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Holistic Assessment Strategy for Hung Hom Station Extension Stage 2 Investigation - Results of Verification of Workmanship Quality for Coupler Connections

According to the holistic assessment strategy of MTR Corporation Limited (MTRCL) regarding the platform slabs and diaphragm walls of the Hung Hom Station Extension under the Shatin to Central Link (SCL) Project accepted by the Government on 5 December 2018, the MTRCL proceeded to commence the relevant work on 10 December.  The first purpose of opening up the concrete is to carry out physical investigation at locations with gaps in the documentation, so as to verify the as-constructed conditions of the connections between the platform slabs and diaphragm walls. The second purpose is that, in view of the allegations on the cutting-short of steel bars, the MTRCL needs to open up certain connections between the platform slabs and diaphragm walls for detailed inspection, and to conduct non-destructive tests to verify the works quality of the coupler connections. The locations of opening-up were randomly selected based on a statistical approach.

According to the information from the coupler’s supplier, proper installation requirements of coupler are:
(1) there shall be a maximum of two full threads exposed; and
(2) the embedded length of the threaded steel bar inside the coupler shall be at least 40 millimetres.

The contractor may use Type B Reinforcement bars at some locations.  Type B reinforcement bars have 22 threads, in which case the installation requirement of coupler will be a maximum of twelve full threads exposed.

The MTRCL uses the phased array ultrasonic test to verify the embedded length of the threaded steel bar inside the coupler. As the allowable measurement tolerance of the test is 3 millimetres, equipment readings below 37 millimetres are regarded as failure in meeting the requirement. The test is carried out by the professional technicians of A.E.S. Destructive and Non-Destructive Testing Limited.

The coupler test results conducted by the MTRCL are given below:

Test Results of Couplers Exposed for the First Purpose
(As at 21 January 2019)

Coupler No.

Location of Coupler Tested

No. of Exposed Thread

Embedded Length - Preliminary Results
(millimetres)
(Remark 1)

Embedded Length –
Formal Test Report
(millimetres)
(Remark 2)

EWL-E44-TT-T1-01-C1

At the top of Area B of East West Line (EWL) slab near eastern Diaphragm Wall

1-2

31.61

31.61

EWL-E44-TT-T1-02-C1

At the top of Area B of EWL slab near eastern Diaphragm Wall

9-10
(Remark 4)

6.22

6.22

EWL-E32-TT-T1-01-C1

At the top of Area Hong Kong Coliseum (HKC) of EWL slab near eastern Diaphragm Wall

0-1

36.65

36.65

EWL-E32-TT-T1-02-C1

At the top of Area HKC of EWL slab near eastern Diaphragm Wall

0-1

42.02

42.02

EWL-E32-TT-T1-03-C1

At the top of Area HKC of EWL slab near eastern Diaphragm Wall

0-1

41.51

41.51

EWL-E35-TT-T1-01-C1

At the top of Area HKC of EWL slab near eastern Diaphragm Wall

0

47.01

47.01

EWL-E35-TT-T1-02-C1

At the top of Area HKC of EWL slab near eastern Diaphragm Wall

0-1

45.70

45.70

EWL-E35-TT-T1-03-C1

At the top of Area HKC of EWL slab near eastern Diaphragm Wall

0-1

43.45

43.45

EWL-E37-TT-T1-01-C1

At the top of Area HKC of EWL slab near eastern Diaphragm Wall

1-2

39.84

39.84

EWL-E37-TT-T1-02-C1

At the top of Area HKC of EWL slab near eastern Diaphragm Wall

1-2

42.51

42.51

EWL-E46-TT-T1-01-C1

At the top of Area B of EWL slab near eastern Diaphragm Wall

0-1

44.04

44.04

EWL-E46-TT-T1-02-C1

At the top of Area B of EWL slab near eastern Diaphragm Wall

2-3

33.00

33.00

EWL-E72-BT-T1-01-C1

At the top of Area C1 of EWL slab near eastern diaphragm wall

0-1

36.39

36.39

EWL-E72-BT-T1-02-C1

At the top of Area C1 of EWL slab near eastern diaphragm wall

0-1

36.88

36.88

 

Test Results of Couplers Exposed for the Second Purpose
(As at 21 January 2019, the latest information is highlighted in blue)

Coupler No.

