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ISSN : 1598-6721(Print)
ISSN : 2288-0771(Online)
The Korean Society of Manufacturing Process Engineers Vol.18 No.1 pp.38-45
DOI : https://doi.org/10.14775/ksmpe.2019.18.1.038

# A Study on the Stability of Shield TBM Thrust Jack in the Behavior of Operating Fluid According to Thrust Force

Hyun-seok Lee*, Yeong-min Na*, Hyun-su Jang*, Ik-hyun Suk*, Sin-hyun Kang**, Hun-tae Kim**, Jong-kyu Park*#
*School of Mechatronics, Changwon National UNIV.
**EM Korea Co., Ltd.
Corresponding Author : chong@changwon.ac.kr Tel: +82-55-213-3605, Fax: +82-55-275-0101
09/11/2018 12/11/2018 13/11/2018

## Abstract

In this paper, the stability of the tunnel boring machine (TBM), used in tunnel excavation, according to the thrust force of the thrust jack was investigated. The existing hydraulic cylinder analysis method is fluid-structure interaction (FSI) analysis, where all of the flow setting and dynamic characteristics should be considered. Therefore, there is a need for a method to solve this problem simply and quickly. To facilitate this, the theoretical pressure in the hydraulic cylinder was calculated and compared with the analytical and experimental results. In the case of the analysis, the pressure generated inside the cylinder was analyzed statically, considering the operating characteristics of the shield TBM, and the stress and pressure were calculated. This method simplifies the analysis environment and shortens the analysis time compared to the existing analysis method. The obtained theoretical and analytical data were compared with the measured data during actual tunneling, and the analysis and experimental data showed a relative error of approximately 23.89%.

# 추력에 따른 동작 유체의 거동에 있어 쉴드 TBM 추진잭의 안정성에 대한 연구

이 현석*, 나 영민*, 장 현수*, 석 익현*, 강 신현**, 김 훈태**, 박 종규*#
*창원대학교 기계공학과
**이엠코리아(주)

## 초록

Ministry of Land, Infrastructure and Transport
18SCIP-B129646-02

Ministry of Education
2018R1A6A1A03024509

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

## 1. Introduction

As urban integration has accelerated around the world, so too has the problem of traffic congestion. To solve this, the importance of tunnels to distribute traffic has been emphasized and a variety of methods have been attempted[1~5]. One of the typical methods is the New Austrian Tunneling Method (NATM), which uses blasting and has the advantages of enabling constructability in diverse geological features and rapid responses to changes in geological features. However, it requires workers with specialized skills during instrumentation and construction, and economic feasibility is degraded in small-scale cross-sections due to the necessity of utilizing many pieces of equipment[6]. As an alternative to NATM, a method using a tunnel boring machine (TBM) has been introduced, by which tunnels are formed as the excavation machine drills through soils underground. As all processes from lining to tunnel muck hauling operations are systematized, the TBM can shorten the construction time and reduce costs as its construction speed is faster than that of NATM.

In general, TBMs are divided into open-type and shielded TBMs. A TBM consists of a cutter head that cuts the ground, a thrust jack for forward movements, and a conveyor that transfers muck out of the way during forward movements. Hydraulic cylinders are widely used in the thrust jack for the forward movement of the TBM. Since the thrust jack is a shape wherein fluid and structure interact flexibly, a variety of studies have been conducted on it[7~9].

Kim et al. conducted a fluid–structure interaction (FSI) analysis for the miniaturization of a valve electro-hydraulic actuator system for offshore plants. They verified the effects of changes in oil viscosity on the actuator's performance according to an increase in working pressure[10].

They also conducted the FSI analysis on cushion device performance in the hydraulic actuator used in offshore plants. Another study proposed optimal design factors by analyzing changes in cushion time and pressure while changing the cushion shape[11]. Kim verified the characteristics of the basic operation of the hydraulic actuator consisting of rack and pinion through the FSI analysis[12].

The aforementioned studies analyzed the behavior and reaction force that occurred when a rod pushed working fluid and it moved. Their studies verified the stress distribution of actuators and evaluated their structural stability. However, their analysis methods require the boundary conditions of liquid flow and should consider the dynamic characteristics according to the fluid movement as well. Accordingly, due to analysis difficulties and an increase in time, simplified analysis methods are needed.

In this regard, this study aimed to calculate the working fluid pressure according to the thrust force of the thrust jack in the FSI analysis; it did so while changing the analysis conditions, thereby verifying the structural stability of the thrust jack. The specifications of the hydraulic cylinder that were applied to the TBM by the company were employed in the thrust jack. The experimental measurements were compared with the thrust jack data measured while performing TBM tunneling by the manufacturing company. The daily excavation distance of the shielded TBM in Korea was 4.93 m on average[13], which meant that the tunneling acceleration of the thrust jack converged on zero. A static analysis can be done if an acceleration of objects is zero despite dynamic state objects. Using this, a theoretical derivation and analysis environment are constructed. That is, the pressure applied to the given hydraulic jacking device is theoretically derived, and its stability is determined through a comparison between FSI analysis and experimental measurements.

## 2. Theory

FSI analysis is a method for numerically analyzing the interaction between fluid and structure. That is, as shown in Fig. 1, the load, pressure, and temperature that occur due to flow are transferred to a structure, and information about deformation is accordingly reflected in the flow again, which is then repeated.

This is the same as the operation principle of hydraulic cylinders, where motion occurs when the internal working fluid inside the cylinder is introduced to the inlet by the compressor and then exits to the outlet. Thus, the flow characteristics of the working fluid and stress applied to the structure are verified in general using the FSI analysis.

