INFORMATION PAPER ON SLOPE SAFETYINTRODUCTION
PROVISIONAL LEGCO PANEL ON PLANNING, LANDS & WORKS
1. This is the fifth of a series of reports to update Members on our programme of slope safety. The first four reports were issued in July 1995, March 1996, August 1996 and May 1997 respectively.
2. In the briefing on the 1997 Policy Address to this Panel on 13 October 1997, the Secretary for Works made a commitment to launch a new 10-year Landslip Preventive Measures (LPM) programme in the year 2000. This initiative follows on from recommendations on slope safety which were given in the 1994 Morgenstern Report, in the 1995 Slope Safety Review Report and in the Select Committee Report on the Kwun Lung Lau Landslip. The report of the Select Committee, published in July 1995, contains a number of detailed recommendations relating to the slope safety programme, many of which endorse the Morgenstern and Slope Safety Review recommendations and existing practice. Progress on implementation of the recommendations in these three reports and other related issues is given in the following sections.
3. Professor Morgenstern's five recommendations (summarised in Appendix A
) arising out of the investigation of the Kwun Lung Lau tragedy of 23 July 1994 are all being implemented. Current progress is as follows :
SLOPE SAFETY REVIEW REPORT
- Measurement of masonry wall thickness. Completed.
- Research into improved means of site characterisation. Phases 1 and 2 field trials of selected non-invasive geophysical methods of site characterization have been completed and the results have been published. The main conclusion from these trials is that none of the methods tested has yet been refined to a point where they can be used reliably for the investigation of slopes or retaining walls in Hong Kong. The proposed Phase 3 of the project is to assess the value of downhole geophysical and optical techniques for detecting weak rock layers, clay seams and rock joints encountered in drillholes.
- Establishment of a Technical Review Board. The Slope Safety Technical Review Board (SSTRB) has had six meetings so far and will meet again in May 1998, when it will complete its three year term of appointment. A new Board will be appointed later in the year, to include an eminent local geotechnical engineer. The new Board is due to hold its first meeting in November 1998.
- Development of a programme for monitoring and inspection of buried services affecting slopes.
The Drainage Services Department (DSD) commenced in 1996 the first consultancy to investigate sewers and drains affecting the stability of fill slopes and retaining walls registered in the 1977/78 Catalogue of Slopes, which is expected to be completed by early 1999. The second consultancy for a similar investigation of sewers and drains affecting the stability of cut slopes registered in the 1977/78 Catalogue of Slopes was awarded earlier this month and will be completed in mid 2000. These investigations also include Highways Department drains. The DSD is planning another consultancy aimed to study the same problem for slopes registered in the New Catalogue of Slopes.
The Water Supplies Department commenced work on inspection of buried watermains affecting slopes in January 1997. Phase I of this work involves slopes in the 1977/78 Catalogue of Slopes, and Phase II will involve slopes in the New Catalogue of Slopes not previously registered in the 1977/78 Catalogue. This work is expected to be completed by 2002.
The Housing Department commenced the detection of leakage of buried services in the vicinity of slopes and retaining walls within land maintained by the Housing Authority in August 1996 which will be completed in August 1998. The need for further work will be considered then.
Action on private owners to inspect and repair their buried services affecting slopes is being taken by the Building Authority under Section 27(c) of the Buildings Ordinance. So far more than 380 cases have been put in hand.
- Adoption of a more integrated approach for slope stability assessment. The GEO has appointed term consultants on an annual basis to assist in implementing the recommendations according to the means proposed by Professor Morgenstern. The first annual consultancy was commissioned in January 1997; the consultants inspected the landslips which occurred in 1997 and undertook independent detailed studies on sixteen selected landslips, including two fatal landslips on 4 June and 2 July, and the landslip at Ching Cheung Road on 3 August 1997. The second annual consultancy commenced in February 1998.
