International Symposium on Underground Excavation and Tunnelling 2-4 February 2006, Bangkok, Thailand

Causes of Shield Segment Damages During Construction Mitsutaka Sugimoto1

1 Department of Civil Engineering, Nagaoka University of Technology, Niigata, Japan ABSTRACT Recently, wider segment, thinner segment, and segment without secondary lining have been adopted to save the construction cost in Japan. Furthermore, since shallow underground space has been congested, urban tunnels have been constructed in deeper underground. As a result, shield segment damage during construction increased. These facts indicate that construction load is one of the dominant loads for segment. Segment damage makes less durability of the shield tunnel. Therefore, JSCE established the technical committee on construction loads on segment during construction in 2003. This paper presents the cause of shield segment damage during construction, based on the interim report by the above TC in 2005. 1. INTRODUCTION The design loads for shield segment in Japan (JSCE, 2001) are shown in Table 1. In this table, “Primary loads” are the basic loads to be always considered in segment design. “Secondary loads” are the loads to act during construction or after completion of the tunnel, which shall be taken into account according to the objective, the construction condition, and location of the tunnel. While, “Special loads” are the loads to be specifically considered according to the ground condition and the tunnel usage. Here, “Construction load” is categorized in “Secondary loads” and is composed of 1) shield jack thrust, 2) backfill grouting pressure, 3) erector operation load, and 4) others.

Wider segment, thinner segment, and segment without secondary lining adopted recently cause shield segment damage during construction, such as crack, striping, and chipping. These facts indicate that construction load is one of the dominant loads for segment.

Through the experience from the huge amount of shield tunnelling works, it was indicated that almost shield segment damages are occurred by the construction loads, the increase of earth pressure due to the consolidation settlement around the tunnel after completion of the tunnelling, and the change of earth pressure due to the adjacent construction work around the tunnel (Koyama, 2001). Segment damage makes less durability of the shield tunnel. Therefore, JSCE established the technical committee on construction loads on segment during construction in 2003. To establish the segment design method taking account of the construction loads during construction, this TC is carrying out the followings: 1)

Table 1. Classification of loads (JSCE, 2001, p.39) Type Loads Primary loads 1. Vertical and horizontal loads

2. Water pressure 3. Dead weight 4. Effects of surcharge 5. Soil reaction

Secondary loads 6. Internal loads 7. Construction loads 8. Effects of earthquake

Special loads 9. Effects of two or more shield tunnels construction

10. Effects of working in the vicinity 11. Effects of ground subsidence 12. Others

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Carry out the questionnaire survey and collect the site data concerned with construction loads to grasp the recent actual status of segment damage; 2) Examine the collecting site data to study the mechanism of shield segment damage during construction; 3) Develop the preliminary evaluation method on construction loads on segment during construction; and 4) Study the segment design method taking account of construction loads during construction.

This paper presents the recent actual status of segment damage and the cause of shield segment damage during construction from the questionnaire survey, and finally, the recommendation for further research to escape the shield segment damage during construction, based on the interim report (JSCE, 2005) by the above TC. 2. SEGMENT DAMAGE The questionnaire survey concerned with construction loads was carried out for 15 major experienced general construction companies to grasp the recent actual status of segment damage. As a result, the information on the shield tunnelling work and the segment damage was obtained from 50 sites. The characteristics of these data are as follows: 1) The grounds at the tunnel are distributed from soft alluvial layer to stiff diluvial layer. 2) About 80% of minimum radius of the tunnel alignment is larger than 50m. 3) The diameters of TBM have a range from 3m to 10m. 4) About 90% of the target segments are RC segment with less than 1.5m width. This section shows the brief summary of the questionnaire survey (JSCE, 2005). Note that this questionnaire survey allows multiple answer, and the answer depends on the subjectivity of the answerer.

Table 2 shows the classification of segment damage during construction, based on the site experience. Figure 1 shows the frequency of segment damage during construction for segment damage type basis, and the number of “Type of segment damage during construction” in Figure 1 corresponds to the number in Table 2. From this figure, the followings were found: the major segment damages are Crack in axial direction (Type 1) and Chipping at segment corner (Type 3); and the next frequent segment damages are Crack/ Stripping around ring joint box (Type 6), Crack/ Stripping around segment joint box (Type 7), and Crack in circumferential direction (Type 2) in descent order.

Figure 2 shows the construction stage at segment damage appearance. From this figure, it was found that about 70% of Crack in axial direction (Type 1) appears at the curve alignment, but even at the straight alignment the same type damage appears. On the other hand, the other type segment damages have no obvious relation with the construction stage and the tunnel alignment. These facts indicate the followings: Type 1 segment damage has much relation with the tunnel alignment; and the other type segment damages get less influence of the construction stage and the tunnel alignment.

