Feasibility Simulation Analysis of Close-Proximity Construction of

Underground Maglev Deep Foundation Pits Under Construction

Jingcheng Chen

1,* a

, Yiwen Yang

, Bo Zeng

, Bin Xie

, Siwei Liu

, Zhen Zhang

and Yang Zhong

China Construction Fifth Engineering Bureau Co., Ltd., Changsha 410004, Hunan, China

China Construction Fifth Engineering Bureau Third Construction Co., Ltd., Changsha 410114, Hunan, China

Hunan Sixth Engineering Co., Ltd., Changsha 410015, Hunan, China

Hunan Airport Management Group Co., Ltd., Changsha 410100, Hunan, China

Keywords: Geotechnical Engineering,·Numerical Analysis,·Deep Foundation Pit,·Close-Proximity Construction.

Abstract: To ensure the safety of deep excavations, construction is typically not allowed within a one-depth range

around the excavation. In the Changsha Airport Comprehensive Transportation Hub project, the proposed

West Parking Building is adjacent to an ongoing deep excavation for maglev construction, imposing

constraints. To optimize the schedule, a construction plan was devised for the West Parking Building near the

maglev deep excavation. Finite element analysis was employed to simulate the maglev deep excavation,

assessing displacements and mechanical changes in the soil and support structures under different scenarios.

The feasibility of the proximity construction plan was predicted, safety measures were proposed, and on-site

implementation validated the analysis accuracy. Results indicate that, under favorable geological conditions,

robust excavation support measures, and an appropriate proximity distance, the impact of proximity

construction on deep excavations is minimal, rendering the plan feasible. This research provides valuable

guidance for deep excavation construction.

1 INTRODUCTION

In recent years, the acceleration of urbanization and

advancements in construction engineering have led to

larger and more complex projects (

Ming 2023

). For

example, these projects face complex and variable

changes, such as groundwater levels and

heterogeneity of soil (

Vasilkin 2018

). While existing

research often qualitatively analyzes specific issues,

there is a lack of systematic, dynamic analysis of the

entire construction process (

Gao X et al. 2023

Against

this backdrop, ensuring the safety, efficiency, and

economic viability of construction plans has become

a pressing challenge in the field of geotechnical

engineering.

Feasibility analysis of project plans is a crucial

step in ensuring the efficient and safe completion of

projects. Consequently, numerous scholars have

conducted research in this area (

A I T, 2021; Zhan et al.

2021

). For instance, Yu Chunhong et al (

Yu et al. 2019

conducted a feasibility analysis of foundation pit

design schemes using anchor systems instead of steel

https://orcid.org/0009-0001-1432-3850

supports through theoretical calculations, addressing

the difficulties and extended timelines associated

with onsite steel support construction. Ma Linwei et

al (

Ma et al. 2022

). conducted research on the

feasibility of cross regional hydrogen water reverse

transportation system engineering based on the

approach of "scheme design and physical modeling

→ economic modeling of single agent operation

mode → analysis of multi agent operation mode"; Cui

Guoyong et al (

Cui et al. 2022

). quantitatively

evaluated the feasibility of the new plan by analyzing

the advantages and disadvantages of using

TBM+main tunnel blasting method in terms of

construction period and cost through construction

organization design, including the plan of connecting

the horizontal guide, construction inclined shaft,

ventilation inclined shaft, and horizontal guide.

Scholars have extensively researched various projects,

employing different methods for feasibility analysis

(

Chen et al. 2020; Hua et al. 2020

). However, there is

scarce literature on the feasibility analysis of

Chen, J., Yang, Y., Zeng, B., Xie, B., Liu, S., Zhang, Z., Zhong and Y.

Feasibility Simulation Analysis of Close-Proximity Construction of Underground Maglev Deep Foundation Pits Under Construction.

DOI: 10.5220/0013636500004671

In Proceedings of the 7th International Conference on Environmental Science and Civil Engineering (ICESCE 2024), pages 271-278

ISBN: 978-989-758-764-1; ISSN: 3051-701X

271

magnetic levitation deep foundation pit construction

using geotechnical engineering simulation software.

This paper uses geotechnical engineering

numerical analysis software to simulate and analyze

the feasibility of deployment plans for close-

proximity construction. The safety of optimized

schemes is validated through onsite implementation.

The goal is to uncover the significant potential of

geotechnical engineering numerical analysis in large

construction projects and provide insights for

improving construction management practices.

2 PROJECT STATUS

The Changsha Airport expansion project involves a

comprehensive transportation hub spanning 492,300

square meters. It comprises an underground facility

with four levels and five tracks, an aboveground

interchange hub, and associated municipal facilities

(see Figure 1). The complex network of deep

foundation pits (see Figure 2) features interconnected

excavations with varying elevations and shapes.

