Dynamics of Freezing-Thawing Soil around Subway Shield Tunnels

199 Pages·2020·8.574 MB·English

by  Zhen-Dong Cui, Zhong-Liang Zhang, Zhi-Xiang Zhan, Peng-Peng He, Chen-Yu Hou, Yan-Kun Zhang

Zhen-Dong Cui · Zhong-Liang Zhang ·
Zhi-Xiang Zhan · Peng-Peng He ·
Chen-Yu Hou · Yan-Kun Zhang
Dynamics
of Freezing-Thawing
Soil around Subway
Shield Tunnels
Dynamics of Freezing-Thawing Soil around
Subway Shield Tunnels
Zhen-Dong Cui Zhong-Liang Zhang
(cid:129) (cid:129)
Zhi-Xiang Zhan Peng-Peng He
(cid:129) (cid:129)
Chen-Yu Hou Yan-Kun Zhang
(cid:129)
Dynamics of
Freezing-Thawing Soil
around Subway Shield
Tunnels
123
Zhen-DongCui Zhong-LiangZhang
State Key Laboratoryfor Geomechanics State Key Laboratoryfor Geomechanics
andDeepUndergroundEngineering,School andDeepUndergroundEngineering,School
of MechanicsandCivil Engineering of MechanicsandCivil Engineering
ChinaUniversityofMiningandTechnology ChinaUniversityofMiningandTechnology
Xuzhou,China Xuzhou,China
Zhi-Xiang Zhan Peng-Peng He
State Key Laboratoryfor Geomechanics State Key Laboratoryfor Geomechanics
andDeepUndergroundEngineering,School andDeepUndergroundEngineering,School
of MechanicsandCivil Engineering of MechanicsandCivil Engineering
ChinaUniversityofMiningandTechnology ChinaUniversityofMiningandTechnology
Xuzhou,China Xuzhou,China
Chen-YuHou Yan-KunZhang
State Key Laboratoryfor Geomechanics State Key Laboratoryfor Geomechanics
andDeepUndergroundEngineering,School andDeepUndergroundEngineering,School
of MechanicsandCivil Engineering of MechanicsandCivil Engineering
ChinaUniversityofMiningandTechnology ChinaUniversityofMiningandTechnology
Xuzhou,China Xuzhou,China
FundedbytheFundamentalResearchFundsfortheCentralUniversities(GrantNo.2018ZZCX04)
andtheNationalKeyResearchandDevelopmentProgram(GrantNo.2017YFC1500702).
ISBN978-981-15-4341-8 ISBN978-981-15-4342-5 (eBook)
https://doi.org/10.1007/978-981-15-4342-5
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Preface
During the operation of the subway, the vibration caused by the subway cyclic
loading exists for a long time, which will reduce the strength of the soft soil
foundation, generate different degrees of settlement and deformation, affect the
deformationofthetunnelaxis,andcausegroundsubsidence.Thetrafficfacilitiesof
many subway constructionprojects are usuallybuilt on soft soil foundation. Inthe
initialstageofoperationaftertheconstructionoffreezingmethod,duetotheaction
of cyclic loading, consolidation deformation settlement often occurs, which has
great safety problems.
Supported by the Fundamental Research Funds for the Central Universities
(Grant No. 2018ZZCX04) and the National Key Research and Development
Program (Grant No. 2017YFC1500702), this monograph studies the dynamic
characteristics of soil around subway shield tunnel by artificial freezing method,
which can provide theoretical basis and guidance for the effective control of
long-term subway settlement and maintaining the safety of subway operation.
Chapter 1 is Introduction. It introduces the progresses of the mechanical prop-
erties of soft clay under cyclic loading, the physical and mechanical properties of
soft clay under freeze-thaw cycle and the macroscopic and microstructural char-
acteristics of soft clay.
Chapter2isArtificialfreezingforby-passofsubwaytunnel.Inthischapter,the
artificial freezing method used in the construction of the by-pass in the silty clay
stratumisintroduced.Thedesignoffreezingparameters,constructiontechnologies,
monitoring of the temperature field and deformation are introduced systematically.
Chapter 3 is Axial strain of silty clay before and after freezing and thawing. In
this chapter, a series of cyclic triaxial tests have been carried out to investigate the
dynamic behavior of soft clays before and after freezing-thawing. The stress-strain
backbone loop, axial strain and excess pore pressure of the grey muck clay are
evaluated and compared under different frequencies and cyclic stress ratios.
