 Introduction
Background
Preliminary Studies of Old Slopes
Detailed Studies of Old Slopes
Progress of Preliminary and Detailed Studies
of Old Slopes
Dangerous Hillside Orders Served on Private
Owners
Special LPM Studies
Upgrading Works to Old Government Slopes
Acceleration
of LPM Programme
10-Year
Extended LPM Project
Introduction
This report is on the Landslip
Preventive Measures (LPM) Programme and is produced
by the Geotechnical
Engineering Office (GEO) of the Civil Engineering
and Development Department for general distribution.
It is issued on a half-yearly basis since October 2003
(before which the report was issued on a quarterly basis)
to provide information on the progress of studies and
works carried out under this Programme. This report
covers progress to 30 September 2009.
Background
Although the GEO has no maintenance responsibility for
land, it is responsible for carrying out an initial
investigation of both public and private man-made slopes
and retaining walls (generally referred to as slopes
in this report) which were formed before the GEO was
established and could pose a risk to life or property.
The GEO also carries out some major slope upgrading
works on behalf of other Government departments.
Since 1976, about $12.9 billion has
been spent on studies and upgrading works on old (i.e.
pre-GEO) slopes under a long-term programme, the LPM
Programme. The Programme provides for the investigation,
in priority order, of man-made slopes in existence when
the GEO (known as the Geotechnical Control Office before
1991) was set up in 1977. The designs of new slopes
which have been built since then have generally been
checked by the GEO to ensure that they conform with
the required safety standards.
The GEO has a Catalogue of Slopes.
The original version was prepared in 1977 and 1978.
Its original purpose was to provide an inventory of
sizeable man-made slopes in existence when the GEO was
established and it focused on slopes in the main urban
areas of Hong Kong and Kowloon and contained about 10,000
slopes.
However, the original Catalogue of
Slopes did not include all slopes formed before 1977,
or the many new slopes that have been formed since.
In July 1994, the GEO commenced a project entitled "Systematic
Identification and Registration of Slopes in the Territory"
to compile a new catalogue of all sizeable man-made
slopes in Hong Kong. The project was completed in September
1998. Since then, the slope cataloguing exercise has
been continuing on a regular basis to include newly
constructed or newly identified slopes that meet the
slope registration criteria. There are now altogether
about 57,000 slopes, including some 2,000 Disturbed
Terrain (DT) features, in the Catalogue of Slopes. A
comprehensive Slope Information System (SIS) containing
pertinent information on the slopes in the New Slope
Catalogue has been developed. The SIS is accessible
by the public through a computer terminal on the 7th
floor of the Civil Engineering and Development Building
at 101 Princess Margaret Road, Kowloon. The slope information
is also available on the Hong Kong Slope Safety Website
(http://hkss.cedd.gov.hk)
since March 1999.
Slope owners have a particular interest
in the data recorded in the Catalogue of Slopes because
they are responsible for maintaining their slopes in
a safe condition. All slopes need to be maintained,
including old slopes and new slopes which are built
to current standards. Routine maintenance works to Government
slopes are neither carried out by the GEO nor paid for
under LPM funding. In order to establish clear responsibility
for maintenance of slopes, the Lands Department commenced
a project - Systematic Identification of Maintenance
Responsibility of Slopes in the Territory (SIMAR) in
June 1996 by engagement of consultants to set up a register
of slope maintenance responsibility for all man-made
slopes in the New Catalogue. A computerized Slope Maintenance
Responsibility Information System has been set up for
public access in Lands Department since December 1999.
Government departments responsible
for the maintenance of Government slopes allocated to
them or under their charge have stepped up their programme
of maintenance in accordance with the standard of practice
promulgated in Geoguide 5 : Guide to Slope Maintenance.
For example, funding to Highways Department for maintenance
works to road-side slopes has been increased from $150
million in 1995/96 to about $200 million in 2000/01.
Similarly, Architectural Services Department has also
received increased funding from $38 million in 1995/96
to about $90 million in 2000/01 to cover the cost of
maintenance works to slopes under its charge.
In 1978, the Government undertook
to carry out an initial screening of both private and
Government man-made slopes in the 1977/78 Catalogue
of Slopes under the LPM Programme. This has now been
extended to the man-made slopes in the New Catalogue.
There are two levels of study under the LPM Programme,
which are referred to in this report as Preliminary
Studies and Detailed Studies respectively.
Preliminary
Studies of Old Slopes
A Preliminary Study essentially consists of a site reconnaissance
during which time the consequence of failure is assessed
and a subjective judgement made of the likelihood of
preventive measures being necessary. While the main
purpose of a Preliminary Study is to identify slopes
requiring a Detailed Study, it also allows slopes with
immediate and obvious signs of danger to be identified,
so that any necessary works can be initiated immediately
to safeguard public safety.