4. The Slope Safety Review Report recommendations (summarised in Appendix B
) concluded that the Morgenstern Report recommendations should be implemented as soon as possible. The current situation with regard to the implementation of the other main recommendations of the Slope Safety Review is as follows :
SELECT COMMITTEE REPORT ON KWUN LUNG LAU LANDSLIP
- Acceleration of the Landslip Preventive Measures (LPM) Programme. The 5-year Accelerated LPM Project from April 1995 to March 2000 is progressing well. By March 2000, some 900 government slopes will have been upgraded and detailed studies for 1,500 private slopes completed to determine the need for issue of Dangerous Hillside Orders under the Buildings Ordinance. Among those screened for study are some 550 slopes adjacent to schools. We have devoted additional resources to speed up this task. We will substantially complete the detailed studies of all 350 private slopes affecting schools by March 1998 and will also complete investigations and necessary improvement works for the 200 government slopes affecting schools by March 1999. The GEO and Education Department have strengthened their communication with school principals on taking early action on necessary slope improvement works and appropriate safety precautions pending their completion. A copy of the latest quarterly report on the LPM Programme is at Attachment 1. The acceleration of the LPM Programme in terms of the total Block Vote expenditure is given at Attachment 2.
- Extension of the LPM Programme to include slopes close to busy roads and footpaths. The LPM Programme has been extended in scope to include the upgrading of selected slopes close to busy roads and footpaths. Warning signs have been erected along busy roads with a history of landslips and at slopes included in upgrading actions to provide advisory warning to road users. Works Bureau has approached Transport Bureau to devise integrated plans to accommodate necessary improvement works for roadside slopes with a history of landslips as part of road improvement projects.
- Review of the system for classifying slopes according to consequence of failure. The review has been completed, and the revised consequence classification system promulgated to the geotechnical profession in Hong Kong.
- Legislative changes to improve geotechnical control. The inter-departmental Standing Committee on Slope Safety is discussing a number of legislative proposals to improve slope safety further. Details on the proposed registration of Geotechnical Engineers for slope safety functions are being worked out. We are actively enforcing the amended Buildings Ordinance to require private owners to investigate and repair their buried sewers and drains affecting slope stability, and would review its effectiveness before considering further legislation to tighten the requirement. We will consider further the inclusion of legislation to compel owners to regularly inspect and maintain their slopes when the results of the SIMAR study are available (see (f) below). In order to strengthen geotechnical control in the development stage of building works, the Building Authority has agreed to amend the Buildings Ordinance to require performance review for site formation/excavation/ foundation works and is seeking a slot in the legislative programme.
- Promotion of slope maintenance. The GEO has continued the public education campaign on slope maintenance throughout 1997, principally through television announcements of public interest, promotional booklets and pamphlets, free guidance documents, media interviews and public seminars, displays at popular shopping centres, advertising in MTR stations, advice to owners and property management companies, and preparation of educational tool kits for schools and other organizations. The GEO Slope Maintenance Hotline has been upgraded to incorporate Putonghua in addition to Cantonese and English, and to include more information on slope maintenance and safety. We will further strengthen the campaign in 1998, including the use of Internet and other multi-media information systems.
- Maintenance responsibilities for all registered slopes. The SIMAR (Systematic Identification of Maintenance Responsibility of Registered Slopes) consultancy study by the Lands Department (Lands D) commenced in July 1996 and will be completed in 1999. So far the maintenance responsibility for around 22,000 slopes has been identified. The SIMAR study is crucial to the implementation of the policy that every man-made slope must be maintained to ensure its safety. We have resolved the legal issue associated with the Personal Data (Privacy) Ordinance in disclosing the SIMAR study results to the public, and are developing a computerized information system to facilitate such disclosure. With over 100 new posts being provided, various government maintenance departments are forming specialized teams to maintain their slopes. Lands D as Government's land manager has taken up the maintenance responsibility for "unallocated" government slopes. The GEO is assisting the departments in slope maintenance by prioritizing the slopes for maintenance actions and in forming some of the teams. The GEO also audits the departments' maintenance works to ensure quality and standard.