Figure 3 shows the position of segment damage during construction. From this figure, the followings were found: segment damage at spring line appears in Type 1 segment damage significantly, compared with the other type segment damages; about 60% of Crack in axial direction (Type 1) appears at A segment and B segment; and about 70% of Chipping at segment corner (Type 3), Crack/ Stripping around ring joint box (Type 6), and Crack/ Stripping around segment joint box (Type 7) appears at B segment and K segment. These facts indicate the followings: Type 1 segment damage is related with the position of segment; and Type 3, Type 6, and Type7 segment damages have much relation with the shape of segment piece, i.e., B segment and K segment.

Figure 4 shows the timing of segment damage during construction. From this figure, the followings were found: Type 1 segment damage does not appear at the segment installation; about 80% of Type 1 segment damage appears during the excavation when the segment is inside tail and at tail passing; and about 80% of Type 3, Type 6, and Type7 segment damage appears at the segment installation and during the excavation. These facts indicate the followings: Type 1 segment damage gets the influence of excavation; and Type 3, Type 6, and Type7 segment damages have a relation with the workmanship.

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Num

ber o

f dam

age

Type of segment damage during construction

:others :invert :crown :spring line :whole segment :A segment :B segment :K segment

Num

ber o

f dam

age

Type of segment damage during construction

:others :excavation at curve :excavation at straight line :initial excavation at curve :initial excavation at straight line

Figure 4. Timing of segment damage during construction (JSCE, 2005, p.19)

Type of segment damage during construction

Num

ber o

f dam

age

:others :just after tail :during excavation, at tail passing:during excavation, inside tail :at segment installation

Figure 3. Position of segment damage during construction (JSCE, 2005, p.19)

Figure 2. Construction stage at segment damage appearance (JSCE, 2005, p.19)

:less than once within 20-30ring :more than once within 20-30ring:more than once within 2-3ring

Figure 1. Frequency of segment damage during construction (JSCE, 2005, p.17)

Type of segment damage during construction

Num

ber o

f dam

age

Table 2. Classification of segment damage during construction (JSCE, 2005, p.17) No. Shield segment

damage Figure

1 Crack in axial dir.

2 Crack in

circumferential dir.

3 Chipping at segment corner

4 Stripping around

segment joint

5 Stripping around

ring joint

6 Crack/ Stripping around ring joint box

7 Crack/ Stripping

around segment joint box

8 Stripping at outer

surface

9 Hair crack at inner surface

10 Appearance of

non-visible crack

11 Buckling of longitudinal rib (steel segment)

12 Deformation of rib(steel segment)

13 Break of joint bolt

14 Others

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Table 3. Classification of cause of segment damage during construction (JSCE, 2005, p.19)Stage Category Cause Refer Design Ground A. Stiff ground

B. Soft ground C. High hydraulic pressure

Tunnel alignment

D. Sharp curve E. Sudden slope transition

TBM F. Insufficient tail clearance G. No articulated mechanism

Segment H. Thinner segment I. Wider segment J. Division pattern of segment K. Characteristics of joint L. Characteristics of sealing material

Construction Shield jack a. Excess jack thrust b. Eccentric each jack thrust on segment piece c. Inclination of jack against segment d. Eccentric total jack thrust acting on segment ring

Fig. 5 b. Fig. 5 c. Fig. 5 d.

Shield tail e. Contact between tail and segment Fig. 5 e. Segment

installation f. Non-flat joint g. Open joint h. Accuracy of segment installation

Fig. 5 f. Fig. 5 g. Fig. 5 h.

Others i. Eccentric grease pressure Fig. 5 i

j. Eccentric grouting pressure k. Improper tightening force of joint l. Insufficient grouting

Fig. 5 j.

3. CAUSE OF SEGMENT DAMAGE Cause of segment damage exists not only at construction stage but also at design stage. Table 3 shows the classification of cause of segment damage during construction, based on the site experience, under the condition that all of the products have a certain accuracy on the dimension and the material property.

The cause of segment damage at design stage comes from ground, tunnel alignment, TBM, and segment. In case of stiff ground (A), since larger ground reaction force does not allow rotation of the TBM, the TBM axis direction has some deviation from the segment axis direction. In case of soft ground (B), the control of TBM at sharp curve is sometimes difficult since less ground reaction force is insufficient to support the jack thrust and the jack moment along the segment. High hydraulic pressure (C) requires the high jack thrust. Sharp curve (D) and sudden slope transition (E) decreases the tail clearance due to geometric condition. Furthermore, composite alignment in horizontal and vertical direction makes the TBM control difficult. Insufficient designed tail clearance (F) and wider segment (I) make the contact between the segment and the tail easily. No articulated mechanism on TBM (G) gives less fitting of the skin plate for the excavation surface around the skin plate. Thinner segment (H) generates the eccentric each jack thrust on the segment piece. Improper division pattern of segment (J) makes the segment installation work difficult. Improper characteristics of joint (K) and improper characteristics of sealing material (L) generate the stress concentration on the segment. The above mentioned is the example of the effect of each cause.

