LUẬN văn THẠC sĩ minimizing influence on existing buildings when tunneling in soft soil

CHAPTER 2 LITERATURE REVIEW 2.1 Empirical method According to Mair and Taylor 1999, ground construction surface movement due to main reasons movement in follow location: bored machine f

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

TRAN QUANG DUC

MINIMIZING THE INFLUENCE ON EXISTING BUILDINGS WHEN TUNNELING

IN SOFT SOIL

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

TRAN QUANG DUC

MINIMIZING THE INFLUENCE ON EXISTING BUILDINGS WHEN TUNNELING

ACKNOWLEDGEMENT

ABTRACT

CONTENT

ACKNOWLEDGEMENT 3

ABTRACT 4

CHAPTER I INTRODUCTION 8

1.1 Background 8

1.2 Outline research 10

CHAPTER 2 LITERATURE REVIEW 11

2.1 Empirical method 11

2.2 Analytical methods 13

2.3 Finite element method using software Plaxis 2D 13

CHAPTER 3 METHODOLOGY 15

3.1 General 15

3.2 Project case study 16

3.2.1 Main properties of Tunnel in HCM MRT line1 17

3.2.2 Construction sequence of underground tunnel 17

3.3 Collection of soil condition data 18

3.3.1 Soil investigation data 18

3.3.2 Groundwater data 20

3.4 Collection of TBM’s operation data 21

3.5 Selection of analysis section 21

3.6 Ground settlement analysis by empirical method 22

3.7 Numerical analysis with Plaxis 2D 23

3.7.1 Mesh model 23

3.7.2 Preparation input data 24

3.7.3 Soil input parameters in Plaxis 2D 28

3.7.4 Properties of tunnel segment 28

3.7.5 Water condition 28

3.7.6 Contraction method 28

3.7.7 Stress reduction method 29

3.8 Collection of monitoring data 30

CHAPTER 4 RESULT AND DISCUSSION 33

Ground surface settlement of the tunnel alignment 33

4.1.1 Ground surface settlement of the tunnel alignment 33

4.1.2 Ground surface settlement in tunneling period 34

4.2 TBM’s operational parameters and its effect on settlement 35

4.3 Analysis of ground surface settlement by Empirical method 37

4.3.1 Trough width parameter (i) 39

4.3.2 Volume loss (VL) 39

4.4 Analysis of ground surface settlement by Plaxis 2D 40

4.4.1Contraction method 40

4.4.2 Stress reduction method 42

4.5 Comparisons of empirical method and numerical method 43

CHAPTER 55 45

CONCLUSIONS AND RECOMMENDATIONS 45

Conclusions 45

5.2 Recommendations 46

REFERENCES 47

FIGURE 52

APENDIX A: TUNNEL MACHINE AND LINNING SEGMENT 67

APENDIX B: GEOLOGY PROFILE 70

APPENDIX C: CROSS BUILDING STRUCTURE 73

CHAPTER I INTRODUCTION

1.1 Background

In Vietnam, big cities such as Hanoi and Ho Chi Minh have reached approximately 10 million population, not including the sub-urban people residing and commuting due to the recent rapid urbanization This creates a dramatically pressure on the infrastructure system and the public transport system Construction of MRT with underground sections

is the optimal and feasible solution to solve these problems of the cities

Figure 1 System map (planned) for Hanoi MRT system to vision 2050 (Hanoi Metropolitan Railway Management Board)

Figure 2 System map (planned) for Hochiminh city MRT system to vision after 2020 (HCMC urban railway management board)

In bored tunel in urban areas, bored tunel with TBMs has recently been a popular and effective method in the world This technique has been developed and applied as a main method for underground MRT projects

The two cities of Hanoi and Ho Chi Minh City are located at the center of the delta with geology condition a mostly consisted of soft soil Deformations including settlements and tilts should be well controlled when bored tunnel in order to protect the existing ground surface and minimize the impacts on existing structures By combining theoretical calculation, software analysis and comparison with monitoring data, results derived from this study can be applied for the bored tunnel design and construction in

geo-conditions in Vietnam in order to obtain effective and safe bored tunnel projects

of predicting settlement displacement

Proposing solutions based on calculated and observed results has been derived in Chapter