However, such a method requires that all the boundary conditions of the flow should be assigned, and all dynamic characteristics should be analyzed. As a result, analysis accessibility is reduced due to the increase in analytical difficulties and time. This problem can be overcome with a simplified method of analysis. Fig. 2

In this regard, this study considered the operation characteristics of the TBM to calculate the pressure that occurs in the working fluid of the cylinder due to the thrust force. The forward speed of the hydraulic cylinder of the TBM manufactured by the company is 57 mm/min, which moves the TBM forward approximately at a rate of 1mm per sec.

In addition, it moves forward at a constant speed except for the initial acceleration, which means that the acceleration converges on zero. Objects in motion can be analyzed statically as shown in Fig. 3 if their acceleration is zero even if their motion state is dynamic. Using this, the pressure generated in the fluid is calculated.

Generally, the pressure in a hydraulic cylinder is calculated by the area and force. The pressure (σ)applied to the fluid can be calculated by the Pascal’s principle, which is as follows, assuming that a constant pressure is applied to the whole area of the chamber.

$σ = F / ( 0.25 ⋅ π D 2 )$
(1)

Here, F refers to the force and D refers to the internal diameter of the chamber.

The specifications of the hydraulic cylinder used by the company are presented in Table 1, and the thrust force used in a single cylinder is employed at a range of 250–390 kN. Based on this, the pressure due to the thrust force is calculated, which is shown in Fig. 4.

The theoretically calculated results are compared with the FIS analysis results and experimental measurements, thereby judging the stability.

## 3. Analysis

### 3.1 Analysis conditions

The analysis model consisted of a chamber and rod in the hydraulic cylinder used in the company, which is shown in Fig. 5. As mentioned in Section 2, this study aimed to analyze the pressure that occurred in the working fluid inside the chamber, as well as the stress due to the pressure, while excluding the inlet and outlet of the working fluid. Software COMSOL Multiphysics was used, the cylinder's material was SCM 440, and the working fluid was non-compressive oil. The physical properties are presented in Table 2. As the rod was moved in the chamber direction only in this configuration, the entire body was fixed. The roller condition was applied between the cylinder and chamber, thereby restricting the movement in the circumferential direction.

In addition, a thrust force was added in the Y-axis direction, the range of which was 270–390 kN with increments of 15 kN. As shown in Fig. 6, the force was increased for 0.5 sec and then maintained after one sec.

The mesh was a free tetrahedral shape, as shown in Fig. 7. It was created with 153,449 nodes when the analysis values started to converge. In addition, the mesh whose value had not converged was re-created through the adaptive mesh refinement function to increase the accuracy of the analysis. The analysis time was zero to 10 sec with increments of one sec.

### 3.2 Analysis results

The analysis results verified that stress was applied to the rod and fluid as a force was applied, as shown in Fig. 8. The maximum stress and pressure applied to the fluid were generated at a location where the fluid and rod met, when the force was 390 kN, and the maximum stress and pressure were 28 and 12 MPa, respectively.

Since the yield stress of SCM 440 was known to be 590 MPa, this structure was stable, and the maximum stress and pressure applied to the fluid from 270 to 390 kN are summarized in Fig. 9. The obtained data were matched and compared with the measurements accumulated through the actual TBM tunneling by the company to verify the analysis results.

## 4. Experiment

For the experimental method, a comparison was conducted with the data accumulated during tunneling conducted from Shin Boryeong to Yeongseo in tunnel construction for power cables by the Korean electric power corporation (KEPCO). The specifications of the TBM used in tunneling are presented in Table 3, and data were measured and extracted by sensors attached to the thrust jack from 07:50 to 23:26 on September 17, 2017.

The measured data are summarized in Table 4, and Fig. 10 shows the comparison graph of theoretical, analytical, and experimental results. The mean error between the analysis and experimental values was around 23.89%, which was due to the difference in actual driving environments, that is, changes in thrust force caused by the ground strength.

## 5. Conclusions

This study verifies the stability of the thrust jack used in tunneling in a shielded TBM by calculating the pressure applied to its fluid. FSI analysis, which was used to verify the operation characteristics of hydraulic cylinders, was generally accompanied by the dynamic characteristics. However, this study analyzed the operation characteristics statically by reflecting the operation characteristics of the thrust jack.

Pressure occurred when a force was applied to a non-compressive fluid in the hydraulic cylinder used by the company; it was calculated in the FSI analysis, and the force varied in a range of 270 to 390 kN. The analysis results verified that the maximum stress and fluid pressure, occurring at 390 kN, were 28 and 12 MPa, respectively. Since the yield stress of SCM 440 was known to be 570 MPa, this cylinder was regarded as stable. Based on this result, experiments were conducted, and experimental results were compared with theoretical and analytical results.

The experiments were based on data measured during tunneling conducted by the company, and the relative error between analysis and experimental values was calculated to be 23.89% on average. This error was due to the friction and viscosity that were not taken into consideration in the analysis, and this study verified that a more simplified method of analysis could be possible in the future.

In future studies, both friction and viscosity will be taken into consideration to raise analysis accuracy.

## Acknowledgments

“This work is supported by the Korea Agency for Infrastructure Technology Advancement(KAIA) grant funded by the Ministry of Land, Infrastructure and Transport(Grant 18SCIP-B129646-02).” also “This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(No.2018R1A6A1A03024509)”

## Figure

Fluid-structure interaction concept
hydraulic cylinder
Equivalent condition of hydraulic cylinder to thrust force
Theoretical pressure according to thrust force
Analysis conditions
Thrust force according to time
Mesh of analysis model
Analysis result
Analysis result according to thrust force
Experimental result

## Table

Specification of thrust jack
Properties of SCM 440, Oil[14]
Specification of TBM
Measured data

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