On the other hand, the cause of segment damage at construction stage is related with shield jack, shield tail, segment installation, and others, as shown in Table 3. Furthermore, some causes are illustrated in Figure 5. The example of the effect of each cause is shown below. Excess jack thrust (a) increases the compressive stress in the segment. Eccentric each jack thrust on segment piece (b) and open joint (g) generate the moment to the segment piece. Eccentric total jack thrust acting on segment ring (d) generates the moment to the segment ring. Inclination of jack against segment (c), contact

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ジャッキ セグメント

ジャッキシュウ（スプレッダ） ひび割れ

Jack spreader

Segment Jack

Stripping

Crack

Segment

Tail brushSkin plate

Jack thrust

Segment

Stripping

Eccentric pressure

Segment

Crack

Jack thrust

Insert

Chipping

Figure 5 Cause of segment damage during construction (JSCE, 2005, p.37)

13

41

28

1

5541

44

6115

0102030

8090

100

e

hd

Num

ber

40506070

shield

jack

Shield

tail

Segmen

t insta

llatio

n

Others

ki, j

lf,g

cb

a7713 33

1

37

32

11211

0102030405060708090

100

Ground

Tunne

l alig

nmen

t

TBM

Segmen

t

ABC

JKL

I

HG

D,E

Num

ber

Figure 6 Frequency of cause of segment damage during construction (JSCE, 2005, p.19)

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between tail and segment (e), non-flat joint (f), less accuracy of segment installation (h), eccentric grease pressure (i), and eccentric grouting pressure (j) generate the stress concentration on the segment. Less tightening force of joint (k) allows the deformation of the segment ring easily. Insufficient grouting (l) decreases the effect of the ground reaction force.

Figure 6 shows the frequency of each cause of segment damage during construction. From this figure, the followings were found. At the design stage, the shape of segment such as thinner segment (H) and wider segment (I), and the tunnel alignment such as sharp curve (D) and sudden slope transition (E) are the major causes of segment damage. While “TBM” in Figure 6 shows small contribution to segment damage, it is noted that insufficient designed tail clearance (F) at “TBM” increases the possibility of the contact between tail and segment (e). At the construction stage, contact between tail and segment (e) in “shield tail” is the major cause of segment damage. The next frequent causes of segment damage are related with “segment installation” such as, non-flat joint (f), open joint (g), and less accuracy of segment installation (h). Eccentric total jack thrust acting on segment ring (d) and eccentric each jack thrust on segment piece (b) in “shield jack” also have a large contribution to segment damage.

For example, the mechanism of Type 1 segment damage due to contact between tail and segment (e) is examined. At the design stage, tunnel alignment (D, E), designed tail clearance (F), TBM with/without articulated mechanism (G), and segment width (I) determine the geometric condition for tail clearance. At the construction stage, ground reaction force (A, B), applied jack moment (d), overcutting area by copy cutter, and so on, determine the shield postulate, where usually the overcutting area has more influence to the shield postulate than the jack moment. Consequently, the inclination of the TBM axis against the segment axis is occurred. Then the distribution of tail clearance becomes non-uniform. Under a certain condition, the shield tail contacts with the segment (e). Furthermore, smaller designed allowance of tail clearance from the viewpoint of the geometric condition, existence of the hardened grouting material inside the tail brush after the intrusion of grouting material due to large tail clearance at the sharp curve, excess grouting pressure (j), and insufficient grease injection to the tail clearance (i), increase the possibility of contact between the tail and the segment. When the shield tail contacts with the segment, Type 1 segment damage appears due to the large moment on the segment, as illustrated in Figure 5 e.. The contact between the tail and the segment makes the segment deformation easily. The segment deformation makes non-flat joint (f), open joint (g), less accuracy of the segment installation (h), eccentric each jack thrust on the segment piece (b), inclination of the jack against the segment (c). Furthermore, non-flat joint (f), open joint (g), and less accuracy of segment installation (h) also depends on the workmanship.

As shown in the above, when a cause of segment damage is examined, it is necessary to remind the followings: 1) The design stage contributes to the segment damage. Therefore, in order to escape segment damage, it is necessary to examine the design conditions carefully. Furthermore, under a certain setting condition at the design stage, it is impossible to escape segment damage, even if the construction work is done correctly. 2) A segment damage usually results from the several causes not only at the design stage but also at the construction stage. 3) A cause is related with another causes complicatedly. 4. RECOMMENDATION To escape the shield segment damage during construction, the following process is required for further research: 1) Grasp the actual status of construction load and segment by measurement. 2) Make clear the major causes of each segment damage and the mechanism of each segment damage, based on empirical rule and site measurement. 3) Develop the analysis method on construction loads on segment during construction. 4) Establish the segment design method taking account of the construction loads during construction.

