基于环剪试验的含钙质结核古土壤剪切特性

姜程程; 范文; 苑伟娜

doi:10.3969/j.issn.0258-2724.20190951

基于环剪试验的含钙质结核古土壤剪切特性

doi: 10.3969/j.issn.0258-2724.20190951

基金项目: 国家自然科学基金（41630634）；国家自然科学基金青年项目（41807238）

详细信息

作者简介:
姜程程（1991—），女，博士研究生，研究方向为地质灾害，E-mail：Irisjiang0603@163.com

通讯作者:
范文（1967—），男，教授，博士生导师，研究方向为地质工程、岩土工程，E-mail：fanwen@chd.edu.cn

中图分类号: TU411
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出版历程
- 收稿日期: 2019-09-30
- 修回日期: 2020-01-11
- 网络出版日期: 2020-03-12
- 刊出日期: 2021-08-15

Shear Properties of Paleosol Containing Calcareous ConcretionsBased on Ring Shear Tests

摘要

摘要: 含钙质结核古土壤在黄土滑坡的剪切带中广泛分布，影响滑坡的剪切特性. 通过固结排水环剪试验，改变轴应力大小，研究不同钙质结核含量下古土壤的剪切力学特性；基于对剪切破坏面的宏观结构分析，总结并提出剪切破坏面的“一”型和“U”型两种破坏形态及平稳、过渡、波动3种破坏模式. 研究结果表明：在低轴应力下，应力-位移曲线均为软化型，具有明显的残余强度特性，随钙质结核含量增大，应变软化特性变弱；在高轴应力下，则表现为硬化型；钙质结核颗粒能增大土的剪切强度、摩擦角，减小黏聚力；剪切带厚度与钙质结核含量正相关，与 D50 负相关；在大位移剪切作用下，颗粒会发生破碎，通过对剪切前后粒径分析，确定了钙质结核主要破碎区间为3～5 mm，破碎率为19.5%～55.5%；古土壤由 0.01～0.05 mm颗粒破碎为 0.002～0.010 mm的较小颗粒.
- 含钙质结核古土壤 /
- 环剪试验 /
- 残余强度 /
- 剪切特性
Abstract: Paleosol containing calcareous concretion is widely distributed in the shear zone of loess landslides and affects the shear failure characteristics of landslides. Based on ring shear tests, the shear characteristics of paleosol with different contents of calcareous concretions under different normal stresses were discussed, and the test results were analyzed from macro-and micro-aspects. The results indicate that under low axial (normal) stress, the stress-displacement curves are of softening type and have obvious residual strength characteristics. With the increase of calcium nodule content, the strain softening characteristics become weak. Under high axial (normal) stress, the stress-displacement curves show strain hardening. Calcareous nodule particles can increase the shear strength and peak friction angle of soil and reduce the cohesion. The thickness of shear band is positively correlated with the content of calcareous concretions and negatively correlated with D50. Particle crushing occurred under the larger deformation. According to the particle size distribution analysis before and after shearing, the breakage of calcareous concretions mainly occurred to particles in the size range of 3−5 mm, with a breakage percentage of 19.5%−55.5%, and the paleosol was broken from 0.01−0.05 mm into smaller particles of 0.002−0.010 mm. Based on macroscopic observation and mechanical analysis of shear failure surfaces, all samples can be divided into two groups with “—” and “U” failure surface patterns, respectively, and three failure modes, including sliding shear mode, turbulent and transitional shear mode.
- paleosol containing calcareous concretions /
- ring shear tests /
- residual strength /
- shear behavior

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图 1 SRS-150 环剪仪

Figure 1. Ring shear apparatus of type SRS-150

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图 2 含钙质结核古土壤

Figure 2. Paleosol containing calcareous concretions

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图 3 $\sigma $ = 90 kPa时试样的环剪试验曲线

Figure 3. Ring shear test curve of sample at $\sigma $ = 90 kPa

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图 4 $\sigma $ = 270 kPa时试样的环剪试验曲线

Figure 4. Ring shear test curve of sample at $\sigma $ = 270 kPa

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图 5 $\sigma $ = 90 kPa时试样的$ {R}_{{\rm{s}}} $与$ {R}_{{\rm{t}}} $拟合

