漠河冻土模拟岩样三轴力学试验及强度多元回归分析

牛成成; 侯绪田; 李阳

doi:10.11911/syztjs.2021049

漠河冻土模拟岩样三轴力学试验及强度多元回归分析

1.
中国石化石油工程技术研究院，北京 102206
2.
中国石油大学（华东）石油工程学院，山东青岛 266580

基金项目: 国家重点研发计划课题“钻井工艺及井筒工作液关键技术研究”（编号：2016YFC0303303）资助

详细信息

作者简介:
牛成成（1986—），男，山东临沂人，2009年毕业于中国石油大学（北京）石油工程专业，2012年获中国石油大学（北京）油气井工程专业硕士学位，副研究员，主要从事钻井技术研究。E-mail：niucc.sripe@sinopec.com。

中图分类号: TE21
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出版历程
- 收稿日期: 2020-10-27
- 修回日期: 2021-04-01
- 网络出版日期: 2021-05-07
- 刊出日期: 2021-06-15

Triaxial Mechanical Tests and Multiple Regression Strength Analysis of Simalted Frozen Soil Sample from Mohe

1.
Sinopec Research Institute of Petroleum Engineering, Beijing, 102206, China
2.
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong, 266580, China

摘要

摘要: 在冻土地层钻探过程中，不合理的作业方案可能引发井壁坍塌、井口沉降等一系列工程问题，而弄清深层冻土力学演化规律是施工设计的基础。为此，用漠河冻土重塑了不同深度冻土的模拟岩样，开展了不同围压、温度条件下的冻土三轴力学试验，分析了不同条件下的冻土应力–应变曲线特征。通过多元回归方法对冻土强度进行了统计分析，进一步构建了冻土强度准则。研究发现：模拟岩样的应力–应变曲线整体呈非线性变形特征，在冻结状态下，温度、围压对土体强度起主要作用；非冻结状态下，其强度由围压和土体深度决定；冻土强度由土体骨架强度和孔隙中冰的胶结强度构成，其骨架强度满足Mohr-Coulomb强度准则，内聚力、内摩擦角随深度增加而增大；孔隙中冰的胶结强度随环境温度降低而增强，随围压增加呈先增强后减弱的趋势。基于此构建了漠河冻土强度准则，验证结果表明，可以较好地表征漠河冻土融化–冻结状态下的强度分布。
- 深层冻土 /
- 低温力学试验 /
- 非线性变形 /
- 多元回归分析 /
- 强度准则 /
- 漠河
Abstract: Improper drilling schemes may cause engineering problems such as wellbore collapse and wellhead subsidence during the drilling of permafrost. The research on mechanical evolution of deep frozen soil paves the way for construction design. In this paper, soil samples at different depths were remolded with the frozen soil from Mohe, and triaxial mechanical tests were carried out under different confining pressures and temperatures to analyze the characteristics of stress–strain curves of frozen soil under different conditions. The strength of frozen soil was statistically studied by multiple regression analysis, and the strength criterion for it was further established. The research results showed that the stress–strain curves of the frozen soil samples presented nonlinear deformation behavior on the whole. In its frozen state, soil strength was controlled mainly by temperature and confining pressure while it was dominated by confining pressure and soil depth in its non-frozen state. In addition, frozen soil strength was composed of the strength of soil skeleton and the cementing strength of ice in pores. The strength of soil skeleton satisfies the Mohr-Coulomb criteria, and the cohesion and internal friction angle increases with soil depth. The cementing strength of ice in pores grows with the decline of ambient temperature, and increases and then decreases as the confining pressure increases. On this basis, the strength criterion for Mohe frozen soil was established, and the verification results proved that it can well characterize the strength distribution of Mohe frozen soil in the melt and frozen state.
- deep frozen soil /
- low-temperature mechanical test /
- nonlinear deformation /
- multiple regression analysis /
- strength criteria /
- Mohe

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图 1 600.00 m深处冻土模拟岩样的应力–应变曲线

Figure 1. Stress–strain curves of frozen soil samples at a depth of 600.00 m

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图 2 冻土低温三轴力学试验强度散点分布

Figure 2. Scatter plots of frozen soil strength based on low-temperature triaxial mechanical test

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图 3 冻土常温三轴力学试验强度散点分布

Figure 3. Scatter plots of frozen soil strength based on triaxial mechanical test at room temperature

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图 4 不同深度融化土的莫尔圆

Figure 4. Mohr circles of melt soil at different depths

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图 5 不同深度土体的内聚力和内摩擦角

Figure 5. Cohesion and internal friction angles in soil at different depths

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图 6 不同温度、围压下孔隙中冰的胶结强度分布

Figure 6. Cementing strength distribution of ice in pores under different temperatures and confining pressures

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图 7 土体强度计算结果与试验结果对比

Figure 7. Comparison between calculated results and test results of soil strength

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表 1 模拟不同深度冻土的压制力及所得岩样的基础参数

Table 1 Simulation of compression pressure on frozen soil at different depths and corresponding basic sample parameters

地层深度/m	压制力/kN	孔隙度，%	含水率，%	含水饱和度，%
50.00	0.480	35.8	19.5	98.85
300.00	2.885	34.3	18.8	95.90
600.00	5.770	33.6	18.3	96.64
800.00	7.693	33.0	17.5	95.14
1 000.00	9.616	32.3	17.2	96.43

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表 2 漠河冻土三轴力学试验方案

Table 2 Triaxial mechanical test protocol of Mohe frozen soil

地层深度/m	温度/℃	围压/MPa
50.00	20/–5/–10/–15/–25	0/1/3
300.00	20/–5/–10/–15/–25	0/3/5
600.00	20/–5/–10/–15/–25	3/5/8
800.00	20/–5/–10/–15/–25	5/8/12
1 000.00	20/–5/–10/–15/–25	5/10/15

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表 3 初次回归结果显著性分析结果

Table 3 Significance analysis of the initial regression results

因素	标准化系数	t值^1）	显著性
截距		3.136	0.002
深度	–0.048	–0.594	0.554
温度	–0.379	–5.666	0
围压	0.744	9.246	0
注：1）指t检验中的t值，下同。

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表 4 线性回归结果显著性分析结果

Table 4 Significance analysis of linear regression results

因素	标准化系数	t值	显著性
截距		3.280	0.002
温度	–0.379	–5.690	0
围压	0.718	10.780	0

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表 5 漠河冻土非线性回归参数估算值

Table 5 Estimated values of nonlinear regression parameters of Mohe frozen soil

参数	估算值	标准误差
c₁	1.534	0.092
c₂	–0.092	0.101
c₃	–0.412	0.004
c₄	–0.009	0.006
c₅	–0.016	0.003
f	–0.187	0.645

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表 6 漠河非冻结土非线性回归参数估算值

Table 6 Estimated values of nonlinear regression parameters in Mohe non-frozen soil

参数	估算值	标准误差
d₁	0.001	0
d₂	–4.186×10^–7	0.031
d₃	0.076	0
d₄	–0.004	0
d₅	0	0
f	0.911	0.087

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