Ensuring safety and efficiency during the

construction phase of these foundation pits is pivotal

to the overall success of the project.

Figure 1: BIM model of structure.

Figure 2: BIM model of deep foundation pit group.

Due to safety concerns, the original plan requires

excavating the West Parking Building pit before

moving on to the magnetic levitation pit. This

sequence, waiting for the completion of the magnetic

levitation structure, significantly impacts the West

Parking Building construction schedule, posing

considerable timeline risks. Urgent optimization of

the West Parking Building pit design or adjustments

to the construction plan are needed to alleviate

schedule pressures (

Figure 3

Figure 3: Status of the construction site.

3 PLAN OF CLOSE-PROXIMITY

CONSTRUCTION

Given that both the magnetic levitation deep pit and

the West Parking Building are in moderately

weathered silty sandstone formations, and the West

Parking Building is situated beyond the rupture plane

of the magnetic levitation deep pit (horizontal angle

45°+φ/2 = 60°), an expedited construction proposal

has been introduced. The optimized plan suggests

commencing the construction of the West Parking

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Building structure in close proximity immediately

after completing the internal support structure

construction of the magnetic levitation deep pit. Due

to construction coordination uncertainties, the most

challenging scenario for this plan might occur when

the magnetic levitation deep pit is excavated to its

bottom while the West Parking Building reaches its

peak load (maximum load), as depicted in Figure 4.

Figure 4: Condition of section 33 of the west parking

building and maglev foundation pit of the original

construction scheme.

To ensure the safe and stable implementation of

the close-proximity construction plan for both the

magnetic levitation deep pit and the West Parking

Building, this study employs the finite element

method to conduct numerical simulations,

quantitatively analyzing the feasibility of the

proposed scheme.

4 NUMERICAL SIMULATION

AND RESULT ANALYSIS

4.1 Numerical Simulation Scheme

Using geotechnical finite element software, a 3D

numerical model was created to simulate and analyze

the safety of the magnetic levitation deep pit under

two scenarios: the original design and the close-

proximity construction plan. The aim is to assess the

feasibility of the close-proximity construction plan. A

3D finite element geometric model was established

for the adjacent area between the magnetic levitation

deep pit and the West Parking Building based on

construction drawings (see Figure 5).

In this area, the West Parking Building is divided

into West 21 Zone (light green), West 22 Zone (dark

green), and West 23 Zone (purple) moving from west

to east, close to the magnetic levitation deep pit. The

yellow marked area far from the magnetic levitation

deep pit is designated as West 1 Zone.

The analysis involves studying ground displacement,

deformation, stress distribution, and internal forces in

the surrounding structures under both scenarios.

Results will be compared with design specifications

to assess the impact of the West Parking Building's

close-proximity construction on the safety of the

magnetic levitation deep pit. The construction plan

considers the most adverse conditions and is

reasonably simplified, as outlined in Table 1.

Table 1: Construction

condition table.

Condition 1. The initial plan Condition 2. Close-proximity construction plan

Initial Stage: West Parking Building pit excavated to design

elevation; magnetic levitation deep pit excavated to the

bottom elevation of the crown beam, with installed

retaining piles, column piles, grid columns, crown beams,

and the initial concrete support.

Step 1: Construction of a 6level structure in West 1 Zone,

considering a 100 kPa load.

Step 2: Excavation of the magnetic levitation deep pit to

the bottom of the second support, with installation of steel

supports, steel girders, and connecting beams.

Step 3: Excavation of the magnetic levitation deep pit to

the bottom elevation without constructing the base slab.

Initial Stage: Same as Scheme 1 "Initial Stage."

Step 1: Same as Scheme 1 "Step 1."

Step 2: Construction of the structure in West 2

Zone, with West 21 and West 22 completing 6

levels considering a load of 100 kPa; West 23

Zone remains unconstructed, serving as a

temporary material storage area with a

temporary load of 20 kPa considered for the

most adverse conditions.

Step 3: Same as Scheme 1 "Step 2."

Step 4: Same as Scheme 1 "Step 3."

Feasibility Simulation Analysis of Close-Proximity Construction of Underground Maglev Deep Foundation Pits Under Construction

273

Figure 5: Formation geometry model.

4.2 Constitutive Model and Parameter

Selection

The Mohr-Coulomb constitutive model is revised to a

combined model with a power law relationship,

comprising both a nonlinear elastic model and an

elastoplastic model. Due to its capability to

synchronize the elastic modulus during loading or

unloading, it is suitable for numerical simulation

studies of excavation in foundation pits. Therefore,

the soil layer in the computational model is

represented by an isotropic modified Mohr-Coulomb

model. Constitutive models for structures such as

crown beams, retaining piles, concrete supports, and

grid columns utilize isotropic linear elastic models.