Chapter 4 is Freezing-thawing on dynamic characteristics of silty clay. In this
chapter, 12 cyclic triaxial tests have been carried out to investigate the dynamic
characteristics of the silty clay before and after freezing-thawing, including the
v
vi Preface
dynamicmodulus,thedampingratio,thedynamicstrainandtheexcessporewater
pressure,etc.
Chapter 5 is Microscopic pore structures of silty clay before and after
freezing-thawingbySEM.Theparametersofmicroscopicporestructureofthesilty
clay, including the pore shape coefficient, the pore orientation anisotropy, the pore
sizedistributionandthefractaldimension,areevaluatedwithdifferentfrequencies,
cyclic stress ratios and freezing temperatures.
Chapter 6 is Microscopic pore structures of silty clay before and after
freezing-thawingbyMIP.Inthischapter,14MIPtestsfollowingthecyclictriaxial
tests of the silty clay of layer No. 5 in Shanghai were conducted to investigate the
variation of the PSD of the silty clay. The effects of freezing-thawing and cyclic
loadings on the PSD of the silty clay were evaluated and the MIP derived water
retention curves of the silty clay were predicted with the van Genuchten model.
Chapter7isDynamicsofsiltyclayaroundsubwayshieldtunnelbeforeandafter
freezingandthawingbynumericalsimulation.Inthischapter,thethree-dimensional
governingequationswerederivedandthesolving methodwasgiven.Thematerial
parameters of the thawing soil and the undisturbed soil used in the numerical sim-
ulationswereobtainedbydynamictriaxialtests.Thedynamicresponseofthawing
soilandundisturbedsoilinthesameenvironmentalconditionswerecomparedand
analyzed.
Chapter8isConclusionsandProspects.Thispartcomprehensivelysummarizes
the research conclusions. Several controversial issues are discussed and then the
further research work and prospects are simply described.
Thismonographhasbeenpreparedwiththecombinedeffortofallresearchersin
the group under Prof. Zhen-Dong Cui’s leading, in which Zhong-Liang Zhang,
Zhi-Xiang Zhan, Chen-Yu Hou, Yan-Kun Zhang andsome other students all have
involved in this comprehensive research work in this monograph.
Xuzhou, People’s Republic of China Prof. Zhen-Dong Cui
February 2020
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Mechanical Properties of Soft Clay Under Cyclic Loading . . . . . . 2
1.3 Physical and Mechanical Properties of Soft Clay Under
Freeze-Thaw Cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Macroscopic and Microstructural Characteristics of Soft Clay . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 Artificial Freezing for by-Pass of Subway Tunnel. . . . . . . . . . . . . . . 13
2.1 Artificial Freezing Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Design of Freezing Parameters of by-Pass . . . . . . . . . . . . . . . . . . 14
2.2.1 Project Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2.2 Design of Thickness of the Freezing Wall. . . . . . . . . . . . . 17
2.2.3 Design of Freezing Holes. . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2.4 Design of Average Temperature of Freezing Wall . . . . . . . 28
2.2.5 Design of Brine Temperature and Flow Rate. . . . . . . . . . . 30
2.3 Construction Technology of the Artificial Freezing Method. . . . . . 31
2.3.1 Procedures of the Freezing Construction . . . . . . . . . . . . . . 31
2.3.2 Technical Parameters of the Freezing Construction . . . . . . 31
2.3.3 Design and Construction of the Emergency Door . . . . . . . 34
2.3.4 Attentions for Freezing Construction. . . . . . . . . . . . . . . . . 41
2.4 Monitoring of the Freezing Engineering. . . . . . . . . . . . . . . . . . . . 43
2.4.1 Construction Monitoring of Freezing Holes
and Freezing Pipes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2.4.2 Monitoring of the Frost Heave Pressure . . . . . . . . . . . . . . 44
2.4.3 Monitoring of the Temperature Field . . . . . . . . . . . . . . . . 44
2.4.4 Monitoring of the Deformation. . . . . . . . . . . . . . . . . . . . . 45
2.4.5 Monitoring of the Freezing Equipment . . . . . . . . . . . . . . . 49
vii
viii Contents
2.5 In-Site Monitoring of the Temperature Field . . . . . . . . . . . . . . . . 51
2.5.1 Analysis of the Brine Temperature . . . . . . . . . . . . . . . . . . 51
2.5.2 Analysis of the Frozen Soil Temperature. . . . . . . . . . . . . . 53
2.5.3 Calculation of Thickness and Average Temperature
of Freezing Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.5.4 Vertical Displacement of Ground Surface During
Active Freezing Period. . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2.5.5 Vertical Displacement of Ground Surface Perpendicular
to Axial Direction of by-Pass . . . . . . . . . . . . . . . . . . . . . . 62
2.5.6 Maximum Deformation and Change Rate of Various