5

CHAPTER 2 LITERATURE REVIEW

2.1 Empirical method

According to Mair and Taylor (1999), ground construction surface movement due to main reasons movement in follow location: bored machine face, along the shield, behind the shield at tail, and consolidation settlement

Figure 2.1 shows the 3D settlement trough on the surface First author, Peck (1969) firstly proposed the settlement trough on the surface due to TBM operation in soft soil

as a Gaussian distribution Some the other authors have confirmed that theoretical (Cording and Hansmire, 1975; Mair et al 1993;) Although some different opinions with Gaussian distribution in some particular cases (Jacobsz, 2003; Vorster, 2006; Farrell et al., 2012) and in Japan (JSSMFE, 1993), the Gaussian still curve commons using in study and industry practice

Figure 2.1 Surface settlement trough induced by bored tunel (Franzius, 2004)

In this study, the Gaussian curve is used to investigate the ground movement when bored

tunel in order to find the effects on existing structures It is can be estimated from the maximum settlement Gaussian distribution (Peck, 1969)

Figure 2.2 Transverse settlement tunnel trough due to bored TBM (Peck, 1969)

In order to forecast surface settlement (Peck, 1969) and subsurface settlement (Mair et al., 1993), the volume loss is often taken by experience and data from existing cases It

is make hardly to assessment the volume loss as generalize In next chapter, the further detail with factors determine settlement will be presented, especially volume loss

Based on Attewell and Farmer (1974), Cording and Hansmire (1975) and Mair and Taylor (1999), the volume loss can obtain by divided component similar settlement:

- Volume loss at the front face of TBM

- Volume loss at along TBM;

- Volume loss at behind TBM tail;

- Volume loss behind the shield tail induced by consolidation Function to determine volume loss as following:

VL = VL,f +VL,s +VL,t +VL,c

Where VL,f is volume loss at the front face of TBM, VL,s Volume loss at along TBM, VL,t

is volume loss at behind TBM tail , and VL,c is volume loss behind the shield tail induced

by consolidation

With the independent calculation, theoretical can compare with analytical and monitoring from case study in practice

2.2 Analytical methods

Method assumptions basically about geometry, homogenous layer, modelling There are some advantages in compare with the empirical method Taking into account the parameters that may affect surface movement such as ground conditions, construction techniques, etc Some author presented issue included: Verruijt & Booker’s method (1996), Loganathan & Poulos’s method (1998) and Bobet’s method (2001) Some assessment about methods:

(i) Verruijt and Booker (1996)’s method

The result of surface settlement shape from Verrujit and Booker's method was not well fit with the observed settlement profile

(ii) Loganathan and Poulos (1998)’s method

It was over predicted for tunnel in soft clay

(iii) Bobet (2001)’s method

This method proposed a deep tunnel in dry soil to extend the new solution for ground movement caused by shallow tunnel in a saturated soil

2.3 Finite element method using software Plaxis 2D

Numerical analyses as finite element method (FEM) is the effective in predict and design

in geotechnical problem With bored tunel using TBM method, Plaxis 2D is software was chosen in this thesis

Material types

Plaxis using three type materials include: non-porous, drained behavior and undrained behavior

Model boundaries: Möller (2006) proposed boundaries for 2D FEM as follow:

Bottom boundary (from tunnel invert to bottom boundary):

h (1.2 ÷2.2) for D = 4 m ÷ 12 m

Mesh width (from tunnel center line to vertical mesh boundary):

W=2D (1 + ) Where C/D is ratio of cover depth and diameter of tunnel

Constitutive model

There are some constitutive models which each method could be more exactly results for corresponding condition Two most popularly constitutive models for TBM projects are the Mohr-Coulomb and Hardening Soil model

(i) Mohr-Coulomb model (MCM)

The Mohr-Coulomb model have well known as the linear elastic perfectly plastic model

The Mohr-Coulomb soil model is used for modeling the behavior of most soils Soil parameters in this model such as shear strength (c, φ), Young’s modulus (Eref) and Poisson ratio (υ) which are familiar to most geotechnical engineering In this thesis, the Young modulus Eref is assume no change and liner