For moderately weathered silty sandstone, the

values for density, cohesive strength, friction angle,

and Poisson's ratio are 23.6 kN/m

, 80 kPa, 30°, and

0.25, respectively. The elastic, secant, tangent, and

unloading moduli are 250 MPa, 321 MPa, 321 MPa,

and 1607 MPa, respectively. For other material

parameters, refer to Table 2 below.

Table 2: Material parameter value table of numerical model.

Uni

Material

(kN/m

)

E(MPa)

Crown beam/Concrete

support/Concrete tie

C30 25 0.20 30000

Column pile C35 25 0.20 31500

Retaining pile C35(reduction) 25 0.20 13230

Grid column/

Steel connectin

bea

Q235B 78 0.25 206000

The final established model core zone comprises

23 computational grid groups, 363, 106 elements, and

69, 569 nodes. The lateral and bottom boundary

conditions are set as hinge supports and vertical

displacement constraints, respectively. The West

Parking Building structure is simplified based on

zoning, and uniformly distributed surface loads are

applied at corresponding positions in the model.

Figure 6 illustrates a detailed view of the calculation

model for the T3 station magnetic levitation pit.

Figure 6: Details of foundation pit calculation model of

Maglev T3 station.

4.3 Calculation Results and Analysis

Figure 7 illustrates vertical displacement contour

maps of the ground and support structures under

Conditions 1 and 2. After the excavation of the soil in

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the magnetic levitation deep pit, the bottom soil

experiences a certain degree of rebound due to the

removal of soil loads, while the surrounding soil

layers of the West Parking Building pit undergo

settlement under the combined effects of construction

loads and soil deformation. A comparison between

Conditions 1 and 2 reveals that the impact of close-

proximity construction on the rebound of the bottom

soil in the magnetic levitation deep pit is minimal.

However, it significantly affects the ground

settlement in West 2 Zone, leading to a slightly

increased settlement of the soil on the south side of

the magnetic levitation deep pit. This shift changes

the focus of settlement from the north side to the south

side in the vicinity of the magnetic levitation deep pit.

Figure 8 shows the horizontal displacement

contour maps of the ground and support structures

under Conditions 1 and 2. After the excavation of the

magnetic levitation deep pit, the horizontal

displacement of the surrounding ground in the Y

direction (north-south) primarily involves the inward

movement of the soil on both sides of the pit. The

maximum deformation is concentrated in the middle

lower part of the retaining piles, with relatively larger

values occurring at locations where there are

significant changes in pit elevation. Comparing

Conditions 1 and 2, close-proximity construction

increases the horizontal displacement of the ground

toward the interior of the magnetic levitation deep pit,

with minimal impact on the form and characteristics

of the ground's horizontal displacement.

Figure 9 presents the deformation contour map of

the retaining piles under Conditions 1 and 2 (enlarged

1500 times to highlight deformation characteristics).

Under the combined action of soil and water pressure,

the retaining piles deform inward towards the

magnetic levitation deep pit, with the maximum

deformation concentrated in the middle lower part

(specifically, 68m above the bottom of the pit).

Comparing Conditions 1 and 2, close-proximity

construction shifts the entire southside retaining pile

parallel to the north side while increasing the

deformation differences between different parts.

However, the load from West 2 Zone has a relatively

small impact on the deformation of the northside

retaining pile.

Figure 10 displays the bending moment contour

map of the retaining piles under Conditions 1 and 2.

The maximum bending moments for the retaining

piles on the north and south sides of the magnetic

levitation deep pit occur at the bottom of the pit.

Comparing Conditions 1 and 2, close-proximity

construction mainly increases the maximum bending

moments of the retaining piles, with a greater increase

on the south side.

Figure 11 illustrates the axial force contour map

of the internal supports under Conditions 1 and 2.

After the excavation of the magnetic levitation deep

pit, both the concrete and steel support experience

axial pressure, with the 112 axis of the concrete

support receiving a higher axial pressure than other

locations. Comparing Conditions 1 and 2, close-

proximity construction increases the axial pressure on

both the concrete and steel supports.

Figure 7: Vertical displacement cloud map of stratum and

supporting structure under different working conditions (a)

Operating condition 1; (b) Operating condition 2.

Feasibility Simulation Analysis of Close-Proximity Construction of Underground Maglev Deep Foundation Pits Under Construction

275

Figure 8: Horizontal displacement cloud map of stratum

and support structure under different working conditions (a)

Operating condition 1; (b) Operating condition 2.

Figure 9: Deformation cloud map of envelope pile under

different working conditions (1500 times larger than actual

deformation) (a) Operating condition 1; (b) Operating

condition 2.

Figure 10: Cloud image of bending moment of retaining

pile under different working conditions (a) Operating

condition 1; (b) Operating condition 2.

Figure 11: Axial force cloud diagram of internal support

(concrete support, steel support) under different working

conditions (a) Operating condition 1; (b) Operating

condition 2.