- Response time to landslide emergencies. We continue to monitor the performance of the emergency organizations of the GEO and of the works departments and to review them as necessary. The GEO would further strengthen its public education campaign on personal safety precautions to be taken by members of the public during the times when Landslip Warnings are broadcast. We will explore further the use of electronic and print media to publicize the warning messages.
5. The progress on implementation of some of the recommendations (summarised in Appendix C
) has been covered in Items 3 and 4 above. Progress on other items is as follows :
NEW CATALOGUE OF SLOPES
- Quality System. The GEO is continuing to enhance its quality management system. A formal Quality System for the divisions directly involved in the LPM Programme is now in place. Assessment and certification audit of the System have been made by the Hong Kong Quality Assurance Agency (HKQAA) and the System was certified as meeting the requirements of ISO 9001 in June 1997.
The GEO is now implementing a formal Quality System for the three district divisions involved in geotechnical control. The documented Quality System and working procedures will be in place in April 1998, and the certification audit of the System by the HKQAA is planned for December 1998.
- Non-Development Clearance (NDC) Programme. The GEO has a programme in place for inspecting the remaining squatters/villages under the current NDC Inspection Programme. The annual report giving progress on squatter clearance has been submitted to the Housing Panel and this Panel. The GEO completed inspections of about 200 squatter villages in the New Territories in early 1997 and started a programme to inspect isolated squatter structures close to these villages. The re-housing of squatters continues and is dictated by practical constraints such as rehousing resources.
6. The current 5-year Accelerated LPM Programme concentrates mainly on man-made slopes in the existing Slope Catalogue compiled in 1977/78, which contains some 10,000 pre-GEO slopes. The task of carrying out preliminary inspections of all sizeable man made slopes in Hong Kong will be completed by April 1998, and a new computer-based Slope Catalogue by September 1998. We initiate immediate action if the preliminary inspections of any slopes show signs of immediate and obvious danger. The remainder will be prioritized for further study, followed where found necessary by upgrading under the LPM Programme for government slopes, and issue of Dangerous Hillside Orders for private slopes.
7. Based on the latest estimate, the total number of sizeable man-made slope in the whole of Hong Kong is about 60,000. This includes 18,000 post-GEO slopes which should have been designed and built to current safety standards, the 10,000 pre-GEO slopes in the 1977/78 Slope Catalogue and some 32,000 additional pre-GEO slopes not registered in the 1977/78 Slope Catalogue. They were not included because the 1977/78 Catalogue concentrated on man-made slopes in the urban areas of Hong Kong Island and Kowloon, and included only the larger man-made slopes in the New Territories. As mentioned in paragraph 2 above, we will embark on a new 10-year LPM project to deal with these pre-GEO slope when the current project is completed in early 2000.
NATURAL HILLSIDES AND BOULDERS
8. Natural hillsides cover some 60% of the total land area of Hong Kong. Landslides on these slopes are a common occurrence. Current government policy is to avoid natural terrain hazards in the planning of new developments wherever possible, discourage extensive engineering works on steep natural slopes, and react to known hazards by arranging appropriate preventive or remedial action. To cope with the effect of increasing demand for land which drives developments closer to natural hillsides, the GEO has mapped the whole of Hong Kong and produced a natural terrain landslide inventory. The GEO has analyzed the inventory to examine correlations between landslide distribution and causal factors, and is now devising a methodology for categorizing natural terrain according to its relative susceptibility to landsliding. Other work underway includes studies into the nature of the landslides, the travel distance of landslide debris, and appropriate landslide mitigation methods. The landslide inventory and reports on the work carried out to date can be viewed on request in the Civil Engineering Library. The overall aim is to zone the hazard from natural terrain landslides and to provide a framework for a future comprehensive risk management strategy.
9. The GEO is also carrying out similar mapping and risk analysis on boulder fields over the whole of Hong Kong, using aerial photograph interpretation. This work is progressing steadily.
LANDSLIP DAMAGE IN 1997
10. 1997 was the wettest year on record. For example, the cumulative rainfall at Shatin for the year was about 4,417 mm and at Sai Kung was 3,973 mm. These amounts far exceed (about double) the mean annual rainfall for the period 1985-1996 at the corresponding locations.
