For discussion PWSC(96-97)24
on 26 June 1996
ITEM FOR PUBLIC WORKS SUBCOMMITTEE
OF FINANCE COMMITTEE
HEAD 704 - DRAINAGE
Public Safety - Landslip prevention
52BL - Investigation of sewers and drains affecting the safety of fill slopes and retaining walls
Members are invited to recommend to Finance Committee the upgrading of 52BL to Category A at an estimated cost of $64.3 million in money-of-the-day prices.
Sewers and drains buried behind fill slopes and retaining walls are susceptible to leakage. This may endanger the stability of the slopes and retaining walls and, in some cases, may cause landslips or collapse of the retaining walls.
2. The Director of Drainage Services (DDS), with the support of the Secretary for Works, proposes to upgrade 52BL to Category A at an estimated cost of $64.3 million in money-of-the-day (MOD) prices for the engagement of consultants to undertake an investigation on the physical conditions of public sewers and drains buried behind and adjacent to fill slopes and retaining walls.
3. The scope of the investigation comprises the following works -
- systematic identification of all public sewers and drains behind and adjacent to approximately 4 920 fill slopes and retaining walls registered under the 1977-78 Catalogue of Slopes1 ;
- internal pipe survey on the structural conditions of all identified sewers and drains;
- setting up of a database containing an inventory of the identified sewers and drains together with the results of the internal pipe survey; and
- development of proposals and cost-effective options for remedial works along with a prioritized implementation programme.
4. In November 1994, Professor N R Morgenstern submitted a report to the Governor on the adequacy of Government's approach to slope safety with suggestions for improvements. The Administration subsequently undertook to develop a programme to monitor and repair buried services to prevent slope failures caused by leaking sewers and drains buried behind and adjacent to fill slopes and retaining walls. Such leakages are mainly due to deterioration of the sewers and drains following prolonged years of service and the opening of pipe joints as a result of ground movement. At present, we do not have sufficient information to formulate such a programme.
5. In early 1995, DDS inspected the first 500 high priority fill slopes in the 1977-78 Catalogue of Slopes. We identified 161 fill slopes containing sewers and drains, 61 of which had buried services with opened joints or cracks requiring remedial works.
6. The progress of the inspection programme has been very slow due to inadequate in-house resources. It has proved difficult to complete the inspection of the 4 920 fill slopes and retaining walls in the 1977-78 Catalogue of Slopes within a reasonable period. To speed up the programme, we propose to conduct an investigation to identify the structural condition of all public sewers and drains buried behind and adjacent to slopes and retaining walls, carry out surveys of these buried services and recommend remedial works. We will also develop an asset inventory and management system for effective management of these sewers and drains.
7. The investigation will require considerable resources over a specified period. Having examined the ways and means of implementing this investigation, DDS concludes that he cannot redeploy existing staff in his department to cover the substantial additional workload as they are fully stretched by the existing works programme. He proposes to engage consultants to undertake the investigation for a period of about 28 months.
8. DDS estimates the cost of the proposed investigation consultancy to be $64.3 million in MOD prices (see paragraph 9 below), made up as follows -
|
|
$ million
|
|
|
(a) Internal pipe survey contract works
|
|
38.2
|
|
|
(b) Consultants' fees for -
|
|
10.4
|
|
|
(i) identification of sewers and drains affecting fill slopes and retaining walls
|
3.2
|
|
|
|
(ii) preparation of tender and related documents for internal pipe survey
|
0.3
|
|
|
|
(iii) supervision of internal pipe survey
|
3.8
|
|
|
|
(iv) setting up of inventory and survey database
|
1.9
|
|
|
|
(v) development of remedial works proposals and options along with an implementation programme
|
1.2
|
|
|
|
(c) Consultants' expenses (including accommodation, travelling, computer facilities, production of reports, etc.)
|
|
0.5
|
|
|
(d) Contingencies
|
|
4.9
|
|
|
|
|
____
|
|
|
Sub-total
|
|
54.0
|
(at December
1995 prices)
|
|
(e) Inflation allowance
|
|
10.3
|
|
|
|
|
____
|
|
|
Total
|
|
64.3
|
(in MOD prices) |
A breakdown by man months of the estimate for consultants' fees is at the Enclosure.