Location of Coupler Tested

No. of Exposed Thread

Embedded Length - Preliminary Results
(millimetres)
(Remark 1)

Embedded Length –
Formal Test Report
(millimetres)
(Remark 2)

EWL-E46-BB-B1-01-C1

At the bottom of  Area B of EWL slab near eastern diaphragm wall

2-3

34.91

34.91

EWL-E46-BB-B1-02-C1

At the bottom of Area B of EWL slab near eastern diaphragm wall

3-4

29.65

29.65

EWL-E46-BB-B1-03-C1

At the bottom of Area B of EWL slab near eastern diaphragm wall

2-3

34.32

34.32

EWL-E70-BB-B1-01-C1

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

2-3

40.51

40.51

EWL-E70-BB-B1-02-C1

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

1-2

36.78

36.78

EWL-E40-TT-T1-01-C1

At the top of Area B of EWL slab near eastern diaphragm wall

9-10
(Remark 3)

39.21

39.21

EWL-E40-TT-T1-02-C1

At the top of Area B of EWL slab near eastern diaphragm wall

10-11
(Remark 3)

40.81

40.81

EWL-E40-TT-T1-03-C1

At the top of Area B of EWL slab near eastern diaphragm wall

11-12
(Remark 3)

38.57

38.57

EWL-E65-BB-B1-01-C1

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

0

42.43

42.43

EWL-E107-BB-B1-01-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

35.34

35.34

EWL-E107-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

6-7

9.40

9.40

EWL-E107-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

40.91

40.91

EWL-E90-BB-B1-01-C1

At the bottom of Area C2 of EWL slab near eastern diaphragm wall

0

41.43

41.43

EWL-E90-BB-B1-02-C1

At the bottom of Area C2 of EWL slab near eastern diaphragm wall

0

43.82

43.82

EWL-E90-BB-B1-03-C1

At the bottom of Area C2 of EWL slab near eastern diaphragm wall

0

43.85

43.85

EWL-E50-BB-B1-01-C1

At the bottom of Area B of EWL slab near eastern diaphragm wall

0

34.80

34.80

EWL-E77-BB-B1-01-C1

At the bottom of Area C2 of EWL slab near eastern diaphragm wall

0

45.22

45.22

EWL-E96-BB-B1-01-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

42.02

42.02

EWL-E112-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

48.72

48.72

EWL-W58-BB-B1-01-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

0-1

40.04

40.04

EWL-W58-BB-B1-02-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

0

45.85

45.85

EWL-W58-BB-B1-03-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

0-1

39.22

39.22

NSL-E68-TT-T1-01-C1

At the top of Area C1 of North South Line (NSL) slab near eastern diaphragm wall

0

39.38

39.38

NSL-E68-TT-T1-02-C1

At the top of Area C1 of NSL slab near eastern diaphragm wall

1-2

40.07

40.07

NSL-E80-TT-T1-01-C1

At the top of Area C2 of NSL slab near eastern diaphragm wall

0

38.01

38.01

NSL-E80-TT-T1-02-C1

At the top of Area C2 of NSL slab near eastern diaphragm wall

0-1

38.33

38.33

NSL-E80-TT-T1-03-C1

At the top of Area C2 of NSL slab near eastern diaphragm wall

0

36.36

36.36

EWL-W112-BB-B1-01-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

3-4

28.54

28.54

EWL-W112-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

2-3

34.99

34.99

EWL-W112-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

35.32

35.32

EWL-E115-BB-B1-01-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

40.78

40.78

EWL-E115-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

42.02

42.02

NSL-E29-TT-T1-01-C1

At the top of Area HKC of NSL slab near eastern Diaphragm Wall

0-1

38.09

38.09

NSL-E29-TT-T1-02-C1

At the top of Area HKC of NSL slab near eastern Diaphragm Wall

0

49.06

49.06

NSL-E29-TT-T1-03-C1

At the top of Area HKC of NSL slab near eastern Diaphragm Wall

0-1

44.05

44.05

EWL-W68-BB-B1-01-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

1-2

35.45

35.45

EWL-W68-BB-B1-02-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

1-2

34.70

34.70

EWL-W68-BB-B1-03-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

1-2

37.58

37.58

EWL-W78-BB-B1-01-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

1-2

37.46

37.46

EWL-W78-BB-B1-02-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

1-2

36.42

36.42

EWL-W78-BB-B1-03-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

1-2

39.05

39.05

EWL-W78-BB-B1-04-C1

At the bottom of Area C1 of EWL slab near western diaphragm wall

2-3

37.66

37.66

EWL-W84-BB-B1-01-C1

At the bottom of Area C2 of EWL slab near western diaphragm wall