11. A total of 548 landslip incidents were reported to the GEO for the year. Most of the incidents occurred in May to August and were located in Shatin, Tsuen Wan, Sai Kung and the north Kowloon area. The Landslip Warning was issued eight times. A 24-hour rainfall of about 800 mm was recorded at the Chinese University, Shatin on 2 July. This is the second highest 24-hour rainfall recorded in Hong Kong since an SAR-wide raingauge network was first established in 1978. A total of 157 landslip reports was received by the GEO in the 2 July rainstorm.
12. Most of the landslips were minor events having a failure volume less than 50 m3 and without significance to the public. The more notable incidents include the following:
- A landslip at Kau Wa Keng (200 m3) on 4 June and a landslip at Ten Thousand Buddha Temple, Shatin (600 m3) on 2 July resulted in one fatality each.
- A landslip at Lido Beach (600 m3) on 2 July caused closure of Castle Peak Road and 8 injuries.
- Landslip and flooding incidents at Tuen Mun Highway near Ting Kau (50 m3) and Pun Shan Tsuen (215 m3) caused complete closure of the highway on 2 July.
- Notable incidents over 50 m3 at Lai King Hill Road on 4 June and at Route Twisk, Lai Ping Road and Sui Wo Road on 2 July caused temporary closure of the roads, including Tai Po Road. The Lai Ping Road failure volume was about 3000 m3.
- Two landslips affecting the KCR track at Chinese University (20 m3) and Fo Tan (50 m3) caused temporary disruption of railway service on 2 July.
- Two landslips at Tao Fung Shan (Shatin) on 2 July with a total failure volume of about 900 m3 destroyed a village house and caused closure of the cemetery.
- A landslip at Ching Cheung Road (6000 m3) caused closure of the road from 3 August to 24 August.
- A landslip at a second location on Route Twisk (500 m3) on 22 August caused closure of the road for about three weeks.
13. The GEO's consultants have carried out independent detailed studies of a total of more than 50 landslips, including the two fatal landslips at Kau Wa Keng on 4 June and at the Ten Thousand Buddha Temple on 2 July, and the landslip at Ching Cheung Road on 3 August. The report on the Ching Cheung Road landslip was published in February 1998; those on the Kau Wa Keng and Ten Thousand Buddha Temple landslips will be published this month. The GEO has established a programme to determine the lessons learned from the landslips investigated and to implement follow-up actions.
Appendices A, B & C
Attachments 1 & 2
13 March 98
RECOMMENDATIONS OF THE PROFESSOR MORGENSTERN REPORT
|(a)||The GEO should implement a program of measuring masonry wall thickness in all cases where Stage 1 Studies have relied on the estimate of wall thickness from old drawings.
|(b)||The Government should develop a program for direct monitoring and repair of buried services at housing estates and other developments in all cases where leakage might impact on slope stability. Priority should be given to older estates where loose fill is known to have been used in site development. Periodic inspection of buried services at hazardous locations should become mandatory. The appropriate period is best established by experience, but a five year interval appears reasonable at this stage.
|(c)||The GEO should introduce a more integrated approach into the slope stability assessment process. A means of doing this is as follows:
|(i)||All landslide occurrences are to be reported to the GEO as an incident report.
|(ii)||Based on the incident report, a senior geotechnical engineer confirms that subsequent slope evaluation can either continue in a separated manner as guided by the slope catalogue or a more integrated approach is called for.
|(iii)||A more integrated approach will normally be based on the scale of a project or development. It will require identification of what is known and what is assumed; it will require identification whether site specific soil properties and special geological features must be determined; and it will require an accounting of all water flow pathways that might affect the site.
|(d)||The GEO should undertake and support elsewhere in Hong Kong research into improved means of site characterization focused on the factors that affect slope instability in Hong Kong. The Writer does not think that the development of slope warning systems for the conditions found in Hong Kong is promising. The critical features are small and numerous and instability often develops in an abrupt manner. However, there are a number of new developments in geophysics such as radar and non-contact resistivity that might be found useful in discovering subsurface defects and enhanced moisture zones.
|(e)||GEO should consider appointing an external Technical Review Board. It is the experience of the Writer with other geotechnically intensive organizations, that an external review board can be of considerable assistance to management in enhancing technical quality improvement, maintaining knowledge of developments elsewhere, keeping abreast of international standards of risk-taking, as well as other aspects associated with the discharge of due diligence.