9. Subject to approval, we will phase expenditure as follows -
|
Year
|
$ million
(Dec 1995)
|
Price
adjustment
factor
|
$ million
(MOD)
|
|
1996 - 97
|
7.2
|
1.07500
|
7.7
|
|
1997 - 98
|
36.0
|
1.18250
|
42.6
|
|
1998 - 99
|
10.8
|
1.30075
|
14.0
|
|
54.0
|
|
64.3
|
10. We have derived the MOD estimates on the basis of the Government's forecasts of trend labour and construction prices for the period 1996 to 1999. We will tender the proposed consultancy on a lump sum basis with provision for inflation adjustment as the consultancy period will last longer than 12 months. We will tender the internal pipe survey component under a standard re-measurement contract because the extent as well as the methods of survey may have to be varied to suit site conditions.
11. The proposed investigation will not give rise to annually recurrent expenditure.
12. As this is an investigation, we consider public consultation unnecessary.
13. The proposed investigation will not have any adverse environmental impacts.
14. The proposed investigation does not require land acquisition.
15. The Secretary for Works undertook a review of slope safety measures in 1994. In the review, he recommended that a programme be developed to monitor and repair buried services at housing estates and other developments where leakage might affect slope stability. We presented a summary of the initial findings of the review to the Legislative Council's Panel on Planning, Lands and Works on 20 December 1994, and published a report on the review on 3 March 1995.
16. The Administration has made a commitment in the 1995 Policy Address to inspect and repair public drains which may affect the stability of slopes.
17. We upgraded 52BL to Category B in January 1996. Subject to approval, the investigation will commence in August 1996 for completion in December 1998. Based on the experience gained towards the end of the investigation, we will create a separate project to carry out investigation for those sewers and drains buried behind some 5 520 cut slopes register under 1977-78 Catalogue of Slopes.
1 -- Consultants engaaged by the Civil Engineering Department compiled the 1977-78 Catalogue of Slopes in 1978. The catalogue contains 4920 man-made fill slopes and retaining walls and 5520 cut slopes scattered throughout the whole territory. The catalogue forms a database of information for Government's further investigation and design of landslip preventive measures.
(JJ100)
Enclosure to PWSC(96-97)24
Breakdown of estimates for consultants' fees
|
Consultants' staff cost
|
|
Estimated man months
|
Average MPS
salary
point
|
Multiplier factor
|
Estimated fee ($million)
|
|
(a) Identification of sewers and drains affecting fill slopes and retaining walls
|
Professional Technical
|
5.0
47.0
|
40
16
|
3
3
|
0.77
2.44
|
|
(b) Preparation of tender and related documents for internal pipe survey
|
Professional Technical
|
1.5
2.0
|
40
16
|
3
3
|
0.23
0.10
|
|
(c) Supervision of internal pipe survey
|
Professional Technical
|
15.0
29.0
|
40
16
|
3
3
|
2.31
1.50
|
|
(d) Setting up of inventory and survey database
|
Professional Technical
|
6.0
19.0
|
40
16
|
3
3
|
0.93
0.98
|
|
(e) Development of remedial works proposals and options with implementation programme
|
Professional Technical
|
7.0
2.0
|
40
16
|
3
3
|
1.08
0.10
_____
|
|
|
Total consultants' staff costs
|
10.44
|
|
Out-of-pocket expenses
|
|
|
|
|
|
|
(a) Consultants' expenses (including accommodation, travelling, computer facilities, production of reports, etc)
|
|
|
|
|
0.50
_____
|
|
|
Total out-of-pocket expenses
|
0.50 |
Notes
- A multiplier factor of 3 is applied to the average MPS point to arrive at the full staff costs including the consultant's overheads and profit, as the staff will be employed in the consultant's' offices. (At 1.4.95, MPS pt. 40 = $51,440 p.m. and MPS pt. 16 = $17,270 p.m.)
- Out-of-pocket expenses are the actual costs incurred. The consultant is not entitled to any additional payment for overheads or profit in respect of these items.
- The figures given above are based on estimates prepared by the Director of Drainage Services. We will only know the actual man months and actual fees when we have selected the consultant through the usual competitive lump sum fee bid system.
(JJ100)
Last Updated on 8 December 1998