0

33.98

33.98

EWL-W84-BB-B1-02-C1

At the bottom of Area C2 of EWL slab near western diaphragm wall

1-2

32.59

32.59

EWL-W84-BB-B1-03-C1

At the bottom of Area C2 of EWL slab near western diaphragm wall

1-2

36.80

36.80

EWL-W115-BB-B1-01-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

44.66

44.66

EWL-W91-BB-B1-01-C1

At the bottom of Area C2 of EWL slab near western diaphragm wall

2-3

32.97

32.97

EWL-W91-BB-B1-02-C1

At the bottom of Area C2 of EWL slab near western diaphragm wall

2-3

34.66

34.66

EWL-W91-BB-B1-03-C1

At the bottom of Area C2 of EWL slab near western diaphragm wall

2-3

37.77

37.77

NSL-E38-TT-T1-01-C1

At the top of Area HKC of NSL slab near eastern Diaphragm Wall

0-1

41.29

41.29

NSL-E38-TT-T1-02-C1

At the top of Area HKC of NSL slab near eastern Diaphragm Wall

0

40.40

40.40

NSL-E38-TT-T1-03-C1

At the top of Area HKC of NSL slab near eastern Diaphragm Wall

0

42.18

42.18

NSL-W73-TT-T1-01-C1

At the top of Area C1 of NSL slab near western Diaphragm Wall

1-2

32.91

32.91

NSL-W73-TT-T1-02-C1

At the top of Area C1 of NSL slab near western Diaphragm Wall

2-3

35.36

35.36

NSL-W73-TT-T1-03-C1

At the top of Area C1 of NSL slab near western Diaphragm Wall

1-2

32.42

32.42

EWL-W129-BB-B1-01-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

40.00

40.00

EWL-W129-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

0-1

38.67

38.67

EWL-W133-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

28.79

28.79

EWL-W136-BB-B1-01-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

33.92

33.92

EWL-W136-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

40.58

40.58

EWL-W136-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

35.49

35.49

NSL-W25-TT-T1-01-C1

At the top of Area HKC of NSL slab near western Diaphragm Wall

0

38.46

38.46

NSL-W25-TT-T1-02-C1

At the top of Area HKC of NSL slab near western Diaphragm Wall

0

39.02

39.02

NSL-W33-TT-T1-01-C1

At the top of Area HKC of NSL slab near western Diaphragm Wall

0-1

40.84

40.84

NSL-W114-TT-T1-01-C1

At the top of Area C3 of NSL slab near western Diaphragm Wall

0

44.17

44.17

NSL-W127-TT-T1-01-C1

At the top of Area C3 of NSL slab near western Diaphragm Wall

1-2

37.73

37.73

EWL-E65-BB-B1-02-C1

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

0-1

45.19

To be provided by MTRCL

EWL-E65-BB-B1-03-C1

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

0-1

42.83

To be provided by MTRCL

EWL-E70-BB-B1-03-C1

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

0

42.66

To be provided by MTRCL

EWL-E77-BB-B1-02-C1

At the bottom of Area C2 of EWL slab near eastern diaphragm wall

0

46.45

To be provided by MTRCL

EWL-E77-BB-B1-03-C1

At the bottom of Area C2 of EWL slab near eastern diaphragm wall

1-2

37.22

To be provided by MTRCL

EWL-E96-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

39.52

To be provided by MTRCL

EWL-E96-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

41.93

To be provided by MTRCL

EWL-E97-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0-1

36.69

To be provided by MTRCL

EWL-E97-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

42.61

To be provided by MTRCL

EWL-E112-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

44.82

To be provided by MTRCL

EWL-E112-BB-B1-04-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0

43.45

To be provided by MTRCL

EWL-E115-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

0-1

39.66

To be provided by MTRCL

EWL-E50-BB-B1-02-C1

At the bottom of Area B of EWL slab near eastern diaphragm wall

0-1

38.58

To be provided by MTRCL

EWL-E50-BB-B1-03-C1

At the bottom of Area B of EWL slab near eastern diaphragm wall

0-1

43.31

To be provided by MTRCL

EWL-W113-BB-B1-01-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

38.07

To be provided by MTRCL

EWL-W113-BB-B1-02-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

7-8

20.86

To be provided by MTRCL

EWL-W113-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

1-2

35.83

To be provided by MTRCL

EWL-W115-BB-B1-03-C1

At the bottom of Area C3 of EWL slab near western diaphragm wall

2-3

35.17

To be provided by MTRCL

NSL-E68-TT-T1-03-C1

At the top of Area C1 of NSL slab near eastern Diaphragm Wall

0

43.11

