility and large secondary consolidation deformation. The consolidation coefficient decreases with the vertical pressure, while the secondary consolidation coefficient ascends with the vertical pressure and then decreases after reaching the peak value. In the conventional triaxial tests, the deep-sea sediment shows strain hardening. The stress path from the consolidated undrained shear tests shows both loading and unloading processes, while only the loading process is found in the consolidated drained shear tests.
- deep sea /
- soft soil /
- microstructure /
- compression /
- shearing /
- oedometer test /
- triaxial test

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图 1 原状深海软土及各试验用土的含水率及在PVC管中的位置

Figure 1. Pictures of natural deep-sea sediment and its water contents in different areas

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图 2 原状深海软土环境电镜扫描图片

Figure 2. SEM images of microstructure of natural deep-sea sediment

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图 3 孔隙比与竖向压力lgp关系

Figure 3. Void ratio versus vertical pressure (lgp)

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图 4 各级荷载下应变与时间lgt关系

Figure 4. Strain versus time (lgt) under different vertical pressures

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图 5 应力-应变等时曲线

Figure 5. Stress-strain relation curves at different time

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各级荷载下试样高度和时间( $\sqrt t$ )的关系

Height of sample versus time ( $\sqrt t$ ) under different vertical pressures

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图 7 不同软土固结系数与竖向压力的关系曲线

Figure 7. Consolidation coefficient versus vertical pressure of different soils

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图 8 各级荷载下孔隙比和时间(lgt)的关系

Figure 8. Void ratio versus time (lgt) under different vertical pressures

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图 9 不同软土次固结系数和竖向压力的关系

Figure 9. Secondary consolidation coefficient versus vertical pressure of different soils

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图 10 lgp-lgp/lgC_α关系

Figure 10. lgp-lgp/lgC_α relation

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图 11 CU中不同围压下偏应力-应变曲线

Figure 11. Deviatoric stress-strain relation curves under different confining pressures in CU tests

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图 12 CU中不同围压下孔压-应变曲线

Figure 12. Pore pressure-strain relation curves under different confining pressures in CU tests

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图 13 CU中有效应力路径

Figure 13. Effective stress paths under different confining pressures in CU tests

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图 14 CD中不同围压下偏应力-应变曲线

Figure 14. Deviatoric stress-strain relation curves under different confining pressures in CD tests

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图 15 CD中不同围压下孔压-应变曲线

Figure 15. Pore pressure-strain relation curves under different confining pressures in CD tests

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图 16 CD中有效应力路径

Figure 16. Effective stress paths under different confining pressures in CD tests

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图 17 CU和CD中峰值偏应力和围压的关系

Figure 17. Peak deviatoric stresses under different confining pressures in CU and CD tests

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表 1 土体基本物化特性

Table 1 Basic material properties of soils

文献	水深/m	含水率/%	天然密度/(g·cm^-3)	相对质量密度	孔隙比	干密度/(g·cm^-3)	pH	有机质含量/%	饱和度/%
刘文涛^[17]	400~2500	110.90	1.41	2.73	3.11				97.11
蒋明镜等^[18]	1187	74.20	1.53	2.66	2.03	0.88	—	—	97.40
Wang等^[20]	—	96.70	—	2.71	—	—	—	—	—
本文	1552	137.87	1.35	2.71	3.79	0.57	7.7	16.53	98.58

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表 2 土体界限含水率及粒径组成

Table 2 Limit water contents and grain-size distribution

文献	液限 w_L/%	塑限 w_P/%	塑性指数 I_P	液性指数 I_L	土样分类	砂砾		粉粒	黏粒
文献	液限 w_L/%	塑限 w_P/%	塑性指数 I_P	液性指数 I_L	土样分类	2~0.25 mm	0.25~0.075 mm	0.075~0.005 mm	＜0.005 mm
刘文涛^[17]	85.07	44.68	40.40	1.64	MH(86)；CH(4)	1.49	1.83	59.44	35.65
蒋明镜等^[18]	60.20	40.90	19.30	1.71	MH	3.91	4.79	58.80	32.50
Wang等^[20]	92.10	14.20	77.90	1.06	CH	0	0.13	69.20	30.60
本文	73.06	57.29	15.77	5.11	MH	0	0	66.90	33.10
注：MH代表高液限粉土，CH代表高液限黏土；括号里数字代表试样个数。

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表 3 土体矿物成分

Table 3 Mineral composition

非黏土矿物含量/%					黏土矿物含量/%
石英	钾长石	斜长石	方解石	石盐	蒙脱石	伊利石	高岭石	绿泥石
21.0	1.6	8.4	25.3	3.0	4.1	21.5	7.2	7.9

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表 4 不同土体压缩指标对比

Table 4 Compression parameters of different soils

位置	文献	压缩指数 C_c	回弹指数 C_s	压缩系数 a_1-2/(MPa^-1)	压缩模量 E_{s, 1-2}/MPa
深海	刘文涛等^[17]			2.28~3.57	1.16~1.64
	蒋明镜等^[18]	0.630	0.056	1.88	—
	蒋明镜等^[18]	0.610	0.096	1.90	—
	Wang等^[20]	0.450	—	1.29	1.80
	本文	1.317	0.076	4.05	0.92
近海	张惠明等^[7]	—	—	1.01~2.30	—
近海	陈晓平等^[9]	—	—	0.83	—

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表 5 不同地区软土C_c/C_α范围

Table 5 C_c/C_α of different soft soils from different areas

文献	土体类型	C_c/C_α范围
天津^[6]	淤泥质黏土	0.0065~0.0143
宁波^[10]	淤泥质/粉质黏土	0.00156~0.0567
大连^[12]	淤泥质黏土	0.052~0.065
广州^[13]	软土	0.027~0.037
本文	粉质黏土	0.0343~0.0632

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表 6 抗剪强度指标

Table 6 Strength parameters obtained by triaxial tests

类型	总黏聚力 c/kPa	总内摩擦角 φ/(°)	有效黏聚力 $c'$ /kPa	有效内摩擦角 $\varphi '$ /(°)
CU	8.33	15.25	12.75	25.34
CD	19.84	23.89	16.92	25.20
刘文涛等^[17] CU	2.33~4.5	10.78~14.57	1.33~3.5	20~27.2
蒋明镜等^[18] CU	3.45	32.20	1.99	38.20

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