(ii) Hardening Soil model (HSM)

The HSM could be considered better than the MCM HSM proposed by Duncan &

Chang (1970), but using plasticity theory not like MCM with elasticity theory In HSM, the strength parameters can be used from the Mohr Coulomb Model including c, φ The stiffness of the model included in Eref50, Erefode, Erefur and m

Modelling segmental lining of tunnel

Plate element based on linear plastic material model often uses to model the segmental lining in Plaxis 2D The equivalent thickness for plate can calculate from this equation:

deq= 12Wood (1975) address the effective moment of inertia as follow:

Ie=Ij+( ) I

In which, where Ij is the moment of inertia of the joints, I is the moment of inertia of the ring, n is the number of joints in the ring (n > 4)

CHAPTER 3 METHODOLOGY

3.1 General

Figure 3.1 Flow chart for methodology

This chapter aims to describe the methodology to achieve these objectives study The study also consists of a comparison to the data collection from case study, the description

DEFINITION OBJECTIVE

LITERATURE REVIEW METHODOLOGY

COLLECTION DATA FOR ANALYSIS GROUT MOVEMENT

EMPIRICAL METHOD FINITE ELEMENT

of empirical method and numerical method

3.2 Project case study

The proposed Ho Chi Minh City Urban Railway Construction Project (Line1) – Contract Package (CP) 1b is approximately 1.75km long and includes following items:

- Two underground station: Opera House Station and Ba Son Station

- Twin bored tunnels (780 m) Cut and Cover (C&C) tunnels (530 m) CP-1b interfaces with CP-1a at the South-West boundary and Contract Package 2 at the North-East boundary As Contract Package 2 is elevated, the C&C box tunnels transition to tracks on embankment via U-shaped structure The twin bored tunnels run between Opera House station and Ba Son station

The interface with CP-1a is at the outer face of Opera House station end wall The subway tunnels run along a corridor in the central urban area of Ho Chi Minh City from

a proposed station at the Opera House to a proposed station at the Ba Son shipyard and cut & cover area Within this corridor, the project may impact nearby and adjacent structures and buried utilities from bored tunel and excavation works

Figure 3.2 The extent of bored tunnel section The case study of study is 1.56 km underground tunnel using TBM with equipment of EPB type The shield tunnels included in 2 bound base on direction East (EB) and West

- Bound (WB) tunnel for two pipeline from Opera House Station (CH 0+805) to Ba Son

Station (CH 1+586), were drilling as figure 3.2 showed The main contractor is Shimizu Maeda Joint venture Operation

3.2.1 Main properties of Tunnel in HCM MRT line1

Table 3.1 Main properties of bored tunnels

Tunnel type Bored tunnel

Tunnel length (m) 780mx2 tunnels= 1560m Segment

Table 3.2 Main parameters of the EPB shield machine

EPB shield parameters Description

EPB Machine

Grouting Type of grouting Liquid A and Liquid B Typical grout filling ratio 100-130%

Geological conditions Alluvium fill, clay and sand The detailed tunnel lining and shield machine is shown from Appendix A

3.2.2 Construction sequence of underground tunnel

The proposed construction method is using a Tunnel Boring Machine The proposed running tunnel segment lining has an internal diameter of 6.05m and a thickness of 300mm The 1200mm wide segmental lining system consists of 5 precast concrete regular segments and 1 key joined by bolts Segment arrangement using 5+1 scheme has been very widely used in the worldwide With fewer segments per ring, ring erection time is significantly shortened but induced forces would generally be increased For this special section, construction sequence is presented in Figure 3.3 below

Figure 3.3 Bored tunnel’s construction sequence

3.3 Collection of soil condition data

3.3.1 Soil investigation data

At tender stage, the soil investigation reports consists of total 18 boreholes are issued for tender for the underground sections of the Ho Chi Minh City Urban Railway Construction Project (Line1) - Contract Package (CP) 1b At technical design stage, 4 numbers of additional boreholes (ABH-1 to ABH-4) were proposed and carried out along the Bored Tunnel area and were completed in March 2015 by SMJO A summary table

of the numbers of boreholes and field tests carried out along the bored tunnel are indicated in the Table 3.3