RECOMMENDATIONS OF THE SLOPE SAFETY REVIEW
|(a)||the five recommendations made in the Morgenstern Report should be followed up as soon as possible;
|(b)||the LPM Programme for the 1977/78 Catalogue of Slopes should be completed by the year 2000;
|(c)||selected 'low consequence-to-life' slopes, such as those affecting busy roads and footpaths, should be included in the LPM Programme;
|(d)||the system for categorizing the likely consequence of failure of individual slopes should be reviewed;
|(e)||detailed proposals for legislative changes should be explored which might help to improve the statutory geotechnical control of private slopes and developments;
|(f)||the public education campaign on slope maintenance should be stepped up, and the "Geoguide on Slope Maintenance" and "Layman's Guide to Slope Maintenance" should be published as soon as possible;
|(g)||detailed proposals should be developed with a view to clearly identifying the maintenance responsibilities for all registered slopes; and
|(h)||measures should be taken to reduce the response time of the Works departments in attending landslide incidents.
RECOMMENDATIONS OF THE SELECT COMMITTEE REPORT ON
KWUN LUNG LAU LANDSLIP
|3.38||For measures to prevent occurrence of similar incidents, Professor Morgenstern has made five recommendations. Works Branch has also formulated some improvement measures for its slope safety programme. The Select Committee consider that there should be a publicly announced timetable for implementing these recommendations.
|3.39||In the light of the Kwun Lung Lau incident, the Select Committee wish to highlight certain areas of concern for the Government's further consideration.
|(A)||There should be a thorough, and then regular, review of the landslip preventive measures and the related systems.
|3.40||The Kwun Lung Lau incident has brought to light certain deficiencies in the Government's methodology and systems for landslip prevention. It is necessary therefore to conduct a thorough review, to be followed by regular reviews, of the methodology and the systems to ensure that it will keep up with new geotechnical engineering development and will benefit from actual experience gained over the years. While Works Branch has already conducted its own internal review, the following warrant further attention:
|(a)||The Stage 1 Studies should be reviewed to ensure that they can effectively identify necessary cases for a Stage 2 Study, in addition to implementing the recommendation of Professor Morgenstern in measuring masonry wall thickness in appropriate cases.
|(b)||Works Branch has recommended to review the risk categorisation system. Subsequent to this, there should be periodical review with a view to establishing a reliable system, which should also be comprehensible to the public.
|(c)||Works Branch has been working on a new catalogue of slopes. Consideration should be given to seeking input from the public to ensure that the new catalogue will be as comprehensive as possible. The new catalogue should also contain all such useful information as assumptions made in any studies; landslip records of the site; and any limitations about the catalogue, etc.
|(d)||Works Branch has pledged to complete the Landslip Preventive Measures Programme of the 1977/78 Catalogue of Slopes by the year of 2000. It is necessary that landslip preventive measures for slopes identified after compilation of this Catalogue should also be carried out as early as practicable.
|(e)||The programme to inspect and clear squatters/villages under dangerous slopes should be accelerated. There should be a timetable for the programme.
|(f)||Works Branch has recommended that all Government slopes which could affect life and property should be allocated to an appropriate maintenance department for regular maintenance. This recommendation should be implemented as soon as possible.
|(B)||It is necessary to establish, review and enforce standards of good practice for slope stability assessment and maintenance.