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5) Carry out the preliminary study on the construction loads on segment during construction, and feed back its information to the design of tunnel alignment, TBM, and segment before start of the construction. 6) Carry out the construction management by using some measurements which are required by the above method. These progress stages are shown in Table 4.

Measurement is important and measurement plan should be made according to the requirements of its objective. Usually, tintensive measurement is required to make clear tmechanism of segment damage, while tmeasurement for construction management shoucover the indexes concerned with the constructiloads on segment.

On the other hand, analysis approach is alnecessary to escape segment damage in advance the prediction of construction loads on segmeFor example, the predicted tail clearandistribution at segment front end section and at tend section by the shield kinematic mod(Sugimoto and Sramoon, 2002)(Sramoon aSugimoto, 2002) is shown in Figure 7, which calculated under the condition that the TBM

excavates the stiff diluvial sandy ground alonghorizontal articulated angle. From this figure, the1) The improper TBM operation generates the inthe shift of TBM center from the segment center. 2) The uniform tail clearance distribution is not ex3) The tail clearance at tail end section is the cbetween tail and shield in this case. Furthermore, the evaluations of the constructionrecently by Leendertse et al. (2001) and Tajima e 5. CONCLUSIONS This paper presents the recent actual status of seduring construction, and the recommendation for2005). Furthermore, the classification of segmencause of segment damage during construction afollowings are concluded: 1) The major segment damages are Crack in axia(Type 3). Type 1 segment damage appears excavation, while Type 3 segment damage ainstallation and during excavation. 2) The major cause of segment damage duringalignment, and the designed tail clearance of TBMsegment, the accuracy of segment installation, Furthermore, the control of the shield postulate is

Table 4. Method vs. objective Method Study on

Mechanism

Preliminary study

Construction management

Empirical rule

yes yes yes

Measurement

yes no yes

Analysis yes yes yes/no

he he he ld on

1.60

1.

1.70

1.75

1.80

1.85

1.90

1.95

2.00

65Segment Segment front endso

by nt. ce ail el

nd is

Figure 7 Distribution of tail clearance at straight line with articulated angle 3

straight line with 5mm overcutting and 3 deg. of followings were found: clination of TBM axis against the segment axis and pected under a certain condition. rucial condition from the view point of the contact

loads by using 3D FEM analysis were carried out t al. (2004).

gment damage, the cause of shield segment damage further research, based on the interim report (JSCE, t damage during construction and the classification of re shown in Table 2 and Table 3 respectively. The

l direction (Type 1) and Chipping at segment corner around spring line at the curve alignment during ppears at B segment and K segment at segment

construction are the shape of segment, the tunnel at the design stage, and the contact between tail and

and the shield jack thrust at the construction stage. also important.

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3) A segment damage usually results from the several causes not only at the design stage but also at the construction stage. 4) A cause is related with another causes complicatedly. ACKNOWLEDGEMENTS The author greatly appreciates the members of the technical committee on construction loads on segment during construction supported by the Japanese Society of Civil Engineering, who contribute to the interim report on construction loads on segment. REFERENCES JSCE, 2001. Japanese standard for shield tunnelling -1996-The third edition, JSCE, Japan. JSCE, 2005. Interim report on construction loads on segment, JSCE, Japan. (in Japanese) KOYAMA Y., 2001. Behaviors of segmental linings constructed by closed-type shield, IS-Kyoto

Short Course Text, Kyoto, pp.113-127. Leendertse W.L., JovampvicP.S., and Blom C.B.M., 2001. Using 3D FEM models for predicting

damage during assembling of shield driven tunnel lining of the Green Heart Tunnel, Proc. of Int. Symp. on Modern Tunneling Science and Technology(IS-KYOTO), Vol. 2, Balkema, pp. 653-656.

Sramoon A. and Sugimoto M., 2002. Theoretical model of shield behavior during excavation: II. Application, J.of Geotechnical and Geoenvironmental Eng., 128(2)2, pp.156-165.

Sugimoto M., and Sramoon A., 2002. Theoretical model of shield behavior during excavation: I.Theory, J.of Geotechnical and Geoenvironmental Eng., 128(2)2, pp.138-155.

Tajima H., Kishida M., Fukai N., and Saitou M., 2004. Study on shield tunnel construction loads using a three dimensional FEM model, Proc. of Tunnel Engineering, Vol. 14, JSCE, pp. 353-360. (in Japanese)

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