Table3.3 Summary table of boreholes and field tests carried out along Bored Tunnel

Borehole

No

Field permeability test

Pressure meter test

Ground water level monitoring Existing borehole at

SMJO The geology in CP-1b area is mainly comprised of Fill, Alluvium and Diluvium material

Alluvial deposits of approximately 30m to 40m thick overlay the harder and denser Diluvium layers The longitudinal section of the geological profile along the alignment

of CP-1b for the bored tunnel are presented and included in Appendix B – Geological Profile

Detailed descriptions of the above geological units are given below:

Elevations at the top of layer range from 1.744m EL at ABH-3 to -0.7m EL at U-177

An isolated 3.7m thick layer of low plasticity firm sandy clay (Ac3) is encountered at LK-H4 beneath Ac2

Silty Fine Sand Layer 1 (As1): The soil material, in general, non-homogeneous to homogeneous material Silt content ratio decreases with depth and changes to fine sand with silt The soil layer is encountered at all boreholes The thickness varies from 3.2m

to 13m and SPT N-value ranges from 1 to 11 with an estimated average of 5 Elevations

at the top of layer range from -0.68m EL at U-152 to -7.8m EL at U-181

Sand Layer 2 (As2): This layer is lowermost in Alluvium deposit and above Hard Clayey Silt of Diluvium Main component of this layer is medium grained to coarse grained sand

This Sand layer is mainly medium dense to dense sand with occasional loose pockets

This sand layer encountered at all boreholes The thickness varies from 16.9m to 27.8m

The SPT Nvalue ranges from 6 to 41 with an estimated average of 15 Elevations at the top of layer range from -4.2m EL at ABH-1 to -17.6m EL at U-180

 Diluvium

Hard Clayey Silt (Dc): This layer is lowermost layer at almost all boreholes Subsurface material consists of homogeneous, hard to very hard, weakly cemented, low permeability, clayey silt This soil is encountered at all boreholes The thickness varies from 2.9m to 21.1m The SPT N-value ranges from 18 to >50 with an estimated average of 34 This soil is mainly hard to very hard clayey soil Elevations at the top of layer range from -30.3m EL at ABH-2 to -35.0m EL at LK-H4

Dense Silty Sand (Ds): This soil layer is lowermost layer at 6 boreholes and encountered below hard clayey silt layer at U-150, U-152, U-160, U-161, U-162 and ABH-1 It consists of nonhomogeneous, very weakly cemented, moderately low permeability, dense to very dense

There are total of 43 boreholes for soil parameters were collected consist of both bored tunnel area and underground station area which in Table 3.4

The longitudinal section of the geological profile along the alignment of the bored tunnel was described in Figure 3.4 The basic properties of soils from bore holes along the tunnel alignment are plotted together in Figure 3.5 to 3.7

3.3.2 Groundwater data

Groundwater table monitoring (standpipe) was carried out at 06 boreholes locations

These locations were monitored over period of approximately 01 month between May

to July 2008 According to ground water monitoring result at water standpipes, ground water table readings from the first soil investigation results range from 1.97 m to 3.83 m below the water table Additionally, water level readings from monitoring wells in layer As1 and As2 in the additional soil investigation, the maximum water level encountered

was 1.67 m below ground level Finally, groundwater level was taken at depth about 2.0

m from ground level in this study analysis

Table 3.4 Ground water collection data

Note:

1) GL: The Level relative to the Ground Level (minus sign refers to the below ground level);

2) EL: The Level relative to the mean sea level;

3) High and Low Groundwater level is decided based on ground water level monitoring results presented in the Soil Investigation Reports

4) Based on Hydrological Survey Report Rev

3.4 Collection of TBM’s operation data

In the WB drill period, the front head pressure data was collected for the along bored tunnel For EB tunnel, face pressure data is only collected from CH 0 + 805 to about CH 1+ 110 Although, the face pressure as well as the grouting front head pressure value is important element effect to ground settlements, but due to the grouting pressure data is unstable and lacking and various other operational issue and hence not taken account into this thesis