To be provided by MTRCL

NSL-W30-TT-T1-01-C1

At the top of Area HKC of NSL slab near western Diaphragm Wall

1-2

43.60

To be provided by MTRCL

NSL-W30-TT-T1-02-C1

At the top of Area HKC of NSL slab near western Diaphragm Wall

1-2

40.92

To be provided by MTRCL

NSL-W30-TT-T1-03-C1

At the top of Area HKC of NSL slab near western Diaphragm Wall

1-2

38.15

To be provided by MTRCL

 

According to the holistic assessment strategy of the MTRCL, upon the completion of opening-up investigation under the second stage and in the third stage, the MTRCL will consolidate test results found in the first two stages, such as as-constructed details of the platforms and quality of works, and take into account the technical data provided by the coupler supplier, conduct a detailed structural analysis on the works for the Hung Hom Station Extension to ascertain if the overall structural integrity of the works is acceptable and determine if it is necessary to conduct strengthening works.
Remark 1: Preliminary results of the phased array ultrasonic test refer to the readings taken on site, subject to verification.
Remark 2: Allowable measurement tolerance of the phased array ultrasonic test is 3 millimetres.
Remark 3: Test results indicate that the steel bars may be Type B Reinforcement bars.  Details are being investigated.
Remark 4: The test results are provided in accordance with the formal test report submitted by MTRCL on 7 January 2019

Other Findings:
In view of the increasing number of notes as the opening up work proceeds, we present them in tabular form for easy reference of the public. All the previous notes have been included in the table below.

 

Item

Date

Location

Within testing location?

Details and follow-up

1

20 December 2018

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

No

One unconnected coupler was found exposed, details are being investigated.

2

22 December 2018

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

No

One unconnected coupler was found exposed, details are being investigated.

3

24 December 2018

At the top of Area HKC of EWL slab near eastern diaphragm wall

No

One coupler was found not connecting to re-bar at one end, details are being investigated.

4

4 January 2019

At the bottom of Area C3 of EWL slab near western diaphragm wall

Yes

One re-bar and a coupler were found to be unconnected and cannot be tested.  The findings have been confirmed.  The number of threads on the re-bar was approximately 11-12.

5

7 January 2019

At the bottom of Area C3 of EWL slab near western diaphragm wall

Yes

One re-bar and a coupler were found to be unconnected and cannot be tested. There was a small gap between the re-bar and coupler. The number of threads on the re-bar was found to be approximately 2-3.

6

12 January 2019

At the bottom of Area C1 of EWL slab near eastern diaphragm wall

No

One unconnected coupler was found exposed, details are being investigated.

7

15 January 2019

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

Yes

One re-bar and a coupler were found to be unconnected and cannot be tested, details are being investigated.

8

16 January 2019

At the top of Area HKC of EWL slab near eastern diaphragm wall

Yes

2 couplers were found not connecting to re-bar at one end, details are being investigated.

9

16 January 2019

At the bottom of Area C1 of EWL slab near western diaphragm wall

Yes

One re-bar and a coupler were found to be unconnected and cannot be tested. The number of threads on the re-bar was found to be approximately 3-4, details are being investigated.

10

17 January 2019

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

No

A hydrophilic strip was found casted into the concrete.

11

19 January 2019

At the bottom of Area C2 of EWL slab near western diaphragm wall

No

A suspected hydrophilic strip was found casted into the concrete, details are being investigated.

12

20 January 2019

At the bottom of Area C3 of EWL slab near eastern diaphragm wall

No

A suspected hydrophilic strip was found casted into the concrete, details are being investigated.

13

20 January 2019

At the top of Area C3 of NSL slab near western diaphragm wall

No

A suspected hydrophilic strip was found casted into the concrete, details are being investigated.

 

Ends