Detailed
Studies of Old Slopes
A Detailed Study is a stability assessment of an existing
slope to decide whether upgrading works are necessary.
Details of a stability assessment are given in Appendix
E of Geoguide 5: Guide to Slope Maintenance. It is based
on a desk study, an interpretation of the general area
from aerial photographs, site observations, stability
analysis, and if necessary, ground investigation. For
a private slope, if ground investigation is required
to confirm whether or not upgrading works are necessary,
the requirement to carry out the ground investigation
is normally passed to the private owners by a statutory
Dangerous Hillside (DH) Order served by the Buildings
Department.
A report on a Detailed Study may:
| (a) |
recommend upgrading
works for Government slopes,
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| (b) |
recommend further
investigation and/or upgrading works for private
slopes by the service of a Statutory Order by the
Buildings Department on private owners,
|
| (c) |
recommend other
specified action (for which purpose a private owner
is advised by an Advisory Letter issued by the Buildings
Department), or
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| (d) |
conclude that upgrading
works are not required provided the slope is maintained
in accordance with the requirements given in Geoguide
5: Guide to Slope Maintenance.
|
Progress of Preliminary
and Detailed Studies of Old Slopes
An indication of the progress of Preliminary Studies
over the last 24 years is illustrated in Figure 1(a)
and that for Detailed Studies is illustrated in Figure
1(b). It is relevant to note that the Preliminary Studies
of all the old slopes in the New Slope Catalogue have
been completed. In Figure 1(b), a breakdown of the progress
of the Detailed Studies carried out on private slopes
(also referred to as safety-screening studies) is also
included.
Figure 1(a) : Progress
of Preliminary Studies
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Figure 1(b) : Progress
of Detailed Studies
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Dangerous Hillside
Orders Served on Private Owners
Where found necessary by a Preliminary Study or a Detailed
Study, a DH Order is served by the Buildings Department
on the owners of the private slopes on the recommendation
of the GEO. The Order requires the owners to carry out
certain investigation and the necessary upgrading works
to the slope. An Order may also be recommended to be
issued after a slope failure has occurred, or as a result
of other stability concerns brought to the attention
of the GEO. The cumulative number of slopes on which
Orders have been served by the Buildings Department
is shown in Figure 2.
Figure 2 : Cumulative
Number of Slopes on Which DH Orders Have Been
Served
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Special LPM Studies
From time to time, the GEO carries out special studies
related to LPM. These studies include :
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Mid-levels Studies
(carried out between 1979 and 1981, resulting in
substantial LPM stabilization works),
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|
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North Point Rock
Slope Study (carried out between 1979 and 1981,
resulting in substantial LPM stabilization works),
|
|
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Studies of slopes
affecting squatters (on-going since 1982),
|
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Study of slopes
along some Water Supplies Department catchwaters
(carried out in 1984, resulting in substantial LPM
stabilization works and squatter clearance),
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Studies of slopes
affecting the Kowloon Canton Railway (carried out
between 1984 and 1990, resulting in substantial
LPM stabilization works),
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Studies of Seymour
Cliffs above Conduit Road (carried out in 1991 and
1992, resulting in substantial LPM stabilization
works),
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Study of slopes
affecting bus shelters (carried out in 1994),
|
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Masonry Wall
Studies (completed in 1996),
|
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Formulation of
New Priority Classification Systems (completed in
1996),
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Quantitative
Risk Assessment (on-going since 1993),
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Systematic Inspection
of Slopes in the Territory (completed in June 1997),
|
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Systematic Identification
and Registration of Slopes in the Territory (completed
in September 1998),
|
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Risk assessment
of landslides and boulder falls from natural terrain
(interim risk guidelines recommended in 1998),
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Natural terrain
landslide study (completed in 2000, resulting in
the compilation of a landslide inventory and promulgation
of guidance on assessment of natural terrain),
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Business Process
Re-engineering on selection of slopes for LPM action
(design phase completed in February 1999, trial
implementation completed in February 2000 and now
adopted in the LPM process),
|
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Study of slopes
affecting schools (carried out between 1995 and
1998, resulting in the identification of some 400
substandard private and government slopes for follow-up
actions which were completed in June 2000),
|
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Territory-wide
quantitative risk assessment of boulder fall hazards
(completed in April 2002),
|
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Natural terrain
hazard studies (on-going since 2000),
|
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Study on mitigation
measures against natural terrain landslide hazards
(on-going since 2001), and
|
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Study on use
of bioengineering measures to repair natural terrain
landslide scars (completed in March 2007)
|
Upgrading Works
to Old Government Slopes
Where old Government slopes are found to be below current
safety standards, they are recommended for upgrading
works. The programme of Government slopes selected for
detailed studies and upgrading works is referred to
an inter-departmental committee, the Landslip Preventive
Measures Committee (LPMC) for consideration, advice
and agreement. The LPMC also considers nominations for
upgrading works by Government departments responsible
for slope maintenance. Figure 3 shows the number of
Government slopes upgraded by the GEO on behalf of other
Government departments.