The data of TBM’s operation such as front head pressure, grouting volume were recorded using an Arigataya (ver 4.6.5) data collection system in shield machine Operation parameter data were record by FECON, the Operation Sub-Contractor

3.5 Selection of analysis section

9 sections from different conditions along tunnel alignment, as presented in Figure 3.4 have been selected for this study The selected sections were based on the geometries of the section and the position of tunnels

Soil profiles and location of settlement markers of all nine sections are illustrated from Figure 3.5 to Figure 3.7 in Appendix

Figure 3.4 Plan for separated sections

3.6 Ground settlement analysis by empirical method

Maximum settlement and parameter were proposed by several author Mostly popular determined in this study as follow”

Sv,max at the ground directly above the tunnel location and the trough width i as follows:

Sv= Sv,max exp( ) Mair et al (1993) proposed the maximum surface settlement in case of undrained

condition (V L = V s) is given by:

Sv,max= .O’Reilly and New (1982) presented equation for position of inflection point; z0is depth

3.7 Numerical analysis with Plaxis 2D

The Plaxsis 2D software have some main model can use in simulate behavior of ground soil In this thesis, the Mohr- Column model (MCM) was chosen The green field condition and short –term ground surface settlement were assumed

3.7.1 Mesh model

The mesh dimensions were given with vertical boundary was equal to (2D+2H) and (H+3.5D) from the surface level to the bottom according to Möller (2006) Where H is depth of tunnel D is the tunnel diameter Chosen mesh is 6‐nodes triangular elements In the nodes at the bottom of the mesh are fixed in both horizontal and vertical directions

At the both sides of the mesh, the nodes are only fixed in along the horizontal direction

The nodes at the upper of the mesh are free movement in all directions The meshed model of all nine sections in Plaxis are shown from Figure 3.12 to Figure 3.14.

3.7.2 Preparation input data

In general, the soil condition were showed in this chapter, subsection 3 All the test results analyzed in case study were obtained for undisturbed samples and were taken from soil investigation for MRT station and bored tunnel

Figure 3.12 Plaxis 2D FEM with mesh distribuition at Section A, B, C

Figure 3.13 Plaxis 2D FEM with mesh generation at Section D, E, F

Figure 3.14 Plaxis 2D FEM with mesh generation at Section G, H, I

3.7.3 Soil input parameters in Plaxis 2D

All of Soil parameters in this model such as weight unit ( sat, unsat) shear strength (c, φ), Young modulus (Eref) and Poisson ratio (υ) cannot difficulty be obtained from laboratory

Table 3.6 Input parameters of MCM in numerical analysis

3.7.4 Properties of tunnel segment

Table 3.7 Input parameter of Tunnel

Table 3.8 Calculation phase for contraction method in 2D FEM Plaxis

3.7.7 Stress reduction method

Table 3.7 shows the detail of analysis phase of stress reduction method for all studied sections The magnitude of the stress reduction factor (β) from 0.7 to 0.8 was used to match the measured ground settlement profiles in first step Then, the stress reduction factor (β) were selected to the surface settlement trough fitted with the actual settlement data In Plaxis load reduction is expressed by the input value ΣMstage in plastic, staged construction It gives the applied proportion of the loading and is 1 for the case that all loads are applied and the plastic calculation phase is completed:

M stage 

Table 3.9 Calculation phase for stress reduction method in 2D FEM Plaxis

3.8 Collection of monitoring data

The monitoring system include in: ground monitoring (ground surface settlement, layered settlement), segment monitoring (segment strain, earth pressure, etc) were established by Main contractor to observe ground and tunnel during construction

multi-The bored tunnel are divided 3 sections A, B, C and monitoring point are allocated with average 20m A total of 50 monitoring arrays and 237 settlement markers of Type C were installed at ground surface along the longitudinal direction of the tunnel and each array consists of 3 to 8 settlements markers In this study, the observed type C were used for analysis Ground movement were provided by Shimizu-Maeda Joint Operation The detail result data were shown in figure 3.15

Figure 3.15 Monitoring plan layout from Opera House Station to Ba Son Station

A short view of settlements markers are shown as follows:

