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CLC number: TU4

On-line Access: 2018-04-04

Received: 2017-09-26

Revision Accepted: 2017-12-13

Crosschecked: 2018-03-07

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Citations:  Bibtex RefMan EndNote GB/T7714

 ORCID:

Hai-zuo Zhou

https://orcid.org/0000-0002-3346-160X

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Journal of Zhejiang University SCIENCE A 2018 Vol.19 No.4 P.266-276

http://doi.org/10.1631/jzus.A1700517


Bearing capacity and failure mechanism of ground improved by deep mixed columns


Author(s):  Hai-zuo Zhou, Gang Zheng, Xiao-xuan Yu, Tian-qi Zhang, Jing-jin Liu

Affiliation(s):  School of Civil Engineering, Tianjin University, Tianjin 300072, China; more

Corresponding email(s):   zhenggang1967@163.com

Key Words:  Bearing capacity, Deep mixed (DM) columns, Surcharge, Failure mechanism


Hai-zuo Zhou, Gang Zheng, Xiao-xuan Yu, Tian-qi Zhang, Jing-jin Liu. Bearing capacity and failure mechanism of ground improved by deep mixed columns[J]. Journal of Zhejiang University Science A, 2018, 19(4): 266-276.

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year="2018",
publisher="Zhejiang University Press & Springer",
doi="10.1631/jzus.A1700517"
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Abstract: 
Extensive research has investigated the bearing capacity of footings placed on leveled ground improved by deep mixed (DM) columns. However, few studies have focused on the effects of the embedment on the bearing capacity of footings on ground reinforced with DM columns. In geotechnical engineering practice underestimation of the limit load has occurred in China because of the increased use of conventional design methods for reinforced ground with embedment. In this investigation, a numerical model using a rigorous limit analysis tool, known as discontinuity layout optimization (DLO), is established. An equivalent area model is employed with an appropriate stress concentration ratio. Subsequently, a set of design charts of bearing capacity coefficients is produced with a special focus on the bearing capacity coefficient Nq and the failure mechanism. The results show that three failure patterns exist in the composite ground reinforced by DM columns. For cases without embedment, the bearing capacity coefficient Nc increases with the area replacement ratio to a certain value due to the occurrence of general shear failure mechanism. The bearing capacity coefficient Nγ decreases with the area replacement ratio, as the equivalent frictional strength of the reinforced region is reduced. When the embedment is considered, the failure mechanism of composite foundation has a significant influence on the coefficient Nq. Specifically, increase of column length leads to a larger value of Nq when block failure is observed. When a general shear failure pattern occurs, the effect of additional column lengths on the coefficient Nq can be neglected.

水泥搅拌桩复合地基的承载力与破坏模式研究

目的:工程规范中采取保守设计方法导致含有埋深的复合地基的承载力被严重低估.本文基于设计表格的方法展示水泥搅拌站复合地基的承载力系数(NcNqNγ),分析埋深存在时的3种破坏模式,探讨承载力系数Nq和破坏模式随着各类因素(桩长、置换率和埋置深度)变化的原因.
创新点:1. 确定简化的均质化水泥搅拌桩加固地基模型; 2. 建立非连续布局优化法(DLO)模型,计算工程实用设计表格; 3. 分析极限承载力系数Nq、破坏模式和各类影响因素的内在关联.
方法:1. 通过等效强度法确定合理的均质化数值计算模型,并与群桩模型和前人研究进行对比验证(图4和表1); 2. 通过极限分析上限解结合非连续布局优化法,进行大量计算,建立极限承载力系数的设计表格(图6~8).
结论:1. 对于无埋深工况,承载力系数Nc随着置换率的增长而增大,直到某一临界值,此时发生实体基础破坏. 2. 在置换率较低时,承载力系数Nγ随着置换率的增长而减小,因为此时加固区内的等效内摩擦角减小. 3. 埋置深度对承载力和破坏模式产生复杂影响;当破坏模式从实体基础转化为复合型破坏时,Nq增长;随着桩长进一步增加,破坏面通过加固区内部时,Nq在减小之后保持不变.

关键词:承载力;水泥搅拌桩;埋置深度;破坏模式

Darkslateblue:Affiliate; Royal Blue:Author; Turquoise:Article

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