Figure 3 : Numbers of
Government Slopes Upgraded by GEO on Behalf
of
Other Government Departments as at 30.9.2009
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Government slopes are included in the LPM Programme under several categories. These include:
| (a) |
Slopes classified
as consequence-to-life Category 1 (i.e. previously
denoted as high consequence with respect to loss
of life in the event of failure). These are generally
slopes close to occupied buildings.
|
| (b) |
Slopes classified
as economic consequence Category A (i.e. previously
denoted as high economic consequence). These are
slopes which would cause significant disruption
to the public in the event of a failure. They include
slopes on major transport routes and, since 1995,
selected slopes affecting busy roads and footpaths.
|
| (c) |
Slopes affecting
cul-de-sac roads. These are slopes along roads where,
in the event of a failure, access for essential
services would be totally interrupted because there
is no other access available.
|
| (d) |
Slopes categorized
as having high indirect consequence-to-life with
respect to loss of life in the event of failure.
These are slopes affecting access to hospitals,
fire stations, airport navigational facilities and
the like.
|
The number of slopes in each of these categories that have been
upgraded under the LPM Programme is shown in Figure
4.
Figure 4: Different Categories
of Slopes Upgraded under the LPM Programme
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Year-by-year information on the number of slopes upgraded
under the LPM Programme and on LPM expenditure is given
in Table 1 below.
Table 1 : Expenditure and Numbers
of Slopes Upgraded under the LPM Programme
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# Figures include cost for urgent repair works to slopes
on Government land and other special studies
+ Figures up to 30.9.2009
Acceleration of
LPM Programme
In 1991, streamlined procedures were introduced to boost
the output of Preliminary and Detailed Studies (see
Figures 1(a) and 1(b)). In 1992, a programme was implemented
to use private sector resources to expedite the progress
of the LPM Programme.
As part of the implementation of the
recommendations of the Slope Safety Review Report issued
by the Works Bureau and endorsed by the Executive Council
in February 1995, the GEO received increased resources
to further accelerate the LPM Programme. Over the five
years commencing on 1 April 1995, the target was to
complete the investigation and the necessary upgrading
works on some 800 substandard government slopes in the
1977/78 Catalogue of Slopes affecting occupied buildings,
schools, hospitals, etc., including selected slopes
affecting busy roads and footpaths, by increasing the
number of in-house staff and engaging more consultants.
Slopes identified in the re-cataloguing exercise as
presenting an immediate and obvious danger were also
investigated and upgraded under the 5-year Accelerated
LPM Project.
10-Year Extended
(2000 – 2010) LPM Project
As a result of the acceleration of the LPM Programme
since 1 April 1995, the output in terms of detailed
studies and upgrading works by the GEO has increased
significantly (see Figure 1(b) and Table 1). The acceleration
of the LPM Programme was originally arranged as a 5-year
project to end in March 2000. As part of Government's
long-term strategy for upgrading and maintaining slopes
registered in the New Catalogue of Slopes, the 10-year
Extended LPM Project was launched in April 2000. This
project will deal with high-priority (in terms of potential
loss of life due to landslides) old (i.e. pre-GEO) slopes
in the New Catalogue of Slopes that do not meet the
current safety standards. Slopes are selected for action
under the 10-year Extended LPM Project in accordance
with a risk-based priority ranking system. The target
is to upgrade another 2,500 substandard Government slopes
and to complete detailed studies (safety-screening studies)
for another 3,000 private slopes by the year 2010. As
before, consultants will be employed in addition to
deployment of in-house staff resources to undertake
the project.
A breakdown of the slopes upgraded under the 10-year
Extended LPM Project is shown in Figures 5(a) and 5(b).
Figure 5 : Breakdown of Slopes Upgraded
under the 10-Year Extended LPM Project
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Post-2010 Landslip Prevention and Mitigation
Program
The GEO has launched a long-term Landslip Prevention and Mitigation
Programme (LPMitP) to dovetail with the 10-year Extended
LPM Project, which is due for completion in 2010. The
LPMitP will be implemented on a rolling basis with the
following annual output:
(a) upgrade 150 government man-made slopes;
(b) conduct safety-screening studies for 100 private
man-made slopes; and
(c) implement studies and necessary risk mitigation
works for 30 natural hillside catchments.
Geotechnical Engineering Office
Civil Engineering and Development Department
October 2009
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