 Hard facilities The settlement markers were allocated on the ground and generally under the road The makers are steel nail of 12 mm diameter 300 mm length or settlement 8 mm diameter in asphalts road

 Procedure The markers are arranged various arrange from 3.5 m – 5.0 m in the transverse direction and 20 m in the longitudinal direction of tunnel Installation procedure is as follows:

- Step 1: Fixed steel nail with a hammer to the determined location

- Step 2: Drilling to make holes at point that hammer cannot fixed

- Step 3: Use additive to permanent settlement point

CHAPTER 4 RESULT AND DISCUSSION The discussion that follow result, will be proposed analysis based on obtained data

Based on the methodologies in previous chapter, the given data input were analyzed and implemented in correspond progress to obtain calculating results In this chapter, these results were shown on and analyze, reasons also were tried explained and discussed

Ground surface settlement of the tunnel alignment

4.1.1 Ground surface settlement of the tunnel alignment

Figure 4.1 The settlement in surface ground along lining

In summary, settlement along lining due to EB tunnel is less than the WB tunnel one

The settlement due to EB tunnel value within 0.3mm - 8 mm

The high value various from 64 -87 mm with WB tunnel through The discussion mainly

as follow:

- High surface settlement at the near station could be due to when departure TBM

the parameter of machine is not good control

- The configuration (twin tunnel and stack tunnel) also effect to settlement of surface ground

- Compare with the allow range in table 4.1, most of monitoring point meet with criteria in planning

- The surface settlement due to the first tunnel (EB tunnel) various within 0.3 mm

to 3 mm The result is more than 1 mm to 20 mm due to WB tunnel

Table 4.1 Allowable settlement for structures by SMJO in plan for monitoring settlement

Item Allowable

value Notes

Historical Important Structures

Opera House Building Differential Settlement 1/1000

Other Structures

Differential Settlement 2/1000 Relative Settlement 15mm

Road area Settlement

20mm Le Loi Area/Nguyen Hue Area

20mm Along Bored Tunnels 70mm* Ba Son Station Area 130mm* Cut & Cover Tunnels (*) : Values following to the values agreed in meeting minutes between SMJO and Ba Son Cooperation dated 24 Aug 2015

4.1.2 Ground surface settlement in tunneling period

Figure 4.2 shows result taken from monitoring makers in one commons section (section

A -CH 0+980) Maximum surface settlement collected around 5mm with EB lining The settlement begun at location 10 m after TBM approaching and develop to around 20 m after that The settlement clearly stable at 30m Figure 4.2 show settlement due to behind

the shield

Figure 4.2 Settlement of surface during tunneling in section A

Tunneling TBM collected data obtain from shield The collecting data of front pressure, grouting volume and tunnels are shown from Figure 4.3 to Figure 4.4

Figure 4.3 Support pressure at front applied at front TBM

The face pressure of WB less than EB When tunneling at EB, the font of TBM pressure within 300 kPa to 350 kPa While WB tunneling, the value various in 250 kPa-140 kPa

Figure 4.4 Applied grouting along shield TBM The value of grout volume of both Bound are similar within 2.0 to 6.5 m3 The TBM’s data in the sections are given in Table 4.2

Table 4.2 TBM tunneling collected data

Figure 4.5 Settlement and grouting along alignment tunnel

In summary, acceptable conclude that the front TBM pressure inversely proportional with settlement at surface ground Largest value were around 10 mm and 43 mm for the

EB tunnel and the WB tunnel There are one dramatically monitoring data with 80 mm

at WB It is suitable with the lowest face pressure and grout volume in figure 4.4; 4.5

The maximum settlement and volume loss determine at the same location at Section D&E The extraordinary result at this couple section and mitigation method will discuss

at last chapter

4.3 Analysis of ground surface settlement by Empirical method

The integration method was used to estimating settlement due to tunneling in theoretical method All the result of section plotted in Figure 4.6a to 4.6i after West bound through

Please see more detail at FIGURE part

The volume loss obtain from data which taken in reality and trough width of EB & WB are given in Table 4.3 and Table 4.4