Year 2006

Review of the 16 July 2006 Landslide on Slope No. 14NE-B/CR180, No. 49 Po Wah Yuen, Yung Shue Wan, Lamma Island

Basic Data

Location of Landslide

Material:
Completely Decomposed Granite

Feature Affected:
Cut Slope and Retaining Wall No. 14NE-B/CR180 (Western portion only)

Volume:
15 m³

Report Reference:
GEO Report No. 234

Description

A minor landslide (15 m³) occurred during light rainfall on a substandard and poorly maintained soil cut slope, which was previously included within two Short Term Tenancy (STT) lease areas. The landslide comprises a typical rain-induced shallow failure.

The slope was established as being substandard by a LPM Stage 2 Study in 2003, following which Warning Letters were issued by Lands Department (LandsD) to the tenants of the respective STTs in January 2005. At the request of the tenants, the STT lease areas incorporating the slope were subsequently terminated by LandsD. No upgrading works were carried out to the slope by the tenants before the termination of the STTs.

LandsD initiated action in December 2005 to re-assess and update the maintenance responsibility of the slope upon the termination of the STTs. The re-assessment was not yet completed at the time of the failure.

Observations

The landslide highlights the potential administrative difficulty in dealing with substandard slopes on STT land.

Cross Section of Landslide

Location Plan

Review of the August 2006 Landslide at Slope No. 11SW-C/FR319 at Ebenezer School and Home for the Visually Impaired, 131 Pok Fu Lam Road, Hong Kong

Basic Data

Location of Landslide

Material:
Concrete, Masonry blocks and Fill

Feature Affected:
Fill Slope and Retaining Wall No. 11SW-C/FR319

Volume:
4 m³

Report Reference:
GEO Report No. 279

Description

The minor failure (4 m³ in volume) principally involved the detachment of a mature tree and parts of a masonry wall of private ownership during a typhoon with fairly light rainfall. Although the incident occurred on an engineered slope feature, the landslide is of no technical interest in terms of the nature of the failure.

The failure disturbed a soil nail head and the corresponding nail installed on the retaining wall. The affected soil nail was subsequently exhumed for inspection.

Observations

The incident revealed two major non-compliances in the construction of the affected soil nail in respect of inadequate nail length and inadequate construction of the grout sleeve as a working nail.

Six nos. of soil nails that were subjected to pull-out tests were subsequently grouted up to form part of the permanent works. This is not the norm in current practice of soil nail construction.

Cross Section of Landslide

Location Plan