Monitoring Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.6 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3 Axial Strain of Silty Clay Before and After Freezing
and Thawing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
3.2 Backbone Curve Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.3 Cyclic Triaxial Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.3.1 Sample Preparation and Soil Properties. . . . . . . . . . . . . . . 69
3.3.2 Test Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.4 Analysis of Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.4.1 The Stress-Strain Relationship of Soft Clay in Cyclic
Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.4.2 Comparison of the Axial Strain Before and After
Freezing and Thawing . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
3.4.3 The Development of Excess Pore Pressure . . . . . . . . . . . . 78
3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4 Freezing-Thawing on Dynamic Characteristics of Silty Clay . . . . . . 85
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.2 Definition of Dynamic Modulus and Damping Ratio . . . . . . . . . . 87
4.2.1 Definition of Dynamic Modulus . . . . . . . . . . . . . . . . . . . . 87
4.2.2 Definition of Damping Ratio . . . . . . . . . . . . . . . . . . . . . . 88
4.3 Cyclic Triaxial Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.3.1 The Schedule of Triaxial Tests. . . . . . . . . . . . . . . . . . . . . 90
4.3.2 The Process of Triaxial Tests . . . . . . . . . . . . . . . . . . . . . . 91
4.4 Results Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.4.1 Dynamic Modulus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.4.2 Damping Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.4.3 Excess Pore Water Pressure and Axial Strain . . . . . . . . . . 99
4.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Contents ix
5 Microscopic Pore Structures of Silty Clay Before and After
Freezing-Thawing by SEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.2 The SEM Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.3 Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
5.3.1 Quantitative Analysis of Test Results . . . . . . . . . . . . . . . . 108
5.3.2 Effects of Magnification on Porosity from
SEM Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.3.3 Further Analysis of Microscopic Pore Structures . . . . . . . . 114
5.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
6 Microscopic Pore Structures of Silty Clay Before and After
Freezing-Thawing by MIP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
6.2 MIP Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
6.3 Test Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134
6.3.1 Effects of Freezing-Thawing on the PSD. . . . . . . . . . . . . . 134
6.3.2 Effects of Frequency on the PSD . . . . . . . . . . . . . . . . . . . 137
6.3.3 Effects of CSR on the PSD . . . . . . . . . . . . . . . . . . . . . . . 140
6.3.4 Prediction of Water Retention Curve. . . . . . . . . . . . . . . . . 141
6.3.5 Analysis of the PSD Using Fractal Theory . . . . . . . . . . . . 147
6.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
7 Dynamics of Silty Clay Around Subway Shield Tunnel Before
and After Freezing and Thawing by Numerical Simulation . . . . . . . 155
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
7.2 Governing Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
7.2.1 Formulations of the Model. . . . . . . . . . . . . . . . . . . . . . . . 157
7.2.2 Equation Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
7.3 Numerical Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
7.3.1 Model Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
7.3.2 Vibration Load of the Train . . . . . . . . . . . . . . . . . . . . . . . 160
7.3.3 Parameters of Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
7.3.4 Damping Parameter and Boundary Conditions. . . . . . . . . . 161
7.4 Analysis of Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
7.4.1 Vibration Acceleration of the Thawing Soil. . . . . . . . . . . . 163
7.4.2 Amplitude-Frequency Curves of the Displacements . . . . . . 163
7.4.3 Attenuation of the Acceleration . . . . . . . . . . . . . . . . . . . . 168
7.4.4 The Maximum Ground Acceleration and Displacement . . . 169
7.4.5 Time-History Curves of the Acceleration . . . . . . . . . . . . . 170
x Contents
7.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
8 Conclusions and Prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
8.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
8.2 Prospects for Further Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Appendix: Major Published Works of the Book Author .... ..... .... 181
Bibliography .. .... .... .... ..... .... .... .... .... .... ..... .... 183