Figure 5. Fitting curves of residual shear strength R_s and peak strength R_t versus calcareous concretion content at $\sigma $ = 90 kPa

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图 6 试样的环剪试验曲线

Figure 6. Ring shear test curve

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图 7 试样黏聚力与摩擦角随剪切位移的变化

Figure 7. Change of cohesion and internal friction angle with shear displacement of sample

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图 8 试样纵剖面剪切破坏形态

Figure 8. Shear failure forms of longitudinal profile

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图 9 $\sigma $ = 90 kPa 时剪切完成后的横剖面破坏形态

Figure 9. Typical failure patterns after shearing at $\sigma $ = 90 kPa

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图 10 剪切带厚度随轴应力的变化

Figure 10. Variation of shear band thickness with normal stress

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图 11 剪切前后古土壤颗粒级配

Figure 11. Gradation diagram of paleosol before and after shearing

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表 1 土样物性参数表

Table 1. Basic physical properties of soil specimen

参数	含水率/%	密度/（g•cm⁻³）	干密度/（g•cm⁻³）	液限 w	塑限 w_p	塑性指数 I_p	土粒比重 G_s
取值	21.27	1.67	1.44	28.1	19.3	8.8	2.71

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表 2 S₂古土壤粒径分布

Table 2. Particle size distribution of S₂ paleosol %

粒组	黏粒组/mm		粉粒组/mm		砂粒组/mm
粒组	细（胶粒）（< 0.002）	粗[0.002～0.005）	细[0.005～0.010）	粗[0.010～0.050）	级细[0.050～0.075）	细[0.075～0.100]
取值	18.78	9.83	18.22	46.78	3.86	0.36

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表 3 试验方案与分组表

Table 3. Test plan and group table

试验编号	轴应力/kPa	C/%
1-1、1-2、1-3	90	0、4、8、12
2-1、2-2、2-3	180
3-1、3-2、3-3	270

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表 4 $\sigma = 90 \;{\rm{kPa}}$时试样的强度与剪切位移的关系

Table 4. Relationship between strength and shear displacement at $\sigma = 90 \;{\rm{kPa}} $

C/%	R_s/kPa	R_s 差/kPa	至 R_t 所需位移/mm	至 R_s 所需位移/mm
0	72.5	7.0～7.2	16.1～17.1	21.4～21.7
4	80.7	6.2～6.6	17.6～18.1	23.0～23.6
8	91.9	5.1～5.9	18.8～20.1	36.8～37.9
1	94.5	2.2～1.8	21.3～21.9	41.9～42.1

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表 5 不同钙质结核含量下试样的软化系数

Table 5. Softness factor of samples tested with different contents of calcareous concretions

C/%	R_c/kPa	R_s/kPa	软化系数
0	79.8	65.5	0.180
4	87.1	80.7	0.073
8	97.1	91.9	0.053
12	98.3	94.5	0.039

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表 6 抗剪强度指标

Table 6. Shear strength indexes

参数	C /%
参数	0	4	8	12
φ/（°）	21.23	23.67	24.22	26.80
c/kPa	14.50	14.51	14.43	14.28

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表 7 样品的矿物成分

Table 7. Mineral proportions of samples %

矿物成分	古土壤	钙质结核
石英+长石	71.0	27.9
方解石	13.2	65.6
黏土矿物	13.5	6.5
其它	2.3	0

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表 8 剪切前后钙质结核粒径分布

Table 8. Size distribution of particles before and after shearing of samples %

状态	轴应力/kPa	粒组（粗）/mm		砾粒组（细）/mm
状态	轴应力/kPa	< 1	[1～2)	[2～3)	[3～4)	[4～5]
剪切前	0	5.20	18.50	41.34	15.15	19.81
	90	5.80	18.40	40.76	14.90	20.14
	180	5.60	18.70	41.26	16.79	17.65
	270	5.50	18.40	41.78	15.99	18.33
剪切后	0	5.80	18.40	41.67	15.74	18.39
	90	6.70	19.80	42.83	16.90	13.77
	180	7.90	23.70	43.26	13.79	11.35
	270	8.50	29.40	47.78	10.36	3.96

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