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Journal of Zhejiang University-SCIENCE A

, Volume 19, Issue 4, pp 266–276 | Cite as

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

  • Hai-zuo Zhou
  • Gang Zheng
  • Xiao-xuan Yu
  • Tian-qi Zhang
  • Jing-jin Liu
Article

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.

Keywords

Bearing capacity Deep mixed (DM) columns Surcharge Failure mechanism 

水泥搅拌桩复合地基的承载力与破坏模式研究

概要

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 (Nc、Nq 和Nγ),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 

CLC number

TU4 

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Copyright information

© Zhejiang University and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.School of Civil EngineeringTianjin UniversityTianjinChina
  2. 2.Key Laboratory of Coastal Civil Engineering Structure and Safety of Ministry of EducationTianjin UniversityTianjinChina
  3. 3.State Key Laboratory of Hydraulic Engineering Simulation and SafetyTianjin UniversityTianjinChina

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