“硬-软-硬”三层黏土上圆形基础的承载力分析

吴炳; 郑敬宾; 王栋

doi:10.13544/j.cnki.jeg.2021-0091

“硬-软-硬”三层黏土上圆形基础的承载力分析

doi: 10.13544/j.cnki.jeg.2021-0091

吴炳^{①, ②,},
郑敬宾^{①, ②, ,},
王栋^{①, ②}

①.
中国海洋大学山东省海洋环境地质工程重点实验室，青岛 266100，中国
②.
中国海洋大学环境科学与工程学院，青岛 266100，中国

基金项目:

国家自然科学基金 51809247

国家自然科学基金 U1806230

山东省自然科学基金 ZR2018BEE043

详细信息

作者简介:
吴炳(1995-)，男，硕士，主要从事海洋岩土工程研究工作. E-mail: wubing@stu.ouc.edu.cn

通讯作者:
郑敬宾(1989-)，男，博士，副教授，主要从事海洋工程地质与岩土工程方面的科研与教学工作. E-mail: zhengjingbin@ouc.edu.cn

中图分类号: P642;P67
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- 被引次数: 0
出版历程
- 收稿日期: 2021-03-04
- 修回日期: 2021-05-21
- 刊出日期: 2021-12-25

STUDY OF BEARING CAPACITY OF SURFACE CIRCULAR FOOTING ON STIFF-SOFT-STIFF CLAYS

WU Bing^{①, ②
,},
ZHENG Jingbin^{①, ②
, ,},
WANG Dong^{①, ②}

①.
Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, Ocean University of China, Qingdao 266100, China
②.
College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China

Funds:

the National Natural Science Foundation of China 51809247

the National Natural Science Foundation of China U1806230

the Natural Science Foundation of Shandong ZR2018BEE043

摘要

摘要: 海洋浅基础设计所遇地层条件通常由于基础大尺寸的特点而涉及多土层剖面，其中“硬-软-硬”三层黏土是最常见的地层条件之一。现行海洋浅基础设计常用的API和ISO规范尚无针对“硬-软-硬”黏土竖向承载力的计算方法。本文基于自升式平台基础设计规范推荐的“bottom-up”预测模型，假定“硬-软-硬”黏土上基础的承载力为“硬-软”黏土冲剪破坏产生的侧向摩阻力与“软-硬”黏土挤压破坏提供的承载力之和。通过有限元模拟分析，验证了“bottom-up”方法所假定破坏模型的合理性，但由于规范推荐的相关公式忽略了上覆土层对挤压破坏模式的影响，使其严重低估了“软-硬”黏土挤压破坏产生的承载力。基于变参数有限元分析结果，本文对挤压破坏承载力公式进行了修正，提出了“硬-软-硬”三层黏土上圆形基础竖向承载力的预测方法。
- 海洋工程地质 /
- 海洋基础 /
- 多层土 /
- 承载力 /
- 破坏模式
Abstract: The stratigraphic configurations for the design of offshore shallow foundations usually involve multi-layer soil profiles due to their large sizes. The stiff-soft-stiff clay deposit is one of the most prevalent configurations. Design methods are not available in the current API and ISO standards for shallow foundations to estimate the bearing capacity of a footing on stiff-soft-stiff clays. Based on the "bottom-up" approach recommended for spudcan foundations of jack-up rig,this paper assumes an analytical model that sums the resistances from the punching shear of the stiff-soft layering system and the squeezing of the soft-stiff layering system. The rationality of this predictive model is verified based on comprehensive FE analyses. The comparison between the predictions from "bottom-up" approach and FE analyses indicates that the assumed model is reasonable and realistic. However,the resistance due to squeezing response is significantly underestimated by the current design formula. Detailed investigations are carried out. It is revealed that this is mainly because the effect of the overlying stiff clay on the squeezing mechanism is neglected. Based on the findings,an improved design formula is proposed for the squeezing response and hence for the design of circular foundations on stiff-soft-stiff clays.
- Marine Engineering Geology /
- Offshore foundation /
- Multi-layer soils /
- Bearing capacity /
- Failure mechanism

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图 1 多层土基础竖向承载力“bottom-up”预测模型(ISO，2016b)

a. 第一步; b.第二步

Figure 1. "Bottom-up" predictive model for foundation bearing capacity on multi-layer soils(ISO, 2016b)

下载: 全尺寸图片幻灯片

图 2 有限元模型设置

Figure 2. Set-up of finite element numerical model

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图 3 有限元结果与理论解对比图(表 1组1)

Figure 3. Comparison of the FE and analytical results(Group 1, Table 1)

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图 4 “bottom-up”方法预测效果(表 1组2)

Figure 4. The performance of "bottom-up" method (Group 2, Table 1)

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图 5 软黏土夹层挤压破坏有限元分析模型

Figure 5. FE model for squeezing of interbedded soft clay

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图 6 有限元解析预测与“bottom-up”预测对比图(表 1组2)

Figure 6. Comparison of FE method and the current ISO method(Group 2, Table 1)

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图 7 d/D对挤压破坏模式的影响(表 1组3)

Figure 7. The influence of d/D on the squeezing mechanism(Group 3, Table 1)

a. d/D=0; b. d/D=0.125; c. d/D=0.5

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图 8 修正系数公式效果(表 1组3)

Figure 8. The performance of the formula improved factor (Group 3, Table 1)

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图 9 s_u1/s_u2对挤压破坏模式的影响(表 1组4)

Figure 9. The influence of s_u1/s_u2 on the squeezing mechanism(Group 4, Table 1)

a. s_u1/s_u2=1; b. s_u1/s_u2=2; c. s_u1/s_u2=4; d. s_u1/s_u2=8

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图 10 s_u1/s_u2对N′_c，23的影响(表 1组4)

Figure 10. The influence of s_u1/s_u2 on N′_{c, 23}(Group 4, Table 1)

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图 11 改进方法预测效果(表 1组5)

Figure 11. The performance of the improved method (Group 5, Table 1)

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表 1 有限元分析参数汇总

Table 1. Summary of performed numerical analyses

组号	t₁/D	t₂/D	d/D	s_u1/s_u2	s_u3/s_u2	目的
1	0.125~0.5	—	0	0.25	1	数值模型验证
2	0.125，0.5	0.125	0	8	1.5~8	变参数分析
3	0.125~0.5	0.125	0.125~0.5	1	4
4	0.125	0.125	0.125	1~8	8
5	0.125~0.5	0.1~0.29	0	3~8	3~8

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表 2 单层土承载力系数比较

Table 2. Comparison of bearing capacity factors of single layer clay

	参考文献	解析方法	承载力系数N_c
单层土	Cox et al.(1961)	理论解	6.05
	Salgado et al.(2004)	塑性上限	6.23
	Salgado et al.(2004)	塑性下限	5.86
	Merifield et al.(2006)	三维有限元	6.05
	Gourvenec et al.(2006)	有限元	5.96
	本研究	有限元	5.98

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表 3 双层土承载力系数比较

Table 3. Comparison of bearing capacity factors of soft-over-stiff clays

	参考文献	解析方法	承载力系数N_c
双层土	Meyerhof et al.(1953)	理论解	7.64
	Merifield et al.(2006)	三维有限元	7.95
	本研究	三维有限元(加密前：最小单元尺寸0.05D)	7.69
		三维有限元(加密后：最小单元尺寸0.025D)	7.44
		二维有限元	7.34

下载: 导出CSV

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