|3.41||The Select Committee accept that the Government has been working hard to establish good standards through publishing geotechnical manuals, guidelines, etc. The Kwun Lung Lau incident is a reminder that reviewing and enforcing standards is as important because the
incident has revealed that certain engineering practices that were being followed by many were not effective. The Select Committee wish to highlight the following -
|(a)||Works Branch has agreed to work out detailed proposals for legislative changes with a view to improving the statutory geotechnical control of the safety standards of new slopes on private land. An outline of the proposal should be available for consultation as soon as possible.
|(b)||At the public hearing the Government representatives indicated that consideration is being given to establishing a statutory certification system similar to the current system for lifts and escalators. An outline of the proposal should be made available for wide public consultation, given its impact on the community.
|(c)||Consideration should be given to requiring preliminary assessments of slope stability to be carried out or certified by senior geotechnical professionals in order to ensure their reliability and effectiveness.
|(d)||Works Branch has initiated to work on a "Geoguide on Slope Maintenance" and a "Layman's Guide to Slope Maintenance". These should be issued as soon as possible. For the Geoguide, consideration should be given to including lessons learnt from previous major landslides, for example, the importance of direct monitoring of subsurface drainage systems and the possible defects of site formation plans, as revealed in the Kwun Lung Lau landslide. For the Layman's Guide, it should contain advice on how owners could engage and instruct consultancy services and how they could monitor their effectiveness. It should also advise owners of the importance of maintaining all relevant documents relating to their slope, including relevant drawings and investigation/inspection reports provided by their consultants.
|(e)||There should be close follow-up in cases where an order under the Buildings Ordinance, Cap. 123, has been issued requiring the owner to investigate the slope and undertake any necessary landslip preventive measures. Where an order is not expeditiously complied with relevant Government departments, such as the Geotechnical Engineering Office and the Home Affairs Department and their District Offices, should offer advice and assistance if genuine difficulties are involved or arrange for the necessary works to be carried in the owner's default. Prosecution should be instituted in appropriate cases.
|(f)||Consideration should be given to obtaining greater involvement of professional institutions concerned in establishing, reviewing and enforcing standards of good practices. The Hong Kong Institution of Engineers, for example, has submitted to the Select Committee that it should have a role to play in the selection and in the composition of the Technical Review Board recommended by Professor Morgenstern.
|(C)||There should be stepped-up measures to promote public awareness and responsibility
|3.42||The Kwun Lung Lau incident has reminded us of the importance to ensure that owners of slopes are aware of their maintenance responsibility. It has also reminded us that landslip prevention is a complex issue requiring commitment and input by the community as a whole. The following requires the Government's attention -
|(a)||Works Branch has agreed to develop detailed proposals with a view to clearly identifying the maintenance responsibilities for all registered slopes. Pending completion of this exercise, publicity should be stepped up to encourage private land owners to seek clarification of their responsibility, if they are not yet clear about it, in particular since there are private land owners who are required to maintain slopes
on adjoining Government land; and there are slopes that are under the maintenance responsibility of different owners. Consideration should also be given to soliciting assistance from the Law Society of Hong Kong to ensure that its members explain clearly to their conveyancing clients their slope maintenance responsibilities. It is also necessary to ensure that developers make it clear in their sales brochures if the property owners are required to bear any slope maintenance responsibility.
|(b)||The Government should encourage members of the public to observe and report significant anomalies indicative of landslip risks. This may help alert the relevant Government departments and owners concerned to take necessary precautionary action.
|(c)||The Government should step up publicity and educational campaigns to promote public awareness of the importance of slope safety and the need of regular slope inspection and maintenance as well as slope stability assessment.
|3.43||The Select Committee further recommend that the Government should submit six-monthly progress reports to the Legislative Council Panel on Planning, Lands and Works regarding the implementation of the various improvement measures.
|3.44||The Select Committee wish to join Professor Morgenstern in his remarks that "There appear to be no exotic phenomena involved in the Kwun Lung Lau landslide and no exotic methods would be required to prevent it." While the various recommendations may help improve the overall system of landslip prevention, it ultimately requires all those who have a duty in the process to faithfully, skilfully and vigilantly carry out their duty.