Strain prediction model of undisturbed silty soft clay under intermittent cyclic loading

doi:10.3785/j.issn.1008-973X.2020.05.006

Journal of ZheJiang University (Engineering Science)

2020, Vol. 54

Issue (5): 889-898 DOI: 10.3785/j.issn.1008-973X.2020.05.006

Civil Engineering, Traffic Engineering

Strain prediction model of undisturbed silty soft clay under intermittent cyclic loading

Qing-qing ZHENG1,2(

),Tang-dai XIA1,2,*(

),Meng-ya ZHANG3,Fei ZHOU1,2

1. College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China
2. Research Center of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China
3. Northeast Electric Power Design Institute Co. Ltd of China Power Engineering Consulting Group, Changchun 130000, China

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Abstract

Most present studies on the plastic strain of soft soil under traffic load ignored the trains leaving intervals. Thus, a series of triaxial undrained dynamic tests including continuous and discontinuous vibration on the undisturbed soft clay consolidated along K₀ line were carried out, considering different relative deviatoric stress levels and different stop-vibration ratios. The purpose is to study the strain development of undisturbed silty soft clay under long-term intermittent cyclic loading. Analysis results of the continuous vibration test show that the relative deviatoric stress level has no effect on the relationship between the normalized plastic strain growth rate and the vibration times, and only affects the equivalent initial strain. The normalized strain growth rate is significantly reduced, and the vibration times required to be stable are reduced, due to the increase of the strength during the intermittency period. The influence law of the stop-vibration ratio on the normalized plastic strain growth rate was analyzed based on the fitting result of hyperbolic function, and results show that the shape parameter of the curve of normalized strain growth rate versus vibration times is linearly related to the stop-vibration ratio. A long-term strain prediction model considering intermittency effect was established. The model consists of two parts, the equivalent initial plastic strain and the normalized growth rate. This model is proved to work well, and is helpful to calculate and analyze the long-term strain of soft soil foundation under subway load.

Key words： intermittent cyclic loading plastic strain explicit model undisturbed soft clay intermittency effect strain growth rate initial strain

Received: 11 April 2019 Published: 05 May 2020

CLC:

TU 435

Corresponding Authors: Tang-dai XIA E-mail: zqq0515@zju.edu.cn;xtd@zju.edu.cn

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Cite this article:

Qing-qing ZHENG,Tang-dai XIA,Meng-ya ZHANG,Fei ZHOU. Strain prediction model of undisturbed silty soft clay under intermittent cyclic loading. Journal of ZheJiang University (Engineering Science), 2020, 54(5): 889-898.

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http://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2020.05.006 OR http://www.zjujournals.com/eng/Y2020/V54/I5/889

间歇性循环荷载下原状淤泥质软黏土应变预测模型

针对以往交通荷载下软土塑性应变的研究大多忽视时间间歇影响的问题，考虑不同相对偏应力水平和停振比，设计不排水连续和停振循环三轴试验，对试样采用沿K₀线的应力路径固结，研究原状淤泥质软黏土在列车间歇性荷载下的长期应变发展规律. 通过分析连续振动试验结果，发现相对偏应力水平对归一化塑性应变增长率与振次的关系无影响，仅影响等效初次塑性应变. 由于在间歇期土体强度增加，在间歇性循环加载下软土归一化应变增长率显著减小，并且趋于稳定所需的振次随之减少. 基于双曲函数拟合结果，分析停振比对归一化应变增长率的影响规律，发现归一化增长率与振次的关系曲线的形状参数与停振比线性相关. 建立考虑间歇效应的塑性应变长期发展曲线预测模型，该模型由等效初次塑性应变计算模型和归一化增长率计算模型两部分组成，经验证模型预测效果较好，可以用于地铁荷载下软土地基长期应变的计算分析.

关键词： 间歇性循环加载, 塑性应变, 显式模型, 原状淤泥质软黏土, 间歇效应, 应变增长率, 初次应变

Tab.1 Main physical parameters of marine sedimentary silt soft soil

Fig.1 Two types of normal dynamic load and waveform applied in this paper

Fig.2 Diagram of efficient stress path of soil sample on triaxial test

Tab.2 Scheme of cyclic loading tests

Fig.3 Diagram of measurement of plastic strain in dynamic loading stage

Fig.4 Development of plastic strain under continuous vibration in normal coordinate system

Fig.5 Development of plastic strain under continuous vibration in double-logarithm coordinate system

Tab.3 Fitting parameters of plastic strain curve under continuous vibration

Fig.6 Results of plastic strain development fitted by two types of functions

Fig.7 Relationship between equivalent initial plastic strain and relative deviatoric stress level under continuous vibration

Tab.4 Fitting parameters of curve of normalized growth rate of plastic strain

Fig.8 Development of normalized growth rate of plastic strain under continuous vibration

Fig.9 Development of plastic strain under intermittent vibration in normal coordinate system

Fig.10 Development of plastic strain under intermittent vibration in double-logarithm coordinate system

Tab.5 Fitting parameters with test results under intermittent vibration

Fig.11 Relationship between equivalent initial plastic strain and relative deviatoric stress level

Fig.12 Development of normalized growth rate of plastic strain under intermittent vibration

Tab.6 Fitting parameters of curve of normalized growth rate of plastic strain under intermittent vibration

Fig.13 Relationship between stop-vibration ratio and fitting parameter

Fig.14 Comparison of measured results and predicted results by proposed model


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