Quantitative analysis was performed on the

computed results extracted from different axial

regions of the magnetic levitation deep pit under

various conditions, comparing displacements with the

original design requirements as shown in Figure 12.

From Figure 12, it is observed that after applying the

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West Parking Building load (Condition 2), the

maximum horizontal, vertical, and deepseated

displacements of the retaining pile head, as well as the

maximum settlement of the surrounding ground, are

all within the original design requirements. The safety

calculations for various indicators in the optimized

deployment plan have passed, and the displacement

increments in Condition 2 relative to Condition 1 are

relatively small. In summary, under the current

conditions, directly constructing the West Parking

Building (with varying construction levels in

different zones) does not compromise the structural

safety of the magnetic levitation deep pit.

Figure 12: Comparison of displacement between different

axis areas and original design requirements.

4.4 Construction Proposal

Although the simulation analysis indicates that the

use of the close-proximity construction approach has

minimal impact on the structural integrity of the

magnetic levitation deep pit, it is imperative to

implement appropriate safety measures to ensure the

project's safety:

(1) Strengthen pit monitoring: Enhance surface

inspections, particularly during the rainy season,

with a focus on crack observations; Timely

collect and compile monitoring data. Report any

alarming values promptly to relevant authorities

for immediate action.

(2) Ensure geological verification: Report any

inconsistencies with survey information

promptly to ensure comprehensive information

management throughout the project.

(3) Develop emergency response plans: Equip

emergency personnel, tools, and materials;

Develop contingency plans for scenarios such as

bottom pressure reversal and the need for

additional anchors or steel supports.

(4) Minimize loadings at intersections: Strictly

prohibit overloading and excessive stacking

phenomena, especially in areas designated for

ridesharing vehicles and social buses.

(5) Provide risk alerts: In case of a sudden increase

in loads during actual construction, immediately

cease operations and notify relevant authorities

for reassessment.

5 RESULT OF FIELD

IMPLEMENTATION

In February 2022, prior to onsite construction

following the optimized deployment plan,

displacement, stress, and water level monitoring

sensors were installed in the magnetic levitation deep

pit. Data were collected at daily intervals. To validate

the applicability of numerical analysis in construction

deployment optimization, monitoring data from the

adjacent section of the magnetic levitation deep pit

and West Parking Building were compared with

numerical simulation results. Due to space limitations,

the analysis focuses on the monitoring data of the

settlement point with the highest average relative

error with numerical simulation results (identified as

CFDB0352). The layout of the settlement monitoring

points is illustrated in Figure 13.

Figure 13: Schematic diagram of settlement monitoring

point layout.

1234

4- Maximum ground settlement around the foundation pit

3- Maximum vertical displacement of support pile top

2- Maximum deep horizontal displacement of support piles

Working condition 1 Working condition 2

Original design requirements

Maximum increment of condition 2 relative to condition 1

Computational Object

Displacement

/mm

-0.5

0.0

0.5

1.0

1.5

2.0

Increment

/mm

1- Maximum horizontal displacement in the Y direction of the support pile top

Support pile Maglev foundation pit

West parking building

foundation pit

CF-DB035-2

15m

Settlement monitoring points

Feasibility Simulation Analysis of Close-Proximity Construction of Underground Maglev Deep Foundation Pits Under Construction

277

Figure 14: Comparison between onsite monitoring data and numerical simulation results of settlement monitoring points.

Figure 14 depicts the comparison curve between

the actual measured data and numerical simulation

results for the monitoring point labeled CFDB0352.

As shown in the onsite monitoring data in Figure 14,

the settlement value at the monitoring point

continuously increased after the optimized

deployment construction began, stabilizing after the

completion of the magnetic levitation deep pit's

negative second floor structure. The average relative

error between the numerical simulation results and

onsite monitoring data is 11.69%. The numerical

simulation results are slightly lower than the onsite

monitoring data, attributed to insufficient

consideration of factors such as upper running

vehicles and backfill loads during the numerical

simulation.

6 CONCLUSION

This study employs dynamic management thinking

and finite element analysis to simulate the feasibility

of a proximity construction plan for an in-progress

underground maglev deep excavation. The on-site

implementation validates the safety of the plan.

Results indicate that, under favorable geological

conditions, robust excavation support measures, and

an appropriate proximity distance, the construction

near the maglev deep excavation poses no threat to

structural safety. This application case effectively

avoids the "nesting" phenomenon, offering valuable

insights for similar construction feasibility analyses.

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-16

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2023/01/08

Capping of Maglev Foundation Pit Structure

2022/12/17

Completion of the negative second floor structure

of the maglev foundation pit

settlement/mm

On site monitoring data

Numerical calculation results

2022/06/09

Convene an expert discussion meeting

Optimization deployment construction begins

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